It is well established that trainee doctors struggle with the transition from medical school to starting work and feel unprepared for many aspects of their new role. There is evidence that suitable induction experiences improve competence and confidence, but available data indicate that trainee doctors on the UK Foundation Programme are commonly not experiencing useful inductions. The aim of the reported research was to explore trainee doctors’ experiences with induction during their first year of the Foundation Programme to identify the most useful characteristics.A questionnaire was designed to explore trainee doctors’ experiences with induction at two points during their first Foundation year, during the first and third of three rotations, to enable all induction experiences on offer during the year to be surveyed. Data were collected using an anonymous questionnaire distributed during a teaching session, with an online version available for those trainees not present. Questions gathered information about characteristics of the inductions, usefulness of components of the inductions and what gaps exist.192 Foundation trainee doctors completed the questionnaire during Rotation 1 and 165 during Rotation 3. The findings indicated that induction experiences at the beginning of the year, including the local Preparation for Professional Practice week, were more useful than those received for later rotations. Longer inductions were more useful than shorter. Departmental inductions were generally only moderately helpful and they missed many important characteristics. Gaps in their inductions identified by many trainees matched those aspects judged to be most useful by those trainees who had experienced these characteristics.Many Foundation trainee doctors are experiencing inadequate inductions, notably at the department level. Trainees are starting rotations in new departments without rudimentary knowledge about their role and responsibilities in that department, where to find equipment and documentation, who to contact and how to contact them, local preferences, policies and procedures. Unsurprisingly, trainees who do receive such information in their inductions regard it as highly useful. Action is urgently needed to improve departmental inductions so that all trainees have the information they require to work confidently and competently in each new department they rotate into.The online version of this article (doi:10.1186/s12909-015-0395-1) contains supplementary material, which is available to authorized users. On graduating medical school in the United Kingdom (UK) newly qualified doctors progress to the Foundation Programme. The Foundation Programme is a two-year training programme which builds on undergraduate education. Trainee doctors work on supervised clinical placements (commonly three placements of four months in length each year), rotating through a number of different specialities. Trainee doctors work to consolidate skills learnt in medical school and further improve their performance.The transition from medical student to trainee doctor can be stressful, and there is evidence that trainee doctors feel unprepared for many aspects of their new role –3. This When considering the impact of both undergraduate medical school and postgraduate medical training on preparedness, Goldacre et al.  argue thThe Foundation Programme requires both a local induction at the start of the first year, including information about the programme and how it will be provided by the particular Foundation School the trainee doctors is registered with, and also clinical induction sessions at the start of each placement . HoweverThe aim of the reported research was to examine the experiences of trainee doctors’ registered with the East Anglian Foundation School (EAFS) with the various induction programmes on offer at their employing National Health Service (NHS) Trust. It was part of a larger study investigating preparedness to practice of first year Foundation doctors.The research was carried out at 13 local hospitals (12 NHS Trusts) in the East of England region employing trainee doctors registered with the EAFS. A questionnaire was designed with the purpose of auditing existing Trust induction procedures for first year Foundation doctors (F1s). This Foundation School has a mandatory week long Preparation for Professional Practice (PfPP) period before the August start date for all new F1s which is comprised of formal teaching and shadowing of the outgoing F1 for their new post; so the audit questionnaire covered the Trust induction, PfPP and departmental inductions for the clinical rotations. Specifically, the questions covered: the number of F1s that had started at the Trust August 2010, what induction programmes were on offer, the timing and length of the programmes, F1 attendance at the programmes (whether attendance was mandatory and percentage attendance), whether any of the induction programmes included shadowing an outgoing F1, whether there was a Trust handbook, who runs the programmes, and the content of the Trust induction. This questionnaire was emailed to the postgraduate medical education offices at each participating Trust at the start of the 2010–11 academic year. Twelve of the 13 hospitals returned a completed questionnaire. The audit results were used to refine the questionnaire for clarity, where needed, to conduct a further audit for the 2011–12 academic year and to develop a questionnaire for F1s asking about their induction experiences during that same 2011–12 academic year. Only the 2011–12 data are reported here.A two-part questionnaire was developed for completion by F1s to explore (i) self-perceived preparedness to practice in a number of areas by undergraduate medical training (data not reported) and (ii) experience with inductions programmes on offer at their employing Trust. As noted previously, the questionnaire was designed following the audit of 2010–11 induction programmes. Additionally, the questionnaire design was influenced by the findings of focus groups and interviews with F1s during that same 2010–11 year about their early weeks of work, which included discussion about their induction experiences . Questiothe most useful aspects of their Trust / PfPP induction week,the most useful aspects of their departmental inductions,any gaps in the inductions,suggestions to fill these gaps, for improving the induction process.In the induction half of the questionnaire, which is the focus of this paper, F1s were asked to provide details of their current Trust and department; in the Rotation 3 questionnaire they were also asked to provide these details for their previous two rotations. They were then asked to indicate the length of their induction for their current department and the usefulness of the departmental handbook and various elements of that induction (18 items). F1s were asked to rate the helpfulness of all the inductions they had experienced during their first Foundation year so far for preparing them for their F1 role. Four open ended questions asked the F1s to provide details of:In the Rotation 3 questionnaire those F1s who had moved Trusts between rotations were asked to comment on their experiences with induction at the new Trust/s. The following demographic data were also collected: gender, age, year of qualification, name of medical school, whether the medical course had been a graduate entry course, and whether the course had included any time shadowing a Foundation doctor (questionnaire available from corresponding author).The invited sample comprised of all 312 trainee doctors currently employed on F1 posts through the EAFS at 12 NHS Trusts  in the East of England region. Two recruitment methods were used. One of the authors visited teaching sessions at as many of the Trusts as could be arranged to introduce the study and distribute hard copies of the questionnaire . F1s were provided the opportunity to complete the questionnaire at that time or complete it later and post it back to the research team using a provided pre-paid envelope. Online completion of the questionnaire was also provided for F1s who had not been in attendance at the teaching session. The EAFS sent the link for the online questionnaire with the participant information sheet attached to all F1s at the start of each phase of data collection, followed by two reminders. The data collection period lasted approximately 2 months to enable the site visits to take place; starting after the F1s had been in post for approximately 4 weeks, to allow them time to settle into their new post and discover what they did and did not know following their induction experiences. For each of the two rotations, participating F1s were provided with the opportunity to be entered into a prize draw to win one of five £50 vouchers from a well-known internet retailer.Whilst the measure of interest (the questionnaire) was repeated on two occasions, the participants were free to complete both or just one of the questionnaires and the questionnaires were anonymous to encourage honest responses. So it was not known which F1s had provided which data, and thus the data were not related. A non-experimental study design was used, where all participants were asked to complete the same questionnaires. Both quantitative and qualitative data were collected through the use of closed and open questions, respectively. The sample was self-selected, in that the participants volunteered to participate by completing a questionnaire that was presented to them.NHS ethical approval was obtained from the Cambridgeshire 4 Research Ethics Committee (reference number 10/H0305/7), and Research and Development approval was obtained from all the 12 Trusts  it was decided to exclude participants who graduated from medical school before 2010 from the analysis, to minimise the effect of recall bias.The audit of induction procedures conducted for the 2011–12 academic year was completed by 11 of the 13 hospitals. At the time of the study, PfPP was up to 7 days in length and took place before the August start date. It included at least 50 % of the time shadowing an outgoing F1. The audit findings indicated that 100 % of the F1s attended PfPP in 9 of the Trusts, 98 % in 1 Trust and 90 % in 1 Trust. All 11 hospitals also had a Trust induction; in 8 of the hospitals this was integrated into PfPP and it was separate in 3 hospitals. All Trusts had a Trust handbook that was distributed to F1 doctors as part of the induction process, this varied in format, including hard copy , online , CD ; 2 hospitals indicated that the handbook was available in more than one format. Only 1 hospital offered shadowing for F1s at the start of their second and third rotations. Ten of the 11 hospitals provided details about the induction experiences on offer to F1 doctors joining from another Trust for their second or third rotation; this generally comprised of the standard Trust induction only.The results of the audit indicated that all Trusts included the following in their induction procedures: Blood Transfusion training, Clinical governance, Fire health and safety, Infection control, IT training, Prescribing skills, Risk management, consent and complaints, Where to access clinical guidelines and protocols, Resuscitation training, Sickness, and Requesting leave & leave allowance. Ten of the 11 hospitals covered the E-portfolio during induction, and the other included it in the first formal F1 teaching session. Thus this content was covered by all hospitals in the early days of the F1s first rotation. Eight to 10 of the hospitals also covered: Career support, Child protection, Equality and Diversity, Hospital at Night, Hospital security, Incident reporting, Locum arrangements, Manual handling, Occupational health, Pharmacy, Review of practical skills.213 F1s completed the questionnaire in Rotation 1  and 185 completed it in Rotation 3 . Questionnaires were received from F1s working at all of the 13 hospitals in both rotations. After removing the data from F1s who had graduated before 2010 and from participants who did not fully complete the questionnaire the final numbers were 192 for Rotation 1 (62 % response rate) and 165 (53 % response rate) for Rotation 3 ; 92 % of whom had graduated in 2011 in both rotations (the rest in 2010).The demographic background information for each rotation separately can be found in Table F1s were asked to rate how helpful their various inductions had been in preparing them for their F1 role on a 7 point scale . Findings indicated that the PfPP induction programme was regarded as being most helpful Table . DepartmShadowing the job they would be doingTime with, and talks from, outgoing F1 doctorsMeeting other staff in the department and other new F1sBeing given local knowledge - learning about local policies, paperwork / forms, learning their way around the hospitalBeing told how to make referrals and request investigationsBeing told who to contact, when and how to contact themTraining on, and getting access to, the computer systemsInformation and training on dealing with emergenciesRevising clinical skills and how to use equipment (e.g. defibrillator)F1s were asked to outline the most useful aspects of the PfPP/Trust inductions they had experienced, the following were highlighted:Being introduced to the full team/department, including the consultant, and being told who does whatBeing given an explanation of what was expected of them as an F1, including their daily duties and responsibilities, their role in the team, and preferences for how tasks are doneHaving the rota explained to them and finding out what they are expected to do on the different shiftsBeing told how to contact different people, including how to contact senior staff for support.Being given a tour of the department and being told where things areBeing given a handbookBeing told how to request investigationsMeeting with, or being given information from, the outgoing F1F1s were also asked to provide details of the most useful aspects of any of the departmental inductions they had experienced during the F1 year, the following areas were mentioned:The F1s were asked to indicate the length of the departmental induction they had received for their current placement. Data from the Rotation 1 and 3 questionnaires were combined as participants were rating different departmental inductions in each questionnaire. The findings indicated that the length of the departmental induction varied widely  was found, indicating that as length of induction increased so did its helpfulness.The majority of those F1s who had had a departmental handbook said that it was useful (86 %), but 42 % of the F1s had not had a departmental handbook at all.The F1s were asked to indicate how useful they had found 18 potential components of the departmental induction using three categories: “Not at all Useful”, “Moderately Useful” and “Extremely Useful”; a “Not covered” option was also available. Again, as different departmental inductions were being rated by different participants, the results from Rotations 1 and 3 were combined.How to order tests and related paperworkSenior support and how to them contact in dayDischarge policies and related paperworkBeing given a tour of department and being shown where everything isBeing told about how to deal with cardiac arrest and where the trolley isSenior support and how to them contact at nightThe teaching sessions, programme, your requirement to attendWhat is expected of you as an F1 in the departmentThe regular duties of the jobAll 18 components were judged to be Extremely Useful by at least a third of the F1s who answered these questions. Over 50 % rated the following components of their departmental induction to be Extremely Useful:Of these most useful aspects of the departmental inductions, 22 % of the F1s who responded to these questions indicated that “Senior support and how to them contact at night” had not been covered in their departmental induction; 37 % indicated that “Being given a tour of department and being shown where everything is” had not been included in their departmental induction; and 46 % reported that “Being told about how to deal with cardiac arrest and where the trolley is” had not been included in their departmental induction.Other useful components of the departmental induction that had been missing for a fifth or more of the participants who answered the departmental induction questions included “Consultant preferences for patient management” (46 %), “Referral policies” (38 %), “Who to contact in different departments” (36 %), “Study leave policies” (27 %), “Handover policies” (25 %), and “Being introduced to key members of the department” (20 %).Not having received a departmental induction at allNot having ID badges, passwords, access codes for doors to enable them to do everything expected of them as soon as they started their jobNot having a tour of the department and/or hospitalA lack of knowledge about their duties and responsibilities, and what was expected of themNot knowing who to contact or how to contact people, particularly senior staff, including out of hoursNot knowing what is involved in being on-call/working out of hours and lack of explanation about handoversLack of explanation about rotas and annual leave policiesWhen asked via an open ended question what gaps the F1s felt there had been across all of the induction experiences available to them the following areas were highlighted:When asked how such gaps could be filled F1s requested a departmental induction, including meeting consultants and other staff, tour and a departmental handbook. More specifically, they wanted more information about their duties and what is expected of them, including on-call/out of hours, and more information about how to do a handover. During the PfPP week, they wanted more time shadowing, including shadowing of on-call/out of hours, talks from the outgoing F1s about day-to-day jobs and how things ‘work’, and for some of the lectures to be revised so as to be more relevant to their needs regarding their day-to-day duties.In the Rotation 3 questionnaire, those F1s who had moved Trusts during the year were asked to provide details about any problems they had encountered due to lack of adequate induction at their new hospital. There were fewer responses to this question, as it did not apply to many of the participants . Several participants commented that they had not encountered any problems or spontaneously mentioned that their induction had been good. The main problem encountered related to lack of familiarity with the new computer systems and the related issue of not having the required accesses  to do what they needed to do at the start of the rotation. A few participants commented that there had been a general lack of information about what was expected of them and that there was no one available to help them and/or they did not know whom to ask. Other participants simply made general comments about not having a departmental induction or having an unspecified poor induction experience.The findings indicate that F1s are undergoing variable induction experiences. Most F1s report that PfPP, the week-long induction provided by the EAFS immediately prior to the August start date, is helpful. Comments indicated that components of this induction programme, including shadowing the outgoing F1 and formal teaching such as revision of clinical skills, are valued by the F1s. This is in line with the findings of focus groups conducted with F1s the previous year at the same 12 Trusts . These FIn contrast to the generally positive PfPP induction experience, the F1s’ experience with the departmental inductions is more variable, particularly in later rotations. The findings from the questionnaires suggest that longer departmental inductions are more useful, but half of the F1s experienced inductions of only 2 h or less, and some did not have a departmental induction at all. Similarly there are multiple components to the departmental inductions judged to be useful by F1s, which many other F1s are not experiencing. These findings are consistent with the earlier focus group study  and suppThe F1s are facing many important gaps in their induction experiences. At the most basic level, many have not been told their duties, responsibilities or what is expected of them. Additionally, they have not been given a tour of the department, so they do not know where anything is. In some cases F1s are unable to do their job when they start a new rotation because they have not been provided with identification badges, passwords for computer systems or access codes for doors to secure areas. They also do not know what is involved in being on-call/working out of hours, how the rotas and handovers at shift changes work, or the annual leave policies. They do not know who to contact or how to contact them, including accessing senior support out-of-hours. Additionally, the audit of inductions indicated that F1s rotating into a new Trust for their second or third rotation generally only receive the standard Trust induction, which does not usually include those aspects that the F1s rated as useful in a departmental induction or the valued components of PfPP such as shadowing the new rotation’s post. As a result many F1s are dealing with considerable uncertainty about rudimentary aspects of their F1 role, which previous research indicates represents an unnecessary additional stressor during this time of transition between medical school and work as a trainee doctor .The induction programme serves a number of purposes. At the most basic level it provides a new employee with information relating to employment matters such as rotas, annual leave procedures, health and safety issues and Trust policies on a variety of topics. This induction is commonly generic and applies to all grades of staff. The findings suggest that most of the Trust inductions addressed these areas. More significantly, for the new F1, the induction programme provides a useful bridge between medical school and clinical practice. If it is effective it should mitigate the anxiety caused by the step change in responsibility that individuals experience during this transition . The PfPThomson et al.  recommenIt is recognised that making quality improvements to departmental inductions will not be an easy task; it is possible that in some Trusts this will not be amenable to central control. As such, the postgraduate medical education offices will be reliant on multiple individuals to determine the department-specific topics necessary for their incoming F1s to know and also to deliver all the agreed-on content. However, in considering the use of clinical rotations in both undergraduate and postgraduate medical education, Holmboe et al.  commenteWhilst F1s from 13 different hospitals were involved in the induction experience questionnaire and the audit involved data from 11 of these hospitals, the key limitation of this study is that it was conducted within the context of a single Foundation School. Whilst the findings reported here do support those of Thomson et al. , who conIn conclusion, trainee doctors need to be supported by adequate and appropriate inductions, to ensure that they are optimally prepared for the specific experience of each clinical placement they undertake during their two years on the Foundation Programme. However the findings of this research indicate that induction experiences, particularly at the department level, are currently not sufficient to meet the F1s’ needs. The findings show that the information and support needs of F1s from their inductions are known; now it is necessary to ensure that all departmental inductions are fully inclusive of this content.


The use of Matlab® lends itself to speedy evaluation and implementation of image processing options on the AGV, but its functioning in such an environment needs to be assessed.Automatic Guided Vehicles (AGVs) are navigated utilising multiple types of sensors for detecting the environment. In this investigation such sensors are replaced and/or minimized by the use of a single omnidirectional camera picture stream. An area of interest is extracted, and by using image processing the vehicle is navigated on a set path. Reconfigurability is added to the route layout by signs incorporated in the navigation process. The result is the possible manipulation of a number of AGVs, each on its own designated colour-signed path. This route is reconfigurable by the operator with no programming alteration or intervention. A low resolution camera and a M The AGV utilises a single digital camera providing omnidirectional (360°) vision for navigation . A reconatlab® for speedy evaluation and implementation of image processing options. An overview of the system is illustrated in The project involved a vision sensor, AGV vision navigation control and the development of a reconfigurable approach to prove the feasibility of using a single software platform like M2.As the surroundings were to be detected by vision, the setup used a webcam using an omni-mirror setup placed on top of a National Instruments  robot platform is shown in A PC was used for the development and initial simulations. The code was then transferred to a laptop for navigation trials. 2.1.atlab® applied Maximum radius represents the height of the frame to be converted and φ the resolution width of the panoramic view, as can be seen in Scaramuzza's research proved that a polar transfer function can be implemented by creating a good panoramic image . The polatlab® with the result shown in This polar transform was applied to atlab® function with a radial step resolution of 1° [® Pentium® 3.4 GHz CPU with 3.25 GB of RAM. atlab® M-file providing the result.on of 1° ,5. This 2.2.® was incorporated for this purpose. From Video Device data block. The Embedded MATLAB function was written incorporating the conversion model seen in The initial development was done on single pictures taken with the omnidirectional photographic setup. These were changed to a video streamed system. SimulinkWith the results obtained in Section 2.1, it seemed imperative to reduce the computation time for acquisition, conversion and display. This could be done by selecting a smaller area of interest in the direction of movement of the AGV as illustrated in 2.3.atlab® has a feature, called bench, to evaluate the processing strength of computers in different calculating areas. The result for the platforms used in Matlab® Central [ Central . Keeping3.atlab® for the navigation and control of an AGV.In a reconfigurable environment it should preferably be possible to alter the route that the AGV needs to travel, depending upon ordering information (origin or pickup point) and delivery of parts (destination) . This co3.1.et al.'s work proved the use of lines on the side of a route or walkway, or alternatively a chroma route could be used for route navigation [atlab®'s “Chroma-based Road Tracking” was altered for this purpose. ® model of the demo [Chroma-based Road Tracking” demo model illustrates the use of the Colour Space Conversion block, the application of Hough Transform block, and the advantage of the Kalman filter block to detect and track information using hue and saturation values of the frames from the video.Sotelo vigation . Matlab®the demo . When ruThe demo model performs a search operation to define the left and right edges of a road by analysing video frames for a change in colour behaviour. The model then selects a line either because of an edge detected, or a line created by a change of chroma pixels, whichever has the greater precedence. The search is initiated from the bottom-centre of each frame and moves to both the upper-left and upper-right hand corners of each frame. From this model outputs were generated to navigate and control the AGV on a set route.3.2.atlab®'s serial communication data block.There was a need to communicate the associated direction commands from the evaluation images of the camera system to the AGV platform. A PIC microcontroller board and software was developed in such a way that the direction control signal of the AGV was sent serially via the USB port of the laptop to the PIC board also using M4.The concept of sign detection in conjunction with route tracking is to provide the AGV controller with an indication as to which route is to be taken when encountering more than one option. This is accomplished by incorporating left- and right turn signs, with a stop sign at its destination. This gives the AGV a reconfigurable route set by the operator, without programming intervention or changes, by placing the required signs along a changeable route. Altering the colour which the AGV responds to, gave rise to alternative routes for different AGV's to follow, best illustrated by Correlation was achieved by implementing templates of the signs after initial detection of the preset colour for the specific AGV. An example of the templates is shown in 4.1.After a potential sign has been detected in consecutive video frames, the model identifies the sign to generate the appropriate command to be sent to the AGV. Examples of signs detected are shown in 4.2.the RGB video signal implementing a tolerance for each colour signal representing this selected route colour;HSV signal rather than the RGB signal; andthe YCbCr signal. This produced better results using the colour signals red (Cr) and blue (Cb).Different methods for colour detection were investigated, which included:Y signal, ® model shown in Using This method proved experimentally the most successful, as the colour selected made the output signal less sensitive to variations in different levels of lighting.4.3.Detecting the command signs successfully posed a problem with respect to the reaction time of the AGV to execute the relevant command. This made a difference in the distance from the sign to the specific position of the AGV.The size of the different signs was standardised to be approximately 18 cm × 18 cm. By knowing the sign size, the distance from the AGV to the sign could be calculated using the number of pixels representing the image size recognised . The distance to the sign selection was developed to be a variable input in the SimulinkDetermining this distance to the sign was achieved by using the area of the bounding box placed around a detected sign and then comparing this pixel count with the required size . When true, the relevant sign command detected was executed. Provision was made for a multiple count of signs detected in a single frame during consecutive frames.® model block where the area of the detected sign (Prod) and the variable distance (Dist) is needed as input with the stop, direction and switch control signals generated as output.atlab® function block code generating the control and switching signals. Only the forward, left, right and stop signals are shown for illustrative purposes.5.Looking at the specifications of the PC and laptop used, the speed of the processor and size of RAM were the major factors that caused the difference in processing power. 5.1.The maximum respective speeds of two different AGV types were 2.7 and 1.3 km per hour without using any vision—as depicted in The speed of 18 cm per frame was clearly too fast to allow for image processing using the laptop. The AGV's speed needed to be reduced, because 6 to 8 frames per second were necessary for proper vision control. This meant that the AGV travelled more than a meter at 6 frames per second (18 cm × 6 frames = 108 cm). This is more than a typical turning circle distance (90 cm) allowed before a control decision could be made. Altering the speed to suit the processing time related to a speed of 6 cm per second, which was not suited for the final industry application. Thus the laptop processing speed was insufficient for such a vision sensor AGV control application.5.2.et al.'s work [In this section the performance of the route navigational system of the AGV was evaluated in terms of following the route as indicated by coloured signs and using vision . As ther.'s work , the movThe results were compared and noted with respect to the orientation of the AGV and its position on the route. What was evident was that the AGV could follow a set route with ease and that the commands generated from the navigation system did give the desired output to the AGV drive controls. 5.3.The sign recognition system provided the route reconfigurability to be applied by the operator by placing the applicable signs along the route for a specific AGV. The sign recognition system was designed and made provision for signs to be detected to a rotated angle of ±7.5°. The signs could however be detected to a maximum rotated angle of 45° for the left and right sign, and 30° rotated angle for the stop sign. Encountering the signs at a horizontal offset angle also did not provide a problem, as the deviation from the straight-on position could vary by as much as 50° without causing a failure in recognising a sign, as can be seen in The AGV movement control acted on the signs control function at a predefined distance, set at 70 cm for evaluation purposes, determined by the set area of the bounding box. The distance between the sign and AGV was determined by the average area of the bounding box seen in  around t6.atlab®. Selecting a webcam and making use of an area of interest enabled the saving of valuable computational time in converting an image.The research covered in this article proved the viability of a developed omnidirectional conversion algorithm written in Matlab® was chosen as the complete software platform generating results, evaluating the camera setup and mirror configuration on a PC and later a laptop. The results obtained proved that the laptop processing time was too slow for omnivision purposes for the mobile system to be implemented in industry.MThe navigational goals, using vision, as described in this article were successfully met by the developed AGV platform and the route navigation with the sign recognition and control implemented. A reconfigurable layout could be achieved with relative success using an AGV recognising only a set colour for its specific route.


Estimation of sample size and power for stepped wedge cluster randomised trials can be determined by one of a number of related methods. These include exact analytical approaches, design effects or simulation. A recent paper compared the design effect to the analytical method. There were some differences between the two approaches. We show here that these differences occur because the design effect approach is only technically correct when there is an equal number of clusters crossing over at each step.The design effect for the stepped wedge cluster randomised trial is only appropriate when there is an equal number of clusters switching at each step. Baio and colleagues  compare Suppose a trial is to be designed to detect a standardised mean difference of 0.25 at 80 % power and 5 % significance. Under individual randomisation a sample size in the region of 250 per arm is needed. This example is constructed to be similar to the example in Table 1 of [The design effect based on the formula by Woertman is:However, using 8 clusters in an SW-CRT with 5 steps does not result in the same number of clusters crossing over at each step (as 8 is not a multiple of 5). So, either 1 or 2 clusters need to cross over at each step. There are, however, different ways of arranging this design. Two possible arrangements are given in Fig. Perhaps the more intuitive arrangement is to have 2 clusters randomised to each of steps 1, 2 and 3 and 1 cluster randomised to each of steps 4 and 5 (Fig. An alternative arrangement, arrangement two in Fig. In some ways the observation presented here is a technicality. But, it might have some interesting ramifications—and insights for maximising efficiency. At the very least, when using the design effect in practical applications, it is important to appreciate this difference and check that the magnitude of the differences in power is not too great.


External wrapping is a surgical method performed to prevent the dilatation of the aorta and to decrease the risk of its dissection and rupture. However, it is also believed to cause degeneration of the aortic wall. A biomechanical analysis was thus performed to assess the stress of the aortic wall subjected to external wrapping.A stress analysis using the finite elements method was carried out on three models: a non-dilated aorta, a moderately dilated aorta and a wrapped aorta. The models were subjected to a pulsatile flow (120/80 mmHg) and a systolic aortic annulus motion of 11 mm.The finite elements analysis showed that the stress exerted on the outer surface of the ascending aorta in the wrapping model (0.05–0.8 MPa) was similar to that observed in the normal aorta (0.03–0.7 MPa) and was lower than in the model of a moderately dilated aorta (0.06–1.4 MPa). The stress on the inner surface of the ascending aorta ranged from 0.2 MPa to 0.4 MPa in the model of the normal aorta, from 0.3 to 1.3 MPa in the model of the dilated aorta and from 0.05 MPa to 0.4 MPa in the wrapping model.The results of this study suggest that the aortic wall is subjected to similar stress following a wrapping procedure to the one present in the normal aorta. The dilatation of the tubular part of the ascending aorta is often diagnosed in patients with aortic valve pathology. Some surgeons prefer the ”watch and wait” approach to a moderately dilated aorta accompanying aortic valve disease. However, this approach carries the risk of a reoperation in case of further aortic dilatation. Thus, most cardiac surgeons choose to replace the dilated tubular part of the ascending aorta or perform other surgical procedures like aortoplasty or wrapping.In the 1970’s, Robicsek et al. published the results of a theoretically less invasive surgical technique, called an aortoplasty . They foThere is some concern that placing an external corset which decreases the size of the dilated fragment of the aorta may increase the stress in the aortic wall and lead to a degeneration resembling the process observed in decubitus.One way of verifying whether a decrease in the diameter of a moderately dilated ascending aorta with an external corset causes any stress increase in the aortic wall is a biomechanical analysis using the finite elements method. This is a computational method, which demonstrates an approximation of the exerted stress that can occur given the necessary entry data of the object and its surroundings .The aim of this study was to assess the stress distribution in the aortic wall following a wrapping procedure. A biomechanical analysis comparing wrapping with a dilated and nondilated aorta using the finite elements method was performed.Three computational models were created for further analysis – models of the normal aorta and a moderately dilated aorta with and without wrapping. The mechanical properties of the aortic wall were established according to data available from other biomechanical studies –14. YounThe diameters of the segments of the model of aorta were as follows: 38 mm at the level of the aortic root, 32 mm at the level of the tubular ascending aorta (45 mm in the model of the moderately dilated aorta) and 28 mm at the level of the descending aorta. The radius of the lesser curvature of the aortic arch was 25 mm. The diameters of the main branches of the aortic arch were 10 mm. In the wrapping technique, the aorta is additionally covered by the vascular prosthesis. In our experience, the aortic wall of the moderately dilated ascending aorta (40–55 mm) does not plicate when its diameter is decreased to approximately 30 mm  were identical in all the simulations. The dimensions of the analyzed models were the only variables. The simulations were carried out using Ansys software .The highest values of stress in the aortic wall were observed at the end of the systole, when arterial pressure was at its peak and the heart muscle was completely contracted and maximally pulled the aortic annulus. All stress values presented in this study were recorded during the above mentioned phase of the heart cycle.The distribution of stress on the outer surface of the ascending aorta which was most similar to that observed in the normal aorta (0.03–0.7 MPa) was seen in the wrapping model (0.05–0.8 MPa). The highest values of stress in the aortic wrapping model were noted near the margins of the vascular prosthesis. Overall, the highest values of stress were observed in the aneurysm model 0.06–1.4 MPa), especially in the area between the lesser curvature of the aortic arch and the tubular part of the ascending aorta. The graphical visualization of the distribution of stress on the outer surface of the models is shown in Fig.  MPa, espIn all the models, the highest values of stress were noticed in the distal part of the ascending aorta, at the junction with the aortic arch. The highest values of stress on the inner surface of the ascending aorta were observed in the aneurysm model (0.3–1.3 MPa). They ranged from 0.2 MPa to 0.4 MPa in the model of the normal aorta and from 0.05 MPa to 0.4 MPa in the aortic wrapping model. The stress values in the aortic wall underneath the vascular prosthesis in the aortic wrapping model were lower than in the model of the normal aorta. There was a 0.1 MPa difference between the stress values around the edges of the vascular prosthesis in the aortic wrapping model (0.2 MPa in the wrapped portion of the aorta vs. 0.3 MPa in the nonwrapped aorta). The graphical presentation of the stress distribution on the inner surface of the ascending aorta in all models is shown in Fig. Aortic wrapping is considered to be a controversial surgical method. To date, the results of wrapping with and without concomitant aortoplasty have been promising , 26, 8. During an isolated wrapping procedure, the diameter of the vessel is decreased without excising its wall. Based on our observations, there are no “wrinkles” or plications of the aortic wall after an isolated wrapping procedure of a moderately dilated aorta. This could result from the residual elasticity of the moderately dilated aorta, which may return to its normal diameter when an external scaffold is applied. One possible explanation is that the arterial pressure pushes the aortic wall against the external scaffold and prevents it from being plicated.To assess the potential unfavorable biomechanical characteristics of the aorta subjected to a wrapping procedure, the analysis of stress distribution in the aortic wall is needed. Such an analysis should then be compared to the values observed in a “healthy aorta”. One of the best methods of defining the stress distribution is a finite elements analysis (FEA). It involves dividing an analyzed object into numerous smaller elements and carrying out mechanical analyses of the model. The results are an approximation of the phenomena that may occur in the real object. This method is primarily used for engineering purposes. It allows the assessment of the distribution of stress and strain and the investigation of the critical regions within an analyzed object. The finite elements analysis has already been used in cardiovascular medicine –19 but tThe values of stress on the inner and outer surfaces of the aorta in the model of external wrapping were comparable to the values observed in the normal aorta. Moreover, the values of stress on the inner surface of the wrapped portion of the aorta were even lower than in the nondilated aorta. This means that from a biomechanical point of view, the inner surface of the wrapped aorta is subjected to lower stress than an unwrapped aorta and should be less likely to dissect.According to the recent data, the aorta mainly dissects before reaching the threshold diameter, which qualifies it for replacement . Thus, aExternal wrapping of the moderately dilated aorta may be a useful procedure accompanying the aortic valve procedure. However, one should be aware of the possible complications associated with this technique. An improper placement of the prosthesis may cause wrap dislocation and aortic redilatation. Aortic wall degeneration has also been observed in several patients, but it did not lead to aortic dissection in any of the patients.Due to technical limitations, the aortic annulus up-and-down motion was simulated without the additional twist that is observed during systole. The simulations were performed on simplified, theoretical models.The results of this study suggest that after a wrapping procedure, the aortic wall is subjected to similar stress that occurs in the normal aorta and lower stress than in the nonwrapped, moderately dilated aorta. From a biomechanical point of view, the wrapped aorta is less likely to dissect than a dilated aorta.


The development of skin-like sensors capable of sensing these stimuli is of great importance for various applications such as robots, touch detection, temperature monitoring, strain gauges etc. Great efforts have been made to develop high performance skin-like sensors, but they are far from perfect and much inferior to human skin as most of them can only sense one stimulus with focus on pressure (strain) or temperature, and are unable to visualize sensations and shape of objects. Here we report a skin-like sensor which imitates real skin with multiple receptors, and a new concept of pain sensation. The sensor with very high resolution not only has multiple sensations for touch, pressure, temperature, but also is able to sense various pains and reproduce the three dimensional shape of an object in contact.Human skin contains multiple receptors, and is able to sense various stimuli such as temperature, pressure, force, corrosion  A user-interactive electronic skin has been demonstrated which is able to visualize pressure distribution using an array of organic light emission diodese.g. thermo-responsive polymers20Human skin is a complex and sensitive system containing multiple receptors. These receptors act as sensors, and are able to sense various stimuli such as thermal variation, light touch, mechanical pressure, deformation and chemical corrosion, with very high sensitivity and resolution2458911131415The skin-like sensor consists of a crisscross conductive network as the receptors (sensors) and a polydimethylsiloxane (PDMS) surface layer as the dermis. The conductive network was made from a multiwall carbon nanotubes (MWCNTs) and PDMS composite. The processing flow for device fabrication is shown in 2 square. Each side of the sensor has 30 electrodes for electrical connection. For the convenience of sensing, the resistance change of 20 pairs of the 30 pair electrodes was measured in the middle part of the sensor, and the sensor was attached to the electrodes of a peripheral circuitry using the conductive silver gel.The materials and device structures were characterized by scanning electron microscope (SEM) . In order to test the performance of the sensor, the sensor was connected to the peripheral circuitry. The circuit design is presented in the SI. The skin-like sensor was cut into 4 × 4 cmThe resistance of conductive lines of the as-made sensor is in the range of 18 kΩ to 21 kΩ, mostly caused by the variation of the MWCNTs content in the channels. The resistances of the sensor vary with cyclic extension due to the relaxation of the composite and the settling down of the CNTs; therefore stabilization was applied before sensing experiments to ensure the change of the resistivity is caused by a stimulus rather than by the relaxation. The resistance of the conductive lines increases slowly with the cyclic extension and eventually stabilizes . Once settled down, the resistance of the conductive lines was found to increase almost linearly with the increase of strain in a range less than 40%, and gradually saturates with further extension. The pressure and touch sensing experiments were conducted mostly in the linear region, while the thermal and pain sensation tests are not limited by the linear relationship.ith conductive line is Rxi in the x-direction as indicated in i in the y-direction, the resistance change before and after the application of a stimulus isWhen the sensor is deformed or damaged by a stimulus such as touch or corrosion, it not only changes the resistance of the conductive line, but also affects the resistance of the surrounding lines, generating a two dimensional (2D) distribution of resistance variation. Assume the resistance of the andrespectively. The ratioith and jth lines perpendicular to each other with the intensity representing the strength of the stimulus. This ratio will be used to visualize various sensations in 2D in this work. An absolute value of |ΔRxi| was used to assess the change ratio, as it can be used to distinguish the type of stimuli as discussed later.will represent the change of the resistance at the point of the A two-point threshold method is normally used for touch sensation which may vary for different parts of a human body. The smallest distance is typically 1 ~ 2 mm, existing on the lip and finger tips2) for sensing as shown in 2. The pressure for the small object is 55.7 Pa, corresponding to a pressure sensitivity (defined as ΔR/RΔP) of 3.6 kPa−1. This detection limit is much smaller than the smallest pressure (>100 Pa) human skin can sense, though larger than some values reported by othersA large force over a relatively large area is needed to activate the pressure receptor which lies deep in the skin. Thermal sensation of skin is a sense that is associated with our need to maintain our internal temperature, and to warn potential harm when the surrounding temperature is too high. The skin-like sensor is able to sense temperature variation owing to the resistivity change of the conductivity lines with temperature. A typical change of the resistance from one conductive line is shown in 27To imitate the sensation of temperature, a heated thick wire of 1 mm in diameter was put on the sensor on a flat surface. The color mappings of the resistance change for the sensor induced by temperatures of 35 and 45 °C are shown in 2. The average force that brought a pain sensation was about 1.98 N. Therefore a force of 2.0 N (corresponding to a pressure of 3.33 × 106 Pa) from the force gauge was then applied to the sensor on a flat surface  was used to imitate the pain induced by the corrosion and distortion of the epidermis as shown by the photo of 2 skin-like sensor. The elongation length of each sensing line can be obtained through the measurement of the resistance change. For simplicity, three conductive lines were chosen from the nine lines for the measurements that cover the center and the edges of the deformed area as shown in An ideal skin-like sensor should, not just sense stimuli, but also “feel” and “reproduce” the shape of an object in touch. Here we demonstrate this feasibility by our E-skin using a ball as a demonstrator as shown in here a and c are constant. With this relationship, we can obtain sufficient points from the surface of the ball to reproduce the shape. The values of the constant a and c can be calculated by solving the equations.where ΔL is the increment of the length, and L is the initial length. L and ΔL are known since the length of the quadratic curves can be estimated from the resistance change measured. The deformation detected by three lines in the x-direction would be the same as those in the y-direction owing to the symmetric structure, therefore the calculation can be further simplified with only three conductive lines measured. The results have demonstrated that the skin-like sensor is capable of detecting and distinguishing sensations induced by different stimuli, and sensing the brief 3D shape of a ball. This paves the way for practical applications. However identification of the types of sensations, especially the pain sensations, requires some judgment. Both the mechanical and corrosion pains are correlated to the positive change of the resistance, while the thermal pain is associated with the negative change of the resistance, allowing the identification of thermal pain. Mechanical pain is associated with the deformation which is recoverable once the force is removed, while corrosion pain is associated with permanent change of the resistance. Therefore, the pain sensations can be distinguished and can be utilized for the development of intelligent skin-like sensor with self-justification for sensations. However, when there are both mechanical and thermal inputs, it is difficult to differentiate the type of stimulation sources. The problem may be solved by integrating more device structures. For example, fractal design2. It was then etched by deep reactive ion etch  to form the crisscross network channels of 50 μm deep and 10 μm wide. The Si wafer was used as the mould to fabricate the sensor. (2). The network channels of the silicon mould were filled with MWCNTs powder with shake, and then the excessive CNTs above the surface of the Si wafer were removed using a razor. The weight of the MWCNTs was ca. 8.5 mg (±10%) after the excessive nanotubes were removed. (3). The silicon mould with MWCNTs in the channels was filled with the degassed prepolymer PDMS (at a ratio of 10:1 for the base to the crosslinker by mass) with the amount prefixed for a sensor and waited for 10 min to let the PDMS penetrate into the gaps of the MWCNTs in the channels. It was then spun at 1000 rpm for 3 sec to obtain a layer of PDMS with a fixed thickness on top of the composite in the channel. (4). The PDMS composite on the Si mold was then solidified in an oven at 90 °C for 30 min. (5). Finally the PDMS E-skin was peeled off the silicon wafer, ready for use.The MWCNTs were purchased from Chengdu Organic Chemical Co. Ltd, China. They have the length distribution of 10 μm to 20 μm, the inner diameter of 5 nm to 15 nm and the outer diameter of 50 nm to 80 nm. The PDMS  based flexible skin-like sensor were fabricated by the following process steps: (1). Crisscross network channels were patterned by photolithography process using positive photoresist (AR-P 5350) on a 4-inch silicon substrate with the size of 4 × 4 cm2, while the thickness of the top PDMS support layer is 250 μm. MWCNTs were used to form a conductive network, and the change of resistivity of the network was used to sense various stimuli.The cross section of the PDMS/MWCNTs composite lines is 50 × 10 μmDevice structures and the details of the conductive lines were characterized by scanning electron microscope (SEM) . The resistance measurements were conducted using a circuitry specially designed for this work or by the probe station (Vector MX100 DC) and the Agilent B1500A semiconductor device analyzer. For temperature sensation experiments, a hot plate  was used which is able to control the temperature down to 1 °C.2 pieces for the sensation experiments. The peripheral circuitry was composed of a microchip (MSP430F149), an A/D converter (ADC7824), 4 decoders (CD4514B) and 4 multiplexers (CD4067B). The large pieces were cramped at the two ends by an electromechanical testing machine . The force gauge  with the precision of 0.001N was used to apply forces on the E-skin in the pain sensation imitation.The samples were cleft into 4 × 4 cmHow to cite this article: Xu, T. et al. High resolution skin-like sensor capable of sensing and visualizing various sensations and three dimensional shape. Sci. Rep.5, 12997; doi: 10.1038/srep12997 (2015).


We study the dynamics of a predator–prey system where predators fight for captured prey besides searching for and handling (and digestion) of the prey. Fighting for prey is modelled by a continuous time hawk–dove game dynamics where the gain depends on the amount of disputed prey while the costs for fighting is constant per fighting event. The strategy of the predator-population is quantified by a trait being the proportion of the number of predator-individuals playing hawk tactics. The dynamics of the trait is described by two models of adaptation: the replicator dynamics (RD) and the adaptive dynamics (AD). In the RD-approach a variant individual with an adapted trait value changes the population’s strategy, and consequently its trait value, only when its payoff is larger than the population average. In the AD-approach successful replacement of the resident population after invasion of a rare variant population with an adapted trait value is a step in a sequence changing the population’s strategy, and hence its trait value. The main aim is to compare the consequences of the two adaptation models. In an equilibrium predator–prey system this will lead to convergence to a neutral singular strategy, while in the oscillatory system to a continuous singular strategy where in this endpoint the resident population is not invasible by any variant population. In equilibrium (low prey carrying capacity) RD and AD-approach give the same results, however not always in a periodically oscillating system (high prey carrying-capacity) where the trait is density-dependent. For low costs the predator population is monomorphic (only hawks) while for high costs dimorphic (hawks and doves). These results illustrate that intra-specific trait dynamics matters in predator–prey dynamics. Felis catus with striking differences in many traits between rural and urban cat populations.Traditionally in Ecology feeding of the predator population on prey is modelled using the Holling type II functional response which depends on the rate of attack and the time it takes to handle prey. We study the effects of an additional behavioural type via modification of the functional response. The modelling approach has been formulated firstly by Auger and Poggiale . The enctactics that both fighting predator individuals play: hawk or dove. This is encapsulated in a pay-off matrix. The pay-off matrix elements give the outcome of the contest between two individuals playing the same or different tactics. At the population level the strategy of the population is quantified by a time dependent continuous population trait being the momentary proportion of the population that plays the hawk tactics (frequency dependence). So, we use the term tactics to indicate how predator individuals act during a contest for already captured, but not jet consumed, prey and the term strategy for the performance of a whole population.This paper deals with the case where part of the captured prey is handled directly and for the other part two predator individuals will fight before consumption. To incorporate this in the model for the trophic interaction between predators and prey, the predator population is divided into three compartments: searcher, feeders and defenders. The ecological processes such as searching and feeding are modelled similar to the classical Holling functional response formulation. In both processes individuals from a single compartment (searchers or feeders) are involved. In a similar way the behavioural processes are modelled, now with encounters between individuals from two different compartments (searchers and feeders) which makes the analysis more complicated. In a number of articles by Auger and Poggiale , Auger eIn an population dynamics context, evolutionary game theory is often combined with inheritance of traits via mutations at the individual level. Then the time-scale of the dynamical behaviour of the trait is slower than that of the prey and predator populations. Here the trait changes are behavioural, due to for instances imitation or learning, and these processes are often much faster than the rate of change of the population sizes. Nevertheless we will use the same terminology except that we replace mutant by variant.replicator dynamics (RD) describing the population trait dynamics was derived for a population where the individuals play a hawk–dove game based on a learning process. The reproductive success (number newborns per unit of time) was the fitness criterion while the number of individuals was constant with the fraction hawks as the continuous time trait. An individual changes its tactic when its pay-off becomes larger than the average pay-off of the population and in this way the trait of the predator population increases (see for instance in the book by Hofbauer and Sigmund ess).In the book by Gintis  the replA reduced predator–prey model was derived by Auger et al.  applyingess is reachable or not). The relationship between these two approaches for discrete time systems with non-overlapping generation was already studied by Dieckmann and Metz  where the resident population is not invasible by any variant population but here we will also encounter a ss that is a neutral stable strategy (nss), see Fig. 9b  appears to have a stabilizing effect that is depending of the costs. Furthermore, elaboration of the AD-approach yields that two predator populations with different trait values and feeding on a single prey population can coexist stably: contrary to the competitive exclusion principle.We will here demonstrate that he RD- and the AD-approach lead to the same results for the system in equilibrium whereby in the RD-approach there is an We consider a predator population p, with density If during this handling phase the individual does not encounter a searching predator it digests the prey (including growth and/or reproduction) and becomes a searcher again  population trait: the RD- and the AD-approach. Crucial is the definition of the fitness and the trait besides the functional dependency of the fitness on the trait .In the RD-approach the ecological model and the contest model are kept separated because the size of the population is kept constant with the derivation of the replicator equation. When the trait dynamics can be assumed to be fast we have an algebraic expression for the trait as a function of the gain and costs (probably time-dependent). That is, the In the adaptive dynamics (AD) theory the fitness,  and Law  describess trait value is fixed by a zero fitness gradient and the same expression as Eq.  under parameter variation. The basics of bifurcation analysis are described in the books  given in Eq. \documentr et al. , Eq. 2)\documentn in Eq. . ObserveWhen the time-scale separation argument is used, the processes described in Eqs.  by the er et al.  and in tThe long-term dynamics predicted by the RD-models are presented in two parameter bifurcation diagrams where the game costs In Fig. r et al.  and in tmentclass2pt{minimrium Eq. , that isr et al.  and are ess trait The bifurcation diagram Fig. mentclasspt{miniman by Eq.  shown inentclass1pt{miniman by Eq.  instead n by Eq. . Consequ(see Eq. ) and notentclass1pt{minima(see Eq. ). Here fThe solutions of the system Eq.  where \dmentclasspt{minimaalue Eq.  is justiWe finish the discussion of the RD system with showing the one-parameter diagram with the prey’s carrying capacity We will use the results given in Figs. Figure There is in the AD approach no change of tactics in the defending stage as was the case in the RD approach. In the AD-approach this change is due to competition between the resident and a variant population when the variant population invades and replaces the resident population. Hence, in order to find the solution for the game equilibrium we test whether the variant being rare can invade the system consisting of the prey and the resident predator. Similar to the fast rate of change of tactics in the RD approach where The equations for the predator–prey system are: Note that a resident individual in n by Eq. : \documeThe average gain of the hawk (resp. dove) equal mentclass2pt{minimThese expressions are equal for both resident and variant populations. The expressions for the different average gains for the two whole resident and variant populations are The dynamics of the three sub-populations In order to find the singular strategy We start with the analysis of the AD-model Eqs.  using syThe non-zero elements in the Jacobian matrix evaluated at the equilibrium where the variant population is absent are indicated in:ss is now fixed by the two equations:ss is the intersection of these two curves.The We can use the special shape of the Jacobian matrix to get analytical expressions for the solution of these equation. We start with the calculation of n in Eq.  we have ng Maple  we foundIn order to explain these results we show the pip-plot in Fig. mentclass2pt{minimn by Eq. . Using mObserve that invasion of the variant population is related to the zero eigenvalue on the nss is invasible by new variants. However, when the next variant population lies in the ’The parameter space In Fig. n in Eq. .Fig. 7TwThese results hold only when the long-term dynamics of the predator–prey system is a stable equilibrium. In the next section we discuss the case where the long-term dynamics is a limit cycle.We continue with the analysis of the limit cycle case with the example where the parameter values are 4 in Eq.  are compauto : a general result of game theory, widely known as the Bishop–Cannings theorem (Bishop and Cannings ss is continuously stable (css). The use of  bifurcation analysis techniques makes it possible to analyse more complex and biologically more realistic models such as the continuous-time predator–prey system.In the literature the AD-approach has often been applied to simple ’toy’ models to get theoretical insight. In Dieckmann and Metz  this wasIn the RD-approach two-parameter stem Eq.  describestem Eq.  are giveentclass1pt{minimaSince the transcritical bifurcation From Figs. In both approaches, the monomorphic and the dimorphic cases are separated by the vertical curve at the same entclass1pt{minimaess as equilibrium of the replicator equation in the RD-approach, the ss in the AD-approach is a nss. New variant populations can coexist with the resident populations forming a stable coalition between two populations with a different trait value. This shows that the introduction of a behavioural process for the predator population makes it possible to have two different predator populations, namely with different trait values, living on one prey population. This is in contradiction with the “competitive exclusion” principle by Hardin . Individuals in a replicator system have localized knowledge concerning the system as a whole Gintis . On the nss value. Notice that this degeneracy, also discussed by Dieckmann and Metz (ss is not degenerated, it is a css. Hence for this predator–prey system oscillatory dynamics does not facilitate coexistence of two predator populations living on a single prey population.When variant populations differ randomly from the resident with myopic learning by trail and error, then for stable equilibria of AD-approach system the trait values remain in general close to the predicted and Metz , exists These results illustrate how intra-specific trait dynamics matters in predator–prey interaction and therefore also in ecosystem dynamics in general.


N fiducial markers from 1D projections is presented and analysed. It applies to semi-active markers and active markers using a single receiver channel.A new method for 3D localization of The novel algorithm computes candidate points using peaks in three optimally selected projections and removes fictitious points by verifying detected peaks in additional projections. Computational complexity was significantly reduced by avoiding cluster analysis, while higher accuracy was achieved by using optimal projections and by applying Gaussian interpolation in peak detection. Computational time, accuracy and robustness were analysed through Monte Carlo simulations and experiments. The method was employed in a prototype MRI guided prostate biopsy system and used in preclinical experiments.an improvement of up to 100 times, compared to the method by Flask et al. (J Magn Reson Imaging 14(5):617–627, The computational time for 6 markers was better than 2 ms, The proposed method is particularly suitable in systems requiring any of the following: high frame rate, tracking of three or more markers, data filtering or interleaving. Magnetic resonance imaging is increasingly being applied to perform interventional procedures such as biopsies, laser induced interstitial thermotherapy, high-intensity focused ultrasound and endoscopy –8. In maFiducial markers may be classified as active, semi-active or passive, each involving different localization techniques –14. An aN semi-active markers in 3D using 1D projections in two orthogonal planes and cluster analysis. Their algorithm requires at least five 1D projections per plane. However, projections with less than N peaks are rejected, so new projections are acquired instead. This results in an acquisition time of about 170 ms.Both active and semi-active markers may be localized using 1D projections, by determining the location of the signal peak, while passive markers demand the use of image processing techniques, for example, template matching . The useN markers using 1D projections [We propose a novel method for fast and accurate localization of jections . The metThe proposed localization method was implemented within a custom made system for image guided prostate biopsy . The app N markers generate N or fewer peaks along a 1D projection. The problem is to compute the 3D coordinates of N markers by using n 1D-projections. Each detected peak defines a plane perpendicular to the corresponding projection direction. In general, three 1D projections of N points define three N planes which intersect at N3 points. As a result N3 – N points are fictitious and must be discarded. This can be done by using additional projections  is the unit vector of the direction of a projection and pk is the position of the peak along this direction.The  candidates are eliminated by using, in turn, the remaining test projections. For each test projection, the projected value of the each candidate point is calculated and the distances between this and the identified peak locations are computed   Fig. .Fig. 3WiA Vector Network Analyzer (Anritsu MS 2026A VNA Master) was used to fine tune the RF marker to A 2D spoiled GRE sequence was modified in order to acquire a predefined set of 1D-projections, each projection including a dephasing gradient to spoil the transverse component of the magnetization prior to the next acquisition. The following parameters were made adjustable from the user interface of the MR host computer: (1) flip-angle, (2) magnitude of the dephaser gradient and (3) time interval between individual projections. Other relevant sequence parameters were TR = 5.6 ms, TE = 3.5 ms, FOV 300 mm, 320 phase encode points.The potential local heating due to electromagnetic coupling to the RF transmitter is an important issue to be considered when using RF semi-active markers in the clinical environment . In ordeQ is the Q-factor of the micro-coil [Mi is the magnetization vector just before the RF pulse, A and B are matrices representing the RF nutation about the x-axis, the precession about z-axis and the T1 and T2 relaxation processes. The transverse component 1 = 160 ms, T2 = 14 ms, TE = 3.5 ms, TR = 5.6 ms) for a marker under repeated excitation and for flip angles αapp, which gives higher amplitude of the received signal, was thus estimated. Experimentally, 1D projections were acquired in the presence of the large water phantoms.The micro-coil locally amplifies the excitation field. For an applied flip angle cro-coil . With \djections . The aimjections , the mag1 field. The signal is in turn dependent on induced RF flux and its orientation with respect to the main field. These dependencies tend to reduce the signal as the coil axis rotates from B1 to B0. In our experiment a marker was placed at the scanner’s isocentre, on top of the water phantom and rotated in steps of 10∘ in the xz plane. At each step, 20 measurements were acquired and the average amplitude of a peak was calculated and compared to the background signal.Orientation of the marker to the main field is an important factor to be considered when designing interventional devices . At someN largest peaks are checked against an experimentally determined signal to noise threshold, λ. The value of SNR is calculated by dividing the magnitude of each peak by the standard deviation of the background noise [N peaks and their adjacent four points on either side. Only the peaks satisfying the threshold are accepted.Inverse Fourier transform of a 1D projection produces a signal with peaks that correspond to the positions of the markers. Correctly identifying the peak is essential for the success of the algorithm. The presence of background noise in the acquired MR signal makes simple thresholding inadequate for robust peak detection. Following the method suggested in [b at the location of the highest signal value, x, and the signal values a and c at the adjacent positions on the left and on the right side of it, respectively [The location of the peak is corrected by applying an algorithm for sub-pixel peak detection. In order to achieve sub-pixel accuracy we have used Gaussian interpolation as suggested in . Gaussiaectively :5\docume A Chi square goodness-of-fit test of the null hypothesis that these variations are from a normal distribution was performed over repeated acquisitions of 1D projections of a marker. The hypothesis was verified and, consequently, a normally distributed variation in the position of a peak was implemented in Monte Carlo simulations of the algorithm.The influence of the SNR on the accuracy of the sub-pixel estimation was explored through simulations. Three points that define the maximum were obtained from the experimental data. Realistic noise was added to the amplitude of all three points and its effect on the estimated peak position was studied.ε.Two markers which have the same coordinate along a gradient direction induce signals at a similar frequency . In thisA large number of simulations and experiments were performed in order to verify the localization method, to determine the required number of projections and to assess the performance in terms of markers localization accuracy, targeting accuracy, robustness and computational time.In addition, the localization method was tested as an integral part of the MRI-guided prostate biopsy system that is currently under development in our research group , 26, 27.N, 105 sets of N points in 3D were generated with the only constraint that they were as least 30 mm apart. Each set of N markers positions was projected onto all projection directions and noise derived from the Gaussian distribution was added to the projections. These values provided the input to the tracking algorithm. The statistical analysis was performed by varying the number of simulated fiducial markers from three to six and the number of projection directions employed from five to 13.Configurations of up to six markers used for the probe localisation were studied. Monte Carlo simulations were performed in order to establish the required number of projections, to assess the accuracy and robustness of 3D localization and to estimate the computational time. For each number of markers The proposed localization method was compared to the method proposed by Flask et al. , which w5 random probe rotations in the range 30°–80° in the sagittal plane and ±25° in the coronal plane. For each probe orientation, the positions of the markers and their projections were computed. Noise derived from the Gaussian distribution was added to the projections. The markers were reconstructed from projections, assigned to the model markers and aligned in least squares fashion with the corresponding nominal points. The position of the biopsy needle tip was computed from known geometry and targeting error was computed as the distance between the computed and the nominal needle tip position.In addition to the marker localisation error, we have analysed the targeting error in a situation when multiple markers are used to track an interventional device within the scanner imaging volume. Targeting error was defined as the distance between corresponding points other than the fiducial points . Figure Experimental accuracy assessment employed a 2 degree-of-freedom, pneumatic, remotely controlled, MR-compatible platform, developed by our group Fig. . The plax and z axes in the range ±40 mm. At each step the marker’s position was measured 20 times by the proposed method and once by the platform’s optical encoders. Standard deviation and maximum distance between the computed positions and the mean value were calculated. The differences between the distances computed using the proposed algorithm and those measured using optical encoders were analyzed.A marker was fixed on the moving arm of the platform Fig.  in orderxy plane. A marker was mounted on a custom-made rotary holder, placed beside a water phantom, rotated through five positions in the range 0–90° and scanned 20 times in each position. A circle was fitted to the resulting 100 points and the distances of the estimated positions from the circle were computed.The accuracy of marker localization was also assessed at various positions in the R2, goodness of fit was computed [yav is the mean of the observed data yi.For the fitted circle computed :6\documeThe assessment of the accuracy under dynamic conditions necessitated the use of independent real-time position measurement that could not be provided with a volunteer present in the scanner. The moving platform was, therefore, used for this purpose in combination with a large water phantom. Dynamic tests involved moving a fiducial marker along predefined trajectories in x and z directions at various speeds, while simultaneously recording the encoder readings and the estimated fiducial positions.The MRI-guided prostate biopsy system employs a remotely operated MRI-compatible manipulator used to position a detachable endorectal probe that serves as the biopsy needle guide. Figure The procedure starts by positioning the pelvic phantom onto the scanner bed and by inserting the probe. The manipulator is then fixed in place on the scanner bed and the probe is attached to it. A preoperative set of images is acquired and the scene is constructed using the transversal and interpolated coronal cross section through the lesion. The clinician identifies the lesion to be targeted, interactively selects the target point and starts the targeting. During the targeting, the scanner streams 1D projections to the navigation workstation, which computes the probe position. The 3D synthetic model of the probe is inserted into the scene in real time and the scene is visualized on the screen in the scanner room Fig. b. To impBefore releasing the needle, a verification scan is performed in the same way as the preoperative one. The position of the targeted lesion is assessed and, if significant movement is detected, then the whole procedure is repeated until satisfactory targeting is achieved. At that point an automatic biopsy gun incorporating an extended, MRI compatible, biopsy needle  is introduced into the device using an elongated handle. The needle is fired and the sample is acquired.Figure Probe localization during the procedure is performed using markers built into the probe, Fig. Preclinical volunteer experiments were conducted in order to verify that the localization method performs successfully under the conditions when the patient is present in the scanner, where the main potential issue is the SNR. The experiments also aimed to verify that the localization method is successful in the presence of physiological movement. In addition, these studies provided an assessment of the setup time and other aspects needed to carry out the intended prostate biopsy procedure, although the tests were strictly non-invasive.Volunteers were healthy men of the age 28, 40 and 53 and weighing 72, 76 and 90 kg, respectively. Volunteers were enrolled in an investigational protocol reviewed and approved by the institutional review board after providing the informed consent. In one set of experiments, a biopsy probe with embedded three markers was detached from the manipulator and held tightly between the subjects’ legs. The markers were continuously localized using the proposed method at ten updates per second over a period of several minutes. Images using the relevant TSE sequence or TSE imaging sequence were also obtained . In other experiments the markers were attached to the volunteers’ anterior abdominal wall using adhesive tape in order to verify that the method is successful in the presence of respiratory movement. Continuous localization was performed at ten updates per second over a period of several minutes.The Q-factor of the microcoil was found to be around 130 without loading, while when loaded by placing it on top of a water phantom the Q-factor was found to be around 120.No measurable temperature change was observed during the experiments with tracking sequence. For the imaging sequence a temperature rise of about 0.2 °C was recorded.αapp, the amplitude of the acquired MR signal is initially larger; however, for the subsequent acquisitions, the amplitude drops faster than for smaller flip angles and reaches values comparable with the measured background signal. The flip angles αapp for which the signal showed higher minimum amplitude of signal over the whole set were 0.2° and 0.3°, the effective flip angle was Figure The experimental signal shows an oscillating trend Fig. b. This wMeasured results in Fig. Using the position of the pixel with the highest intensity for peak localization, would lead to a maximum error of 0.5 pixel, or 0.6 mm in this work. By using Gaussian interpolation, the maximum peak localization error was reduced to 0.283 mm Table . The ChiN peaks are not used in their computation. The only consequence is that in situations with less than N peaks along some direction the tolerance needs to be enlarged to the size of two pixels.A situation involving two close peaks is illustrated in Fig. It was also noted that a single marker may cause the occurrence of two distinct peaks in a single projection. In all such cases the distance between these two peaks was exactly one pixel. This can potentially cause serious problems as a fictitious peak may be higher than some real peak and, therefore, lead to entirely inaccurate conclusions. However, this was solved by a simple remedy: if two peaks are exactly one pixel apart, then the smaller of the two is neglected. In this way the problem becomes the same as the one explained above and, as such, it does not affect the accuracy.One more effect has been identified that needs attention. If the density of the material within the coil is non-uniform, or, if the shape of the material within a coil is not spherical, the maximum signal intensity may not appear at the centre of the coil, depending on the orientation of the coil. This may affect the accuracy of localization—so every effort has been made to make the shape symmetric and the homogeneity of the material in the coil uniform, as much as possible.N markers in a set of experiments. Table 6 simulations of N markers, with N = 3, 4, 5, 6. The number of 1D projections was increased from five up to 13. These results show that robustness is improved with an increased number of projections and that more projections are needed with an increased number of markers. In all cases simulated variation in peak localization was σpeak = 0.08 mm.The robustness of the proposed method was expressed in terms of a percentage of successful localizations of However, the results in Table Two aspects can be observed. Firstly, although the algorithm robustness may be already high, the maximum error may be significantly reduced by increasing the number of projections, and this is particularly evident for The influence of background noise on the accuracy of peak detection in 1D projections was explored through simulations. It was found that the background noise does influence the accuracy of the sub-pixel peak localization, as illustrated in Fig. Figure Table Table Figure The corresponding statistics for independent translations in the x and z directions are presented in Table R2 = 0.9979.Figure The results of dynamic tests, involving controlled movement of the platform carrying the marker at different speeds are shown in Fig. Table The MRI guided biopsy procedure was carried out in five trials, involving the integrated system and the use of the pelvic model and the prostate phantoms described previously. A trial was considered to be successful if the target sample was acquired, which was evident from its colour, and this was achieved in all trials. Figure During targeting, the displayed images of the needle appeared somewhat jittery due to the noise, so a moving average filter that averages five samples was implemented. The stability of the images was improved noticeably, but at the expense of introducing an error due to the delay in the computed positions. Conveniently, this error diminishes as the movement becomes slower in the final phase of the targeting.In all experiments involving volunteers the localization method was found to perform successfully, without failures, i.e., correct peaks were always identified under prolonged operation lasting several minutes. Experiments involving the biopsy probe taped and held tightly between the subject’s legs showed that the SNR of the marker signal was sufficiently high under coil loading and noise conditions similar to that during the intervention. When the markers were taped to the subject’s anterior abdominal wall, where maximum motion artefacts might be expected due to the respiratory motion, the results did not indicate any signal smearing and the localization performed equally successfully over periods of several minutes.N markers simultaneously.The localization method described here has been shown to be both accurate and fast, while being able to track Gaussian interpolation the accuracy of the position of the peak estimation was significantly improved compared to using the Maximum Pixel Intensity method.Using a set of 13 pre-defined 1D projections was shown to be optimal in terms of minimizing the localization error and maximizing the robustness, while the penalty in terms of computational time was minimal. The number of projections can be traded against robustness and accuracy for optimized results in a specific situation. Furthermore, by using the The algorithm is heuristic and two failure modes were identified. First, the algorithm fails if any two markers are positioned too close to each other in relation to the tolerance ε will keep some fictitious points in. Our experiments and simulations indicated that the main factors to be considered when determining the tolerance value are the stochastic nature of the peak position and the identification of peaks that are very close to each other.Optimizing the value of the tolerance ε is an important but complex problem to address. Too small a value for ε will remove too many candidate points whereas too large N peaks are detected. In this way, merged peaks were represented by the identified one. This solution did not affect the accuracy nor robustness of our localization method, since the candidate points are computed by making use only of the projections that do have N distinct peaks.By setting the tolerance to ten standard deviations, the stochastic nature was resolved. However, the situation is different when the two peaks are close to each other. It was found that peak merging may occur when peaks are within two pixels from one another and that the position of the identified peak is not affected by merging. In order to accommodate peak merging, the tolerance was automatically enlarged to two pixels size in situations where fewer than It is well known  that posThe proposed method may be applied to localize either semi-active or active markers, when only one receiver channel is used. However, we have focused on the use of semi-active markers, as it simplifies the instrument design, manufacturing and testing, and avoids cabling issues and the associated safety hazards . We have0, as was the case in the prostate biopsy system.It was observed that, when a human subject is present in the scanner, the peak amplitude of the marker signal may decrease, but it was still sufficiently high for the peak detection method to function correctly and consistently. In practice, obtaining a sufficiently strong signal from the markers can always be expected to be a concern, so the interventional system should be designed such that this is not compromised. Marker orientation to the main field is a key aspect and it is preferable to adopt a manipulator configuration that ensures that markers are always kept perpendicular to BThe dynamic tracking test proved the reliability of the method in the presence of motion, with accuracy depending on the speed. For the anticipated speeds of tool movement in interventional procedures, the marker positional error was estimated to be within 1 mm.In preclinical trials the targeting time for prostate biopsy was found to be of the order of 5 min. The proposed prostate biopsy MR-guided method was considered by the clinical staff to offer significant advantages in terms of being able to target previously identified lesions, avoiding the need for extensive random sampling and increasing the accuracy of the biopsies.Targeting errors such as those due to mechanical deflection of the needle during firing have not been assessed and are potentially significant. Under these conditions, pre-clinical trials were conducted to investigate the ability to successfully sample small targets, of the size specified by the clinician as being clinically relevant. Although these trials were successful, a detailed accuracy of the interventional system needs to be carried out as part of future work, in order to fully assess the errors and influence of factors such as needle firing speed and tissue properties.In the proposed prostate biopsy procedure, the anatomical MR images are only acquired near the start of the intervention, just before the targeting begins, and immediately before a possible needle release. In the latter case the images are used for the verification of the targeting before the needle is released. Both stages involve obtaining multiple images across the volume of interest, in which the clinician recognizes and identifies the target lesion. In this situation the main benefit of the high update rate of the probe tracking is an improved control of the probe position. In other applications it may be required to update specific MR images simultaneously with tracking, so the faster localization method will help improve the overall image acquisition speed.Preclinical trials have also revealed that the noise in the system may result in a noticeable jitter in the estimated position of the probe, which may prove distracting to the clinician, especially when performing fine adjustments of the manipulator during targeting. This was easily overcome by implementing a simple moving average filter, resulting in a much steadier display. As a consequence of the fast sampling time (10 Hz), averaging of the last five positions and the slow movement of the probe in the final phase of a targeting, the lag introduced by filtering was not noticeable and it did not impede operator’s actions in any way. The use of the Kalman filter would be an optimal solution for this problem and it will be considered in the next stages of system development.N markers in 3D based on a novel algorithm for processing 1D projections was presented and proved to be considerably faster than previously proposed methods. Computational time for up to six markers required less than 2 ms. High accuracy was achieved by using optimal reference projections to compute candidate points and by applying Gaussian interpolation in peak detection. An update rate of 10 Hz was achieved with localization error lower than 0.3 mm. The reliability of the method when markers move while performing an intervention was demonstrated and resulted in maximum error 0.7 mm for a speed anticipated by interventional procedures. Experimental targeting error was estimated to be about 1 mm and, we predict a reduction of up to two times by employing up to six markers. An important aspect of the manipulator design is that its remote-centre mechanism maintains the orientation of the markers perpendicular to the main field in all positions, maximizing the peak amplitudes during tracking. Accurate marker localization leads to accurate accurate and consistent targeting in MR guided interventions, while the speed of the method enables high frame-rate display that is comfortable for the clinician and enhances the overall performance.A method for localization of