Evaluation of transmit efficiency and SAR for a tight fit transceiver human head phased array at 9.4 T.
Ultra-high field (UHF, ≥7 T) tight fit transceiver phased arrays improve transmit (Tx) efficiency (B1+ /√P) in comparison with Tx-only arrays, which are usually larger to fit receive (Rx)-only arrays inside. One of the major problems limiting applications of tight fit arrays at UHFs is the anticipated increase of local tissue heating, which is commonly evaluated by the local specific absorption rate (SAR). To investigate the tradeoff between Tx efficiency and SAR when a tight fit UHF human head transceiver phased array is used instead of a Tx-only/Rx-only RF system, a single-row eight-element prototype of a 400 MHz transceiver head phased array was constructed. The Tx efficiency and SAR of the array were evaluated and compared with that of a larger Tx-only array, which could also be used in combination with an 18-channel Rx-only array. Data were acquired on the Siemens Magnetom whole body 9.4 T human MRI system. Depending on the head size, positioning and the RF shim strategy, the smaller array provides from 11 to 23% higher Tx efficiency. In general, the Tx performance, evaluated as B1+ /√SAR, i.e. the safety excitation efficiency (SEE), is also not compromised. The two arrays provide very similar SEEs evaluated over 1000 random RF shim sets. We demonstrated that, in general, the tight fit transceiver array improves Tx performance without compromising SEE. However, in specific cases, the SEE value may vary, favoring one of the arrays, and therefore must be carefully evaluated.
['Avdievich|N I|NI|', 'Hoffmann|J|J|', 'Shajan|G|G|', 'Pfrommer|A|A|', 'Giapitzakis|I A|IA|', 'Scheffler|K|K|', 'Henning|A|A|']
D065638:Absorption, Radiation D001921:Brain D004735:Energy Transfer D004867:Equipment Design D019544:Equipment Failure Analysis D006801:Humans D060526:Magnetic Fields D008279:Magnetic Resonance Imaging D019047:Phantoms, Imaging D011829:Radiation Dosage D000069079:Radiation Exposure D015203:Reproducibility of Results D012680:Sensitivity and Specificity D014159:Transducers
SAR transceiver phased arrays RF head coil transceiver versus transmit-only/receive-only system transmit efficiency improvement ultra-high field MRI