Real-time simultaneous shim and motion measurement and correction in glycoCEST MRI using double volumetric navigators (DvNavs).
PURPOSE
CEST MRI allows for indirect detection of molecules with exchangeable protons, measured as a reduction in water signal because of continuous transfer of saturated protons. CEST requires saturation pulses on the order of a second, as well as repeated acquisitions at different offset frequencies. The resulting extended scan time makes CEST susceptible to subject motion, which introduces field inhomogeneity, shifting offset frequencies and causing distortions in CEST spectra that resemble true CEST effects. This is a particular problem for molecules that resonate close to water, such as hydroxyl group in glycogen. To address this, a technique for real-time measurement and correction of motion and field inhomogeneity is proposed.


METHODS
A CEST sequence was modified to include double volumetric navigators (DvNavs) for real-time simultaneous motion and shim correction. Phantom tests were conducted to investigate the effects of motion and shim changes on CEST quantification and to validate the accuracy of DvNav motion and shim estimates. To evaluate DvNav shim and motion correction in vivo, acquisitions including 5 experimental conditions were performed in the calf muscle of 2 volunteers.


RESULTS
Phantom data show that DvNav-CEST accurately estimates frequency and linear gradient changes because of motion and corrects resulting image distortions. In addition, DvNav-CEST improves CEST quantification in vivo in the presence of motion.


CONCLUSION
The proposed technique allows for real-time simultaneous motion and shim correction with no additional scanning time, enabling accurate CEST quantification even in the presence of motion and field inhomogeneity.
['Simegn|Gizeaddis L|GL|', 'Van der Kouwe|Andre J W|AJW|', 'Robertson|Frances C|FC|', 'Meintjes|Ernesta M|EM|', 'Alhamud|Ali|A|']
D000328:Adult D000465:Algorithms D016477:Artifacts D064368:Healthy Volunteers D006801:Humans D007089:Image Enhancement D007090:Image Interpretation, Computer-Assisted D007091:Image Processing, Computer-Assisted D021621:Imaging, Three-Dimensional D016014:Linear Models D008279:Magnetic Resonance Imaging D008297:Male D009038:Motion D018482:Muscle, Skeletal D019047:Phantoms, Imaging D015203:Reproducibility of Results
double volumetric navigator DvNav CEST glycogen motion correction B0 correction chemical exchange saturation transfer