Program Information
Improved Chemical Exchange Saturation Transfer (CEST) with a Multiple Gradient Echo Sequence
K Hwang*, S Fahrenholtz, C MacLellan, J Yung, R Stafford, The University of Texas MD Anderson Cancer Center, Houston, TX
Presentations
SU-K-708-12 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 708
Purpose: Chemical exchange saturation transfer (CEST) is an imaging approach that observes the change in water signal with the application of off-resonance saturation pulses at multiple frequencies to produce a z-spectrum. One potential disadvantage of gradient echo CEST sequences is the inefficiency caused by RF duty cycle or SAR limits when used with long, narrow bandwidth saturation pulses. We propose the use of a multiple fast gradient echo (MFGRE) acquisition to regain signal efficiency in CEST imaging, while also introducing the potential for chemical shift imaging in a CEST sequence.
Methods: Off-resonance saturation preparation pulses were added to each repetition of a gradient echo sequence, which acquired data in a linear view order to allow chemical exchange to occur before the center of k-space was acquired. Hanning-shaped saturation pulses with a duration of 75 msec and peak B1 of 3.0 uT were applied, at frequencies ranging from +7 to -7 ppm at intervals of 0.25 ppm, for a total of 57 offset frequencies. For the MFGRE variant, 16 unipolar echoes were acquired for each saturation offset frequency. A phantom consisting of two eggs was imaged in a 3T clinical scanner. Multiecho data was magnitude averaged across echoes to produce a single z-spectrum. ARMA modeling was also applied to the complex multiecho data to extract water and lipid peaks and detect their frequencies. A frequency correction was then applied to center each spectrum on water, producing a water-only z-spectrum at the center frequency.
Results: 2D spectra were successfully reconstructed, and water and lipid signals were clearly separated for each saturation frequency offset. Contamination from fat was eliminated in reconstructed water-only z-spectra, which were improved further with correction to the water frequency.
Conclusion: Using an MFGRE sequence improves SNR efficiency for CEST imaging and can better isolate saturation transfer effects on water.
Funding Support, Disclosures, and Conflict of Interest: K Hwang receives research funding support from GE Healthcare.
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