ANALYSIS OF ON-RESONANCE AND OFF-RESONANCE MAGNETIZATION-TRANSFER TECHNIQUES

Three methods of performing magnetization transfer (MT) MR imaging are analyzed: (a) off-resonance continuous wave, (b) off-resonance shaped pulses, and (c) on-resonance binomial pulses. With two-pool Bloch-mod el simulations, signal levels from ''MT active'' spin systems were cal culated, with reference to direct saturation of ''MT inactive'' system s, allowing calculation of contrast due to MT, Simulations demonstrate several trends with variation of excitation amplitude and offset freq uency for the off-resonance methods and with variation of excitation a mplitude and pulse shape ''order'' for binomial pulses. The simulation s show that nominally optimized versions of each of these approaches p rovide essentially equivalent contrast at a given level of applied MT power, contrary to previous claims. Experiments with an MT-inactive ph antom, with a whole-body system, show results with off-resonance pulse s to be in good agreement with simulations, whereas binomial-pulse exp eriments show anomalously large direct saturation,