Optimization of on-resonant magnetization transfer contrast in coronary vein MRI.

Magnetization transfer contrast has been used commonly for endogenous tissue contrast improvements in angiography, brain, body, and cardiac imaging. Both off-resonant and on-resonant RF pulses can be used to generate magnetization transfer based contrast. In this study, on-resonant magnetization transfer preparation using binomial pulses were optimized and compared with off-resonant magnetization transfer for imaging of coronary veins. Three parameters were studied with simulations and in vivo measurements: flip angle, pulse repetitions, and binomial pulse order. Subsequently, first or second order binomial on-resonant magnetization transfer pulses with eight repetitions of 720° and 240° flip angle were used for coronary vein MRI. Flip angles of 720° yielded contrast enhancement of 115% (P < 0.0006) for first order on-resonant and 95% (P < 0.0006) for off-resonant magnetization transfer. There was no statistically significance difference between off-resonant and on-resonant first order binomial Magnetization transfer at 720°. However, for off-resonance pulses, much more preparation time is needed when compared with the binomials but with considerably reduced specific absorption rate.