Magnetization transfer contrast (MTC): Optimization of the off-resonance and on-resonance MTC methods at 0.5 and 1.5 T

Aim: To compare technical parameters and clinically relevant aspects of on- and off-resonance MTC sequences in mid- and high-field MR systems. Material and Methods: Both on- and off-resonance techniques were combined w ith an FFE sequence using 0.5 and 1.5 Tesla superconducting systems. Parame ters were systematically measured by scanning a cadaveric knee joint. Signa l-to-noise ratios and MT ratios for fat, cartilage and reference solution ( copper sulphate) were determined. Minimal TR and the energy absorption rate were also compared. Results: The MT effect at 1.5 T was more pronounced. However, using optimiz ed parameters, clinically adequate MT contrast was achieved with both techn iques and both MT units. The most important parameters for the off-resonanc e method are pulse angle and off-centre frequency; for the on-resonance met hod, pulse angle and number of composite pulse elements. Energy absorption was below 2 W/kg. Minimal TR was prolonged by up to 400 %. Conclusion: In order to produce MTC images, optimized parameters should be applied. Using optimized pulse parameters, adequate MTC imaging is achievab le with mid- and high-field systems using on- and off-resonance techniques. To ensure comparability of MTC studies, the pulse parameters need to be gi ven, and, ideally, standardized.