[Magnetization transfer contrast (MTC): optimizing off-resonance and on-resonance frequency 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 with an FFE sequence using 0.5 and 1.5 Tesla superconducting systems. Parameters were systematically measured by scanning a cadaveric knee joint. Signal-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 optimized parameters, clinically adequate MT contrast was achieved with both techniques and both MT units. The most important parameters for the off-resonance method are pulse angle and off-centre frequency; for the on-resonance method, 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 achievable with mid- and high-field systems using on- and off-resonance techniques. To ensure comparability of MTC studies, the pulse parameters need to be given, and, ideally, standardized.