Optimum setting of binomial pulses for magnetization transfer contrast.

Investigation of the cause of image artifacts generated by a magnetization transfer (MT) sequence using binomial-pulse trains led to findings of imperfections in the pulses. These imperfections caused anomalous direct saturation of the free water, which was localized due to the static magnetic field inhomogeneity. In the case of single binomial pulses a loss of overall MT response across the field of view results. Two methods of correcting the imperfections and removing the artifact have been established using interactive adjustment of sub-pulse lobes and phase swapping of pulse trains. These imperfections may be present in many systems and may have led to erroneous judgements of the value of binomial pulses for MT imaging. A technique for interrogating the frequency spectrum of the binomial-pulse train has been utilized, allowing its optimization. The use of accurate and optimized binomial pulses may yet prove to be preferable to pulsed off-resonance methods for quantitative, clinical MT imaging.