A general-approach to selection of multiple cubic volume elements using the Isis technique

The ISIS method is used regularly for the selection of a single cubic volume of tissue for in vivo investigation by high-resolution NMR spectroscopy. This technique has been extended on a theoretical basis to include the simultaneous selection of a number of cubes, the signals from which can be either assessed individually or in certain circumstances coadded to produce improvement in signal-to-noise ratio. The modification requires additional selective RF pulses in the spatial encoding prepulse period, and spatially localized spectra are produced by addition and subtraction of NMR signals in a manner similar to the original ISIS technique

Fast bound pool fraction mapping via steady‐state magnetization transfer saturation using single‐shot EPI

PURPOSE: To enable clinical applications of quantitative magnetization transfer (qMT) imaging by developing a fast method to map one of its fundamental model parameters, the bound pool fraction (BPF), in the human brain. THEORY AND METHODS: The theory of steady-state MT in the fast-exchange approximation is used to provide measurements of BPF, and bound pool transverse relaxation time ( T 2 B ). A sequence that allows sampling of the signal during steady-state MT saturation is used to perform BPF mapping with a 10-min-long fully echo planar imaging-based MRI protocol, including inversion recovery T1 mapping and B1 error mapping. The approach is applied in 6 healthy subjects and 1 multiple sclerosis patient, and validated against a single-slice full qMT reference acquisition. RESULTS: BPF measurements are in agreement with literature values using off-resonance MT, with average BPF of 0.114(0.100-0.128) in white matter and 0.068(0.054-0.085) in gray matter. Median voxel-wise percentage error compared with standard single slice qMT is 4.6%. Slope and intercept of linear regression between new and reference BPF are 0.83(0.81-0.85) and 0.013(0.11-0.16). Bland-Altman plot mean bias is 0.005. In the multiple sclerosis case, the BPF is sensitive to pathological changes in lesions. CONCLUSION: The method developed provides accurate BPF estimates and enables shorter scan time compared with currently available approaches, demonstrating the potential of bringing myelin sensitive measurement closer to the clinic