Bloch simulations towards direct detection of oscillating magnetic fields using MRI with spin-lock sequence.

A new MRI method using the spin-lock sequence has attracted wide attention because of its potential for detecting small oscillating magnetic fields. However, as the mechanism involved is complicated, we visualized the magnetization performance during the spin-lock sequence in order to better understand interaction of the spin-lock pulse and the externally applied oscillating magnetic fields by means of a fast-and-simple method using matrix operations to solve a time-dependent Bloch equation. To improve spin-lock imaging in the detection of small magnetic fields (in an fMRI experiment that modeled neural magnetic fields), we observed that the phenomenon decreases MR signals, which led us to investigate how spin-lock parameters cause the MR signal to decrease; based on this, we determined that MR signals decrease in oscillating magnetic fields that are resonant with the spin-lock pulse.

Acquisition parameters for diffusion tensor imaging to emphasize fractional anisotropy: phantom study.

Diffusion tensor imaging (DTI) is a magnetic resonance (MR) imaging technique that has attracted attention in recent years for applications such as nerve fiber tracking, neurography, and tumor detection. In DTI measurements, 2 motion-probing gradient (MPG) pulses are applied to evaluate water diffusion. In DTI for nerve fiber tracking, acquisition parameters, such as strength, duration, and separation of MPGs, influence the MR signal.