Correction of artefacts caused by Maxwell terms in section shift echo planar imaging

摘要

The method involves producing an NMR image using an echo planar pulse sequence. A phase shift, phi (m,z), is calculated for each NMR signal, m, and each section located at z in the echo planar pulse sequence. A frequency shift, DELTA f(z), is calculated for each section located at z. The echo planar pulse sequence is applied by generating an RF excitation pulse, generating a readout magnetic field gradient with alternating value, to generate a corresponding sequence of NMR echo signals, and receiving each NMR signal and demodulating each signal with an RF reference signal which has been phase-shifted by the corresponding calculated phase shift phi (m,z) and frequency-shifted by the calculated frequency shift DELTA f(z). Each demodulated NMR echo signal is stored to form a NMR data set, from which an image may be reconstructed.