| 摘要 |
<p>In a spin-echo magnetic resonance sequence a phase encoding gradient magnetic field (39) is applied after the 180 DEG rephasing pulse (321). After detection of the spin-echo signal (33) the position dependent phases are compensated for by applying a further gradient magnetic field (39'), identical in size but opposite in sign. The phase difference ( phi 32,1- phi 31,1) between the RF-pulses (311,321) applied within a sequence is constant over the sequences. With no position dependent effects left at the end of a sequence the next sequence can be stated immediately following the earlier one. A repetition time TR substantially shorter than the spin-spin relaxation time T2 is feasible, thereby developing a steady state of the magnetisation. A TR of 50 ms or less can be obtained, as well as strong signals for long T2 substances and good T2 contrast. RF spoiling by changing phases of RF-pulses in subsequent sequences can destroy the T2 signal and provide images with pure T1 contrast. <IMAGE></p> |
