Peter Heubes

Pulse sequence with non-constant scan repetition time for a nuclear magnetic resonance tomography apparatus

A pulse sequence is disclosed for a nuclear magnetic resonance tomography apparatus wherein the scans are executed with a non-constant repetition time, such as due to ECG triggering. Normally, the non-constancy of the repetition time in a nuclear magnetic resonance tomography apparatus results in a deterioration of the quality of the images, due to eddy currents. In the pulse sequence disclosed herein, gradient pulses having a chronological mean value are inserted in the pause between two successive scans, this chronological mean value being equal to the chronological mean value of the corresponding gradients during the scans. The disturbing influence of variable repetition times on the image quality is thus eliminated.

Method for avoiding image occlusions in nuclear magnetic resonance tomography apparatus that are operated with multi-echo sequences

In a method for avoiding image occlusions in nuclear magnetic resonance tomography apparatus that are operated with multi-echo sequences, at a time t0, a cross-magnetization in spins is generated in an examination subject with an excitation radio-frequency pulse. At times t1, t3, t5 . . . , at least two refocusing radio-frequency pulses that re-phase the cross-magnetization follow and read-out intervals follow at times t2, t4, t6 . . . The following condition is satisfied in at least one direction for the gradients G activated during the pulse sequence: ##EQU1## Even given quadratic gradient terms, thus, no phase difference occurs between a primary and a stimulated echo path. The presence of such a phase difference causes an image occlusion, and thus such occlusions are avoided by eliminating such a phase difference.