Boef Johannes Hendrik Den

Method of and device for determining a nuclear magnetization distribution in a region of a body

During measurement cycles for generating and sampling FID signals in NMR imaging devices, a 180° pulse and subsequently a 90° excitation pulse are added to the pulse sequence. The 180° pulse produces an additional echo signal. During (the maximum of) the echo signal, the 90° pulse is generated. The waiting period occurring before the beginning of a next measurement cycle can thus be substantially reduced without giving rise to a significant signal loss in the echo signals to be generated during said cycle. In addition to a reduction of the measurement time, NMR images with different contrasts (other intensity distribution) can be provided.

METHOD OF REDUCING ARTEFACTS IN IMAGES FORMED BY MEANS OF FOURIER ZEUGMATOGRAPHY

NMR images formed by means of Fourier zeugmatography contain disturbing artefacts which are caused by coherent interference signals (for example, off-set signals, non-ideal 180° reversing pulses). In accordance with the invention, an additional phase difference (Δφ=π in the case of even rows, and Δφ=π. (m-1)/m rad/sec in the case of m odd rows) is generated and the signal samples taken from the resonance signals are stored in adjacently situated rows of an image frequency matrix. The values in every second row of the matrix are changed to cancel said additional phase-difference, so that the contributions of the coherent interference signals to the matrix are influenced by the additional phase shift; if the additional phase shift is π rad/sec, the values of every second row of interference signals in the direction of the columns are simply inverted. During Fourier transormation of the columns, therefore, the artefacts caused by the interference signals are shifted towards the border of the image.