Implications of respiratory motion for the quantification of2D MR spectroscopic imaging data in the abdomen

Abstract

Magnetic resonance spectroscopic imaging (MRSI) studies in the abdomenor breast are acquired in the presence of respiratory motion. Thismodifies the point spread function (PSF) and hence the reconstructedspectra. We evaluated the quantitative effects of both periodic andaperiodic motion on spectra localized by MRSI. Artefactual signalchanges, both the modification of native to a voxel and spurioussignals arising elsewhere, depend primarily upon the motion amplituderelative to the voxel dimension. A similar dependence on motionamplitude was observed for simple harmonic motion (SHM), quasi-periodicmotion and random displacements. No systematic dependence upon theperiod or initial phase of SHM or on the array size was found.There was also no significant variation with motion direction relativeto the internal and external phase-encoding directions. In measuredexcursion ranges of 20 breast and abdominal tumours, 70% moved ⩽ 5 mm, while 30% moved 6-23 mm. The diaphragm and fatty tissuesin the gut typically moved ~ 15-20 mm. While tumour/organexcursions less than half the voxel dimension do not substantiallyaffect native signals, the bleeding in of strong lipid signals will beproblematic in 1H studies. MRSI studies in the abdomen, even ofrelatively well-anchored tumours, are thus likely to benefit from theaddition of respiratory triggering or other motion compensationstrategies.