Three-dimensional FLASH MR imaging of thorax and abdomen without triggering or gating

Abstract

FLASH (fast low-angle shot) imaging is a new technique for rapid two- and three-dimensional (2D and 3D) MRI with high signal-to-noise, high spatial resolution and low sensitivity to motions. In particular, transverse magnetizations are strongly dephased by rapid motions with time constants of several milliseconds. They are not refocused by the gradient echo signal used for FLASH imaging and therefore do not contribute to the image. Artifacts due to motions with longer time constants are averaged out by multiple data acquisitions either because of a statistical nature of the dynamic process itself or, in the case of periodic motions, because of the incoherent data sampling with respect to the time period. In general, the large number of signal acquisitions necessary for a true 3D data set turns out to be sufficient for this purpose. Since 128 3 3D FLASH MR images require measuring times of only 4 min, even two or four accumulations of entire 3D data sets remain within acceptable clinical measuring times. The method for the first time depicts high-quality three-dimensional views of the thoracic and abdominal anatomy in enddiastole and endexspiratory rest without the need of gating or triggering. 3D FLASH images will be of great medical utility, especially in cases where topographic information is needed as, for example, for radiation therapy and angiography planning or preoperative diagnosis.