and axial T2-weighted imaging are obtained using single-shot echo-train spin-echo technique (such as single-shot fast spin-echo [SSFSE] or half- Fourier acquisition single-shot turbo spin-echo [HASTE]) with moderate T2-weighting, using an echo time (TE) of approximately 180 milliseconds ( Fig. 1 ). A complementary axial fast spin-echo T2-weighted sequence is obtained using respiratory triggering, fat suppression, and a shorter TE of approximately 90 milliseconds. T1-weighted imaging is initially performed using a breath-hold spoiled gradient echo sequence in which both in-phase and opposed-phase echoes are recorded. Subsequently, breath-hold precontrast and postcontrast T1-weighted imaging is obtained using a two- dimensional (2D) spoiled gradient echo sequence with fat suppression ( Figs. 2–6 ). We also routinely obtain axial diffusion-weighted imaging using echo planar imaging because of the emerging role in various MR applications, particularly oncologic imaging. 5 However, the anatomic features of the abdomen are often less clearly seen on diffusion-weighted images than standard T1- weighted and T2-weighted sequences. For patients undergoing specific investigations of the liver or spleen, a dynamic postcontrast technique replaces the standard precontrast and postcontrast T1-weighted imaging sequence. This dynamic sequence uses a breath-hold axial three-dimensional (3D) spoiled gradient echo technique that permits volumetric data acquisition with thinner reconstructed imaging sections. 6 The sequence usually includes a precontrast data set, followed by postcontrast data obtained in the arterial, venous, and equilibrium phases of enhancement
(basics | abbreviations | parameters)