Breath-hold 3D MR angiography of the renal vasculature using a contrast-enhanced multiecho gradient-echo technique

OBJECTIVE. Significant evolution of contrast-enhanced MR angiography for ev aluating vascular diseases in the abdomen has occurred during the past seve ral years. The state-of-the-art gradient-echo imaging technique employs a s hort echo time (TE) and a short repetition time (TR) for rapid vascular ima ging with contrast-enhanced MR angiography, However, because of the short T R (less than or equal to 3-8 msec), the background stationary tissue become s saturated, with resultant poor contrast resolution of visceral organs, Th e authors present a new approach to vascular imaging using a multiecho grad ient-echo technique,vith a TR sufficiently long (41 msec) to image the rena l vasculature and parenchyma without background tissue suppression. METHODS. Twenty-four partitions (3D slab thickness = 72 mm) with an in-plan e resolution of 224 x 256 were obtained in 21 seconds. Three measurements w ere performed with an interscan delay of 8 seconds. In the pulse sequence, the partition loop is defined as the innermost loop, in which Kz views are acquired centrically for a fixed Ky, followed by Ky views in a conventional linear or sequential order. The partition encodings are segmented to permi t multiple encodings in which two TR loops were used to span a total of 24 echoes with 12 along the positive and 12 along the negative direction in k space. A large bandwidth of 650 Hz/pixel was used to keep the echo train le ngth short, with an echo spacing of 1.86 msec, A frequency-selective fat sa turation pulse was placed before slab-selective excitation. The other param eters in the pulse sequence were TR/TE/flip = 41/2.2/45; the field of view was 360 to 390 mm, Maximum intensity projections of each 3D contrast-enhanc ed measurement were performed, The vascular-to-background contrast, bowel-r elated magnetic susceptibility artifact, and background stationary signals were subjectively graded. The authors examined the utility of this technique in 16 randomly selected patients (3 normal, 13 abnormal) with varied renal vasculature and parenchy mal abnormalities. Results were confirmed with conventional x-ray angiograp hy, surgery, or clinical follow-up, RESULTS. Vascular-to-background contrast was graded as very good (grade III /III) in all cases, The bowel-related magnetic susceptibility artifacts wer e not considered significant. Background visceral organ soft tissue contras t was not suppressed and was graded as good (grade III/III) in all cases. E ight hemodynamically significant (>50% diameter) stenoses in seven patients were accurately assessed (one with fibromuscular dysplasia), Three patient s with renal masses (two with renal cell carcinoma and one with renal lymph oma) were accurately assessed for arterial anatomy and venous extension. Ot her renal venous abnormalities seen were retroaortic renal vein (n = 1), ch ronic occlusion (n = 1), and accessories (total of five) (n = I). Conclusions. Rapid breath-hold contrast-enhanced MR angiography of the rena l vasculature with a multiecho gradientecho using a long TR depicted the re nal vasculature with high vessel-to-background contrast without significant bowel-related susceptibility artifact and without background visceral orga n tissue signal suppression, resulting in high background soft tissue contr ast resolution.