MR Angiography of Stenosis and Aneurysm Models in the Pulsatile Flow: Variation with Imaging Parameters and Concentration of Contrast Media

ABSTRACT

PURPOSE: The image quality of magnetic resonance angiography (MRA) varies according to the imaging techniques applied and the parameters affected by blood flow patterns, as well as by the shape of the blood vessels. This study was designed to assess the influence on signal intensity and its distribution of the geometry of these vessels, the imaging parameters, and the concentration of contrast media in MRA of stenosis and aneurysm models. MATERIALS AND METHODS: MRA was performed in stenosis and aneurysm models made of glass tubes, using pulsatile flow with viscosity and flow profile similar to those of blood. Slice and maximum intensity projection (MIP) images were obtained using various imaging techniques and parameters ; there was variation in repetition time, flip angle, imaging planes, and concentrations of contrast media. On slice images of three-dimensional (3D) time-of-flight (TOF) techniques, flow signal intensity was measured at five locations in the models, and contrast ratio was calculated as the difference between flow signal intensity (SI) and background signal intensity (SIb) divided by background signal intensity or (SI-SIb)/SIb. MIP images obtained by various techniques and using various parameters were also analyzed, with emphasis in the stenosis model on demonstrated degree of stenosis, severity of signal void and image distortion, and in the aneurysm model, on degree of visualization, distortion of contour and distribution of signals. RESULTS: In 3D TOF, the shortest TR (36 msec) and the largest FA (50 degree) resulted in the highest contrast ratio, but larger flip angles did not effectively demonstrate the demonstration of the peripheral part of the aneurysm . Loss of signal was most prominent in images of the stenosis model obtained with parallel or oblique planes to the flow direction. The two-dimensional TOF technique also caused signal void in stenosis, but precisely demonstrated the aneurysm, with dense opacification of the peripheral part. The phase contrast technique showed some distortions in the imaging of stenosis, and partial opacification of ananeurysm. Contrast enhanced imaging offered no advantages in the imaging of the stenosis, but was excellent for demonstration of the aneurysm. CONCLUSION: This study demonstrates a spectrum of MRA images of stenosis and aneurysm model according to variation in imaging parameters and the concentration of contrast media.