SCMR 22nd Annual Scientific Sessions
Clinical breath-hold Gd CE-MRA is limited in spatial resolution/coverage.USPIO-enhancedsteady-stateMRA has been successfully used for patients with poor renal function1. However, navigated scan requires a long scan time and may suffer from breathing artifacts. This study aims to develop a highly accelerated (R=25), high-resolution compressed sensing MRA (CS-MRA2) technique and test in patients.
16 patients were recruited: 13 with abdominal vascular diseases and 3 scheduled for TAVR. Ferumoxytol was slowly infused, and images were acquired during the steady state. Three MRA protocols were performed at 3T for abdomen MRA: 1) Free-breathing high-resolution MRA, 0.8mm isotropic, 2-minute, 48cm head-foot coverage. 2) Clinical breath-hold low-resolution MRA, 1.3-1.5mm isotropic, 25-second breath-hold, 36cm coverage. 3) Compressed sensing breath-hold, high-resolution MRA2, 0.8mm isotropic, 15-second breath-hold, 48cm coverage. For the CS-MRA a highly under-sampled (R=25) Cartesian spiral phyllotaxis sampling pattern was used and reconstructed on the scanner online (takes 5mintues) with an iterative SENSE technique. Two radiologists graded the image quality (1-5 scale) of the large vessels (aorta/iliac) and renal arteries, and measured the aorta diameter. Lumen-to-muscle contrast ratio, lumen signal inhomogeneity (SD/mean), and sharpness were quantified and compared.
Results: All three sequences achieved good and comparable image quality for large vessels (average scores >3.8, p=0.11, Figure 1&2). However, the free-breathing protocol had poor delineation of renal arteries (score 2.0±0.9) while breath-hold protocols had significantly improved image quality (low-res MRA 3.4±0.9, and CS-MRA 4.1±0.8, p<0.001). CS-MRA had the highest contrast ratio and lumen sharpness (p<0.01). All free breathing MRAs suffered from significant breathing artifacts and low-resolution breath-hold MRAs had limited coverage and the lowest sharpness (resolution). On the contrary, breath-hold CS-MRAs had the best image quality, highest sharpness for the shortest scan time. For TAVR patients (Figure 3), good image quality was achieved within a 19 second breath-hold (gated, acquisition window 120ms and 1.2x1.2x2mm3 resolution), while traditional navigator gated scan takes up to 10 mintues with the similar coverage and resolution.
For abdomen MRA, we achieved good image quality with a 25-fold acceleration (15-second), 0.8mm isotropic resolution (1/5 voxel size of clinical breath-hold MRA) and a large coverage. The higher resolution of CS-MRA significantly increased the image sharpness, which improved the evaluation of smaller arterial vasculature in the abdomen. The shorter breath-hold duration could improve the patient comfort and increase successful rate. In addition, the technique is applicable directly to first-pass Gadolinium CE-MRA. It is also a promising tool for pre-surgical planning of TAVR and needs additional validation in more patients.