Currently, the most widely used approach in first-pass peripheral MRA is the so-called stepping table subtraction method^1,2. It involves corresponding 3D acquisitions before and during the initial arterial passage of a contrast agent to suppress background signal by subtraction, typically at three or four table positions to cover the vascular tree from the infrarenal aorta down to the feet. Recently, a subtractionless method was proposed, which relies on fat suppression to reduce background signal instead³. It was shown to offer advantages over the subtraction method in terms of SNR and CNR, robustness to motion, and scan time, in both theory and practice^3,4. The first clinical study with this method was performed at 1.5 T³. The purpose of this work was to investigate the basic feasibility of subtractionless first-pass peripheral MRA at 3 T, in particular with three stations only, and to qualitatively compare image quality with the established subtraction method.Six patients were examined on a 3 T Ingenia scanner (Philips Healthcare, Best, Netherlands). During and after injection of 10 ml Gadovist (Bayer Healthcare, Berlin, Germany) at 0.5 ml/s, contrast-enhanced images were acquired successively at three table positions, each with a FOV of 430 x 400-450 x 180-200 mm³, using a 3D T₁-weighted spoiled dual-gradient-echo sequence with a TE₁/TE₂/TR of 1.5-1.6/2.8-2.9/4.4-4.7 ms. The measured spatial resolution increased from 1.3 x 1.3 x 2.8 mm³ at the first, abdominal station to 1.0 x 1.0 x 1.5 mm³ at the third, lower leg station. Scan times ranged from 13 s for the first station to 26 s for the third station, with an 8-fold acceleration by SENSE and a partial Fourier factor of 0.7. A direct comparison between the subtraction and the subtractionless method was enabled by additionally collecting corresponding non-contrast-enhanced images before injection. Moreover, RF shimming was performed at each station.
Water images were reconstructed from the contrast-enhanced images using mDIXON with a multi-peak spectral model of fat⁵, and subtraction images were generated from the first gradient echo images. The comparison between water and subtraction images was thus made on the basis of equal effective acquisition times. For visualization, coronal MIPs were calculated for each station and were stitched together to reach a virtual FOV of 1210 mm in FH direction.Stitched coronal MIPs obtained in two selected patients are shown in Figs. 1 and 2. While all stations suffer from bulk patient motion in the first case, primarily the abdominal station is affected by inconsistent breathholds in the second case. Resulting misregistration artifacts reduce the vessel-to-background contrast and even conceal vasculature in the subtraction images, whereas the subtractionless method effectively eliminates them. Compared to 1.5 T, the expected higher SNR in the water images was visually less striking, probably due to the overall better SNR with a single dose of contrast agent at 3 T. Limitations to the useable FOV due to B₀ inhomogeneity, manifesting as signal drop toward the corners of the rectangular FOV at each station, were more noticeable at 3 T, but basically concerned subtraction images and water images alike, as seen in the upper right leg in Fig. 3. Signal loss in the right femoral artery, previously reported without RF shimming by others⁶, was not observed. Remaining spatial variations of B₁⁺ only led to minor inhomogeneity in the residual background signal in the water images, especially in the right musculus tibialis anterior, as also seen in Fig. 3.This work demonstrates the basic feasibility of subtractionless three-station first-pass peripheral MRA at 3 T in patients. Compared to the subtraction method, the suppression of misregistration artifacts induced by bulk patient motion was the most striking improvement. In view of the considerable number of elderly among the patients examined with peripheral MRA, this is considered as a significant advance toward reliable, high image quality. Using four stations allows avoiding most of the mentioned additional challenges encountered at 3 T, but prolongs the scan time by about 20 s. A virtual FOV of 1210 mm, as reached in this work with three stations, suffices for most patients and seems attainable with the subtractionless method at 3 T based on the results obtained so far.