Improved venous suppression and spatial resolution with SENSE in elliptical centric 3D contrast-enhanced MR angiography

Abstract

The elliptical centric (EC) view order samples a 3DFT acquisition from the center of k-space outward, and when applied to contrast-enhanced MR angiography (CE-MRA) provides intrinsic venous suppression. This is because the veins enhance several seconds after the scan is initiated, and are thus encoded solely by noncentral k-space frequencies. A separate method, sensitivity encoding (SENSE), accelerates the k-space sampling rate by reducing the phase FOV or, equivalently, by increasing the k-space sampling interval, and has been used to increase spatiotemporal resolution. We hypothesized that by combining SENSE with EC, sampling of central k-space would be accelerated and the k-space radius at which the veins first showed contrast enhancement would be increased over a reference scan, thus providing improved venous suppression and spatial resolution without additional scan time. This hypothesis was studied with the use of phantom and carotid CE-MRA experiments, and the results demonstrated an approximate 25% reduction in venous signal when SENSE was used.

FIG. 1

Simplified illustrations of the accumulated k-space trajectory with EC view order for (a) non-SENSE and (b) twofold Y-SENSE cases in the k_Y-k_Z plane, using scan parameters from the flow phantom study. The first 200 views are shown in each plot. Note the greater k-space area coverage with SENSE EC in b due to a twofold increase in Δk_Y.

FIG. 2

Schematic of the flow phantom. Arrows define directional flow within the tubes, and arteries (tubes 2 and 3) and veins (tubes 1 and 4) are labeled. Note the static resolution phantom, and placement of surface coils along the L/R Y-axis.

FIG. 3

MIP images from the flow phantom experiment using EC view order (a) without SENSE and (b) with SENSE for T_start = 10 s. Note the improvement in resolution bars (enlarged inset). The distance per line pair for each set of better-resolved bars is indicated in millimeters. Numbers above the vessels in image a correspond to those in Fig. 2. Note the significant venous suppression with SENSE for vessel 4 (dashed box) in b. c: Bar graph illustrating venous enhancement (% arterial signal) versus T_start for non-SENSE and SENSE acquisitions. SENSE significantly suppressed venous signal (P < 0.001) for T_start values < 10 s (T_start = 6–10 s). For T_start = 12–14 s, venous overlay was not suppressed by SENSE, principally because the EC acquisition was initiated during onset of the venous phase.

FIG. 4

Results from volunteer study 7, in which the SENSE scan was acquired first. Mask-subtracted MIP images are shown for (a) non-SENSE and (b) SENSE acquisitions. Areas of venous enhancement are noted in the (a) non-SENSE image (open arrowheads), while corresponding locations in the (b) SENSE image (arrows) show significant venous suppression of approximately 20%, and improved conspicuity of the arteries.