Accelerated Time-of-Flight Magnetic Resonance Angiography with Sparse Undersampling and Iterative Reconstruction for the Evaluation of Intracranial Arteries

Abstract

Objective: To compare the image quality of three-dimensional time-of-flight (TOF) magnetic resonance angiography (MRA) with sparse undersampling and iterative reconstruction (sparse TOF) with that of conventional TOF MRA.

Materials and methods: This study included 56 patients who had undergone sparse TOF MRA for intracranial artery evaluation on a 3T MR scanner. Conventional TOF MRA scans were also acquired from 29 patients with matched acquisition times and another 27 patients with matched scanning parameters. The image quality was scored using a five-point scale based on the delineation of arterial vessel segments, artifacts, overall vessel visualization, and overall image quality by two radiologists independently, and the data were analyzed using the non-parametric Wilcoxon signed-rank test. Contrast ratios (CRs) of vessels were compared using the paired t test. Interobserver agreement was calculated using the kappa test.

Results: Compared with conventional TOF at the same spatial resolution, sparse TOF with an acceleration factor of 3.5 could reduce acquisition time by 40% and showed comparable image quality. In addition, when compared with conventional TOF with the same acquisition time, sparse TOF with an acceleration factor of 5 could also achieve higher spatial resolution, better delineation of vessel segments, fewer artifacts, higher image quality, and a higher CR (p < 0.05). Good-to-excellent interobserver agreement (κ: 0.65-1.00) was obtained between the two radiologists.

Conclusion: Compared with conventional TOF, sparse TOF can achieve equivalent image quality in a reduced duration. Furthermore, using the same acquisition time, sparse TOF could improve the delineation of vessels and decrease image artifacts.

Keywords: Intracranial vessels; Iterative reconstruction; Magnetic resonance angiography (MRA); Sparse; Time-of-Flight (TOF).

Fig. 1. Axial MIP images from conventional TOF (A) and sparse TOF (B) using same spatial resolution in 60-year-old man.

Display of lesion in left MCA is poorer on conventional TOF (A) because of motion artifacts (arrow). MCA = middle cerebral artery, MIP = maximum intensity projection, sparse TOF = TOF with sparse undersampling and iterative reconstruction, TOF = time-of-flight

Fig. 2. Statistical analysis of CRs between conventional TOF and sparse TOF on original and MIP images.

A, B. CR shows no difference on original images but shows slight increase on MIP images for scanning-resolution-matched sparse TOF compared with that of conventional TOF (0.64 ± 0.05 vs. 0.61 ± 0.05, ^**p < 0.001). C, D. CR increased from 0.58 ± 0.06 to 0.60 ± 0.06 on original images (^*p < 0.05) and from 0.59 ± 0.04 to 0.64 ± 0.04 on MIP images (^**p < 0.001) on scanning-time-matched sparse TOF compared with conventional TOF. CR = contrast ratio, orig = original images

Fig. 3. Axial MIP images from conventional TOF (A, C) and sparse TOF (B, D) using same scanning time in two patients.

A and B are from 46-year-old woman and C and D are from 70-year-old man with left MCA stenosis. Delineation of fine vessels is better with sparse TOF than conventional TOF (arrowheads). Moreover, display of vessel stenosis is clearer with sparse TOF than with conventional TOF (arrows).