Time-of-Flight Magnetic Resonance Angiography With Sparse Undersampling and Iterative Reconstruction: Comparison With Conventional Parallel Imaging for Accelerated Imaging

Objectives The aim of this study was to evaluate the clinical feasibility of accelerated time-of-flight (TOF) magnetic resonance angiography with sparse undersampling and iterative reconstruction (sparse TOF). Materials and Methods The local institutional review board approved the study protocols. Twenty healthy volunteers were recruited (mean age, 31.2 years; age range, 22-52 years; 14 men, 6 women). Both sparse TOF and parallel imaging (PI) TOF were obtained on a 3 T scanner. Acceleration factors were 3, 4, 5, 6, and 8 for sparse TOF (Sp 3x, Sp 4x, Sp 5x, Sp 6x, and Sp 8x, respectively) and 2, 3, 4, and 6 for PI TOF (PI 2x, PI 3x, PI 4x, and PI 6x, respectively). Images were reconstructed on the scanner, and maximum intensity projection images were subjected to visual evaluation, wherein each segment of the major brain arteries was independently evaluated by 2 radiologists on a 4-point scale (1, poor; 2, limited; 3, moderate/good quality for diagnosis; and 4, excellent). As a quantitative evaluation, the apparent contrast-to-background deviation (apparent CBD) was calculated at the level of the basilar artery and the pons. Results A total number of 1800 segments were subjectively evaluated. There was substantial agreement regarding vessel visualization ( = 0.759). Sparse TOF received scores above 3 (good for diagnosis) at any acceleration factor up to the third segments of major arteries. The middle and distal segments of PI 4x and PI 6x were graded below 3 (limited or poor diagnostic value). Sp 3x, 4x, 5x, and 6x retained diagnostic information (graded above 3), even at distal segments. The apparent CBD of sparse TOF at any acceleration factor was equivalent to that of PI 2x, whereas the apparent CBD of PI 3x, PI 4x, and PI 6x attenuated with the acceleration factor. Conclusions Sparse TOF can achieve better image quality relative to PI TOF at higher acceleration factors. The diagnostic quality of distal branches (A2/3, M4, P4) was maintained with Sp 6x, which achieved a shorter acquisition time less than half of PI 2x.