7 Tesla Time-of-Flight MRA in Adolescents

BACKGROUND AND PURPOSE: The increased signal-to-noise ratio (SNR) at 7 Tesla (7T) enables higher spatial resolution for neurovascular imaging, yet its application in pediatric magnetic resonance angiography (MRA) remains underexplored. This study systematically evaluates the advantages of 7T time-of-flight (TOF) MRA compared to 3T in pediatric patients, hypothesizing that 7T would provide superior vessel contrast and increased vascular volume, given the use of smaller voxels, as well as higher SNR, despite these smaller voxels.

MATERIALS AND METHODS: This HIPAA-compliant, IRB-approved retrospective study included pediatric patients (<19 years) who underwent 7T TOF MRA. Controls consisted of either same-subject 3T MRAs within 6 months (when available) or age-and sex-matched 3T MRA subjects. Imaging parameters were optimized for spatial resolution at 7T to achieve 0.3-0.4 mm isotropic voxels. Quantitative analysis included contrast ratio (CR) and SNR measurements for the ICA, M1 to M4 arterial segments, and lenticulostriate perforating arteries. Vascular volume was assessed using 3D segmentation. Semiquantitative vessel conspicuity ratings and motion artifact scoring were performed by blinded neuroradiologists.

RESULTS: Fifteen patients (10 with 7T MRA, 5 with matched 3T controls) and 20 MRAs were analyzed. CR was significantly higher at 7T for perforators, M3, and M4 branches (P < 0.05), with the greatest improvement in M4 branches. Vascular volume was 147% greater at 7T (P = 0.018), reflecting improved small vessel depiction and segmentation. Semiquantitative analysis showed significantly better vessel conspicuity at 7T for M4 branches and lenticulostriate perforators (P < 0.01). Motion artifact scores were similar between field strengths (P = 0.118).

CONCLUSIONS: 7T TOF MRA significantly enhances vascular contrast and improves visualization of small arteries compared to 3T, making it a valuable tool for pediatric cerebrovascular imaging.

ABBREVIATIONS: CR＝ Contrast Ratio; LSA＝ Lenticulostriate Perforating Arteries