Phase-contrast magnetic resonance angiography of foot at 5T ultra-high field strength 5T : Visualization of distal small vessels and enhancement by warm water immersion.

Background: Ultra-high field strength magnetic resonance has been proven to offer improved visualization of the distal intracranial vessels and branches, but its effectiveness for visualization of the peripheral vasculature has not been investigated. We aimed to assess the visualization of distal lower-extremity vessels using three-dimensional phase-contrast magnetic resonance angiography (3D PC-MRA) at 5T field strength in combination with warm water immersion (WWI).

Methods: Participants were prospectively recruited and underwent 3T, and 5T 3D PC-MRA of the feet with and without WWI (water temperature between 40°C and 45°C for a duration of 10 minutes). Patients with suspected lower-extremity peripheral arterial disease underwent computed tomography angiography for lesion identification. Signal-to-noise ratio (SNR), subjective scoring, quantitative vessel segmentation, and flow velocity were performed to assess vessel visualization before and after WWI. Friedman's test was conducted to determine statistical significance.

Results: Out of 30 participants (mean age, 46.2 ± 5.9; males, 20; lower-extremity vessel disease, 10), 900 vessel segments were available for evaluation. 5T images showed significantly higher scores for image quality and foot vessel visualization than 3T (all P < 0.05). WWI further improved the visualizing scores (percentage of score 3: 40.2% (193/480), 66.2% (318/480)), SNR (44.27 vs 67.78, P < 0.001), total branch count (151.92 ± 29.17 vs 225.63 ± 16.76; P < 0.001), and the flow velocity (0.72 ± 0.03 vs 0.48 ± 0.11 cm/s; P < 0.001).

Conclusion: 3D PC-MRA at 5T effectively visualizes foot vessels in patients with lower-extremity disease. Furthermore, WWI can significantly enhance the depiction of distal and small vessels.