Figure 4. Real-time ²⁹Si MRI catheter tracking.

Individual scans showing movement of the large urinary catheter through a gelatin phantom at a frame rate of 6.25 FPS; bottom right figure shows composite of all twenty ²⁹Si images (not all shown individually) over the course of 3.2 seconds. Co-registered with a single ¹H scan (greyscale) after conclusion of ²⁹Si images (colored scale). Inset picture shows silicon particles inside polarizing tube next to urinary catheter and gelatin phantom; during the experiment, the sample tube containing the silicon particles is placed inside the urinary catheter (utilizing the existing port near the catheter tip, not shown), where it rests between the two red horizontal lines drawn on the catheter. Pertinent imaging parameters, as well as Supplemental Video S4 (showing a real-time video of the catheter tracking in Fig. 4), are included in the Supplementary Materials.