SU‐E‐CAMPUS‐I‐03: Characterization of Flow Velocity in a 7T Small Animal MR Scanner Using a Prototype Phase‐Contrast MRA Phantom

Purpose: To determine if velocity measurements from phase‐contrast magnetic resonance angiography (PC‐MRA) are consistent with volumetric flow measurements, using a phantom with known flow in a 7T small animal MR scanner for a given velocity encode (Venc) setting. Methods: A prototype phase‐contrast phantom was constructed using plastic tubing and attached to a peristaltic pump. Volumetric flow through the phantom was directly measured by fluid weight, followed by acquisition of PC‐MRA images at high and low Venc settings, which bracketed tube velocities. Image post‐processing resulted in PC‐MRA velocities in cm/sec, which were correlated to pump RPM and measured volumetric flow using a linear regression model. Laminar flow across tube profiles was tested for verification. System noise was obtained using a central water cylinder in the phantom design. Results: A linear relationship between pump RPM and both volumetric and PC‐MRA flow velocities was demonstrated with excellent correlation between measured volumetric flow, used as the reference standard, and PC‐MRA velocity (R2 0.96–0.99). Laminar flow was present in each tube determined by the integral of the laminar equation with PC‐MRA mean/maximum flow. System noise was found to be very low, 0.38–0.51% of Venc, accounting for very good precision of flow measurements. Conclusion: PC‐MRA velocities at 7T were demonstrated to be accurate within 0.2–2.8 cm/sec, with one measurement difference of 5.0 cm/sec at higher velocity, relative to a known flow velocity in a prototype phantom. Many animal studies utilize quantitative PC‐MRA, however, an internal reference standard is lacking. Considering that variability in gradient and RF performance may introduce inaccuracy in phase‐encoded flow as well as excitation localization it is important to have a known reference standard while scanning. This prototype phantom potentially allows for in vivo quantitative PC‐MRA acquisition with simultaneous measurement of known flow velocity in the phantom for flow calibration and validity testing.