Characterization of Flow Velocity in a 7T Small Animal MR Scanner Using a Prototype Phase-Contrast MRA Phantom
W Randazzo*, N Yanasak, Medical College of Georgia at Georgia Regents University, Augusta, GASU-E-CAMPUS-I-3 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
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.