Tomography 2019 03;5(1):77-89
TECHNA Institute, University Health Network, Toronto, ON, Canada.
Accurate, patient-specific measurement of arterial input functions (AIF) may improve model-based analysis of vascular permeability. This study investigated factors affecting AIF measurements from magnetic resonance imaging (MRI) magnitude (AIF) and phase (AIF) signals, and compared them against computed tomography (CT) (AIF), under controlled conditions relevant to clinical protocols using a multimodality flow phantom. The flow phantom was applied at flip angles of 20° and 30°, flow rates (3-7.5 mL/s), and peak bolus concentrations (0.5-10 mM), for in-plane and through-plane flow. Spatial 3D-FLASH signal and variable flip angle T1 profiles were measured to investigate in-flow and radiofrequency-related biases, and magnitude- and phase-derived Gd-DTPA concentrations were compared. MRI AIF performance was tested against AIF via Pearson correlation analysis. AIF was sensitive to imaging orientation, spatial location, flip angle, and flow rate, and it grossly underestimated AIF peak concentrations. Conversion to Gd-DTPA concentration using T1 taken at the same orientation and flow rate as the dynamic contrast-enhanced acquisition improved AIF accuracy; yet, AIF metrics remained variable and significantly reduced from AIF at concentrations above 2.5 mM. AIF performed equivalently within 1 mM to AIF across all tested conditions. AIF, but not AIF, reported equivalent measurements to AIF across the range of tested conditions. AIF showed superior robustness.