Research Project: Dynamic Contrast-enhanced MRI (DCE-MRI) Flow Validation
Sunder Rajan, PhD
Dynamic contrast-enhanced MRI (DCE-MRI) allows the study of contrast agent kinetics in tissue, using pharmacokinetic models, to estimate exchange rates of tracer between the tissue compartments. Although DCE-MRI is being increasingly used, the technique suffers from lack of standardization. In this work, a flow phantom is used to validate the DCE-MRI data chain.
A flow phantom was constructed using a polysulfone dialyzer cartridge (Fresnius F160NR™). The fluid-filled cartridge mimics a two compartment system, with the intra-fiber region representing the intravascular volume. Degassed water was passed at constant flow rates through the axial ports to mimic blood flow. A 25 ml bolus of Gd-DTPA solution (Magnevist™) was injected at constant flow rate (Medrad injector) into the flow system. The passage of tracer was imaged (Philips Achieva 3T, 6-channel coil, B1 map correction, T1 mapping with dual flip SPGR, Generalized Kinetic Modeling (GKM) using custom software). T1 Standards were taped to the dialyzer for T1 confirmation. The input function was measured in the tube upstream of the dialyzer. The clearance rate of the contrast agent was measured, after passage of bolus. The clearance rate constant, (Kep), increased with flow rate and reached a permeability limit above 150 ml/min (0.57 min -1) 300 ml/min. The measurements were reproducible (0.56 ± 0.03 sec -1 at 150 ml/min, n=4. This flow phantom setup is used to test the reproducibility in the data acquisition of DCE MRI. Previous work has been limited to static phantoms.
Flow phantom setup using a dialyzer cartridge.
The side ports are sealed except during the flushing out phase.
An example of the parametric map of Ktrans obtained from a cross-sectional slice of the phantom. The inset shows the signal of the input function and the fit of the clearance of contrast from the slice.