DOI: 10.25549/usctheses-c40-323556
title: Validation of highly accelerated DCE-MRI using a novel perfusion phantom

description: The goal of this work is to quantify the test-retest repeatability and reproducibility of a sparse sampling and constrained reconstruction DCE-MRI using a novel quantitative perfusion flow phantom. Several emerging sparse-sampling and constrained reconstruction DCE-MRI methods have achieved significantly higher spatiotemporal resolution and coverage than conventional methods. This has necessitated a reliable way to quantify the test-retest repeatability and reproducibility of these novel DCE-MRI methods. ❧ In-vivo DCE-MRI reproducibility testing requires repeated gadolinium contrast injections which have been shown to have negative effects on the human subject because of gadolinium deposition [1]. Hence precludes the use of such a methodology to perform test-retest repeatability and reproducibility of DCE-MRI. The alternative is to use a phantom, which can reliably simulate tissue curves and can be used as a proxy for a human subject. Fortunately, a recent development of a perfusion flow phantom at the Princess Margaret hospital in Toronto for reliability testing in computed tomography (CT) and its subsequent commercialization by Shelley medical has created an exciting opportunity to perform test-retest repeatability and reproducibility study in DCE-MRI. The perfusion flow phantom, developed for quantifying test-retest repeatability and reproducibility in DCE-CT, has been modified by the vendor to be used in MRI for testing. This application of the phantom to MRI is novel and is an important step towards validating novel DCE-MRI methods. ❧ My task was to design appropriate sequence parameters to establish an experimental method to perform test-retest repeatability and reproducibility study of a novel sparse sampling and constrained reconstruction DCE-MRI. This task required solving challenges with physical options on the flow phantom and MRI acquisition options which resulted in successfully fine tuning the parameters for test-retest repeatability and reproducibility in sparse sampling and constrained reconstruction DCE-MRI. I have computed intra-day, inter-day and inter-sequence reproducibility using percentage difference (PD, 100*abs(a-b)/mean(a,b)) of pharmaco-kinetic (PK) parameter values, normalized root mean square error (NRMSE) and Pearson correlation coefficient (PCC) (refer III-1.5) between the concentration-time curves obtained from a manually delineated region of interest. The PD in intra-day repeatability of Kᵗʳᵃⁿˢ (quantifies the forward transfer of concentration from the vasculature to extracellular-extravascular space) was 2.11 (absolute difference in Kᵗʳᵃⁿˢ was 0.0004 min⁻¹), vₑ (fractional extracellular-extravascular volume relative to unit tissue volume) was 0 (absolute difference in vₑ was 0) and vp (fractional blood plasma volume relative to unit tissue volume) was 11.36 (absolute difference in vp was 0.013) using the sparse sampling and constrained DCE-MRI. The PD in inter-day reproducibility of Kᵗʳᵃⁿˢ, vₑ and vp was 11.58, 13.86 and 175.86 (with absolute differences being 0.019 min⁻¹, 0.1297 and 0.0962) respectively for the sparse sampling and constrained reconstruction DCE MRI. ❧ I have shown that the intra-day repeatability of sparse sampling and constrained reconstruction DCE-MRI algorithm was excellent using PD between the PK parameters, NRMSE and PCC obtained from the concentration-time curves. The utility of using a perfusion phantom to perform test-retest repeatability and reproducibility study of novel DCE methods in place of a human subject was done as a proof of concept. We believe, this is an important step towards accurately quantifying the test-retest repeatability and reproducibility of novel DCE-MRI methods without the need for a human subject.