Modeling Relaxation Effects during Bolus Passage through Leaky Vasculature using the Finite Perturber Method

INTRODUCTION: Dynamic susceptibility contrast MRI (DSC-MRI) is a novel tool that has shown promise to increase the predictive power of diagnostic imaging, for example in the assessment of brain tumor grade [1]. Alterations in microvascular parameters such as blood volume and vascular permeability induced by pathological angiogenesis are detectable with DSC-MRI. However, the basic assumptions of DSC-MRI analysis are violated by contrast agent extravasation and recirculation, making it challenging to reliably quantify microvascular parameters in common brain pathologies such as brain tumors, stroke, and infection [2]. While analytical expressions for correcting contrast agent extravasation effects have been proposed, they are limited by computational approximations and assumptions regarding the underlying pathological vasculature [2]. Since microvessel geometry is a significant determinant of DSC-MRI contrast [3], we recently developed a novel computational platform called the finite perturber method (FPM), with which we can quantify susceptibility-induced contrast arising from arbitrary microvascular geometries [4]. In this preliminary work, we extended the FPM by incorporating a compartmental model to simulate arterial bolus passage and contrast agent extravasation. This allowed us to quantify the effects of contrast agent extravasation on the measured gradient-echo (GE) and spin-echo (SE) DSC-MRI signals, providing a powerful framework for assessing the complex dependence of the DSC-signal on the underlying microvasculature.