Investigation of the Effect of Tissue Water Dynamics on Compartmental MRI Measurements using Contrast Enhanced Relaxometry and SPECT

Abstract

Magnetic resonance imaging (MRI) provides methods for characterizing tissue micro-structure using relaxation-based measurements with and without the use of contrast agents (CA). Two techniques, dynamic contrast enhanced MRI (DCE-MRI) and multiple spin-echo (MSE) imaging, often employ two-pool models to obtain estimates of tissue compartment sizes. These estimates can be biased, however, by tissue water dynamics. Alternate strategies, such as single photon emission computed tomography (SPECT) imaging, can provide measures of tissue compartment size unbiased by water exchange. In this work, DCE-MRI measurements in rat brain tumor were compared to a dual-isotope SPECT method to assess the accuracy of estimates of the extracellular volume fraction extracted from common pharmacokinetic models. In addition, quantitative SPECT was used to validate a novel contrast enhanced MSE method, in injured rat skeletal muscle, for estimating in vivo inter-compartmental water exchange. In an effort to translate similar MSE techniques to human imaging, an accelerated method for accurate compartmental relaxometry was also evaluated.