Simulation of microvascular MRI signal changes in the presence of amyloid‐beta plaques or microbleeds

Abstract

AbstractBackgroundThere is currently no study in the literature that has evaluated microvascular (MV) alterations with accumulation of amyloid‐beta plaque proteins or the presence of microbleeds in the AD brain. Therefore, in this study, we simulated MRI signal changes by assuming three different environmental conditions in the imaging voxel: only the normal MV structures, normal MV structures in the presence of amyloid‐beta plaques, and normal MV structures in the presence of microbleeds. Alterations in MV imaging indices such as mean vessel diameter, vessel size index, mean vessel density, blood volume fraction, and microvessel‐weighted imaging were calculated by using the differences in relaxation rates, ΔR2* and ΔR2, through Monte Carlo simulations with application of FPM for the three conditions.MethodThe following MV indices were calculated using the simulation results of the differences in the transverse relaxation rates, ΔR2* and ΔR2: mean vessel diameter (mVD), vessel size index (VSI), mean vessel density (Q), blood volume fraction (BVf), and microvessel‐weighted imaging (MvWI).The simulations were repeated with three different main magnetic field strengths (1.5 T, 3 T, and 7 T) and two different contrast agents, Gadolinium (Gd)–chelated and Superparamagnetic Iron Oxide Nanoparticles (SPION) in three different voxel environmental conditions of only the MV structures, MV structures with amyloid‐beta plaques, and MV structures with microbleeds.ResultIn the amyloid‐plaque model, mVD and VSI decreased with increasing plaque loads, but BVf, Q, and MvWI increased with increasing plaque loads. In the microbleed model, the MV indices of mVD and VSI increased with increasing vessel size. The MV indices of mVD, BVF, VSI and MvWI increased with increasing microbleed loads, but Q did not.ConclusionAll MV indices were sensitive enough to map accumulations of amyloid plaques, but did not vary with increasing vessel size. The MV indices, except Q, were sensitive to changes in microbleed loads and microvessel size. Therefore, we recommend evaluating MV structure changes in the AD human brain using 3T MRI with a Gadolinium (Gd) contrast agent.