Feasibility of Spin‐ and Gradient‐Echo Dynamic Susceptibility Contrast MRI for Microvascular Characterization at 7 Tesla

Abstract

ABSTRACT Perfusion MRI, especially dynamic susceptibility contrast (DSC), is vital for glioma diagnosis and monitoring. While gradient‐echo DSC is the current recommended implementation, combined spin‐ and gradient‐echo (SAGE) DSC additionally allows for vessel size imaging (VSI) and has shown feasibility for microvascular characterization at 3 T. Higher field strength MRI offers increased contrast, resolution and signal‐to‐noise ratio, providing potential to improve microvascular characterization. This feasibility study aimed to implement a protocol for SAGE‐DSC at 7 T and study its potential for microvascular characterization. SAGE‐DSC was acquired in eight patients undergoing treatment for glioma (four females, median age 57 years) at 3 and 7 T. Data were analyzed using the temporal signal‐to‐noise ratio (tSNR) and contrast‐to‐noise ratio (CNR) and by comparing perfusion maps, VSI and vascular architectural imaging (VAI). Simulations were performed to study the relationship between vessel size and ∆R2* for SAGE‐DSC at 3 and 7 T. Contrast agent dosage could be reduced while maintaining higher CNR at 7 T (but lower tSNR). Assessment by an experienced neuroradiologist showed similar rCBV map quality at 3 and 7 T. VSI maps showed the same normal‐appearing gray‐to‐white matter ratios while in‐plane resolution improved at least 52% at 7 T. VAI hysteresis loops at both field strengths traversed the same counter‐clockwise direction, with increased loop areas reflecting increased susceptibility effects at 7 T. Simulations confirmed the higher sensitivity of gradient‐echo and the higher specificity of spin‐echo to the microvasculature, with peak spin‐echo specificity moving from 3 μm at 3 T towards 1.5 μm at 7 T. This study confirmed the feasibility of using SAGE‐DSC at 7 T for microvascular characterization. rCBV and VSI maps show similar behavior while allowing for reduced contrast agent dosage and improved resolution. The spin‐echo specificity shifted towards smaller vessel radii for increasing field strengths. These findings form the basis for exploration and validation in larger patient populations.