Feasibility of Spin- and Gradient-Echo Dynamic Susceptibility Contrast MRI for Microvascular Characterization at 7...

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 $∆R_2^{\left(*\right)}$ 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.