344 Comparison of Magnetic Resonance Relaxometry and Apparent Diffusion Coefficient for Tissue Cell Density Quantification in Glioma Imaging: Exploratory Study via 11C-methionine PET and Validation via Stereotactic Tissue Sampling

Abstract

INTRODUCTION: Visualization of non-contrast-enhancing tumor lesions in glioma is one of the most crucial yet challenging issues for patients with this pathology. METHODS: Participants comprised of patients with low- or high-grade glioma. Correlation between T1-, T2-relaxation time, ADC, and 11C-methionine uptake as measured by positron emission tomography was investigated, followed by comparing T1-, T2-relaxation time, ADC with tumor cell density as measured by stereotactic image-guided tissue sampling. MR relaxometry was achieved by converting Magnetization Prepared Rapid Gradient Echo (MP2RAGE) images and multi-echo T2-weighted images via Bayesian inference modeling. RESULTS: T1-relaxation time >1850 ms but <3200 ms or T2-relaxation time >115 ms, but <225 ms under 3T were indicative of high 11C-methionine uptake. Stereotactic tissue sampling study confirmed that only the T1-relaxation time of 1850-3200 ms was significantly indicative of higher tumor cell density (p = 0.02). ADC was unable to show a significant correlation with 11C-methionine uptake or with tumor cell density. Synthetic tumor load images were successfully reconstructed using T1- and T2-relaxation mapping. CONCLUSION: T1-relaxation time correlated well with tumor cell density in glioma tissues, while neither T2-relaxation time nor ADC showed significant correlation. The ideal ranges for identifying high tumor load tissues was 1850-3200 ms for T1-relaxation time measured at 3 T.