Quantification of tumour microstructure in low and high-grade brain tumours using VERDICT MRI: an initial feasibility study

INTRODUCTION: VERDICT (Vascular, Extracellular, and Restricted Diffusion for Cytometry in Tumours) MRI is a diffusion imaging technique which gives information about tumour microstructure beyond ADC measures and structural imaging. VERDICT uses a three-compartment mathematical model to estimate tissue parameters such as cell density, radius and vascular perfusion, and can differentiate malignant prostate cancer from benign pathology. We report the first application of VERDICT to human brain tumours, where we characterise a mix of low and high-grade gliomas. METHODS: 9 untreated patients with brain tumours (3 glioblastoma, 1 metastatic carcinoma, 3 astrocytoma, 2 oligodendroglioma) were scanned at 3T (Achieva, Philips). Multi b-value (9 shells from b = 80–3000 s/mm2) diffusion MRI was conducted in combination with a 15-direction DTI scan. Acquisition time was 12 minutes. A three-compartment mathematical model was applied consisting of a ‘Sphere’ to represent restricted diffusion in cells, a ‘Ball’ to represent isotropic diffusion and a ‘Stick’ to represent vascular diffusion1. VERDICT parameter maps were generated based on these compartments. RESULTS: ADC was highest in GBMs, whilst astrocytoma and oligodendroglioma had comparable mean ADC and metastatic carcinoma demonstrated the lowest ADC. VERDICT parameter maps in GBMs showed a rim of increased cellular density parameter compared to the centre, consistent with a necrotic core and showed areas of increased signal in the peri-tumour zone suggestive of increased cellular density. Astrocytoma VERDICT parameter maps also showed areas of increased signal within the tumour, suggesting that VERDICT may be more sensitive to tumour microstructure compared to conventional imaging. CONCLUSION: VERDICT is feasible in human gliomas and potentially provides information on internal tumour microstructure. We are currently working on further validation with detailed histological analysis and optimisation of scan times to develop a clinically viable sequence that could potentially have important implications for pre-surgical planning and assessment of therapeutic response.