Conventional MRI evaluation of gliomas

Abstract

MRI using T(1) weighted, T(2) weighted and gadolinium-enhanced sequences plays a central clinical role in diagnosis, characterisation, surveillance and therapeutic monitoring of gliomas. Such conventional MRI protocols provide high resolution multiplanar structural information, and substantially improved tissue characterisation compared with CT. However, the MRI signal lacks biological specificity, e.g. T(2) weighted dependent signal abnormality is dominated by tissue water content, and contrast enhancement reflects a non-specific increase in blood-brain barrier permeability. This limits non-invasive glioma diagnosis, characterisation and therapeutic planning and assessment of active tumour load may be confounded by treatment-related effects. The complex features of glioma morphology and often subtle changes between MRI examinations are also frequently difficult to detect reliably by visual inspection of the images, even by an experienced radiologist. Moreover, the most widely used response criteria in clinical practice and therapeutic trials rely on linear measurements of enhancing tumour and are further challenged by the irregular shape and heterogeneous composition of gliomas. This contributes to the poor correlation of these criteria with hard clinical endpoints. While conventional MRI is widely available and provides essential anatomical information, the lack of pathology-specific biomarkers available from standard MRI sequences and methods of image analysis used limit overall diagnostic and prognostic efficacy of the examination.

Figure 1

Grade III astrocytoma. (a) Fluid-attenuated inversion-recovery image demonstrates the sizeable non-enhancing component of the tumour compared to (b) the modest enhancement demonstrated on the gadolinium-enhanced spin echo T₁ weighted study.