Quantitative voxel-based analysis of T1-weighted MRI signal intensity

Abnormalities in the brain generally manifest on MRI as changes in shape (morphometry) or changes in the nature of the tissue (signal intensity). Voxel-based statistical analysis approaches are able to objectively detect such changes throughout the brain. For example, Voxel Based Morphometry (VBM) [2] and Voxel Based T2relaxometry (VBR) [3] can detect subtle changes in tissue volume and T2 signal intensity respectively. Whilst VBM can be applied to any imaging modality with sufficient contrast between tissue classes (such as T1-weighted MRI), a fully quantitative modality is usually required for the direct detection of signal intensity changes. Thus the application of a voxel-based approach for direct detection of signal differences in T1-weighted MRI would not normally be considered. The intensity of conventional T1-weighted images depends on multiple factors such as shim, coil loading and receiver gain settings, and can vary markedly across imaging sessions and subjects. Whilst quantitative T1-relaxomety may be able to avoid these problems, sequences to achieve this at high-resolution and a reasonable imaging time are not routinely available on clinical scanners. We therefore sought to determine the sensitivity of the Voxel-Based Iterative Sensitivity (VBIS) approach when applied to T1weighted images.