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disease activity & severity index (DAI/DSI)
This project focuses on coordinating available MRI variables into a common reference, creating a simple yet specific surrogate for disease activity and severity in multiple sclerosis. A distinction between the two concepts is important especially in the view of the complex dynamics of multiple sclerosis, expressed both in MRI evaluation and disability.
Disease Severity
Disease Severity measures the extent of visible pathology reflecting how much damage has occurred by the disease. This measure is integrative in nature, i.e. it seeks to reflect the sum of lasting, potentially irreversible, tissue damage. Candidates for a disease severity index (DSI) are:
- T2 WM lesion morphometry: global and regional lesion volume
- global parenchymal atrophy: global and regional volumes of white- and gray matter as well as global parenchymal atrophy (BPF)
- regional structural atrophy: volumes of white- and gray matter regions and anatomical substructures (e.g. caudate, cortical thinning, corpus callosum, hippocampus etc.)
- T1 chronic black hole morphometry: number and volume of T1 black holes
- integrated counts of contrast-enhancing T1Gd-DTPA lesions (from serial MRI)
- absolute of self-normalized concentration levels of N-acetyl aspartate, captured by MR spectroscopy
- normalized levels of diffuse GM T2-hypointensity
Disease Activity
Disease Activity, on the other hand, is a differential measure. It is meant to represent the extent of currently active disease, i.e. the level of ongoing pathological activity. Disease activity is one of the principal variables in monitoring disease progression and studying therapeutic effect. Conceptually one could understand the DAI as a temporal derivative of the DSI, i.e. in a progressive degenerative disease model, disease activity eventually leads to increments in disease severity. This also has consequences on acquisition, since most activity variables require a follow-up exam, i.e. they arise from a longitudinal study, whereas the DSI in most cases can be obtained from a single MRI snapshot, i.e. in a single exam. Candidates for the disease activity index (DAI) are:
- T1 contrast enhancing lesion (Gd-DTPA) morphometrics: number, volume, location & characterization
- enlarging and resolving T2 lesion volume
- new and resolved T2 lesion volume and number
- atrophy rates: trends in global and/or regional tissue atrophy, i.e. WM/GM/BPF atrophy rates
- rates and changes in any of the above DSI variables