Table 1.
Technical background and pathological specificity and sensitivity of quantitative MRI techniques
| Quantitative MRI technique | Contrast mechanism | Measure(s) | Specificity to multiple sclerosis pathology | Sensitivity to multiple sclerosis pathology |
|---|---|---|---|---|
| qT1 | Recovery of longitudinal magnetization | T1-RT/R1 | Low: myelin/axons/cells/macro- and micro molecules/water) | High: (lesions and NAT) |
| T2 relaxometry |
Loss of spin Coherence of water pools (myelin layers, intracellular, intra-axonal, extracellular) |
T2-RT/R2 | Low: myelin/axons/cells/water) | High: (lesions and NAT) |
| MWI | Loss of spin coherence of water molecules trapped in myelin | MWF | High: myelin | High: (lesions and NAT) |
| MTI | Exchange of magnetization between free protons and macromolecular protons (proteins/lipids) | MTR | Low: myelin/macromolecules (e.g. lipid/protein in biological membranes) extracellular water | High: (lesions and NAT) |
| DTI | Diffusivity of water proteins (intracellular-extracellular) | MD, RD/AD, FA |
Low Highly dependent on tissue structure (e.g. fibre crossing/activated microglia/cells) |
High: (lesions and NAT) |
| Diffusion-based models of microstructure |
Modelling of water compartments Modelling of the diffusion magnetic resoance signals |
Restricted water fraction (CHARMED) Axon calibre (ACTIVEX) Diffusion Kurtosis ICVF ODI fis |
High ODI: neurite dispersion Moderate NDI: myelin and axonal count fis: Neurite and soma |
High: (lesions and NAT, little evidence) |
| QSM | Local changes in tissue composition cause frequency shifts (measured by phase images) | Magnetic susceptibility | Low: Influenced by changes in iron/myelin/water content | Moderate: (lesions) |
| Perfusion MRI | ||||
| ASL | Magnetically labelled blood is used as endogenous tracer |
CBV CBF MTT Ktrans Ve Vp |
Moderate: linked to mitochondrial energetic failure; linked to elevated levels of endothelin-1 | Moderate: (NAT) |
| DSC | Susceptibility effect of the paramagnetic contrast agent leads to signal loss in T2/T2*-weighted images | |||
| DCE | Wash-in, plateau, wash-out of contrast enhancement |
The evaluation of ‘specificity’ and ‘sensitivity’ of quantitative MRI measures has been made along two criteria: (i) the strength of correlation between quantitative MRI measures with a given neuropathological feature (specificity); and (ii) the number of neuropathological features measured with quantitative MRI (sensitivity). Based on those criteria, an expert consensus was reached a consensus among the participants of the MAGNIMS workshop (Basel, December 2019) on ‘Quantitative MRI towards clinical application in MS’. ASL = arterial spin labelling; CBF = cerebral blood flow; CBV = cerebral blood volume; DCE = dynamic contrast-enhanced; DSC = dynamic susceptibility contrast; fis = soma signal fraction; GM = grey matter; GRASE = gradient and spin echo; ICVF = intracellular volume fraction; Ktrans = transfer constant; MTI = magnetization transfer imaging; MTT = mean transit time; MWI = myelin water imaging; NDI = neurite density index; ODI = orientation dispersion index; Ve = fractional volume of the extracellular space; Vp = fractional volume of the plasma space.