Our Imaging Acquisition Research Group is led by Professor Gareth Barker.
Conventional Magnetic Resonance Imaging (MRI) uses the MR scanner as a camera; taking pictures that allow visualisation of focal defects (e.g. lesions), high-contrast objects (e.g. tumours) or normal anatomy. Outcome measures, such as change in size or appearance, are subjective (and therefore hard to reproduce). An alternative approach is to treat the MR scanner as a scientific instrument, and used to probe subtle ‘invisible’ (diffuse or small) changes. Accuracy (closeness to truth) and reproducibility (test-retest reliability) of measurements must then be considered, and techniques must be optimised to maximize these.
The MR scanner is controlled by a set of software programs and parameter setting collectively known as a ‘pulse sequence’. Signal intensity from most MR pulse sequences does not relate directly to any single physical parameter, but by combining images collected in different ways it is possible to calculate values which do relate to fundamental properties of the substance being imaged. Calculating such fundamental parameters allows quantitative, rather than simply qualitative, assessment, with values being compared to normal ranges. This should give results that are less scanner dependent, making longitudinal or multi-centre studies much easier, and may potentially also increase sensitivity to changes associated with disease.
There are a number of parameters that can be quantified by MR, and researcher at the CNS have developed and implemented techniques to allow measurement of T1, T2, magnetisation transfer related parameters (ranging from the relatively simple Magnetisation Transfer Ratio (MTR) to the rate constants and volume fractions of the different tissue compartments involved), diffusion parameters (including diffusivity and anisotropy) and perfusion. The quantitative numbers these techniques provide are being used to probe brain myelination, to investigate the direction and structure of white matter tracts, to measure the physiological changes related to both normal brain function and to pharmaceutical challenges, along with applications as diverse as evaluation the perfusion in the placenta mothers at risk of having low birth weight children and investigation of markers of risk of dementia.