11/7/2023 0 Comments Laura fink measurements![]() Multicentre imaging studies are desirable for several reasons. Measuring actual quantities, such as volume, relaxation time or transfer constant, has meant in principle we are able to obtain values independent of the scanner used and the particular way the measurement was carried out. Analysing the sources of intercentre variation, with insight into the MR physics aspects of the imaging process, and then reducing them where possible has allowed progress to be made. Yet there is a strong imperative to be able to carry out meaningful multicentre studies so clinical drug trials with a large number of subjects can take place in a reasonable time. A common difficulty is a measurement made at one centre is often not reproducible at another centre and to pool measurements from several centres into a large trial reduces its statistical power. There have been many approaches to carrying out multicentre imaging studies. These include dynamic contrast-enhanced and dynamic susceptibility contrast gadolinium imaging, T 1, diffusion, magnetisation transfer, spectroscopy, tumour volume, arterial spin labelling and CT perfusion. ![]() Specific tissue parameters are analysed in detail to identify the major sources of variation and the most appropriate phantoms or normal studies. Sources of variation that are generic to any imaging method and analysis parameters include MR sequence mismatch, B 1 errors, CT effective tube potential, region of interest generation and segmentation procedure. In a serial study of disease progression or treatment effect, individual patients should receive all of their scans at the same centre the power is then limited by the within-subject reproducibility. In a cross-sectional study, all groups should be represented at each centre and the effect of centre added as a covariate in the statistical analysis. In a multicentre study or treatment trial, between-centre variation should be minimised. ![]() Techniques for temperature monitoring and control are given. MR phantoms have benefits and they are necessary for some parameters ( e.g. diffusion or magnetisation transfer) because the normal biological range is low (<2–3%) and the measurements will reflect this, provided the acquisition sequence is controlled. Normal white matter forms an excellent standard for some MRI parameters ( e.g. Differences between centres can be characterised, understood and minimised by use of phantoms (test objects) and normal control subjects. ![]() Multicentre imaging studies of brain tumours (and other tumour and brain studies) can enable a large group of patients to be studied, yet they present challenging technical problems. ![]()
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