Courtesy of Dr Mary Joan MacLeod, Dr Lionel Broche and Prof David Lurie, this image compares brain images acquired with CT (top row) and with fast field-cycling imaging (bottom row) in four ischaemic stroke patients with good clinical recovery. CT images show (a) cerebellar infarct, (b) right occipital infarct, (c) right occipital infarct and (d) CT reported as normal in young patient with bilateral middle cerebral artery territory symptoms at presentation. Fast field-cycling (FFC) images acquired between 200 and 0.2 mT at the level of the lesion showed variations in T1 dispersion signal that have been stratified on a colour scale using Matlab. The infarct regions measured by FFC correlate well with the abnormalities in CT images, and indicate the potential to reveal information at the molecular level that is not accessible to CT.
FFC-MRI is a novel imaging technique that cycles through multiple ultra-low magnetic field strengths during image acquisition. Whereas the external magnetic field strength is fixed in conventional MRI (e.g., 1.5 T, 3 T, 7 T), FFC imaging systematically varies the external magnetic field strength in order to access new types of endogenous contrast, such as the T1 dispersion signal. This measurement of how a tissue’s T1 varies with magnetic field provides new information about molecular dynamics that may allow earlier and more reliable diagnosis of some medical conditions.
The above images from stroke patients represent the first clinical application of FFC imaging. Scanning was performed on the world’s only FFC-MRI scanner for whole-body human imaging, at the University of Aberdeen.