Courtesy of Prof Neil Roberts and Lucy Hiscox, this image illustrates Magnetic Resonance Elastography (MRE), a new MRI-based technique that enables non-invasive palpation (i.e. ‘touching’) of living tissues so as to measure their mechanical properties (i.e. stiffness). In order to achieve this, sound waves must be introduced into the tissue via an appropriate actuator (in this case a gently vibrating head pillow) and images of the harmonic oscillation of the sound waves within the tissues are captured by a conventional MRI sequence modified by additional motion-encoding field gradients synchronised to the applied vibrations.
After the acquisition, image analysis techniques incorporating mathematical inversion algorithms or alternatively, finite-element-based reconstruction, are used to analyse the phase information in the time series imaging data and measure the wavelength of the sound waves. The wavelength of the sound waves increases as tissue stiffness increases and the final result is displayed as a voxel by voxel map of tissue stiffness (i.e. elastogram). MRE has exquisite sensitivity for detecting changes in the mechanical properties of brain tissue and may potentially be used to diagnose and monitor progression and treatment response in a wide range of neurological disorders.
The MRE images shown above were acquired at the Clinical Research Imaging Centre (CRIC) which is part of Edinburgh Imaging, a virtual hub of expertise in Medical Imaging at the University of Edinburgh, and comprise (a) T1-weighted sagittal view of the human brain with transverse slice of interest indicated, and which in (b) has been segmented using FreeSurfer software, to show specific anatomical regions of the medical temporal lobe. In (c) the MRE wave motion in the transverse image is shown as an phase image, and in (d) the corresponding stiffness map is displayed with regions of the medial temporal lobe, which include the hippocampus, outlined.
An animated phase image shows the MRE wave motion from (c):
The images have been supplied by Lucy Hiscox, a SINAPSE PhD student based at the Alzheimer Scotland Dementia Research Centre at the University of Edinburgh. Lucy has developed a state of the art protocol for brain MRE and is applying this to assess mechanical changes in cognitively healthy ageing prior to the study of patients with prodromal Alzheimer’s disease. The work is supervised by Professor Neil Roberts, Professor John Starr and Professor Edwin van Beek, funded by Alzheimer Scotland and supported by collaboration with Charité – Universtätsmedizin Berlin, the University of Illinois at Urbana-Champaign, USA and the Thayer School of Engineering, Dartmouth College USA.