Multimodal magnetic resonance imaging of frontotemporal lobar degeneration

• Main Author: Beaumont, Helen
• Published: University of Manchester 2015
• Subjects: 616.8; magnetic resonance MRI arterial spin labelling ASL DTI diffusion perfusion arrival time frontotemporal dementia lobar degeneration semantic behavioural
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.668549

Frontotemporal lobar degeneration (FTLD) is a heterogeneous group of illnesses which can be difficult to diagnose. Modern diagnostic criteria require the presence of imaging abnormalities, but these are not always seen in the early stages of the illness. Hence there is a need to consider the use of more advanced MR techniques. This thesis reports the results of a multimodal MRI study of patients with FTLD, and considers two things: how well data from the different modalities can classify patients, and how well the different modalities can identify affected tissue. FTLD is thought to involve alterations in cerebral blood flow, but it is possible that microvascular changes will alter additional perfusion parameters, such as the time taken for blood to reach the tissue (the arrival time). Multi-time point arterial spin labelling (ASL) measurements have the ability to extract the relevant parameters. I consider the parameters involved in modelling these data, and report the accuracy of cerebral blood flow (CBF) measurement achievable in a clinically acceptable time. FTLD patients have atrophy in the frontal and temporal lobes, regions problematic for MRI because of susceptibility artefacts caused by adjacent air spaces. I consider two ASL MR read-out sequences (gradient-echo and spin-echo)and show that spin-echo images give higher signal in frontal and temporal regions than gradient-echo. ASL, T1-weighted and diffusion-weighted images were collected for a group of 17 FTLD patients and 18 controls. I found decreased CBF in highly atrophied regions of cortical grey matter in patients, but this deficit was not seen when corrected for atrophy. An increased arrival time was seen in regions adjacent to the atrophied regions, but a decreased arrival time was seen in the atrophied regions; this is a novel finding. The diffusion metrics of fractional anisotropy (FA) and particularly mean diffusivity (MD) are found to be highly sensitive to differences in FTLD patients. I speculate that this is an increased sensitivity to atrophy because of the increased signal from cerebrospinal fluid. I combine the regional values of all the modalities in a classification method to distinguish patients from controls, and establish a combination of region and modality that classified 21/22 subjects correctly. This exploratory study is the first time all three modalities have been combined in a study of FTLD patients; it shows that combining MR modalities may lead to improved classification of FTLD patients and better identification of affected tissue.