Multimodal Magnetic Resonance Imaging of Frontotemporal Lobar Degeneration

UoM administered thesis: Phd

  • Authors:
  • Helen Beaumont

Abstract

Frontotemporal lobar degeneration (FTLD) is a heterogeneous group of illnesseswhich can be difficult to diagnose. Modern diagnostic criteria require the presenceof imaging abnormalities, but these are not always seen in the early stages of theillness. 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 classifypatients, and how well the different modalities can identify affected tissue.FTLD is thought to involve alterations in cerebral blood flow, but it is possiblethat microvascular changes will alter additional perfusion parameters, such as thetime taken for blood to reach the tissue (the arrival time). Multi-time point arterialspin labelling (ASL) measurements have the ability to extract the relevant parameters.I consider the parameters involved in modelling these data, and reportthe accuracy of cerebral blood flow (CBF) measurement achievable in a clinicallyacceptable time. FTLD patients have atrophy in the frontal and temporal lobes,regions problematic for MRI because of susceptibility artefacts caused by adjacentair spaces. I consider two ASL MR read-out sequences (gradient-echo and spinecho)and show that spin-echo images give higher signal in frontal and temporalregions than gradient-echo.ASL, T1-weighted and diffusion-weighted images were collected for a group of 17FTLD patients and 18 controls. I found decreased CBF in highly atrophied regionsof cortical grey matter in patients, but this deficit was not seen when corrected foratrophy. An increased arrival time was seen in regions adjacent to the atrophiedregions, but a decreased arrival time was seen in the atrophied regions; this is anovel finding. The diffusion metrics of fractional anisotropy (FA) and particularlymean 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 theincreased signal from cerebrospinal fluid.I combine the regional values of all themodalities in a classification method to distinguishpatients from controls, and establish a combination of region and modalitythat classified 21/22 subjects correctly. This exploratory study is the first timeall three modalities have been combined in a study of FTLD patients; it shows thatcombining MR modalities may lead to improved classification of FTLD patientsand better identification of affected tissue.

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Original languageEnglish
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Award date31 Dec 2015