High Spatial Resolution Diffusion-Weighted Imaging (DWI) of Ischemic Stroke and Transient Ischemic Attack (TIA)

• Author / Creator

  Hafermehl, Kyle T

• Diffusion-weighted imaging (DWI) is the most sensitive imaging technique available to identify ischemic lesions. This magnetic resonance imaging (MRI) technique exploits (non-invasively and in a short scan time) early changes to water mobility caused by metabolic failure of neurons by tagging water molecules and tracking their movement, enabling DWI to detect diffusion restriction (interpreted to indicate infarction in ischemic stroke) within minutes of symptom manifestation. Ischemic stroke and transient ischemic attack are an increasingly diagnosed affliction of the cerebrovascular system causing both death and loss of independence, relying on the utilization of neuroimaging to assist in identification of infarctions and probable etiology in order to initiate the most effective treatment path. But clinical DWI is still obtained using resolution that is insufficient to identify small ischemic lesions in minor ischemic stroke and transient ischemic attack (TIA). The experiment within this thesis utilized high spatial resolution DWI sequence to detect ischemic lesions present within acute ischemic stroke and transient ischemic attack patients (n = 48). The decreased voxel size (4.7T, 3.4 mm3; 1.5T, 4.5 mm3; 3.0T, 3.4 mm3) and slice thickness (4.7T, 1.5 mm; 1.5T, 2 mm; 3.0T, 1.5 mm) was achieved at the expense of additional time (4.7T, 210 s; 1.5T, 293 s; 3.0T, 259 s) and incorporated into the stroke protocol on 1.5T, 3T and 4.7T magnetic field strength scanners. Ischemic lesions were identified on the high resolution DWI (n = 94) that remained undetected on lower spatial resolution DWI (n = 65) typically utilized on clinical scanners. Undetected ischemic lesions (n = 29) were very small and more often located within the cortex. Ischemic lesions were consistently measured to be smaller in volume and demonstrated decreased apparent diffusion coefficient values on the high resolution DWI by reducing partial volume effects with adjacent non infarcted tissue. Improving the spatial resolution of diffusion-weighted imaging sequences and taking advantage of high magnetic fields, improves patient diagnosis and potentially their prognosis by accurate assessment of ischemic lesion patterns and lesion volume and mean diffusivity (MD) estimation. Future work is necessary to combine the high resolution diffusion imaging acquisition parameters used in this thesis with high resolution MRI modalities that evaluate tissue perfusion in order to systematically study transient ischemic attack longitudinally and identify permanent tissue damage.

• Subjects / Keywords

  • Ischemic stroke
  • Diffusion-weighted imaging
  • Transient ischemic attack

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3P84416B

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.