Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Medical Biophysics

Supervisor

Ting-Yim Lee

Abstract

Clinical studies indicate that about 30% ~ 50% of patients have cognitive impairment after the first or recurrent stroke. Ischemic injury, particularly subcortical lesions, caused by stroke has been demonstrated to further exacerbate cognitive impairment of Alzheimer’s disease (AD) and vascular dementia. However, the mechanisms whereby cerebrovascular abnormalities contribute to neurodegeneration at early stage of disease and eventually to cognitive decline remain unclear. CT perfusion and positron emission tomography (PET) were used to investigate early mechanisms in a rat comorbid model of cerebral ischemia (CI) and β-amyloid (Aβ, a pathological hallmark of AD) toxicity, and in patients with small subcortical ischemic lesions.

Chapter 2 investigates the early hemodynamic disturbances within the first month after transient CI insult in the presence of Aβ toxicity in the comorbid rat model. CT perfusion revealed significantly lower cerebral blood flow (CBF) and blood volume (CBV) at acute phase due to the transient ischemia, and increased CBF and CBV in the ipsilateral striatum of CI+Aβ and CI groups at the first week post ischemia. These results suggest that CI is the primary driving factor of cerebrovascular abnormalities at early stage, and prolonged hyperperfusion and hypervolemia may imply reperfusion-related injury and downstream inflammation. Chapter 3 further addresses these questions with CT Perfusion-PET imaging.

Chapter 3 describes the temporal profiles of blood-brain barrier (BBB) disruption and neuroinflammation over 3 months after CI with and without concurrent Aβ toxicity in the comorbid rat model. CT perfusion showed significantly higher BBB permeability surface product (BBB-PS) in the ipsilateral striatum of CI+Aβ group at day 7, month 2 and 3, as compared to CI and sham group. PET imaging revealed the highest level of neuroinflammation as reflected by the significantly increased 18F-FEPPA uptake due to microglial activation in the striatal lesion of CI+Aβ group at day 7 and 14. The temporal features of these cererbrovascular and cellular changes may serve as early imaging biomarkers for development of cognitive impairment in high-risk patients post ischemic insult.

Chapter 4 investigates the temporal changes in BBB-PS and cerebral perfusion using CT perfusion over the first 3 months after small lacunar/subcortical stroke in patients. This longitudinal investigation suggests the chronic BBB leakage detected by CT perfusion may contribute to cognitive impairment and associated pathology in lacunar/subcortical stroke.

Overall, the imaging results presented in this thesis have demonstrated that BBB-PS, CBF, CBV and activated microglia can be used as imaging biomarkers for delineating the early pathogenic pattern and underlying contribution of cerebral ischemia to the disease development in the animal comorbid model and subcortical stroke patients.

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