Abstract
With the merit of high spatial resolution and non-invasive, investigations on the hemodynamic changes with age via magnetic resonance imaging (MRI) techniques have flourished for years. The understanding of normal age-associated values in brain would help evaluate not only clinical-pathologic conditions but also normal aging processes. In addition, animal studies provide approaches to better understanding in the field of age-related neuroscience research. This thesis first explores the reproducibility of rat fMRI study by employing electric mystacial pad stimulation under isoflurane anesthesia. Results showed that all rats exhibited reproducible activation in primary somatosensory barrel field cortex (S1BF), secondary somatosensory cortex (S2) and the primary somatosensory jaw region cortex (S1J) in all fMRI sessions in 3 successive weeks. Once the reproducibility was tested, we had examined age-related changes in the animal fMRI studies for the first time. In terms of the spatial extent of activation, induced signal change, hemodynamic delay and temporal contrast-to-noise ratio, there was no significantly different between 3-month-old and 15-month-old rats. These findings suggested the further age-related correlation is not needed in rodent fMRI studies composed of rats aging up to 15-month-old. The final part of this thesis is designed to assess age-related differences in global cerebral metabolic rate of oxygen (CMRO2) in a relatively large cohort (118 subjects) with a wide age range (18-74 years). Computation of CMRO2 is based on global cerebral blood flow (CBF) obtained from phase-contrast MRI and venous oxygen saturation (Yv) measurements in the superior sagittal sinus with a T2 relaxation experiment. The central finding is that CMRO2 increases with age, suggesting the aged brain may engage more energy to maintain the same functionality. In addition, women have a slower rate of CMRO2 change when compared to men (P<0.001 for interaction term), indicating a sex-difference in its temporal pattern.