Effects of aging on BOLD hemodynamic response: Healthy aging versus Alzheimer disease

A “cognitive stress test” can be used to bring out astute brain irregularities that would otherwise stay undetected during a resting state functional Magnetic Resonance Imaging (fMRI). Hemodynamic Response Function (HRF) may be used to distinguish non-demented and demented Alzheimer's Type (DAT) from young adults. Previous studies have reported opposite findings for Blood-Oxygenation-Level-Dependent (BOLD) HRF of dementia versus young cases. In this paper, it is shown that the reported results contradict due to different algorithms used to extract HRF as well as noise effects. Also, an effective denoising method is here proposed to achieve a proper HRF. Proposed denoising algorithm leads to the compatible HRF results even if different extraction methods are used. Using the denoising process, it is shown that the list of activated voxels dramatically changes. Also, no significant difference is achieved in terms of amplitude HRF peak between non-demented and DAT subjects invoking the proposed denoising process.