The differences we see with stronger surface-based cluster relationships between CBF and p-tau181 compared to the stronger regional relationships between CBF and tau PET may reflect the nuances of a bidirectional relationship between CBF and tau pathology; small local cerebrovascular injury could contribute more to plasma p-tau181 concentration, whereas insoluble neurofibrillary tangle deposits themselves could contribute more to globally decreased CBF. This evidence concerns the gene MAPT and Neurofibrillary tangles.