Inclusion Criteria:  Patients with probable Alzheimer's disease, based upon cognitive testing (MMSE) and SPECT imaging. Controls will be participants without known cognitive impairment or Alzheimer's disease. Subjects capable of giving informed consent. Age 21 and above  Exclusion Criteria:  MRI-incompatible condition detected in the MR screening sheet such as some metallic implanted devices (see MR screening sheet in the project files). Claustrophobia Waist circumference larger than 102 cm, due to the limited bore size of the scanner. Restrictions to mobility such that patients are unable to be positioned in scanner by trained research radiographer e.g. severe kyphosis Cognitive impairment of sufficient severity that the participant does not have capacity to give informed consent Pregnancy Persons who might not adequately understand verbal explanations or written information given in English, or who have special communication needs Dementia of sufficient severity that the participant cannot give informed consent