There are no potential adverse effects of a properly conducted MRI scan. The magnetic field and RF pulses are not known to cause any physical harm in properly selected subjects. Such selection will involve careful screening of the patients' medical history for any surgery or accidents that might have introduced metal to their bodies e.g. cerebral artery aneurysm clips or a metal foreign body in an eye. This will require a review of the patient's notes once consent has been given and a written checklist at the time of MRI scan. Such patients are not scanned in standard clinical practice and would also be excluded from the study.