Visits 2 - 5: MRI Study Days MRI study days will take place in the level A annex of the SPMIC, in the QMC. Visits will be at least 1 week apart to minimise any carryover effect. Participants will fast from 8pm on the evening before the Study Day. Water will be permitted after 8pm. On the morning of the Study Day participants will not eat or drink, other than a few sips of water to assist swallowing of essential medicines.