The aim of the research study is to look at a new type of MRI scanning that can measure the amount of sodium in different parts of the body. Sodium (or 'salt') levels are very important in maintaining health, and high levels lead to high blood pressure. This is very important to patients with kidney disease, as the kidney is the main organ that regulates the amount of sodium in the body. It is possible to measure blood sodium levels, but this does not tell us how much sodium is present in other areas of the body. Previously, it has not been possible measure this. Sodium MRI (Na-MRI) is a new type of MRI scanning that can directly measure sodium in other parts of body such as skin, muscles, kidneys, and brain. The investigators believe that this will help to guide treatment in patients with kidney disease who are on haemodialysis, research studies are needed to prove the benefits.