For the optimisation study, 20 healthy volunteers will be recruited. For the application study 80 patients (20 Hodgkin's lymphoma, 20 head and neck tumour, and 40 glioma) will be investigated. Most of these patients will be due for an MRI as part of their standard care pathway; in these cases exchange-sensitive MRI will be added to the standard imaging sequence. For those who are not otherwise due for MRI, both standard and exchange-sensitive MRI will be acquired.