The short proton relaxation times, T1 and T2, in MR images of malignant melanomas differs from that of most other tumours. It has been suggested that this is due to the melanin content of these tumours, since this substance  expresses strong paramagnetic properties. However, also amelanotic melanomas display a similar MRI, which makes this explanation less likely. We have previously shown that both T1 and T2 values may be influenced when the water distribution within the tumour is changed in vitro and in vivo. Peroral administration of glucose and fructose induces an increase of the T2 signal intensity and a decrease of the T1 signal intensity with 2 h, in both pigmented and amelanotic tumours. In melanomas treated with irradiation it is possible to register a shift in the water distribution, and over time a continuous decrease in the water content by T2. Recurrence of disease is manifested as an increased T2 signal intensity.

These results have been confirmed by light and electron microscopical findings. All these influences on MRI are caused by changes in the sorbitol metabolism of the tumour cells. The administration of glucose and fructose together leads to alterations in the intra-tumour water distribution which can be registered as changes in T1 and T2 signal intencities.