Photodiagnosis (PD), also known as Photodynamic Diagnosis (PDD) is the use of light-sensitive drugs to indicate the presence of cancer.
The same drugs that are used for the treatment of cancer (PDT) can be used to assist in its diagnosis.
As in the case of PDT, the drug is first administered to the patient. After a suitable delay, which can be a few hours or a few days depending on the drug, the tumour site is then illuminated from light (usually from a laser).
The colour of the light used for PD is different from what is used for PDT. This causes the drug to glow.
In subdued lighting, the glow can be easily seen. This indicates the presence of the drug which shows where the tumour is located.
The Scottish PDT Centre has treated many patients using the fluorescence from the drug to guide the surgeon during surgery.
Examples include certain types of brain cancer, and tumours located in the upper urinary tract.