Positron emission tomography:Technique and application in urological oncology

First the principles of Positron Emission Tomography (PET) are described. PET is one of the nuclear imaging techniques. PET, in contrast to the conventional nuclear techniques like the scintigraphy and SPECT, uses physiological molecules in which non radio active atoms like oxygen or carbon are replaced by the radio active form, which emits positrons. This replacement does not change the chemical structure so the radio active molecule is metabolized in the same way as the original non radio active molecule. This allows PET not only to image but also to quantify the metabolism. Next we present a review about PET and urological oncology. Until now the application of PET in this field of oncology is limited. This is due to the fact that fluor-18-deoxyglucose, the currently most investigated tracer in PET, is rapidly excreted in the urine and radio activity accumulates in the bladder. This accumulation of radio activity in the bladder makes proper evaluation of the retroperitoneum and organs within the pelvic area like the bladder and the prostate difficult. The ideal tracer for PET in urological oncology therefore should not be excreted in the urine. Carbon 11 labeled amino acids like tyrosine and choline are not excreted in the urine and were recently used with success in the imaging of bladder and prostate cancer. The clinical use of 11C-Choline PET is now investigated in patients suffering from bladder or prostate cancer in our institute.