MAGNETIC-RESONANCE SPECTROSCOPIC STUDIES ON REAL-TIME CHANGES IN RIF-1 TUMOR METABOLISM AND BLOOD-FLOW DURING AND AFTER PHOTODYNAMIC THERAPY

Magnetic resonance spectroscopy (MRS) in situ was used to study changes in P-31 metabolism occurring during and after treatment of murine RIF-1 tumours with photodynamic therapy (PDT). Tumours were irradiated using a fibreoptic light delivery system while the mice were in position within the magnet. Changes in P-31-MRS were observable during and immediately after treatments of several minutes' duration. Both the extent and duration of the increase in the P-i/total ratio were light dose dependent. The effect on the metabolism was also affected by the lime interval (TL) between administering the photosensitiser disulphonated phthalocyanine, (AlS(2)Pc) and the light. With a dose of 50 J the increase in P-i/total was much faster when TL was Ih than when TL was 24 h. This difference in rate probably reflects differences in the distribution of AlS(2)Pc within the tumour. Significant decreases in pH were only seen after a light dose of 50 J when TL was 1 h. Blood flow measurements using deuterium uptake were also carried out using MRS. These experiments showed that for a dose of 50 J the level of blood how wits reduced by approximately 90% of the control value within 10 min from the end of the 8 min light treatment. This occurred irrespective of the value of TL. The data indicate that it is possible to observe very early changes in P-31 metabolism that can be attributed to direct cellular damage as opposed to the later changes indicative of overall tumour hypoxia caused by vascular damage.