Magnetic resonance imaging (MRI) and spectroscopy (MRS) to monitor and control experimental laser surgery

We have proposed the use of MRI for monitoring and control of interstitial laser surgery, in order to improve the accuracy and reduce the invasiveness of these procedures. To expand the knowledge base about the MR appearance of laser-induced tissue damage, we applied MR imaging and phosphorus-31 MR spectroscopy to detect the changes induced in various tissues by radiation from an Nd:YAG laser at 1060 nm wavelength delivered interstitially through a fiber optic waveguide. A range of laser energies was applied, and laser pulse parameters were varied. Proton MR images of the laser-produced lesions were compared with the histological appearance in brain and liver tissue of experimental animals. The spatial extent of laser effects differed among tissue types, and this was well reflected on MR images. The distribution of MR signal change resulting from different laser exposures was also demonstrated. Experimental laser surgery was performed in animal brain and bladder. Images taken before, during, and after laser irradiation allowed us to distinguish between reversible thermal and permanent effects. This information was utilized to tailor the destruction of preselected targets while minimizing damage to surrounding tissues. Qualitative changes were also revealed on phosphorus spectra. Irreversible lesions were characterized by overall line broadening and a decrease in ATP. There was also a large relative increase in the inorganic phosphate region of the spectrum. These demonstrations are a big step toward achieving our ultimate goal, the development of MR-controlled laser surgery.