DYNAMIC MRI-GUIDED INTERSTITIAL LASER THERAPY - A NEW TECHNIQUE FOR MINIMALLY INVASIVE SURGERY

Interstitial laser therapy (ILT) is a promising therapeutic technique in which laser energy is delivered percutaneously to various depths in tissue. In this study, the authors compared high-speed magnetic reson ance imaging (MRI) of ILT in tissues during treatment with post-treatm ent histopathologic specimens. The use of 5-second MRI scans allowed d etection of thermal damage by the 1064-nm neodymium:yttrium-aluminum-g arnet laser in ex vivo liver and brain tissues. These tissues were tre ated by ILT with 20 W of laser output for 5 to 30 seconds via a 600-mu m fiberoptic inserted 1 cm into the specimens at a power density of 7 kW/cm(2) at the tip of the bare fiber. Sequential MRI measurements of lesion areas made during and after treatment were compared to measure ments of laser-induced tissue damage in histolopathologic sections. Fa st MRI scans and tissue histology both demonstrated increased lesion s ize with time of ILT. Serial images obtained during ILT detected therm al changes as areas of low signal intensity that exceeded the size of the post-treatment lesions as measured on either final MRI or histolog y. The thermal effects detectable by these high-speed MRI sequences ca n be used to monitor laser-induced tissue changes during therapy, ther eby providing a valuable noninvasive method for the intraoperative ass essment of heat distribution during ILT.