Ultrasonically guided interstitial Nd-YAG laser diffuser tip hyperthermia: an in vitro study.

Ultrasonically guided interstitial Nd-YAG laser diffuser tip hyperthermia is a new technique that involves placement of a laser fiber in solid tissue under ultrasound guidance followed by irradiation from within the area to be treated. We have previously described a diffuser tip modification of the bare laser fiber, that proved to produce spherical coagulations of predictable size. In the present paper we describe the development of an ultrasonically guided technique which permits simultaneous laser irradiation and interstitial temperature measurements under real time ultrasound monitoring. The laser lesion appeared on the ultrasound image as a hyperechoic area growing in size with time as energy was applied. Macroscopically the laser lesion emerged as a sphere with a central cavity delineated by a rim of charred tissue and beyond this a larger zone of whitish coagulation. The correlation coefficient (Pearson's r) between ultrasonically and macroscopically measured diameter of the laser lesion was calculated to r = 0.89. It is concluded that ultrasonically guided interstitial Nd-YAG laser diffuser tip hyperthermia may have a potential as a tool in the future treatment of ultrasonically visible neoplasias like liver metastases and prostate cancer.