HEPATIC INTERSTITIAL LASER PHOTOCOAGULATION - AN INVESTIGATION OF THERELATIONSHIP BETWEEN ACUTE THERMAL LESIONS AND THEIR SONOGRAPHIC IMAGES

OBJECTIVES. The relationship between hepatic interstitial laser photoc oagulation (ILP) lesions and their acute ultrasound images was evaluat ed. In addition, the natural history of ILP lesions in normal pig live r was documented. METHODS. Eighteen pigs underwent laparotomy and ultr asound-monitored ILP. In part 1 of the study, 12 pigs each had four se parate exposures (1.50 W for 60, 100, 300, and 500 seconds) and were d ivided into four groups according to when they were killed (0, 3, 7, a nd 21 days). In part 2 of the study, six pigs each had two sequential exposures (1.60 W for 1,000 and then 500 seconds) at separate hepatic sites. Survival time was 3 days. Necropsy and histologic examination w ere performed in all animals. In 0- and 3-day survivors, actual therma l lesions were compared with ''early'' (immediately after ILP) and ''l ate'' (1 hour after ILP) ultrasound images. RESULTS. In the 300-, 500- , and 1,000-second exposures of parts 1 and 2, thermal lesions were ov erestimated or approximated by early ultrasound and were underestimate d or approximated by late ultrasound, Analysis of variance showed stat istically significant differences between thermal lesions and their ea rly and late ultrasound images (F = 18.6, P < .001, no interactions). Time-growth characteristics of ILP lesions were reasonably consistent on ultrasound; exceptions were identifiable 200 seconds into the expos ure. In part 2, ultrasound changes were minimal in five of six 500-sec ond (second sequential) technically satisfactory exposures. Thermal le sions were seen at necropsy. All lesions healed by formation of granul ation tissue and collagen. CONCLUSIONS. During ILP, early ultrasound i mages frequently overestimate actual thermal lesions. Ultrasound-monit ored ILP of tumors may be most effective if, on early ultrasound, echo genic changes extend beyond the tumor margins. Late ultrasound images underestimate or approximate thermal lesions. Their value in clinical ILP should be investigated. It is unclear why ultrasound images of pro ven thermal lesions were not seen during 5 of 6 otherwise satisfactory 500-second ILP exposures performed immediately after 1,000-second exp osures.