Magnetic resonance imaging of laser phototherapy: initial experience

Abstract

Interventional magnetic resonance imaging (MRI) is a newly established field, made possible by improvements in imaging times and the development of nonferromagnetic materials. Interstitial laser therapy (ILT) is a promising new technology in which laser energy is adininistered percutaneously via optical fibers. In this study, MRI was used to image acute experimental lesions induced nv ILT. Nine experimental lesions were induced in the musculature of an adult swine using an argon laser,' with output power of 1–4 watts, and exposure times of 10–40 s. T2-weighted images were obtained immediately after laser energy administration. The animal was then sacrificed and lesions were dissected and examined histologically. On MRI, target like lesions were seen with a high intensity center surrounded by two alternating concentric rings of low and high intensity. Histologically, concentric zones of tissue disruption were present. A center cavity was surrounded by a zone of coagulative necrosis, followed by a zone of vascuolated tissue abutting normal muscle. We conclude that MRI is capable of imaging acute histological changes. Appropriate development of a scale relating MR changes to acute and long-term histologic changes will allow us to optimize 3 D control and monitoring of ILT.