MEDICAL IMAGING-SYSTEMS FOR FEEDBACK-CONTROL OF INTERSTITIAL LASER PHOTOCOAGULATION

Interstitial laser photocoagulation (ILP) is a minimally invasive technique in which solid tumor tissue is destroyed thermally by directing near-infrared laser energy into the tumor through one or more optical fibers implanted interstitially. Both abdominal ultrasound imaging and magnetic resonance (MR) imaging of the brain can produce high contrast images of ILP lesions in real or near-real time, during and after ILP. These images provide feedback data that can be used to control dynamically the shape of the ILP lesion. Image-based feedback control of ILP requires that contrast boundaries in images acquired during or immediately after ILP (acute images) correlate with the volumes of irreversibly damaged tissue that result several days later (chronic lesion). An image-to-actual function (IAF) is developed here as a transformation that relates acute lesion images to resulting chronic lesions. Algorithms for controlling ILP based on the IAF are presented for control by both human operator (open loop) and computer (closed loop). Preliminary studies indicate that MR image-based control of ILP in the brain should be possible using both open and closed loops. Unreliable IAF's may limit ultrasound image-based control of ILP in abdominal tumors to control based on images acquired a few minutes after stopping the irradiation.