A system for performing MRI-guided transurethral prostate thermal therapy has been developed. Ultrasound energy is delivered from a multi-element heating applicator incorporating single or dual-frequency planar transducers. The heating applicators produce a directional heating pattern, and have the capability to generate an arbitrary three-dimensional thermal damage pattern in tissue. The delivery system includes five independent channels, each capable of producing up to 50W of RF power. An MRI-compatible motor has also been developed to control the rotation of the heating applicator inside the bore of a clinical 1.5T MR scanner. The capability to perform quantitative thermometry during heating with these heating applicators has been evaluated in a thermal gel material (TGM) developed in our lab with tissue-mimicking ultrasound and thermal properties.
Laser thermal therapy (LTT) is a minimally invasive surgical technique used to destroy solid tumors while minimizing damage to adjacent normal tissues. Optical energy, delivered through fibers implanted into the target volume, raises tissue temperatures above 60 degree(s)C resulting in coagulative necrosis (thermal damage). Thermal damage volumes, however, can be irregular and unpredictable, resulting from dynamic changes in the tissue properties during treatment. A closed-loop feedback fuzzy logic controller for LTT was developed with the tissue treated as a black-box system. Preliminary testing was conducted for simulated LTT with a single spherically emitting source fiber at the center of 5 mm and 10 mm diameter target tissues. Dynamic changes in blood perfusion and tissue optical properties due to heating were incorporated into the LTT simulator. Input laser power was modulated to control the temperature field in an attempt to reach target temperatures at the source (90 degree(s)C to avoid tissue charring) and at the target boundary (55 degree(s)C). In all simulations, thermal damage based on Arrhenius formulation ((Omega) equals 1) was reached at the target boundary. The controller also responded efficiently to unexpected, rapid temperature changes.