Background: Our research group has been developing a microwave imaging system for monitoring thermal therapy. Previously, we demonstrated proof of concept for this system in both phantom and animal experiments where the temperatures of the heated regions were artificially controlled by inserting tubes with heated saline. One of the more pressing challenges has been integrating it with a viable therapy device. In this study we demonstrate a scanned focused ultrasound system that can generate desired heating patterns in conjunction with our microwave imaging system for monitoring the thermal distribution.

Methods: We have designed and fabricated a focused ultrasound (HIFU) device which we can be used to scan focal regions and various heating patterns and does not pose integration problems with respect to the microwave coupling liquid incompatibilities. The steering device allows for full 3D scanning in a compact form based on supporting the transducer at only three points (3PS). The 3PS system is set up such that the three associated motors are positioned underneath the imaging tank and control the 3D steering of the transducer by only vertical motion of the support rods through the tank base seals. This configuration is sufficiently small that it can fit within the limited space within the antenna array of our clinical microwave breast imaging system.
The microwave system acquired imaging data sets at a rate of 5 per minute which is sufficient to capture the temporal temperature distribution variations while the images were reconstructed off-line. (The next generation system will be able to acquire data at a rate of 20 - 30 data sets per second.)

Results: Several experiments were performed to generate an array of different heating patterns. The reconstructed images demonstrated excellent spatial registration of the heated zone shapes and locations with respect to the actual heating patterns. In addition, single point temperature measurements also correlated well with actual imaged property rises in assessing the temporal aspect of the system.

Conclusions: These results clearly demonstrate our ability to integrate our thermal imaging capability with a viable therapy device and deliver the thermal energy in a clinically relevant setting.