B-scan imaging and thermal lesion monitoring using miniaturized dual-functionality ultrasound arrays

A key potential advantage for ultrasound therapy is the ability to treat and image tissue using the same device. The recent development of miniaturized dual-functionality (image and treatment) probes, capable of both high power and broad bandwidth, has allowed real-time imaging and monitoring of thermal lesioning with complete coregistration of image and treatment regions of interest. High-quality B-scan images and useful monitoring information can be obtained during therapy planning and treatment. B-scan image quality is quantitatively comparable to that of current transabdominal ultrasound arrays. Challenges associated with limited probe dimensions and channel count are met using interpolation, filtering, and reverberation reduction methods that improve image definition and contrast. Tissue boundaries and critical structures are clearly delineated in phantoms and in vivo. In addition to real-time B-scan visualization, techniques employed include quantification of tissue backscatter and attenuation changes, and analysis of echo waveform changes to detect boiling and tissue modification. Gas activity, associated with gross B-scan changes as well as large waveform and attenuation changes, consistently implies tissue ablation for the exposure conditions studied. However, preliminary experience suggests that absence of large echo changes does not consistently predict absence of ablation, and that the magnitude of echo changes shows limited correlation with the severity of ablation.