KEYWORDS: Ultrasonography, 3D image processing, Tissues, Thermography, Acoustics, Data acquisition, 3D acquisition, Stereoscopy, Visualization, Liver cancer
Three dimensional heat-induced echo-strain imaging is a potentially useful tool for monitoring the formation of thermal
lesions during ablative therapy. Heat-induced echo-strain, known as thermal strain, is due to the changes in the speed of
propagating ultrasound signals and to tissue expansion during heat deposition. This paper presents a complete system for
targeting and intraoperative monitoring of thermal ablation by high intensity focused acoustic applicators. A special
software interface has been developed to enable motor motion control of 3D mechanical probes and rapid acquisition of
3D-RF data (ultrasound raw data after the beam-forming unit). Ex-vivo phantom and tissue studies were performed in a
controlled laboratory environment. While B-mode ultrasound does not clearly identify the development of either necrotic
lesions or the deposited thermal dose, the proposed 3D echo-strain imaging can visualize these changes, demonstrating
agreement with temperature sensor readings and gross-pathology. Current results also demonstrate feasibility for realtime
computation through a parallelized implementation for the algorithm used. Typically, 125 frames per volume can
be processed in less than a second. We also demonstrate motion compensation that can account for shift within frames
due to either tissue movement or positional error in the US 3D imaging probe.
The success of prostate brachytherapy depends on the faithful delivery of a dose plan. In turn, intraoperative
localization and visualization of the implanted radioactive brachytherapy seeds enables more proficient and
informed adjustments to the executed plan during therapy. Prior work has demonstrated adequate seed reconstructions
from uncalibrated mobile c-arms using either external tracking devices or image-based fiducials for
c-arm pose determination. These alternatives are either time-consuming or interfere with the clinical flow of the
surgery, or both. This paper describes a seed reconstruction approach that avoids both tracking devices and
fiducials. Instead, it uses the preoperative dose plan in conjunction with a set of captured images to get initial
estimates of the c-arm poses followed by an auto-focus technique using the seeds themselves as fiducials to refine
the pose estimates. Intraoperative seed localization is achieved through iteratively solving for poses and seed
correspondences across images and reconstructing the 3D implanted seeds. The feasibility of this approach was
demonstrated through a series of simulations involving variable noise levels, seed densities, image separability and
number of images. Preliminary results indicate mean reconstruction errors within 1.2 mm for noisy plans of 84
seeds or fewer. These are attained for additive noise whose standard deviation of the 3D mean error introduced
to the plan to simulate the implant is within 3.2 mm.
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