Thermal ablation has been proved safe and effective as the treatment for liver tumors that are not suitable for
resection. Currently, manually performed thermal ablation is greatly dependent on the surgeon's acupuncture
manipulation against hand tremor. Besides that, inaccurate or inappropriate placement of the applicator will
also directly decrease the final treatment effect. In order to reduce the influence of hand tremor, and provide an
accurate and appropriate guidance for a better treatment, we develop an ultrasound-directed robotic system for
thermal ablation of liver tumors. In this paper, we will give a brief preliminary report of our system. Especially,
three innovative techniques are proposed to solve the critical problems in our system: accurate ultrasound calibration
when met with artifacts, realtime reconstruction with visualization using Graphic Processing Unit (GPU)
acceleration and 2D-3D ultrasound image registration. To reduce the error of point extraction with artifacts, we
propose a novel point extraction method by minimizing an error function which is defined based on the geometric
property of our N-fiducial phantom. Then realtime reconstruction with visualization using GPU acceleration is
provided for fast 3D ultrasound volume acquisition with dynamic display of reconstruction progress. After that,
coarse 2D-3D ultrasound image registration is performed based on landmark points correspondences, followed by
accurate 2D-3D ultrasound image registration based on Euclidean distance transform (EDT). The effectiveness
of our proposed techniques is demonstrated in phantom experiments.
KEYWORDS: Ultrasonography, 3D image processing, 3D image reconstruction, 3D acquisition, Position sensors, Visualization, Transmitters, Video, Volume visualization, Medical imaging
Freehand 3D ultrasound makes use of a 2D ultrasound system and a position sensor to reconstruct 3D ultrasound
images. To achieve real-time reconstruction while acquisition, the reconstruction volume must be determined
in advance. In this paper, a novel technique is proposed to address the problem effectively. This technique
consists of two steps: the interactive selection of the region of interest (ROI), and the automatic determination
of the reconstruction volume. The tracked B-scan is used as a vivid tool to explore the target object. After
the decision of the principal directions of the target object, four B-scans are designated to enclose the ROI. The
reconstruction volume corresponding to the ROI is then figured out automatically according to the four tracked
B-scans. The presented technique can fast predetermine a compact reconstruction volume aligned with the best
viewing direction. Furthermore, the technique is convenient for the clinician and comfortable for the patient.
The efficient and flexible nature of the technique is demonstrated on a real-time freehand system.
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