UBC Theses and Dissertations
3D volume ultrasound : probe calibration and extended field-of-view Poon, Tony Chingtoa
Real-time 3D ultrasound is a new generation ultrasound system that uses a dedicated hand-held probe to create volume data sets instead of standard 2D cross-sectional images. For applications in image-guided surgery and radiation therapy, a position tracker is added to the probe so that the volumes can be located in space. Calibration plays a critical role in determining the overall accuracy of an ultrasound volume tracking system. In this thesis, three calibration methods are developed specifically for 3D probes. The three methods are based on a IXI-wire phantom, a cube phantom and a stylus. The performance of each method is evaluated in terms of calibration reproducibility, point accuracy and reconstruction accuracy by distance measurement. The mean errors in the reproducibility tests are 1.50 mm (IXI-wire), 1.16 mm (cube) and 5.13 mm (stylus). The RMS errors of the point accuracy measure are 2.15 mm (IXI-wire), 4.91 mm (cube) and 2.36 mm (stylus). The RMS errors of the reconstruction accuracy by distance measure are 1.52 mm (IXI-wire), 1.59 mm (cube) and 1.85 mm (stylus). Overall, the LXI-wire phantom achieved the best results among the three. 3D extended field-of-view ultrasound creates panoramic views from a set of volume acquired from a dedicated 3D ultrasound machine and a position tracker. A simple compounding technique can then be used to combine the volumes together using only the position measurements but some misalignment remains. We applied two different registration methods to correct these errors in the overlapping regions. The first method divides the overlap into smaller blocks and warps the blocks to best align the features. The second method uses rigid body registration of the blocks. Experiments in vitro and in vivo showed that block-based registration with warping produced the most reproducible results and the greatest increase in similarity among the overlapping regions. It also produced the best reconstruction accuracy with a mean distance measurement error of 0.4 mm on a fetus phantom.
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