UBC Theses and Dissertations

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UBC Theses and Dissertations

Patient and probe tracking during freehand ultrasound Flaccavento, Giselle


The measurement of the relative location of images acquired using freehand ultrasound is often required for panoramic ultrasound, ultrasound assisted surgery, and 3D ultrasound. It can be necessary to keep the patient still for up to 8 min or hold their breath for up to 45 sec. This can be difficult or impossible for a sick patient. Our system intends to minimize the need for patient breath holds and physical restraints during image acquisition. In this thesis, we present a system that uses an inexpensive trinocular camera system that measures the probe location with respect to the patient's body by calculating the location of both the probe and the patient. The goal is to find the location of the ultrasound images relative to the patient's skin. Using an Optotrak as a reference, the accuracy of the camera is tested. Based on the results obtained, we can estimate that at a distance of approximately 1000 mm from the camera, the location of a patch on a curved surface (such as the patient), with a size of approximately 20 x 20 mm, can be calculated to within ±2 mm. The probe location can be calculated to an accuracy between —2.3 mm and 1.8 mm when the object attached to the probe has an area of approximately 90 x 40 mm. A consistency test is created using the camera and a calibrated probe. The results of this test show that the mean distance between the points calculated using only the camera and the points calculated using the calibrated probe with the camera are —6.7mm, 1.2mm, and 1.6mm, in the x-, y-, and z-directions. Since tracking of the area being examined during ultrasound has not been performed using other tracking systems, our system offers an improvement for freehand tracking techniques. Other systems used for tracking patient motion during an ultrasound scan, have not been able to track the area being scanned as the markers used for tracking would interfere with the examination. In our system, the features overlaid on the patient's skin do not interfere with the ultrasound probe.

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