3-D ULTRASOUND IMAGING: OPTIMAL VOLUMETRIC RECONSTRUCTION
A drawback of conventional 2-D ultrasound imaging is the requirement that the physician mentally reconstruct 3-D anatomy given multiple 2-D image slices. This report reviews attempts to overcome this problem using 3-D ultrasonic imaging. It is argued that free-hand imaging holds the most promise for effective and inexpensive 3-D ultrasound. In the free-hand paradigm, the physician is allowed to move the probe freely over the region of interest, while a sensing device records the position of each 2-D image slice. The set of 2-D images and position data are subsequently used to reconstruct a 3-D data set which can be rendered on a computer monitor or used for volumetric data analysis. Initial tests show that measurement errors, including image artifacts, are significant enough to obscure and distort diagnostically important information. An investigation into the sources of measurement error is used as a basis for improving the quality of the 3-D reconstruction. Reduction of measurement errors by image registration is feasible during the reconstruction stage. A novel reconstruction algorithm which performs registration of image slices is described. Several experiments are then performed and the resulting reconstructions are much clearer and of greatly enhanced diagnostic utility. The registration is achieved by applying visual tracking techniques outside their traditional area of application. Since the algorithm is automatic and incremental, it can be easily incorporated into existing 3-D ultrasound systems. Future research will attempt to improve the registration method and apply it to a variety of clinical cases.
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