Three‐dimensional ultrasound imaging of the prostate
Prostate cancer is the most commonly diagnosed cancer in men in North America. Since its introduction in 1971, transrectal ultrasound(TRUS) has evolved into one of the primary tools for the evaluation of prostate disease. However, with conventional TRUS, diagnosticians must mentally integrate a series of 2D images in order to develop an impression of the 3D anatomy, and the accurate and precise estimation of prostate volume is difficult. Moreover, an examination takes 10–20 min, often resulting in patient discomfort. We propose using 3D TRUS to overcome these problems. In this thesis, we describe a 3D ultrasound imaging system, analyze the distortion in its images due to miscalibration, and study its performance in estimating prostate volume. Our system consists of three elements: (i) a conventional ultrasound machine and TRUS probe; (ii) a custom-built assembly for rotating the probe under microcomputer control; and (iii) a microcomputer with an 8-bit video frame grabber. A typical scan of 200 2D B-mode images takes 13 s, so that the entire examination takes under 5 min. These images can then be rapidly reconstructed into a 3D image using an algorithm we describe, and interactively displayed using standard software. Also, we describe procedures for accurately calibrating the reconstruction parameters, so that distortions in the shape, length, area, and volume of the 3D image of an object are all less than 1%. We also show that manual planimetry of 3D TRUSimages can be used to estimate prostate volumes in vitro with 2.6% accuracy and 2.5% precision, and in vivo with 5.1% intra-observer variability and 11.4% inter-observer variability. By comparison, with the height-width-length method (Volume=π/6HWL) with conventional 2D TRUSimages,in vivo estimates had 11.5% intra-observer variability and 13.5% inter-observer variability. Thus 3D TRUS overcomes some of the limitations of 2D TRUS, and has great potential as a tool for the diagnosis, study, and management of prostate disease.