The University of British Columbia

This paper proposes a novel ultrasonic imaging approach for detecting brachytherapy seeds. Accurate and fast seed localization plays a key role in computing dosimetry for prostate brachytherapy. However, the B-mode transrectal ultrasound (TRUS)imaging currently being used does not adequately visualize implanted seeds, because the diameter of the seeds is small and visualization is hampered by speckle noise and angulation of the specular reflection of the seeds. Based on the fact that much more ultrasound wave energy is reflected from metal seeds than from other scatterers in tissue, we developed a new seed detection method directly using ultrasound radio frequency (RF) signals. The method monitors the average power of the RF signals to measure the reflected wave energy. Each RF scan line is subdivided into a sequence of short segments with the same length and overlapping. The average power of each segment is computed by Fourier based or parametric spectral analysis approaches. In the new method, logarithmic compression is not applied to the raw RF data, and the average power is proportional to the sum of the squares of the signal amplitude. Therefore, the method produces significantly higher contrast than conventional B-mode TRUS. Furthermore, the average power algorithm can be implemented very efficiently since no numerical optimization is required. Phantom and ex vivo experiments show that the new technique successfully detects implanted brachytherapy seeds, and produces superior results compared with B-mode TRUS imaging.