Prostate brachytherapy seed segmentation using spoke transform

Permanent implantation of radioactive seeds is a viable and effective therapeutic option widely used today for early stage prostate cancer. In order to perform intraoperative dosimetry the seed locations must be determined accurately with high efficiency. However, the task of seed segmentation is often hampered by the wide range of signal-to-noise ratios represented in the x-ray images due to highly non-uniform background. To circumvent the problem we have developed a new method, the spoke transform, to segment the seeds from the background. This method uses spoke-like rotating line segments within the two concentric windows. The mean intensity value of the pixels that fall on each rotated line segment best describing the intersection between the seed that we are trying to segment is chosen. The inner window gives an indication of the background level immediately surrounding the seeds. The outer window is an isolated region not being segmented and represents a non-seed area in need of enhancement and a detection decision. The advantages of the method are its ability (1) to work with spatially varying local backgrounds and (2) to segment the hidden seeds. Pd-103 and I-125 images demonstrate the effectiveness of the spoke transform.