Intraoperative dosimetric quality assurance in prostate brachytherapy critically depends on discerning the three-dimensional (3D) locations of implanted seeds. The ability to reconstruct the implanted seeds intraoperatively will allow us to make immediate provisions for dosimetric deviations from the optimal implant plan. A method for seed reconstruction from segmented C-arm fluoroscopy images is proposed. The 3D coordinates of the implanted seeds can be calculated upon resolving the correspondence of seeds in multiple x-ray images. We formalize seed-matching as a combinatorial optimization problem, which has salient features: (a) extensively studied solutions by the computer science community; (b) proof for the nonexistence of any polynomial time exact algorithm; and (c) a practical pseudo-polynomial algorithm that mostly runs in O(N3) time using any number of images. We prove that two images are insufficient to correctly match the seeds, while a third image renders the matching problem to be of nonpolynomial complexity. We utilize the special structure of the problem and propose a pseudopolynomial time algorithm. Using three presegmented images, matching and reconstruction of brachytherapy seeds using the Hungarian algorithm achieved complete matching in simulation experiments; and 98.5% in phantom experiments. 3D reconstruction error for correctly matched seeds has a mean of 0.63 mm, and 0.9 mm for incorrectly matched seeds. The maximum seed reconstruction error in each implant was typically around 1.32 mm. Both on synthetic data and in phantom experiments, matching rate and reconstruction error achieved using presegmented images was found to be sufficient for prostate brachytherapy. The algorithm is extendable to deal with arbitrary number of images without any loss in speed or accuracy. The algorithm is sufficiently generic to provide a practical solution to any correspondence problem, across different imaging modalities and features.
Deterministic loading of single atoms onto arbitrary two-dimensional lattice points has recently been demonstrated, where by dynamically controlling the optical-dipole potential, atoms from a probabilistically loaded lattice were relocated to target lattice points to form a zero-entropy atomic lattice. In this atom rearrangement, how to pair atoms with the target sites is a combinatorial optimization problem: brute-force methods search all possible combinations so the process is slow, while heuristic methods are time-efficient but optimal solutions are not guaranteed. Here, we use the Hun-garian matching algorithm as a fast and rigorous alternative to this problem of defect-free atomic lattice formation. Our approach utilizes an optimization cost function that restricts collision-free guiding paths so that atom loss due to collision is minimized during rearrangement. Experiments were performed with cold rubidium atoms that were trapped and guided with holographically controlled optical-dipole traps. The result of atom relocation from a partially filled 7-by-7 lattice to a 3-by-3 target lattice strongly agrees with the theoretical analysis: using the Hungarian algorithm minimizes the collisional and trespassing paths and results in improved performance, with over 50% higher success probability than the heuristic shortest-move method.
Motivation: Intraoperative dosimetric optimization of TRUS‐guided prostate brachytherapy implants requires localization of seeds relative to prostate[1], for which radiographic fiducial‐based registration of fluoroscopy and TRUS seems appropriate[2,3]. It is critical to mount the fiducials rigidly and stabilize the prostate, because TRUS and fluoroscopy are sequential and the moving TRUS probe may dislocate the prostate. Transrectal approach provides the shortest distance to the implanted seeds and prostate, thereby maximizing registration accuracy. Method and Materials: A precision‐machined transrectal sheath containing fiducials is mounted rigidly on the stepper and wraps around the TRUS probe. It mechanically decouples the prostate from the TRUS probe and thus stabilizes the prostate. Acoustic impedance, wall thickness, and diameter were optimized. Acoustic coupling is maintained by circulating liquid gel. The system is depressurized during probe motion. Two embodiments accommodate various types of radiographic fiducial markers. A closed 360‐degree sheath of 30mm diameter was developed for conics that are extremely robust to segmentation and image distortion, being mathematically invariant to projective transformation. A partial 180‐degree sheath was developed for straight lines and point fiducials that are computationally simpler to localize but inherently less accurate. The sheath connects to a commercially available TRUS stepper. Results: Phantom and in‐vivo canine tests were performed. Prostate motion and sheath stability were quantitatively analyzed with volume CT by tracking both structures and implanted markers while the TRUS probe was retracted by 5mm increments. With the sheath in place, prostate and sheath both were stationary in CT imaging and the fiducials did not interfere with the TRUS image. Excellent acoustic coupling was achieved during probe motion with acceptable degradation of ultrasound image quality. Funding: NIH‐1R41CA106152‐01A, NIH‐1R43CA099374‐01, NSF‐9731478.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.