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Owing to its rarity and non-specific clinical features, a diagnosis of obturator hernia is often delayed until the patient presents with intestinal obstruction. Often the diagnosis is made on a Computed Tomography (CT) scan or during exploratory laparotomy. While a laparoscopic approach is well described in an elective scenario, open surgery through a midline laparotomy has been the preferred approach for obturator hernia with intestinal obstruction. However, a few cases of obstructed obturator hernia have been reported that have been managed laparoscopically. We present our experience of two elderly patients who presented with intestinal obstruction. A CT scan helped clinch the diagnosis of obturator hernia as the cause and both were managed laparoscopically.

Introduction: An aberrant left hepatic artery (aLHA) may be seen in 8%–15% of cases1,2 and a replaced LHA (rLHA) may be seen in ~2%–11% of cases.1,3 An aLHA and a rLHA assume significant importance...

Objective: The purpose of this research is to evaluate common and uncommon variant of hepatic arterial anatomy that usually come across during Hepatic Angiographies. Study Design: Cross sectional study. Methods: This study included 50 patients having history of Hepatocellular Carcinoma from May to October 2015. Hepatic Angiography (Transarterial chemoembolization for management of Hepatoma and identification of classical and variant anatomy of hepatic artery) was evaluated in angiography unit. All procedures were performed on Digital Subtraction Angiography (DSA) machine (Toshiba KXO100 G). Selective DSA of the superior mesenteric artery and celiac trunk is performed initially to evaluate the frequency of normal and variant arterial anatomy and secondly to determine origin and course of tumor-feeding vessels. Evaluation of common and uncommon variants of hepatic arteries was done by using Michel’s classification as reference standard. Results: Age of the patient range from 40 – 80 years, 35 of whom were males. Fifty patients underwent angiographic procedure of viscera. Normal anatomy of hepatic artery was found in twenty eight (56%) cases. In six (12%) cases we found the replaced form of right hepatic artery (RHA) originating from visceral superior mesenteric artery. In five (10%) cases we found the replaced form of left hepatic artery (LHA) originating from left gastric artery (LGA), the combination of both these anomalies in one (2%) patient. Four (8%) cases had the left gastric artery giving rise to accessory left hepatic artery in conjunction with the common hepatic artery of celiac axis giving rise to typical right or left hepatic artery. In another four (8%) cases anatomic variation was noted in form of a dual arterial supply noted as common hepatic artery of celiac axis giving rise to typical left or right hepatic artery in conjunction with superior mesenteric artery giving rise to accessory right hepatic artery. In two (4%) cases superior mesenteric artery had replaced the celiac trunk completely. Conclusion: Visceral angiography with evaluation of common and uncommon variants of hepatic artery are very crucial not only for proper preoperative evaluation in hepato biliary surgeries but also in many diagnostic and therapeutic interventional procedures. We have found that it is of utmost importance to have a detailed and complete information and understanding of anatomic variations of hepatic artery both common and uncommon variants in order to avoid hazardous complications which can happen with incomplete information.

Myocardial infarction (MI) is one of the leading causes of death in the world. Small animal studies have shown that stem-cell therapy offers dramatic functional improvement post-MI. An endomyocardial catheter injection approach to therapeutic agent delivery has been proposed to improve efficacy through increased cell retention. Accurate targeting is critical for reaching areas of greatest therapeutic potential while avoiding a life-threatening myocardial perforation. Multimodal image fusion has been proposed as a way to improve these procedures by augmenting traditional intra-operative imaging modalities with high resolution pre-procedural images. Previous approaches have suffered from a lack of real-time tissue imaging and dependence on X-ray imaging to track devices, leading to increased ionizing radiation dose. In this paper, we present a new image fusion system for catheter-based targeted delivery of therapeutic agents. The system registers real-time 3D echocardiography, magnetic resonance, X-ray, and electromagnetic sensor tracking within a single flexible framework. All system calibrations and registrations were validated and found to have target registration errors less than 5 mm in the worst case. Injection accuracy was validated in a motion enabled cardiac injection phantom, where targeting accuracy ranged from 0.57 to 3.81 mm. Clinical feasibility was demonstrated with in-vivo swine experiments, where injections were successfully made into targeted regions of the heart.

Congenital adrenal hyperplasia (CAH) owing to 21-hydroxylase deficiency is an autosomal recessive disorder caused by mutations in the CYP21A2 gene. Females affected with classical CAH are at risk for genital ambiguity, but can be treated in utero with dexamethasone before 9 gestational weeks to prevent virilization. Early genetic diagnosis is unavailable through current invasive methods of chorionic villus sampling and amniocentesis. New developments in prenatal genetic testing utilize fetal DNA extracted from maternal blood through noninvasive methods, which allow the determination of fetal gender and the diagnosis of CAH at an early gestational age (

The success of prostate brachytherapy critically depends on delivering adequate dose to the prostate gland. Intraoperative localization of the implanted seeds provides potential for dose evaluation and optimization during therapy. A reduced-dimensionality matching algorithm for prostate brachytherapy seed reconstruction (REDMAPS) that uses multiple X-ray fluoroscopy images obtained from different poses is proposed. The seed reconstruction problem is formulated as a combinatorial optimization problem, and REDMAPS finds a solution in a clinically acceptable amount of time using dimensionality reduction to create a smaller space of possible solutions. Dimensionality reduction is possible since the optimal solution has approximately zero cost when the poses of the acquired images are known to be within a small error. REDMAPS is also formulated to address the "hidden seed problem" in which seeds overlap on one or more observed images. REDMAPS uses a pruning algorithm to avoid unnecessary computation of cost metrics and the reduced problem is solved using linear programming. REDMAPS was first evaluated and its parameters tuned using simulations. It was then validated using five phantom and 21 patient datasets. REDMAPS was successful in reconstructing the seeds with an overall seed matching rate above 99% and a reconstruction error below 1 mm in less than 5 s.

Spontaneous rupture of the rectum is a rare occurrence. A total laparoscopic approach to rectal perforation has only occasionally been reported. We report an unusual case of a young boy who developed a spontaneous rupture of the rectum following a trivial fall. A magnetic resonance imaging revealed a tear in the rectum at the peritoneal reflection with the omentum plugging it. He denied any history of rectal instrumentation or abnormal sexual activity. He had no history of constipation or rectal prolapse. The tear was repaired laparoscopically and a covering loop sigmoid colostomy was added. He made an uneventful post-operative recovery. Spontaneous rupture of the rectum can occur in younger age groups and even in the absence of significant trauma. One needs to diligently bring out a history of rectal trauma. Equally important is to rule out any underlying pathological condition. A laparoscopic approach is feasible, especially in early cases.

Ultrasound (US) imaging is one of the modalities commonly used for interventional guidance. It offers many advantages over other imaging systems such as MRI, CT, and fluoroscopy in that it is considerably cheaper, is portable, offers real-time imaging, and has no radiation exposure. Recent developments have led to the advancement of 3DUS technology, making it a more feasible alternative to 2D US imaging, despite its higher cost. Among 3D US technology includes real-time 3D transesophageal echocardiography (TEE) enabling US imaging of the heart from within the body. Unfortunately, there are many disadvantages of US that must be addressed. Due to the presence of speckle, the image quality is very poor, especially away from the focal zone. The imaging field-of-view (FOV) is also quite limited, due to the size of the US transducer. These disadvantages significantly limit the usability of US for many interventional procedures.

The use of electromagnetic (EM) tracking is an important guidance tool that can be used to aid procedures requiring accurate localization such as needle injections or catheter guidance. Using EM tracking, the information from different modalities can be easily combined using pre-procedural calibration information. These calibrations are performed individually, per modality, allowing different imaging systems to be mixed and matched according to the procedure at hand. In this work, a framework for the calibration of a 3D transesophageal echocardiography probe to EM tracking is developed. The complete calibration framework includes three required steps: data acquisition, needle segmentation, and calibration. Ultrasound (US) images of an EM tracked needle must be acquired with the position of the needles in each volume subsequently extracted by segmentation. The calibration transformation is determined through a registration between the segmented points and the recorded EM needle positions. Additionally, the speed of sound is compensated for since calibration is performed in water that has a different speed then is assumed by the US machine. A statistical validation framework has also been developed to provide further information related to the accuracy and consistency of the calibration. Further validation of the calibration showed an accuracy of 1.39 mm.

A feature-based registration was developed to align biplane and tracked ultrasound images of the aortic root with a preoperative CT volume. In transcatheter aortic valve replacement, a prosthetic valve is inserted into the aortic annulus via a catheter. Poor anatomical visualization of the aortic root region can result in incorrect positioning, leading to significant morbidity and mortality. Registration of pre-operative CT to transesophageal ultrasound and fluoroscopy images is a major step towards providing augmented image guidance for this procedure. The proposed registration approach uses an iterative closest point algorithm to register a surface mesh generated from CT to 3D US points reconstructed from a single biplane US acquisition, or multiple tracked US images. The use of a single simultaneous acquisition biplane image eliminates reconstruction error introduced by cardiac gating and TEE probe tracking, creating potential for real-time intra-operative registration. A simple initialization procedure is used to minimize changes to operating room workflow. The algorithm is tested on images acquired from excised porcine hearts. Results demonstrate a clinically acceptable accuracy of 2.6mm and 5mm for tracked US to CT and biplane US to CT registration respectively.

C-arm fluoroscopy images are frequently used for qualitative assessment of prostate brachytherapy. Three-dimensional seed reconstruction from C-arm images is necessary for intraoperative dosimetry and quantitative assessment. Seed reconstruction requires accurately known C-arm poses. We propose to measure the C-arm rotation angles and computationally compensate for inevitable C-arm motion to compute the pose. We compensate the translational motions of a C-arm, such as oscillation, sagging and wheel motion using a three-level optimization algorithm and obviate the need for full pose tracking using external trackers or fiducials. We validated our approach on simulated and 100 clinical data sets from 10 patients and gained on average, a seed matching rate of 98.5%, projection error of 0.33 mm (STD = 0.21 mm) and computation time of 19.8 s per patient, which must be considered as clinically excellent results. We also show that without motion compensation the reconstruction is likely to fail.

This paper describes a clinically translatable interventional guidance platform to improve the accuracy and precision of stem cell injections into a beating heart. The proposed platform overlays live position of an injection catheter onto a fusion of a pre-procedural MR roadmap with real-time 3D transesophageal echocardiography (TEE). Electromagnetic (EM) tracking is used to initialize the fusion. The fusion is intra-operatively compensated for respiratory motion using a novel algorithm that uses peri-operative full volume ultrasound images. Validation of the system on a moving heart phantom produced a landmark registration accuracy of 2.8 ± 1.45mm. Validation on animal in vivo data produced an average registration accuracy of 2.2 ± 1.8 mm; indicating that it is feasible to reliably and robustly fuse the MR road-map with catheter position using 3D ultrasound in a clinical setting.

Live three dimensional (3D) transesophageal echocardiography (TEE) provides real-time imaging of cardiac structure and function, and has been shown to be useful in interventional cardiac procedures. Its application in catheter based cardiac procedures is, however, limited by its limited field of view (FOV). In order to mitigate this limitation, we register pre-operative magnetic resonance (MR) images to live 3D TEE images. Conventional multimodal image registration techniques that use mutual information (MI) as the similarity measure use statistics from the entire image. In these cases, correct registration, however, may not coincide with the global maximum of MI metric. In order to address this problem, we present an automated registration algorithm that balances a combination global and local edge-based statistics. The weighted sum of global and local statistics is computed as the similarity measure, where the weights are decided based on the strength of the local statistics. Phantom validation experiments shows improved capture ranges when compared with conventional MI based methods. The proposed method provided robust results with accuracy better than 3 mm (5°) in the range of -10 to 12 mm (-6 to 3°), -14 to 12 mm (-6 to 6°) and -16 to 6 mm (-6 to 3°) in x-, y-, and z- axes respectively. We believe that the proposed registration method has the potential for real time intra-operative image fusion during percutaneous cardiac interventions.

Purpose To evaluate a prototypical system of dynamic intraoperative dosimetry for prostate brachytherapy using registered ultrasound and fluoroscopy (RUF) with a nonisocentric C-arm (GE OEC, Salt Lake City, UT) and to compare intraoperative dosimetry of RUF as well as ultrasound-based seed localization (USD) with Day 0 CT dosimetry. Methods Seed positions were independently determined using RUF and USD. RUF uses a radio-opaque fiducial for registration to ultrasound and 3-dimensional reconstruction of seeds relative to prostate using nonisocentric C-arm fluoroscopy. Postimplant CT was performed on Day 0. Squared differences between dosimetric measures for RUF vs. CT and USD vs. CT were calculated and mean squared differences evaluated. Paired t test was used to evaluate which method was more closely aligned with CT. Accuracies of USD and RUF compared with CT were estimated using a nonparametric approach. Results Six patients were treated and compared with USD. RUF identified areas of underdosage intraoperatively in all patients and median 5 additional seeds were placed. In 40 of 42 measures, RUF was equally or more closely correlated with CT than USD. USD showed statistically significant variation from CT for 6 of 7 parameters compared with 1 of 7 parameters for RUF. Mean squared differences from CT were significantly smaller for RUF in 4 of 7 parameters compared with USD. Conclusions Dynamic intraoperative dosimetry is possible with a conventional nonisocentric C-arm. Compared with an USD method, RUF-based intraoperative dosimetry was more closely aligned with immediate postimplant CT. RUF identified areas of underdosage, which were not detected using USD.

X-ray fluoroscopy is widely used for intra-operative dosimetry in prostate brachytherapy. Three-dimensional locations of the implanted radioactive seeds can be calculated from multiple X-ray images upon resolving the correspondence of seeds. This is usually modeled as an assignment problem that is NP-hard. We propose an algorithm that allows us to derive an equivalent problem of reduced dimensionality based on practical observation that the optimal solution has almost zero cost if the C-arm pose is known. The reduced problem is efficiently solved by linear programming in polynomial time. Additionally, our method solves the hidden seeds problem. Simulation results demonstrate that the implanted seeds can be localized with a matching rate of ≥ 98.8 % and reconstruction error of ≤ 0.37 mm using three images with hidden seeds in a few seconds when the pose of the C-arm is known.

Favorable outcome in prostate brachytherapy critically depends on the accurate placement of radioactive sources in their planned locations. Unfortunately, there is variety of mechanical factors that cause the seeds to divert from their planned locations. While this problem has been known to brachytherapists, current technology does not allow for reliable localization of the implanted sources, thereby prohibiting the prediction and modification of seed distribution intra-operatively. The Research Objective of the proposal is to develop and evaluate ex-vivo a method for intra-operative localization of the implanted seeds in relation to the prostate, to facilitate in-situ dosimetric optimization and exit dosimetry. In particular, we will: [1] Registration of Ultrasound to Fluoroscopy (RUF): Develop methods for reconstruction of seed implants from X-ray fluoroscopy and spatially register them to the prostate anatomy identified in TRUS [2] System Integration: Integrate the above methods in a software package and link it with the FDA-approved CMS Interplant prostate brachytherapy system to enable in-situ dosimetry calculation [3] Experimental Validation: Evaluate the performance of the RUF system on phantoms and pre-recorded patient data.

C-arm fluoroscopy is ubiquitous in contemporary surgery, but it lacks the ability to accurately reconstruct three-dimensional (3D) information. A major obstacle in fluoroscopic reconstruction is discerning the pose of the x-ray image, in 3D space. Optical/magnetic trackers tend to be prohibitively expensive, intrusive and cumbersome in many applications. We present single-image-based fluoroscope tracking (FTRAC) with the use of an external radiographic fiducial consisting of a mathematically optimized set of ellipses, lines, and points. This is an improvement over contemporary fiducials, which use only points. The fiducial encodes six degrees of freedom in a single image by creating a unique view from any direction. A nonlinear optimizer can rapidly compute the pose of the fiducial using this image. The current embodiment has salient attributes: small dimensions (3x3x5 cm); need not be close to the anatomy of interest; and accurately segmentable. We tested the fiducial and the pose recovery method on synthetic data and also experimentally on a precisely machined mechanical phantom. Pose recovery in phantom experiments had an accuracy of 0.56 mm in translation and 0.33 deg. in orientation. Object reconstruction had a mean error of 0.53 mm with 0.16 mm STD. The method offers accuracies similar to commercial tracking systems,more » and appears to be sufficiently robust for intraoperative quantitative C-arm fluoroscopy. Simulation experiments indicate that the size can be further reduced to 1x1x2 cm, with only a marginal drop in accuracy.« less

Purpose: C-arm fluoroscopy is ubiquitous in contemporary surgery, but it lacks the ability to accurately reconstruct 3D information. A major obstacle in fluoroscopic reconstruction is discerning the pose of the X-ray image, in 3D space. Optical/magnetic trackers are prohibitively expensive, intrusive and cumbersome. Method: We present single-image-based fluoroscope tracking (FTRAC) with the use of an external radiographic fiducial consisting of a mathematically optimized set of points, lines, and ellipses. The fiducial encodes six degrees of freedom in a single image by creating a unique view from any direction. A non-linear optimizer can rapidly compute the pose of the fiducial using this image. The current embodiment has salient attributes: small dimensions (3 x 3 x 5 cm), it need not be close to the anatomy of interest and can be segmented automatically. Results: We tested the fiducial and the pose recovery method on synthetic data and also experimentally on a precisely machined mechanical phantom. Pose recovery had an error of 0.56 mm in translation and 0.33° in orientation. Object reconstruction had a mean error of 0.53 mm with 0.16 mm STD. Conclusion: The method offers accuracies similar to commercial tracking systems, and is sufficiently robust for intra-operative quantitative C-arm fluoroscopy.

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.

C-arm fluoroscopy is modelled as a perspective projection, the parameters of which are estimated through a calibration procedure. It has been universally accepted that precise intra-procedural calibration is a prerequisite for accurate quantitative C-arm fluoroscopy guidance. Calibration, however, significantly adds to system complexity, which is a major impediment to clinical practice. We challenge the status quo by questioning the assumption that precise intra-procedural calibration is really necessary. We derived theoretical bounds for the sensitivity of 3D measurements to mis-calibration. Experimental results corroborated the theory in that mis-calibration in the focal spot by as much as 50 mm still allows for tracking with an accuracy of 0.5 mm in translation and 0.65o in rotation, and such mis-calibration does not impose any additional error on the reconstruction of small objects.

Conventional freehand 3D ultrasound (US) is a complex process, involving calibration, scanning, processing, volume reconstruction, and visualization. Prior to calibration, a position sensor is attached to the probe for tagging each image with its position and orientation in space; then calibration process is performed to determine the spatial transformation of the scan plan with respect to the position sensor. Finding this transformation matrix is a critical, but often underrated task in US-guided surgery. The purpose of this study is to enhance previously known calibration methods by introducing a novel calibration fixture and process. The proposed phantom is inexpensive, easy to construct, easy to scan, while yielding more data points per image than previously known designs. The processing phase is semi-automated, allowing for fast processing of a massive amount of data, which in turn increases accuracy by reducing human errors.

Brachial plexus tumours are a rare entity. Schwannomas are benign nerve sheath tumours and only about 5% arise from the brachial plexus. Due to its rarity and complex anatomical location they can pose a formidable challenge to surgeons. We present a case of a young patient who presented with an axillary swelling three months after a lymph node biopsy from the same axilla, which turned out to be a Schwannoma arising for the medial cord of the brachial plexus.

Purpose/Objective(s): The ability to more accurately determine dosimetry intraoperatively during permanent prostate brachytherapy may assist clinicians in improving dosimetric and clinical results. Our purpose was to compare a novel system of registered ultrasound and fluoroscopy (RUF) with the current method of ultrasound (US) based seed localization (a.k.a. real time) for intraoperatively predicting dosimetry, using post-implant CT as a standard.

Purpose: Intra‐operative dosimetryoptimization of TRUS‐guided prostate brachytherapy requires localization of seeds relative to the prostate [Todor et al. PMB 48(9):1153–71]. Method and Materials: Seeds were reconstructed from C‐arm fluoroscopy, registered to TRUS, and exported to commercial brachytherapy system for dosimetryoptimization. Technical obstacles included pose‐dependant C‐arm calibration; distortion correction; pose estimation of C‐arm images; registering C‐arm to TRUS; and seed reconstruction. We proved that calibration is not critical and distortion correction in AP suffices. A radiographic tracking fiducial was attached in known pose over the template to recover the C‐arm pose from a single image, relative to the template. The 3D coordinates of the segmented seeds are calculated upon resolving the correspondence of seeds in the multiple C‐arm images, by formalizing seed‐matching as a network‐flow problem [Jain et al. Med Phys, 32(11):3475–92]. The seed locations are exported in template coordinates to the Interplant® commercial system for dosimetry analysis and optimization.Results: In precision‐machined hard phantoms with 40–100 seeds, we correctly reconstructed 98.5% seeds with a mean 3D accuracy of 0.63mm (0.91mm error for mismatched seeds). In soft tissue phantoms with 45–87 seeds and clinically realistic 15° C‐arm motion, we correctly reconstructed 100% seeds with 1.5mm absolute accuracy (0.25mm relative accuracy), and registered them to the prostate segmented from TRUS with an accuracy of 3.4mm (0.82mm relative). In a Phase‐1 clinical trial, so far on 4 patients with 66–84 seeds, we achieved intra‐operative monitoring of seed distribution and dosimetry. We optimized the V100 dose by inserting 3–9 additional seeds. Conclusion: Intra‐operative doseoptimization is possible with an average C‐arm, at negligible additional cost to existing clinical installations. Conflict of Interest: The work has been done in collaboration with Acoustic MedSystems for seed import into the Interplant®. Keywords: Prostate Brachytherapy, Intra‐operative Dosimetry.Support: DoD/PC‐050170, DoD/PC‐050042, NIH‐1R43CA099374, NSF‐9731478.

Purpose: Intra‐operative dosimetry in prostate brachytherapy critically depends on discerning the 3‐D locations of implanted seeds. The accuracy of 3‐D seed reconstruction step is, in turn, limited by the accuracy with which the position and orientation of individual implanted seed in the fluoroscopic images can be found. A method for robustly segmenting the seeds in fluoroscopic images is proposed here. Methods and Materials: The process of determining the locations and orientations of implanted seeds is sub‐divided into three main steps. In the first step, the image is segmented by shape‐size based morphological approach to eliminate background noise and do away with non‐uniform brightness of the image, to get seed‐like regions. These regions are either single seeds or overlapping multiple seed clusters. In the second step, the regions are analyzed and classified definitively, in a two‐phase statistical process coupled with information extraction from original intensity image, into two classes: single seed and overlapping multiple seed cluster. In the third step, the region belonging to overlapping multiple seed cluster is resolved into its constituent individual seeds through a simple and novel technique. Results: The proposed algorithm was tested on a set of ten clinical fluoroscopic images. The algorithm correctly determines the seeds with overall average of 99.57%. The clusters are not correctly resolved only in two images (2 clusters each, 1.7% and 1.6% of total seeds in respective implants). One false positive (noise labeled as seed) each is reported in two images, both the cases being where the tip of catheter appears to be of the size and shape of seed. Conclusions: The algorithm builds on an existing framework of morphological processing and provides further improvements in classification and cluster resolution. The algorithm appears to be robust and accurate despite the poor resolution of clinical images.

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.

Purpose: Intra‐operative dosimetric optimization of TRUS‐guided prostate brachytherapy implants requires localization of seeds relative to prostate [1]. Analytical tools are available to intra‐operatively tailor an implant‐plan, thereby accounting for inevitable deviations [2]. Method and Materials: The majority of the practitioners have C‐arm fluoroscopes in the treatment room, making intra‐operative dosimetry feasible with little additional cost. The obstacles towards intra‐operative dosimetry are: (a) discerning the 3D poses of fluoro images, (b) registering fluoroscopy to TRUS, and (c) establish seed correspondences in multiple fluoro images. We address the first two issues by single‐image‐based fluoroscope tracking (FTRAC) fiducial with salient attributes: small dimensions (3×3×5cm); need not be close to the anatomy of interest; auto‐segmentable; and mathematically robust to segmentation, calibration, and image distortion errors. The 3D coordinates of the segmented seeds are calculated upon resolving the correspondence of seeds in the multiple X‐ray images, achieved by an algorithm called MARSHAL. We formalize seed‐matching as a network flow problem, which has salient features: (a) extensively studied exact solutions, (b) performance claims on the space‐time complexity, (c) optimality bounds on the final solution. Results: The FTRAC fiducial tracks a C‐arm to an accuracy of 0.56mm in translation and 0.33° in orientation, comparable to commercial tracking systems. On pre‐segmented images, MARSHAL achieved 100% correct matching in simulation experiments. In experiments on a precision‐machined phantom, the FTRAC and MARSHAL correctly matched and reconstructed 98.5% of the seeds with a mean 3D accuracy of 0.63mm, while the mean error for the mismatched 1.5% of seeds was only 0.91mm. Conclusion: Performance of FTRAC and MARSHAL appear to be adequate for intra‐operative dosimetry in brachytherapy.