Bladder Phantom Research Articles

Cost-Efficient Video Synthesis and Evaluation for Development of Virtual 3D Endoscopy.

Objective: 3D reconstruction of the shape and texture of hollow organs captured by endoscopy is important for the diagnosis and surveillance of early and recurrent cancers. Better evaluation of 3D reconstruction pipelines developed for such applications requires easy access to extensive datasets and associated ground truths, cost-efficient and scalable simulations of a range of possible clinical scenarios, and more reliable and insightful metrics to assess performance. Methods: We present a computer-aided simulation platform for cost-effective synthesis of monocular endoscope videos and corresponding ground truths that mimic a range of potential settings and situations one might encounter during acquisition of clinical endoscopy videos. Using cystoscopy of the bladder as model case, we generated an extensive dataset comprising several synthesized videos of a bladder phantom. We then introduce a novel evaluation procedure to reliably assess an individual 3D reconstruction pipeline or to compare different pipelines. Results: To illustrate the use of the proposed platform and evaluation procedure, we use the aforementioned dataset and ground truths to evaluate a proprietary 3D reconstruction pipeline (CYSTO3D) for bladder cystoscopy videos and compared it with a general-purpose 3D reconstruction pipeline (COLMAP). The evaluation results provide insight into the suggested clinical acquisition protocol and several potential areas for refinement of the pipeline to improve future performance. Conclusion: Our work proposes an endoscope video synthesis and reconstruction evaluation toolset and presents experimental results that illustrate usage of the toolset to efficiently assess performance and reveal possible problems of any given 3D reconstruction pipeline, to compare different pipelines, and to provide technically or clinically actionable insights.

Quantification and correction of distortion in diffusion-weighted MRI at 1.5 and 3 T in a muscle-invasive bladder cancer phantom for radiotherapy planning

Limited visibility of post-resection muscle-invasive bladder cancer (MIBC) on CT hinders radiotherapy dose escalation of the residual tumour. Diffusion-weighted MRI (DW-MRI) visualises areas of high tumour burden and is increasingly used within diagnosis and as a biomarker for cancer. DW-MRI could, therefore, facilitate dose escalation, potentially via dose-painting and/or accommodating response. However, the distortion inherent in DW-MRI could limit geometric accuracy. Therefore, this study aims to quantify DW-MRI distortion via imaging of a bladder phantom. A phantom was designed to mimic MIBC and imaged using CT, DW-MRI and T2W-MRI. Fiducial marker locations were compared across modalities and publicly available software was assessed for correction of magnetic susceptibility-related distortion. Fiducial marker locations on CT and T2W-MRI agreed within 1.2 mm at 3 T and 1.8 mm at 1.5 T. The greatest discrepancy between CT and apparent diffusion coefficient (ADC) maps was 6.3 mm at 3 T, reducing to 1.8 mm when corrected for distortion. At 1.5 T, these values were 3.9 mm and 1.7 mm, respectively. Geometric distortion in DW-MRI of a model bladder was initially >6 mm at 3 T and >3 mm at 1.5 T; however, established correction methods reduced this to <2 mm in both cases. A phantom designed to mimic MIBC has been produced and used to show distortion in DW-MRI can be sufficiently mitigated for incorporation into the radiotherapy pathway. Further investigation is therefore warranted to enable individually adaptive image-guided radiotherapy of MIBC based upon DW-MRI.

A novel endoimaging system for endoscopic 3D reconstruction in bladder cancer patients

Introduction The methods employed to document cystoscopic findings in bladder cancer patients lack accuracy and are subject to observer variability. We propose a novel endoimaging system and an online documentation platform to provide post-procedural 3D bladder reconstructions for improved diagnosis, management and follow-up. Material and methods The RaVeNNA4pi consortium is comprised of five industrial partners, two university hospitals and two technical institutes. These are grouped into hardware, software and clinical partners according to their professional expertise. The envisaged endoimaging system consists of an innovative cystoscope that generates 3D bladder reconstructions allowing users to remotely access a cloud-based centralized database to visualize individualized 3D bladder models from previous cystoscopies archived in DICOM format. Results Preliminary investigations successfully tracked the endoscope's rotational and translational movements. The structure-from-motion pipeline was tested in a bladder phantom and satisfactorily demonstrated 3D reconstructions of the processing sequence. AI-based semantic image segmentation achieved a 0.67 dice-score-coefficient over all classes. An online-platform allows physicians and patients to digitally visualize endoscopic findings by navigating a 3D bladder model. Conclusions Our work demonstrates the current developments of a novel endoimaging system equipped with the potential to generate 3D bladder reconstructions from cystoscopy videos and AI-assisted automated detection of bladder tumors.

Preclinical and Clinical Evaluation of a Novel, Variable-View, Rigid Endoscope for Female Cystoscopy

OBJECTIVETo evaluate the preclinical and clinical performance of the pivoting lens rigid Endocameleon (ECAM) endoscope in white light cystoscopy (WLC). MATERIALS AND METHODSPreclinical evaluation was performed ex vivo in CT-based, anatomically accurate and validated bladder phantoms. Six defined tasks with objective endpoints were compared between ECAM-WLC and rigid WLC (30° view angle, rWLC) in 30 interventions. Subsequently, the comparison was transferred to in vivo n = 21 interventions. A validated usability score (System Usability Scale, SUS) as well as physician and patient-related outcomes were assessed using Likert-scale-based questionnaires. Intra- and postinterventional complications were recorded according to the Clavien-Dindo classification. RESULTSThe ex vivo evaluation showed a significant superiority of ECAM-WLC in 4 of 6 endoscopic tasks. Noteworthy is the lower pressure on the bladder neck due to the endoscopesalteration of the endoscope (4/60 vs 17/60, P <.0001) and a more precise imaging of all bladder regions (22/30 vs 30/30, P = .046), including the anterior wall (0/30 vs 28/30, P <.0001). In vivo, surgeons rated the ECAM-WLC with an “excellent” SUS of 86.79%, also expressing that ECAM-WLC would enhance bladder surface visualization (4.52/5.0 ± 0.51), with a preferred use for ECAM-WLC during their next cystoscopy (4.62 ± 0.50). Patients reported ECAM-WLC to be less painful (4.5/5.0 ± 0.84) compared to rWLC. No intervention-related complications were observed. CONCLUSIONECAM-WLC is a safe and accessible procedure that could improve conventional diagnostic WLC by combination of the advantages of fWLC and rWLC.

TURBot: A System for Robot-Assisted Transurethral Bladder Tumor Resection

Staging and treatment of nonmuscle-invasive bladder tumors using transurethral resection of bladder tumors (TURBT) is challenging due to limitations in intravesicular tool dexterity, visualization and risk of bladder wall perforation. Currently, TURBT is achieved via a rigid resectoscope. This dexterity limitation is exacerbated when tumors are located in the bladder neck region. To address these limitations, an endoscopic robotic system called TURBot was developed. The paper presents the design considerations, modeling, and control challenges that were addressed to enable the first robot-assisted in vivo TURBT. The design and control of a slave robot comprised of a multisegment continuum robot capable of deploying a micro snake-like continuum robot for control of an ablation laser, a grasper, and a fiberscope is presented. A strategy for constrained telemanipulation is presented based on the redundancy resolution with varying task dimension that is commensurate with the level of constraint experienced by the robot during transurethral deployment. In addition to evaluation in animals, TURBot resection is compared against manual resection in a mockup user study using a human bladder phantom. The contributions of this paper present key steps that pave the way toward successful clinical robot-assisted TURBT.

P257] Feasibility planning study to improve local control for muscle-invasive bladder cancer using theragnostic imaging and isotoxic dose escalation

Purpose Outcomes for muscle-invasive bladder cancer (MIBC) have changed little over recent decades, with long-term survival remaining around 50% in the UK [1] . Standard radiotherapy treatment involves trans-urethral resection and uniform radiotherapy to the whole bladder. Visualisation of bladder tumour on computed tomography (CT) is poor, but diffusion-weighted magnetic resonance imaging (DW-MRI) provides good visibility of volumes of high tumour burden. Theragnostic imaging using DW-MRI could therefore enable dose escalation to such volumes, however, geometric distortion inherent in DW-MRI requires consideration. In this study geometric distortion was quantified and accounted for, and dose was escalated isotoxically to simulated tumours within the bladder, with calculation of corresponding increases in local control. The aim was to facilitate individualised patient treatments with biologically-adapted radiotherapy (BART) to isotoxically increase tumour control probability (TCP). Methods An in-house bladder phantom was imaged using CT and DW-MRI and distortion in DW-MRI quantified. Tumours were simulated on a patient planning CT in various locations within the bladder and a margin added to accommodate distortion effects, emulating DW-MRI-registered images. Dose distributions were calculated with tumours receiving the maximum possible dose escalation beyond the standard 64 Gy in 32 fractions whilst maintaining normal tissue constraints, and bladder wall receiving 48 Gy, 52 Gy or 56 Gy. Poisson-based TCP models fitted to clinical trials data were used with clonogenic cell density assumed to be 10 7 cm - 3 in tumours and ranging between 0 and 10 7 cm - 3 within the bladder wall. Feasibility of delivery and effect on TCP was assessed via dose accumulation using cone beam CT. Results Maximum dose escalation to 78 Gy was possible for all inferior tumours. Superior, anterior, posterior and lateral tumours could be isotoxically escalated to 70 Gy, 71 Gy, 72 Gy and 72 Gy respectively regardless of tumour volume. Corresponding improvements in TCP ranged from 6 – 8% for superior tumours to 10 – 15% for inferior tumours. Conclusions Theragnostic imaging using DW-MRI was investigated for BART aiming to isotoxically increase TCP. This study indicates that such an approach could enable personalised radiotherapy treatment for MIBC and isotoxically improve outcomes.

A Low-Cost, Durable and Re-Usable Bladder Phantom: Teaching Intravesical Ultrasound Contrast Administration

Contrast-enhanced voiding urosonography (ceVUS) is a radiation-free and highly sensitive examination for detecting vesicoureteral reflux and imaging the urethra in children. This examination is performed with ultrasound and intravesical administration of a gas-filled microbubble US contrast agent. The U.S. Food and Drug Administration recently approved the use of a US contrast agent for ceVUS in children. Because of the growing interest among physicians and US technologists in using ceVUS in children, a urinary bladder phantom was developed to teach intravesical ultrasound contrast administration to perform ceVUS procedures. Described here are the preparation and utility of a low-cost, durable and re-usable phantom that simulates the administration, distribution and effects of different US parameters on US contrast agent appearance in the bladder during ceVUS in children.

A realistic pelvic phantom for electrical impedance measurement

Objective: To design and fabricate an anatomically and conductively accurate phantom for electrical impedance studies of non-invasive bladder volume monitoring. Approach: A modular pelvic phantom was designed and fabricated, consisting of a mechanically and conductively stable boundary wall, a background medium, and bladder phantoms. The wall and bladders are made of conductive polyurethane. The background material is an ultrasound gel-based mixture, with conductivity matched to a weighted average of the pelvic cavity organs, bone, muscle and fat. The phantom boundary is developed using a computer tomography model of a male human pelvis. The bladder phantoms were designed to correlate with human bladder dimensions. Electrical impedance measurements of the phantom were recorded, and images produced using six different bladder phantoms and a realistic finite element model. Main results: Five different bladder volumes were successfully imaged using an empty bladder as a reference. The average conductivity index from the reconstructed images showed a strong positive correlation with the bladder phantom volumes. Significance: A conductively and anatomically accurate pelvic phantom was developed for non-invasive bladder volume monitoring using electrical impedance measurements. Several bladders were designed to correlate with actual human bladder volumes, allowing for accurate volume estimation. The conductivity of the phantom is accurate over 50–250 kHz. This phantom can allow changeable electrode location, contact and size; multi-layer electrodes configurations; increased complexity by addition of other organ or bone phantoms; and electrode movement and deformation. Overall, the pelvic phantom enables greater scope for experimentation and system refinement as a precursor to in-man clinical studies.

Evaluation of deformable image registration between external beam radiotherapy and HDR brachytherapy for cervical cancer with a 3D-printed deformable pelvis phantom

In this study, we developed a 3D-printed deformable pelvis phantom for evaluating spatial DIR accuracy. We then evaluated the spatial DIR accuracies of various DIR settings for cervical cancer. A deformable female pelvis phantom was created based on patient CT data using 3D printing. To create the deformable uterus phantom, we first 3D printed both a model of uterus and a model of the internal cavities of the vagina and uterus. We then made a mold using the 3D printed uterus phantom. Finally, urethane was poured into the mold with the model of the internal cavities in place, creating the deformable uterus phantom with a cavity into which an applicator could be inserted. To create the deformable bladder phantom, we first 3D printed models of the bladder and of the same bladder scaled down by 2mm. We then made a mold using the larger bladder model. Finally, silicone was poured into the mold with the smaller bladder model in place to create the deformable bladder phantom with a wall thickness of 2mm. To emulate the anatomical bladder, water was poured into the created bladder. We acquired phantom image without applicator for EBRT. Then, we inserted the applicator into the phantom to simulate BT. In this situation, we scanned the phantom again to obtain the phantom image for BT. We performed DIR using the two phantom images in two cases: Case A, with full bladder (170ml) in both EBRT and BT images; and Case B with full bladder in the BT image and half-full bladder (100ml) in the EBRT image. DIR was evaluated using Dice similarity coefficients (DSCs) and 31 landmarks for the uterus and 25 landmarks for the bladder. A hybrid intensity and structure DIR algorithm implemented in RayStation with four DIR settings was evaluated. On visual inspection, reasonable agreement in shape of the uterus between the phantom and patient CT images was observed for both EBRT and BT, although some regional disagreements in shape of the bladder and rectum were apparent. The created phantom could reproduce the actual patient's uterus deformation by the applicator. For both Case A and B, large variation was seen in landmark error among the four DIR parameters. In addition, although DSCs were comparable, moderate differences in landmark error existed between the two different DIR parameters selected from the four DIR parameters (i.e., DSC=0.96, landmark error=13.2±5.7 mm vs. DSC=0.97, landmark error=9.7±4.0mm). This result suggests that landmark error evaluation might thus be more effective than DSC for evaluating DIR accuracy. Our developed phantom enabled the evaluation of spatial DIR accuracy for the female pelvic region for the first time. Although the DSCs are high, the spatial errors can still be significant and our developed phantom facilitates their quantification. Our results showed that optimization is needed to identify suitable DIR settings. For determining suitable DIR settings, our method of evaluating spatial DIR accuracy using the 3D-printed phantom may prove helpful.

3D reconstruction of cystoscopy videos for comprehensive bladder records.

White light endoscopy is widely used for diagnostic imaging of the interior of organs and body cavities, but the inability to correlate individual 2D images with 3D organ morphology limits its utility for quantitative or longitudinal studies of disease physiology or cancer surveillance. As a result, most endoscopy videos, which carry enormous data potential, are used only for real-time guidance and are discarded after collection. We present a computational method to reconstruct and visualize a 3D model of organs from an endoscopic video that captures the shape and surface appearance of the organ. A key aspect of our strategy is the use of advanced computer vision techniques and unmodified, clinical-grade endoscopy hardware with few constraints on the image acquisition protocol, which presents a low barrier to clinical translation. We validate the accuracy and robustness of our reconstruction and co-registration method using cystoscopy videos from tissue-mimicking bladder phantoms and show clinical utility during cystoscopy in the operating room for bladder cancer evaluation. As our method can powerfully augment the visual medical record of the appearance of internal organs, it is broadly applicable to endoscopy and represents a significant advance in cancer surveillance opportunities for big-data cancer research.

Interfractional variation in bladder volume and its impact on cervical cancer radiotherapy: Clinical significance of portable bladder scanner.

A constant bladder volume (BV) is essential to direct the radiotherapy (RT) of pelvic tumors with precision. The purpose of this study was to investigate changes in BV and their impact on cervical cancer RT and to assess the clinical significance of a portable bladder scanner (BS) in achieving a constant BV. A standard bladder phantom (133 ml) and measurements of actual urine volume were both used as benchmarks to evaluate the accuracy of the BS. Comparisons of BS with computed tomography (CT), cone-beam CT (CBCT), and an ultrasound diagnostic device (iU22) were made. Twenty-two consecutive patients with cervical cancer treated with external beam radical RT were divided into an experimental group (13 patients) and a control group (9 patients). In the experimental group, the BV was measured multiple times by BS pre-RT until it was consistent with that found by planning CT. Then a CBCT was performed. The BV was measured again immediately post-RT, after which the patient's urine was collected and recorded. In the control group, CBCT only was performed pre-RT. Interfractional changes in BV and their impact on cervical cancer RT were investigated in both groups. The time of bladder filling was also recorded and analyzed. In measuring the volume of the standard bladder phantom, the BS deviated by 1.4% in accuracy. The difference between the measurements of the BS and the iU22 had no statistical significance (linear correlation coefficient 0.96, P < 0.05). The BV measured by the BS was strongly correlated with the actual urine volume (R = 0.95, P < 0.05), planning CT (R = 0.95, P < 0.05), or CBCT (R = 0.91, P < 0.05). Compared with the BV at the time of CT, its value changed by -36.1% [1 SD (standard deviation) 42.3%; range, -79.1%-29.4%] in the control group, and 5.2% (1 SD 21.5%; range, -13.3%-22.1%) in the experimental group during treatment. The change in BV affected the target position in the superior-inferior (SI) direction but had little or no effect in the anterior-posterior and right-left directions. Based on the collected data, the target displacement in the SI direction was reduced from 2.0 to 0.4 mm, while the CTV-to-PTV (CTV: clinical target volume; PTV: planning target volume) margin in the SI direction was reduced from 11.1 to 6.4 mm. The BV increased by 3.7 ± 1.0 ml/min (range, 1.7-4.7 ml/min), which depended on the amount of water ingested by the patient (R = 0.96, P < 0.05). No correlation was found between the rate of urinary inflow and the patient's body mass. The authors were able to reduce the workload of measuring by using individual patient information including the patient's age, the water-drinking amount, time at which water-drinking began, and patient's diet. Changes in the BV have an influence on the RT of cervical cancer. A consistent and reproducible BV is acquired by using a portable BS, whereby the target displacement and CTV-to-PTV margin can be both reduced in the SI direction.

Development of Multisegment Steering Mechanism and 3-D Panorama for Automated Bladder Surveillance System

A cystoscope is an invaluable tool for bladder cancer surveillance and lower urinary tract pathology diagnosis. The performance of cystoscopy can be improved by automating the procedure to ensure rapid and complete inspection, having a predicted pathway for imaging. This paper proposes a versatile, wire-driven, multisegment mechanism for steering an imaging probe to follow optimal, preprogrammed scan trajectories. A novel flexible imaging probe scanning fiber endoscope (SFE) of 1.2 mm in diameter generates high-quality reflectance or fluorescent images. A 3-D panoramic reconstruction view of the bladder is generated by custom software to confirm comprehensive surveillance and improve clinical efficiency. The kinematics and controllability of the proposed mechanism are analyzed. The multiple degrees-of-freedom of the mechanism provide the advantage of maintaining the camera perpendicular to the bladder wall with a safety distance. The measured experimental results show 8.1% and 5.1% tip position and orientation errors, respectively, to the theoretical simulation predictions. Within a synthetic bladder phantom made from patient-specific geometry information, the apparatus is able to generate a 3-D panorama of about 60% of the bladder's inner surface, while accepting 50% image overlap between adjacent images. The novel imaging capability of the SFE, combined with a robotized multisegment steering mechanism and an image stitching software, proposes potential advancements to the multimodal 3-D panorama of the bladder.

3D 초음파 영상에서 방광 내 잔뇨량 추정을 위한 새로운 알고리즘

For the patients with bladder dysfunction, measurement of urine volume inside the bladder is very critical to avoid bladder failure. In measuring urine volume inside a bladder, low-resolution 3D ultrasound images are widely used. However, urine volume estimation from 3D ultrasound images is prone to big errors and inconsistency because of low spatial resolution and low signal-to-noise ratio of ultrasound images. We developed a new robust volume estimation algorithm which is not computationally expensive. We tested the algorithm on a lab-built ultrasound bladder phantom and volunteers. The average error rate of the human bladder volume estimation was 5.9% which was better than the commercial machine.

Multimodal 3D cancer-mimicking optical phantom.

Three-dimensional (3D) organ-mimicking phantoms provide realistic imaging environments for testing various aspects of optical systems, including for evaluating new probe designs, characterizing the diagnostic potential of new technologies, and assessing novel image processing algorithms prior to validation in real tissue. We introduce and characterize the use of a new material, Dragon Skin (Smooth-On Inc.), and fabrication technique, air-brushing, for fabrication of a 3D phantom that mimics the appearance of a real organ under multiple imaging modalities. We demonstrate the utility of the material and technique by fabricating the first 3D, hollow bladder phantom with realistic normal and multi-stage pathology features suitable for endoscopic detection using the gold standard imaging technique, white light cystoscopy (WLC), as well as the complementary imaging modalities of optical coherence tomography and blue light cystoscopy, which are aimed at improving the sensitivity and specificity of WLC to bladder cancer detection. The flexibility of the material and technique used for phantom construction allowed for the representation of a wide range of diseased tissue states, ranging from inflammation (benign) to high-grade cancerous lesions. Such phantoms can serve as important tools for trainee education and evaluation of new endoscopic instrumentation.

A non-rigid point matching method with local topology preservation for accurate bladder dose summation in high dose rate cervical brachytherapy

GEC-ESTRO guidelines for high dose rate cervical brachytherapy advocate the reporting of the D2cc (the minimum dose received by the maximally exposed 2cc volume) to organs at risk. Due to large interfractional organ motion, reporting of accurate cumulative D2cc over a multifractional course is a non-trivial task requiring deformable image registration and deformable dose summation. To efficiently and accurately describe the point-to-point correspondence of the bladder wall over all treatment fractions while preserving local topologies, we propose a novel graphic processing unit (GPU)-based non-rigid point matching algorithm. This is achieved by introducing local anatomic information into the iterative update of correspondence matrix computation in the ‘thin plate splines-robust point matching’ (TPS-RPM) scheme. The performance of the GPU-based TPS-RPM with local topology preservation algorithm (TPS-RPM-LTP) was evaluated using four numerically simulated synthetic bladders having known deformations, a custom-made porcine bladder phantom embedded with twenty one fiducial markers, and 29 fractional computed tomography (CT) images from seven cervical cancer patients. Results show that TPS-RPM-LTP achieved excellent geometric accuracy with landmark residual distance error (RDE) of 0.7 ± 0.3 mm for the numerical synthetic data with different scales of bladder deformation and structure complexity, and 3.7 ± 1.8 mm and 1.6 ± 0.8 mm for the porcine bladder phantom with large and small deformation, respectively. The RDE accuracy of the urethral orifice landmarks in patient bladders was 3.7 ± 2.1 mm. When compared to the original TPS-RPM, the TPS-RPM-LTP improved landmark matching by reducing landmark RDE by 50 ± 19%, 37 ± 11% and 28 ± 11% for the synthetic, porcine phantom and the patient bladders, respectively. This was achieved with a computational time of less than 15 s in all cases with GPU acceleration. The efficiency and accuracy shown with the TPS-RPM-LTP indicate that it is a practical and promising tool for bladder dose summation in adaptive cervical cancer brachytherapy.

Characterization of deformation and physical force in uniform low contrast anatomy and its impact on accuracy of deformable image registration.

Little is known about the effect of force on organ deformation and consequently its impact on precision dose delivery. The purpose of this study was to evaluate the fundamental relationship between anatomic deformation and its causative physical force to ascertain if a threshold limit exists for deformable image registration (DIR) accuracy in uniform low contrast anatomy, beyond which its applicability may be clinically inappropriate. To simulate a simplified model, a tissue equivalent deformable bladder phantom with 21 implanted fiducial markers was developed using a viscoelastic polymer. The bladder phantom was deformed by applying a force in increments from 10 to 70 N. DIR accuracy was studied using intensity based mim and Velocity B-spline algorithms by comparing the 3D vector of the 21 marker locations at the original target image with the synthetically derived marker positions from each target image obtained from DIR. The relationship between applied force in 1D deformation along the axis of applied force and 3D deformation of the phantom showed a linear response. The maximum and average displacements of markers exhibited a nonlinear response to the applied force. In the absence of implanted markers, DIR performance was suboptimal with a threshold limit of only 20 N (5 mm deformation) beyond which the average marker error was ≥3 mm. DIR performance improved significantly with the addition of only one marker for the intensity based mim algorithm. In contrast, the Velocity B-spline algorithm showed reduced sensitivity to the number of markers introduced in both the source and target images. The limits of applicability of DIR are strongly dependent on the magnitude of deformation. There is a threshold limit beyond which the accuracy of DIR fails in uniform low contrast anatomy. The sensitivity of the DIR performance to the number of fiducial markers present indicates that if DIR performance is solely assessed with the contrast rich features present in clinical anatomy, the results may not be reflective of the true DIR performance in uniform low contrast anatomy.

Contrast-enhanced voiding urosonography phantom study: intravenous iodinated and gadolinium-based contrast agents may cause false-negative results in assessment of vesicoureteral reflux in children.

Contrast-enhanced voiding urosonography (ce-VUS) is commonly requested simultaneously to other diagnostic imaging necessitating intravenous contrast agents. To date there is limited knowldedge about intravesical interactions between different types of contrast agents. To assess the effect of excreted intravenous iodinated and gadolinium-based contrast agents on the intravesical distribution of ultrasound contrast within contrast-enhanced voiding urosonography. Iodinated (iomeprol, iopamidol) and gadolinium-based (gadoterate meglumine) contrast agents were diluted to bladder concentration and injected into balloons filled with saline solution. CT scans were performed to assess the contrast distribution in these phantoms. Regions of interest were placed at the top and bottom side of each balloon and Hounsfield units (HU) were measured. Three other balloons were filled with saline solution and contrast media likewise. The ultrasound contrast agent sulphur hexafluoride was added and its distribution was assessed using sonography. MDCT scans showed a separation of two liquid layers in all bladder phantoms with the contrast layers located at the bottom and the saline solution at the top. Significant differences of the HU measurements at the top and bottom side were observed (P < 0.001-0.007). Following injection of ultrasound contrast agent, US showed its distribution exclusively among the saline solution. False-negative results of contrast-enhanced voiding urosonography may occur if it is performed shortly after imaging procedures requiring intravenous contrast.

SU‐E‐J‐44: Design a Platform and Phantom Model for Photoacoustic Imaging in Combination with CT

Purpose:Our (long‐term) objective is to develop a US manipulator that will provide in situ radiation response and image‐guided therapy for bladder cancer based on photoacoustic molecular imaging.Methods:A platform was devised to provide a reproducible positional frame of reference for targeting anatomic structure between MDCT and US scans, in lieu of CBCT, and to fuse photoacoustic molecular imaging. US and photoacoustic scans are taken of a patient while in the CT scanner and IRMT. Through co‐registration, based on anatomical positions, we identified a common coordinate system to be used in Eclipse. A bladder phantom was constructed to validate anatomical tracking via US and photoacoustic imaging. We tested the platform using phantom model to demonstrate validity once moved from the CT couch to the linear accelerator couch.Results:This platform interlocks with Varian exact couch index points for reproducibility of positioning. Construction from low Z material and sized appropriately to fit in CT/IMRT gantry. Error in conversion from cylindrical coordinates of the manipulator to X, Y, Z coordinates of the treatment couch was less than 1mm. We measured the bladder size in 3 different directions in both Eclipse from the CT and Acuson from US. The error was less than 2mm in all directions. CT and US images were co‐registered in MATLAB. Co‐registration of photoacoustic images is still being developed.Conclusion:For Linear Accelerators without on board imaging, MV portal images are not a viable option for the localization of soft tissue anatomy. We believe our manipulator provides an alternative using US imaging, which will be examined in an upcoming clinical trial. We plan to examine the value of hypoxia guided treatment through photoacoustic imaging during this trial.

SU‐E‐J‐84: Is There a Threshold Limit in the Accuracy of Deformable Image Registration (DIR)? A Validation Study Using Deformable Bladder Phantom with Implanted Markers

Purpose:To establish the fundamental relationship between deformation and its causative physical force using a deformable bladder phantom. To ascertain if a threshold limit exists for DIR accuracy, beyond which its applicability in deformed anatomy may be clinically inappropriate.Methods:A tissue equivalent deformable bladder phantom with 21 implanted aluminum markers was developed using a viscoelastic polymer with Youngs modulus and physical density properties comparable to human bladder. Applied force on the organ was incrementally varied from 10N to 70N which in turn deforms the organ. DIR accuracy was studied for commercially available algorithms (MIM and Velocity AI) by comparing the centroid (3D vector) of the 21 marker locations at the undeformed CT (ground truth) with synthetically derived marker positions from each target image from DIR.Results:The relationship between applied force and both 1D deformation along the axis of applied force (R2 =0.98) and 3D deformation as quantified by the 95 percentile hausdorff distance (R2 =0.96) showed a linear response. The maximum 1D deformation (compression) ranged from 3mm to 28 mm. A threshold limit at 30N (maximum 13mm 1D and 6.8mm 3D deformation) was established beyond which average registration error of 21 markers was ≥ 2mm for all algorithms studied. Utilizing the Reg Refine feature of the MIM software, the marker accuracy beyond 50N improved by 2mm while average marker error using Velocity multipass deformation was ≤3mm up to 50N.Conclusions:he accuracy of DIR was evaluated using a tissue equivalent mass and density conserving bladder phantom in the best case scenario using 21 implanted aluminum high contrast markers to improve the accuracy. The limits of applicability of DIR are strongly dependent on the magnitude of deformation. There is a threshold limit beyond which the accuracy of DIR fails for the range of mass and density conserving deformation studied.

Three-dimensional, distendable bladder phantom for optical coherence tomography and white light cystoscopy

We describe a combination of fabrication techniques and a general process to construct a three-dimensional (3-D) phantom that mimics the size, macroscale structure, microscale surface topology, subsurface microstructure, optical properties, and functional characteristics of a cancerous bladder. The phantom also includes features that are recognizable in white light (i.e., the visual appearance of blood vessels), making it suitable to emulate the bladder for emerging white light+optical coherence tomography (OCT) cystoscopies and other endoscopic procedures of large, irregularly shaped organs. The fabrication process has broad applicability and can be generalized to OCT phantoms for other tissue types or phantoms for other imaging modalities. To this end, we also enumerate the nuances of applying known fabrication techniques (e.g., spin coating) to contexts (e.g., nonplanar, 3-D shapes) that are essential to establish their generalizability and limitations. We anticipate that this phantom will be immediately useful to evaluate innovative OCT systems and software being developed for longitudinal bladder surveillance and early cancer detection.