bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reliability of EUCLIDIAN: An autonomous robotic system for image‐guided prostate brachytherapy
Authors: Podder Tarun K. , Buzurovic Ivan , Huang Ke , Showalter Timothy , Dicker Adam P. , Yu Yan 
Published: December 2010

Purpose:Recently, several robotic systems have been developed to perform accurate and consistent image‐guided brachytherapy. Before introducing a new device into clinical operations, it is important to assess the reliability and mean time before failure (MTBF) of the system. In this article, the authors present the preclinical evaluation and analysis of the reliability and MTBF of an autonomous robotic system, which is developed for prostate seed implantation.Methods:The authors have considered three steps that are important in reliability growth analysis. These steps are: Identification and isolation of failures, classification of failures, and trend analysis. For any one‐of‐a‐kind product, the reliability enhancement is accomplished through test‐fix‐test. The authors have used failure mode and effect analysis for collection and analysis of reliability data by identifying and categorizing the failure modes. Failures were classified according to severity. Failures that occurred during the operation of this robotic system were considered as nonhomogenous Poisson process. The failure occurrence trend was analyzed using Laplace test. For analyzing and predicting reliability growth, commonly used and widely accepted models, Duane's model and the Army Material Systems Analysis Activity, i.e., Crow's model, were applied. The MTBF was used as an important measure for assessing the system's reliability.Results:During preclinical testing, 3196 seeds (in 53 test cases) were deposited autonomously by the robot and 14 critical failures were encountered. The majority of the failures occurred during the first few cases. The distribution of failures followed Duane's postulation as well as Crow's postulation of reliability growth. The Laplace test index was −3.82, indicating a significant trend in failure data, and the failure intervals lengthened gradually. The continuous increase in the failure occurrence interval suggested a trend toward improved reliability. The MTBF was 592 seeds, which implied that several prostate seed implantation cases would be possible without encountering any critical failure. The shape parameter for the MTBF was 0.3859 , suggesting a positive reliability growth of this robotic system. At 95% confidence, the reliability for deposition of 65 seeds was more than 90%.Conclusions:Analyses of failure mode strongly indicated a gradual improvement of reliability of this autonomous robotic system. High MTBF implied that several prostate seed implant cases would be possible without encountering any critical failure.
Diagnostic efficacy of computer extracted image features in optical coherence tomography of the precancerous cervix
Authors: Kang Wei , Qi Xin , Tresser Nancy J. , Kareta Margarita , Belinson Jerome L. , Rollins Andrew M. 
Published: December 2010

Purpose:To determine the diagnostic efficacy of optical coherence tomography (OCT) to identify cervical intraepithelial neoplasia (CIN) grade 2 or higher by computer‐aided diagnosis (CADx).Methods:OCT has been investigated as a screening/diagnostic tool in the management of preinvasive and early invasive cancers of the uterine cervix. In this study, an automated algorithm was developed to extract OCT image features and identify CIN 2 or higher. First, the cervical epithelium was detected by a combined watershed and active contour method. Second, four features were calculated: The thickness of the epithelium and its standard deviation and the contrast between the epithelium and the stroma and its standard deviation. Finally, linear discriminant analysis was applied to classify images into two categories: Normal/inflammation/CIN 1 and CIN 2/CIN 3. The algorithm was applied to 152 images (74 patients) obtained from an international study.Results:The numbers of normal/inflammatory/CIN 1/CIN 2/CIN 3 images are 74, 29, 14, 24, and 11, respectively. Tenfold cross‐validation predicted the algorithm achieved a sensitivity of 51% (95% CI: 36%–67%) and a specificity of 92% (95% CI: 86%–96%) with an empirical two‐category prior probability estimated from the data set. Receiver operating characteristic analysis yielded an area under the curve of 0.86.Conclusions:The diagnostic efficacy of CADx in OCT imaging to differentiate high‐grade CIN from normal/low grade CIN is demonstrated. The high specificity of OCT with CADx suggests further investigation as an effective secondary screening tool when combined with a highly sensitive primary screening tool.
Inclusion of the treatment couch in portal dose image prediction for high precision EPID dosimetry
Authors: Ali Ali Sid Ahmed M. , Dirkx Maarten L. P. , Breuers Marcel G. J. , Heijmen Ben J. M. 
Published: December 2010

Purpose:When comparing predicted portal dose images (PDIs) to PDIs acquired by an EPID during treatment delivery, differences are often observed. These differences may be partially attributed to beam attenuation by parts of the treatment couch not taken into account in the PDI prediction. In order to improve the agreement, a model for the treatment couch was derived and included in the PDI prediction.Methods:A CT scan was used to model the couch top. The model for the couch top base was derived by iteratively matching the predicted and measured PDIs for gantry angles of 0°, 45°, and 90°. For PDI prediction, the modeled treatment couch was added to the CT scan of a patient or phantom by using the recorded couch positions from the record and verify system. To validate the couch model, PDI measurements were performed for a range of couch positions and gantry angles, both with and without an anatomical phantom in the beam.Results:After including the couch model in the PDI prediction for beams passing through the couch without phantom, the mean local dose differences between measured and predicted PDIs were reduced from up to 5.5% to less than 1.0% at each gantry angle. Similar results were obtained for measurements with a lung phantom on the couch. Although the couch model was originally derived by using a 6 MV photon beam, the results showed that it is also applicable for a 10 MV beam.Conclusions:A model of the treatment couch was derived and included in the PDI prediction, yielding a substantially improved agreement between measured and predicted PDIs, which makes interpretation of the observed deviations more straightforward.
Comparative study of density analysis using automated whole breast ultrasound and MRI
Authors: Moon Woo Kyung , Shen Yi‐Wei , Huang Chiun‐Sheng , Luo Sheng‐Chy , Kuzucan Aida , Chen Jeon‐Hor , Chang Ruey‐Feng 
Published: December 2010

Purpose:The purpose of this study is to compare the measurements of breast density using three‐dimensional (3‐D) automated whole breast ultrasound (ABUS) and magnetic resonance imaging (MRI).Methods:In this study, 3‐D ABUS and MRI breast images were obtained from 40 patients—bilaterally in 27 patients and unilaterally (due to operation in the contralateral breast) in 13 patients. To differentiate the fibroglandular and fatty tissues in ABUS and MRI images, the fuzzy C‐mean classifier was used. Calculated values for percent density and breast volume from the two modalities were compared to and correlated with linear regression analysis. Intraoperator and interoperator variations among eight cases were evaluated to verify the consistency of the density analysis.Results:Mean percent density and breast volume derived from ABUS ( and , respectively) and MRI images ( and ) demonstrated good correlation ( and ). Intraoperator and interoperator analyses yielded slightly larger coefficients of variation for percent density and breast volume in ABUS compared to MRI. However, the differences were not statistically significant.Conclusions:ABUS and MRI showed high correlation for breast density and breast volume quantification. Both modalities could provide useful breast density information to physicians.
Spatiotemporal motion estimation for respiratory‐correlated imaging of the lungs
Authors: Vandemeulebroucke Jef , Rit Simon , Kybic Jan , Clarysse Patrick , Sarrut David 
Published: December 2010

Purpose: Four‐dimensional computed tomography (4D CT) can provide patient‐specific motion information for radiotherapy planning and delivery. Motion estimation in 4D CT is challenging due to the reduced image quality and the presence of artifacts. We aim to improve the robustness of deformable registration applied to respiratory‐correlated imaging of the lungs, by using a global problem formulation and pursuing a restrictive parametrization for the spatiotemporal deformation model.Methods: A spatial transformation based on free‐form deformations was extended to the temporal domain, by explicitly modeling the trajectory using a cyclic temporal model based on B‐splines. A global registration criterion allowed to consider the entire image sequence simultaneously and enforce the temporal coherence of the deformation throughout the respiratory cycle. To ensure a parametrization capable of capturing the dynamics of respiratory motion, a prestudy was performed on the temporal dimension separately. The temporal parameters were tuned by fitting them to diaphragm motion data acquired for a large patient group. Suitable properties were retained and applied to spatiotemporal registration of 4D CT data. Registration results were validated using large sets of landmarks and compared to consecutive spatial registrations. To illustrate the benefit of the spatiotemporal approach, we also assessed the performance in the presence of motion‐induced artifacts.Results: Cubic B‐splines gave better or similar fitting results as lower orders and were selected because of their inherently stronger regularization. The fitting and registration errors increased gradually with the temporal control point spacing, representing a trade‐off between achievable accuracy and sensitivity to noise and artifacts. A piecewise smooth trajectory model, allowing for a discontinuous change of speed at end‐inhale, was found most suitable to account for the sudden changes of motion at this breathing phase. The spatiotemporal modeling allowed a reduction of the number of parameters of 45%, while maintaining registration accuracy within 0.1 mm. The approach reduced the sensitivity to artifacts.Conclusions: Spatiotemporal registration can provide accurate motion estimation for 4D CT and improves the robustness to artifacts.
Finite element based bladder modeling for image‐guided radiotherapy of bladder cancer
Authors: Chai Xiangfei , van Herk Marcel , van de Kamer Jeroen B. , Hulshof Maarten C. C. M. , Remeijer Peter , Lotz Heidi T. , Bel Arjan 
Published: December 2010

Purpose:A biomechanical model was constructed to give insight into pelvic organ motion as a result of bladder filling changes.Methods:The authors used finite element (FE) modeling to simulate bladder wall deformation caused by urine inflow. For ten volunteers, a series of MRI scans of the pelvic area was recorded at regular intervals of 10 min over 1 h. For the series of scans, the bladder volume gradually increased while the rectal volume was constant. The MR image with the bladder volume closest to 250 ml was selected as the reference in each volunteer. All pelvic structures were defined from the reference image including bladder wall, small bowel, prostate (male), uterus (female), rectum, pelvic bone, and the rest of the body. These structures were translated to FE meshes. Using appropriate material properties for all organs, deformations of these organs as a response to changing bladder pressure were computed.Results:The computation results showed realistic anisotropic deformation of the bladder wall: The bladder became more elongated in the cranial and anterior directions with increasing bladder volume. After fitting the volume of the computed bladder to the actual bladder volume on the test images, the computed bladder shape agreed well with the real bladder shape (overlap from 0.79 to 0.93). The average mean bladder wall prediction errors of all the volunteers were 0.31 cm average and 0.29 cm SD.Conclusions:In conclusion, a FE based mechanical bladder model shows promise for the prediction of the short‐term bladder shape change using only one pelvic scan and volume change of the bladder as input. The accuracy levels achieved with this method are likely mostly limited by inaccuracies in material properties and sliding tissue between organs, which has not been modeled. This model can potentially be used to improve image‐guided radiotherapy for bladder cancer patients, i.e., by prediction short‐term bladder deformation.
On Monte Carlo modeling of megavoltage photon beams: A revisited study on the sensitivity of beam parameters
Authors: Chibani Omar , Moftah Belal , Ma C.‐M. Charlie 
Published: December 2010

Purpose:To commission Monte Carlo beam models for five Varian megavoltage photon beams (4, 6, 10, 15, and 18 MV). The goal is to closely match measured dose distributions in water for a wide range of field sizes (from to ). The second objective is to reinvestigate the sensitivity of the calculated dose distributions to variations in the primary electron beam parameters.Methods:TheGEPTS Monte Carlo code is used for photon beam simulations and dose calculations. The linear accelerator geometric models are based on (i) manufacturer specifications, (ii) corrections made by Chibani and Ma [“On the discrepancies between Monte Carlo dose calculations and measurements for the 18 MV Varian photon beam,” Med. Phys. 34, 1206–1216 (2007)], and (iii) more recent drawings. Measurements were performed using pinpoint and Farmer ionization chambers, depending on the field size. Phase space calculations for small fields were performed with and without angle‐based photon splitting. In addition to the three commonly used primary electron beam parameters ( is the mean energy, FWHM is the energy spectrum broadening, and is the beam radius), the angular divergence of primary electrons is also considered.Results:The calculated and measured dose distributions agreed to within 1% local difference at any depth beyond 1 cm for different energies and for field sizes varying from to . In the penumbra regions, the distance to agreement is better than 0.5 mm, except for 15 MV (0.4–1 mm). The measured and calculated output factors agreed to within 1.2%. The 6, 10, and 18 MV beam models use , while the 4 and 15 MV beam models require and 0.6°, respectively. The parameter sensitivity study shows that varying the beam parameters around the solution can lead to 5% differences with measurements for small (e.g., ) and large (e.g., ) fields, while a perfect agreement is maintained for the field. The influence of on the central‐axis depth dose and the strong influence of on the lateral dose profiles are demonstrated.Conclusions:Dose distributions for very small and very large fields were proved to be more sensitive to variations in, , and in comparison with the field. Monte Carlo beam models need to be validated for a wide range of field sizes including small field sizes (e.g., ).
Sensitivity analysis of a geometric calibration method using projection matrices for digital tomosynthesis systems
Authors: Li Xinhua , Zhang Da , Liu Bob 
Published: December 2010

Purpose:To study the sensitivity of a geometric calibration method using projection matrices for digital tomosynthesis systems.Methods:A generic geometric calibration method for tomographic imaging systems has been presented in our previous work. The method involves a scan of a calibration phantom with multiple markers. Their locations in projection images are detected and are associated with their 3D coordinates to compute projection matrices, which can be used in subsequent image reconstruction. The accuracy of geometric calibration may be affected by errors in the input data of marker positions. The effects of errors may depend on the number of markers and the volume surrounded by them in 3D space. This work analyzed the sensitivity of the calibration method to the above factors. A 6 cm CIRS breast research phantom and a prototype breast tomosynthesis system were used for our tests. A high contrast ring and two small speck groups were reconstructed in various testing cases for comparison. To achieve quantitative assessment, a point detection mask was adopted for detecting signals and for computing changes between testing cases and the regular geometric calibration.Results:When 3D coordinates and 2D projections of markers were accurate, all tested numbers of markers, 6–44, provided similar high quality reconstructions of the ring and the two speck groups. Errors in marker positions resulted in image degradations and signal changes, which increased with fewer markers and smaller volume surrounded by markers in the 3D object space. Signal changes of small specks were more significant than those of the ring. Errors in marker projections produced drastic image degradations. Coplanar marker placement caused a failure in projection matrix computation.Conclusions:For practical geometric calibration phantom design, ample markers are desired. They need to have a large volumetric coverage in the 3D space and be far from being coplanar. Precise determination of marker projections on detector planes is crucial for accurate geometric calibration and for small object detection using the reconstructed images.
A fast double template convolution isocenter evaluation algorithm with subpixel accuracy
Authors: Winey Brian , Sharp Greg , Bussière Marc 
Published: December 2010

Purpose: To design a fast Winston Lutz (fWL) algorithm for accurate analysis of radiation isocenter from images without edge detection or center of mass calculations.Methods: An algorithm has been developed to implement the Winston Lutz test for mechanical/radiation isocenter agreement using an electronic portal imaging device (EPID). The algorithm detects the position of the radiation shadow of a tungsten ball within a stereotactic cone. The fWL algorithm employs a double convolution to independently find the position of the sphere and cone centers. Subpixel estimation is used to achieve high accuracy. Results of the algorithm were compared to (1) a human observer with template guidance and (2) an edge detection/center of mass (edCOM) algorithm. Testing was performed with high resolution (0.05mm/px, film) and low resolution (0.78mm/px, EPID) image sets.Results: Sphere and cone center relative positions were calculated with the fWL algorithm for high resolution test images with an accuracy of compared to for the human observer, and for the edCOM algorithm. The fWL algorithm required 0.01 s per image compared to 5 s for the edCOM algorithm and 20 s for the human observer. For lower resolution images the fWL algorithm localized the centers with an accuracy of compared to for the edCOM algorithm.Conclusions: A fast (subsecond) subpixel algorithm has been developed that can accurately determine the center locations of the ball and cone in Winston Lutz test images without edge detection or COM calculations.
Comparing performance of many‐core CPUs and GPUs for static and motion compensated reconstruction of C‐arm CT data
Authors: Hofmann Hannes G. , Keck Benjamin , Rohkohl Christopher , Hornegger Joachim 
Published: December 2010

Purpose:Interventional reconstruction of 3‐D volumetric data from C‐arm CT projections is a computationally demanding task. Hardware optimization is not an option but mandatory for interventional image processing and, in particular, for image reconstruction due to the high demands on performance. Several groups have published fast analytical 3‐D reconstruction on highly parallel hardware such as GPUs to mitigate this issue. The authors show that the performance of modern CPU‐based systems is in the same order as current GPUs for static 3‐D reconstruction and outperforms them for a recent motion compensated image reconstruction algorithm.Methods:This work investigates two algorithms: Static 3‐D reconstruction as well as a recent motion compensated algorithm. The evaluation was performed using a standardized reconstruction benchmark, RABBIT CT, to get comparable results and two additional clinical data sets.Results:The authors demonstrate for a parametric B‐spline motion estimation scheme that the derivative computation, which requires many write operations to memory, performs poorly on the GPU and can highly benefit from modern CPU architectures with large caches. Moreover, on a 32‐core Intel® Xeon® server system, the authors achieve linear scaling with the number of cores used and reconstruction times almost in the same range as current GPUs.Conclusions:Algorithmic innovations in the field of motion compensated image reconstruction may lead to a shift back to CPUs in the future. For analytical 3‐D reconstruction, the authors show that the gap between GPUs and CPUs became smaller. It can be performed in less than 20 s (on‐the‐fly) using a 32‐core server.
Prostate brachytherapy postimplant dosimetry: Automatic plan reconstruction of stranded implants
Authors: Chng N. , Spadinger I. , Morris W. J. , Usmani N. , Salcudean S. 
Published: December 2010

Purpose:Plan reconstruction for permanent implant prostate brachytherapy is the process of determining the correspondence between planned and implanted seeds in postimplant analysis. Plan reconstruction informs many areas of brachytherapy quality assurance, including the verification of seed segmentation, misplacement and migration assessment, implant simulations, and the dosimetry of mixed‐activity or mixed‐species implants.Methods:An algorithm has been developed for stranded implants which uses the interseed spacing constraints imposed by the suture to improve the accuracy of reconstruction. Seventy randomly selected clinical cases with a mean of 23.6 (range 18–30) needles and mean density of 2.0 (range 1.6–2.6) were automatically reconstructed and the accuracy compared to manual reconstructions performed using a custom 3D graphical interface.Results:Using the automatic algorithm, the mean accuracy of the assignment relative to manual reconstruction was found to be. Fifty‐two of the 70 cases (74%) were error‐free; of seeds in the remaining cases, were found to be attributed to the correct strand and were correctly connected to their neighbors. Any necessary manual correction using the interface is usually straightforward. For the clinical data set tested, neither the number of seeds or needles, average density, nor the presence of clusters was found to have an effect on reconstruction accuracy using this method.Conclusions:Routine plan reconstruction of stranded implants can be performed with a high degree of accuracy to support postimplant dosimetry and quality analyses.