Publications

2012
Nguyen PL, Chen M-H, Zhang Y, Tempany CM, Cormack RA, Beard CJ, Hurwitz MD, Suh WW, D'Amico AV. Updated results of magnetic resonance imaging guided partial prostate brachytherapy for favorable risk prostate cancer: implications for focal therapy. J Urol. 2012;188 (4) :1151-6.Abstract
PURPOSE: We report updated results of magnetic resonance imaging guided partial prostate brachytherapy and propose a definition of biochemical failure following focal therapy. MATERIALS AND METHODS: From 1997 to 2007, 318 men with cT1c, prostate specific antigen less than 15 ng/ml, Gleason 3 + 4 or less prostate cancer received magnetic resonance imaging guided brachytherapy in which only the peripheral zone was targeted. To exclude benign prostate specific antigen increases due to prostatic hyperplasia, we investigated the usefulness of defining prostate specific antigen failure as nadir +2 with prostate specific antigen velocity greater than 0.75 ng/ml per year. Cox regression was used to determine the factors associated with prostate specific antigen failure. RESULTS: Median followup was 5.1 years (maximum 12.1). While 36 patients met the nadir +2 criteria, 16 of 17 biopsy proven local recurrences were among the 26 men who also had a prostate specific antigen velocity greater than 0.75 ng/ml per year (16 of 26 vs 1 of 10, p = 0.008). Using the nadir +2 definition, prostate specific antigen failure-free survival for low risk cases at 5 and 8 years was 95.1% (91.0-97.3) and 80.4% (70.7-87.1), respectively. This rate improved to 95.6% (91.6-97.7) and 90.0% (82.6-94.3) using nadir +2 with prostate specific antigen velocity greater than 0.75 ng/ml per year. For intermediate risk cases survival was 73.0% (55.0-84.8) at 5 years and 66.4% (44.8-81.1) at 8 years (the same values as using nadir +2 with prostate specific antigen velocity greater than 0.75 ng/ml per year). CONCLUSIONS: Requiring a prostate specific antigen velocity greater than 0.75 ng/ml per year in addition to nadir +2 appears to better predict clinical failure after therapies that target less than the whole gland. Further followup will determine whether magnetic resonance imaging guided brachytherapy targeting the peripheral zone produces comparable cancer control to whole gland treatment in men with low risk disease. However, at this time it does not appear adequate for men with even favorable intermediate risk disease.
Egger J, Kapur T, Nimsky C, Kikinis R. Pituitary adenoma volumetry with 3D Slicer. PLoS One. 2012;7 (12) :e51788.Abstract
In this study, we present pituitary adenoma volumetry using the free and open source medical image computing platform for biomedical research: (3D) Slicer. Volumetric changes in cerebral pathologies like pituitary adenomas are a critical factor in treatment decisions by physicians and in general the volume is acquired manually. Therefore, manual slice-by-slice segmentations in magnetic resonance imaging (MRI) data, which have been obtained at regular intervals, are performed. In contrast to this manual time consuming slice-by-slice segmentation process Slicer is an alternative which can be significantly faster and less user intensive. In this contribution, we compare pure manual segmentations of ten pituitary adenomas with semi-automatic segmentations under Slicer. Thus, physicians drew the boundaries completely manually on a slice-by-slice basis and performed a Slicer-enhanced segmentation using the competitive region-growing based module of Slicer named GrowCut. Results showed that the time and user effort required for GrowCut-based segmentations were on average about thirty percent less than the pure manual segmentations. Furthermore, we calculated the Dice Similarity Coefficient (DSC) between the manual and the Slicer-based segmentations to proof that the two are comparable yielding an average DSC of 81.97±3.39%.
Gholami B, Norton I, Tannenbaum AR, Agar NYR. Recursive feature elimination for brain tumor classification using desorption electrospray ionization mass spectrometry imaging. Conf Proc IEEE Eng Med Biol Soc. 2012;2012 :5258-61.Abstract
The metabolism and composition of lipids is of increasing interest for understanding and detecting disease processes. Lipid signatures of tumor type and grade have been demonstrated using magnetic resonance spectroscopy. Clinical management and ultimate prognosis of brain tumors depend largely on the tumor type, subtype, and grade. Mass spectrometry, a well-known analytical technique used to identify molecules in a given sample based on their mass, can significantly improve the problem of tumor type classification. This work focuses on the problem of identifying lipid features to use as input for classification. Feature selection could result in improvements in classifier performance, discovery of biomarkers, improved data interpretation, and patient treatment.
Fedorov A, Beichel R, Kalpathy-Cramer J, Finet J, Fillion-Robin J-C, Pujol S, Bauer C, Jennings D, Fennessy FM, Sonka M, et al. 3D Slicer as an image computing platform for the Quantitative Imaging Network. Magn Reson Imaging. 2012;30 (9) :1323-41.Abstract

Quantitative analysis has tremendous but mostly unrealized potential in healthcare to support objective and accurate interpretation of the clinical imaging. In 2008, the National Cancer Institute began building the Quantitative Imaging Network (QIN) initiative with the goal of advancing quantitative imaging in the context of personalized therapy and evaluation of treatment response. Computerized analysis is an important component contributing to reproducibility and efficiency of the quantitative imaging techniques. The success of quantitative imaging is contingent on robust analysis methods and software tools to bring these methods from bench to bedside. 3D Slicer is a free open-source software application for medical image computing. As a clinical research tool, 3D Slicer is similar to a radiology workstation that supports versatile visualizations but also provides advanced functionality such as automated segmentation and registration for a variety of application domains. Unlike a typical radiology workstation, 3D Slicer is free and is not tied to specific hardware. As a programming platform, 3D Slicer facilitates translation and evaluation of the new quantitative methods by allowing the biomedical researcher to focus on the implementation of the algorithm and providing abstractions for the common tasks of data communication, visualization and user interface development. Compared to other tools that provide aspects of this functionality, 3D Slicer is fully open source and can be readily extended and redistributed. In addition, 3D Slicer is designed to facilitate the development of new functionality in the form of 3D Slicer extensions. In this paper, we present an overview of 3D Slicer as a platform for prototyping, development and evaluation of image analysis tools for clinical research applications. To illustrate the utility of the platform in the scope of QIN, we discuss several use cases of 3D Slicer by the existing QIN teams, and we elaborate on the future directions that can further facilitate development and validation of imaging biomarkers using 3D Slicer.

Kapur T, Egger J, Damato A, Schmidt EJ, Viswanathan AN. 3T MR-guided Brachytherapy for Gynecologic Malignancies. Magn Reson Imaging. 2012;30 (9) :1279-90.Abstract

Gynecologic malignancies are a leading cause of death in women worldwide. Standard treatment for many primary and recurrent gynecologic cancer cases includes external-beam radiation followed by brachytherapy. Magnetic resonance (MR) imaging is beneficial in diagnostic evaluation, in mapping the tumor location to tailor radiation dose and in monitoring the tumor response to treatment. Initial studies of MR guidance in gynecologic brachytherapy demonstrate the ability to optimize tumor coverage and reduce radiation dose to normal tissues, resulting in improved outcomes for patients. In this article, we describe a methodology to aid applicator placement and treatment planning for 3 Tesla (3-T) MR-guided brachytherapy that was developed specifically for gynecologic cancers. This methodology has been used in 18 cases from September 2011 to May 2012 in the Advanced Multimodality Image Guided Operating (AMIGO) suite at Brigham and Women's Hospital. AMIGO comprises state-of-the-art tools for MR imaging, image analysis and treatment planning. An MR sequence using three-dimensional (3D)-balanced steady-state free precession in a 3-T MR scanner was identified as the best sequence for catheter identification with ballooning artifact at the tip. 3D treatment planning was performed using MR images. Items in development include software designed to support virtual needle trajectory planning that uses probabilistic bias correction, graph-based segmentation and image registration algorithms. The results demonstrate that 3-T MR image guidance has a role in gynecologic brachytherapy. These novel developments have the potential to improve targeted treatment to the tumor while sparing the normal tissues.

Pursley J, Risholm P, Fedorov A, Tuncali K, Fennessy FM, Wells III WM, Tempany CM, Cormack RA. A Bayesian nonrigid registration method to enhance intraoperative target definition in image-guided prostate procedures through uncertainty characterization. Med Phys. 2012;39 (11) :6858-67.Abstract

PURPOSE: This study introduces a probabilistic nonrigid registration method for use in image-guided prostate brachytherapy. Intraoperative imaging for prostate procedures, usually transrectal ultrasound (TRUS), is typically inferior to diagnostic-quality imaging of the pelvis such as endorectal magnetic resonance imaging (MRI). MR images contain superior detail of the prostate boundaries and provide substructure features not otherwise visible. Previous efforts to register diagnostic prostate images with the intraoperative coordinate system have been deterministic and did not offer a measure of the registration uncertainty. The authors developed a Bayesian registration method to estimate the posterior distribution on deformations and provide a case-specific measure of the associated registration uncertainty. METHODS: The authors adapted a biomechanical-based probabilistic nonrigid method to register diagnostic to intraoperative images by aligning a physician's segmentations of the prostate in the two images. The posterior distribution was characterized with a Markov Chain Monte Carlo method; the maximum a posteriori deformation and the associated uncertainty were estimated from the collection of deformation samples drawn from the posterior distribution. The authors validated the registration method using a dataset created from ten patients with MRI-guided prostate biopsies who had both diagnostic and intraprocedural 3 Tesla MRI scans. The accuracy and precision of the estimated posterior distribution on deformations were evaluated from two predictive distance distributions: between the deformed central zone-peripheral zone (CZ-PZ) interface and the physician-labeled interface, and based on physician-defined landmarks. Geometric margins on the registration of the prostate's peripheral zone were determined from the posterior predictive distance to the CZ-PZ interface separately for the base, mid-gland, and apical regions of the prostate. RESULTS: The authors observed variation in the shape and volume of the segmented prostate in diagnostic and intraprocedural images. The probabilistic method allowed us to convey registration results in terms of posterior distributions, with the dispersion providing a patient-specific estimate of the registration uncertainty. The median of the predictive distance distribution between the deformed prostate boundary and the segmented boundary was ≤3 mm (95th percentiles within ±4 mm) for all ten patients. The accuracy and precision of the internal deformation was evaluated by comparing the posterior predictive distance distribution for the CZ-PZ interface for each patient, with the median distance ranging from -0.6 to 2.4 mm. Posterior predictive distances between naturally occurring landmarks showed registration errors of ≤5 mm in any direction. The uncertainty was not a global measure, but instead was local and varied throughout the registration region. Registration uncertainties were largest in the apical region of the prostate. CONCLUSIONS: Using a Bayesian nonrigid registration method, the authors determined the posterior distribution on deformations between diagnostic and intraprocedural MR images and quantified the uncertainty in the registration results. The feasibility of this approach was tested and results were positive. The probabilistic framework allows us to evaluate both patient-specific and location-specific estimates of the uncertainty in the registration result. Although the framework was tested on MR-guided procedures, the preliminary results suggest that it may be applied to TRUS-guided procedures as well, where the addition of diagnostic MR information may have a larger impact on target definition and clinical guidance.

Orringer DA, Vago DR, Golby AJ. Clinical Applications and Future Directions of Functional MRI. Semin Neurol. 2012;32 (4) :466-75.Abstract

First described for use in mapping the human visual cortex in 1991, functional magnetic resonance imaging (fMRI) is based on blood-oxygen level dependent (BOLD) changes in cortical regions that occur during specific tasks. Typically, an overabundance of oxygenated (arterial) blood is supplied during activation of brain areas. Consequently, the venous outflow from the activated areas contains a higher concentration of oxyhemoglobin, which changes the paramagnetic properties of the tissue that can be detected during a T2-star acquisition. fMRI data can be acquired in response to specific tasks or in the resting state. fMRI has been widely applied to studying physiologic and pathophysiologic diseases of the brain. This review will discuss the most common current clinical applications of fMRI as well as emerging directions.

O'Donnell LJ, Rigolo L, Norton I, Wells III WM, Westin C-F, Golby AJ. fMRI-DTI modeling via landmark distance atlases for prediction and detection of fiber tracts. Neuroimage. 2012;60 (1) :456-70.Abstract

The overall goal of this research is the design of statistical atlas models that can be created from normal subjects, but may generalize to be applicable to abnormal brains. We present a new style of joint modeling of fMRI, DTI, and structural MRI. Motivated by the fact that a white matter tract and related cortical areas are likely to displace together in the presence of a mass lesion (brain tumor), in this work we propose a rotation and translation invariant model that represents the spatial relationship between fiber tracts and anatomic and functional landmarks. This landmark distance model provides a new basis for representation of fiber tracts and can be used for detection and prediction of fiber tracts based on landmarks. Our results indicate that the measured model is consistent across normal subjects, and thus suitable for atlas building. Our experiments demonstrate that the model is robust to displacement and missing data, and can be successfully applied to a small group of patients with mass lesions.

Liu X, Tuncali K, Wells III WM, Morrison PR, Zientara GP. Fully automatic 3D segmentation of iceball for image-guided cryoablation. Conf Proc IEEE Eng Med Biol Soc. 2012;2012 :2327-30.Abstract

The efficient extraction of the cryoablation iceball from a time series of 3D images is crucial during cryoablation to assist the interventionalist in determining the coverage of the tumor by the ablated volume. Conventional semi-automatic segmentation tools such as ITK-SNAP and 3D Slicer's Fast Marching Segmentation can attain accurate iceball segmentation in retrospective studies, however, they are not ideal for intraprocedure real time segmentation, as they require time-consuming manual operations, such as the input of fiducials and the extent of the segmented region growth. In this paper, we present an innovative approach for the segmentation of the iceball during cryoablation, that executes a fully automatic computation. Our approach is based on the graph cuts segmentation framework, and incorporates prior information of iceball shape evolving in time, modeled using experimentally-derived iceball growth parameters. Modeling yields a shape prior mask image at each timepoint of the imaging time series for use in the segmentation. Segmentation results of our method and the ITK-SNAP method are compared for 8 timepoints in 2 cases. The results indicate that our fully automatic approach is accurate, robust and highly efficient compared to manual and semi-automatic approaches.

Fedorov A, Tuncali K, Fennessy FM, Tokuda J, Hata N, Wells III WM, Kikinis R, Tempany CM. Image registration for targeted MRI-guided transperineal prostate biopsy. J Magn Reson Imaging. 2012;36 (4) :987-92.Abstract

PURPOSE: To develop and evaluate image registration methodology for automated re-identification of tumor-suspicious foci from preprocedural MR exams during MR-guided transperineal prostate core biopsy. MATERIALS AND METHODS: A hierarchical approach for automated registration between planning and intra-procedural T2-weighted prostate MRI was developed and evaluated on the images acquired during 10 consecutive MR-guided biopsies. Registration accuracy was quantified at image-based landmarks and by evaluating spatial overlap for the manually segmented prostate and sub-structures. Registration reliability was evaluated by simulating initial mis-registration and analyzing the convergence behavior. Registration precision was characterized at the planned biopsy targets. RESULTS: The total computation time was compatible with a clinical setting, being at most 2 min. Deformable registration led to a significant improvement in spatial overlap of the prostate and peripheral zone contours compared with both rigid and affine registration. Average in-slice landmark registration error was 1.3 ± 0.5 mm. Experiments simulating initial mis-registration resulted in an estimated average capture range of 6 mm and an average in-slice registration precision of ±0.3 mm. CONCLUSION: Our registration approach requires minimum user interaction and is compatible with the time constraints of our interventional clinical workflow. The initial evaluation shows acceptable accuracy, reliability and consistency of the method.

Tokuda J, Tuncali K, Iordachita I, Song S-E, Fedorov A, Oguro S, Lasso A, Fennessy FM, Tempany CM, Hata N. In-bore Setup and Software for 3T MRI-guided Transperineal Prostate Biopsy. Phys Med Biol. 2012;57 (18) :5823-40.Abstract

MRI-guided prostate biopsy in conventional closed-bore scanners requires transferring the patient outside the bore during needle insertion due to the constrained in-bore space, causing a safety hazard and limiting image feedback. To address this issue, we present our custom-made in-bore setup and software to support MRI-guided transperineal prostate biopsy in a wide-bore 3 T MRI scanner. The setup consists of a specially designed tabletop and a needle-guiding template with a Z-frame that gives a physician access to the perineum of the patient at the imaging position and allows the physician to perform MRI-guided transperineal biopsy without moving the patient out of the scanner. The software and Z-frame allow registration of the template, target planning and biopsy guidance. Initially, we performed phantom experiments to assess the accuracy of template registration and needle placement in a controlled environment. Subsequently, we embarked on our clinical trial (N = 10). The phantom experiments showed that the translational errors of the template registration along the right-left (RP) and anterior-posterior (AP) axes were 1.1 ± 0.8 and 1.4 ± 1.1 mm, respectively, while the rotational errors around the RL, AP and superior-inferior axes were (0.8 ± 1.0)°, (1.7 ± 1.6)° and (0.0 ± 0.0)°, respectively. The 2D root-mean-square (RMS) needle-placement error was 3 mm. The clinical biopsy procedures were safely carried out in all ten clinical cases with a needle-placement error of 5.4 mm (2D RMS). In conclusion, transperineal prostate biopsy in a wide-bore 3T scanner is feasible using our custom-made tabletop setup and software, which supports manual needle placement without moving the patient out of the magnet.

Egger J, Tokuda J, Chauvin L, Freisleben B, Nimsky C, Kapur T, Wells III WM. Integration of the OpenIGTLink Network Protocol for Image-guided Therapy with the Medical Platform MeVisLab. Int J Med Robot. 2012;8 (3) :282-90.Abstract

BACKGROUND: OpenIGTLink is a new, open, simple and extensible network communication protocol for image-guided therapy (IGT). The protocol provides a standardized mechanism to connect hardware and software by the transfer of coordinate transforms, images, and status messages. MeVisLab is a framework for the development of image processing algorithms and visualization and interaction methods, with a focus on medical imaging. METHODS: The paper describes the integration of the OpenIGTLink network protocol for IGT with the medical prototyping platform MeVisLab. The integration of OpenIGTLink into MeVisLab has been realized by developing a software module using the C++ programming language. RESULTS: The integration was evaluated with tracker clients that are available online. Furthermore, the integration was used to connect MeVisLab to Slicer and a NDI tracking system over the network. The latency time during navigation with a real instrument was measured to show that the integration can be used clinically. CONCLUSIONS: Researchers using MeVisLab can interface their software to hardware devices that already support the OpenIGTLink protocol, such as the NDI Aurora magnetic tracking system. In addition, the OpenIGTLink module can also be used to communicate directly with Slicer, a free, open source software package for visualization and image analysis.

Kósa G, Jakab P, Székely G, Hata N. MRI Driven Magnetic Microswimmers. Biomed Microdevices. 2012;14 (1) :165-78.Abstract

Capsule endoscopy is a promising technique for diagnosing diseases in the digestive system. Here we design and characterize a miniature swimming mechanism that uses the magnetic fields of the MRI for both propulsion and wireless powering of the capsule. Our method uses both the static and the radio frequency (RF) magnetic fields inherently available in MRI to generate a propulsive force. Our study focuses on the evaluation of the propulsive force for different swimming tails and experimental estimation of the parameters that influence its magnitude. We have found that an approximately 20 mm long, 5 mm wide swimming tail is capable of producing 0.21 mN propulsive force in water when driven by a 20 Hz signal providing 0.85 mW power and the tail located within the homogeneous field of a 3 T MRI scanner. We also analyze the parallel operation of the swimming mechanism and the scanner imaging. We characterize the size of artifacts caused by the propulsion system. We show that while the magnetic micro swimmer is propelling the capsule endoscope, the operator can locate the capsule on the image of an interventional scene without being obscured by significant artifacts. Although this swimming method does not scale down favorably, the high magnetic field of the MRI allows self propulsion speed on the order of several millimeter per second and can propel an endoscopic capsule in the stomach.

Orringer DA, Golby AJ, Jolesz FA. Neuronavigation in the Surgical Management of Brain Tumors: Current and Future Trends. Expert Rev Med Devices. 2012;9 (5) :491-500.Abstract

Neuronavigation has become an ubiquitous tool in the surgical management of brain tumors. This review describes the use and limitations of current neuronavigational systems for brain tumor biopsy and resection. Methods for integrating intraoperative imaging into neuronavigational datasets developed to address the diminishing accuracy of positional information that occurs over the course of brain tumor resection are discussed. In addition, the process of integration of functional MRI and tractography into navigational models is reviewed. Finally, emerging concepts and future challenges relating to the development and implementation of experimental imaging technologies in the navigational environment are explored.

Ross RW, Galsky MD, Febbo P, Barry M, Richie JP, Xie W, Fennessy FM, Bhatt RS, Hayes J, Choueiri TK, et al. Phase 2 Study of Neoadjuvant Docetaxel Plus Bevacizumab in Patients with High-risk Localized Prostate Cancer: A Prostate Cancer Clinical Trials Consortium Trial. Cancer. 2012;118 (19) :4777-84.Abstract

BACKGROUND: Treatment of high-risk localized prostate cancer remains inadequate. The authors performed a phase 2 multicenter trial of neoadjuvant docetaxel plus bevacizumab before radical prostatectomy. METHODS: Eligibility included any of the following: prostate-specific antigen (PSA) >20 ng/mL or PSA velocity >2 ng/mL/y, cT3 disease, any biopsy Gleason score 8 to 10, and Gleason score 7 with T3 disease by endorectal magnetic resonance imaging (MRI) at 1.5 T. Also, those with ≥50% biopsy cores involved and either Gleason score 7, PSA >10, or cT2 disease were eligible. Patients were treated with docetaxel 70 mg/m(2) every 3 weeks for 6 cycles and bevacizumab 15 mg/m(2) every 3 weeks for 5 cycles. The primary endpoint was partial response by endorectal MRI. RESULTS: Forty-one patients were treated. Median age was 55 years (range, 40-66 years). Baseline characteristics included: median PSA, 10.1 ng/mL; cT2, 49%, cT3, 32%; and Gleason score 8 to 10, 73%. Thirty-eight of 41 (93%) patients completed all 6 cycles. Grade ≥3 adverse events were rare, although 3 of 41 (7%) experienced febrile neutropenia. Twelve patients (29%; 95% confidence interval [CI], 16%-45%) achieved a >50% reduction in tumor volume, and 9 patients (22%; 95% CI, 11%-38%) achieved a >50% post-treatment decline in PSA. Thirty-seven of the 41 patients underwent radical prostatectomy; there were no complete pathologic responses. CONCLUSIONS: Neoadjuvant docetaxel and bevacizumab is safe, and results in reductions in both tumor volume and serum PSA, in men with high-risk localized prostate cancer. The role of neoadjuvant chemotherapy in prostate cancer, and perioperative antiangiogenic therapy in general, requires further elucidation through ongoing and planned trials.

Azagury DE, Ryou M, Shaikh SN, San José Estépar R, Lengyel BI, Jagadeesan J, Vosburgh KG, Thompson CC. Real-time Computed Tomography-based Augmented Reality for Natural Orifice Transluminal Endoscopic Surgery Navigation. Br J Surg. 2012;99 (9) :1246-53.Abstract

BACKGROUND: Natural orifice transluminal endoscopic surgery (NOTES) is technically challenging owing to endoscopic short-sighted visualization, excessive scope flexibility and lack of adequate instrumentation. Augmented reality may overcome these difficulties. This study tested whether an image registration system for NOTES procedures (IR-NOTES) can facilitate navigation. METHODS: In three human cadavers 15 intra-abdominal organs were targeted endoscopically with and without IR-NOTES via both transgastric and transcolonic routes, by three endoscopists with different levels of expertise. Ease of navigation was evaluated objectively by kinematic analysis, and navigation complexity was determined by creating an organ access complexity score based on the same data. RESULTS: Without IR-NOTES, 21 (11·7 per cent) of 180 targets were not reached (expert endoscopist 3, advanced 7, intermediate 11), compared with one (1 per cent) of 90 with IR-NOTES (intermediate endoscopist) (P = 0·002). Endoscope movements were significantly less complex in eight of the 15 listed organs when using IR-NOTES. The most complex areas to access were the pelvis and left upper quadrant, independently of the access route. The most difficult organs to access were the spleen (5 failed attempts; 3 of 7 kinematic variables significantly improved) and rectum (4 failed attempts; 5 of 7 kinematic variables significantly improved). The time needed to access the rectum through a transgastric approach was 206·3 s without and 54·9 s with IR-NOTES (P = 0·027). CONCLUSION: The IR-NOTES system enhanced both navigation efficacy and ease of intra-abdominal NOTES exploration for operators of all levels. The system rendered some organs accessible to non-expert operators, thereby reducing one impediment to NOTES procedures.

Risholm P, Janoos F, Pursley J, Fedorov A, Tempany CM, Cormack RA, Wells III WM. Selection of optimal hyper-parameters for estimation of uncertainty in MRI-TRUS registration of the prostate. Med Image Comput Comput Assist Interv. 2012;15 (Pt 3) :107-14.Abstract

Transrectal ultrasound (TRUS) facilitates intra-treatment delineation of the prostate gland (PG) to guide insertion of brachytherapy seeds, but the prostate substructure and apex are not always visible which may make the seed placement sub-optimal. Based on an elastic model of the prostate created from MRI, where the prostate substructure and apex are clearly visible, we use a Bayesian approach to estimate the posterior distribution on deformations that aligns the pre-treatment MRI with intra-treatment TRUS. Without apex information in TRUS, the posterior prediction of the location of the prostate boundary, and the prostate apex boundary in particular, is mainly determined by the pseudo stiffness hyper-parameter of the prior distribution. We estimate the optimal value of the stiffness through likelihood maximization that is sensitive to the accuracy as well as the precision of the posterior prediction at the apex boundary. From a data-set of 10 pre- and intra-treatment prostate images with ground truth delineation of the total PG, 4 cases were used to establish an optimal stiffness hyper-parameter when 15% of the prostate delineation was removed to simulate lack of apex information in TRUS, while the remaining 6 cases were used to cross-validate the registration accuracy and uncertainty over the PG and in the apex.

Moradi M, Janoos F, Fedorov A, Risholm P, Kapur T, Wolfsberger LD, Nguyen PL, Tempany CM, Wells III WM. Two solutions for registration of ultrasound to MRI for image-guided prostate interventions. Conf Proc IEEE Eng Med Biol Soc. 2012;2012 :1129-32.Abstract

Ultrasound-guided prostate interventions could benefit from incorporating the radiologic localization of the tumor which can be acquired from multiparametric MRI. To enable this integration, we propose and compare two solutions for registration of T2 weighted MR images with transrectal ultrasound. Firstly, we propose an innovative and practical approach based on deformable registration of binary label maps obtained from manual segmentation of the gland in the two modalities. This resulted in a target registration error of 3.6±1.7 mm. Secondly, we report a novel surface-based registration method that uses a biomechanical model of the tissue and results in registration error of 3.2±1.3 mm. We compare the two methods in terms of accuracy, clinical use and technical limitations.

O'Donnell LJ, Wells III WM, Golby AJ, Westin C-F. Unbiased groupwise registration of white matter tractography. Med Image Comput Comput Assist Interv. 2012;15 (Pt 3) :123-30.Abstract

We present what we believe to be the first investigation into unbiased multi-subject registration of whole brain diffusion tractography of the white matter. To our knowledge, this is also the first entropy-based objective function applied to fiber tract registration. To define the probability of fiber trajectories for the computation of entropy, we take advantage of a pairwise fiber distance used as the basis for a Gaussian-like kernel. By employing several values of the kernel's scale parameter, the method is inherently multi-scale. Results of experiments using synthetic and real datasets demonstrate the potential of the method for simultaneous joint registration of tractography.

2011
Kapur T, Tempany CM, Jolesz FA. Proceedings of the 4th Image Guided Therapy Workshop. Image Guided Therapy Workshop. 2011;4 :1-121. 2011 IGT Workshop Proceedings

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