Publications by Year: 2016

2016
Mallory MA, Losk K, Camuso K, Caterson S, Nimbkar S, Golshan M. Does "Two is Better Than One" Apply to Surgeons? Comparing Single-Surgeon Versus Co-surgeon Bilateral Mastectomies. Ann Surg Oncol. 2016;23 (4) :1111-6.Abstract
BACKGROUND: Bilateral mastectomies (BM) are traditionally performed by single surgeons (SS); a co-surgeon (CS) technique, where each surgeon concurrently performs a unilateral mastectomy, offers an alternative approach. We examined differences in general surgery time (GST), overall surgery time (OST), and patient complications for BM performed by CS and SS. METHODS: Patients undergoing BM with tissue expander reconstruction (BMTR) between January 2010 and May 2014 at our center were identified through operative case logs. GST (incision to end of BM procedure), reconstruction duration (RST) (plastic surgery start to end of reconstruction) and OST (OST = GST + RST) was calculated. Patient age, presence/stage of cancer, breast weight, axillary procedure performed, and 30-day postoperative complications were extracted from medical records. Differences in GST and OST between CS and SS cases were assessed with a t test. A multivariate linear regression was fit to identify factors associated with GST. RESULTS: A total of 116 BMTR cases were performed [CS, n = 67 (57.8 %); SS, n = 49 (42.2 %)]. Demographic characteristics did not differ between groups. GST and OST were significantly shorter for CS cases, 75.8 versus 116.8 min, p < .0001, and 255.2 versus 278.3 min, p = .005, respectively. Presence of a CS significantly reduces BMTR time (β = -38.82, p < .0001). Breast weight (β = 0.0093, p = .03) and axillary dissection (β = 28.69, p = .0003) also impacted GST. CONCLUSIONS: The CS approach to BMTR reduced both GST and OST; however, the degree of time savings (35.1 and 8.3 %, respectively) was less than hypothesized. A larger study is warranted to better characterize time, cost, and outcomes of the CS-approach for BM.
Manuel MM, Cho LP, Catalano PJ, Damato AL, Miyamoto DT, Tempany CM, Schmidt EJ, Viswanathan AN. Outcomes with Image-based Interstitial Brachytherapy for Vaginal Cancer. Radiother Oncol. 2016;120 (3) :486-92.Abstract

PURPOSE: To compare clinical outcomes of image-based versus non-image-based interstitial brachytherapy (IBBT) for vaginal cancer. METHODS AND MATERIALS: Of 72 patients with vaginal cancer treated with brachytherapy (BT), 47 had image guidance (CT=31, MRI=16) and 25 did not. Kaplan-Meier (KM) estimates were generated for any recurrence, local control (LC), disease-free interval (DFI), and overall survival (OS) and Cox models were used to assess prognostic factors. RESULTS: Median age was 66 and median follow-up time was 24months. Median cumulative EQD2 dose was 80.8Gy in the non-IBBT group and 77Gy in the IBBT group. For non-IBBT versus IBBT, the 2-year KM LC was 71% vs. 93% (p=0.03); DFI was 54% vs. 86% (p=0.04); and OS 52% vs. 82% (p=0.35). On multivariate analysis, IBBT was associated with better DFI (HR 0.24, 95% CI 0.07-0.73). Having any 2 or more of chemotherapy, high-dose-rate (HDR) BT or IBBT (temporally correlated variables) significantly reduced risk of relapse (HR=0.33, 95% CI=0.13-0.83), compared to having none of these factors. CONCLUSION: Over time, the use of chemotherapy, HDR, and IBBT has increased in vaginal cancer. The combination of these factors resulted in the highest rates of disease control. Image-guided brachytherapy for vaginal cancer patients maximizes disease control.

Guenette JP, Tuncali K, Himes N, Tatli S, Lee TC. Spine Cryoablation: A Multimodality Image-Guided Approach for Tumors Adjacent to Major Neural Elements. AJNR Am J Neuroradiol. 2016;37 (12) :2396-9.Abstract

We report percutaneous cryoablation of spine tumors in 7 consecutive patients (5 men, 2 women [mean age, 47 years; range, 17-68 years]) by using intraprocedural image monitoring of ice ball margins to protect adjacent neural elements. Complete tumor ablation was achieved in all patients without neurologic complication. Pain relief was achieved in 4 of 5 (80%) patients; the patient with persistent pain was later found to have enlarging metastases at other sites.

Li M, Miller K, Joldes GR, Kikinis R, Wittek A. Biomechanical Model for Computing Deformations for Whole-body Image Registration: A Meshless Approach. Int J Numer Method Biomed Eng. 2016;32 (12).Abstract

Patient-specific biomechanical models have been advocated as a tool for predicting deformations of soft body organs/tissue for medical image registration (aligning two sets of images) when differences between the images are large. However, complex and irregular geometry of the body organs makes generation of patient-specific biomechanical models very time-consuming. Meshless discretisation has been proposed to solve this challenge. However, applications so far have been limited to 2D models and computing single organ deformations. In this study, 3D comprehensive patient-specific nonlinear biomechanical models implemented using meshless Total Lagrangian explicit dynamics algorithms are applied to predict a 3D deformation field for whole-body image registration. Unlike a conventional approach that requires dividing (segmenting) the image into non-overlapping constituents representing different organs/tissues, the mechanical properties are assigned using the fuzzy c-means algorithm without the image segmentation. Verification indicates that the deformations predicted using the proposed meshless approach are for practical purposes the same as those obtained using the previously validated finite element models. To quantitatively evaluate the accuracy of the predicted deformations, we determined the spatial misalignment between the registered (i.e. source images warped using the predicted deformations) and target images by computing the edge-based Hausdorff distance. The Hausdorff distance-based evaluation determines that our meshless models led to successful registration of the vast majority of the image features. Copyright © 2016 John Wiley & Sons, Ltd.

Kapur T, Tempany CM. Proceedings of the 8th Image Guided Therapy Workshop. Image Guided Therapy Workshop. 2016;8 :1-68. 2016 IGT Workshop Proceedings
Tempany CM. Multi-modal Image Guided Therapy: Novel Personalized Approaches in Oncology. Keynote Speech at the 2016 MICCAI Meeting. Int Conf Med Image Comput Comput Assist Interv. 2016 Oct;. 2016;19.Abstract Clare Tempany MICCAI 2016 Invited Talk
Guenette JP, Himes N, Giannopoulos AA, Kelil T, Mitsouras D, Lee TC. Computer-Based Vertebral Tumor Cryoablation Planning and Procedure Simulation Involving Two Cases using MRI-Visible 3D Printing and Advanced Visualization. AJR Am J Roentgenol. 2016;207 (5) :1128-31.Abstract

OBJECTIVE: We report the development and use of MRI-compatible and MRI-visible 3D printed models in conjunction with advanced visualization software models to plan and simulate safe access routes to achieve a theoretic zone of cryoablation for percutaneous image-guided treatment of a C7 pedicle osteoid osteoma and an L1 lamina osteoblastoma. Both models altered procedural planning and patient care. CONCLUSION: Patient-specific MRI-visible models can be helpful in planning complex percutaneous image-guided cryoablation procedures.

Chansakul T, Chen PN, Lee TC, Tierney T. Interventional MR Imaging for Deep-Brain Stimulation Electrode Placement. Radiology. 2016;281 (3) :940-6.Abstract

Purpose To investigate the safety and targeting errors of deep-brain stimulation (DBS) electrodes placed under interventional magnetic resonance (MR) imaging, which allows near real-time anatomic placement without physiologic mapping. Materials and Methods Retrospectively evaluated were 10 consecutive patients (five women, five men) with a mean age of 59.9 years (age range, 17-79 years). These patients underwent interventional MR imaging-guided DBS placement for movement disorders from September 2013 to August 2014 for placement of 19 DBS electrodes in cases where traditional frame-based surgery may be challenging because of the following: dystonia resulting in difficulty in placing the patients in frame, patient's inability or unwillingness to tolerate awake surgery, or anatomic anomaly or variant that could increase the risk of bleeding from microelectrode mapping. Outcomes measured included perioperative hemorrhage, death, and stroke, and electrode functionality assessed at 2 weeks after the operation. In addition, the mean radial error and mean trajectory error were calculated. Results No intraoperative neurologic complications (n = 10 [95% confidence interval: 0%, 31%]) were observed. One patient developed aspiration pneumonia in the postoperative period. Mean radial error was 0.7 mm ± 0.4 (standard deviation) and mean trajectory error was 0.5 mm ± 0.4. All leads delivered clinically effective stimulation. Conclusion Interventional MR imaging-guided DBS electrode placement may be a safe and effective alternative to conventional frame-based surgery in well-selected patients.

Zhang F, Savadjev P, Cai W, Song Y, Verma R, Westin C-F, O'Donnell LJ. Fiber Clustering Based White Matter Connectivity Analysis for Prediction of Autism Spectrum Disorder using Diffusion Tensor Imaging, in IEEE International Symposium on Biomedical Imaging. ; 2016 :564-7.Abstract

Autism Spectrum Disorder (ASD) has been suggested to associate with alterations 
in brain connectivity. In this study, we focus on a fiber clustering tractography segmentation 
strategy to observe white matter connectivity alterations in ASD. Compared to another 
popular parcellation-based approach for tractography segmentation based on cortical 
regions, we hypothesized that the clustering-based method could provide a more 
anatomically correspondent division of white matter. We applied this strategy to conduct a population-based group statistical analysis for the automated prediction of ASD. We obtained a maximum classification accuracy of 81.33% be- tween ASDs and controls, compared to the results of 78.00% from the parcellation-based method.

Zhang ISBI 2016 Paper
Preiswerk F, Toews M, Cheng C-C, Chiou J-yuan G, Mei C-S, Schaefer LF, Hoge WS, Schwartz BM, Panych LP, Madore B. Hybrid MRI Ultrasound Acquisitions, and Scannerless Real-time Imaging. Magn Reson Med. 2016.Abstract

PURPOSE: To combine MRI, ultrasound, and computer science methodologies toward generating MRI contrast at the high frame rates of ultrasound, inside and even outside the MRI bore. METHODS: A small transducer, held onto the abdomen with an adhesive bandage, collected ultrasound signals during MRI. Based on these ultrasound signals and their correlations with MRI, a machine-learning algorithm created synthetic MR images at frame rates up to 100 per second. In one particular implementation, volunteers were taken out of the MRI bore with the ultrasound sensor still in place, and MR images were generated on the basis of ultrasound signal and learned correlations alone in a "scannerless" manner. RESULTS: Hybrid ultrasound-MRI data were acquired in eight separate imaging sessions. Locations of liver features, in synthetic images, were compared with those from acquired images: The mean error was 1.0 pixel (2.1 mm), with best case 0.4 and worst case 4.1 pixels (in the presence of heavy coughing). For results from outside the bore, qualitative validation involved optically tracked ultrasound imaging with/without coughing. CONCLUSION: The proposed setup can generate an accurate stream of high-speed MR images, up to 100 frames per second, inside or even outside the MR bore. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

Schmidt EJ, Watkins RD, Zviman MM, Guttman MA, Wang W, Halperin HA. A Magnetic Resonance Imaging–Conditional External Cardiac De brillator for Resuscitation within the Magnetic Resonance Imaging Scanner Bore. Circ Cardiovasc Imaging. 2016;9 :e005091.Abstract

Subjects undergoing cardiac arrest within a magnetic resonance imaging (MRI) scanner are currently removed from the bore and then from the MRI suite, before the delivery of cardiopulmonary resuscitation and de brillation, potentially increasing the risk of mortality. This precludes many higher-risk (acute ischemic and acute stroke) patients from undergoing MRI and MRI-guided intervention. An MRI-conditional cardiac de brillator should enable scanning with de brillation pads attached and the generator ON, enabling application of de brillation within the seconds of MRI after a cardiac event. An MRI-conditional external de brillator may improve patient acceptance for MRI procedures. Methods and Results—A commercial external de brillator was rendered 1.5 Tesla MRI-conditional by the addition of novel radiofrequency lters between the generator and commercial disposable surface pads. The radiofrequency lters reduced emission into the MRI scanner and prevented cable/surface pad heating during imaging, while preserving all the de brillator monitoring and delivery functions. Human volunteers were imaged using high speci c absorption rate sequences to validate MRI image quality and lack of heating. Swine were electrically brillated (n=4) and thereafter de brillated both outside and inside the MRI bore. MRI image quality was reduced by 0.8 or 1.6 dB, with the generator in monitoring mode and operating on battery or AC power, respectively. Commercial surface pads did not create artifacts deeper than 6 mm below the skin surface. Radiofrequency heating was within US Food and Drug Administration guidelines. De brillation was completely successful inside and outside the MRI bore. Conclusions—A prototype MRI-conditional de brillation system successfully de brillated in the MRI without degrading the image quality or increasing the time needed for de brillation. It can increase patient acceptance for MRI procedures.

Bersvendsen J, Toews M, Danudibroto A, Wells WM, Urheim S, San José Estépar R, Samset E. Robust Spatio-Temporal Registration of 4D Cardiac Ultrasound Sequences. Proc SPIE Int Soc Opt Eng. 2016;9790.Abstract
Registration of multiple 3D ultrasound sectors in order to provide an extended field of view is important for the appreciation of larger anatomical structures at high spatial and temporal resolution. In this paper, we present a method for fully automatic spatio-temporal registration between two partially overlapping 3D ultrasound sequences. The temporal alignment is solved by aligning the normalized cross correlation-over-time curves of the sequences. For the spatial alignment, corresponding 3D Scale Invariant Feature Transform (SIFT) features are extracted from all frames of both sequences independently of the temporal alignment. A rigid transform is then calculated by least squares minimization in combination with random sample consensus. The method is applied to 16 echocardiographic sequences of the left and right ventricles and evaluated against manually annotated temporal events and spatial anatomical landmarks. The mean distances between manually identified landmarks in the left and right ventricles after automatic registration were (mean ± SD) 4.3 ± 1.2 mm compared to a reference error of 2.8 ± 0.6 mm with manual registration. For the temporal alignment, the absolute errors in valvular event times were 14.4 ± 11.6 ms for Aortic Valve (AV) opening, 18.6 ± 16.0 ms for AV closing, and 34.6 ± 26.4 ms for mitral valve opening, compared to a mean inter-frame time of 29 ms.
Ciris PA, Balasubramanian M, Damato AL, Seethamraju RT, Tempany-Afdhal CM, Mulkern RV, Viswanathan AN. Characterizing Gradient Echo Signal Decays in Gynecologic Cancers at 3T using a Gaussian Augmentation of the Monoexponential (GAME) Model. J Magn Reson Imaging. 2016;44 (4) :1020-30.Abstract

PURPOSE: To assess whether R2* mapping with a standard Monoexponential (ME) or a Gaussian Augmentation of the Monoexponential (GAME) decay model better characterizes gradient-echo signal decays in gynecological cancers after external beam radiation therapy at 3T, and evaluate implications of modeling for noninvasive identification of intratumoral hypoxia. MATERIALS AND METHODS: Multi-gradient-echo signals were acquired on 25 consecutive patients with gynecologic cancers and three healthy participants during inhalation of different oxygen concentrations at 3T. Data were fitted with both ME and GAME models. Models were compared using F-tests in tumors and muscles in patients, muscles, cervix, and uterus in healthy participants, and across oxygenation levels. RESULTS: GAME significantly improved fitting over ME (P < 0.05): Improvements with GAME covered 34% of tumor regions-of-interest on average, ranging from 6% (of a vaginal tumor) to 68% (of a cervical tumor) in individual tumors. Improvements with GAME were more prominent in areas that would be assumed hypoxic based on ME alone, reaching 90% as ME R2* approached 100 Hz. Gradient echo decay parameters at different oxygenation levels were not significantly different (P = 0.81). CONCLUSION: R2* may prove sensitive to hypoxia; however, inaccurate representations of underlying data may limit the success of quantitative assessments. Although the degree to which R2 or σ values correlate with hypoxia remains unknown, improved characterization with GAME increases the potential for determining any correlates of fit parameters with biomarkers, such as oxygenation status. J. MAGN. RESON. IMAGING 2016;44:1020-1030.

Tempany CM. Opportunities for Multiparametric MRI with PI-RADS v2 to Make a Difference. Future Oncol. 2016;12 (21) :2397-9.
Gombos EC, Jayender J, Richman DM, Caragacianu DL, Mallory MA, Jolesz FA, Golshan M. Intraoperative Supine Breast MR Imaging to Quantify Tumor Deformation and Detection of Residual Breast Cancer: Preliminary Results. Radiology. 2016;281 (3) :720-9.Abstract
Purpose To use intraoperative supine magnetic resonance (MR) imaging to quantify breast tumor deformation and displacement secondary to the change in patient positioning from imaging (prone) to surgery (supine) and to evaluate residual tumor immediately after breast-conserving surgery (BCS). Materials and Methods Fifteen women gave informed written consent to participate in this prospective HIPAA-compliant, institutional review board-approved study between April 2012 and November 2014. Twelve patients underwent lumpectomy and postsurgical intraoperative supine MR imaging. Six of 12 patients underwent both pre- and postsurgical supine MR imaging. Geometric, structural, and heterogeneity metrics of the cancer and distances of the tumor from the nipple, chest wall, and skin were computed. Mean and standard deviations of the changes in volume, surface area, compactness, spherical disproportion, sphericity, and distances from key landmarks were computed from tumor models. Imaging duration was recorded. Results The mean differences in tumor deformation metrics between prone and supine imaging were as follows: volume, 23.8% (range, -30% to 103.95%); surface area, 6.5% (range, -13.24% to 63%); compactness, 16.2% (range, -23% to 47.3%); sphericity, 6.8% (range, -9.10% to 20.78%); and decrease in spherical disproportion, -11.3% (range, -60.81% to 76.95%). All tumors were closer to the chest wall on supine images than on prone images. No evidence of residual tumor was seen on MR images obtained after the procedures. Mean duration of pre- and postoperative supine MR imaging was 25 minutes (range, 18.4-31.6 minutes) and 19 minutes (range, 15.1-22.9 minutes), respectively. Conclusion Intraoperative supine breast MR imaging, when performed in conjunction with standard prone breast MR imaging, enables quantification of breast tumor deformation and displacement secondary to changes in patient positioning from standard imaging (prone) to surgery (supine) and may help clinicians evaluate for residual tumor immediately after BCS. (©) RSNA, 2016 Online supplemental material is available for this article.
Kapur T, Pieper S, Fedorov A, Fillion-Robin J-C, Halle M, O'Donnell L, Lasso A, Ungi T, Pinter C, Finet J, et al. Increasing the Impact of Medical Image Computing using Community-based Open-access Hackathons: The NA-MIC and 3D Slicer Experience. Med Image Anal. 2016;33 :176-80.Abstract

The National Alliance for Medical Image Computing (NA-MIC) was launched in 2004 with the goal of investigating and developing an open source software infrastructure for the extraction of information and knowledge from medical images using computational methods. Several leading research and engineering groups participated in this effort that was funded by the US National Institutes of Health through a variety of infrastructure grants. This effort transformed 3D Slicer from an internal, Boston-based, academic research software application into a professionally maintained, robust, open source platform with an international leadership and developer and user communities. Critical improvements to the widely used underlying open source libraries and tools-VTK, ITK, CMake, CDash, DCMTK-were an additional consequence of this effort. This project has contributed to close to a thousand peer-reviewed publications and a growing portfolio of US and international funded efforts expanding the use of these tools in new medical computing applications every year. In this editorial, we discuss what we believe are gaps in the way medical image computing is pursued today; how a well-executed research platform can enable discovery, innovation and reproducible science ("Open Science"); and how our quest to build such a software platform has evolved into a productive and rewarding social engineering exercise in building an open-access community with a shared vision.

Li X, Li C, Fedorov A, Kapur T, Yang X. Segmentation of Prostate from Ultrasound Images using Level Sets on Active Band and Intensity Variation Across Edges. Med Phys. 2016;43 (6) :3090.Abstract

PURPOSE: In this paper, the authors propose a novel efficient method to segment ultrasound images of the prostate with weak boundaries. Segmentation of the prostate from ultrasound images with weak boundaries widely exists in clinical applications. One of the most typical examples is the diagnosis and treatment of prostate cancer. Accurate segmentation of the prostate boundaries from ultrasound images plays an important role in many prostate-related applications such as the accurate placement of the biopsy needles, the assignment of the appropriate therapy in cancer treatment, and the measurement of the prostate volume. METHODS: Ultrasound images of the prostate are usually corrupted with intensity inhomogeneities, weak boundaries, and unwanted edges, which make the segmentation of the prostate an inherently difficult task. Regarding to these difficulties, the authors introduce an active band term and an edge descriptor term in the modified level set energy functional. The active band term is to deal with intensity inhomogeneities and the edge descriptor term is to capture the weak boundaries or to rule out unwanted boundaries. The level set function of the proposed model is updated in a band region around the zero level set which the authors call it an active band. The active band restricts the authors' method to utilize the local image information in a banded region around the prostate contour. Compared to traditional level set methods, the average intensities inside∖outside the zero level set are only computed in this banded region. Thus, only pixels in the active band have influence on the evolution of the level set. For weak boundaries, they are hard to be distinguished by human eyes, but in local patches in the band region around prostate boundaries, they are easier to be detected. The authors incorporate an edge descriptor to calculate the total intensity variation in a local patch paralleled to the normal direction of the zero level set, which can detect weak boundaries and avoid unwanted edges in the ultrasound images. RESULTS: The efficiency of the proposed model is demonstrated by experiments on real 3D volume images and 2D ultrasound images and comparisons with other approaches. Validation results on real 3D TRUS prostate images show that the authors' model can obtain a Dice similarity coefficient (DSC) of 94.03% ± 1.50% and a sensitivity of 93.16% ± 2.30%. Experiments on 100 typical 2D ultrasound images show that the authors' method can obtain a sensitivity of 94.87% ± 1.85% and a DSC of 95.82% ± 2.23%. A reproducibility experiment is done to evaluate the robustness of the proposed model. CONCLUSIONS: As far as the authors know, prostate segmentation from ultrasound images with weak boundaries and unwanted edges is a difficult task. A novel method using level sets with active band and the intensity variation across edges is proposed in this paper. Extensive experimental results demonstrate that the proposed method is more efficient and accurate.

Zaidi HA, De Los Reyes K, Barkhoudarian G, Litvack ZN, Bi WL, Rincon-Torroella J, Mukundan S, Dunn IF, Laws ER. The Utility of High-resolution Intraoperative MRI in Endoscopic Transsphenoidal Surgery for Pituitary Macroadenomas: Early Experience in the Advanced Multimodality Image Guided Operating Suite. Neurosurg Focus. 2016;40 (3) :E18.Abstract

OBJECTIVE: Endoscopic skull base surgery has become increasingly popular among the skull base surgery community, with improved illumination and angled visualization potentially improving tumor resection rates. Intraoperative MRI (iMRI) is used to detect residual disease during the course of the resection. This study is an investigation of the utility of 3-T iMRI in combination with transnasal endoscopy with regard to gross-total resection (GTR) of pituitary macroadenomas. METHODS: The authors retrospectively reviewed all endoscopic transsphenoidal operations performed in the Advanced Multimodality Image Guided Operating (AMIGO) suite from November 2011 to December 2014. Inclusion criteria were patients harboring presumed pituitary macroadenomas with optic nerve or chiasmal compression and visual loss, operated on by a single surgeon. RESULTS: Of the 27 patients who underwent transsphenoidal resection in the AMIGO suite, 20 patients met the inclusion criteria. The endoscope alone, without the use of iMRI, would have correctly predicted extent of resection in 13 (65%) of 20 cases. Gross-total resection was achieved in 12 patients (60%) prior to MRI. Intraoperative MRI helped convert 1 STR and 4 NTRs to GTRs, increasing the number of GTRs from 12 (60%) to 16 (80%). CONCLUSIONS: Despite advances in visualization provided by the endoscope, the incidence of residual disease can potentially place the patient at risk for additional surgery. The authors found that iMRI can be useful in detecting unexpected residual tumor. The cost-effectiveness of this tool is yet to be determined.

Hata N, Song S-E, Olubiyi O, Arimitsu Y, Fujimoto K, Kato T, Tuncali K, Tani S, Tokuda J. Body-mounted Robotic Instrument Guide for Image-guided Cryotherapy of Renal Cancer. Med Phys. 2016;43 (2) :843-53.Abstract

PURPOSE: Image-guided cryotherapy of renal cancer is an emerging alternative to surgical nephrectomy, particularly for those who cannot sustain the physical burden of surgery. It is well known that the outcome of this therapy depends on the accurate placement of the cryotherapy probe. Therefore, a robotic instrument guide may help physicians aim the cryotherapy probe precisely to maximize the efficacy of the treatment and avoid damage to critical surrounding structures. The objective of this paper was to propose a robotic instrument guide for orienting cryotherapy probes in image-guided cryotherapy of renal cancers. The authors propose a body-mounted robotic guide that is expected to be less susceptible to guidance errors caused by the patient's whole body motion. METHODS: Keeping the device's minimal footprint in mind, the authors developed and validated a body-mounted, robotic instrument guide that can maintain the geometrical relationship between the device and the patient's body, even in the presence of the patient's frequent body motions. The guide can orient the cryotherapy probe with the skin incision point as the remote-center-of-motion. The authors' validation studies included an evaluation of the mechanical accuracy and position repeatability of the robotic instrument guide. The authors also performed a mock MRI-guided cryotherapy procedure with a phantom to compare the advantage of robotically assisted probe replacements over a free-hand approach, by introducing organ motions to investigate their effects on the accurate placement of the cryotherapy probe. Measurements collected for performance analysis included accuracy and time taken for probe placements. Multivariate analysis was performed to assess if either or both organ motion and the robotic guide impacted these measurements. RESULTS: The mechanical accuracy and position repeatability of the probe placement using the robotic instrument guide were 0.3 and 0.1 mm, respectively, at a depth of 80 mm. The phantom test indicated that the accuracy of probe placement was significantly better with the robotic instrument guide (4.1 mm) than without the guide (6.3 mm, p<0.001), even in the presence of body motion. When independent organ motion was artificially added, in addition to body motion, the advantage of accurate probe placement using the robotic instrument guide disappeared statistically [i.e., 6.0 mm with the robotic guide and 5.9 mm without the robotic guide (p = 0.906)]. When the robotic instrument guide was used, the total time required to complete the procedure was reduced from 19.6 to 12.7 min (p<0.001). Multivariable analysis indicated that the robotic instrument guide, not the organ motion, was the cause of statistical significance. The statistical power the authors obtained was 88% in accuracy assessment and 99% higher in duration measurement. CONCLUSIONS: The body-mounted robotic instrument guide allows positioning of the probe during image-guided cryotherapy of renal cancer and was done in fewer attempts and in less time than the free-hand approach. The accuracy of the placement of the cryotherapy probe was better using the robotic instrument guide than without the guide when no organ motion was present. The accuracy between the robotic and free-hand approach becomes comparable when organ motion was present.

Ciris PA, Balasubramanian M, Seethamraju RT, Tokuda J, Scalera J, Penzkofer T, Fennessy FM, Tempany-Afdhal CM, Tuncali K, Mulkern RV. Characterization of Gradient Echo Signal Decays in Healthy and Cancerous Prostate at 3T Improves with a Gaussian Augmentation of the Mono-Exponential (Game) Model. NMR Biomed. 2016;29 (7) :999-1009.Abstract

A biomarker of cancer aggressiveness, such as hypoxia, could substantially impact treatment decisions in the prostate, especially radiation therapy, by balancing treatment morbidity (urinary incontinence, erectile dysfunction, etc.) against mortality. R2 (*) mapping with Mono-Exponential (ME) decay modeling has shown potential for identifying areas of prostate cancer hypoxia at 1.5T. However, Gaussian deviations from ME decay have been observed in other tissues at 3T. The purpose of this study is to assess whether gradient-echo signal decays are better characterized by a standard ME decay model, or a Gaussian Augmentation of the Mono-Exponential (GAME) decay model, in the prostate at 3T. Multi-gradient-echo signals were acquired on 20 consecutive patients with a clinical suspicion of prostate cancer undergoing MR-guided prostate biopsies. Data were fitted with both ME and GAME models. The information contents of these models were compared using Akaike's information criterion (second order, AICC ), in skeletal muscle, the prostate central gland (CG), and peripheral zone (PZ) regions of interest (ROIs). The GAME model had higher information content in 30% of the prostate on average (across all patients and ROIs), covering up to 67% of cancerous PZ ROIs, and up to 100% of cancerous CG ROIs (in individual patients). The higher information content of GAME became more prominent in regions that would be assumed hypoxic using ME alone, reaching 50% of the PZ and 70% of the CG as ME R2 (*) approached 40 s(-1) . R2 (*) mapping may have important applications in MRI; however, information lost due to modeling could mask differences in parameters due to underlying tissue anatomy or physiology. The GAME model improves characterization of signal behavior in the prostate at 3T, and may increase the potential for determining correlates of fit parameters with biomarkers, for example of oxygenation status.

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