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Featured researches published by D Du.


International Journal of Radiation Oncology Biology Physics | 2015

High-Quality T2-Weighted 4-Dimensional Magnetic Resonance Imaging for Radiation Therapy Applications

D Du; Shelton D. Caruthers; Carri Glide-Hurst; Daniel A. Low; H. Harold Li; Sasa Mutic; Yanle Hu

PURPOSE The purpose of this study was to improve triggering efficiency of the prospective respiratory amplitude-triggered 4-dimensional magnetic resonance imaging (4DMRI) method and to develop a 4DMRI imaging protocol that could offer T2 weighting for better tumor visualization, good spatial coverage and spatial resolution, and respiratory motion sampling within a reasonable amount of time for radiation therapy applications. METHODS AND MATERIALS The respiratory state splitting (RSS) and multi-shot acquisition (MSA) methods were analytically compared and validated in a simulation study by using the respiratory signals from 10 healthy human subjects. The RSS method was more effective in improving triggering efficiency. It was implemented in prospective respiratory amplitude-triggered 4DMRI. 4DMRI image datasets were acquired from 5 healthy human subjects. Liver motion was estimated using the acquired 4DMRI image datasets. RESULTS The simulation study showed the RSS method was more effective for improving triggering efficiency than the MSA method. The average reductions in 4DMRI acquisition times were 36% and 10% for the RSS and MSA methods, respectively. The human subject study showed that T2-weighted 4DMRI with 10 respiratory states, 60 slices at a spatial resolution of 1.5 × 1.5 × 3.0 mm(3) could be acquired in 9 to 18 minutes, depending on the individuals breath pattern. Based on the acquired 4DMRI image datasets, the ranges of peak-to-peak liver displacements among 5 human subjects were 9.0 to 12.9 mm, 2.5 to 3.9 mm, and 0.5 to 2.3 mm in superior-inferior, anterior-posterior, and left-right directions, respectively. CONCLUSIONS We demonstrated that with the RSS method, it was feasible to acquire high-quality T2-weighted 4DMRI within a reasonable amount of time for radiation therapy applications.


Journal of Applied Clinical Medical Physics | 2016

A comparative study of automatic image segmentation algorithms for target tracking in MR‐IGRT

Yuan Feng; Iwan Kawrakow; Jeff Olsen; Parag J. Parikh; C. Noel; O. Wooten; D Du; Sasa Mutic; Yanle Hu

On‐board magnetic resonance (MR) image guidance during radiation therapy offers the potential for more accurate treatment delivery. To utilize the real‐time image information, a crucial prerequisite is the ability to successfully segment and track regions of interest (ROI). The purpose of this work is to evaluate the performance of different segmentation algorithms using motion images (4 frames per second) acquired using a MR image‐guided radiotherapy (MR‐IGRT) system. Manual contours of the kidney, bladder, duodenum, and a liver tumor by an experienced radiation oncologist were used as the ground truth for performance evaluation. Besides the manual segmentation, images were automatically segmented using thresholding, fuzzy k‐means (FKM), k‐harmonic means (KHM), and reaction‐diffusion level set evolution (RD‐LSE) algorithms, as well as the tissue tracking algorithm provided by the ViewRay treatment planning and delivery system (VR‐TPDS). The performance of the five algorithms was evaluated quantitatively by comparing with the manual segmentation using the Dice coefficient and target registration error (TRE) measured as the distance between the centroid of the manual ROI and the centroid of the automatically segmented ROI. All methods were able to successfully segment the bladder and the kidney, but only FKM, KHM, and VR‐TPDS were able to segment the liver tumor and the duodenum. The performance of the thresholding, FKM, KHM, and RD‐LSE algorithms degraded as the local image contrast decreased, whereas the performance of the VP‐TPDS method was nearly independent of local image contrast due to the reference registration algorithm. For segmenting high‐contrast images (i.e., kidney), the thresholding method provided the best speed (<1 ms) with a satisfying accuracy (Dice=0.95). When the image contrast was low, the VR‐TPDS method had the best automatic contour. Results suggest an image quality determination procedure before segmentation and a combination of different methods for optimal segmentation with the on‐board MR‐IGRT system. PACS number(s): 87.57.nm, 87.57.N‐, 87.61.Tg


Practical radiation oncology | 2015

Magnetic resonance imaging-based treatment planning for prostate cancer: Use of population average tissue densities within the irradiated volume to improve plan accuracy

Yanle Hu; Wangyang Zhao; D Du; H. Omar Wooten; J.R. Olsen; Jeff M. Michalski; Sasa Mutic

PURPOSE The purpose of this study was to investigate the feasibility of using population average tissue densities within the irradiated volume to improve the dosimetric accuracy of magnetic resonance imaging-based treatment plans for prostate cancer. METHODS AND MATERIALS Computed tomography images and radiation therapy treatment plans from 20 patients with prostate cancer were reviewed retrospectively. Patient anatomy was segmented into fat, nonfat soft tissue, and bone. Population average tissue densities within the irradiated volume were obtained. Two bulk density override plans were generated using the tissue densities reported in International Commission on Radiation Units & Measurements Report 46 and those obtained in this study, respectively. Both plans were compared to the clinically approved computed tomography-based plan to assess dosimetric accuracy. RESULTS The population average tissue densities within the irradiated volume obtained in this study were found to be different from those reported in International Commission on Radiation Units & Measurements Report 46. Use of the population average tissue densities within the irradiated volume reduced dosimetric errors for all dose metrics, for example, V100 (percentage of prostate volume receiving 100% of the prescription dose; 0.32% vs 1.73%), D95 (dose covering 95% of the target volume; 0.32% vs 0.92%), D50 (dose covering 50% of the target volume; 0.30% vs 0.89%), and maximum dose to bladder (0.37% vs 0.78%), rectum (0.35% vs 0.95%), and penile bulb (0.23% vs 0.49%). All improvements were statistically significant. CONCLUSIONS Use of population average tissue densities within the irradiated volume by the density override technique can improve the dosimetric accuracy of magnetic resonance imaging-based treatment plans for prostate cancer.


Medical Physics | 2014

TU-C-BRE-04: 3D Gel Dosimetry Using ViewRay On-Board MR Scanner: A Feasibility Study

L Zhang; D Du; O.L. Green; V Rodriguez; H Wooten; Zhiyan Xiao; Deshan Yang; Yanle Hu; H Li

PURPOSE MR based 3D gel has been proposed for radiation therapy dosimetry. However, access to MR scanner has been one of the limiting factors for its wide acceptance. Recent commercialization of an on-board MR-IGRT device (ViewRay) may render the availability issue less of a concern. This work reports our attempts to simulate MR based dose measurement accuracy on ViewRay using three different gels. METHODS A spherical BANG gel dosimeter was purchased from MGS Research. Cylindrical MAGIC gel and Fricke gel were fabricated in-house according to published recipes. After irradiation, BANG and MAGIC were imaged using a dual-echo spin echo sequence for T2 measurement on a Philips 1.5T MR scanner, while Fricke gel was imaged using multiple spin echo sequences. Difference between MR measured and TPS calculated dose was defined as noise. The noise power spectrum was calculated and then simulated for the 0.35 T magnetic field associated with ViewRay. The estimated noise was then added to TG-119 test cases to simulate measured dose distributions. Simulated measurements were evaluated against TPS calculated doses using gamma analysis. RESULTS Given same gel, sequence and coil setup, with a FOV of 180×90×90 mm3, resolution of 3×3×3 mm3, and scanning time of 30 minutes, the simulated measured dose distribution using BANG would have a gamma passing rate greater than 90% (3%/3mm and absolute). With a FOV 180×90×90 mm3, resolution of 4×4×5 mm3, and scanning time of 45 minutes, the simulated measuremened dose distribution would have a gamma passing rate greater than 97%. MAGIC exhibited similar performance while Fricke gel was inferior due to much higher noise. CONCLUSIONS The simulation results demonstrated that it may be feasible to use MAGIC and BANG gels for 3D dose verification using ViewRay low-field on-board MRI scanner.


Medical Physics | 2014

WE-G-17A-01: Improving Tracking Image Spatial Resolution for Onboard MR Image Guided Radiation Therapy Using the WHISKEE Technique

Yanle Hu; Sasa Mutic; D Du; O.L. Green; Q Zeng; Roger Nana; J Patrick; S Shvartsman

PURPOSE To evaluate the feasibility of using the weighted hybrid iterative spiral k-space encoded estimation (WHISKEE) technique to improve spatial resolution of tracking images for onboard MR image guided radiation therapy (MR-IGRT). METHODS MR tracking images of abdomen and pelvis had been acquired from healthy volunteers using the ViewRay onboard MRIGRT system (ViewRay Inc. Oakwood Village, OH) at a spatial resolution of 2.0mm*2.0mm*5.0mm. The tracking MR images were acquired using the TrueFISP sequence. The temporal resolution had to be traded off to 2 frames per second (FPS) to achieve the 2.0mm in-plane spatial resolution. All MR images were imported into the MATLAB software. K-space data were synthesized through the Fourier Transform of the MR images. A mask was created to selected k-space points that corresponded to the under-sampled spiral k-space trajectory with an acceleration (or undersampling) factor of 3. The mask was applied to the fully sampled k-space data to synthesize the undersampled k-space data. The WHISKEE method was applied to the synthesized undersampled k-space data to reconstructed tracking MR images at 6 FPS. As a comparison, the undersampled k-space data were also reconstructed using the zero-padding technique. The reconstructed images were compared to the original image. The relatively reconstruction error was evaluated using the percentage of the norm of the differential image over the norm of the original image. RESULTS Compared to the zero-padding technique, the WHISKEE method was able to reconstruct MR images with better image quality. It significantly reduced the relative reconstruction error from 39.5% to 3.1% for the pelvis image and from 41.5% to 4.6% for the abdomen image at an acceleration factor of 3. CONCLUSION We demonstrated that it was possible to use the WHISKEE method to expedite MR image acquisition for onboard MR-IGRT systems to achieve good spatial and temporal resolutions simultaneously. Y. Hu and O. green receive travel reimbursement from ViewRay. S. Mutic has consulting and research agreements with ViewRay. Q. Zeng, R. Nana, J.L. Patrick, S. Shvartsman and J.F. Dempsey are ViewRay employees.


Medical Physics | 2014

SU‐D‐17A‐06: A Criterion to Determine Appropriate Respiratory Sampling Range for Respiratory Amplitude Triggered 4DMRI

D Du; T Zhao; H Li; Sasa Mutic; Yanle Hu

PURPOSE To establish a criterion to determine appropriate respiratory sampling range for respiratory amplitude triggered 4D magnetic resonance imaging (MRI). The proposed criterion tried to seek a balance between triggering efficiency and motion coverage. METHODS Respiratory signal were acquired from 4 healthy volunteer using the pneumatic bellow. The respiratory sampling range was defined as a percentage of the full respiratory range. The triggering efficiency was determined by the percentage of breathing cycles that could cover respiratory sampling range. The triggering efficiency was plotted against the respiratory sampling range. Regions that could achieve at least 50% triggering efficiency and 80% of full respiratory range were identified. RESULTS A region that satisfies the criterion of at least 50% triggering efficiency and 80% of full respiratory range could be identified for all 4 volunteers, which offers a good balance between triggering efficiency and respiratory sampling range. CONCLUSIONS A practical and reasonable criterion has been established to determine appropriate respiratory sampling range for respiratory amplitude triggered 4DMRI. The respiratory sampling range determined by this criterion can guide the amplitude triggered 4DMRI scan efficiently and effectively.


Medical Physics | 2014

SU-E-J-157: Improving the Quality of T2-Weighted 4D Magnetic Resonance Imaging for Clinical Evaluation

D Du; S Caruthers; Carri Glide-Hurst; D Low; S Mutic; Yanle Hu

PURPOSE To develop an imaging technique that enables us to acquire T2- weighted 4D Magnetic Resonance Imaging (4DMRI) with sufficient spatial coverage, temporal resolution and spatial resolution for clinical evaluation. METHODS T2-weighed 4DMRI images were acquired from a healthy volunteer using a respiratory amplitude triggered T2-weighted Turbo Spin Echo sequence. 10 respiratory states were used to equally sample the respiratory range based on amplitude (0%, 20%i, 40%i, 60%i, 80%i, 100%, 80%e, 60%e, 40%e and 20%e). To avoid frequent scanning halts, a methodology was devised that split 10 respiratory states into two packages in an interleaved manner and packages were acquired separately. Sixty 3mm sagittal slices at 1.5mm in-plane spatial resolution were acquired to offer good spatial coverage and reasonable spatial resolution. The in-plane field of view was 375mm × 260mm with nominal scan time of 3 minutes 42 seconds. Acquired 2D images at the same respiratory state were combined to form the 3D image set corresponding to that respiratory state and reconstructed in the coronal view to evaluate whether all slices were at the same respiratory state. 3D image sets of 10 respiratory states represented a complete 4D MRI image set. RESULTS T2-weighted 4DMRI image were acquired in 10 minutes which was within clinical acceptable range. Qualitatively, the acquired MRI images had good image quality for delineation purposes. There were no abrupt position changes in reconstructed coronal images which confirmed that all sagittal slices were in the same respiratory state. CONCLUSION We demonstrated it was feasible to acquire T2-weighted 4DMRI image set within a practical amount of time (10 minutes) that had good temporal resolution (10 respiratory states), spatial resolution (1.5mm × 1.5mm × 3.0mm) and spatial coverage (60 slices) for future clinical evaluation.


Medical Physics | 2014

SU-E-J-142: Performance Study of Automatic Image-Segmentation Algorithms in Motion Tracking Via MR-IGRT

Yuan Feng; I Kawrakow; Jeffrey R. Olsen; Parag J. Parikh; C. Noel; H Wooten; D Du; S Mutic; Yanle Hu

PURPOSE Evaluate commonly used segmentation algorithms on a commercially available real-time MR image guided radiotherapy (MR-IGRT) system (ViewRay), compare the strengths and weaknesses of each method, with the purpose of improving motion tracking for more accurate radiotherapy. METHODS MR motion images of bladder, kidney, duodenum, and liver tumor were acquired for three patients using a commercial on-board MR imaging system and an imaging protocol used during MR-IGRT. A series of 40 frames were selected for each case to cover at least 3 respiratory cycles. Thresholding, Canny edge detection, fuzzy k-means (FKM), k-harmonic means (KHM), and reaction-diffusion level set evolution (RD-LSE), along with the ViewRay treatment planning and delivery system (TPDS) were included in the comparisons. To evaluate the segmentation results, an expert manual contouring of the organs or tumor from a physician was used as a ground-truth. Metrics value of sensitivity, specificity, Jaccard similarity, and Dice coefficient were computed for comparison. RESULTS In the segmentation of single image frame, all methods successfully segmented the bladder and kidney, but only FKM, KHM and TPDS were able to segment the liver tumor and the duodenum. For segmenting motion image series, the TPDS method had the highest sensitivity, Jarccard, and Dice coefficients in segmenting bladder and kidney, while FKM and KHM had a slightly higher specificity. A similar pattern was observed when segmenting the liver tumor and the duodenum. The Canny method is not suitable for consistently segmenting motion frames in an automated process, while thresholding and RD-LSE cannot consistently segment a liver tumor and the duodenum. CONCLUSION The study compared six different segmentation methods and showed the effectiveness of the ViewRay TPDS algorithm in segmenting motion images during MR-IGRT. Future studies include a selection of conformal segmentation methods based on image/organ-specific information, different filtering methods and their influences on the segmentation results. Parag Parikh receives research grant from ViewRay. Sasa Mutic has consulting and research agreements with ViewRay. Yanle Hu receives travel reimbursement from ViewRay. Iwan Kawrakow and James Dempsey are ViewRay employees.


Medical Physics | 2013

SU‐E‐J‐201: Correlations Between Mechanical and Structural Anisotropy: A Foundation for Non‐Invasively Assessing Radiation Injury

Yuan Feng; R Okamoto; D Du; Sasa Mutic; G Genin; P Bayly; Yanle Hu

Purpose: Tour long‐term goal is to develop techniques for evaluating radiation injury based upon mechanical changes to tissue. Here, we study the mechanical response of white matter ex vivo using dynamic shear testing (DST) and indentation testing in an animal model, with the goals of establishing in normal (non‐radiation‐injured) tissue (1) a baseline degree of mechanical anisotropy, and (2) correlations between mechanical and structural anisotropy. Methods: Fresh whole brains were acquired from local slaughter house. White matter samples were dissected and from the central corpus callosum region, while gray matter samples were acquired from temporal region. Dynamic shear testing and indentation testing were applied to both white and gray matter samples. White matter samples were tested in shear with axonal fibers aligned or perpendicular to the shear force direction, and in indentation with the fiber axis parallel or perpendicular to the long side of the indenter head. Gray matter samples were tested in an arbitrary direction and rotated 90 degrees for the second test, for each testing procedure. Shear modulus and indentation stiffness were calculated for each sample. Results: The storage and loss moduli of the white matter samples were significantly larger when the samples were tested with primary axonal fibers aligned with the shearing direction. The indentation stiffness was also significantly higher when indented perpendicular to the fiber direction. No significant differences were observed for gray matter samples for both testing procedures. Conclusion: The results confirm that white matter exhibits larger moduli when stretched or sheared along the fiber direction; mechanical anisotropy correlates with structural anisotropy. The mechanical isotropy observed in gray matter is consistent with the structural isotropy. These results will be useful for investigations of changes in mechanical properties after radiation therapy in cerebral tumor patients, and for numerical modeling of surgery and traumatic brain injury (TBI).


Medical Physics | 2013

SU‐E‐J‐178: Patient‐Specific Bulk Electron Density Overridden Planning for Prostate and Brain Cancer

D Du; H Wooten; Yuan Feng; Jeffrey R. Olsen; S Mutic; Yanle Hu

Purpose: To evaluate the use of patient‐specific bulk electron density overridden plans for prostate and brain IMRT dose calculations. Methods: CT images and IMRT treatment plans for 10 prostate cancer patients and 10 brain cancer patients were retrospectively reviewed and analyzed. For each patient, a region of interest(ROI) was selected to cover all radiation beam paths plus 1cm margins in both superior and inferior directions. Patient anatomy within the ROI was segmented into fat, non‐fat soft tissue, bone and air based on CT number ranges of [−,‐50], [−,49,200], [201,4000], [− 1200,−800], respectively. Average electron densities for each tissue type were obtained from CT values for each patient, and all plans were recalculated on patient‐specific density overridden datasets to generate patient‐specific bulk density overridden plans. These overridden plans were compared to the clinically approved CT‐based plan using dose‐volume metrics for PTV coverage and OAR sparing. Results: Dose deviations between the patient‐specific density overridden plan and the clinically approved plan were minimal. Most parameters used to describe planning target volume coverage and OAR sparing were within 0.3% of approved CT based plans and all parameters were within 1% of the approved CT based plans. Conclusion: This study demonstrates that by assigning patient‐specific bulk electron densities to different tissue types, the dosimetric error of the patient‐specific bulk density overridden plans is within 1% of the approved CT based plan. This, patient‐specific bulk density override technique may potentially be used to map the CT values from CT images to MR images.

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Yanle Hu

Washington University in St. Louis

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Sasa Mutic

Washington University in St. Louis

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O.L. Green

Washington University in St. Louis

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H Li

Washington University in St. Louis

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H Wooten

Washington University in St. Louis

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H. Harold Li

Washington University in St. Louis

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J.R. Olsen

Washington University in St. Louis

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O. Wooten

Washington University in St. Louis

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Parag J. Parikh

Washington University in St. Louis

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S Mutic

University of Washington

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