Jeffrey H. Siewerdsen
Other affiliations: University of Michigan, University of Toronto, University of Rochester ...read more
Bio: Jeffrey H. Siewerdsen is an academic researcher from Johns Hopkins University. The author has contributed to research in topics: Image quality & Imaging phantom. The author has an hindex of 63, co-authored 513 publications receiving 17202 citations. Previous affiliations of Jeffrey H. Siewerdsen include University of Michigan & University of Toronto.
Papers published on a yearly basis
TL;DR: A kV cone-beam CT imaging system based on a large-area, flat-panel detector has been successfully adapted to a medical linear accelerator and is capable of producing images of soft tissue with excellent spatial resolution at acceptable imaging doses.
Abstract: Purpose: Geometric uncertainties in the process of radiation planning and delivery constrain dose escalation and induce normal tissue complications. An imaging system has been developed to generate high-resolution, soft-tissue images of the patient at the time of treatment for the purpose of guiding therapy and reducing such uncertainties. The performance of the imaging system is evaluated and the application to image-guided radiation therapy is discussed. Methods and Materials: A kilovoltage imaging system capable of radiography, fluoroscopy, and cone-beam computed tomography (CT) has been integrated with a medical linear accelerator. Kilovoltage X-rays are generated by a conventional X-ray tube mounted on a retractable arm at 90° to the treatment source. A 41 × 41 cm 2 flat-panel X-ray detector is mounted opposite the kV tube. The entire imaging system operates under computer control, with a single application providing calibration, image acquisition, processing, and cone-beam CT reconstruction. Cone-beam CT imaging involves acquiring multiple kV radiographs as the gantry rotates through 360° of rotation. A filtered back-projection algorithm is employed to reconstruct the volumetric images. Geometric nonidealities in the rotation of the gantry system are measured and corrected during reconstruction. Qualitative evaluation of imaging performance is performed using an anthropomorphic head phantom and a coronal contrast phantom. The influence of geometric nonidealities is examined. Results: Images of the head phantom were acquired and illustrate the submillimeter spatial resolution that is achieved with the cone-beam approach. High-resolution sagittal and coronal views demonstrate nearly isotropic spatial resolution. Flex corrections on the order of 0.2 cm were required to compensate gravity-induced flex in the support arms of the source and detector, as well as slight axial movements of the entire gantry structure. Images reconstructed without flex correction suffered from loss of detail, misregistration, and streak artifacts. Reconstructions of the contrast phantom demonstrate the soft-tissue imaging capability of the system. A contrast of 47 Hounsfield units was easily detected in a 0.1-cm-thick reconstruction for an imaging exposure of 1.2 R (in-air, in absence of phantom). The comparison with a conventional CT scan of the phantom further demonstrates the spatial resolution advantages of the cone-beam CT approach. Conclusions: A kV cone-beam CT imaging system based on a large-area, flat-panel detector has been successfully adapted to a medical linear accelerator. The system is capable of producing images of soft tissue with excellent spatial resolution at acceptable imaging doses. Integration of this technology with the medical accelerator will result in an ideal platform for high-precision, image-guided radiation therapy.
TL;DR: The analytical model for CNR provides a quantitative understanding of the relationship between CNR, dose, and spatial resolution and allows knowledgeable selection of the acquisition and reconstruction parameters that, for a given SPR, are required to restore the CNR to values achieved under conditions of low x-ray scatter.
Abstract: A system for cone-beam computed tomography (CBCT) based on a flat-panel imager (FPI) is used to examine the magnitude and effects of x-ray scatter in FPI-CBCT volume reconstructions. The system is being developed for application in image-guided therapies and has previously demonstrated spatial resolution and soft-tissue visibility comparable or superior to a conventional CT scanner under conditions of low x-ray scatter. For larger objects consistent with imaging of human anatomy (e.g., the pelvis) and for increased cone angle (i.e., larger volumetric reconstructions), however, the effects of x-ray scatter become significant. The magnitude of x-ray scatter with which the FPI-CBCT system must contend is quantified in terms of the scatter-to-primary energy fluence ratio (SPR) and scatter intensity profiles in the detector plane, each measured as a function of object size and cone angle. For large objects and cone angles (e.g., a pelvis imaged with a cone angle of 6 degrees), SPR in excess of 100% is observed. Associated with such levels of x-ray scatter are cup and streak artifacts as well as reduced accuracy in reconstruction values, quantified herein across a range of SPR consistent with the clinical setting. The effect of x-ray scatter on the contrast, noise, and contrast-to-noise ratio (CNR) in FPI-CBCT reconstructions was measured as a function of SPR and compared to predictions of a simple analytical model. The results quantify the degree to which elevated SPR degrades the CNR. For example, FPI-CBCT images of a breast-equivalent insert in water were degraded in CNR by nearly a factor of 2 for SPR ranging from approximately 2% to 120%. The analytical model for CNR provides a quantitative understanding of the relationship between CNR, dose, and spatial resolution and allows knowledgeable selection of the acquisition and reconstruction parameters that, for a given SPR, are required to restore the CNR to values achieved under conditions of low x-ray scatter. For example, for SPR = 100%, the CNR in FPI-CBCT images can be fully restored by: (1) increasing the dose by a factor of 4 (at full spatial resolution); (2) increasing dose and slice thickness by a factor of 2; or (3) increasing slice thickness by a factor of 4 (with no increase in dose). Other reconstruction parameters, such as transaxial resolution length and reconstruction filter, can be similarly adjusted to achieve CNR equal to that obtained in the scatter-free case.
TL;DR: The development and performance of a system for x-ray cone-beam computed tomography using an indirect-detection flat-panel imager (FPI) is presented, and the applicability of FPI-based CBCT systems to tomographic localization and image-guidance for radiotherapy is considered.
Abstract: The development and performance of a system for x-ray cone-beam computed tomography (CBCT) using an indirect-detection flat-panel imager (FPI) is presented. Developed as a bench-top prototype for initial investigation of FPI-based CBCT for bone and soft-tissue localization in radiotherapy, the system provides fully three-dimensional volumetric image data from projections acquired during a single rotation. The system employs a 512 x 512 active matrix of a-Si:H thin-film transistors and photodiodes in combination with a luminescent phosphor. Tomographic imaging performance is quantified in terms of response uniformity, response linearity, voxel noise, noise-power spectrum (NPS), and modulation transfer function (MTF), each in comparison to the performance measured on a conventional CT scanner. For the geometry employed and the objects considered, response is uniform to within 2% and linear within 1%. Voxel noise, at a level of approximately 20 HU, is comparable to the conventional CT scanner. NPS and MTF results highlight the frequency-dependent transfer characteristics, confirming that the CBCT system can provide high spatial resolution and does not suffer greatly from additive noise levels. For larger objects and/or low exposures, additive noise levels must be reduced to maintain high performance. Imaging studies of a low-contrast phantom and a small animal (a euthanized rat) qualitatively demonstrate excellent soft-tissue visibility and high spatial resolution. Image quality appears comparable or superior to that of the conventional scanner. These quantitative and qualitative results clearly demonstrate the potential of CBCT systems based upon flat-panel imagers. Advances in FPI technology (e.g., improved x-ray converters and enhanced electronics) are anticipated to allow high-performance FPI-based CBCT for medical imaging. General and specific requirements of kilovoltage CBCT systems are discussed, and the applicability of FPI-based CBCT systems to tomographic localization and image-guidance for radiotherapy is considered.
TL;DR: Investigation and evaluation of image reconstruction from data collected at projection views significantly fewer than what is used in current CBCT imaging demonstrate that, depending upon scanning conditions and imaging tasks, algorithms based on constrained TV-minimization can reconstruct images of potential utility from a small fraction of the data used in typical, currentCBCT applications.
Abstract: Flat-panel-detector x-ray cone-beam computed tomography (CBCT) is used in a rapidly increasing host of imaging applications, including image-guided surgery and radiotherapy. The purpose of the work is to investigate and evaluate image reconstruction from data collected at projection views significantly fewer than what is used in current CBCT imaging. Specifically, we carried out imaging experiments using a bench-top CBCT system that was designed to mimic imaging conditions in image-guided surgery and radiotherapy; we applied an image reconstruction algorithm based on constrained total-variation (TV)-minimization to data acquired with sparsely sampled view-angles and conducted extensive evaluation of algorithm performance. Results of the evaluation studies demonstrate that, depending upon scanning conditions and imaging tasks, algorithms based on constrained TV-minimization can reconstruct images of potential utility from a small fraction of the data used in typical, current CBCT applications. A practical implication of the study is that the optimization of algorithm design and implementation can be exploited for considerably reducing imaging effort and radiation dose in CBCT.
TL;DR: Motion of the prostate and seminal vesicles during a time frame similar to a standard treatment session is reduced compared to that reported in interfraction studies.
Abstract: PURPOSE: To quantify prostate motion during a radiation therapy treatment using cine-magnetic resonance imaging (cine-MRI) for time frames comparable to that expected in an image-guided radiation therapy treatment session (20-30 min). MATERIALS AND METHODS: Six patients undergoing radiation therapy for prostate cancer were imaged on 3 days, over the course of therapy (Weeks 1, 3, and 5). Four hundred images were acquired during the 1-h MRI session in 3 sagittal planes through the prostate at 6-s intervals. Eleven anatomic points of interest (POIs) have been used to characterize prostate/bony pelvis/abdominal wall displacement. Motion traces and standard deviation for each of the 11 POIs have been determined. The probability of displacement over time has also been calculated. RESULTS: Patients were divided into 2 groups according to rectal filling status: full vs. empty rectum. The displacement of POIs (standard deviation) ranged from 0.98 to 1.72 mm for the full-rectum group and from 0.68 to 1.04 mm for the empty-rectum group. The low standard deviations in position (2 mm or less) would suggest that these excursions have a low frequency of occurrence. The most sensitive prostate POI to rectal wall motion was the mid-posterior with a standard deviation of 1.72 mm in the full-rectum group vs. 0.79 mm in the empty-rectum group (p = 0.0001). This POI has a 10% probability of moving more than 3 mm in a time frame of approximately 1 min if the rectum is full vs. approximately 20 min if the rectum is empty. CONCLUSION: Motion of the prostate and seminal vesicles during a time frame similar to a standard treatment session is reduced compared to that reported in interfraction studies. The most significant predictor for intrafraction prostate motion is the status of rectal filling. A prostate displacement of <3 mm (90%) can be expected for the 20 min after the moment of initial imaging for patients with an empty rectum. This is not the case for patients presenting with full rectum. The determination of appropriate intrafraction margins in radiation therapy to accommodate the time-dependent uncertainty in positional targeting is a topic of ongoing investigations for the on-line image guidance model.
TL;DR: An overview of 3D Slicer is presented as a platform for prototyping, development and evaluation of image analysis tools for clinical research applications and the utility of the platform in the scope of QIN is illustrated.
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.
01 Jan 2000
TL;DR: This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices, in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation.
Abstract: NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …
01 Jan 2004
TL;DR: Comprehensive and up-to-date, this book includes essential topics that either reflect practical significance or are of theoretical importance and describes numerous important application areas such as image based rendering and digital libraries.
Abstract: From the Publisher: The accessible presentation of this book gives both a general view of the entire computer vision enterprise and also offers sufficient detail to be able to build useful applications. Users learn techniques that have proven to be useful by first-hand experience and a wide range of mathematical methods. A CD-ROM with every copy of the text contains source code for programming practice, color images, and illustrative movies. Comprehensive and up-to-date, this book includes essential topics that either reflect practical significance or are of theoretical importance. Topics are discussed in substantial and increasing depth. Application surveys describe numerous important application areas such as image based rendering and digital libraries. Many important algorithms broken down and illustrated in pseudo code. Appropriate for use by engineers as a comprehensive reference to the computer vision enterprise.
TL;DR: An iterative algorithm, based on recent work in compressive sensing, that minimizes the total variation of the image subject to the constraint that the estimated projection data is within a specified tolerance of the available data and that the values of the volume image are non-negative is developed.
Abstract: An iterative algorithm, based on recent work in compressive sensing, is developed for volume image reconstruction from a circular cone-beam scan. The algorithm minimizes the total variation (TV) of the image subject to the constraint that the estimated projection data is within a specified tolerance of the available data and that the values of the volume image are non-negative. The constraints are enforced by the use of projection onto convex sets (POCS) and the TV objective is minimized by steepest descent with an adaptive step-size. The algorithm is referred to as adaptive-steepest-descent-POCS (ASD-POCS). It appears to be robust against cone-beam artifacts, and may be particularly useful when the angular range is limited or when the angular sampling rate is low. The ASD-POCS algorithm is tested with the Defrise disk and jaw computerized phantoms. Some comparisons are performed with the POCS and expectation-maximization (EM) algorithms. Although the algorithm is presented in the context of circular cone-beam image reconstruction, it can also be applied to scanning geometries involving other x-ray source trajectories.
TL;DR: Significant advances in the techniques of radiation treatment and progress made in understanding the biology of cancer cell responses to radiation will endeavor to increase the survival and reduce treatment side effects for cancer patients.
Abstract: In recent years remarkable progress has been made towards the understanding of proposed hallmarks of cancer development and treatment. However with its increasing incidence, the clinical management of cancer continues to be a challenge for the 21st century. Treatment modalities comprise of radiation therapy, surgery, chemotherapy, immunotherapy and hormonal therapy. Radiation therapy remains an important component of cancer treatment with approximately 50% of all cancer patients receiving radiation therapy during their course of illness; it contributes towards 40% of curative treatment for cancer. The main goal of radiation therapy is to deprive cancer cells of their multiplication (cell division) potential. Celebrating a century of advances since Marie Curie won her second Nobel Prize for her research into radium, 2011 has been designated the Year of Radiation therapy in the UK. Over the last 100 years, ongoing advances in the techniques of radiation treatment and progress made in understanding the biology of cancer cell responses to radiation will endeavor to increase the survival and reduce treatment side effects for cancer patients. In this review, principles, application and advances in radiation therapy with their biological end points are discussed.