[Show abstract][Hide abstract] ABSTRACT: The addition of a pair of magnetic field gradient pulses had initially provided the measurement of spin motion with nuclear magnetic resonance (NMR) techniques. In the adaptation of DW-NMR techniques to magnetic resonance imaging (MRI), the taxonomy of mathematical models is divided in two categories: model matching and spectral methods. In this review, the methods are summarized starting from early diffusion weighted (DW) NMR models followed up with their adaptation to DW MRI. Finally, a newly introduced Fourier analysis based unifying theory, so-called Complete Fourier Direct MRI, is included to explain the mechanisms of existing methods.
International Journal of Imaging Systems and Technology 03/2012; 22(1):44-52. · 0.64 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Small mammals, namely mice and rats, play an important role in biomedical research. Imaging, in conjunction with accurate therapeutic agent delivery, has tremendous value in small animal research since it enables serial, non-destructive testing of animals and facilitates the study of biomarkers of disease progression. The small size of organs in mice lends some difficulty to accurate biopsies and therapeutic agent delivery. Image guidance with the use of robotic devices should enable more accurate and repeatable targeting for biopsies and delivery of therapeutic agents, as well as the ability to acquire tissue from a pre-specified location based on image anatomy. This paper presents our work in integrating a robotic needle guide device, specialized stereotaxic mouse holder, and magnetic resonance imaging, with a long-term goal of performing accurate and repeatable targeting in anesthetized mice studies.
[Show abstract][Hide abstract] ABSTRACT: Blast-related traumatic brain injury (bTBI) and post-traumatic stress disorder (PTSD) have been of particular relevance to the military and civilian health care sectors since the onset of the Global War on Terror, and TBI has been called the "signature injury" of this war. Currently there are many questions about the fundamental nature, diagnosis, and long-term consequences of bTBI and its relationship to PTSD. This workshop was organized to consider these questions and focus on how brain imaging techniques may be used to enhance current diagnosis, research, and treatment of bTBI. The general conclusion was that although the study of blast physics in non-biological systems is mature, few data are presently available on key topics such as blast exposure in combat scenarios, the pathological characteristics of human bTBI, and imaging signatures of bTBI. Addressing these gaps is critical to the success of bTBI research. Foremost among our recommendations is that human autopsy and pathoanatomical data from bTBI patients need to be obtained and disseminated to the military and civilian research communities, and advanced neuroimaging used in studies of acute, subacute, and chronic cases, to determine whether there is a distinct pathoanatomical signature that correlates with long-term functional impairment, including PTSD. These data are also critical for the development of animal models to illuminate fundamental mechanisms of bTBI and provide leads for new treatment approaches. Brain imaging will need to play an increasingly important role as gaps in the scientific knowledge of bTBI and PTSD are addressed through increased coordination, cooperation, and data sharing among the academic and military biomedical research communities.
Journal of neurotrauma 07/2009; 26(12):2127-44. · 4.25 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Combat medics have a vital role in the protection of wounded soldiers in the battlespace. However, their duties expose them to great risks. Furthermore, these medics are a limited resource and must be carefully tasked in order to provide maximum benefit to their units. For these reasons, we are applying the American GNC Corporation's (AGNC) Coremicro(R) Robotic System for autonomous evaluation of battlefield casualties. These robots are intended to navigate to a casualty, determine his/her overall health status, and perform limited diagnostic imaging in order to assess the presence of injuries that would prevent or complicate extraction. In this paper, we describe development work on some of the key components of the proposed robotic system, namely the overall concept of operations (ConOps) and initial testing of infrared and ultrasound imaging cameras. When fully deployed, this system will act as a medical force multiplier, enabling improved care of wounded soldiers and protecting the health and safety of military medical personnel.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 01/2009; 2009:467-70.
[Show abstract][Hide abstract] ABSTRACT: The current climate of rapid technological evolution is reflected in newer and better methods to modulate and direct radiation beams for cancer therapy. This Vision 20/20 paper focuses on part of this evolution, locating and targeting moving tumors. The two processes are somewhat independent and in principle different implementations of the locating and targeting processes can be interchanged. Advanced localization and targeting methods have an impact on treatment planning and also present new challenges for quality assurance (QA), that of verifying real-time delivery. Some methods to locate and target moving tumors with radiation beams are currently FDA approved for clinical use-and this availability and implementation will increase with time. Extensions of current capabilities will be the integration of higher order dimensionality, such as rotation and deformation in addition to translation, into the estimate of the patient pose and real-time reoptimization and adaption of delivery to the dynamically changing anatomy of cancer patients.
Medical Physics 01/2009; 35(12):5684-94. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We are currently developing a PET/CT based navigation system for guidance of biopsies and radiofrequency ablation (RFA) of early stage hepatic tumors. For these procedures, combined PET/CT data can potentially improve current interventions. The diagnostic efficacy of biopsies can potentially be improved by accurately targeting the region within the tumor that exhibits the highest metabolic activity. For RFA procedures the system can potentially enable treatment of early stage tumors, targeting tumors before structural abnormalities are clearly visible on CT. In both cases target definition is based on the metabolic data (PET), and navigation is based on the spatial data (CT), making the system highly dependent upon accurate spatial alignment between these data sets. In our institute all clinical data sets include three image volumes: one CT, and two PET volumes, with and without CT-based attenuation correction. This paper studies the effect of the CT-based attenuation correction on the registration process. From comparing the pairs of registrations from five data sets we observe that the point motion magnitude difference between registrations is on the same scale as the point motion magnitude in each one of the registrations, and that visual inspection cannot identify this discrepancy. We conclude that using non-rigid registration to align the PET and CT data sets is too variable, and most likely does not provide sufficient accuracy for interventional procedures.
[Show abstract][Hide abstract] ABSTRACT: PET (Positron Emission Tomography) scanning has become a dominant force in oncology care because of its ability to identify regions of abnormal function. The current generation of PET scanners is focused on whole-body imaging, and does not address aspects that might be required by surgeons or other practitioners interested in the function of particular body parts. We are therefore developing and testing a new class of hand-operated molecular imaging scanners designed for use with physical examinations and intraoperative visualization. These devices integrate several technological advances, including (1) nanotechnology-based quantum photodetectors for high performance at low light levels, (2) continuous position tracking of the detectors so that they form a larger 'virtual detector', and (3) novel reconstruction algorithms that do not depend on a circular or ring geometry. The first incarnations of this device will be in the form of a glove with finger-mounted detectors or in a "sash" of detectors that can be draped over the patient. Potential applications include image-guided biopsy, surgical resection of tumors, assessment of inflammatory conditions, and early cancer detection. Our first prototype is in development now along with a clinical protocol for pilot testing.
[Show abstract][Hide abstract] ABSTRACT: Dynamically compensating for target motion during radiotherapy will increase treatment accuracy. A laboratory system for real-time target tracking with a dynamic MLC has been developed. In this study, the geometric accuracy limits of this DMLC target tracking system were evaluated.
A motion simulator was programmed to follow patient-derived tumor motion paths, parallel to the leaf motion direction. A target attached to the simulator was optically tracked, and the leaf positions adjusted to continually align the DMLC beam aperture to the target. Analysis of the tracking accuracy was based on video images of the target and beam alignment. The system response time was determined and the tracking error measured. Response time-corrected tracking accuracy was also calculated to investigate the accuracy limits of an improved system.
The response time of the system is 160 +/- 2 ms. The geometric precision for tracking patient motion is 0.6 to 1.1 mm (1 sigma) for the 3 patient datasets tested, with tracking errors relative to the original patient motion of 35, 40, and 100%.
A DMLC target tracking system has been developed that can account for detected motion parallel to the leaf motion direction. The tracking error has a negligible systematic component. Reducing the response time will further increase the overall system accuracy.
International Journal of Radiation OncologyBiologyPhysics 09/2006; 65(5):1579-84. · 4.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Dynamic or 4D images (in which a section of the body is repeatedly imaged in order to capture physiological motion) are becoming increasingly important in medicine. These images are especially critical to the field of image-guided therapy, because they enable treatment planning that reflects the realistic motion of the therapy target. Although it is possible to acquire static images and deform them based on generalized assumptions of normal motion, such an approach does not account for variability in the individual patient. To enable the most effective treatments, it is necessary to be able to image each patient and characterize their unique respiratory motion, but software specifically designed around the needs of 4D imaging is not widely available. We have constructed an open source application that allows a user to manipulate and analyze 4D image data. This interface can load DICOM images into memory, reorder/rebin them if necessary, and then apply deformable registration methods to derive the respiratory motion. The interface allows output and display of the deformation field, display of images with the deformation field as an overlay, and tables and graphs of motion versus time. The registration is based on the open source Insight Toolkit (ITK) and the interface is constructed using the open source GUI tool FLTK, which will make it easy to distribute and extend this software in the future.
[Show abstract][Hide abstract] ABSTRACT: 4D images (3 spatial dimensions plus time) using CT or MRI will play a key role in radiation medicine as techniques for respiratory motion compensation become more widely available. Advance knowledge of the motion of a tumor and its surrounding anatomy will allow the creation of highly conformal dose distributions in organs such as the lung, liver, and pancreas. However, many of the current investigations into 4D imaging rely on synchronizing the image acquisition with an external respiratory signal such as skin motion, tidal flow, or lung volume, which typically requires specialized hardware and modifications to the scanner. We propose a novel method for 4D image acquisition that does not require any specific gating equipment and is based solely on open source image registration algorithms. Specifically, we use the Insight Toolkit (ITK) to compute the normalized mutual information (NMI) between images taken at different times and use that value as an index of respiratory phase. This method has the advantages of (1) being able to be implemented without any hardware modification to the scanner, and (2) basing the respiratory phase on changes in internal anatomy rather than external signal. We have demonstrated the capabilities of this method with CT fluoroscopy data acquired from a swine model.
[Show abstract][Hide abstract] ABSTRACT: An effective treatment method for organs that move with respiration (such as the lungs, pancreas, and liver) is a major goal of radiation medicine. In order to treat such tumors, we need (1) real-time knowledge of the current location of the tumor, and (2) the ability to adapt the radiation delivery system to follow this constantly changing location. In this study, we used electromagnetic tracking in a swine model to address the first challenge, and to determine if movement of a marker attached to the skin could accurately predict movement of an internal marker embedded in an organ. Under approved animal research protocols, an electromagnetically tracked needle was inserted into a swine liver and an electromagnetically tracked guidewire was taped to the abdominal skin of the animal. The Aurora (Northern Digital Inc., Waterloo, Canada) electromagnetic tracking system was then used to monitor the position of both of these sensors every 40 msec. Position readouts from the sensors were then tested to see if any of the movements showed correlation. The strongest correlations were observed between external anterior-posterior motion and internal inferior-superior motion, with many other axes exhibiting only weak correlation. We also used these data to build a predictive model of internal motion by taking segments from the data and using them to derive a general functional relationship between the internal needle and the external guidewire. For the axis with the strongest correlation, this model enabled us to predict internal organ motion to within 1 mm.
[Show abstract][Hide abstract] ABSTRACT: Tracking organ motion due to respiration is important for precision
treatments in interventional radiology and radiation oncology, among
other areas. In interventional radiology, the ability to track and
compensate for organ motion could lead to more precise biopsies for
applications such as lung cancer screening. In radiation oncology,
image-guided treatment of tumors is becoming technically possible, and
the management of organ motion then becomes a major issue. This paper
will review the state-of-the-art in respiratory motion and present two
related clinical applications. Respiratory motion is an important topic
for future work in image-guided surgery and medical robotics. Issues
include how organs move due to respiration, how much they move, how the
motion can be compensated for, and what clinical applications can
benefit from respiratory motion compensation. Technology that can be
applied for this purpose is now becoming available, and as that
technology evolves, the subject will become an increasingly interesting
and clinically valuable topic of research.