Benchtop experiments have proven the utility of a stationary computed tomography (CT) scanner for head imaging. The purpose of this study was for system control development and integration in a clinical setting for clinical use and evaluation. Software and interfaces for technologist operation of the complete system during patient scanning were also developed. A clinical imaging bed was integrated with the x-ray control system with off-the-shelf microcontrollers to drive the development of the system for clinical evaluation. The clinical imaging system is composed of three carbon nanotube (CNT) x-ray source arrays and nine strip detectors. 135 projections are acquired per slice at 120kVp, 10mA, and 2.95ms exposure per projection. Anthropomorphic phantoms have been imaged in preparation for the first patients. Reconstruction was performed using adaptive steepest descent projection onto convex set (ASD-POCs) method. Scanner performance parameters were measured. Images are evaluated by neuroradiologists. A working stationary head CT (sHCT) system has been developed for patient imaging evaluation. Image quality is sufficient for starting the observational clinical trial as shown in images of the ACR accreditation phantom and KYOTO head phantoms. This preliminary study has shown that the sHCT system is ready for patient imaging studies. Clinical utility will be assessed in a patient study with patients with prior head trauma.
We demonstrate a prototypical orthogonal tomosynthesis (OT) system for potential whole-body scanning. The system is enabled by a carbon nanotube (CNT) linear x-ray source array positioned orthogonally to a limited field-of-view (FOV) detector. The multiple X-ray sources are individually addressed to acquire sets of projections while translating the sample over a fixed collimated strip on the detector for full-volume coverage. The OT system was constructed by adding a multislot collimator and a translation bed to the existing stationary digital chest tomosynthesis (s-DCT) system. The OT system was evaluated against the s-DCT system by imaging an anthropomorphic chest phantom. Nine equally spaced x-ray sources spanning ~14° were selected to acquire projections of the phantom at multiple discrete translation steps measuring 19 mm. Qualitatively, feature conspicuity of soft tissue and osseous thoracic structure in the OT reconstruction was comparable to the s-DCT reconstruction. The results of this singular experiment demonstrate the feasibility of using CNTbased tomosynthesis as a whole-body imager for mobile on-field applications.
Purpose: The purpose of this study was to evaluate a novel stationary head CT system (sHCT) enabled by the carbon nanotube (CNT) field emission x-ray source array for volumetric head imaging. A data processing and image reconstruction package was developed and demonstrated for the system. Methods: The experimental sHCT system consisted of three CNT x-ray source arrays placed in parallel imaging planes separately. During imaging, the sources stayed stationary while only the bed advancing through a tunnel formed by the parallel planes. In each imaging cycle, 135 projections were acquired over 232 degrees of view. A CT ACR 464 phantom and a Kyoto head phantom were imaged to evaluate the system performance. Image uniformity, signal to noise ratio, spatial resolution, CT number and detectability were investigated for the proposed system. All images were processed and reconstructed with an iterative reconstruction-based package. Total-variation (TV) regularization methods such as the adaptive steepest descent projection onto convex set (ASDPOCS) algorithm were implemented to reduce noises and artifacts caused by the reduced projection views. Results: Volumetric data with good uniformity, high spatial resolution, and detectability for both high- and low-resolution features were demonstrated for the proposed sHCT scanner. Two scan protocols, step-and-shoot and continuous mode were compared and proved to provide similar image quality while the latter increased the total scan speed. The SIRTASDPOCS algorithm effectively suppressed the sparse-view and limited-view artifact and enhance the contrast noise ratio. Conclusion: We demonstrated the feasibility of sHCT for volumetric head imaging using multiple CNT x-ray source arrays. The device provides 3D images with high fidelity. The prototype sHCT system is being installed at the UNC hospital for a patient imaging study.
Cone-beam computed tomography (CBCT) provides volumetric scans while keeping a relatively low dose and cost. This characteristic makes CBCT favorable in the field of dentistry, but the frequent presence of metallic objects in patients causes metal artifact that severely degrades the resulting images. Dual-energy CT provides more information about the materials which can be used to synthesize virtual monoenergetic images (VMI) to reduce metal artifacts. In this work, we investigated and optimized a dual-energy cone-beam CT (DE-CBCT) system using a carbon-nanotube CNT x-ray source with dual focal spots and spectral filtrations. We used two x-ray spectra generated by applying spectral filters at a constant x-ray tube voltage. We imaged an anthropomorphic head phantom with metal beads. The projection images were reconstructed separately using an iterative CT reconstruction algorithm and bilateral filtering is applied to the reconstructed images for denoising. The VMIs were synthesized from the denoised reconstructed images using an image domain decomposition method and displayed noise comparable to the images obtained from a single energy. The resulting VMIs displayed fewer metal artifacts compared to the single energy images of the same object from a clinical CBCT scanner. To optimize the spectral separation, we implemented a filter selection algorithm and improved the mean energy separation from 13keV to 17.5keV while maintaining the same x-ray output. We also demonstrated the ability of this system to independently control the imaging dose of the two energy scans by varying the x-ray exposure current and time using the dual focal spot CNT source.
X-ray Computed Tomography (CT) is an indispensable imaging modality in the medical field, notably in the diagnosis of traumatic brain injury and brain hemorrhage. Existing clinical CT systems, all of which use rotating x-ray sources, are too complex for practical deployment in resource-poor environments. A stationary array of sources and detectors with sufficient angular coverage and focal spot density could potentially simplify the image acquisition hardware and generate adequate projection data for CT reconstruction. In this study, we present a stationary head CT (s-HCT) prototype which combines projection data from three separate but parallel imaging planes into a complete volumetric iterative CT reconstruction. The fully operational scanner features three carbon nanotube (CNT) x-ray source arrays with 45 distributed focal spots each, and an Electronic Control System (ECS) for high speed control of the x-ray exposure from each focal spot. Projection data is acquired by translating the object along the z-axis at constant speed to expose all three imaging planes for the full dataset. As the object is moving at constant speed, 135 views are collected every 0.44 s (cycle time). The 3D iterative reconstruction designed specifically for the s-HCT configuration has been used to produce phantom images for initial assessment of the spatial resolution. A linear collimator was designed and constructed for the reduction of cross-plane scatter. Finally, the prototype has been able to acquire these images in scan times comparable to those of commercial scanners (<1min), indicating the CNT x-ray and s-HCT technologies are developed enough for clinical trials.
Purpose: The invention of carbon nanotube (CNT) x-ray source arrays has enabled the development of novel imaging systems, including stationary tomosynthesis and stationary computed tomography (CT) with fast data acquisition, mechanically robust structures, and reduced image blur from source–detector motion. In this work, we report the results of simulation studies of potential system configurations for a stationary head CT (s-HCT) using linear CNT x-ray sources and detector arrays.
Approach: We explored s-HCT configurations that utilize one, two, and three linear CNT source arrays. Simulations were implemented using three digital phantoms with both CPU and GPU computing. Sinogram coverage was used for qualitative evaluation of the CT projection collection efficiency for each configuration. A modified low-contrast Shepp–Logan (SL) phantom was implemented for image quality assessment using quantitative metrics. Different iterative reconstruction (IR) methods were compared with both qualitative and quantitative assessments.
Results: Sinogram coverage of s-HCT configurations was sensitive to the number of CNT source arrays and geometry. The simulations suggest that a s-HCT configuration with three planes gives near complete sinogram coverage. Such a configuration enables accurate reconstruction of the low-contrast SL phantom and considerably diminished artifacts caused by the system geometry.
Conclusions: An optimized s-HCT system configuration with three linear CNT x-ray source arrays is feasible. IR algorithms can diminish artifacts caused by sparse and asymmetrical scans. The proposed s-HCT system configuration is currently under construction.
X-ray Computed Tomography (CT) is an indispensable imaging modality in the diagnosis of traumatic brain injury and brain hemorrhage. While the technology and the associated system components have been refined over the last several decades, all modern CT systems still rely on the principle of rotating sources and detectors. The rotating gantry adds a high degree of complexity to the overall system design, and could be eliminated in favor of a configuration of stationary x-ray sources and detectors. Such a change could potentially enable CT systems to be better suited for austere environments. Furthermore, the image acquisition speed would no longer be limited by the maximum rotating speed of the gantry. Unfortunately, due to the size and bulk of existing commercial x-ray sources, such a configuration is impossible to build with a sufficient number of focal spots. Recently, carbon nanotube (CNT) x-ray source arrays have been used in various stationary imaging configurations to generate diagnostic quality tomosynthesis images in the fields of mammography, dentistry, and orthopedics. In this study, we present a potential stationary head CT (s-HCT) design which combines projection data from 3 separate but parallel imaging planes for a complete CT fan-beam reconstruction. The proposed scanner consists of 3 CNT x-ray source arrays with a large number distributed focal spots each, and an Electronic Control System (ECS) for high speed control of the x-ray exposure from each focal spot. The projection data was collected by an array of multi-row detectors. For this unique imaging configuration, a customized geometry calibration procedure was developed. A linear collimator was designed and constructed for the reduction of cone-angle scatter. Finally, volumetric CT slice data was acquired through z-axis translation of the imaging object.
Purpose: Carbon nanotube (CNT) based field-emission x-ray source arrays allow the development of robust stationary computed tomography (CT) imaging systems with no gantry movement. There are many technical considerations that constrain the optimal system design. The aim of this work is to assess the image quality of a proposed Stationary Head CT (sHCT) system through simulation. Methods: In our previous work, we defined a system design consisting of three parallel imaging planes. Each plane consists of a CNT x-ray source array with a large number of linearly distributed focal spots and three strip detector modules. Each imaging plane is rotated 120° with respect to the adjacent plane to provide maximum projection view coverage of the region of interest (ROI). An iterative reconstruction algorithm based on the ASTRA toolbox was developed for the specific sHCT system. The ACR 464 phantom and a set of clinical head CT data were used to assess the system design and image quality. Imaging performance was evaluated both quantitatively and qualitatively. Results: The simulation results suggest that the proposed sHCT design is feasible and high-fidelity CT images can be obtained. The reconstructed image of the ACR 464 phantom reproduces accurate CT numbers. The reconstructed CT images for the human head confirm the capability of this prototype for identifying low contrast pathologies. Conclusion: A three-plane sHCT system is evaluated in this work. The iterative reconstruction algorithm produces high image quality in terms of uniformity, signal-to-noise ratio, signal-to-contrast ratio and structural information. Further work on the optimization of the current sHCT system will focus on speed up of volumetric image data collection in system hardware and further improvement of the reconstruction image quality through regularization and incorporating of machine leaning techniques.
Purpose: Today’s state-of-the-art CT systems rely on a rotating gantry to acquire projections spanning up to 360 degrees around the head and/or body. By replacing the rotating source and detector with a stationary array of x-ray sources and line detectors, a head CT scanner could be potentially constructed with a small footprint and fast scanning speed. The purpose of this project is to design and construct a stationary head CT (s-HCT) scanner capable of diagnosis of stroke and head trauma patients in limited resource areas such as forward operating bases. Here we present preliminary imaging results which demonstrate the feasibility of such a system using carbon nanotube (CNT) x-ray source arrays.
Methods: The feasibility study was performed using a benchtop setup consisting of an x-ray source array with 45 distributed focal spots, each operating at 120kVp, and an Electronic Control System (ECS) for high speed control of the x-ray output from individual focal spots. The projection data was collected by an array of detectors configured specifically for head imaging. The basic performance of the CNT x-ray source array was characterized. By rotating the object in discrete angular steps, a potential s-HCT configuration was emulated. The collected projection images were reconstructed using an iterative reconstruction algorithm developed specifically for this configuration. Evaluation of the image quality was completed by comparing this image of the ACR CT phantom obtained with the s-HCT to that obtained by a clinical CT scanner.
Results: The CNT x-ray source array was found to have a consistent focal spot size of 1.3×1.1 mm2 for all beams (IEC 1.0). At 120 kVp the HVL was measured to be 5.8 mm Al. Axial images have been acquired with slice thickness 2.5 mm to evaluate the imaging performance of the s-HCT system. Contrast-noise-ratio was measured for the acrylic (120 HU) and water (0 HU) materials in the ACR CT 464 phantom Module 01. A value of 5.2 is reported for the benchtop setup with an entrance dose of 2.9 mGy, compared to the clinical measurement of 30.5 found at 74.5 mGy. These images demonstrate that the s-HCT system based on CNT x-ray source arrays is feasible.
Conclusion: Customized CNT x-ray sources were developed specifically for head CT imaging. The feasibility of using this source array to construct a s-HCT scanner has been demonstrated by emulating a potential CT configuration. It is shown that diagnostic quality CT images can be obtained using the proposed system geometry. These preliminary images provide confidence that a s-HCT system can be constructed for clinical evaluation.
Purpose: The invention of carbon nanotube (CNT) x-ray source array has allowed development of many novel imaging systems including stationary tomosynthesis devices for breast, chest and dental imaging. This technology enables stationary computed tomography with potentially a fast data acquisition rate and a mechanically robust structure by eliminating the rotating gantry. It reduces the image blur caused by the mechanical motion. The purpose of this work is to explore possible system configurations of stationary head CT (s-HCT) using fixed-position linear CNT x-ray source arrays and detector arrays. Methods: Sinogram coverage is used for qualitative evaluation on the CT projection data collection efficiency for a given configuration. Accordingly, the configuration is optimized based on the coverage in sinogram space. To evaluate the system feasibility on imaging low-contrast brain tissues, a modified low-contrast Shepp-Logan phantom is implemented for quality assessment using quantitative metrics. Different Iterative Reconstruction methods are compared for both qualitative and quantitative assessment as well. Results: The sinogram coverage of s-HCT configurations changes significantly with different number of CNT source arrays used, as well as the layout of the geometry. Preliminary results suggest that a s-HCT configuration with three planes gives a nearly completed sinogram coverage which provides enough information to reconstruct image with good quality. Different reconstruction techniques are used for such configuration with a low-contrast head phantom. High-quality images are reconstructed for the proposed configuration. Conclusion: An optimized s-HCT system configuration can be built with few linear CNT x-ray source arrays. Given such configuration, Iterative Reconstruction algorithms in conjunction with Total-Variation Regularization provides highquality images even for low-contrast objects.
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