Portable chest x-ray (PCXR) is commonly employed in intensive care units (ICU). CXR provides valuable information but is hindered by structural overlap. Digital chest tomosynthesis (DCT) removes overlap, yielding quasi-three- dimensional images. Spatially distributed x-ray source arrays eliminate complex mechanical motion and are well-suited for mobile systems. The purpose of this study is to design and optimize a compact and portable DCT system employing a linear field emission x-ray source array in lieu of a conventional moving source, balancing image quality with size and clinical practicality. A prototype stationary DCT system was used to test a variety of system configurations. Tomosynthesis scans of an anthropomorphic phantom were performed repeatedly to generate an image ensemble. Subsets were selected for reconstruction to investigate the impact of spatial distribution on image quality. Reconstruction slice images were evaluated by visualization of simulated lung nodules and presence of artifact to determine the optimal source configuration. Reconstruction slice images demonstrated out-of-plane artifact in configurations with low projection image density. Narrow angular span compromised the visualization of structures and low contrast features. Of the evaluated configurations, one was determined to best balance image quality with physical constraints, utilizing 15 projections covering an angular span of 23 degrees. Bedside 3D imaging is achievable by use of x-ray source arrays. A configuration was determined that generates good image quality in a size conducive to design of a mobile tomosynthesis system. Such a system should provide increased clinical utility compared to 2D radiography in the ICU.
Develop and test an implementation for prospective cardiac and respiratory gated imaging on a multisource stationary computed tomography (CT) system. Prospective cardiac gated imaging is commonplace in cardiovascular imaging, but has yet to be demonstrated on a multisource stationary gantry imaging system. The purpose of this study is to demonstrate the potential of the scanner for clinical use. The existing stationary head computed tomography scanner (s-HCT) was converted into a prospective cardiac CT scanner. A step-and-shoot protocol was implemented with logic for firing the x-ray sources upon the incidence of a physiologically correlated trigger signal, generated using a respiratory sensor and/or EKG, processed on the BioVet to generate a logic-level gating signal. To demonstrate system performance, a dynamic respiratory phantom was imaged with and without gating, then imaged while stationary for reference. Images of the respiratory phantom with gating applied were nearly indistinguishable from the reference image. Ungated images varied largely from the reference. Separation between bead centers from reference deviated by 0.1mm with gating, compared to 8.4mm ungated. We successfully developed and demonstrated a multisource stationary CT capable of prospective cardiac gated acquisitions. Images demonstrate gated scans are not easily distinguishable from reference, and ungated images are substantially different from the reference. Phantom studies show the potential for this implementation and show value for pre-clinical animal experimentation.
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.
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: Digital chest tomosynthesis is an attractive alternative to computed tomography (CT) for some clinical tasks but lacks the sensitivity for detection of small lung nodules due to scattered radiation. Conventional scatter mitigation techniques are not ideal. The purpose of this study was to provide an update on a human imaging study in patients with lung lesions incorporating an alternative scatter correction method. Method: Human subjects with known lung lesions were imaged with an experimental stationary digital chest tomosynthesis (s-DCT) system. A customized primary sampling device (PSD) was used to collect sparse primary beam samples prior to the normal scan. A primary sampling scatter correction (PSSC) algorithm was used to compute scatter and correct projections prior to reconstruction. Reconstruction image quality was evaluated in both scatter-corrected and uncorrected images and compared to clinical CT images by a board-certified radiologist. Results: Scatter corrected reconstruction slice images were found to exhibit improved conspicuity of a ground glass opacity in one example case. Pulmonary vasculature was also enhanced in a subject with high body mass index. These example cases are shown with quantitative evaluation. Reconstruction slice images with scatter correction exhibit greater uniformity in histogram distribution, allowing visualization of a larger range of anatomy at any window and level than their corresponding uncorrected counterparts. Conclusions: A low-dose, patient-specific scatter correction has been demonstrated in thirty-eight subjects in a human imaging study. The PSSC technique was found to enhance visualization and improve overall reconstruction image quality. A comprehensive reader study will determine clinical efficacy.
Purpose: Scatter reduction remains a challenge for chest tomosynthesis. The purpose of this study was to validate a lowdose patient-specific method of scatter correction in a large animal model and implement the technique in a human imaging study in a population with known lung lesions. Method: The porcine and human subjects were imaged with an experimental stationary digital chest tomosynthesis system. Full field projection images were acquired, as well as with a customized primary sampling device for sparse sampling of the primary signal. A primary sampling scatter correction algorithm was used to compute scatter from the primary beam information. Sparse scatter was interpolated and used to correct projections prior to reconstruction. Reconstruction image quality was evaluated over multiple acquisitions in the animal subject to quantify the impact of lung volume discrepancies between scans. Results: Variations in lung volume between the full field and primary sample projection images induced mild variation in computed scatter maps, due to acquisitions during separate breath holds. Reconstruction slice images from scatter corrected datasets including both similar and dissimilar breath holds were compared and found to have minimal differences. Initial human images are included. Conclusions: We have evaluated the prototype low-dose, patient-specific scatter correction in an in-vivo porcine model currently incorporated into a human imaging study. The PSSC technique was found to tolerate some lung volume variation between scans, as it has a minimal impact on reconstruction image quality. A human imaging study has been initiated and a reader comparison will determine clinical efficacy.
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.
Orthopedic tomosynthesis is emerging as an attractive alternative to digital radiography (DR), with increased sensitivity for some clinical tasks, including fracture diagnosis and staging and follow-up of arthritis. Commercially available digital tomosynthesis (DTS) systems are complex, room-sized devices. A compact tomosynthesis system for extremity imaging (TomoE) was previously demonstrated using carbon nanotube (CNT) x-ray source array technology. The purpose of this study was to evaluate the prototype device in preparation for an Institutional Review Board (IRB)- approved patient imaging study and evaluate initial patient images.
A tabletop device was constructed using a short CNT x-ray source array, operated in three positions, and a flat panel digital detector. Twenty-one x-ray projection images were acquired at incident angles from -20 to +20 degrees in various clinical orientations, with entrance doses matched to commercial in-room DTS scanners. The projection images were reconstructed with an iterative reconstruction technique in 1mm slices. Cadaveric specimen and initial participant images were reviewed by radiologists for feature conspicuity and diagnostic accuracy.
TomoE image quality was found to be superior to DR, with reconstruction slices exhibiting visual conspicuity of trabecular bone, delineation of joint space, bone erosions, fractures, and clear depiction of normal anatomical features. The scan time was fifteen seconds with mechanical translation. Skin entrance dose was verified to be 0.2mGy. TomoE device image quality has been evaluated in cadaveric specimens and dose was calibrated for a patient imaging study. Initial patient images depict a high level of anatomical detail an increase in diagnostic value compared to DR.
Purpose: Chest tomosynthesis is an attractive alternative to computed tomography (CT) for lung nodule screening, but reductions in image quality caused by radiation scatter remains an important limitation. Conventional anti-scatter grids result in higher patient dose, and alternative approaches are needed. The purpose of this study was to validate a lowdose patient-specific approach to scatter correction for an upcoming human imaging study.
Method: A primary sampling device (PSD) was designed and scatter correction algorithm incorporated into an experimental stationary digital chest tomosynthesis (s-DCT) system for this study to directly compute scatter from the primary beam information. Phantom and an in-vivo porcine subject were imaged. Total scan time was measured and image quality evaluated.
Results: Comparison of reconstruction slice images from uncorrected and scatter-corrected projection images reveals improved image quality, with increased feature conspicuity. Each scan in the current setup required twelve seconds, in addition to one second for PSD retraction, for a total scan time of 25 seconds.
Conclusions: We have evaluated the prototype low-dose, patient-specific scatter correction methodology using phantom studies in preparation for a clinical trial. Incorporating only 5% of additional patient dose, the reconstruction slices exhibit increased visual conspicuity of anatomical features, with the primary drawback of increased total scan time. Though used for tomosynthesis, the technique can be easily translated to digital radiography in lieu of an anti-scattering grid.
Tomosynthesis imaging has been demonstrated as an alternative to MRI and CT for orthopedic imaging. Current commercial tomosynthesis scanners are large in-room devices. The goal of this study was to evaluate the feasibility of designing a compact tomosynthesis device for extremity imaging at the point-of-care utilizing a carbon nanotube (CNT) x-ray source array. The feasibility study was carried out using a short linear CNT source array with limited number of x-ray emitting focal spots. The short array was mounted on a translation stage and moved linearly to mimic imaging configurations with up to 40 degrees angular coverage at a source-to-detector distance of 40cm. The receptor was a 12x12cm flat panel digital detector. An anthropomorphic phantom and cadaveric wrist specimens were imaged at 55kVp under various exposure conditions. The projection images were reconstructed with an iterative reconstruction algorithm. Image quality was assessed by musculoskeletal radiologists. Reconstructed tomosynthesis slice images were found to display a higher level of detail than projection images due to reduction of superposition. Joint spaces and abnormalities such as cysts and bone erosion were easily visualized. Radiologists considered the overall utility of the tomosynthesis images superior to conventional radiographs. This preliminary study demonstrated that the CNT x-ray source array has the potential to enable tomosynthesis imaging of extremities at the point-of-care. Further studies are necessary to optimize the system and x-ray source array configurations in order to construct a dedicated device for diagnostic and interventional applications.
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