In this study, multi-view synthetic radiographs of patients generated from stationary intraoral tomosynthesis (sIOT) images were compared with standard bitewing (SBW) radiographs in terms of proximal tooth overlap and image quality. Patient sIOT images from a previous study were used to create seven synthetic radiographs with different viewing angles through specialized code. The proximal tooth overlap, contrast, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were calculated for representative patient data sets. The synthetic radiographs had a minimum overlap of 0%, median overlap of 0%, maximum overlap of 14%, and interquartile range of 0%. The SBW radiographs had a minimum overlap of 13%, median overlap of 23.5%, maximum overlap of 49%, and interquartile range of 14.5%. The ratio of mean contrast, mean CNR, and mean SNR between the synthetic radiographs and the SBW radiographs were 3.81, 2.63, and 0.821 respectively. The synthetic radiographs had decreased proximal overlap and increased contrast and CNR compared to SBW radiographs. These results suggest that synthetic radiographs can reduce proximal overlap and improve contrast compared to SBW radiographs.
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.
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.
KEYWORDS: Digital breast tomosynthesis, Mammography, Image processing, 3D image processing, Digital image processing, Digital mammography, 3D image reconstruction, Modulation transfer functions
Purpose. Report advances being made in synthetic mammography applied to carbon nanotube-enabled stationary digital breast tomosynthesis (sDBT). Methods. The potential value of adding Laplacian decomposition, feature-enhancement algorithms, and weighted recombination to the tunable forward-projection steps developed previously to generate synthetic mammograms for sDBT was studied in this phantom-based comparison of sDBT to full field digital mammography (FFDM) and moving-source or conventional DBT. Contrast-to-noise ratio (CNR) and the full-width-at-half-maximum (FWHM) of the signal intensity were used to compare the display of microcalcification and mass features in the FFDM image and the synthetic images generated by sDBT and DBT. These findings guided modifications in the sDBT image processing chain, seeking to maximize the display of clinically-important features in the sDBT-based synthetic image. Results. Decomposing each reconstructed image slice into its high, mid, and low-frequency components yielded images emphasizing a different feature of clinical importance: microcalcifications, masses, and background density. Applying feature-enhancement algorithms to these images followed by weighted recombination during forward projection yielded an sDBT-based synthetic image that displayed masses with a higher CNR than the FFDM image and the synthetic image generated by DBT. Additionally, microcalcifications that could be visualized in all three modalities were displayed with a higher CNR in the synthetic images generated by DBT and sDBT compared to the FFDM image. Conclusion. Adding Laplacian decomposition, feature-enhancement, and weighted recombination steps to the image processing chain that generates a synthetic image from information collected by sDBT improved the display of clinicallyimportant features. Advancing the synthetic mammography capability of sDBT is important, as it will help complete the evolution of this promising technology to a viable clinical tool.
Purpose. Explore the potential value of displaying information collected by stationary intraoral tomosynthesis (sIOT) as multi-view synthetic radiographs, using vertical root fractures (VRFs) as a model system.
Methods. Filled and unfilled extracted tooth roots containing artificially-induced VRFs were imaged by sIOT and standard periapical radiography. sIOT collected 7 views across a 12° angle span, providing information for an image processing chain that included reconstruction, weighting, and forward projection to generate a set a synthetic two-dimensional (2D) images. Qualitative assessments of fracture conspicuity were used for comparison.
Results. The conspicuity of VRFs changed significantly with the angle of imaging, suggesting benefit to displaying a set of synthetic images across a span of viewing angles. Although high-density in-plane and out-of-plane artifacts, which could limit the conspicuity of VRFs, were prominent in the three-dimensional (3D) stack of reconstructed image slices, these artifacts were minimal in the synthetic radiographs. As such, some fractures were displayed more clearly in the synthetic 2D images compared to the reconstructed 3D image stack. Also, in some cases, the fractures were more conspicuous in the sIOT-generated synthetic images than the standard periapical radiographs.
Conclusion. Multi-view synthetic radiography can improve the display of VRFs in images generated by sIOT. As such, this approach to dental imaging may offer a useful clinical tool, with potential application to a host of imaging tasks.
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.
Purpose. Investigate synthetic mammography approaches for carbon nanotube (CNT)-enabled stationary digital breast tomosynthesis (sDBT).
Methods. Projection images of breast-mimicking phantoms containing soft-tissue masses and microcalcification clusters collected by sDBT were used to develop weighted-intensity forward-projection algorithms that generated a synthetic mammogram from the reconstructed 3D image space. Reconstruction was accomplished by an adapted fan-volume modification of the simultaneous iterative reconstruction technique. Detectability indices were used to quantify mass and calcification visibility. The image processing chain was then applied to projection views collected by sDBT on women with “suspicious” breast lesions detected by standard screening 2D digital mammography.
Results. Quantifying detectability allowed correlation between the visibility of clinically-important image features and the order of the polynomial weighting function used during forward projection. The range of weighted functions exists between the extremes of an average-intensity projection (zero-order) and maximum-intensity projection (infinite-order), with lower order weights emphasizing soft-tissue features and higher-order weights emphasizing calcifications.
Application of these algorithms to patient images collected by sDBT, coupled with dense-artifact reduction and background equalization steps, produced synthetic mammograms on which additional post-processing approaches can be explored, with the actual mammogram providing a reference for comparison.
Conclusions. An image-processing chain with adjustable weighting during forward projection, dense-artifact reduction, and background equalization can yield a range of sDBT-based synthetic mammograms that display clinically-important features differently, potentially improving the ability to appreciate the association of masses and calcifications.
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.
Stationary intraoral tomosynthesis (sIOT) is an experimental imaging approach using a fixed array of carbon nanotubeenabled x-ray sources to produce a series of projections from which three-dimensional information can be reconstructed and displayed. Customized to the dental workspace, the first-generation sIOT tube is compact, easy-to-operate, and designed to interface with standard digital intraoral detectors. The purpose of this work was to explore the utility of the sIOT device across a range of dental pathologies and thereby identify limitations potentially amenable to correction through post-acquisition processing. Phantoms, extracted human teeth, and cadaveric specimens containing caries, fractures, and dilacerated roots, often associated with amalgam restorations, were imaged using tube settings that match the kVp and mA used in conventional clinical 2D intraoral imaging. An iterative reconstruction approach generated a stack of image slices through which the reader scrolls to appreciate depth relationships. Initial experience demonstrated an improved ability to visualize occlusal caries, interproximal caries, crown and root fractures, and root dilacerations when compared to 2D imaging. However, artifacts around amalgam restorations and metal implants proved problematic, leading to the incorporation of an artifact reduction step in the post-acquisition processing chain. These findings support the continued study of sIOT as a viable limited-angle tomography tool for dental applications and provide a foundation for the ongoing development of image processing steps to maximize the diagnostic utility of the displayed images.
High resolution imaging of the chest is dependent on a breath hold maintained throughout the imaging time. However, pediatric and comatose patients are unable to follow respiration commands. Gated tomosynthesis could offer a lower dose, high in-plane resolution imaging modality, but current systems are unable to prospectively gate in a reasonable scan time. In contrast, a carbon nanotube (CNT) based linear x-ray source array offers both the angular span and precise control necessary to generate x-ray projections for gated tomosynthesis. The goal of this study was to explore the first clinical use of the CNT linear x-ray source array for gated clinical chest imaging. Eighteen pediatric cystic fibrosis patients were recruited for this study, with 13 usable image sets. The s-GDCT system consists of a CNT linear x-ray source array coupled with a digital detector. A respiration signal derived from a respiratory belt served as a gating signal with sources fired sequentially when the imaging window and maximum inspiration window coincided. Images were reconstructed and reviewed for motion blur and ability to identify major anatomical structures. Image quality was highly dependent on quality of the respiration gating signal, and a correlation was found between qualitative image quality and height of the respiration peak. We demonstrate the first prospectively gated evaluation of the stationary digital chest tomosynthesis patients in pediatric patients. Though further refinements in projection selection and respiratory gating approaches are necessary, this study demonstrates the potential utility of this low dose imaging approach.
KEYWORDS: Digital breast tomosynthesis, Iodine, Breast, Image processing, X-rays, 3D image processing, Image quality, Reconstruction algorithms, Signal attenuation, X-ray imaging
Stationary digital breast tomosynthesis (sDBT) is an emerging technology in which the single rotating x-ray tube is replaced by a fixed array of multiple carbon nanotube-enabled sources, providing a higher spatial and temporal resolution. As such, sDBT offers a promising platform for contrast-enhanced (CE) imaging. However, given the minimal enhancement above background with standard operational tube settings and iodine dosing, CE breast imaging requires additional acquisition steps to isolate the iodine signal, using either temporal or dual energy subtraction (TS or DES) protocols. Also, correcting for factors that limit contrast is critical, and scatter and noise pose unique challenges during tomosynthesis. This phantom-based study of CE sDBT compared different postacquisition scatter correction approaches on the quality of the reconstructed image slices. Beam-pass collimation was used to sample scatter indirectly, from which an interpolated scatter map was obtained for each projection image. Scatter-corrected projections provided the information for reconstruction. Comparison between the application of different scatter maps demonstrated the significant effect that processing has on the contrast-to-noise ratio and feature detectability (d′) in the final displayed images and emphasized the critical importance of scatter correction during DES.
KEYWORDS: Digital breast tomosynthesis, X-ray sources, Breast, Imaging systems, Dual energy imaging, Spatial resolution, Signal to noise ratio, Carbon nanotubes, Iodine, Image processing, Photovoltaics, Diagnostics, Signal attenuation, Reconstruction algorithms
Digital breast tomosynthesis (DBT) captures some depth information and thereby improves the conspicuity of breast lesions, compared to standard mammography. Using contrast during DBT may also help distinguish malignant from benign sites. However, adequate visualization of the low iodine signal requires a subtraction step to remove background signal and increase lesion contrast. Additionally, attention to factors that limit contrast, including scatter, noise, and artifact, are important during the image acquisition and post-acquisition processing steps. Stationary DBT (sDBT) is an emerging technology that offers a higher spatial and temporal resolution than conventional DBT. This phantom-based study explored contrast-enhanced sDBT (CE sDBT) across a range of clinically-appropriate iodine concentrations, lesion sizes, and breast thicknesses. The protocol included an effective scatter correction method and an iterative reconstruction technique that is unique to the sDBT system. The study demonstrated the ability of this CE sDBT system to collect projection images adequate for both temporal subtraction (TS) and dual-energy subtraction (DES). Additionally, the reconstruction approach preserved the improved contrast-to-noise ratio (CNR) achieved in the subtraction step. Finally, scatter correction increased the iodine signal and CNR of iodine-containing regions in projection views and reconstructed image slices during both TS and DES. These findings support the ongoing study of sDBT as a potentially useful tool for contrast-enhanced breast imaging and also highlight the significant effect that scatter has on image quality during DBT.
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