Scatter radiation severely degrades the image quality. Measurement-based scatter correction methods sample the scatter signal at sparsely distributed points, from which the scatter profile is estimated and deterministically removed from the projection image. The estimation of the scatter profile is generally done through a spline interpolation and the resulting scatter profile is quite smooth. Consequently, the noise is intact and the signal-to-noise ratio is reduced in the projection image after scatter correction, leading to image artifacts and increased noise in the reconstruction images. We propose a simple and effective method, referred to as filtered scatter-to-primary ratio (f-SPR) estimation, to estimate the scatter profile using the sparsely sampled scatter signal. Using the primary sampling device and the stationary digital tomosynthesis systems previously developed in our lab, we evaluated and compared the f-SPR method in comparison with existing methods in terms of contrast ratio, signal difference-to-noise ratio, and modulation transfer function. A significant improvement in image quality is observed in both the projection and the reconstruction images using the proposed method.
Despite recent advances in dental radiography, the diagnostic accuracies for some of the most common dental diseases have not improved significantly, and in some cases remain low. Intraoral x-ray is the most commonly used x-ray diagnostic tool in dental clinics. It however suffers from the typical limitations of a 2D imaging modality including structure overlap. Cone-beam computed tomography (CBCT) uses high radiation dose and suffers from image artifacts and relatively low resolution. The purpose of this study is to investigate the feasibility of developing a stationary intraoral tomosynthesis (s-IOT) using spatially distributed carbon nanotube (CNT) x-ray array technology, and to evaluate its diagnostic accuracy compared to conventional 2D intraoral x-ray. A bench-top s-IOT device was constructed using a linear CNT based X-ray source array and a digital intraoral detector. Image reconstruction was performed using an iterative reconstruction algorithm. Studies were performed to optimize the imaging configuration. For evaluation of s-IOT’s diagnostic accuracy, images of a dental quality assurance phantom, and extracted human tooth specimens were acquired. Results show s-IOT increases the diagnostic sensitivity for caries compared to intraoral x-ray at a comparable dose level.
Computed Tomography (CT) is the gold standard for image evaluation of lung disease, including lung cancer and cystic fibrosis. It provides detailed information of the lung anatomy and lesions, but at a relatively high cost and high dose of
radiation. Chest radiography is a low dose imaging modality but it has low sensitivity. Digital chest tomosynthesis (DCT) is an imaging modality that produces 3D images by collecting x-ray projection images over a limited angle. DCT is less expensive than CT and requires about 1/10th the dose of radiation. Commercial DCT systems acquire the
projection images by mechanically scanning an x-ray tube. The movement of the tube head limits acquisition speed. We recently demonstrated the feasibility of stationary digital chest tomosynthesis (s-DCT) using a carbon nanotube
(CNT) x-ray source array in benchtop phantom studies. The stationary x-ray source allows for fast image acquisition. The objective of this study is to demonstrate the feasibility of s-DCT for patient imaging. We have successfully imaged 31 patients. Preliminary evaluation by board certified radiologists suggests good depiction of thoracic anatomy and pathology.
Digital tomosynthesis is a type of limited angle tomography that allows 3D information to be reconstructed
from a set of x-ray projection images taken at various angles using an x-ray tube, a mechanical arm to rotate the tube
about the object, and a digital detector. Tomosynthesis reconstruction requires the precise location of the detector with
respect to each x-ray source, forcing all current clinical tomosynthesis systems to use a physically coupled source and
detector so the geometry is always known and is always the same. This limits the imaging geometries and its large size
is impractical for mobile or field operations. To counter this, we have developed a free form tomosynthesis with a
decoupled, free-moving source and detector that uses a novel optical method for accurate and real-time geometry
calibration to allow for manual, hand-held tomosynthesis and even CT imaging.
We accomplish this by using a camera, attached to the source, to track the motion of the source relative to the
detector. Attached to the detector is an optical pattern and the image captured by the camera is then used to determine
the relative camera/pattern position and orientation by analyzing the pattern distortion and calculating the source
positions for each projection, necessary for 3D reconstruction. This allows for portable imaging in the field and also as
an inexpensive upgrade to existing 2D systems, such as in developing countries, to provide 3D image data. Here we
report the first feasibility demonstrations of free form digital tomosynthesis systems using the method.
The coronary artery calcium score (CACS) measures the buildup of calcium on the coronary artery wall and has
been shown to be an important predictor of the risk of coronary artery diseases (CAD). Currently CACS is measured
using CT, though the relatively high cost and high radiation dose has limited its adoption as a routine screening
procedure. Digital Chest Tomosynthesis (DCT), a low dose and low cost alternative to CT, and has been shown to
achieve 90% of sensitivity of CT in lung disease screening. However commercial DCT requires long scanning time
and cannot be adapted for high resolution gated cardiac imaging, necessary for CACS. The stationary DCT system (s-
DCT), developed in our lab, has the potential to significantly shorten the scanning time and enables high resolution
cardiac gated imaging. Here we report the preliminary results of using s-DCT to estimate the CACS. A phantom heart
model was developed and scanned by the s-DCT system and a clinical CT in a phantom model with realistic coronary
calcifications. The adapted fan-beam volume reconstruction (AFVR) method, developed specifically for stationary
tomosynthesis systems, is used to obtain high resolution tomosynthesis images. A trained cardiologist segmented out
the calcifications and the CACS was obtained. We observed a strong correlation between the tomosynthesis derived
CACS and CT CACS (r2 = 0.88). Our results shows s-DCT imaging has the potential to estimate CACS, thus providing
a possible low cost and low dose imaging protocol for screening and monitoring CAD.
Digital chest tomosynthesis (DCT) provides superior image quality and depth information for thoracic imaging at relatively low dose, though the presence of strong photon scatter degrades the image quality. In most chest radiography, anti-scatter grids are used. However, the grid also blocks a large fraction of the primary beam photons requiring a significantly higher imaging dose for patients. Previously, we have proposed an efficient low dose scatter correction technique using a primary beam sampling apparatus. We implemented the technique in stationary digital breast tomosynthesis, and found the method to be efficient in correcting patient-specific scatter with only 3% increase in dose. In this paper we reported the feasibility study of applying the same technique to chest tomosynthesis. This investigation was performed utilizing phantom and cadaver subjects. The method involves an initial tomosynthesis scan of the object. A lead plate with an array of holes, or primary sampling apparatus (PSA), was placed above the object. A second tomosynthesis scan was performed to measure the primary (scatter-free) transmission. This PSA data was used with the full-field projections to compute the scatter, which was then interpolated to full-field scatter maps unique to each projection angle. Full-field projection images were scatter corrected prior to reconstruction. Projections and reconstruction slices were evaluated and the correction method was found to be effective at improving image quality and practical for clinical implementation.
Digital chest tomosynthesis (DCT) is a 3D imaging modality which has been shown to approach the diagnostic capability of CT, but uses only one-tenth the radiation dose of CT. One limitation of current commercial DCT is the mechanical motion of the x-ray source which prolongs image acquisition time and introduces motion blurring in images. By using a carbon nanotube (CNT) x-ray source array, we have developed a stationary digital chest tomosynthesis (s- DCT) system which can acquire tomosynthesis images without mechanical motion, thus enhancing the image quality. The low dose and high quality 3D image makes the s-DCT system a viable imaging tool for monitoring cystic fibrosis (CF) patients. The low dose is especially important in pediatric patients who are both more radiosensitive and have a longer lifespan for radiation symptoms to develop. The purpose of this research is to evaluate the feasibility of using s-DCT as a faster, lower dose means for diagnosis and monitoring of CF in pediatric patients. We have created an imaging phantom by injecting a gelatinous mucus substitute into porcine lungs and imaging the lungs from within an anthropomorphic hollow chest phantom in order to mimic the human conditions of a CF patient in the laboratory setting. We have found that our s-DCT images show evidence of mucus plugging in the lungs and provide a clear picture of the airways in the lung, allowing for the possibility of using s- DCT to supplement or replace CT as the imaging modality for CF patients.
Chest tomosynthesis is a low-dose 3-D imaging modality that has been shown to have comparable sensitivity as CT in detecting lung nodules and other lung pathologies. We have recently demonstrated the feasibility of stationary chest tomosynthesis (s-DCT) using a distributed CNT X-ray source array. The technology allows acquisition of tomographic projections without moving the X-ray source. The electronically controlled CNT x-ray source also enables physiologically gated imaging, which will minimize image blur due to the patient’s respiration motion. In this paper, we investigate the feasibility of prospective gated chest tomosynthesis using a bench-top s-DCT system with a CNT source array, a high- speed at panel detector and realistic patient respiratory signals captured using a pressure sensor. Tomosynthesis images of inflated pig lungs placed inside an anthropomorphic chest phantom were acquired at different respiration rate, with and without gating for image quality comparison. Metal beads of 2 mm diameter were placed on the pig lung for quantitative measure of the image quality. Without gating, the beads were blurred to 3:75 mm during a 3 s tomosynthesis acquisition. When gated to the end of the inhalation and exhalation phase the detected bead size reduced to 2:25 mm, much closer to the actual bead size. With gating the observed airway edges are sharper and there are more visible structural details in the lung. Our results demonstrated the feasibility of prospective gating in the s-DCT, which substantially reduces image blur associated with lung motion.
We have recently demonstrated the feasibility of stationary digital chest tomosynthesis (s-DCT) using a dis- tributed carbon nanotube x-ray source array. The technology has the potential to increase the imaging resolution and speed by eliminating source motion. In addition, the flexibility in the spatial configuration of the individual sources allows new tomosynthesis imaging geometries beyond the linear scanning mode used in the conventional systems. In this paper, we report the preliminary results on the effects of the tomosynthesis imaging geometry on the image quality. The study was performed using a bench-top s-DCT system consisting of a CNT x-ray source array and a flat-panel detector. System MTF and ASF are used as quantitative measurement of the in-plane and in-depth resolution. In this study geometries with the x-ray sources arranged in linear, square, rectangular and circular configurations were investigated using comparable imaging doses. Anthropomorphic chest phantom images were acquired and reconstructed for image quality assessment. It is found that wider angular coverage results in better in-depth resolution, while the angular span has little impact on the in-plane resolution in the linear geometry. 2D source array imaging geometry leads to a more isotropic in-plane resolution, and better in-depth resolution compared to 1D linear imaging geometry with comparable angular coverage.
Chest tomosynthesis is an imaging modality that provides 3D sectional information of a patients thoracic cavity
using limited angle x-ray projections. Studies show that tomosynthesis can improve the detection of subtle
lung nodules comparing to conventional radiography at a lower radiation dose than CT. In the conventional
design, the projection images are collected by mechanically moving a single x-ray source to different viewing
angles. We investigated the feasibility of stationary chest tomosynthesis using the distributed CNT x-ray source
array technology, which can generate a scanning x-ray beam without any mechanical motion. A proof-of-concept
system was constructed using a short linear source array and a at panel detector. The performance of the source
including the flux was evaluated in the context of chest imaging. The bench-top system was characterized and
images of a chest phantom were acquired and reconstructed. The preliminary results demonstrate the feasibility
of stationary chest tomosynthesis using the CNT x-ray source array technology.
Carbon nanotube (CNT) micro-focus x-ray tubes have been demonstrated as a novel technology for in-vivo
small animal imaging. It enables simultaneous respiratory and cardiac gated prospective CT imaging of free
breathing animals with high temporal resolution. Operating the
micro-focus CNT x-ray source at high power is
required to achieve high temporal resolution. The thermal loading of the anode focal spot is a limiting factor in
determining the maximum power of an x-ray tube. In this paper, we developed a reliable simulation model to
quantitatively analyze the anode heat load of the CNT x-ray source operating in both DC and pulse modes. The
anode temperature distribution is simulated using finite element analysis. The model is validated by comparing
simulation results for the micro-focus x- ray tube with reported experimental results. We investigated the
relationship between the maximum power and the effective focal spot size for CNT micro-CT system running
in both DC and pulse modes. Our results show that when operating in pulse mode, the maximum power of the
CNT x-ray source can be significantly higher than when operating in DC mode. In DC mode, we found that the
maximum power scales non-linearly with the effective focal spot size as P(in W) = (0.25/ sin θ+1.6)f0.73s (in μm),
where 1/sin θ is the projection factor for a given anode angle θ. However, in pulse mode the maximum power
linearly increases with the effective focal spot size asP(in W) = (0.20/ sin θ+0.35)fs(in μm), and is significantly
higher than that in the DC mode. This implies that it is feasible to improve the micro-CT temporal resolution
further without sacrificing the image quality. The simulation method developed here also enables us to analyze
the thermal loading of the other CNT x-ray sources for other applications, such as the stationary digital breast
tomosynthesis scanner and the CNT microbeam radiation therapy system.