Coherence property of x-rays is critical in the grating-based differential phase contrast (DPC) imaging because it is the physical foundation that makes any form of phase contrast imaging possible. Loss of coherence is an important experimental issue, which results in increased image noise and reduced object contrast in DPC images and DPC cone beam CT (DPC-CBCT) reconstructions. In this study, experimental results are investigated to characterize the visibility loss (a measurement of coherence loss) in several different applications, including different-sized phantom imaging, specimen imaging and small animal imaging. Key measurements include coherence loss (relative intensity changes in the area of interest in phase-stepping images), contrast and noise level in retrieved DPC images, and contrast and noise level in reconstructed DPC-CBCT images. The influence of size and composition of imaged object (uniform object, bones, skin hairs, tissues, and etc) will be quantified. The same investigation is also applied for moiré pattern-based DPC-CBCT imaging with the same exposure dose. A theoretical model is established to relate coherence loss, noise level in phase stepping images (or moiré images), and the contrast and noise in the retrieved DPC images. Experiment results show that uniform objects lead to a small coherence loss even when the attenuation is higher, while objects with large amount of small structures result in huge coherence loss even when the attenuation is small. The theoretical model predicts the noise level in retrieved DPC images, and it also suggests a minimum dose required for DPC imaging to compensate for coherence loss.
Differential phase contrast (DPC) imaging is reported to be able to deliver higher contrast-to-noise ratio (CNR)
compared to attenuation-based x-ray imaging technologies. Due to the nature of attenuation contrast, the conventional
cone beam CT (CBCT) technology has limitations in characterizing breast lesions with sufficiently high contrast and
spatial resolution. As an alternative, the grating-based DPC-CBCT technology is potentially a powerful tool for breast
imaging. However, limited by current grating fabrication techniques, a full field-of-view (FOV) that covers the whole
breast is not practical at present. Previously by our group, a volume-of-interest (VOI) imaging method, which
incorporates DPC-CBCT into a dedicated attenuation-based CBCT imaging system, was presented. In the method, the
CBCT scan was performed to localize the suspicious volume and then a VOI scan by DPC-CBCT characterized the
suspicious volume with higher contrast and resolution. In this work, we investigated the performance of DPC-CBCT
VOI imaging by performing a phantom study using our bench-top DPC-CBCT system with a hospital-grade X-ray tube.
A cylinder water phantom with a size of over twice of the FOV of our DPC-CBCT system was designed. The phantom
contains four different materials and it was scanned at four different dose levels. In thick object scanning, phase
wrapping errors cause artifacts for DPC-CBCT VOI imaging. A low-pass filter was designed to reduce the artifacts. In
order to compare the DPC-CBCT VOI with attenuation-based CBCT, the scanning data were used to reconstruct both
phase coefficient image and attenuation coefficient image. The reconstructed images will be quantitatively and visually
evaluated with regards to contrast, noise level and artifacts.
In principle, differential phase contrast (DPC) imaging allows the use of a hospital grade x-ray tube that has a large focal
spot size and a wide polychromatic spectrum. It should be noted that due to the integration of interference patterns over
the entire spectrum, the fringe contrast in the final intensity image is lower than that from a monochromatic spectrum.
Therefore better image quality should be potentially obtained if the energy-dependent interference patterns can be
analyzed separately. The key idea of the proposed spectral DPC imaging approach is to acquire DPC images for each
photon energy channel, which is named spectral DPC images. The final DPC image can be computed by summing up
these spectral DPC images or just computed using certain 'color' representation algorithms to enhance desired features.
This research is a feasibility study based on computer simulations to investigate how the spectral DPC method works for
a DPC-based cone beam CT (DPC-CBCT) system. The spectral DPC imaging approach is applied to an x-ray spectral
centered at 30keV, which is divided into four energy channels in simulation. A simple numerical phantom with low
contrast inserts is used and the entire imaging process is simulated using Fresnel diffraction theory. Phase stepping
approach is used to manifest and retrieve phase information. The phantom is scanned over a full circular trajectory and
the Hilbert filter-based FBP algorithm is used to compute the DPC-CBCT reconstruction. The reconstruction from the
proposed spectral DPC-CBCT is compared to that from the conventional DPC-CBCT that only takes detector images for
the integrated polychromatic spectrum. The uniformity, noise level and contrast of the inserts in the reconstruction are
measured and compared. Simulation results indicate that the spectral DPC imaging approach can improve object contrast and reduce noise for DPC-CBCT.
The phase stepping algorithm is commonly used for phase retrieval in grating-based differential phase-contrast (DPC)
imaging, which requires multiple intensity images to compute one DPC image. It is not efficient for data acquisition,
especially in the case of dynamic imaging using either DPC imaging or DPC-based come beam CT (DPC-CBCT)
imaging. A Fourier transform-based approach has been developed for fringe pattern analysis in optics, and it was
recently implemented into a synchrotron-based DPC tomography system. In this research, this approach is further
developed for a bench-top DPC-CBCT imaging system with a hospital-grade x-ray tube. The key idea is to separate
carrier fringes and object information in Fourier domain of the interferogram and to reconstruct the differentiated phase
information using the object information. Only one interferogram is required for phase retrieval at a cost of spatial
resolution. The fringes of moiré patterns are used as the carrier fringes, and a phantom is scanned to evaluate the
approach. Various interferograms with different carrier fringe frequencies are investigated and the reconstruction image
quality is evaluated in terms of contrast, noise and sharpness. The results indicated that the DPC images can be
effectively retrieved using the Fourier transform-based approach and the reconstructed phase coefficient showed better
contrast compared to that of attenuation-based contrast. The spatial resolution is acceptable in the phantom studies
although it is not as good as the results of phase-stepping approach. The Fourier transform-based phase retrieval
approach is able to greatly simplify data acquisition, to improve the temporal resolution and to make it possible for
dynamic DPC-CBCT imaging. It is promising for perfusion imaging where spatial resolution is not a concern.
Differential phase contrast technique could be the next breakthrough in the field of CT imaging. While traditional
absorption-based X-ray CT imaging is inefficient at differentiating soft tissues, phase-contrast technique offers great
advantage as being able to produce higher contrast images utilizing the phase information of objects. Our long term goal
is to develop a gantry-based hospital-grade X-ray tube differential phase contrast cone-beam CT (DPC-CBCT)
technology which is able to achieve higher contrast noise ratio (CNR) in soft tissue imaging without increasing the dose
level. Based on the micro-focus system built last year, a bench-top hospital-grade X-ray tube DPC-CBCT system is
designed and constructed. The DPC-CBCT system consists of an X-ray source, i.e. a hospital-grade X-ray tube and a
source grating, a high-resolution detector, a rotating phantom holder, a phase grating and an analyzer grating. Threedimensional
(3-D) phase-coefficients are reconstructed, providing us with images enjoying higher CNR than, yet
equivalent dose level to, a conventional CBCT scan. Three important aspects of the system are investigated: a) The The
system's performance in term of CNR of the reconstruction image with regard to dose levels, b) the impacts of different
phase stepping schemes, i.e. 5 steps to 8 steps, in term of CNR on the reconstruction images, and c) the influence of
magnification or position of the phantom on image quality, chiefly CNR. The investigations are accomplished via
phantom study.
Differential phase contrast (DPC) imaging, which utilizes phase shift information of X-ray, has the potential of
dramatically increasing the contrast in biological sample imaging compared to attenuation-based method that relies on
X-ray absorption information, since the X-ray phase is much more sensitive than the attenuation during transmission. In
a DPC imaging system, the phase stepping method is widely used to obtain DPC images: at each angle the phase grating
is shifted incrementally to produce a set of images and then the so obtained images are used to retrieve DPC image.
However, DPC imaging requires a high mechanical precision to perform phase stepping, which is generally one order
higher than the period of phase grating. Given that phase grating period is generally 2-4 um, the requirement of
mechanical accuracy and stability are very demanding (<0.5um) and difficult to meet in a system with rotating gantry. In
this paper, we present a method that is able to greatly relax the requirement of mechanical accuracy and stability by
stepping the source grating rather than the analyzer grating. This method is able to increase the system's mechanical
tolerance without compromising image quality and make it feasible to install the system on a rotating gantry to perform
differential phase-contrast cone beam CT (DPC-CBCT). It is also able to increase the grating shifting precision and as a
result improve the reconstructed image quality. Mechanical tolerance investigation and image quality investigation at
different phase stepping schemes and different dose levels will be carried out on both the original modality and the new
modality, the results will be evaluated and compared. We will deliberately create random mechanical errors in phase
stepping and evaluate the resulting DPC images and DPC-CBCT reconstructions. The contrast, noise level and sharpness
will be evaluated to assess the influence of mechanical errors. By stepping the source grating, the system is expected to
tolerate an error of 6-7 times bigger than that with analyzer grating stepping.
Differential phase-contrast (DPC) technique is promising as the next breakthrough in the field of X-ray CT imaging.
Utilizing the long ignored X-ray phase information, Differential phase-contrast (DPC) technique has the potential of
providing us with projection images with higher contrast in a CT scan without increasing the X-ray dose. While
traditional absorption-based X-ray imaging is not very efficient at differentiating soft tissues, differential phase-contrast
(DPC) is promising as a new method to boast the quality of the CT reconstruction images in term of contrast noise ratio
(CNR) in soft tissue imaging. In order to validate and investigate the use of DPC technique in cone-beam CT imaging
scheme, a new bench-top micro-focus DPC-based cone-beam computed tomography DPC-CBCT system has been
designed and constructed in our lab for soft tissue imaging. The DPC-CBCT system consists of a micro-focus X-ray tube
(focal spot 8 μm), a high-resolution detector, a rotating phantom holder and two gratings, i.e. a phase grating and an
analysis. The detector system has a phosphor screen, an optical fiber coupling unit and a CMOS chip with an effective
pixel pitch of 22.5 microns. The optical elements are aligned to minimize unexpected moiré patterns, and system
parameters, including tube voltage (or equivalently X-ray spectrum), distances between gratings, source-to-object
distance and object-to-detector distance are chosen as practicable to be applied in a rotating system. The system is tested
with two simple phantoms for performance evaluation. 3-D volumetric phase-coefficients are reconstructed. The
performance of the system is compared with conventional absorption-based CT in term of contrast noise ratio (CNR)
under the condition of equal X-ray dose level.
In recent years, the in-line phase-contrast (in-line PC) technique has been implemented using synchrotrons and microfocus x-ray tubes for soft tissue imaging as the in-line PC's image quality enhancement. In this study, a new in-line phase-contrast cone-beam CT (PC-CBCT) system has been designed and tested in our lab to produce higher image quality enhancement. The PC-CBCT system consists of a micro-focus x-ray tube, a high-resolution detector and a rotating phantom holder. The nominal focal spot size is 9 microns, which is expected to produce partially coherent x-rays.
The detector system has a phosphor screen, an optical fiber coupling unit and a CMOS chip with an effective pixel
pitch of 22.5 microns. Some key system parameters, including tube voltage (or x-ray spectrum), source-to-object
distance and object-to-detector distance were balanced and optimized to achieve enough spatial coherence and degree of
interference to acquire edge-enhanced phase-contrast images as projection images. The phantom holder was rotated for
360 degrees with a step of 1.2 degrees, and during the rotation in-line PC images were acquired at all angular positions.
The FDK algorithm was applied to compute the reconstruction using the edge-enhanced PC images. Small soft tissue
samples (breast tissues and animal organs) were scanned and reconstructed. The tomographic images showed enhanced
structure edges and details.
Cone Beam Breast CT imaging (CBBCT) is a promising tool for diagnosis of breast tumors and calcifications. However, as the sizes of calcifications in early stages are very small, it is not easy to distinguish them from background tissues because of the relatively high noise level. Therefore, it is necessary to enhance the visualization of calcifications for accurate detection. In this work, the Papoulis-Gerchberg (PG) method was introduced and modified to improve calcification characterization. PG method is an iterative algorithm of signal extrapolation and has been demonstrated to be very effective in image restoration like super-resolution (SR) and inpainting. The projection images were zoomed by bicubic interpolation method, then the modified PG method were applied to improve the image quality. The reconstruction from processed projection images showed that this approach can effectively improve the image quality by improving the Modulation Transfer Function (MTF) with a limited increase in noise level. As a result, the detectability of calcifications was improved in CBBCT images.
The newly developed differential phase-contrast (DPC) imaging technique has attracted increasing interest among
researchers. In a DPC system, the self-imaging effect and the
phase-stepping method are implemented through three
gratings to manifest phase contrast, and differentiated phase images can be obtained. An important advantage of this
technique is that hospital-grade x-ray tubes can be used, allowing much higher x-ray output power and faster image
processing than with micro-focus in-line phase-contrast imaging. A DPC-CT system can acquire images from different
view angles along a circular orbit, and tomographic images can be reconstructed. However, the principle of DPC
imaging requires multiple exposures to compute any differentiated phase image at each view angle, which raises
concerns about radiation exposure via x-ray dose. Computer simulations are carried out to study the dose efficiency for
DPC-CT for volume-of-interest breast imaging. A conceptual
CBCT/DPC-CT hybrid imaging system and a numerical
breast phantom are designed for this study. A FBP-type reconstruction algorithm is optimized for the VOI
reconstruction. Factors including the x-ray flux and detector pixel size are considered and their effects on reconstruction
image quality in terms of noise level and contrast-to-noise ratio are investigated. The results indicate that with a pixel
size of 20 microns and a dose level of 5.7mGy, which is equivalent to the patient dose of a two-view mammography
screening or a dedicated CBCT breast imaging scan, much better tissue contrast and spatial resolution can be achieved
using the DPC-CT technique. It is very promising for possible application at pathology-level in vivo study for human
breasts.
In flat-panel detector-based cone-beam computed-tomography breast imaging (CBCTBI) systems, scatter is an important factor that degrades image quality. It has been shown that despite the use of a large air gap, scatter still causes problems when imaging breast phantoms with our CBCTBI prototype. As a result, linear attenuation coefficient (LAC) distortion is obvious in the reconstruction; it appears as cupping artifacts and contrast loss. A simplified beam-stop array (BSA) algorithm is presented in this paper to solve this problem practically and efficiently. When the breast is positioned along the rotational axis, the scatter profiles from different views along a circular orbit are similar, and thus it is possible to use only one x-ray shot with the BSA in place for scatter pattern estimation, and this BSA image is used to generate a scatter pattern for all projections. The result of this scatter correction algorithm is compared with the reconstruction image over a small field of view, where scatter is assumed to be negligible, and the relative reconstruction error (RRE) is evaluated. The reconstruction is not sensitive to the estimation of scatter profile curvature, but is sensitive to the estimation of scatter intensity. It is shown as well that for any angular position where the BSA image is taken, the RRE is very small. The results show that the BSA algorithm works well for our CBCTBI prototype system with almost unchanged x-ray exposure.
Routine quality control assessments of medical equipment are crucial for an accurate patient medical treatment as
well as for the safety of the patient and staff involved. These regular evaluations become especially important when
dealing with radiation-emitting equipment. Therefore, a quality control (QC) program has been developed to
quantitatively evaluate imaging systems by measuring standard parameters related to image quality such as the
Modulation Transfer Function (MTF), the Noise Power Spectrum (NPS), uniformity, linearity and noise level among
others. First, the methods of evaluating the aforementioned parameters have been investigated using a cone beam CT
imaging system. Different exposure techniques, phantoms, acquisition modes of the flat panel detector (FPD) and
reconstruction algorithms relevant to a clinical environment were all included in this investigation. Second, using the
results of the first part of this study, a set of parameters for the QC program was established that yields both, an accurate
depiction of the system image quality and an integrated program for easy and practical implementation. Lastly, this QC
program will be implemented and practiced in our cone beam CT imaging system. The results using our available
phantoms demonstrate that the QC program is adequate to evaluate stability and image quality of this system since it
provides comparable parameters to other QC programs.
This work is a feasibility study of a phase-contrast cone-beam CT (CBCT) system for ROI (region of interest)
reconstruction in breast imaging that incorporates the in-line holography technique into a cone-beam CT system. A
conventional CBCT scan is done first to find any suspicious lesion, followed by a phase-contrast CBCT scan of the ROI
for detailed characterization. The phase-contrast in-line holographic images are generated using Fresnel theory through
computer simulation, and the projected phase maps, as line integrals of the phase coefficient of the scanned breast, are
retrieved using phase-attenuation duality theory. In this way the object's phase coefficient, as the object function, can be
reconstructed using these projected phase maps through FDK algorithm. The reconstruction error is calculated to
evaluate the accuracy of this approach. The noise property of this approach is investigated as well by adding Poisson
noise to the holographic images. The projected phase maps are retrieved and the object function is reconstructed in the
presence of noise. The results show that the object's phase coefficient can be reconstructed with very small
reconstruction error, and the noise level can be greatly reduced compared to the conventional CBCT system. In
conclusion, the phase-contrast CBCT breast imaging approach is very promising to provide better image quality and to
lower x-ray dose level for tumor characterization.
KEYWORDS: Holography, Reconstruction algorithms, Signal attenuation, Holograms, Sensors, 3D image reconstruction, X-rays, Imaging systems, Optical engineering, Near field diffraction
A phase-contrast cone-beam computed tomography (PC CBCT) system is proposed for small-animal imaging that incorporates the in-line holography technique into CBCT system. Theoretical analysis shows that the in-line holographic image can be approximately transformed into line integrals of an object function composed of an attenuation term and a phase term. The Fresnel diffraction theory is applied to generate in-line holographic images along a circular orbit, and the Feldkamp-Davis-Kress algorithm is applied to reconstruct the object function. The proposed system was investigated using a numerical phantom, and the reconstruction was evaluated using the edge-enhancement factor and the relative reconstruction error. The reconstruction results show that all the structures in the numerical phantom are bounded with enhanced edges with negligible artifacts. These enhanced edges make the reconstruction visually sharper and clearer. The results show that while the relative reconstruction errors are very close to that of the conventional CBCT reconstruction, having a small cone angle, weak attenuation, small focal spot size, and high-resolution detector are preferred for a greater edge-enhancement effect.
The purpose of the study is to characterize the imaging performance of the recently built novel cone beam breast CT (CBBCT) scanner. This CBBCT scanner system has one x-ray source and one flat panel detector (Varian's PaxScan 4030CB) mounted on a rotating assembly. A patient table is mounted above the rotating tube/detector assembly. The table has a hole through it that allows a woman's breast to hang pendant in the imaging volume at the rotation axis. The tube/detector assembly rotates around the rotation axis and acquires multiple 2D projection images of the uncompressed breast located at the rotation axis in 10 seconds. Slip ring technology allows continuous rotation of the x-ray tube/detector assembly concentric to the opening in the table to achieve multiple circle scans. Also, it has a controlled vertical motion during the rotation to perform a spiral scan over 20 cm of travel. The continuous 360° rotation is designed to have speeds up to 1 rev/sec. This system was validated through a series of breast-imaging phantom studies and and patient studies. The results show that the image quality of the CBBCT scanner is excellent and all phantom masses (tissue-equivalent carcinomas) and calcifications as well as human subjects' masses, calcifications and abnormalities can be detected faithfully using the CBBCT technique with a glandular dose level less than or equal to that of a single two-view mammography exam. The results indicate that the CBBCT imaging system has much better detectability of small breast tumors compared to the conventional mammography system.
A new breast-shaped compensation filter has been designed and fabricated for breast imaging using our newly built
breast imaging (CBCTBI) system, which is able to scan an uncompressed breast with pendant geometry. The shape of
this compensation filter is designed based on an average-sized breast phantom. Unlike conventional bow-tie
compensation filters, its cross-sectional profile varies along the chest wall-to-nipple direction for better compensation for
the shape of a breast. Breast phantoms of three different sizes are used to evaluate the performance of this compensation
filter. The reconstruction image quality was studied and compared to that obtained without the compensation filter in
place. The uniformity of linear attenuation coefficient and the uniformity of noise distribution are significantly improved,
and the contrast-to-noise ratios (CNR) of small lesions near the chest wall are increased as well. Multi-normal image
method is used in the reconstruction process to correct compensation flood field and to reduce ring artifacts.
The purpose of this study is to characterize a newly built flat panel detector (FPD)-based cone beam CT
(CBCT) prototype for dynamic imaging. A CBCT prototype has been designed and constructed by completely
modifying a GE HiSpeed Advantage (HSA) CT gantry, incorporating a newly acquired large size real-time FPD (Varian
PaxScan 4030CB), a new x-ray generator and a dual focal spot angiography x-ray tube that allows the full coverage of
the detector. During data acquisition, the x-ray tube and the FPD can be rotated on the gantry over Nx360 degrees due
to integrated slip ring technology with the rotation speed of one second/revolution. With a single scan time of up to 40
seconds , multiple sets of reconstructions can be performed for dynamic studies. The upgrade of this system has been
completed. The prototype was used for a series of preliminary phantom studies: different sizes of breast phantoms, a
Humanoid chest phantom and scatter correction studies. The results of the phantom studies demonstrate that good
image quality can be achieved with this newly built prototype.
Phase-contrast imaging uses the phase coefficient rather than the attenuation coefficient alone to image objects.
Consequently, it may resolve some structures that have similar attenuation coefficients but different phase coefficients
as their surroundings. Phase contrast imaging is also an edge-enhanced imaging technique. With this method, the
boundary of inside small structures could be easily determined. In this paper, the possibility of incorporating the phase
contrast in-line method into the current cone beam CT (CBCT) system was explored. Starting from the interference
formula of in-line holography, some mathematical assumptions were made and thus, the terms in the interference
formula could be approximately expressed as a line integral that is the requirement for all CBCT algorithms. So, the
CBCT reconstruction algorithms, such as the FDK algorithm could be applied for the in-line holographic projections,
with some mathematical imperfection. A point x-ray source and a high-resolution detector were assumed for computer
simulation. The reconstructions for cone-beam CT imaging were studied. The results showed that all the lesions in the
numerical phantom could be observed with an enhanced edge. However, due to the edge-enhancement nature of the inline
holographic projection, the reconstructed images had obvious streak artifacts and numerical errors. The image
quality could be improved by using a hamming window during the filtering process. In the presence of noise, the
reconstructions from the in-line holographic projections showed clearer edges than the normal CT reconstructions did.
Finally it was qualitatively illustrated that small cone angle and weak attenuation were preferred in this method.
In flat-panel detector-based cone-beam CT breast imaging (CBCTBI), scatter is an important factor that
degrades image quality. It has been shown that despite the use of a large air gap, scatter still causes problems when
imaging a large breast phantom with our CBCTBI prototype. The SPR at the center region near the chest wall of a C-cup
phantom is about 0.5, and this value goes up to 0.9 for the D-cup phantom. As a result, the linear attenuation
coefficient (LAC) distortion and reduced contrast were obvious in the reconstruction slices. To conquer the scattering
problem, the beam-stop array (BSA) algorithm was presented in previous papers by our group. Since the breast is nearly
axially symmetric, only one or two more projections for scatter images are required for the BSA algorithm. Therefore,
the angular interpolation part in the algorithm could be simplified. The accuracy of the BSA algorithm is evaluated with
a water phantom and the error of LAC reconstruction is proven to be less than 2%. The results of a C-cup phantom
study shows that the LAC distortion in CBCT breast imaging could be corrected, and the CNR of target tumors is
increased by a small amount. The number of sampled scattering patterns for CBCTBI is also discussed. The results
showed that the BSA algorithm worked well for our CBCTBI prototype system. It could remove the scatter efficiently
and improve the image quality.
The clinical goal of breast imaging is to detect tumor masses when they are as small as possible, preferably less
than 10 mm in diameter. Conventional screen-film mammography is the most effective tool for the early detection of
breast cancer currently available. However, conventional mammography has relatively low sensitivity for the detection
of small breast cancers (under several millimeters). Specificity and the positive predictive value of mammography
remain limited owing to an overlap in the appearance of benign and malignant lesions, and surrounding structure. We
propose to address the limitations accompanying conventional mammography by incorporating a cone beam CT
reconstruction technique with a recently developed flat panel detector (FPD). We have performed a computer
simulation study and preliminary phantom studies to prove the feasibility of developing an FPD-based cone beam CT
breast imaging technique for a small size normal breast phantom. In this study, we report the design and construction
of a novel FPD-based cone beam breast CT scanner prototype. In addition, we present the results of phantom studies
performed on our current FPD-based cone beam CT scanner prototype, which uses the same flat panel detector
proposed for the cone beam breast CT scanner prototype, to predict the image performance of the novel cone beam
breast CT scanner, while we are completing the construction of the system.
The purpose of this study is to perform a preliminary evaluation of a newly constructed flat panel detector (FPD)-based system for cone beam CT imaging applications. A prototype flat-panel detector-based cone beam CT imaging system has been designed and constructed by modifying a GE HiSpeed Advantage CT scanner. The prototype consists of a modified GE CT HiSpeed Advantage CT gantry, an x-ray tube, a 397mm x 298mm Varian PaxScan 4030CB real time flat-panel detector mounted on the gantry, a CT table and an on-gantry PC to control image acquisition. Another PC workstation serving as an operating console controls the CT gantry and CT table, and sends trigger pulses to dedicated electronic interface modules to control radiographic exposure and to initiate data acquisition. Captured image data sets are first stored in the on-gantry computer and then downloaded from the on-gantry PC to the operating console for high-speed 3D image reconstruction. During data acquisition, the x-ray tube and the FPD can be rotated on the gantry over Nx360 degrees due to integrated slip ring technology. With a single scan, this device is able to acquire up to three hundred two-dimensional projections (1024 x 768 x 16 bits) for direct 3D reconstruction within 10 seconds. This system was used for a series of preliminary phantom studies and small animal studies. Using the continuous scan mode of the scanner, a few hundred projections were acquired for all volume scans. Direct 3D reconstructions were obtained to evaluate the system for cone beam CT for lung imaging applications. The preliminary results indicate that the newly built flat panel detector-based cone beam CT scanner works as expected and the low contrast resolution of the FPD-based CBCT system is approaching that of a multi-slice CT.
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