[Show abstract][Hide abstract] ABSTRACT: Synchrotron-radiation-based microcomputed-tomography (SR-μCT) is a powerful tool for yielding 3D structural information of high spatial and contrast resolution about a specimen preserved in its natural state. A large number of projection views are required currently for yielding SR-μCT images by use of existing algorithms without significant artifacts. When a wet biological specimen is imaged, synchrotron x-ray radiation from a large number of projection views can result in significant structural deformation within the specimen. A possible approach to reducing imaging time and specimen deformation is to decrease the number of projection views. In the work, using reconstruction algorithms developed recently for medical computed tomography (CT), we investigate and demonstrate image reconstruction from sparse-view data acquired in SR-μCT. Numerical results of our study suggest that images of practical value can be obtained from data acquired at a number of projection views significantly lower than those used currently in a typical SR-μCT imaging experiment.
The Review of scientific instruments 04/2011; 82(4):043706. · 1.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To develop a backprojection-filtration (BPF) algorithm with improved noise properties over the existing BPF algorithm through utilizing (approximate) redundant information in circular cone-beam or fan-beam scans.
The backprojection steps in the existing filtered-backprojection (FBP) and BPF algorithms for fan-beam and cone-beam projections invoke spatially varying weighting factors, which may not only increase the computational load in image reconstruction but also, more importantly, result in reconstruction artifacts. Redundant information in fan-beam projections has been exploited for eliminating the weighting factor in the existing FBP algorithm. However, the new FBP algorithm cannot be applied to image reconstruction in a region of interest from transversely truncated data. In this work, the authors identify approximate data redundancy in circular cone-beam projections and propose a new BPF algorithm in which the approximate data redundancy is exploited for eliminating the spatially varying weighting factor in the existing BPF algorithm.
The authors have implemented and evaluated the proposed BPF algorithm in numerical studies of reconstructing 3D images from both the nontruncated and truncated projection data in a circular cone-beam scan. The results of numerical studies demonstrate that the proposed BPF algorithm retains the resolution property of the existing BPF algorithm, and that it can also reconstruct accurately ROI images from truncated data. More importantly, the results also indicate that the proposed BPF algorithm not only is computationally more efficient but also yields generally lower image variances than the existing BPF algorithm.
A BPF algorithm was proposed that not only retains the desirable properties of the existing BPF algorithm but also possesses improved computational and noise properties over the latter.
Medical Physics 03/2010; 37(3):1201-9. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The back-projection-filtration (BPF) algorithm has been applied to image reconstruction for cone-beam configurations with general source trajectories. The BPF algorithm can reconstruct 3-D region-of-interest (ROI) images from data containing truncations. However, like many other existing algorithms for cone-beam configurations, the BPF algorithm involves a back-projection with a spatially varying weighting factor, which can result in the non-uniform noise levels in reconstructed images and increased computation time. In this work, we propose a BPF algorithm to eliminate the spatially varying weighting factor by using a rebinned geometry for a general scanning trajectory. This proposed BPF algorithm has an improved noise property, while retaining the advantages of the original BPF algorithm such as minimum data requirement.
[Show abstract][Hide abstract] ABSTRACT: X-ray fluorescence computed tomography (XFCT) is a synchrotron-based imaging modality employed for mapping the distribution of elements within slices or volumes of intact specimens. A pencil beam of external radiation is used to stimulate emission of characteristic X-rays from within a sample, which is scanned and rotated through the pencil beam in a first-generation tomographic geometry. One limitation of XFCT is the long image acquisition time required to acquire a complete set of line integrals one-by-one. Typically, even if only a portion of a slice through the object is of interest, measurement lines are acquired spanning the entire object at every projection view over 180 degrees to avoid reconstructing images with so-called truncation artifacts. In this work, we show that when attenuation is negligible, recent developments in tomographic reconstruction theory can be used to reduce the scanning effort required to reconstruct regions of interest within the slice. The new theory provides explicit guidance as to which line integrals must be measured for a given ROI and also provides a backprojection-filtration reconstruction algorithm that averts the truncation artifacts that typically plague filtered backprojection reconstructions from truncated data. This is demonstrated through simulation studies and with real synchrotron-based XFCT data.
[Show abstract][Hide abstract] ABSTRACT: Reverse helical cone-beam computed tomography (CBCT) is a scanning configuration for potential applications in image-guided radiation therapy in which an accurate anatomic image of the patient is needed for image-guidance procedures. The authors previously developed an algorithm for image reconstruction from nontruncated data of an object that is completely within the reverse helix. The purpose of this work is to develop an image reconstruction approach for reverse helical CBCT of a long object that extends out of the reverse helix and therefore constitutes data truncation.
The proposed approach comprises of two reconstruction steps. In the first step, a chord-based backprojection-filtration (BPF) algorithm reconstructs a volumetric image of an object from the original cone-beam data. Because there exists a chordless region in the middle of the reverse helix, the image obtained in the first step contains an unreconstructed central-gap region. In the second step, the gap region is reconstructed by use of a Pack-Noo-formula-based filteredback-projection (FBP) algorithm from the modified cone-beam data obtained by subtracting from the original cone-beam data the reprojection of the image reconstructed in the first step.
The authors have performed numerical studies to validate the proposed approach in image reconstruction from reverse helical cone-beam data. The results confirm that the proposed approach can reconstruct accurate images of a long object without suffering from data-truncation artifacts or cone-angle artifacts.
They developed and validated a BPF-FBP tandem algorithm to reconstruct images of a long object from reverse helical cone-beam data. The chord-based BPF algorithm was utilized for converting the long-object problem into a short-object problem. The proposed approach is applicable to other scanning configurations such as reduced circular sinusoidal trajectories.
Medical Physics 01/2010; 37(1):32-9. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The goal of this research is to obtain systematic understandings of the effects of various physical factors that are important in breast tomosynthesis imaging and to develop techniques for effectively dealing with their effects and for reducing radiation dose. During the second year of the project we have achieved fruitful results based upon the progress made in our first year of the project. Specifically, we have further investigated the performance of the total-variation (TV) based algorithm under different data conditions and different constraint parameters. Furthermore, we have also proposed and investigated a new tomosynthesis imaging method with non-planar trajectories for yielding more data information with the same amount of imaging dose. We have also simulated the scatter in tomosynthesis breast imaging by convolving the ideal projection data with angular dependent scatter kernel.
[Show abstract][Hide abstract] ABSTRACT: Flying-focal-spot (FFS) technique has been used for improving the sampling condition in advanced clinical CT by collecting multiple cone-beam data sets with the focal-spot at different locations at each "projection view". It has been demonstrated that the increased sampling rate in FFS scans can substantially reduce aliasing artifacts in reconstructed images. However, the increase of the sampling density through multiple illuminations at each view can result in the increase of radiation dose to the imaged subject. In this work, we have applied a compressive-sensing (CS)-based algorithm to image reconstruction from data acquired in FFS scans. The results of the study demonstrate that aliasing artifacts observed images reconstructed by use of analytic algorithms can be suppressed effectively in images reconstructed with this CS-based algorithm from only data acquired at one FFS scan.
[Show abstract][Hide abstract] ABSTRACT: Non-circular scanning geometries such as helix or circular sinusoid have been used or proposed for cone-beam computed tomography (CBCT), because they provide sufficient data for numerically stable and exact image reconstruction within the scanned volume. Analytic algorithms have been developed for image reconstruction from cone-beam data acquired with a full-scan circular sinusoidal trajectory. In this work, we propose an innovative imaging approach in which a reduced-scan circular sinusoidal trajectory is used for acquiring data sufficient for exact 3D image reconstruction. A filtered backprojection (FBP) algorithm based on Pack-Noo's reconstruction formula is applied for image reconstruction in reduced-scan circular sinusoidal scans. We have conducted numerical studies to demonstrate the reduced-scan approach and to validate the FBP reconstruction algorithm in the proposed approach. The proposed scanning method can contribute to increasing the throughput of a scanner, while improving the image quality compared to a conventional circular scan.
Journal of X-Ray Science and Technology 01/2009; 17(3):189-205. · 1.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: X-ray fluorescence computed tomography (XFCT) is a synchrotron-based imaging modality employed for mapping the distribution of elements within slices or volumes of intact specimens. A pencil beam of external radiation is used to stimulate emission of characteristic X-rays from within a sample, which is scanned and rotated through the pencil beam in a first-generation tomographic geometry. It has long been believed that for each slice, the acquired measurement lines must span the entire object at every projection view over 180 degrees to avoid reconstructing images with so-called truncation artifacts. However, recent developments in tomographic reconstruction theory have overturned those long-held beliefs about minimum-data requirements and shown that it is possible to obtain exact reconstruction of ROIs from truncated projections. In this work, we show how to exploit these developments to allow for region of interest imaging in XFCT.
[Show abstract][Hide abstract] ABSTRACT: Helical scanning configuration has been used widely in diagnostic cone-beam computed tomography (CBCT) for acquiring data sufficient for exact image reconstruction over an extended volume. In image-guided radiation therapy (IGRT) and other applications of CBCT, it can be difficult, if not impossible, to implement mechanically a multiple-turn helical trajectory on the imaging systems due to hardware constraints. However, imaging systems in these applications often allow for the implementation of a reverse helical trajectory in which the rotation direction changes between two consecutive turns. Because the reverse helical trajectory satisfies Tuy's condition, when projections of the imaged object are nontruncated, it yields data sufficient for exact image reconstruction within the reverse helix volume. The recently developed chord-based algorithms such as the backprojection filtration (BPF) algorithm can readily be applied to reconstructing images on chords of a reverse helical trajectory, and they can thus reconstruct an image within a volume covered by the chords. Conversely, the chord-based algorithms cannot reconstruct images within regions that are not intersected by chords. In a reverse helix volume, as shown below, chordless regions exist in which no images can thus be reconstructed by use of the chord-based algorithms. In this work, based upon Pack-Noo's formula, a shift-invariant filtered backprojection (FBP) algorithm is derived for exact image reconstruction within the reverse helix volume, including the chordless region. Numerical studies have also been conducted to demonstrate the chordless region in a reverse helix volume and to validate the FBP algorithm for image reconstruction within the chordless region. Results of the numerical studies confirm that the FBP algorithm can exactly reconstruct an image within the entire reverse helix volume, including the chordless region. It is relatively straightforward to extend the FBP algorithm to reconstruct images for general trajectories, including reverse helical trajectories with variable pitch, tilted axis, and/or additional segments between turns.
Medical Physics 08/2008; 35(7):3030-40. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: X-ray differential phase-contrast tomography (DPCT) is a method for reconstructing the spatial distribution of the X-ray refractive index within an object from knowledge of differential projection data. Assuming geometrical optics wave propagation, these data describe the angles by which the probing optical beams are deflected by the object due to refraction. Phase-sensitive X-ray imaging methods such as diffraction enhanced imaging can measure the required beam-deflection data, and are being actively developed for medical imaging applications. In this work, we investigate and demonstrate the applicability of algorithms recently developed for conventional tomography for obtaining region-of-interest images in DPCT from knowledge of truncated differential projection data. A preliminary numerical study is conducted to validate and demonstrate the proposed reconstruction algorithm.
[Show abstract][Hide abstract] ABSTRACT: In classical tomosynthesis, the x-ray source generally is moved along a curve segment, such as a circular trajectory, within a plane that is perpendicular to the detector plane. Studies suggest that when the angular coverage and number of projection views are limited, it can be difficult to reconstruct accurate images within planes perpendicular to the detector plane in classical tomosynthesis. In this work, we investigate imaging strategies in tomosynthesis using trajectories that are not confined within a plane perpendicular to the detector plane. We expect that such trajectories can increase data information and thus lead reconstructed images with improved quality. Numerical studies were conducted for evaluating the image-reconstruction quality in classical tomosynthesis and tomosynthesis with trajectories that are not confined within a plane perpendicular to the detector plane. The results of the studies indicated that, with the same number of views, (or equivalenntly, the same amount of image radiation), data acquired in tomosynthesis with the trajectories that are not confined within a plane perpendicluar to the detector plane generally contain more information than that acquired with classical tomosynthesis and can thus yield images with improved quality.
[Show abstract][Hide abstract] ABSTRACT: Current dedicated, cone-beam breast CT scanners generally use a circular scanning configuration largely because it is relatively easy to implement mechanically. It is also well-known, however, that a circular scanning configuration produces insufficient cone-beam data for reconstrucing accurate 3D breast images. Approximate algorithms, such as FDK has been widely applied to reconstruct images from circular cone-beam data. In the FDK reconstruction, it is possible to observe artifacts such as intensity decay for locations that are not within the plane containing the circular source trajectory. Such artifacts may potentially lead to false positive and/or false negative diagnosis of breast cancer. Non-circular imaging configurations may provide data sufficient for accurate image reconstruction. In this work, we implement, investigate innovative, non-circular scanning configurations such as helical and saddle configurations for data acquisition on a dedicated, cone-beam breast CT scanner, and develop novel algorithms to reconstruct accurate 3D images from these data. A dedicated, cone-beam breast CT scanner capable of performing non-circular scanning configurations was used in this research. We have investigated different scanning configurations, including helical and saddle configurations. A Defrise disk phantom and a dead mouse were scanned by use of these configurations. For each configuration, cone-beam data were acquired at 501 views over each turn. We have reconstructed images using our BPF algorithm from data acquired with the helical scanning configuration.
[Show abstract][Hide abstract] ABSTRACT: Chord-based algorithms can eliminate cone-beam artifacts in images reconstructed from a clinical computed tomography (CT) scanner. The feasibility of using chord-based reconstruction algorithms was evaluated with three clinical CT projection data sets. The first projection data set was acquired using a clinical 64-channel CT scanner (Philips Brilliance 64) that consisted of an axial scan from a quality assurance phantom. Images were reconstructed using (1) a full-scan FDK algorithm, (2) a short-scan FDK algorithm, and (3) the chord-based backprojection filtration algorithm (BPF) using full-scan data. The BPF algorithm was capable of reproducing the morphology of the phantom quite well, but exhibited significantly less noise than the two FDK reconstructions as well as the reconstruction obtained from the clinical scanner. The second and third data sets were obtained from scans of a head phantom and a patient's thorax. For both of these data sets, the BPF reconstructions were comparable to the short-scan FDK reconstructions in terms of image quality, although sharper features were indistinct in the BPF reconstructions. This research demonstrates the feasibility of chord-based algorithms for reconstructing images from clinical CT projection data sets and provides a framework for implementing and testing algorithmic innovations.
[Show abstract][Hide abstract] ABSTRACT: Some of the recently developed image reconstruction algorithms for cone-beam computed tomography (CBCT) involve the computation of the finite Hilbert transform. We have previously studied noise property of the finite Hilbert transform and observed that it can be used for potentially improving the image noise property within a region of interest (ROI) in IGRT. Imaging radiation dose is one of the critical issues in IGRT, and in addition to existing dose-reduction schemes by use of ROI imaging, it is possible to achieve further patient dose reduction through modulating beam intensity so that a sub-ROI in the ROI be exposed by high flux of x-ray photons and the rest of the ROI be exposed by low flux of them. In this work, we investigate the technique for obtaining sub-ROI images, which is supposed to include the target under treatment, with high contrast-to-noise ratio (CNR) and the images within the rest of the ROI with low CNR. Numerical studies have been conducted as a preliminary in this work.
[Show abstract][Hide abstract] ABSTRACT: The back-projection filtration (BPF)algorithm is capable of reconstructing ROI images from truncated data acquired with a wide class of general trajectories. However, it has been observed that, similar to other algorithms for convergent beam geometries, the BPF algorithm involves a spatially varying weighting factor in the backprojection step. This weighting factor can not only increase the computation load, but also amplify the noise in reconstructed images The weighting factor can be eliminated by appropriately rebinning the measured cone-beam data into fan-parallel-beam data. Such an appropriate data rebinning not only removes the weighting factor, but also retain other favorable properties of the BPF algorithm. In this work, we conduct a preliminary study of the rebinned BPF algorithm and its noise property. Specifically, we consider an application in which the detector and source can move in several directions for achieving ROI data acquisition. The combined motion of the detector and source generally forms a complex trajectory. We investigate in this work image reconstruction within an ROI from data acquired in this kind of applications.
[Show abstract][Hide abstract] ABSTRACT: PURPOSE
The proposed reverse helical CBCT can considerably increase volume coverage than the current circular CBCT in IGRT. It, however, poses a significantly challenging image reconstruction task. In this work, we seek to develop and evaluate algorithms for accurate image reconstruction in reverse helical CBCT for IGRT.
METHOD AND MATERIALS
Current on-board CBCT scanner on a modern radiation therapy unit uses only a circular scan, which cannot yield data sufficient for reconstructing accurate 3D images, and the reconstructible volume of which is limited by the size of the detector. Diagnostic CT employs the slip-ring technology to achieve a multiple-turn helical scanning configuration for reconstructing 3D volumetric images. The on-board imager, however, can only reverse its rotation after each turn. A reverse helical scanning configuration is, therefore, proposed in this work. Accurate algorithm for image reconstruction for this novel scanning configuration is also proposed. Numerical studies using different phantoms relevant to IGRT were conducted to validate and evaluate the proposed reverse helical configuration and reconstruction algorithm.
We have implemented the algorithm for reconstructing accurate 3D images from reverse helical cone-beam data, and have performed numerical studies to validate and evaluate the proposed algorithm. Shepp-Logan and other phantoms were successfully reconstructed from two-turn reverse helical cone-beam data by use of the proposed algorithm. Results of our numerical studies confirm that the reverse helical scanning configuration can yield sufficient data for accurate 3D reconstruction and that the proposed algorithm can reconstruct accurately 3D images from the reverse helical cone-beam data.
A reverse helical CBCT with the proposed reconstruction algorithm is promising in increasing the reconstructible volume of the image and in improving the accuracy of the image for IGRT.
Cone-beam computed tomography (CBCT) plays an important role in image-guided radiation therapy (IGRT). We investigate and develop an innovative, reverse helical CBCT to benefit IGRT in this work.
Radiological Society of North America 2007 Scientific Assembly and Annual Meeting; 11/2007
[Show abstract][Hide abstract] ABSTRACT: PURPOSE
Current dedicated, cone-beam breast CT scanners use only a circular scan, which cannot yield data sufficient for reconstructing accurate 3D breast images. In this work, we implement and investigate innovative, non-circular scanning configurations such as helical and saddle configurations on a dedicated, cone-beam breast CT scanner, and develop algorithms to reconstruct accurate 3D images from these data.
METHOD AND MATERIALS
A dedicated, cone-beam breast CT scanner capable of performing non-circular scanning configurations was used. Helical, saddle, and additional scanning configurations were studied. Different physical phantoms were scanned by use of these configurations. For each of the configurations, cone-beam data were acquired at 501 views over each turn. The back-projection filtration method was used for reconstructing 3D images from the acquired data. We have also conducted simulation studies in which the actual scanning configurations and physical phantoms were simulated for evaluation of the mechanical inaccuracy in actual scans and its impact on reconstruction accuracy.
Our investigation confirms that the dedicated, cone-beam breast CT scanner under study is capable of performing innovative, non-circular scanning configurations for acquiring cone-beam data sufficient for accurate reconstruction of 3D images. We have also conducted studies of reconstruction of images in targeted regions of interest (ROI) within the breast, and the results of these studies demonstrated that accurate ROI images can be reconstructed from truncated cone-beam data. These non-circular imaging configurations yield more accurate images than the conventional circular configuration. The effect of physical factors, such as scatter and beam-hardening, on reconstructed images can be observed in the real data studies for certain situations.
We have investigated and developed innovative scanning configurations and reconstruction algorithms for a dedicated, cone-beam breast CT.
This research is to investigate and develop innovative, optimal scanning configurations and accurate reconstruction algorithms for a dedicated, cone-beam breast CT scanner.
Radiological Society of North America 2007 Scientific Assembly and Annual Meeting; 11/2007
[Show abstract][Hide abstract] ABSTRACT: Recently, there has been much progress in algorithm development for image reconstruction in cone-beam computed tomography (CT). Current algorithms, including the chord-based algorithms, now accept minimal data sets for obtaining images on volume regions-of-interest (ROIs) thereby potentially allowing for reduction of X-ray dose in diagnostic CT. As these developments are relatively new, little effort has been directed at investigating the response of the resulting algorithm implementations to physical factors such as data noise. In this paper, we perform an investigation on the noise properties of ROI images reconstructed by using chord-based algorithms for different scanning configurations. We find that, for the cases under study, the chord-based algorithms yield images with comparable quality. Additionally, it is observed that, in many situations, large data sets contain extraneous data that may not reduce the ROI-image variances.
IEEE Transactions on Medical Imaging 11/2007; 26(10):1328-44. · 4.03 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the last few years, mathematically exact algorithms, including the backprojection-filtration (BPF) algorithm, have been developed for accurate image reconstruction in helical cone-beam CT. The BPF algorithm requires minimum data, and can reconstruct region-of-interest (ROI) images from data containing truncations. However, similar to other existing reconstruction algorithms for helical cone-beam CT, the BPF algorithm involves a backprojection with a spatially varying weighting factor, which is computationally demanding and, more importantly, can lead to undesirable numerical properties in reconstructed images. In this work, we develop a rebinned BPF algorithm in which the backprojection invokes no spatially varying weighting factor for accurate image reconstruction from helical cone-beam projections. This rebinned BPF algorithm is computationally more efficient and numerically more stable than the original BPF algorithm, while it also retains the nice properties of the original BPF algorithm such as minimum data requirement and ROI-image reconstruction from truncated data. We have also performed simulation studies to validate and evaluate the rebinned BPF algorithm.
Physics in Medicine and Biology 10/2007; 52(18):5497-508. · 2.70 Impact Factor