Search

BACKGROUND: X-ray cone-beam computed laminography (CL) is widely used for large flat objects that computed tomography (CT) cannot investigate. The rotation angle of axis tilt makes geometric correction of CL system more complicated and has more uncertain factors. Therefore, it is necessary to evaluate sensitivity of the geometric parameters of CL system in advance. OBJECTIVE: This study aims to objectively and comprehensively evaluate sensitivity of CL geometric parameters based on the projection trajectory. METHODS: This study proposes the Minimum Deviation Unit (MDU) to evaluate sensitivity of CL geometric parameters. First, the projection trajectory formulas are derived according to the spatial relationship of CL system geometric parameters. Next, the MDU of the geometric parameters is obtained based on the projection trajectories and used as the evaluation index to measure the sensitivity of parameters. Then, the influence of the rotation angle of the axis tilt and magnification on the MDU of the parameters is analyzed. RESULTS: At low magnification, three susceptible parameters (η, u0, v0) with MDU less than 1 (° or mm) must be calibrated accurately to avoid geometric artifacts. The sensitivity of CL parameters increases as the magnification increases, and all parameters become highly sensitive when the magnification power is greater than 10. CONCLUSION: The results of this study have important guiding significance for the subsequent further parameter calibration. [ABSTRACT FROM AUTHOR]

The Precision of geometric parameters is the key requirement for grating-based phase-contrast CT and attenuationbased CT in cone-beam geometry. By extending our fan-beam geometric calibration work via Locally Linear Embedding (LLE) into the cone-beam case, here we calibrate the geometric parameters of our in-house phase-contrast CT system with attenuation projection data. Numerical and experimental studies show that the LLE-based calibration method is feasible to calibrate 8 parameters of the cone-beam geometry that improves reconstruction quality significantly. [ABSTRACT FROM AUTHOR]

X-ray computed tomography is an established volume imaging technique used routinely in medical diagnosis, industrial non-destructive testing, and a wide range of scientific fields. Traditionally, computed tomography uses scanning geometries with a single axis of rotation together with reconstruction algorithms specifically designed for this setup. Recently there has however been increasing interest in more complex scanning geometries. These include so called X-ray computed laminography systems capable of imaging specimens with large lateral dimensions or large aspect ratios, neither of which are well suited to conventional CT scanning procedures. Developments throughout this field have thus been rapid, including the introduction of novel system trajectories, the application and refinement of various reconstruction methods, and the use of recently developed computational hardware and software techniques to accelerate reconstruction times. Here we examine the advances made in the last several years and consider their impact on the state of the art. [ABSTRACT FROM AUTHOR]

BACKGROUND: Limited-angle problem occurs in many applications of X-ray computed tomography (CT) and it will lead to artifacts. OBJECTIVE: In this paper, we present the tomographic imaging of pipeline which is in service by cone-beam computed tomography (CBCT). And our purpose is to suppress the artifacts caused by the limited-angle problem. METHODS: First, traditional helical scanning strategy is adopted for the pipeline where can be fully scanned, and the slices with less or no defects from the reconstructed image are selected to constitute the prior image. Then a limited-angle reverse helical scanning strategy is developed for the pipeline where can be scanned within limited angular range. Second, considering the constraint of the prior image and the resemblance among slices of pipeline, an image model which incorporates the Schatten p(0 < p < 1)-norm penalty term is developed. Finally, split Bregman algorithm based method is utilized to solve the model. RESULTS: Numerical results show that our method is efficient and feasible in suppressing artifacts and it is superior to popular methods when the angular range is small. CONCLUSION: The developed method is promising in suppressing the artifacts in limited-angle problems, and it can be potentially used in pipeline testing. [ABSTRACT FROM AUTHOR]

The cone-beam reconstruction theory has been proposed by Kirillov in 1961, Tuy in 1983, Feldkamp in 1984, Smith in 1985, Pierre Grangeat in 1990. The Fourier slice theorem is proposed by Bracewell 1956, which leads to the Fourier image reconstruction method for parallel-beam geometry. The Fourier slice theorem is extended to fan-beam geometry by Zhao in 1993 and 1995. By combining the above mentioned cone-beam image reconstruction theory and the above mentioned Fourier slice theory of fan-beam geometry, the Fourier slice theorem in cone-beam geometry is proposed by Zhao 1995 in short conference publication. This article offers the details of the derivation and implementation of this Fourier slice theorem for cone-beam geometry. Especially the problem of the reconstruction from Fourier domain has been overcome, which is that the value of in the origin of Fourier space is 0/0. The 0/0 type of limit is proper handled. As examples, the implementation results for the single circle and two perpendicular circle source orbits are shown. In the cone-beam reconstruction if a interpolation process is considered, the number of the calculations for the generalized Fourier slice theorem algorithm is O(N^4), which is close to the filtered back-projection method, here N is the image size of 1-dimension. However the interpolation process can be avoid, in that case the number of the calculations is O(N^5). [ABSTRACT FROM AUTHOR]

The power and flexibility of polynomial surfaces are unleashed when their degrees are no longer restricted to four or lower, as they are used in early CT phantoms. They have proved useful and appropriate for geometric simulation of human and animal anatomy. In this paper a general algorithm is presented for the x-ray transform of any polynomial surface, as long as its ray-surface intersection equation is implemented on the computer. A versatile and powerful polynomial utility C++ class is created to simplify the implementation. Three groups of surfaces are implemented and applied to build a heart phantom closely simulating the Visible Man's heart. The x-ray transform algorithm is tested and verified by the successful reconstruction of the heart phantom. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Bolus-chasing CT angiography is an important new imaging mode for imaging cardiovascular structures and peripheral vessels. The adaptive bolus-chasing method implies a variable pitch spiral cone-beam CT scan. In this paper, we extend 2D-weighted, 3D-weighted and tilted plane FDK algorithms for variable pitch spiral cone-beam CT. Numerical simulation tests with high pitches and large cone angles are performed. Our results demonstrate that the tilted plane Feldkamp-type reconstruction algorithm shows the highest tolerance to the data incompleteness, the 3D-weighted half-scan FDK algorithm is the best choice for the practical variable pitch cone-beam CT, and the exact reconstruction algorithms perform less satisfactorily when a dataset is incomplete. However, the exact algorithms can be used for high accuracy reconstruction offline if a dataset is complete. Our work may facilitate development of practical variable pitch helical cone-beam CT. [ABSTRACT FROM AUTHOR]

Since Katsevich's work on cone-beam CT in 2002, a series of new reconstruction formulae for cone-beam and fan-beam reconstruction have been published. To understand these new results in a unified way, two schemes were proposed in the literature: one is based on the Radon formula, while the other on the Tuy formula. In the paper, we present a general two-step scheme for parallel-, fan- and cone-beam CT based on the inverse Fourier transform. We first derive parallel-beam formulae and then translate them to the divergent-beam case via a standardized method. This complete framework not only provides a single mechanism for the deduction of most existing CT formulae but also generates new algorithms. Meanwhile, along the development of this new framework some minor flaws are identified and fixed in publications. Additionally, the traditional assumption that an object be compactly supported inside a scanning trajectory is no longer needed. [ABSTRACT FROM AUTHOR]

Conventionally, the FDK algorithm is used to reconstruct images in many imaging systems where cone-beam projections are acquired from a single circular scanning path in a 2π angular range (full scan mode) and has been heuristically extended to a π+fan angle angular range (short-scan mode). In this paper, a new cone-beam reconstruction algorithm is derived for a single arc source trajectory with an equal weighting scheme. This algorithm is derived in the Katsevich framework. Since the single arc does not satisfy Tuy's data sufficiency condition, the resulting algorithm is an approximate reconstruction algorithm. The feature of one-dimensional (1D) shift-invariant filtering in the conventional FDK algorithm is nicely preserved. The new algorithm includes a voxel dependent backprojection step of weighted combinations of 1D Hilbert filtered data, after an initial differentiation operation. In comparing the new algorithm with the standard FDK: the new algorithm intrinsically handles full scan, short scan and super-short scan modes. Numerical simulations have been performed to validate the algorithm, and demonstrate more quantitatively correct density values when reconstructing points away from the central slice. Noise performance was assessed for both the new algorithm and the FDK algorithm using simulated Poisson noise. [ABSTRACT FROM AUTHOR]

For dynamic CT reconstruction, we have conceptualized a triple-source helical cone-beam scanning mode, and formulated a backprojected-filtration (BPF) algorithm for exact image reconstruction. The algorithm uses data from the three inter-helix PI-arcs related to the inter-helix PI-lines and the minimum detection windows defined for the triple-source configuration. The proof of the formula is based on Tuy's inversion formula and the geometric relations of inter-helix PI-lines. Simulation results demonstrate the validity of the reconstruction algorithm. The BPF algorithm is also extended for the (2N+1)-source helical cone-beam CT. [ABSTRACT FROM AUTHOR]

In this paper, we propose a helical cone-beam scanning configuration of triple symmetrically located X-ray sources, and study minimum detection windows to extend the traditional Tam-Danielsson window for exact image reconstruction. For three longitudinally displaced scanning helices of the same radius and a source location on any helix, the corresponding minimum detection window is bounded by the most adjacent turns respectively selected from the other two helices. The height of our proposed minimum detector window is only 1/3 of that in the single helix case. Associated with proposed minimum detection windows, we define the inter-helix PI-line and establish its existence and uniqueness property: through any point inside the triple helices, there exists one and only one inter-helix PI-line for any pair of the helices. Furthermore, we prove that cone-beam projection data from such a triple-source helical scan are sufficient for exact image reconstruction. Although there are certain redundancies among those projection data, the redundant part cannot be removed by shrinking the detector window without violating the data sufficiency condition. Those results are important components for development of exact or quasi-exact image reconstruction algorithms in the case of triple-source helical cone-beam scanning in the future. [ABSTRACT FROM AUTHOR]

In this paper, variable pitch helical cone-beam CT is studied. We prove a sufficient condition for the existence of PI-lines inside this variable pitch helix. Under this condition, we propose a new scanning configuration, called a spring scan, which can be used to scan a cylindrical object support. Based on Zou and Pan's BPF algorithm, we develop an exact BPF-type reconstruction algorithm for helical cone-beam CT in which the pitch of the helix varies with rotation angles. The algorithm includes four steps and can be used in region-of-interest (ROI) reconstruction by the PI-line determination step without a rebinning procedure as other BPF algorithms. Moreover, the algorithm can exactly reconstruct the object image only using the projection data within the Tam-Danielsson window, while Katsevich's algorithm requires more data than it. Furthermore, we test the proposed algorithm using the 3D Shepp-Logan phantom by a spring scan. The numerical results are described to support the correctness of the algorithm. [ABSTRACT FROM AUTHOR]

A state of the art X-ray micro-CT scanner takes about 20 seconds to acquire a full dataset, which is too slow to capture the rapidly beating heart of small animals. We have been working to develop the first electron-beam micro-CT (EBMCT) prototype for cardiac imaging of the mice and rats. In this paper, we describe the background on electron-beam CT (EBCT) and emphasize the needs for EBMCT. Then, we present a top-level design and a preliminary physical analysis for the first EBMCT scanner. The proposed EBMCT prototype would allow 0.03–0.01 s temporal resolution (35–70 half-scans per second) with 0.2 mm spatial resolution and 10% contrast resolution. Finally, we discuss a few related issues to further highlight that this project is not only important for basic biomedical research but also feasible technically. [ABSTRACT FROM AUTHOR]

The most popular Feldkamp algorithm for cone-beam image reconstruction assumes a scanning circle, and performs well only with a small cone angle. In this report, we propose a Feldkamp-type algorithm to increase the cone angle by several folds at a radiation dose comparable to that required by the classic Feldkamp algorithm. In our scheme, two half-scans of different radii are used. Then, approximate reconstructions from two half-scans are combined to produce a superior image volume by utilizing a relationship between the half-scan reconstruction error and the scanning locus radius. The merit of this half-scan error reduction based (HERB) algorithm is demonstrated in numerical simulation with the 3D Shepp-Logan phantom. [ABSTRACT FROM AUTHOR]