X-ray 3D rotational angiography based on C-arm systems has become a versatile and established tomographic imaging modality for high contrast objects in interventional environment. Improvements in data acquisition, e.g...
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ISBN:
(纸本)0819457213
X-ray 3D rotational angiography based on C-arm systems has become a versatile and established tomographic imaging modality for high contrast objects in interventional environment. Improvements in data acquisition, e.g. by use of flat panel detectors, will enable C-arm systems to resolve even low-contrast details. However, further progress will be limited by the incompleteness of data acquisition on the conventional short-scan circular source trajectories. Cone artifacts, which result from that incompleteness, significantly degrade image quality by severe smearing and shading. To assure data completeness a combination of a partial circle with one or several line segments is investigated. A new and efficient reconstruction algorithm is deduced from a general inversion formula based on 3D Radon theory. The method is theoretically exact, possesses shift-invariant filteredbackprojection (FBP) structure, and solves the long object problem. The algorithm is flexible in dealing with various circle and line configurations. The reconstruction method requires nothing more than the theoretically minimum length of scan trajectory. It consists of a conventional short-scan circle and a line segment approximately twice as long as the height of the region-of-interest. Geometrical deviations from the ideal source trajectory are considered in the implementation in order to handle data of real C-arm systems. Reconstruction results show excellent image quality free of cone artifacts. The proposed scan trajectory and reconstruction algorithm assure excellent image quality and allow low-contrast tomographic imaging with C-arm based cone-beam systems. The method can be implemented without any hardware modifications on systems commercially available today.
The filteredbackprojection (FBP) algorithm is widely used in computed tomography for inverting the two-dimensional Radon transform. In this paper, we analyze the processing of an inconsistent data function by the FBP...
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The filteredbackprojection (FBP) algorithm is widely used in computed tomography for inverting the two-dimensional Radon transform. In this paper, we analyze the processing of an inconsistent data function by the FBP algorithm (in its continuous form). Specifically, me demonstrate that an image reconstructed using the FBP algorithm can be represented as the sum of a pseudoinverse solution and a residual image generated from an inconsistent component of the measured data. This reveals that, when the original data function is in the range of the Radon transform, the image reconstructed using the FBP algorithm corresponds to the pseudoinverse solution. When the data function is inconsistent, we demonstrate that the FBP algorithm makes use of a nonorthogonal projection of the data function to the range of the Radon transform.
In multi-slice spiral computed tomography (CT) there is an obvious trend in adding more and more detector rows. The goals are numerous: volume coverage, isotropic spatial resolution, and speed. Consequently, there wil...
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ISBN:
(纸本)0819452831
In multi-slice spiral computed tomography (CT) there is an obvious trend in adding more and more detector rows. The goals are numerous: volume coverage, isotropic spatial resolution, and speed. Consequently, there will be a variety of scan protocols optimizing clinical applications. Flexibility in table feed requires consideration of data redundancies to ensure efficient detector usage. Until recently this was achieved by approximate reconstruction algorithms only. However, due to the increasing cone angles there is a need of exact treatment of the cone beam geometry. A new, exact and efficient 3-PI algorithm for considering three-fold data redundancies was derived from a general, theoretical framework based on 3D Radon inversion using, Grangeat's formula. The 3-PI algorithm possesses a simple and efficient structure. This publication deals with a thorough evaluation of the performance of the 3-PI algorithm in comparison to the I-PI method for non-redundant data. Image quality of the 3-PI algorithm is superior. The prominent spiral artifacts and other discretization artifacts are significantly reduced due to averaging effects when taking into account redundant data. Certainly signal-to-noise ratio is increased. The computational expense is comparable even to that of approximate algorithms. The 3-PI algorithm proves its practicability for applications in medical imaging.
Proposed is a theoretically exact formula for inversion of data obtained by a spiral computed tomography ( CT) scan with a two- dimensional detector array. The detector array is supposed to be of limited extent in the...
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Proposed is a theoretically exact formula for inversion of data obtained by a spiral computed tomography ( CT) scan with a two- dimensional detector array. The detector array is supposed to be of limited extent in the axial direction. The main property of the formula is that it can be implemented in a truly filteredbackprojection fashion. First, one performs shift- invariant filtering of a derivative of the cone beam projections, and, second, the result is backprojected in order to form an image. Another property is that the formula solves the so- called long object problem. Limitations of the algorithm are discussed. Results of numerical experiments are presented.
In this paper the quantitative approach to 3D reconstruction of refractive index inhomogeneity of static phase object is presented. The method combines multidirectional phase shifting interferometry technique with tom...
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In this paper the quantitative approach to 3D reconstruction of refractive index inhomogeneity of static phase object is presented. The method combines multidirectional phase shifting interferometry technique with tomographic reconstruction. It is aimed on testing of optical material and elements with both symmetric and non-symmetric refractive index distributions. The optimisation of the parameters used in filteredbackprojection reconstruction algorithm is performed in order to maximise the overall accuracy of measurement. Experiments are performed to verify the methodology and parameters obtained from optimisation procedure. The results prove high performance of the proposed measuring procedure. (C) 2002 Elsevier Science Ltd. All rights reserved.
Image reconstruction algorithm for three-dimensional laser optoacoustic imaging system (LOIS) is proposed and tested in computer-simulating experiments. It was assumed that (1) acoustic transducers were evenly distrib...
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ISBN:
(纸本)0819443573
Image reconstruction algorithm for three-dimensional laser optoacoustic imaging system (LOIS) is proposed and tested in computer-simulating experiments. It was assumed that (1) acoustic transducers were evenly distributed with 3-degree interval along polar and azimuthal angles on the surface of a 100-mm diameter hemisphere, (2) all optoacoustic sources were located inside the hemisphere of a slightly smaller diameter. At the first stage of calculations, the initial data in a form of spherical surface integrals were converted into the plane surface integrals. We deduced an approximate analytical formula for this conversion. At the second stage, the three-dimensional Radon transform algorithm was applied for reconstruction of optoacoustic sources. Three-dimensional images of computer-simulated spherical objects were generated. Quality of reconstructed images was evaluated with the following four criteria: (1) the noise level on the entire tomogram, (2) the step-transfer function, (3) the loss-of-contrast function and (4) the contrast-dimension relation. These quality criteria may be employed to characterize any tomography systems regardless of the type of technology employed. Image analysis demonstrated that the artifact level associated with data conversion from spherical into planar coordinates did not exceed 10%. A 1-mm spatial resolution could be obtained with the proposed algorithm, provided the signal-to-noise ratio equals approximately 3 on the tomogram. Very small (0.5-mm diameter) and small (3-mm diameter) spherical tumors could be revealed on optoacoustic tomograms if their contrast equals at least 6 and 0.3, respectively.
Mathematical model of image reconstruction for two-dimensional optoacoustic imaging system is described. It was assumed that (1) receiving transducers are uniformly distributed along the perimeter of a 60-mm radius ri...
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ISBN:
(纸本)0819439347
Mathematical model of image reconstruction for two-dimensional optoacoustic imaging system is described. It was assumed that (1) receiving transducers are uniformly distributed along the perimeter of a 60-mm radius ring with 2.1-mm gaps between transducer centers and (2) initial data were known with 0.1-mm increments. The algorithm of radial back projection with convolution was used for optoacoustic image reconstruction. The convolution was evaluated with modified Shepp-Logan (MSL) and rectangular (RECT) space spectrum windows. Linear interpolation was applied for calculation of the convolution at the intermediate space points. The following four criteria were employed for estimation of resulting image quality: (1) noise level on entire tomogram, (2) a jump transfer function, (3) loss contrast function and (4) the contrast-dimension relation. Theoretical expressions for these parameters were derived and used for optimization of the proposed algorithm. Two-dimensional images of computer simulated spherical objects were reconstructed. It was shown that 0.1-mm spatial resolution could be obtained provided the signal-to-noise ratio equals approximately 3 at the tomogram. A very small (0.2-mm diameter) tumor and a small (2-mm diameter) tumor could be clearly revealed at the tomogram if their optical absorption contrast equals at least 2 and 0.1 respectively.
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