- Hetal Babla;Richard Conwell;
Scatter correction in single photon emission computed tomography(SPECT) has been focused on either using multiple-window acquisition technique or the scatter modeling technique in iterative image reconstruction.We propose a technique that uses only the emission data for scatter correction in SPECT.We assume that the scatter data can be approximated by convolving the primary data with a scatter kernel followed by the normalization using the scatter-to-primary ratio(SPR).Since the emission data is the superposition of the primary data and the scatter data,the convolution normalization process approximately results in the sum of the scatter data and a convolved version of scatter data with the kernel.By applying a proper scaling factor,we can make the estimation approximately equal to or less than the scatter data anywhere in the projection domain.Phantom and patient cardiac SPECT studies show that using the proposed emission-based scatter estimation can effectively reduce the scatter-introduced background in the reconstructed images.And additionally,the computational time for scatter correction is negligible as compared to no scatter correction in iterative image reconstruction.
2010年01期 v.15 1-10页 [查看摘要][在线阅读][下载 873K] [下载次数：30 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - Damien Vintache;Bernard Humbert;David Brasse;
The iterative reconstruction algorithms for X-ray CT image reconstruction suffer from their high computational cost.Recently Nvidia releases common unified device architecture(CUDA),allowing developers to access to the processing power of Nvidia graphical processing units(GPUs),in order to perform general purpose computations.The use of the GPU,as an alternative computation platform,allows decreasing processing times,for parallel algorithms.This paper aims to demonstrate the feasibility of such an implementation for the iterative image reconstruction.The ordered subsets convex(OSC) algorithm,an iterative reconstruction algorithm for transmission tomography,has been developed with CUDA.The performances have been evaluated and compared with another implementation using a single CPU node.The result shows that speed-ups of two orders of magnitude,with a negligible impact on image accuracy,have been observed.
2010年01期 v.15 11-16页 [查看摘要][在线阅读][下载 283K] [下载次数：182 ] |[网刊下载次数：0 ] |[引用频次：10 ] |[阅读次数：0 ] - Frank Dennerlein;Holger Kunze;Frédéric Noo;
A direct filtered-backprojection(FBP) reconstruction algorithm is presented for circular cone-beam computed tomography(CB-CT) that allows the filter operation to be applied efficiently with shift-variant band-pass characteristics on the kernel function.Our algorithm is derived from the ramp-filter based FBP method of Feldkamp et al.and obtained by decomposing the ramp filtering into a convolution involving the Hilbert kernel(global operation) and a subsequent differentiation operation(local operation).The differentiation is implemented as a finite difference of two(Hilbert filtered) data samples and carried out as part of the backprojection step.The spacing between the two samples,which defines the low-pass characteristics of the filter operation,can thus be selected individually for each point in the image volume.We here define the sample spacing to follow the magnification of the divergent-beam geometry and thus obtain a novel,depth-dependent filtering algorithm for circular CB-CT.We evaluate this resulting algorithm using computer-simulated CB data and demonstrate that our algorithm yields results where spatial resolution and image noise are distributed much more uniformly over the field-of-view,compared to Feldkamp's approach.
2010年01期 v.15 17-24页 [查看摘要][在线阅读][下载 1079K] [下载次数：64 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] - Fabian Stopp;Christian Winne;Emanuel Jank;Erwin Keeve;
In this paper we propose a new method for evaluating image recording strategies for limited angle tomography.In limited angle tomography exact three-dimensional(3-D) reconstruction is not achievable.With this method a metric for the reachable reconstruction quality by defined X-ray source trajectories is calculated.The result of our method is independent of reconstruction algorithms.Our approach is based on the gradients of the scanned volume and their grade of determinability.Compared to simulated reconstruction accuracy with simultaneous algebraic reconstruction techniques,the method of evaluation shows the same dependencies on X-ray source trajectories.By using the proposed method different source trajectories for a limited angle range are comparable with respect to the reachable reconstruction quality.
2010年01期 v.15 25-29页 [查看摘要][在线阅读][下载 594K] [下载次数：28 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] -
Iterative methods are popular choices in image reconstruction fields due to their capability of recovering object information from incomplete acquisition data.However,the computation process involves frequent uses of forward and backward projections that are computationally expensive.Past research has proved that a forward projector that can produce high quality images is crucial to achieve a good convergence rate.In this paper a high performance iterative reconstruction framework is introduced,where two most popular iterative algorithms:Simultaneous Algebraic Reconstruction Technique(SART) and Ordered-subsets Expectation Maximization(OSEM) are supported.The framework utilizes Siddon's ray-driven method to generate forward projected images.Benefited from functionalities offered by current generation of graphics processing units(GPUs),it achieves better performance when compared to previous GPU implementations that use grid-interpolated methods,on top of the significant speedups over CPU-based solutions.
2010年01期 v.15 30-35页 [查看摘要][在线阅读][下载 534K] [下载次数：62 ] |[网刊下载次数：0 ] |[引用频次：5 ] |[阅读次数：0 ] - Harald Schndube;Karl Stierstorfer;Frédéric Noo;
We present a theoretically-exact and stable computed tomography(CT) reconstruction algorithm that is capable of handling interrupted illumination and therefore of using all measured data at arbitrary pitch.This algorithm is based on a differentiated backprojection(DBP) on M-lines.First,we discuss the problem of interrupted illumination and how it affects the DBP.Then we show that it is possible to take advantage of some properties of the DBP to compensate for the effects of interrupted illumination in a mathematically exact way.From there,we have developed an efficient algorithm which we have successfully implemented.We show encouraging preliminary results using both computer-simulated data and real data.Our results show that our method is capable of achieving a substantial reduction of image noise when decreasing the helix pitch compared with the maximum pitch case.We conclude that the proposed algorithm defines for the first time a theoretically-exact and stable reconstruction method that is capable of beneficially using all measured data at arbitrary pitch.
2010年01期 v.15 36-43页 [查看摘要][在线阅读][下载 914K] [下载次数：20 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - HSIEH Hohui;HSIAO Ingtsung;
The goal of this paper is to investigate different reconstruction methods for solving the limited angle problem in reconstructing the projection data from a stationary multi-pinhole system based on a three-head clinical single photon emission computed tomography(SPECT) camera.Three iterative reconstruction approaches were studied including maximum likelihood expectation maximization(MLEM),maximum a posteriori expectation maximization(MAPEM) with a smoothing prior,and an alternating optimization schemes from MLEM and total variation(TV) optimization.A three-headed multipinhole SPECT was simulated with apertures of nine 1-mm pinholes each,and covered scanning volume of 6-mm diameter.The reconstructions were optimized for various iterations based on visual inspections,and finally 20 iterations were applied for each method.For both MLEM-TV and MAPEM-TV,various initial reconstructions before TV optimization were studied.The smoothing parameter for MAPEM and the gradient descent constant for TV were also investigated through visual comparison.The preliminary results showed the 3 reconstruction methods generated compatible images,and can restore the images from projection data suffering limited angular sampling.However,MLEM was noisy for low-count and highly limited angle data,and thus suitable smoothing in MAPEM alleviated this problem.Initial reconstructions were necessary for better edge enhancement in TV.The conclusion is that TV might be potential in producing more edge-enhanced images if all parameters were optimized.
2010年01期 v.15 44-49页 [查看摘要][在线阅读][下载 560K] [下载次数：34 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - Kjell Erlandsson;Brian F Hutton;
The ability to correctly quantify activity concentration with single photon emission computed tomography(SPECT) is limited by its spatial resolution.Blurring of data between adjacent structures,which is known as partial volume effects,can be compensated for by utilizing high resolution structural information from other imaging modalities such as CT or MRI.Previously developed partial volume correction(PVC) methods normally assume a spatially invariant point spread function.In SPECT this is not a good approximation,since the resolution varies with the distance from the collimator.A new method,p-PVC,was developed in this paper,which takes into account the distance dependent blurring.The method operates in projection space and is combined with filtered back-projection(FBP) reconstruction.Results from simulations show that similar quantitative results could be obtained with p-PVC+FBP as with OSEM with resolution recovery,although with better structural definition and an order of magnitude faster.
2010年01期 v.15 50-55页 [查看摘要][在线阅读][下载 376K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - LEVINE Margo S;SIDKY Emil Y;
A consistency condition is developed for computed tomography(CT) projection data acquired from a straight-line X-ray source trajectory.The condition states that integrals of normalized projection data along detector lines parallel to the X-ray path must be equal.The projection data is required to be untruncated only along the detector lines parallel to the X-ray path,a less restrictive requirement compared to Fourier conditions that necessitate completely untruncated data.The condition is implemented numerically on simple image functions,a discretization error bound is estimated,and detection of motion inconsistencies is demonstrated.The results show that the consistency condition may be used to quantitatively compare the quality of projection data sets obtained from different scans of the same image object.
2010年01期 v.15 56-61页 [查看摘要][在线阅读][下载 660K] [下载次数：33 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - William G Hawkins;
We utilize the Novikov-Natterer algorithm for non-uniform attenuation to invert the backscatter projections formed by the scatter of X-rays.The backscatter signal is treated as an emitter in a non-uniformly attenuating medium.This type of tomography has applications in radiology and dentistry for which metals effectively block the transmission of X-rays.Scanning for metals also has applications in security/baggage screening.The results show that when the forward scattering angle is zero,the algorithm,with a redefinition of the density function f,reduces to the PET attenuation correction.
2010年01期 v.15 62-67页 [查看摘要][在线阅读][下载 398K] [下载次数：23 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - SIDKY Emil Y;
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.
2010年01期 v.15 68-73页 [查看摘要][在线阅读][下载 984K] [下载次数：41 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - SIDKY Emil Y;ZHOU Otto;
There has been a renewed interest in algorithm development for image reconstruction from highly incomplete data in computed tomography(CT).Such algorithms may lead to reduced imaging dose and time,and to the design of innovative configurations tailored to specific imaging tasks.In recent years,a carbon-nanotube(CNT)-based field-emission x-ray source has been developed,which offers easy electronic control of radiation and thus can be an ideal candidate for gated imaging.We have recently proposed algorithms for image reconstruction from fan-and cone-beam data collected at highly sparse angular views through minimization of the total-variation(TV) of the image subject to the condition that the estimated data are consistent with the measured data.In this work,we investigate and demonstrate the application of the TV-minimization algorithm to reconstructing images from mouse data acquired with a CNT-based CT scanner at a number of views much lower than what is used in conventional CT imaging.The results demonstrate that the TV-minimization algorithm can yield images with quality comparable to those obtained from a large number of views by use of the conventional algorithms.The significance of the work may lie in that the substantial reduction of projection views promised by the TV-minimization algorithm can be exploited for reducing imaging dose and time or for improving temporal resolution in tasks such as dynamic imaging.
2010年01期 v.15 74-78页 [查看摘要][在线阅读][下载 1863K] [下载次数：48 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - CHO Seungryong;SIDKY Emil Y;
We investigate the feasibility of dual-energy method for image contrast enhancement in small animal studies using a low kV X-ray radiographic system.A robust method for X-ray spectrum estimation from transmission measurements,based on expectation-maximization(EM) method,is applied to an X-ray specimen radiographic system for dual energy imaging of a mouse.From transmission measurements of two known attenuators at two different X-ray tube voltages,the X-ray energy spectra are reconstructed using the EM-based method.From the spectra information thus obtained,the transmission data for bone and soft tissue in terms of various thicknesses are generated.Two polynomial functions of transmission data are then sought for to fit the inverted thicknesses of bone and soft-tissue.Scatters in cone-beam projection data acquired at two X-ray energies were corrected.From the scatter-corrected data,a bone thickness map is separated from a soft-tissue thickness map by use of the polynomial functions.
2010年01期 v.15 79-86页 [查看摘要][在线阅读][下载 700K] [下载次数：32 ] |[网刊下载次数：0 ] |[引用频次：2 ] |[阅读次数：0 ] - Thomas Khler;Tobias Klinder;Udo van Stevendaal;Cristian Lorenz;Peter Forthmann;
This paper investigates a reconstruction method for helical computed tomography which compensates for the motion artifacts in the thorax caused by patient breathing.The method takes into account a motion vector field determined from a four-dimensional(4-D) uncompensated image data set.Surface models of the lung and the ribs are tracked through the 4-D data set to create motion information within the entire thorax.Finally,an image is reconstructed using motion compensated back-projection.The results show that due to the use of shape models for the motion estimation,the method is fast and robust.Furthermore,since the surfaces are tracked individually,reconciling the opposite motion direction of the lung and rib cage is avoided in one motion vector field.
2010年01期 v.15 87-95页 [查看摘要][在线阅读][下载 2971K] [下载次数：23 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 马天予;缪寅斌;戴甜甜;
Accurate geometrical calibration is critical to obtaining high resolution and artifact free reconstructed images for modern animal single photon emission computed tomography(SPECT) systems.Although there have been many published works on the calibration of various SPECT systems,few studies have been done to evaluate the efficacy of the proposed calibration methods in a quantitative manner.This paper presents a numerical method to assess both the uniqueness and the quantitative accuracy of SPECT calibration,which is based on analyzing the singular value decomposition(SVD) components of the Jacobian matrix from a least-square cost function of the calibration.The proposed method is firstly validated by applying it to the calibration of a single pinhole SPECT system and comparing the results with those derived using a published method,and is then used to optimize the calibration setup for a slit-slat SPECT system.With the proposed method,a minimum required number of point source projections to achieve the desired calibration accuracy can be estimated and used as figure-of-merit to evaluate the goodness of a calibration setup.An inverse-square relationship between the calibration accuracy and the number of sampled projections is revealed.Optimal calibration setup is determined through an exhaustive search among all the possibilities of point source arrangements under certain conditions.We demonstrate that for the studied system,the best calibration accuracy is achieved by arranging the point source over the edge of FOV with evenly-spaced angular positions.Point source experiments were conducted to validate the proposed method.
2010年01期 v.15 96-101页 [查看摘要][在线阅读][下载 929K] [下载次数：41 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 陈荣昌;谢红兰;Luigi Rigon;杜国浩;Edoardo Castelli;肖体乔;
In line X-ray phase contrast micro-computed tomography(IL-XPCT),which can be implemented at third generation synchrotron radiation sources or by using a micro-focus X-ray tube,is a powerful technique for non-destructive,high-resolution investigations of a broad variety of materials.At the Shanghai Synchrotron Radiation Facility(SSRF),the X-ray Imaging and Biomedical Applications Beamline was built and started regular user operation in May 2009.Both qualitative(without phase retrieval) and quantitative(with phase retrieval) three-dimensional IL-XPCT experimental techniques have been established at the beamline.IL-XPCT experiments of a test sample(plastic pipes) used to evaluate the technique,and of a biological sample(locust) at the beamline are reported.Two series of images,qualitative and quantitative,including tomographic slices and three-dimensional rendering images were obtained.In qualitative images,there is a strong edge-enhancement which leads to very clear sample contours,while in quantitative images,the edge-enhancement fades but quantitative measurement of sample's phase information could be achieved.The experiments demonstrate that the combination of qualitative and quantitative images is useful for biological sample studies.
2010年01期 v.15 102-107页 [查看摘要][在线阅读][下载 1387K] [下载次数：62 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] - 梁文轩;张辉;胡广书;
This paper presents an optimized implementation of the FDK algorithm on a single fixed-point TMS320C6455 digital signal processor(DSP).Software pipelining and proper configuration of the data transfer enables a 2563 volume to be reconstructed in about 42 seconds from 360 projections with very good accuracy.This implementation reveals the potential of modern high-performance DSPs in accelerating image reconstruction,especially when cost and power consumption are emphasized.
2010年01期 v.15 108-113页 [查看摘要][在线阅读][下载 465K] [下载次数：68 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] Axial scan along circular trajectory has been the most desirable in clinical and preclinical applications.However,due to the violation of the data sufficiency condition,the reconstruction accuracy of axial scan deteriorates rapidly with increasing detector z-dimension.A number of algorithms have been proposed thus far to improve the reconstruction accuracy.It is well understood that,the larger the radius of circular trajectory,the more accurate the reconstruction.Ultimately,the reconstruction becomes accurate if the trajectory radius reaches infinite.Inspired by such observations,an asymptotic weighting scheme is proposed here for axial scan at large cone angles to improve reconstruction accuracy.In practice,there may be other ways to implement the asymptotic 3-D weighting scheme,and we present one approach in this paper with preliminary results.Further investigation may enable this asymptotic weighting scheme to improve reconstruction accuracy significantly,enabling numerous applications in which axial scan at large z-dimension is desired.
2010年01期 v.15 114-119页 [查看摘要][在线阅读][下载 726K] [下载次数：29 ] |[网刊下载次数：0 ] |[引用频次：1 ] |[阅读次数：0 ] - 金鑫;李亮;陈志强;张丽;邢宇翔;
This paper gives an efficient approach to reconstruct moving multiple objects(multi-object).Each object has independently rigid motion which includes translation and rotation.The traditional FBP algorithm can resolve the one-object motion problem rather well.However,it suffers from perceptible motion artifacts in multi-object cases.This paper proposes a new motion-compensated reconstruction approach with a priori knowledge of the rigid motion model.Both an FBP-type and an ART-type algorithm were derived.In an effort to evaluate the proposed algorithms,we have performed numerical studies by using different rigid motion models.Quantitative results demonstrate that the proposed FBP-type and ART-type algorithms can reconstruct multi-object free of motion artifacts.
2010年01期 v.15 120-126页 [查看摘要][在线阅读][下载 1082K] [下载次数：42 ] |[网刊下载次数：0 ] |[引用频次：3 ] |[阅读次数：0 ] - 陈志强;郑杰;李亮;徐荣栏;金鑫;黄娅;
A three-dimensional(3-D) phantom for the density distribution of the plasmasphere is established .The imaging processes of the extreme ultraviolet(EUV) Imager are computer-simulated,in which the Earth shelter is treated as a main problem.A modified ART method is devised to resolve the incomplete data reconstruction problem to validate and evaluate the proposed methods.The cone-beam EUV data are simulated based on the 3-D phantom from both a circular and semi-circular trajectories.Quantitative reconstruction results demonstrate the correctness of the proposed modified ART algorithm.The CT technique can be used to calculate the global density of the plasmasphere from the EUV data.
2010年01期 v.15 127-132页 [查看摘要][在线阅读][下载 1026K] [下载次数：38 ] |[网刊下载次数：0 ] |[引用频次：4 ] |[阅读次数：0 ] -
<正>Tsinghua Science and Technology (Tsinghua Sci Technol), a comprehensive academic journal sponsored by Tsinghua University, is published bimonthly. This journal aims at presenting the up-to-date scientific achievements
2010年01期 v.15 133页 [查看摘要][在线阅读][下载 654K] [下载次数：19 ] |[网刊下载次数：0 ] |[引用频次：0 ] |[阅读次数：0 ] 下载本期数据