Fast iterative beam hardening correction based on frequency splitting in computed tomography qiao yanga,b, matthias elterb, ingo schasiepenb, nicole maassb and joachim horneggera,c apattern recognition lab, friedrichalexanderuniversity erlangennuremberg, erlangen, germany b siemens ag, healthcare sector, erlangen, germany c school in advanced optical. Correction of beam hardening in xray radiograms manuel baur,1 norman uhlmann,2 thorsten p oschel,1 andmatthias schr oter1,3, a 1institute for multiscale simulation, friedrichalexanderuniversit at, n agelsbachstrasse 49b, 91052 erlangen, germany 2fraunhofer institute for integrated circuits, flugplatzstrasse 75, 90768 furth, germany 3max planck institute for. Since ct reconstruction algorithms assume that this linear relationship holds artifacts are generated in the final image due to the beam hardening. A method of ct beam hardening calibration comprising. This software takes xray image data for a number of known samples, and fits them to a. Segmentationfree empirical beam hardening correction for ct. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Development of a beam hardening correction method for a. This method does not require xray spectrum measurement. The effect is conceptually similar to a highpass filter, in that only higher energy photons are left to contribute to the beam and thus the mean beam energy is.
Pdf beamhardening correction for xray ct projection images. Thus, the penetrating power of xray will continue to increase. The term beam hardening is used both to describe the appearance of an artefact in tomographic images and to describe the underlying principles. Oct 09, 2012 howto video for using gsi viewer 3d for beam hardening artifact reduction in the spine. In this work a simulationbased method is presented for correcting beam hardening, this method is applied to industrial xray ct measurement tasks and demonstrated to improve ct image quality. Can you recommend a free software or imagej plugin to. Method for beam hardening correction in quantitative computed. For a cone beam ct geometry, the computational complexity becomes even more signi. Beam hardening what is it and how to reduce it north star.
We postulate that, in addition to the greater cardiac output and central blood volume of larger patients, beam hardening also makes a significant contribution to the reduced aortic attenuation at ct angiography in these patients. Beamhardening correction method based on original sinogram. We forward projected ham, corrected projection values according to a polynomial correction, and reconstructed a correction image to obtain the. Beam hardening correction in iterative tomographic image reconstruction. A postreconstruction method for correcting the beamhardening artifacts in computed tomography ct images is proposed. Beamhardening correction for ct image of a rhomb of calcite, field of view 18 mm. Considering the former first, figure 1 illustrates a typical reconstructed image with beam hardening artefacts a uncorrected and b corrected. Beam hardening occurs because i xray attenuation in a given material is energy dependent and ii data collection in ct systems is not energy selective. Beam hardening correction for computed tomography images.
Iterative correction of beam hardening artifacts in ct. Pdf simulation of beam hardening in xray tomography and. Iterative correction methods for the beam hardening. Multiple beam hardening correction bhc methods have been described 3. Knowledge of these artifacts is important because they can mimic pathology e. Due to the polychromatic characteristics of xray sources the ratio of attenuated and incoming intensity is not exactly exponential with the material thickness. An empirical correction method for beamhardening artifact. Beamhardening artefact definition of beamhardening. A method for simultaneous image reconstruction and beam hardening correction pengchong jin, charles a. Rectangular beam, concrete beam, precast concrete beam. Beam hardening correction in multispectral mammography. This e ect is known as beam hardening and can cause artefacts such as cupping, the apparent higher density near the edge of a sample, and streaking, dark shadows between areas of relatively high density. Beam hardening correction for xray computed tomography of.
To reduce beam hardening artifacts it is usual to prefilter the xray beam with the builtin. Correction of beam hardening artefacts in microtomography for. Machinelearningbased nonlinear decomposition of ct images. Beam hardening can be a pernicious artifact because it changes the ct value of a material or void depending upon its location in an image. The algorithm identified a highenhancing fluidfilled vessel or chamber as a potential source of beam hardening if the structure exceeded an attenuation of 250 hu appendix e1. Referenceless beam hardening correction in 3d computed. Statics steel and concrete beam deflection calculator for. In this paper, we present an iterative beam hardening correction method for cone beam ct. Apart from the segmentation step, ebhc does not require assumptions on the spectra or on the type of material involved. Development and quantitative assessment of a beam hardening correction model for preclinical microct by sucheta mohapatra a thesis submitted in partial fulfillment of the requirements for the master of science degree in biomedical engineering in the graduate college of the university of iowa december 2012 thesis supervisor.
Citeseerx referenceless beam hardening correction in 3d. Simulation of beam hardening in xray tomography and its correction using linearisation and prefiltering approaches. The next section describes how to download and run the software. Fessler, segmentationfree statistical image reconstruction for polyener. Specimens of several material combinations were tested with ct and beam hardening corrected with the proposed algorithm. Image j tomogram, xray attenuation, computed tomography, filter. Using this method, the reconstructed image will suffer less from beam hardening artefact as less low energy xray has been.
Greater beam hardening was measured with higher tube voltages, resulting in a greater loss of aortic attenuation. A general beamhardening correction technique is presented. The authors assumed that a pixel in a ct image can be decomposed into equivalent tissue percentages, depending on its ct number. Xporenetworkmodeling allows for characterization and modeling of a set of connected areas, with spheres and lines representing those areas and their connections. Sparse xray ct image reconstruction and blind beam hardening correction via mass attenuation discretization abstract we develop a nonlinear sparse xray computed tomography ct image reconstruction method that accounts for beam hardening effects due to polychromatic xray sources.
It leads to various artifacts in reconstruction images and reduces image quality. Beam hardening correction in multispectral mammography abstract beam hardening is a phenomenon that distorts images taken with a nonmonochromatic xray source. We propose a new method to reduce the effects of nonlinearities such as beam hardening in computed tomography ct images. The aim of this study was to develop a fast and accurate beam hardening correction method which can deal with beam hardening artifacts induced by multimaterials objects. Image reconstruction of xray tomography by using image j platform. Metal artifacts are caused by nonlinear beamhardening effects combined with other factors such as scatter and poisson noise. Artifact is the main cause of decrease in image quality and in some cases the artifact render the image useless. A ct scan or computed tomography scan formerly computerized axial tomography scan or cat scan makes use of computerprocessed combinations of many xray measurements taken from different angles to produce crosssectional tomographic images virtual slices of specific areas of a scanned object, allowing the user to see inside the object without cutting. Highenhancing material image and waterenhancing material image were produced to calculate the amount of beam hardening and to reconstruct a corrected image fig 2. The scanning was of an aluminum annulus pipe was accomplished with a restrictive source collimator, limiting the beam to approximately 1cm in height at the detector. Calibrationfree beam hardening correction for myocardial perfusion imaging using ct jacob levi department of physics, case western reserve university, cleveland, oh 44106, usa brendan l.
By assuming that the materials composing scanned object are known and that they are distinguishable by their linear attenuation coefficients at some given energy, the beam hardening correction problem is converted into a nonlinear system problem. Beam hardening artifacts are highly undesirable for a medical diagnosis, because details in the reconstructed image are severely disturbed or completely lost. The algorithm is based on the observation that beam hardening artifacts mainly appear in the lower frequency components of the image and cause more correction iterations than correction in high frequency components. Pang s c and genna s 1977 reconstruction tomography in diagnostic radiology and nuclear medicine ed m m terpogossian baltimore, md. An iterative approach to the beam hardening correction in. A modelbased image reconstruction algorithm with simultaneous beam hardening correction for xray ct pengchong jin, charles a. However, the use of polychromatic xray sources can cause image artifacts and overall image degradat ion through beam hardening bh effects 1. A thin metal plate can be placed between the xray source and the object to reduce the amount of soft xray therefore there are higher percentage of hard xray in the beam, i. Correcting beam hardening at downscaled images will signi cantly limit the computational time but is still. This dataset contains beam hardening correction macros, running on imagej software.
Segmentation free statistical image reconstruction for polyener. Ct artifacts are common and can occur for various reasons. We calculate a base value as the mean value within a stable region. Iterative beam hardening correction for multimaterial objects. We make use of a tilted parallel beam geometry for an approximation of the beam. The method works iterative and without any reference measurements. Beam hardening correction in iterative tomographic image. It is this effective hardening of the beam that means that a plot of the log of the attenuation against material thickness is not linear, as would be the case if a monochromatic xray source was used. Based on spectrum estimation, the nonlinear attenuation process of the xray projection was modeled by reprojecting a template image with the estimated polychromatic spectrum. The theoretical part of this paper describes background for formation of this undesirable phenomenon which influences considerably quality of final images. This model can then be used to generate corrections appropriate for a single material to convert the observed. According to the wavefront setbased characterizations of streaking artefacts in 2b, singular lines representing streaking artefacts are included in all intersections of tangent spaces for two. Multimaterial beam hardening correctionmmbhc in computed tomography qiao yang, nicole maass, mengqiu tian, matthias elter, ingo schasiepen, andreas maier, and joachim hornegger abstractin computed tomography ct, the nonlinear attenuation characteristics of polychromatic xrays cause beam hardening artifacts in the reconstructed images.
A ct artefact caused by computer errors due to sudden changes in tissue density, from a relatively low density in brain tissue to a high density in bone. Bimobject corporation, acknowledged by investors with a global red herring 100 award, and a public company on nasdaq omx. A correction method for beam hardening, involving simple operations of the original polychromatic projection sinogram, is here presented based on the analysis of three physics characteristics implied by beam hardening. In the paper, we analyze the phenomenon of xray beam hardening, and discuss the relation between the xray beam. Because of this polychromaticity, beers law, which states that the ratio of the attenuated and incoming xray beam is exponential with the thickness of the material, is no longer valid.
Automated high accuracy, rapid beam hardening correction in xray computed tomography of multimineral, heterogeneous core samples. In addition to the beamhardening effect, quality and accuracy of xray ct reconstruction are often affected by the nonuniform xray illumination. Segmentationfree empirical beam hardening correction for. By assuming that the materials composing scanned object are known and that they are distinguishable by their linear attenuation coefficients at some given energy, the beam hardening correction problem is converted into a nonlinear system problem, which is then solved. However, its correction performance is highly dependent on the empirical determination of a scaling factor, which is used to. Beam hardening effect since the xray ct scan we are using a continuous xray, and it will continue to harden the radiation quality when the xray pass through the object. The original image is shown at normal a and high contrast b to highlight beamhardening artifacts in air and solid, as well as central ring artifact. However, the use of polychromatic xray sources can cause image artifacts and overall image degradation through beam hardening bh effects 1. Schuller s1, sawall s1, stannigel k2, hulsbusch m2, ulrici j2, hell e2, kachelrie. Artifacts and partialvolume effects utct university of texas.
Sauer, member, ieee abstractbeam hardening is a well known effect in ct scanners that is cause by a combination of a broad polychromatic source xray spectrum and energydependent material attenuation. This dataset contains beam hardening correction macros, running on imagej. An example of analytical corrections for beamhardening is shown in figure 5. The scope of this paper is the presentation of a method which allows performing a beam hardening correction on ct images of multimaterial objects without any knowledge about the used xray spectrum and present materials. Beam hardening is a wellknown effect in xray ct scanning that is caused by the interaction of a broad polychromatic source. This software takes xray image data for a number of known samples, and fits them to a model of the beam hardening process which occurs when a broad spectrum source is used to image a sample. An iterative approach to the beam hardening correction in cone beam ct proceedings authors. This postreconstruction method does not require the original projection data. Correction for beam hardening in computed tomography. A ct scan, or computed tomography scan is a medical imaging procedure that uses computerprocessed combinations of many xray measurements taken from different angles to produce crosssectional tomographic images virtual slices of specific areas of a scanned object, allowing the user to see inside the object without cutting. For a cone beam ct geometry, the computational complexity becomes even more significant.
It does not require any a priori knowledge of the material, distance from the source or the scan conditions current, energy, nor any segmentation of phases or calibration scan on phantom data. A modelbased correction method for beam hardening artefacts. In this work, we demonstrate the significant reduction of beam hardening artifacts by using an iterative reconstruction scheme which consists of a backward and a forward projector. This paper proposes a new method to correct beam hardening artifacts caused by the presence of metal in polychromatic xray computed tomography ct without degrading the intact anatomical images. Second, the accurate absorbent model of certain metal image is calculated according to the spectrum distribution of certain xray beam source and energy. We make use of a tilted parallel beam geometry for an approximation of the beam hardening effects in cone beam geometry. Can you recommend a free software or imagej plugin to remove. Sauer, member, ieee abstract beam hardening is a well known effect in ct scanners that is cause by a combination of a broad polychromatic. In the paper, we analyze the phenomenon of xray beam hardening, and discuss the relation between the x. The radiation spectrum can be changed by filtering the xrays after they exit the xray tube. To reduce beam hardening artifacts in ct in case of an unknown xray spectrum and unknown. The artifact correction is capable of correcting beam hardening artifacts for different scan parameters and scan scenarios.
A new approach for reducing beam hardening artifacts in. Jul 05, 2015 create an account or sign in to comment. Ct image correction for beam hardening using simulated. The artifacts inhibit the measurement from establishing a reliable scale for ct images. Creation of the beam hardening artifact springerlink.
The drawback of this method is that it needs a specific type of object. Method of ct beam hardening calibration free patents online. In this paper, we propose an iterative beam hardening correction method that is applicable for the case with multiple materials. Beam hardening correction with an iterative scheme using an. Effect of beam hardening on arterial enhancement in. Simulated projections through an uncorrected reconstructed image are used to correct for beam hardening. You need to be a member in order to leave a comment. Beam hardening is the phenomenon that occurs when an xray beam comprised of polychromatic energies passes through an object, resulting in selective attenuation of lower energy photons. Macovski a, alvarez r e, chan j l and stonestrom j p 1975 image processing for 2d and 3d reconstruction from projections, stanford, ca, august 47 pp mb15 to 8 opt. Johnsonv i applied science laboratory, oe medical systems, milwaukee, wi 53201 zdepmtmcnt of.
In the vernacular, this is referred to as hardening the radiation or beam hardening. Sauer,member, ieee abstractbeam hardening is a wellknown effect in xray ct scanning that is caused by the interaction of a broad polychro. Pdf iterative correction of beam hardening artifacts in ct. Knowledge of the impinging xray spectrum or the materials absorption characteristics is not necessary. The bonecorrection method has been widely adopted to compensate for beam hardening artifacts. The beam hardening will result in artifact as reconstruction image in xray tict.
The beamhardening artefacts are seen in figure 7 b, although the monochromatic image, in principle, should not have the beamhardening artefacts. So, if you have the chance, retake the images and try to minimize the beam hardening, for example, using a metal filter in front of the beam source. A linearization beamhardening correction method for xray. Metal artifact reduction for polychromatic xray ct based on a beam hardening corrector. Simulation, racing, open world, action, adventure, casual. The effect is conceptually similar to a highpass filter, in that only higher energy photons are left to contribute to the beam and thus the mean beam energy is increased hardened 1. Computed tomography, beam hardening, artefact correction, linearisation, spectrum estimation.
When the xray beam travels through an object, the lowenergy photons are absorbed more than the highenergy photons. The empirical beam hardening correction is an interesting alternative to conventional iterative higher order beam hardening correction algorithms. Eck department of biomedical engineering, case western reserve university, cleveland, oh 44106, usa rachid fahmi. Depending on the filter material used and the filter thickness, the low frequency portion of the radiation is attenuated. Metal artifact reduction for polychromatic xray ct based on. Development and quantitative assessment of a beam hardening. The image on the left shows the effects of beam hardening when measuring a light alloy casting. Data consistency conditionbased beamhardening correction. This report discusses the development of a correction for these distortions. A hardware corrections built into the ct scanner, including filtration by thin metal plates that physically harden the x. Fund for scientific research flanders, belgium keywords. Fast iterative beam hardening correction based on frequency. Pdf the effect of beam hardening on resolution in xray.
The purpose of this study is to analyse the effects of beam hardening on the. A method for simultaneous image reconstruction and beam. Multimaterials beam hardening artifacts correction for. Thus, the attempt to utilize a single ct number range to identify and quantify the extent of a particular material can become problematic. Knowledge of the ct computerized tomography scanner xray spectrum is necessary. The polychromatic nature of the xray beams and their effects on the reconstructed image are often disregarded. Jun, 2015 the beamhardening artefacts are seen in figure 7 b, although the monochromatic image, in principle, should not have the beamhardening artefacts. A modelbased image reconstruction algorithm with simultaneous beam hardening correction for xray ct abstract. First, the metal image is segmented by thresholding an initial image, where the metal traces are identified in the initial projection data using the forward projection of the metal image. Nov 27, 2001 the problem of constructing a ct image without beam hardening errors is to find. This paper focuses on description, implementation and simulation of a specific artifact beam hardening which occurs in ct examinations. Sparse xray ct image reconstruction and blind beam hardening.
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