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Dual-energy computed tomography (CT) can be used in radiotherapy treatment planning for the calculation of absorbed dose distributions. The aim of this work is to evaluate whether there is room for improvement in the accuracy of the Monoenergetic Plus algorithm by Siemens Healthineers. A Siemens SOMATOM Force scanner was used to scan a cylindrical polymethyl methacrylate phantom with four rod-inserts made of different materials. Images were reconstructed using ADMIRE and processed with Monoenergetic Plus. The resulting CT numbers were compared with tabulated values and values simulated by the proof-of-a-concept algorithm DIRA developed by the authors. Both the Monoenergetic Plus and DIRA algorithms performed well; the accuracy of attenuation coefficients was better than about ±1% at the energy of 70 keV. Compared with DIRA, the worse performance of Monoenergetic Plus was caused by its (i) two-material decomposition to iodine and water and (ii) imperfect suppression of the beam hardening artifact in ADMIRE. Funding: CancerfondenSwedish Cancer Society [CAN 2017/1029, CAN 2018/622]; Swedish state government [LiO-602731]; Swedish county councils, the ALF-agreement [LiO-602731]; Patientsakerhetsforskning Region Ostergotland [LiO-724181]; VetenskapsradetSwedish Research Council [VR-NT 2016-05033]

Rationale and Objectives To compare degradation of the image quality due to beam hardening artifacts in reduced-iodine-dose virtual monochromatic imaging (VMI) between a new fast kVp switching dual-energy computed tomography (CT) scanner (Revolution CT) and the conventional dual-energy scanner (Discovery CT). Materials and Methods First, a phantom study was performed to quantitatively evaluate beam hardening artifacts in images obtained by VMI reconstruction at different energy levels. In the second study, we performed a retrospective evaluation of the images of 28 patients who had undergone reduced-iodine (300 mg/kg) dual-energy scanning in both Revolution CT and Discovery CT. We evaluated each image quantitatively by measuring the contrast-to-noise ratio (CNR) and qualitatively by scoring the artifacts and image quality. We also calculated the modulation transfer function (MTF) and noise power spectrum (NPS) of the two scanners. Results In the phantom study, VMI reconstruction of the CT images at 40–70 keV was associated with a significantly greater reduction in the severity of the artifacts in the Revolution CT images as compared to the Discovery CT images. In the retrospective study, there were no significant differences in the CT value of the aorta, noise, or CNR between the two scanners, but the scores for image quality were significantly higher in the Revolution CT images as compared to the Discovery CT images. The MTF of Revolution CT was higher than that of Discovery CT, reflecting the better spatial resolution. Conclusion In Revolution CT, beam hardening artifacts were reduced in reduced-iodine VMI at lower energy levels compared to Discovery CT, contributing to better image quality.

Cone-beam computed tomography (CBCT) has become increasingly important as a low-radiation imaging technique with high resolution. The current new generation CBCT’s aim to optimize the benefits of CBCT while limiting the traditional disadvantages with features such as a larger gantry, higher tube voltage and a moveable table. Very promising is the current development of dual energy CBCT for detecting bone marrow edema, a better soft tissue visualization and reduction of beam hardening artifact. implementation of iterative reconstructions and artificial intelligence in high-end CBCT is a potential tool in a further very substantial dose reduction.

This article presents a two-stage method for beam hardening artifact correction of dental cone beam computerized tomography (CBCT). The proposed artifact reduction method is designed to improve the quality of maxillofacial imaging, where soft tissue details are not required. Compared to standard CT, the additional difficulty of dental CBCT comes from the problems caused by offset detector, FOV truncation, and low signal-to-noise ratio due to low X-ray irradiation. To address these problems, the proposed method primarily performs a sinogram adjustment in the direction of enhancing data consistency, considering the situation according to the FOV truncation and offset detector. This sinogram correction algorithm significantly reduces beam hardening artifacts caused by high-density materials such as teeth, bones, and metal implants, while tending to amplify special types of noise. To suppress such noise, a deep convolutional neural network is complementarily used, where CT images adjusted by the sinogram correction are used as the input of the neural network. Numerous experiments validate that the proposed method successfully reduces beam hardening artifacts and, in particular, has the advantage of improving the image quality of teeth, associated with maxillofacial CBCT imaging.

A new empirical method has been proposed for the suppression of beam hardening artifacts. It utilizes discrete cosine transform based missing data estimation and an edge-preserving smoothing filter. The method does not need any information about the experiment specification or the X-ray spectrum used and the material being inspected. The corrections are done in the image domain. The proposed method is first tested on three test samples. It is then applied to the cylindrical sample made of Perspex, aluminiumand steel. The results are compared with that of the existing work and the outcome is promising. The horizontal line profile and other parametric comparisons indicate that the proposed method can suppress beam-hardening artifacts significantly. The application of Sobolev space error analysis has also been made to ensure good global reconstruction.

Beam hardening caused cupping and light or dark streaks are one of the major problems in computer tomographic imaging. There are many possibilities to manage beam hardening artifacts. Deep learning is a set of techniques that proved to be useful in various fields, and it is more and more commonly used in computer tomography as well. Our goal in this paper was to reduce beam hardening artifact using deep convolutional neural networks and to develop a model, which can improve the quality of the beam hardening distorted image with the presence of high amount of electrical noise. Moreover, we investigated various ways of fusing deep neural networks with the process of computer tomographic imaging. For these purposes we produced a large heterogeneous simulated dataset. We tested the performance of four convolutional networks-based methods for correcting the distorted data at various stages of the tomographic imaging pipeline. The evaluations were based on three different error measures. The evaluations have shown that the best result can be achieved by the method which makes the reconstructions step as a part a neural network. This method was capable of removing a significant amount of distortion in case of high level of electrical noise.

Nondestructive evaluation (NDE) of additively manufactured (AM) parts is important for understanding the impacts of various process parameters and qualifying the built part. X-ray computed tomography (XCT) has played a critical role in rapid NDE and characterization of AM parts. However, XCT of metal AM parts can be challenging because of artifacts produced by standard reconstruction algorithms as a result of a confounding effect called “beam hardening.” Beam hardening artifacts complicate the analysis of XCT images and adversely impact the process of detecting defects, such as pores and cracks, which is key to ensuring the quality of the parts being printed. In this work, we propose a novel framework based on using available computer-aided design (CAD) models for parts to be manufactured, accurate XCT simulations, and a deep-neural network to produce high-quality XCT reconstructions from data that are affected by noise and beam hardening. Using extensive experiments with simulated data sets, we demonstrate that our method can significantly improve the reconstruction quality, thereby enabling better detection of defects compared with the state of the art. We also present promising preliminary results of applying the deep networks trained using CAD models to experimental data obtained from XCT of an AM jet-engine turbine blade.

Dual-energy computed tomography (DECT) has shown a great potential for lowering range uncertainties, which is necessary for truly leveraging the Bragg peak in proton therapy. However, analytical stopping-power-ratio (SPR) estimation methods have limitations in resolving the influence from the beam-hardening artifact, i.e. CT number variation of the same object scanned under different imaging conditions, such as different patient size and location in the field-of-view (FOV). We present a convolutional neural network (CNN)-based framework to estimate proton SPR that accounts for patient geometry variation and addresses CT number variation. The proposed framework was tested on both prostate and head-and-neck (HN) patient datasets. Simulated CT images were used in order to have a well-defined ground-truth SPR for evaluation. Two training scenarios were evaluated: training with patient CT images (ideal scenario) and training with computational phantoms (realistic scenario). For the training in ideal scenario, computational phantoms were created based on 120 kVp patient CT images using a custom-defined density and material translation curve. Then, 80 kVp and 150 kVp Sn DECT image pairs were obtained using ray-tracing simulation, and their corresponding SPR was calculated from the known density and elemental compositions. For the training in realistic scenario, computational phantoms were created based on the geometry of calibration phantoms. For both scenarios, evaluation was performed on the phantoms created from patient CT images. Compared to a conventional parametric model, U-net trained with computational phantoms (realistic scenario) reduced the SPR estimation uncertainty (95th percentile) of the prostate patient from 1.10% to 0.71%, and HN patient from 2.11% to 1.20%. With the U-net trained with patient images (ideal scenario) uncertainty values were 0.32% and 0.42% for prostate and HN patients, respectively. These results suggest that CNN has great potential to improve the accuracy of SPR estimation in proton therapy by incorporating individual patient geometry information.

BACKGROUND: Cylindrical phantoms are often imaged by X-ray computed tomography (CT) to evaluate the extent of beam hardening (or cupping artifact) resulting from a polychromatic X-ray source. OBJECTIVE: Our goal was to derive analytical expressions for the reconstructed image of a homogeneous cylindrical phantom exhibiting a cupping artifact, to permit a quantitative comparison with experimental cupping data. METHODS: A filtered backprojection method was employed to obtain the analytical cupping profile for the phantom, assuming that the projection data could be approximated as a power series with respect to the sample penetration thickness. RESULTS: The cupping profile was obtained analytically as a series of functions by employing Ramachandran filtering with an infinite Nyquist wavenumber. The quantitative relationship between the power series of the projection and the nth moment of the linear attenuation coefficient spectrum of the phantom was also determined. Application of the obtained cupping profile to the evaluation of the practical reconstruction filters with a finite Nyquist wavenumber and to the best choice of the contrast agent was demonstrated. CONCLUSIONS: The set of exact solutions derived in this work should be applicable to the analysis of cylindrical phantom experiments intended to evaluate CT systems.

X-ray computed tomography (XCT) became an important instrument for quality assurance in industry products as a non-destructive testing tool for inspection, evaluation, analysis and dimensional metrology. Thus, a high-quality image is required. Due to the polychromatic nature of X-ray energy in XCT, this leads to errors in attenuation coefficient which is generally known as beam hardening artifact. This leads to a distortion or blurring-like cupping and streak in the reconstruction images, where a significant decrease in imaging quality is observed. In this paper, recent research publications regarding common practical correction methods that were adopted to improve an imaging quality have been discussed. It was observed from the discussion and evaluation, that a problem behind beam hardening reduction for the multi-materials object, especially in the absence of prior information about X-ray spectrum and material characterizations would be a significant research contribution, if the correction could be achieved without the need to perform forward projections and multiple reconstructions.

PURPOSE This study aims to propose a physics-based method of reducing beam-hardening artifacts induced by high-attenuation materials such as metal stents or other metallic implants. METHODS The proposed approach consists of deriving a sinogram inconsistency formula representing the energy dependence of the attenuation coefficient of high-attenuation materials. This inconsistency formula more accurately represents the inconsistencies of the sinogram than that of a previously reported formula (called the MAC-BC method). This is achieved by considering the properties of the high-attenuation materials, which include the materials' shapes and locations and their effects on the incident X-ray spectrum, including their attenuation coefficients. RESULTS Numerical simulation and phantom experiment demonstrate that the modeling error of MAC-BC method are nearly completely removed by means of the proposed method. CONCLUSION The proposed method reduces beam-hardening artifacts arising from high-attenuation materials by relaxing the assumptions of the MAC-BC method. In doing so, it outperforms the original MAC-BC method. Further research is required to address other potential sources of metal artifacts, such as photon starvation, scattering, and noise.

Background The beam hardening artifact is one of most important modalities of metal artifact for polychromatic X-ray computed tomography (CT), which can impair the image quality seriously. Objective An iterative approach is proposed to reduce beam hardening artifact caused by metallic components in polychromatic X-ray CT. Methods According to Lambert-Beer law, the (detected) projections can be expressed as monotonic nonlinear functions of element geometry projections, which are the theoretical projections produced only by the pixel intensities (image grayscale) of certain element (component). With help of a prior knowledge on spectrum distribution of X-ray beam source and energy-dependent attenuation coefficients, the functions have explicit expressions. Newton-Raphson algorithm is employed to solve the functions. The solutions are named as the synthetical geometry projections, which are the nearly linear weighted sum of element geometry projections with respect to mean of each attenuation coefficient. In this process, the attenuation coefficients are modified to make Newton-Raphson iterative functions satisfy the convergence conditions of fixed pointed iteration(FPI) so that the solutions will approach the true synthetical geometry projections stably. The underlying images are obtained using the projections by general reconstruction algorithms such as the filtered back projection (FBP). The image gray values are adjusted according to the attenuation coefficient means to obtain proper CT numbers. Results Several examples demonstrate the proposed approach is efficient in reducing beam hardening artifacts and has satisfactory performance in the term of some general criteria. In a simulation example, the normalized root mean square difference (NRMSD) can be reduced 17.52% compared to a newest algorithm. Conclusions Since the element geometry projections are free from the effect of beam hardening, the nearly linear weighted sum of them, the synthetical geometry projections, are almost free from the effect of beam hardening. By working out the synthetical geometry projections, the proposed approach becomes quite efficient in reducing beam hardening artifacts.

Objective: to explain the meaning and to illustrate technical artifacts (aliasing as well as the ring artifact) and beam hardening (metal artifact) that can be present in the dentomaxillofacial cone beam computed tomography (CBCT), and to check the accessibility of free illustrations of these artifacts in medical publications. Material and methods: One observer applied five search equations using database PubMed. The exclusion criteria were: experimental studies, animal studies, studies not related to dentomaxillofacial area, and articles with closed access. There was no time limit for the search of articles. We limited our search to English and French language. Results: Only 3 articles out of 434 publications were retained after application of inclusion/exclusion criteria. In these articles only 4 annotated figures were freely accessible in medical publications from PubMed. In this paper we presented examples of aliasing, ring artifact, and beam artifacts from I-CAT, Carestream 9000 3D (Kodak), and Planmeca Promax 3D Mid CBCT. The intensity of beam hardening artifact varies from major degradation of image (i.e., subperiosteal implants, bridges, crowns, dental implants, and orthodontic fix appliances), through mean degradation (screws securing titanium mesh, head of mini-implant) to no beam hardening on metallic devices (orthodontic anchorage, orthodontic contention wire) or on dense objects (endodontic treatments, impression materials, Lego box). Some beam hardening artifacts arising from nasal piercing, hairs, or hearing aid device may be present on the image but they will not disturb the evaluation of the field of view. Conclusions: reduction of aliasing artifact is related with the improvement of detectors quality. The presence of ring artifact means that CBCT device has lost its calibration. The field of view (FOV) needs to be reduce in order to avoid scanning regions susceptible to beam hardening (e.g., metallic restorations, dental implants). Finally, the accessibility to open knowledge on technique -related CBCT artifacts seems extremely limited when searching at PubMed database.

To investigate the performance of a reconstruction algorithm, single-energy metal artifact reduction (SEMAR), against standard reconstruction in cardiac computed tomography (CT) studies of patients with implanted metal and in a defibrillator lead phantom.From a retrospective, cross-sectional clinical study with institutional review board approval of 118 patients with implanted metal, 122 cardiac CT studies from November 2009 to August 2016 performed on a 320-detector row scanner with standard and SEMAR reconstructions were included. The maximum beam hardening artifact radius, artifact attenuation variation surrounding the implanted metal, and image quality on a 4-point scale (1-no/minimal artifact to 4-severe artifact) were assessed for each reconstruction. A defibrillator lead phantom study was performed at different tube potentials and currents with both reconstruction methods. Maximum beam hardening artifact radius and average artifact attenuation variation were measured.In the clinical study, SEMAR markedly reduced the maximum beam hardening artifact radius by 77% (standard: 14.8 mm [IQR 9.7-22.2] vs. SEMAR: 3.4 mm [IQR 2.2-7.1], p 0.0001) and artifact attenuation variation by 51% (standard: 130.0 HU [IQR 75.9-184.4] vs. SEMAR: 64.3 HU [IQR 48.2-89.2], p 0.0001). Image quality improved with SEMAR (standard: 3 [IQR 2-3.5] vs. SEMAR: 2 [IQR 1-2.5], p 0.0001). The defibrillator lead phantom study confirmed these results across varying tube potentials and currents.SEMAR reconstruction achieved superior image quality and markedly reduced maximum beam hardening artifact radius and artifact attenuation variation compared to standard reconstruction in 122 clinical cardiac CT studies of patients with implanted metal and in a defibrillator lead phantom study.

CT images are often affected by beam-hardening artifacts due to the polychromatic nature of the X-ray spectra. These artifacts appear in the image as cupping in homogeneous areas and as dark bands between dense regions, such as bones. This paper proposes a simplified statistical reconstruction method for X-ray CT based on Poisson statistics that accounts for the non-linearities caused by beam hardening. The main advantages of the proposed method over previous algorithms is that it avoids the preliminary segmentation step, which can be tricky, especially for low-dose scans, and it does not require knowledge of the whole source spectrum, which is often unknown. Each voxel attenuation is modeled as a mixture of bone and soft tissue by defining density-dependent tissue fractions, maintaining one unknown per voxel. We approximate the energy-dependent attenuation corresponding to different combinations of bone and soft tissue, so called beam-hardening function, with the 1D function corresponding to water plus two parameters that can be tuned empirically. Results on both simulated data with Poisson sinogram noise and two rodent studies acquired with the ARGUSCT system showed a beam hardening reduction (both cupping and dark bands) similar to analytical reconstruction followed by post-processing techniques, but with reduced noise and streaks in cases with low number of projections, as expected for statistical image reconstruction. This work was partially funded by NIH grants R01-HL-098686 and U01 EB018753, by Spanish Ministerio de Economia y Competitividad (projects TEC2013-47270-R and RTC-2014-3028-1) and the Spanish Ministerio de Economia, Industria y Competitividad (projects DPI2016-79075-R AEI/FEDER, UE - Agencia Estatal de Investigación and DTS17/00122 Instituto de Salud Carlos III - FIS), and co-financed by ERDF (FEDER) Funds from the European Commission, “A way of making Europe”. The CNIC is supported by the Spanish Ministerio de Economia, Industria y Competitividad and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505). En prensa

Background:Dual energy computed tomography (DECT) is highly accurate for the diagnosis of gout. However, many artifacts have been described (1,2) such as nail bed, skin, beam hardening, sub-millimeter and vascular artifacts). Their presence can lead to a risk of over-diagnosis (false positives).Objectives:Main objective of this case-control study was to determine the optimal DECT settings post-treatment parameters (ratio and attenuation coefficient (HU)) in order to reduce the frequency of lower limb artifacts in patients with suspected gout of the lower limbs.Methods:Seventy-seven patients hospitalized for suspected gout arthritis (feet/ankles and/or knees) who received a DECT imaging were consecutively included (final diagnosis of 43 gout and 34 other rheumatic disorders). Different post-treatment settings were evaluated from the Syngovia software: an R1 (standard) setting with a ratio at 1.36 and minimum attenuation at 150 HU; an R2 setting with a ratio at 1.28 and minimum attenuation at 170 HU and an R3 setting with a ratio at 1.28 and minimum attenuation at 120 HU. The frequency of each artifact according to the 3 settings was determined. Diagnostic accuracy of R1 and R2 settings has been calculated. Correlations between artefacts and patient’s clinical characteristics were obtained by performing a Spearman test.Results:The R2 setting (170 HU, ratio=1.28) significantly reduced the presence of knee and foot/ankle artifacts compared to the standard R1 setting (85% and 94% decrease in beam hardening and clumpy artifacts in the ankle and foot, respectively (p < 0.001); a decrease of 71%, 60% and 88% respectively of meniscal beam hardening, beam hardening and submillimeter artifacts in the knee (p < 0.001). The use of R3 setting lead to a significant increase of some artifacts (clumpy artifacts, skin artifacts, beam hardening and nail beds.). In addition, our results found a positive correlation between the presence of deposits of knee menisci beam hardening chondrocalcinosis. Body mass index was also positively correlated with the presence of knee beam hardening artifact. Compared to standard setting, the use of R2 settings decreased sensitivity (0.79 [95CI: 0.65;0.88] versus 0.90 [95CI: 0.78;0.96] and increased specificity (0.86 [95CI: 0.71;0.93) versus 0.63 [95CI: 0.47;0.77] (pConclusion:Applying a ratio of 1.28 and a minimum attenuation of 170 HU (R2 settings) in DECT post-processing eliminates the majority of the artifacts located on the lower limbs, particularly the clumpy artifact and the beam hardening artifact.References:[1]Neogi T, Jansen TLTA, Dalbeth N, Fransen J, Schumacher HR, Berendsen D, et al. 2015 Gout classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Ann Rheum Dis. 2015;74:1789-98.[2]Mallinson PI, Coupal T, Reisinger C, Chou H, Munk PL, Nicolaou S, et al. Artifacts in dual-energy CT gout protocol: a review of 50 suspected cases with an artifact identification guide. AJR 2014;203:W103-109.Disclosure of Interests:None declared.

Over one million total joint replacement surgeries were performed in the US in 2013 alone, and this number is expected to more than double by 2030. Traditional imaging techniques for postoperative evaluation of implanted devices, such as radiography, computerized tomography, or ultrasound, utilize ionizing radiation, suffer from beam hardening artifact, or lack the inherent high contrast necessary to adequately evaluate soft tissues around the implants, respectively. Magnetic resonance imaging (MRI), due to its ability to generate multiplanar, high-contrast images without the use of ionizing radiation is ideal for evaluating periprosthetic soft tissues but has traditionally suffered from in-plane and through-plane data misregistration due to the magnetic susceptibility of implanted materials. A recent renaissance in the interest of imaging near arthroplasty and implanted orthopedic hardware has led to the development of new techniques that help to mitigate the effects of magnetic susceptibility. This article describes the challenges of performing imaging near implanted orthopedic hardware, how to generate clinically interpretable images when imaging near implanted devices, and how the images may be interpreted for clinical use. We will also describe current developments of utilizing MRI to evaluate implanted orthopedic hardware. Level of Evidence: 3 J. Magn. Reson. Imaging 2017

Computed tomography is one of the most commonly used imaging equipment for CNS diseases. In the last decades, the development of multidetector CT can effectively reduce the beam hardening artifact and metallic artifact. Novels of CT techniques would contribute to the achievements of neuroradiology.

Introduction Computed tomography (CT) has proved highly reliable for cervical spine trauma screening. Nevertheless, rare instances of equivocal imaging findings may lead to misdiagnosis and wrongful management. The role of CT artifacts in this setting has been overlooked. We report 2 cases in which CT-generated artifacts mimicked type II odontoid fractures and nearly misled clinical management. Case reports and literature review Both patients suffered low energy falls and underwent cervical spine CT that disclosed an apparent dislocated type II odontoid fracture. Upon close inspection and review of the initial CT, the artifactual nature of the supposed fractures was exposed as motion artifact, avoiding unneeded surgery. In one of the cases, beam hardening artifact contributed to the false diagnosis. A review of the literature on false-positives in spinal trauma due to CT-generated artifacts was conducted, returning 14 reported cases, all of which generated by motion artifacts. To the best of our knowledge, this is the first report of beam hardening artifact contributing to such complication. Conclusion With this report, type II odontoid fracture becomes the most common type of artifactual false-positive. The most frequent culprit is motion artifact, but beam hardening artifacts may also play a role. Anatomical factors such as proximity of C2 to the oropharynx and large range of motion of the occipito-atlanto-axial articulation complex might contribute to susceptibility for contamination by motion artifact. CT sagittal reconstructions more easily disclose odontoid fractures, but are also more prone to contamination by artifacts. In order to mitigate these errors, we stress the importance of clinical correlation and critical analysis of the axial images, noticing any blurring or doubling of the bony contours, accompanied by distortion of the adjacent soft tissues, particularly the pharyngeal air column. The CT localizer scout film can also be helpful when in doubt, as well as pursuing repeat scans or alternative imaging methods.

OBJECTIVES: The aim of the current study is to evaluate the accuracy and the precision of raw-data-based relative electron density (RED(raw)) and the calibration-based RED (RED(cal)) at a range of low-RED to high-RED for tissue-equivalent phantom materials by comparing them with reference RED (RED(ref)) and to present the difference of RED(raw) and RED(cal) for the contrast medium using dual-energy CT (DECT). METHODS: The RED(raw) images were reconstructed by raw-data-based decomposition using DECT. For evaluation of the accuracy of the RED(raw), RED(ref) was calculated for the tissue-equivalent phantom materials based on their specified density and elemental composition. The RED(cal) images were calculated using three models: Lung-Bone model, Lung-Ti model and Lung-Ti (SEMAR) model which used single-energy metal artifact reduction (SEMAR). The difference between RED(raw) and RED(cal) was calculated. RESULTS: In the titanium rod core, the deviations of RED(raw) and RED(cal) (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) from RED(ref) were 0.45%, 50.8%, 15.4% and 15.0%, respectively. The largest differences between RED(raw) and RED(cal) (Lung-Bone model, Lung-Ti model and Lung-Ti model with SEMAR) in the contrast medium phantom were 8.2%, −23.7%, and 28.7%, respectively. However, the differences between RED(raw) and RED(cal) values were within 10% at 20 mg/ml. The standard deviation of the RED(raw) was significantly smaller than the RED(cal) with three models in the titanium and the materials that had low CT numbers. CONCLUSION: The RED(cal) values could be affected by beam hardening artifacts and the RED(cal) was less accurate than RED(raw) for high-Z materials as titanium. ADVANCES IN KNOWLEDGE: The raw-data-based reconstruction method could reduce the beam hardening artifact compared with image-based reconstruction and increase the accuracy for the RED estimation in high-Z materials, such as titanium and iodinated contrast medium.

A Contrast and Attenuation‐map Linearity Improvement (CALI) framework is proposed for cone‐beam CT (CBCT) images used for brain stereotactic radiosurgery (SRS). The proposed framework is tailored to improve soft tissue contrast of a new point‐of‐care image‐guided SRS system that employs a challenging half cone beam geometry, but can be readily reproduced on any CBCT platform. CALI includes a pre‐ and post‐processing step. In pre‐processing we apply a shading and beam hardening artifact correction to the projections, and in post‐processing step we correct the dome/capping artifact on reconstructed images caused by the spatial variations in X‐ray energy generated by the bowtie‐filter. The shading reduction together with the beam hardening and dome artifact correction algorithms aim to improve the linearity and accuracy of the CT‐numbers (CT#). The CALI framework was evaluated using CatPhan to quantify linearity, contrast‐to‐noise (CNR), and CT# accuracy, as well as subjectively on patient images acquired on a clinical system. Linearity of the reconstructed attenuation‐map was improved from 0.80 to 0.95. The CT# mean absolute measurement error was reduced from 76.1 to 26.9 HU. The CNR of the acrylic insert in the sensitometry module was improved from 1.8 to 7.8. The resulting clinical brain images showed substantial improvements in soft tissue contrast visibility, revealing structures such as ventricles which were otherwise undetectable in the original clinical images obtained from the system. The proposed reconstruction framework also improved CT# accuracy compared to the original images acquired on the system. For frameless image‐guided SRS, improving soft tissue visibility can facilitate evaluation of MR to CBCT co‐registration. Moreover, more accurate CT# may enable the use of CBCT for daily dose delivery measurements.

OBJECTIVE The aim of this study was to quantitatively compare the reduction in beam hardening artifact (BHA) and variance in computed tomography (CT) numbers of virtual monochromatic energy (VME) images obtained with 3 dual-energy computed tomography (DECT) systems at a given radiation dose. METHODS Five different iodine concentrations were scanned using dual-energy and single-energy (120 kVp) modes. The BHA and CT number variance were evaluated. RESULTS For higher iodine concentrations, 40 and 80 mgI/mL, BHA on VME imaging was significantly decreased when the energy was higher than 50 keV (P = 0.003) and 60 keV (P < 0.001) for GE, higher than 80 keV (P < 0.001) and 70 keV (P = 0.002) for Siemens, and higher than 40 keV (P < 0.001) and 60 keV (P < 0.001) for Toshiba, compared with single-energy CT imaging. CONCLUSIONS Virtual monochromatic energy imaging can decrease BHA and improve CT number accuracy in different dual-energy computed tomography systems, depending on energy levels and iodine concentrations.

The assessment of myocardial perfusion using single-energy (SE) imaging is influenced by beam-hardening artifacts (BHA). We sought to explore the ability of dual-energy (DE) imaging to attenuate the presence of BHA. Myocardial signal density (SD) was evaluated in 2240 myocardial segments (112 for each energy level) and in 320 American Heart Association segments among the SE group. Compared to DE reconstructions at the best energy level, SE acquisitions showed no significant differences overall regarding myocardial SD or signal-to-noise ratio. The segments most commonly affected by BHA showed significantly lower myocardial SD at the lowest energy levels, progressively normalizing at higher energy levels.

Computed tomography (CT) number is a calculated value reflecting the X-ray attenuation coefficient in an image voxel, generally expressed in Hounsfield units (HU), where the CT number of water is 0 HU. Because of the fact that X-ray photon absorption by material is energy-dependent and that the standard X-ray source is polychromatic, CT number of any material is generally not constant but variable depending on factors, such as the model of CT scanner, reconstruction algorithm, tube voltage, distribution of the examined object, and patient size.1–5 Clinically, the CT number of small simple renal cysts may be shifted upward on a contrast-enhanced CT to exhibit “pseudo-enhancement” that may affect the differential diagnosis between tumors and benign cysts. Beam hardening effect has been proposed as a cause for the pseudo-enhancement.4,6–11 In conventional CT, the polychromaticity of the X-rays causes beam hardening artifacts (BHA)12 and averaging attenuation effect in the image and leads to CT attenuation value shifts especially in obese patients and for tissues in the central region of body.5,13 Iterative methods have been proposed to reduce beam hardening artifacts12 and recover the attenuation map,14 but iterative methods can be computationally slow. On the other hand, the recently introduced dual energy spectral CT with single-source dual tube voltage fast switching technique provides monochromatic images depicting how the imaged object would appear under single-energy X-ray photons.15 Monochromatic images are found to have better correlation between CT numbers and iodine concentrations,15 and better CT number consistency, regardless of the phantom shape.16 The purpose of this study was to evaluate the ability of monochromatic images in spectral CT imaging to reduce beam hardening artifact and to provide accurate CT number measurement under various beam hardening conditions in a phantom study.

The beam hardening (BH) artifact produced by root filling materials in cone-beam computed tomographic (CBCT) images is influenced by their radiologic K absorption edge values. The purpose of this study was to describe a novel technique to characterize BH artifacts in CBCT images produced by 3 root canal filling materials and to evaluate the effects of a zirconium (Zr)-based root filling material with a lower K edge (17.99 keV) on the production of BH artifacts.The palatal root canals of 3 phantom model teeth were prepared and root filled with gutta-percha (GP), a Zr root filling material, and calcium hydroxide paste. Each phantom tooth was individually imaged using the CS 9000 CBCT unit (Carestream, Atlanta, GA). The "light" and "dark" components of the BH artifacts were quantified separately using ImageJ software (National Institutes of Health, Bethesda, MD) in 3 regions of the root. Mixed-design analysis of variance was used to evaluate differences in the artifact area for the light and dark elements of the BH artifacts.A statistically significant difference in the area of the dark portion of the BH artifact was found between all fill materials and in all regions of the phantom tooth root (P .05). GP generated a significantly greater dark but not light artifact area compared with Zr (P .05). Moreover, statistically significant differences between the areas of both the light and dark artifacts were observed within all regions of the tooth root, with the greatest artifact being generated in the coronal third of the root (P .001).Root canal filling materials with lower K edge material properties reduce BH artifacts along the entire length of the root canal and reduce the contribution of the dark artifact.

Purpose To describe a case of left eye corneal perforation, cataract, hyphema, and intraocular foreign body after airsoft pellet injury. Methods The authors reviewed the medical history and diagnostic imaging of a 12-year-old boy injured by a pellet from an airsoft gun. Typically, plastic airsoft pellets cause blunt trauma to the globe, which can lead to visual disability from corneal abrasion or hyphema. Initial computed tomography of the left orbit showed a 6.1 mm × 7.6-mm radiodense foreign body with beam-hardening artifact, a radiographic feature associated with metallic objects. Results The patient was taken to the operating room for globe repair, lensectomy, vitrectomy, and removal of intraocular foreign body. The removed foreign body was a plastic airsoft pellet. Conclusion This is the first report of a plastic intraocular foreign body showing beam-hardening artifact. This finding may have implications in the diagnosis and management of retained intraocular or intraorbital plastic foreign bodies.

Computed tomography (CT) has been used to obtain 3D data from an object or patient. However, most of CT uses polychromatic energy and that results in beam hardening artifact. Therefore, many methods for correcting beam hardening were proposed. Linearization method and post reconstruction method are main category of beam hardening correction method. Especially empirical approaches were commonly used at linearization method; however, empirical methods do not guarantee the linearity of projection data because it uses reconstructed image to decide linearity. Therefore, corrected images are not monochromatic CT images because we could not specify the energy. Proposed method use linearization method as a basic concept. However, we had considered about the relationship between path length and projection data and then found a way to specify the energy of corrected images because proposed method linearizes the projection data fundamentally. Moreover, calculation time for making corrected sinogram was very short. Therefore, this method can be used practically.

Iodine is conventionally used as a contrast agent in hydrological laboratory experiments using polychromatic X-ray computed tomography (CT) to monitor two-phase Darcy flow in porous geological media. Undesirable beam hardening artifacts, however, render the quantitative analysis of the obtained CT images difficult. CT imaging of porous sand/bead packs saturated with iodine and tungsten-bearing aqueous solutions, respectively, was performed using a medical CT scanner. We found that sodium polytungstate (Na6H2W12O40) significantly reduced the beam hardening compared with potassium iodide (KI). This result is attributable to the location of the K absorption edge of tungsten, which is nearer to the peak of the polychromatic X-ray source spectrum than that of iodine. As sodium polytungstate is chemically stable and less toxic than other heavy element bearing compounds, we recommend it as a promising contrast agent for hydrological CT experiments.

There is a difficulty because of classifying the anatomical structure in the neck CT scan by the beam hardening artifact no more than disease and it including the 6, 7 number cervical spine and intervertebral disk. In case of enforcing the neck CT scan cause of the inner diameter of beam artifact tried to be inquired by the image evaluation according to the change of the image evaluation according to the direction of the shoulder joint applying the variation method of a posture and location and Kernel value and it was most appropriate, the lion tax and Kernel value try to be searched for through an experiment. Somatom Sensation 16 (Siemens, Enlarge, Germany) equipment was used in a patient 30 people coming to the hospital for the neck CT scan. A workstation used the AW 4.4 version (GE, USA). According to a direction and location of the shoulder joint, the patient posture gave a change to the direction of the shoulder joint as the group S it gave a change as three postures and placed the both arms comfortably and helps a group N and augmented unipolar left in the wealthy merchant and group P it memorized the both hands and ordered the eversion and drops below to the utmost and enforced a scan. By using a reconstructing method as the second opinion, it gave and reconstructed the Kernel value a change based on scan data with B 10 (very smooth), B 20 (smooth), B 30 (medium smooth), B 40 (medium), B 50 (medium sharp), B 60 (sharp), and B 70 (very sharp). By using image data which gave the change of the examination posture and change of the Kernel value and are obtained, we analyzed through the noise value measurement and image evaluation of. The outside wire eversion orders the both hands and the examination posture is cost in the neck CT scan with the group P it drops below to the utmost. And in case of when reconstructing with B 40 (medium) or B 50 (medium sharp) being most analyzed into the inappropriate posture and Kernel value and applying the Kernel value to a clinical, it is considered to be very useful.

A high-resolution in vivo micro-CT system for combining with fluorescence molecular tomography (FMT), was constructed and applied in small animal imaging. The fast scanning micro-CT system designed to provide high-resolution anatomic information and reconstruction priors, consisted of a flat panel detector (FPD) based on amorphous silicon (a-Si) and a micro-focus x-ray tube. The Feldkamp algorithm was adopted in image reconstruction with graphic processing unit (GPU). The system spatial resolution of 13 lp/mm was achieved when the diameter of image field was 6 cm with the system magnification factor of 4. No obvious beam hardening artifact was observed in transaxial image of a water phantom after correction. The contrast-to-noise ratio (CNR) study of various tissue phantoms was also presented. The in-vivo imaging of an anesthetic mouse was performed to demonstrate the feasibility of our system.

The paper deals with design of complex simulation environment which is able to simulate on the base of mathematical techniques individual reconstructions methods which are normally used on Computed Tomography (CT). Primary attention is focused on The Single Back Projection technique (SBP) and The Filtered Back Projection (FBP). There is a significant benefit with comparison of normally used mathematical software. This simulation instrument is fully dynamic. Individual transformation methods are generated by form dynamic simulations which graphically explain the process of whole reconstruction procedure. The second part deals with simulation of Beam Hardening artifact. It is special type of artifact which significantly deteriorates CT images. This artifact is created especially on the surround of metal object. This simulation is important especially in term of manifestation of artifact. Simulation is helpful for design of filter for Beam Hardening suppressing as well. The complex simulation environment is performed in software MATLAB.

Microfocus computed tomography (μCT) is a non-destructive technique allowing visualization of the internal microstructure of objects. This technique can be used to quantify the maceral content and to define the cleat system within coal samples. However, a number of artifacts intrinsic to the technique hamper the optimal quantitative use of μCT. One of the most important artifacts is beam hardening, which generates streaks on the images near dense inclusions such as ankerite or pyrite and makes the border of the sample appear denser than in reality. These artifacts can be minimized by using a dual-energy method in which two sets of scans, taken at a different energy level, are combined. In this study existing dual-energy methods are combined into a new technique and adapted to be more ideally suitable for coal samples. The method is calibrated with an artificial sample made of a Plexiglas cylinder in which two aluminum rods are built-in. Plexiglas and aluminum were selected since their X-ray attenuation properties are similar to those of vitrinite and dense phases, such as ankerite, respectively. The method is tested on a coal sample bearing relatively high percentages of iron minerals. The corrected and uncorrected images from one representative slice through the sample are compared with reflected light-microscopy images from the corresponding polished surface. The results show that the applied approach creates images in which the border does not appear denser than in reality and in which the artificial streaks near dense inclusions are removed. In addition, size measurements of the ankerite veins and grains in the sample are much more accurate based on the corrected images. It is therefore assumed that the proposed dual-energy algorithm minimizes the beam hardening artifact. However, the corrected images have a lower signal-to-noise ratio than the uncorrected images. Consequently this approach magnifies to some extent other artifacts (noise, scatter and partial volume effect) which are also present in the uncorrected images. Some solutions to correct for these artifacts and to improve the developed dual-energy method are proposed.

Trabecular bone screws are commonly used for fixation of fractures in order to increase holding power in the fine sponge bone. The success of skeletal anchorage using mini screws is related to their stability in the bone tissue. Factors that influence the immediate stability of metal implants are related to the design of the device to the quantity and quality of bone and to insertion technique. The present work studied bone interface contact parameter by x-ray microtomography. The results identified the importance of evaluating the metallic artifact around the mini screws, which can be assessed by different pixel size dilation image processing. It can be noted a correlation pattern between beam hardening artifact correction and bone interface contact measurements.

This paper focuses on description, implementation and simulation of a specific artifact - Beam hardening - which occurs in CT examinations. The theoretical part of this paper describes background for formation of this undesirable phenomenon which influences considerably quality of final images. The practical part deals with simulation and viewing of the images with the Beam hardening artifact.

Purpose: A prototype reconstruction algorithm that can provide direct electron density (ED) images from single energy CT scans is being currently developed by Siemens Healthcare GmbH. This feature can eliminate the need for kV specific calibration curve for radiation treatemnt planning. An added benefit is that beam-hardening artifacts are also reduced on direct-ED images due to the underlying material decomposition. This study is to quantitatively analyze the reduction of beam-hardening artifacts on direct-ED images and suggest additional clinical usages. Methods: HU and direct-ED images were reconstructed on a head phantom scanned on a Siemens Definition AS CT scanner at five tube potentials of 70kV, 80kV, 100kV, 120kV and 140kV respectively. From these images, mean, standard deviation (SD), and local NPS were calculated for regions of interest (ROI) of same locations and sizes. A complete analysis of beam-hardening artifact reduction and image quality improvement was conducted. Results: Along with the increase of tube potentials, ROI means and SDs decrease on both HU and direct-ED images. The mean value differences between HU and direct-ED images are up to 8% with absolute value of 2.9. Compared to that on HU images, the SDs are lower on direct-ED images, and the differences are up to 26%. Interestingly, the local NPS calculated from direct-ED images shows consistent values in the low spatial frequency domain for images acquired from all tube potential settings, while varied dramatically on HU images. This also confirms the beam -hardening artifact reduction on ED images. Conclusions: The low SDs on direct-ED images and relative consistent NPS values in the low spatial frequency domain indicate a reduction of beam-hardening artifacts. The direct-ED image has the potential to assist in more accurate organ contouring, and is a better fit for the desired purpose of CT simulations for radiotherapy.

Proceedings of: 2012 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC). Anaheim, California, USA. October 29 - November 3, 2012 CT images are often affected by beam hardening artifacts (cupping and dark streaks) due to the polyenergetic nature of the X-ray beam. FDK is still the favorite reconstruction algorithm in commercial X-ray CT scanners. Several correction methods have been proposed to be included in an FDK reconstruction scheme. We present a complete correction scheme for beam hardening artifact correction in an FDK based reconstruction scenario that accounts for both cupping artifact and dark streaks avoiding the need of the knowledge of the source spectrum. The proposed correction scheme includes two steps: a linearization step of projection data and a post-reconstruction step. The first step assumes that the object is homogeneous and uses a linearization function that is calculated empirically in a previous calibration process with a simple phantom. The second step is based in the theoretical study described in Joseph and Spital, and calculates the non-linear beam-hardening distortion from a bone segmentation of the reconstructed image. The proposed correction scheme was evaluated in real studies acquired with a cone-beam micro-CT scanner: three polymethylmethacrylate cylinders (3, 4, and 6 cm diameter), a two-density cylindrical phantom and three rodent studies. Results show an average cupping reduction of 84 % in the three homogeneous phantoms and an average dark streaks reduction of 80 % in the two-density phantom and the three rodent studies. The proposed method could be incorporated easily in any cone beam micro-CT scanner and substitutes the need of the knowledge of the spectrum by empirical measurements and two parameters. Since it is based on empirical measurements, we expected to correct the artifacts derived from scattering. This work was supported in part by projects TEC2008-06715 and TEC2007-64731 (Ministerio de Ciencia e Innovaci6n), EU-FP7 FMTXCT-201792, ARTEMIS S2009/DPI-1802 (Comunidad de Madrid), and European Regional Development Funds (FEDER) and CDTI under the CENIT program (AMIT project, CEN-20101014). Publicado

Background Quantitative myocardial CT perfusion (CTP) is susceptible to beam-hardening (BH) artifact from conventional single-energy (kVp) CT (SECT) scanning, which can mimic perfusion deficits. Objective We evaluated the minimization of BH artifact with dual-energy (kVp) CT (DECT) generated monochromatic CT images to improve perfusion estimates. Methods We investigated the performance of DECT with a scanner capable of rapid kVp switching with respect to (1) BH artifact in a myocardium phantom model comparing SECT with image-based DECT and projection-based DECT, (2) optimal imaging parameters for measuring iodine concentration at high contrast-to-noise ratio in a tissue characterization phantom model, and (3) the feasibility of a dynamic time-resolved scan protocol with the projection-based DECT technique to measure myocardial perfusion in normal (nonischemic) porcine. Results In a myocardium phantom model, projection-based DECT 70 keV was better able to minimize the difference in the attenuation of the myocardium (19.9 HU) between having and not having contrast in the heart chambers in comparison to SECT using 80 kVp (30.4 HU) or 140 kVp ( 23.3 HU) and image-based DECT 70 keV (27.5 HU). Further, projection-based DECT 70 keV achieved the highest contrast-to-noise ratio (3.0), which exceeded that from imaged-based DECT 70 keV (2.0), 140 kVp SECT (1.3), and 80 kVp SECT (2.9). In 5 normal pigs, projection-based DECT at 70 keV provided a more uniform perfusion estimate than SECT. Conclusion By effectively reducing BH artifact, projection-based DECT may permit improved quantitative myocardial CTP compared with the conventional SECT technique.

Coronary CT Angiography (CTA) is limited in patients with calcified plaque and stents. CTA is unable to confidently differentiate fibrous from lipid plaque. Fast switched dual energy CTA offers certain advantages. Dual energy CTA removes calcium thereby improving visualization of the lumen and potentially providing a more accurate measure of stenosis. Dual energy CTA directly measures calcium burden (calcium hydroxyapatite) thereby eliminating a separate non-contrast series for Agatston Scoring. Using material basis pairs, the differentiation of fibrous and lipid plaques is also possible. Patency of a previously stented coronary artery is difficult to visualize with CTA due to resolution constraints and localized beam hardening artifacts. Monochromatic 70 keV or Iodine images coupled with Virtual Non-stent images lessen beam hardening artifact and blooming. Virtual removal of stainless steel stents improves assessment of in-stent re-stenosis. A beating heart phantom with 'cholesterol' and 'fibrous' phantom coronary plaques were imaged with dual energy CTA. Statistical classification methods (SVM, kNN, and LDA) distinguished 'cholesterol' from 'fibrous' phantom plaque tissue. Applying this classification method to 16 human soft plaques, a lipid 'burden' may be useful for characterizing risk of coronary disease. We also found that dual energy CTA is more sensitive to iodine contrast than conventional CTA which could improve the differentiation of myocardial infarct and ischemia on delayed acquisitions. These phantom and patient acquisitions show advantages with using fast switched dual energy CTA for coronary imaging and potentially extends the use of CT for addressing problem areas of non-invasive evaluation of coronary artery disease.

Light reflection from a surface is described by the bidirectional reflectance distribution function (BRDF). In this paper, BRDF effects in reflection tomography are studied using modeled range-resolved reflection from well-characterized geometrical surfaces. It is demonstrated that BRDF effects can cause a darkening at the interior boundary of the reconstructed surface analogous to the well-known beam hardening artifact in x-ray transmission computed tomography (CT). This artifact arises from reduced reflection at glancing incidence angles to the surface. It is shown that a purely Lambertian surface without shadowed components is perfectly reconstructed from range-resolved measurements. This result is relevant to newly fabricated carbon nanotube materials. Shadowing is shown to cause crossed streak artifacts similar to limited-angle effects in CT reconstruction. In tomographic reconstruction, these effects can overwhelm highly diffuse components in proximity to specularly reflecting elements. Diffuse components can be recovered by specialized processing, such as reducing glints via thresholded measurements.