Dual-energy Material Research Articles

Using edge-preserving algorithm with non-local mean for significantly improved image-domain material decomposition in dual-energy CT

Increased noise is a general concern for dual-energy material decomposition. Here, we develop an image-domain material decomposition algorithm for dual-energy CT (DECT) by incorporating an edge-preserving filter into the Local HighlY constrained backPRojection reconstruction (HYPR-LR) framework. With effective use of the non-local mean, the proposed algorithm, which is referred to as HYPR-NLM, reduces the noise in dual-energy decomposition while preserving the accuracy of quantitative measurement and spatial resolution of the material-specific dual-energy images. We demonstrate the noise reduction and resolution preservation of the algorithm with an iodine concentrate numerical phantom by comparing the HYPR-NLM algorithm to the direct matrix inversion, HYPR-LR and iterative image-domain material decomposition (Iter-DECT). We also show the superior performance of the HYPR-NLM over the existing methods by using two sets of cardiac perfusing imaging data. The DECT material decomposition comparison study shows that all four algorithms yield acceptable quantitative measurements of iodine concentrate. Direct matrix inversion yields the highest noise level, followed by HYPR-LR and Iter-DECT. HYPR-NLM in an iterative formulation significantly reduces image noise and the image noise is comparable to or even lower than that generated using Iter-DECT. For the HYPR-NLM method, there are marginal edge effects in the difference image, suggesting the high-frequency details are well preserved. In addition, when the search window size increases from to , there are no significant changes or marginal edge effects in the HYPR-NLM difference images. The reference drawn from the comparison study includes: (1) HYPR-NLM significantly reduces the DECT material decomposition noise while preserving quantitative measurements and high-frequency edge information, and (2) HYPR-NLM is robust with respect to parameter selection.

Virtual Non-Contrast CT Using Dual-Energy Spectral CT: Feasibility of Coronary Artery Calcium Scoring.

ObjectiveTo evaluate the feasibility of coronary artery calcium scoring based on three virtual noncontrast-enhanced (VNC) images derived from single-source spectral dual-energy CT (DECT) as compared with true noncontrast-enhanced (TNC) images.Materials and MethodsThis prospective study was conducted with the approval of our Institutional Review Board. Ninety-seven patients underwent noncontrast CT followed by contrast-enhanced chest CT using single-source spectral DECT. Iodine eliminated VNC images were reconstructed using two kinds of 2-material decomposition algorithms (material density iodine-water pair [MDW], material density iodine-calcium pair [MDC]) and a material suppressed algorithm (material suppressed iodine [MSI]). Two readers independently quantified calcium on VNC and TNC images. The Spearman correlation coefficient test and Bland-Altman method were used for statistical analyses.ResultsCoronary artery calcium scores from all three VNC images showed excellent correlation with those from the TNC images (Spearman's correlation coefficient [ρ] = 0.94, 0.88, and 0.89 for MDW, MDC, and MSI, respectively; p < 0.001 for all pairs). Measured coronary calcium volumes from VNC images also correlated well with those from TNC images (ρ = 0.92, 0.87, and 0.91 for MDW, MDC, and MSI, respectively; p < 0.001 for all pairs). Among the three VNC images, coronary calcium from MDW correlated best with that from TNC. The coronary artery calcium scores and volumes were significantly lower from the VNC images than from the TNC images (p < 0.001 for all pairs).ConclusionThe use of VNC images from contrast-enhanced CT using dual-energy material decomposition/suppression is feasible for coronary calcium scoring. The absolute value from VNC tends to be smaller than that from TNC.

Dual-Energy CT: Spectrum of Thoracic Abnormalities.

Recent studies have demonstrated that dual-energy computed tomography (CT) can provide useful information in several chest-related clinical indications. Compared with single-energy CT, dual-energy CT of the chest is feasible with the use of a radiation-dose-neutral scanning protocol. This article highlights the different types of images that can be generated by using dual-energy CT protocols such as virtual monochromatic, virtual unenhanced (ie, water), and pulmonary blood volume (ie, iodine) images. The physical basis of dual-energy CT and material decomposition are explained. The advantages of the use of virtual low-monochromatic images include reduced volume of intravenous contrast material and improved contrast resolution of images. The use of virtual high-monochromatic images can reduce beam hardening and contrast streak artifacts. The pulmonary blood volume images can help differentiate various parenchymal abnormalities, such as infarcts, atelectasis, and pneumonias, as well as airway abnormalities. The pulmonary blood volume images allow quantitative and qualitative assessment of iodine distribution. The estimation of iodine concentration (quantitative assessment) provides objective analysis of enhancement. The advantages of virtual unenhanced images include differentiation of calcifications, talc, and enhanced thoracic structures. Dual-energy CT has applications in oncologic imaging, including diagnosis of thoracic masses, treatment planning, and assessment of response to treatment. Understanding the concept of dual-energy CT and its clinical application in the chest are the goals of this article.

A feasibility study for anatomical noise reduction in dual-energy chest digital tomosynthesis

Lung cancer is the leading cause of cancer death worldwide. Thus, early diagnosis is of considerable importance. For early screening of lung cancer, computed tomography (CT) has been used as the gold standard. Chest digital tomosynthesis (CDT) is a recently introduced modality for lung cancer screening with a relatively low radiation dose compared to CT. The dual energy material decomposition method has been proposed for better detection of pulmonary nodules by means of reducing anatomical noise. In this study, the possibility of material decomposition in CDT was tested by both a simulation study and an experimental study using a CDT prototype. The Geant4 application for tomographic emission (GATE) v6 and tungsten anode spectral model using interpolating polynomials (TASMIP) codes were used for the simulation study to create simulated phantom shapes consisting of five inner cylinders filled with different densities of bone and airequivalent materials. Furthermore, the CDT prototype system and human phantom chest were used for the experimental study. CDT scan in both the simulation and experimental studies was performed with linear movement and 21 projection images were obtained over a 30 degree angular range with a 1.5 degree angular interval. To obtain materialselective images, a projectionbased energy subtraction technique was applied to high and low energy images. The resultant simulation images showed that dual-energy reconstruction could achieve an approximately 32% higher contrast to noise ratio (CNR) in images and the difference in CNR value according to bone density was significant compared to single energy CDT. Additionally, image artifacts were effectively corrected in dual energy CDT simulation studies. Likewise the experimental study with dual energy produced clear images of lung fields and bone structure by removing unnecessary anatomical structures. Dual energy tomosynthesis is a new technique; therefore, there is little guidance regarding its integration into clinical practice and this study can be used to improve the diagnostic efficiency of lung field and spinal bone screening using CDT.

MO‐FG‐204‐03: Using Edge‐Preserving Algorithm for Significantly Improved Image‐Domain Material Decomposition in Dual Energy CT

Purpose:To significantly improve dual energy CT (DECT) imaging by establishing a new theoretical framework of image‐domain material decomposition with incorporation of edge‐preserving techniques.Methods:The proposed algorithm, HYPR‐NLM, combines the edge‐preserving non‐local mean filter (NLM) with the HYPR‐LR (Local HighlY constrained backPRojection Reconstruction) framework. Image denoising using HYPR‐LR framework depends on the noise level of the composite image which is the average of the different energy images. For DECT, the composite image is the average of high‐ and low‐energy images. To further reduce noise, one may want to increase the window size of the filter of the HYPR‐LR, leading resolution degradation. By incorporating the NLM filtering and the HYPR‐LR framework, HYPR‐NLM reduces the boost material decomposition noise using energy information redundancies as well as the non‐local mean. We demonstrate the noise reduction and resolution preservation of the algorithm with both iodine concentration numerical phantom and clinical patient data by comparing the HYPR‐NLM algorithm to the direct matrix inversion, HYPR‐LR and iterative image‐domain material decomposition (Iter‐DECT).Results:The results show iterative material decomposition method reduces noise to the lowest level and provides improved DECT images. HYPR‐NLM significantly reduces noise while preserving the accuracy of quantitative measurement and resolution. For the iodine concentration numerical phantom, the averaged noise levels are about 2.0, 0.7, 0.2 and 0.4 for direct inversion, HYPR‐LR, Iter‐ DECT and HYPR‐NLM, respectively. For the patient data, the noise levels of the water images are about 0.36, 0.16, 0.12 and 0.13 for direct inversion, HYPR‐LR, Iter‐DECT and HYPR‐NLM, respectively. Difference images of both HYPR‐LR and Iter‐DECT show edge effect, while no significant edge effect is shown for HYPR‐NLM, suggesting spatial resolution is well preserved for HYPR‐NLM.Conclusion:HYPR‐NLM provides an effective way to reduce the generic magnified image noise of dual–energy material decomposition while preserving resolution.This work is supported in part by NIH grants 7R01HL111141 and 1R01‐EB016777. This work is also supported by the Natural Science Foundation of China (NSFC Grant No. 81201091), Fundamental Research Funds for the Central Universities in China, and Fund Project for Excellent Abroad Scholar Personnel in Science and Technology.

Breast Density Evaluation Using Spectral Mammography, Radiologist Reader Assessment, and Segmentation Techniques: A Retrospective Study Based on Left and Right Breast Comparison

The purpose of this study was to compare the precision of mammographic breast density measurement using radiologist reader assessment, histogram threshold segmentation, fuzzy C-mean segmentation, and spectral material decomposition. Spectral mammography images from a total of 92 consecutive asymptomatic women (aged 50-69years) who presented for annual screening mammography were retrospectively analyzed for this study. Breast density was estimated using 10 radiologist reader assessment, standard histogram thresholding, fuzzy C-mean algorithm, and spectral material decomposition. The breast density correlation between left and right breasts was used to assess the precision of these techniques to measure breast composition relative to dual-energy material decomposition. In comparison to the other techniques, the results of breast density measurements using dual-energy material decomposition showed the highest correlation. The relative standard error of estimate for breast density measurements from left and right breasts using radiologist reader assessment, standard histogram thresholding, fuzzy C-mean algorithm, and dual-energy material decomposition was calculated to be 1.95, 2.87, 2.07, and 1.00, respectively. The results indicate that the precision of dual-energy material decomposition was approximately factor of two higher than the other techniques with regard to better correlation of breast density measurements from right and left breasts.

Separation of hepatic iron and fat by dual-source dual-energy computed tomography based on material decomposition: an animal study.

ObjectiveTo explore the feasibility of dual-source dual-energy computed tomography (DSDECT) for hepatic iron and fat separation in vivo.Materials and MethodsAll of the procedures in this study were approved by the Research Animal Resource Center of Shanghai Ruijin Hospital. Sixty rats that underwent DECT scanning were divided into the normal group, fatty liver group, liver iron group, and coexisting liver iron and fat group, according to Prussian blue and HE staining. The data for each group were reconstructed and post-processed by an iron-specific, three-material decomposition algorithm. The iron enhancement value and the virtual non-iron contrast value, which indicated overloaded liver iron and residual liver tissue, respectively, were measured. Spearman's correlation and one-way analysis of variance (ANOVA) were performed, respectively, to analyze statistically the correlations with the histopathological results and differences among groups.ResultsThe iron enhancement values were positively correlated with the iron pathology grading (r = 0.729, p<0.001). Virtual non-iron contrast (VNC) values were negatively correlated with the fat pathology grading (r = −0.642,p<0.0001). Different groups showed significantly different iron enhancement values and VNC values (F = 25.308,p<0.001; F = 10.911, p<0.001, respectively). Among the groups, significant differences in iron enhancement values were only observed between the iron-present and iron-absent groups, and differences in VNC values were only observed between the fat-present and fat-absent groups.ConclusionSeparation of hepatic iron and fat by dual energy material decomposition in vivo was feasible, even when they coexisted.

Advances in computed tomography evaluation of skull base diseases.

Introduction Computed tomography (CT) is a key component in the evaluation of skull base diseases. With its ability to clearly delineate the osseous anatomy, CT can provide not only important tips to diagnosis but also key information for surgical planning. Objectives The purpose of this article is to describe some of the main CT imaging features that contribute to the diagnosis of skull base tumors, review recent knowledge related to bony manifestations of these conditions, and summarize recent technological advances in CT that contribute to image quality and improved diagnosis. Data Synthesis Recent advances in CT technology allow fine-detailed evaluation of the bony anatomy using submillimetric sections. Dual-energy CT material decomposition capabilities allow clear separation between contrast material, bone, and soft tissues with many clinical applications in the skull base. Dual-energy technology has also the ability to decrease image degradation from metallic hardwares using some techniques that can result in similar or even decreased radiation to patients. Conclusions CT is very useful in the evaluation of skull base diseases, and recent technological advances can increase disease conspicuity resulting in improved diagnostic capabilities and enhanced surgical planning.

Iterative dual energy material decomposition from spatial mismatched raw data sets.

Today's clinical dual energy computed tomography (DECT) scanners generally measure different rays for different energy spectra and acquire spatial mismatched raw data sets. The deficits in clinical DECT technologies suggest that mainly image based material decomposition methods are in use nowadays. However, the image based material decomposition is an approximate technique, and beam hardening artifacts remain in decomposition results. A recently developed image based iterative method for material decomposition from inconsistent rays (MDIR) can achieve much better image quality than the conventional image based methods. Inspired by the MDIR method, this paper proposes an iterative method to indirectly perform raw data based DECT even with completely mismatched raw data sets. The iterative process is initialized by density images that were obtained from an image based material decomposition. Then the density images are iteratively corrected by comparing the estimated polychromatic projections and the measured polychromatic projections. Only three iterations of the method are sufficient to greatly improve the qualitative and quantitative information in material density images. Compared with the MDIR method, the proposed method needs not to perform additional water precorrection. The advantages of the method are verified with numerical experiments from inconsistent noise free and noisy raw data.

A Flexible Method for Multi-Material Decomposition of Dual-Energy CT Images

The ability of dual-energy computed-tomographic (CT) systems to determine the concentration of constituent materials in a mixture, known as material decomposition, is the basis for many of dual-energy CT's clinical applications. However, the complex composition of tissues and organs in the human body poses a challenge for many material decomposition methods, which assume the presence of only two, or at most three, materials in the mixture. We developed a flexible, model-based method that extends dual-energy CT's core material decomposition capability to handle more complex situations, in which it is necessary to disambiguate among and quantify the concentration of a larger number of materials. The proposed method, named multi-material decomposition (MMD), was used to develop two image analysis algorithms. The first was virtual unenhancement (VUE), which digitally removes the effect of contrast agents from contrast-enhanced dual-energy CT exams. VUE has the ability to reduce patient dose and improve clinical workflow, and can be used in a number of clinical applications such as CT urography and CT angiography. The second algorithm developed was liver-fat quantification (LFQ), which accurately quantifies the fat concentration in the liver from dual-energy CT exams. LFQ can form the basis of a clinical application targeting the diagnosis and treatment of fatty liver disease. Using image data collected from a cohort consisting of 50 patients and from phantoms, the application of MMD to VUE and LFQ yielded quantitatively accurate results when compared against gold standards. Furthermore, consistent results were obtained across all phases of imaging (contrast-free and contrast-enhanced). This is of particular importance since most clinical protocols for abdominal imaging with CT call for multi-phase imaging. We conclude that MMD can successfully form the basis of a number of dual-energy CT image analysis algorithms, and has the potential to improve the clinical utility of dual-energy CT in disease management.

Urinary stones: The contribution of dual energy CT and material decomposition

Urinary stones: The contribution of dual energy CT and material decomposition

A dual-energy material decomposition method for high-energy X-ray cargo inspection

Dual-energy X-ray imaging can provide material-specific image information, which is very useful in inspection tasks. Accurate and efficient material decomposition is desirable in such tasks, and we developed a fast and efficient dual-energy calibration method for high-energy X-ray cargo inspection. We designed a calibration phantom consisting of a half cylinder of lead and a half cylinder of carbon. We used a least-squares method to determine the material decomposition formula from the calibration-phantom data. To test the feasibility of the proposed method, we designed a cargo phantom in a simulation study. Material decomposition was successfully conducted, so we expect the proposed calibration method to play an important role in high-energy X-ray imaging for cargo inspection.

Kidney Stone Volume Estimation from Computerized Tomography Images Using a Model Based Method of Correcting for the Point Spread Function

We propose a method to improve the accuracy of volume estimation of kidney stones from computerized tomography images. The proposed method consisted of 2 steps. A threshold equal to the average of the computerized tomography number of the object and the background was first applied to determine full width at half maximum volume. Correction factors were then applied, which were precalculated based on a model of a sphere and a 3-dimensional gaussian point spread function. The point spread function was measured in a computerized tomography scanner to represent the response of the scanner to a point-like object. Method accuracy was validated using 6 small cylindrical phantoms with 2 volumes of 21.87 and 99.9 mm(3), and 3 attenuations, respectively, and 76 kidney stones with a volume range of 6.3 to 317.4 mm(3). Volumes estimated by the proposed method were compared with full width at half maximum volumes. The proposed method was significantly more accurate than full width at half maximum volume (p <0.0001). The magnitude of improvement depended on stone volume with smaller stones benefiting more from the method. For kidney stones 10 to 20 mm(3) in volume the average improvement in accuracy was the greatest at 19.6%. The proposed method achieved significantly improved accuracy compared with threshold methods. This may lead to more accurate stone management.

A comparative study of a dual‐energy‐like imaging technique based on counting‐integrating readout

The recent introduction of a specific electronic readout chip, designed for the processing of the same signal pulses from an x-ray sensor in one integrating and one counting channel in each pixel E. Kraft et al., [IEEE Trans. Nucl. Sci. 54, 383-390 (2007)]; E. Kraft, "Counting and integrating microelectronics development for direct conversion X-ray imaging," Ph.D. thesis, 2007; J. Fink, "Characterization of the imaging performance of the simultaneously counting and integrating X-ray detector CIX," Ph.D. thesis, 2010, enables an alternative to conventional dual-energy imaging methods. As shown in a previous paper, the proposed alternative benefits from positively correlated noise in the raw data, inherent to the counting-integrating readout (CIX), which results in a reduction of basis image noise after dual-energy decomposition. In the present paper, the authors compare the new approach to dual-energy imaging to two conventional dual-energy techniques, the dual-kV technique and the dual-crystal technique and to a photon-counting technique based on two energy windows. The study is based on x-ray computed tomography (CT) simulations of an anthropomorphic head phantom, where the signal-to-noise ratios and the contrast-to-noise ratios in basis material images and quasi-monochromatic images at 60 keV are compared. Moreover, a simple pictorial illustration of the relevance of input noise correlations in the noise-propagation process during the dual-energy basis material decomposition are presented, as well as measurement data for the correlation obtained as a function of the x-ray flux rate. Under the idealized assumptions of the absence of scatter and detector imperfections like K-escape, crosstalk and detector noise, our comparison shows that among the dual-energy techniques investigated, the CIX concept together with the dual-kV technique performs best, confirming the mitigating effect of correlated measurement data on the dual-energy basis material decomposition. The novel concept of simultaneous counting of photons and integrating the x-ray energy flux has a large potential for dual-energy applications in both projection and tomographic x-ray imaging. Future work will have to focus on the sensitivity of the CIX dual-energy concept to scattered radiation, detector imperfections and high x-ray fluxes.

Newer CT applications and their alternatives: what is appropriate in children?

Innovations in image acquisition and reconstruction technologies have greatly expanded the range of CT applications available in the routine clinical setting. CT images of sub-millimeter resolution can now be acquired of entire body regions in a few seconds or even sub-second time, allowing depiction of fine anatomical detail uncompromised by motion artifact. With sophisticated visualization software, image data can be processed into multiplanar, volume-rendered, cine and other formats to better display anatomical abnormalities and facilitate newer applications such as CT angiography, enterography, urography, tracheobronchography and cardiac CT. Newer applications including dual-energy material decomposition CT are furthering the transition of CT from a purely morphological to a combined anatomical, functional and metabolic imaging technique. These newer applications have largely been pioneered in adult populations, and heightened concern of the risk of carcinogenesis from ionizing radiation tempers dissemination of their use in children. Similar information can often be gleaned from alternative imaging modalities without ionizing radiation exposure, such as MRI and US, and what is most appropriate in children will depend on relative diagnostic efficacy, cost, availability and local expertise.

CT scanner x‐ray spectrum estimation from transmission measurements

In diagnostic CT imaging, multiple important applications depend on the knowledge of the x-ray spectrum, including Monte Carlo dose calculations and dual-energy material decomposition analysis. Due to the high photon flux involved, it is difficult to directly measure spectra from the x-ray tube of a CT scanner. One potential method for indirect measurement involves estimating the spectrum from transmission measurements. The expectation maximization (EM) method is an accurate and robust method to solve this problem. In this article, this method was evaluated in a commercial CT scanner. Two step-wedges (polycarbonate and aluminum) were used to produce different attenuation levels. Transmission measurements were performed on the scanner and the measured data from the scanner were exported to an external computer to calculate the spectra. The EM method was applied to solve the equations that represent the attenuation processes of polychromatic x-ray photons. Estimated spectra were compared to the spectra simulated using a software provided by the manufacturer of the scanner. To test the accuracy of the spectra, a verification experiment was performed using a phantom containing different depths of water. The measured transmission data were compared to the transmission values calculated using the estimated spectra. Spectra of 80, 100, 120, and 140 kVp from a dual-source CT scanner were estimated. The estimated and simulated spectra were well matched. The differences of mean energies were less than 1 keV. In the verification experiment, the measured and calculated transmission values were in excellent agreement. Spectrum estimation using transmission data and the EM method is a quantitatively accurate and robust technique to estimate the spectrum of a CT system. This method could benefit studies relying on accurate knowledge of the x-ray spectra from CT scanner.

Dual-Source Dual-Energy CT With Additional Tin Filtration: Dose and Image Quality Evaluation in Phantoms and In Vivo

The objective of this study was to investigate the effect on radiation dose and image quality of the use of additional spectral filtration for dual-energy CT using dual-source CT (DSCT). A commercial DSCT scanner was modified by adding tin filtration to the high-kV tube, and radiation output and noise were measured in water phantoms. Dose values for equivalent image noise were compared between the dual-energy mode with and without tin filtration and the single-energy mode. To evaluate dual-energy CT material discrimination, the material-specific dual-energy ratio for calcium and that for iodine were determined using images of anthropomorphic phantoms. Data were additionally acquired from imaging a 38-kg pig and an 87-kg pig, and the noise of the linearly mixed images and virtual noncontrast images was compared between dual-energy modes. Finally, abdominal dual-energy CT images of two patients of similar sizes undergoing clinically indicated CT were compared. Adding tin filtration to the high-kV tube improved the dual-energy contrast between iodine and calcium as much as 290%. Data from our animal study showed that tin filtration had no effect on noise in the dual-energy CT mixed images but decreased noise by as much as 30% in the virtual noncontrast images. Virtual noncontrast images of patients acquired using 100 and 140 kV with added tin filtration had improved image quality relative to those generated using 80 and 140 kV without tin filtration. Tin filtration of the high-kV tube of a DSCT scanner increases the ability of dual-energy CT to discriminate between calcium and iodine without increasing dose relative to single-energy CT. Furthermore, the use of 100- and 140-kV tube potentials allows improved dual-energy CT imaging of large patients.

Design and experiment of dual-energy X-ray material recognition using a 950 keV X-band Linac

The 950 keV portable X-band (9.4 GHz) linear accelerator (Linac) provides on-site high-energy X-ray inspection, including material recognition up to a certain precision. We have developed an X-band Linac system and have achieved the maximum 950 keV X-ray by using the low-power magnetron (250 kW) in a 2-μs pulse length. We have already experimentally verified the dual-energy X-ray material recognition with and without an energy filter. Further, the array of the scintillator detector for dual-energy X-ray measurement without the energy filter is numerically analyzed and designed for much quicker measurements. Updated results will be presented.

Inhibition of glycogen synthase kinase-3β attenuates glucocorticoid-induced bone loss

Aims Long-term glucocorticoid administration is known to induce bone deterioration. Glycogen synthase kinase-3β (GSK-3β) signaling reportedly participates in bone remodeling. This study investigated whether GSK-3β inhibitor could regulate glucocorticoid-induced inhibition of osteoblast differentiation in vitro or bone mass in vivo. Main methods MC3T3-E1 osteoblasts were treated with kinase-inactive GSK-3β mutant and 6-bromoindirubin-3′-oxim (BIO) and then exposed to 1 µM dexamethasone. Survival and osteoblast differentiation of cell cultures were assessed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end-labeling, quantitative RT-PCR, and von Kossa staining. Mineral density, biomechanical properties and microenvironments of BIO- and glucocorticoid-treated rat bone tissues were analyzed using dual-energy X-ray absorptiometry, material testing, and histomorphometry, respectively. Key findings Glucocorticoid decreased levels of phosphorylated Ser9-GSK-3β and β-catenin in osteoblast cultures. Kinase-inactive GSK-3β mutant and BIO treatments attenuated dexamethasone-induced inhibition of β-catenin, Runx2 abundance, and osteoblast differentiation but suppressed glucocorticoid-induced apoptosis of cell cultures. Exogenous BIO treatment alleviated methylprednisolone-induced impairment of mineral density, biomechanical strength, trabecular bone volume, osteoblast surface, and bone formation rate of rat bone tissue. BIO treatment also attenuated glucocorticoid-induced promotion of osteoclast surface and marrow adipocyte volume in bone tissue. Bone cells adjacent to glucocorticoid-stressed bone tissue displayed strong phosphorylated Ser9-GSK-3β and β-catenin immunostaining following BIO treatment. Significance Inhibition of GSK-3β abrogated glucocorticoid-induced bone loss by increasing β-catenin- and Runx2-mediated osteoblast differentiation. Controlling GSK-3β signaling in bone cells may be a strategy for preventing glucocorticoid-induced osteopenia.

WE-D-332-02: X-Ray Spectra Optimization for Dual-Energy Imaging Using Dual-Source CT

Purpose: To optimize the filtration of the two x-ray tubes of a dual-source CT (DSCT) system in order to achieve better separation between the low and high energy spectra used for dual-energy imaging, thereby increasing the sensitivity of dual-energy material discrimination techniques. Method and Materials: The x-ray spectra used in DSCT were simulated using proprietary software. Additional filtration of the low-energy spectrum would decrease the number of photons reaching the detector resulting in unacceptable image noise. Thus, we reduced the factory-installed filtration for the 80 kVp spectrum in order to increase the number of low-energy photons and concentrated our efforts on optimizing the filtration for the high-energy spectrum. We evaluated 15 filter materials, with the aim of minimizing the overlap between the two spectra. For simplicity, only single-element materials (nonvolatile, solid at room temperature, machinable, etc.) within the atomic number range 40⩽Z⩽ 83 were considered. The filter thickness was selected in 0.1 mm increments so that the detector signal (integrated energy) at isocenter was similar for both spectra at the same mAs. The difference between mean energies and the ratio of the 140 and 80 kVp detector signals, each integrated below 80 kVp, were evaluated. The optimization was performed for both head and body virtual phantoms. Results: Seven materials were found to perform similarly well at proper thicknesses. Spectral separation was increased from 25.7 to 50.1 keV (head phantom) and 28.6 to 52.6 keV (body phantom). The spectral overlap was reduced from 427% to 5–7% (head) and from 458% to 1–2% (body). Conclusion: Using independent filter materials and thicknesses, separation of the two DSCT spectra used for dual-energy imaging can be increased by almost a factor of 2 and the spectral overlap reduced by more than a factor of 425. Conflict of Interest: Research partially supported by Siemens Medical Solutions.