Virtual Monochromatic Spectral Images Research Articles

Diagnostic efficiency of single source dual energy CT in differentiating adrenal adenoma from adrenal metastasis

Background: The distinction between incidental adrenal lesions is still difficult in diagnostic imaging whereas Dual energy CT has not been thoroughly tested for its ability to diagnose adrenal lesions. This study utilizes dual energy CT to identify between the two most prevalent adrenal neoplasms, adrenal metastasis and adrenal adenomas.Objective:To evaluate the efficacy of non-enhanced single-source dual-energy computed tomography (ssDECT) in differentiating metastases from adenomas in adrenal glands Materials and methods :This is a retrospective study conducted in the department of radio diagnosis of Mysore medical college and research institute after receiving the approval from our institutional ethical committee.A total of fifty six patients (32 men,24 women) with 31 adrenal metastases (AMs) and 32 adrenal adenomas (AAs) underwent a plain dual-energy CT imaging from March 2021 to October 2022 were included. The CT number from the virtual monochromatic spectral (VMS) image sets were measured for the AMs and AAs. The difference of CT numbers between AMs and AAs was statistically compared by P value and the box plot curve. Results: The CT number (medium, range) of metastases (50.47, 29.93 HU at 40 keV and 29.00, 9.36 HU at 140 keV) was significantly higher than that of adenomas (0.76, 33.04 to 13.73, 18.96 HU) at each energy level from 40 to 140 keV (P <.05).Conclusion: Using CT numbers obtained from virtual monochromatic images of single source dual energy CT can be used to differentiate adenomas from adrenal metastasis. The Median CT number of metastases was higher than that of adenomas at 40 Kev and 140 Kev. The median CT number of metastases decreased with increase in incident photon energy in Kev and median CT number of adenomas increased with increase in incident photon energy in Kev. Keywords- Virtual monochromatic spectral (VMS) image,Dual energy computed tomography, adrenal lesions, differential diagnosis.

A Deep Learning Image Reconstruction Algorithm for Improving Image Quality and Hepatic Lesion Detectability in Abdominal Dual-Energy Computed Tomography: Preliminary Results

This study aimed to compare the performance of deep learning image reconstruction (DLIR) and adaptive statistical iterative reconstruction-Veo (ASIR-V) in improving image quality and diagnostic performance using virtual monochromatic spectral images in abdominal dual-energy computed tomography (DECT). Sixty-two patients [mean age ± standard deviation (SD): 56 years ± 13; 30 men] who underwent abdominal DECT were prospectively included in this study. The 70-keV DECT images in the portal phase were reconstructed at 5-mm and 1.25-mm slice thicknesses with 40% ASIR-V (ASIR-V40%) and at 1.25-mm slice with deep learning image reconstruction at medium (DLIR-M) and high (DLIR-H) levels and then compared. Computed tomography (CT) attenuation, SD values, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured in the liver, spleen, erector spinae, and intramuscular fat. The lesions in each reconstruction group at 1.25-mm slice thickness were counted. The image quality and diagnostic confidence were subjectively evaluated by two radiologists using a 5-point scale. For the 1.25-mm images, DLIR-M and DLIR-H had lower SD, higher SNR and CNR, and better subjective image quality compared with ASIR-V40%; DLIR-H performed the best (all P values < 0.001). Furthermore, the 1.25-mm DLIR-H images had similar SD, SNR, and CNR values as the 5-mm ASIR-V40% images (all P > 0.05). Three image groups had similar lesion detection rates, but DLIR groups exhibited higher confidence in diagnosing lesions. Compared with ASIR-V40% at 70 keV, 70-keV DECT with DLIR-H further reduced image noise and improved image quality. Additionally, it improved diagnostic confidence while ensuring a consistent lesion detection rate of liver lesions.

Virtual monochromatic spectral CT imaging in preoperative evaluations for intraductal spread of breast cancer: comparison with conventional CT and MRI

PurposeTo investigate the efficacy of virtual monochromatic spectral computed tomography imaging (VMI) in the preoperative evaluation for intraductal spread of breast cancer.Materials and methodsTwenty-four women who underwent spectral CT and were pathologically diagnosed with ductal carcinoma with a ≥ 2-cm noninvasive component were retrospectively enrolled in Group 1. Twenty-two women with 22 lesions pathologically diagnosed with ductal carcinoma in situ or microinvasive carcinoma were enrolled in Group 2. We compared the contrast-to-noise ratios (CNRs) of the lesions on conventional 120-kVp CT images and 40-keV VMIs in Group 1. Two board-certified radiologists measured the maximum diameters of enhancing areas on 120-kVp CT, 40-keV VMI, and MRI in Group 2 and compared with histopathological sizes.ResultsThe quantitative assessment of Group 1 revealed that the mean ± SD of the CNRs in the 40-keV images were significantly greater than those in the 120-kVp images (5.5 ± 1.9 vs. 3.6 ± 1.5, p < 0.0001). The quantitative assessment of Group 2 demonstrated that the lesion size observed in the conventional 120-kVp CT images by both readers was significantly underestimated as compared to the histopathological size (p = 0.017, 0.048), whereas both readers identified no significant differences between the lesion size measured on 40-keV VMI and the histopathological data. In a comparison with MRI, 40-keV VMI provided measurement within a 10-mm error range in more lesions as compared to the conventional 120-kVp CT.ConclusionVMI improves the evaluation of intraductal spread and is useful for the preoperative evaluations of breast cancer.

Application of metal artifact reduction software in gemstone spectral computed tomography for patients after total knee arthroplasty

BackgroundTo explore the feasibility and effectiveness of the metal artifact reduction software (MARs) reconstruction algorithm in reducing metal artifacts of knee prostheses and to explore the optimal monochromatic level of virtual monochromatic spectral (VMS) images for artifact reduction to provide high-quality images and reliable diagnosis in patients after total knee arthroplasty (TKA).MethodsA total of 31 patients underwent gemstone spectral computed tomography. VMS images with MARs and without MARs were obtained at different energy levels (80, 100, 120, and 140 keV). Two observers scored each group of images, and interobserver agreement was evaluated. Artificial indices (AIs), percentage500HU and structural similarity index measure (SSIM) values were calculated in the objective analysis to evaluate the image quality and impact of metal artifacts.ResultsThe consistency of the scores of the 2 observers was good (kappa value =0.78), and the score of the VMS images with MARs was higher than that of VMS images without MARs. AI values and percentage500HU of the MARs group were significantly lower than those of the without MARs group, while SSIM values were significantly higher. In the comparison of different keV images, the AI value decreased with the increase in keV in the range of 80–120 keV, but there was no significant difference between the 120 keV images and 140 keV images. In the group with MARs, the percentage500HU of 100–140 keV images was significantly lower than that of the 80 keV images, but there was no significant difference between 100, 120, and 140 keV images. In the group without MARs, the percentage500HU was significantly different among all keV groups.ConclusionsVMS images combined with the MARs algorithm can significantly reduce the metal artifacts of knee prostheses and improve image quality. At an energy level of 100–120 keV, a good metal artifact removal effect and soft tissue contrast can be achieved, and the best metal artifact removal effect can be achieved at 140 keV.

Diagnostic accuracy of dual-energy computed tomography angiography in the differentiation of benign and malignant pelvic masses

PurposeThe dual-energy computed tomography(CT) angiography can accurately display subtle details of blood vessels and their surroundings. We aimed to apply dual-energy CT angiography and virtual monochromatic spectral(VMS) images to pelvic mass imaging and evaluate its value of distinguishing between benign and malignant pelvic masses. MethodsThe prospective study was approved by the Institutional Review Board and all participants signed informed consent forms. From August 2018 to July 2020, consecutive female patients with pelvic mass undergone dual-source third-generation CT angiography. The 40 keV VMS images were reconstructed to display mass morphology and corresponding feeding arteries. All images were evaluated by two radiologists blinded to diagnosis(with 9 years and 10 years of experience in CT reading).Disagreements were solved by consensus. The final diagnosis was using histopathology results as the gold standard. Interobserver variability was calculated using Cohen’s kappa and Quadratic Weighted Kappa. The differences between benign and malignant masses were compared using the chi-square test. Accuracy rate, sensitivity, specificity, and the area under the curve (AUC) were calculated as the primary indices for diagnostic accuracy. McNemar test was used to evaluate the difference in diagnostic accuracy between dual-energy CT angiography images and original CT images. A two-tailed P < 0.05 was considered statistically significant. ResultsA total of 64 patients with 28 malignant masses and 47 benign masses were included. The characteristics of malignant masses showed the branch number of the main feeding artery was ≥ 3(71.4%, 20/28), the course of feeding artery(100%, 28/28) and the mass shape(85.7%, 24/28) were both irregulars. Those characteristics all had statistical differences between benign and malignant masses(all P = 0.000). The Models using the course of feeding artery as a predictor, the accuracy, sensitivity and positive likelihood ratio were 89.3% (95 % CI: 0.801, 0.947), 100% (95 % CI: 0.850, 1) and 5.875(95 % CI: 3.125, 11.044), respectively. The diagnostic accuracy of every model by dual-energy CT angiography was significantly higher than that by original CT imaging(all P = 0.000). ConclusionsThe dual-energy CT angiography can distinguish malignant pelvic masses from benign masses by providing characteristic images of feeding arteries and mass shape.

Impact of noise reduction on radiation dose reduction potential of virtual monochromatic spectral images: Comparison of phantom images with conventional 120 kVp images using deep learning image reconstruction and hybrid iterative reconstruction

PurposeTo assess the effects of deep learning image reconstruction (DLIR) and hybrid iterative reconstruction (HIR) on the image quality of virtual monochromatic spectral (VMS) images and to investigate the dose reduction potential of the VMS and conventional 120 kVp images. MethodsA cylindrical phantom simulating an adult abdomen was used. The contrast was set to 60 (medium) and 300 (high) Hounsfield units. CT acquisitions were performed at three dose levels: 12, 9, and 6 mGy. Images were reconstructed via filtered back projection (FBP), DLIR, and HIR. The noise power spectrum (NPS) and task transfer function (TTF) were measured, and the system performance (SP) function was calculated (TTF2/NPS). ResultsThe noise magnitudes at low spatial frequencies with DLIR and HIR were lower than that with FBP by 45.6% and 24.4%, respectively. Compared to the FBP results, the TTF values at 50% with DLIR at medium and high contrast changed by –13.2% and +25.3% with the VMS images and –2.0% and +9.3% with the 120 kVp images, respectively. In the VMS and 120 kVp images, compared to the SP values of 12 mGy FBP images, SP values of 6 mGy DLIR images decreased at medium contrast and increased at high contrast. ConclusionsDLIR achieved better noise reduction than HIR. The spatial resolution of VMS-DLIR varied significantly depending on the contrast. The image quality of VMS-DLIR and 120 kVp-DLIR potentially decrease in medium contrast tasks and increase in high contrast tasks with 50% dose reduction.

Utility of Dual-Energy CT in Abdominal Interventions

AbstractDual-energy computed tomography (DECT) is an emerging CT technique based on data acquisition at two different settings. Various postprocessing techniques generate different sets of images, each with unique advantages. With DECT, it is possible to obtain virtual unenhanced images from monochromatic reconstructions and attenuation maps of different elements, thereby improving the detection and characterization of a variety of lesions. Presently, DECT is widely used to evaluate pulmonary embolism, characterize abdominal masses, determine the composition of urinary calculi, and detect tophi in gout. CT angiography is an essential prerequisite for endovascular intervention. DECT allows a better quality of angiographic images with a lesser dose of contrast. Various postprocessing techniques in DECT also help in a better evaluation of response to locoregional therapy. Virtual noncontrast images and iodine map differentiate residual or recurrent tumors from intrinsically hyperdense materials. Superior metallic artifact reduction allows better evaluation of vascular injuries adjacent to bony fractured fragments or previously deployed embolization coils. In addition to metal artifacts reduction, virtual monochromatic spectral imaging could further mitigate metal artifacts during CT-guided biopsy, providing an improved depiction of lesions and safe and versatile access for long puncture pathways. This article reviews and illustrates the different applications of DECT in various abdominal interventions. Familiarity with the capabilities of DECT may help interventional radiologists to improve their practice and ameliorate patient care.

Technical Note: Quality assessment of virtual monochromatic spectral images on a dual energy CT scanner

To assess the quality of images obtained on a dual energy computed tomography (CT) scanner. Image quality was assessed on a 64 detector-row fast kVp-switching dual energy CT scanner (Revolution GSI, GE Medical Systems). The Catphan phantom and a low contrast resolution phantom were employed. Acquisitions were performed at eight different radiation dose levels that ranged from 9mGy to 32mGy. Virtual monochromatic spectral images (VMI) were reconstructed in the 40-140keV range using all available kernels and iterative reconstruction (IR) at four different blending levels. Modulation Transfer Function (MTF) curves, image noise, image contrast, noise power spectrum and contrast to noise ratio were assessed. In-plane spatial resolution at the 10% of the MTF curve was 0.60mm-1. In-plane spatial resolution was not modified with VMI energy and IR blending level. Image noise was reduced from 16.6 at 9mGy to 6.7 at 32mGy, while peak frequency remained within 0.14±0.01mm-1. Image noise was reduced from 14.3 at IR 10% to 11.5 at IR 50% at a constant peak frequency. The lowest image noise and maximum peak frequency were recorded at 70keV. Our results have shown how objective image quality is varied when different levels of radiation dose and different settings in IR are applied. These results provide CT operators an in depth understanding of the imaging performance characteristics in dual energy CT.

Metal artefact reduction of different alloys with dual energy computed tomography (DECT)

To evaluate the influence of dual-energy CT (DECT) and Virtual monochromatic spectral (VMS) imaging on: (1) the artefact size of geometrically identical orthopaedic implants consisting of three different compositions and (2) the image quality of the surrounding bone, three similar phantoms—each featuring one femoral stem composed of either titanium, chrome-cobalt or stainless steel surrounded by five calcium pellets (200 mg hydroxyapatite/calcium carbonate) to simulate bony tissue and one reference pellet located away from the femoral stem—were built. DECT with two sequential scans (80 kVp and 140 kVp; scan-to-scan technique) was performed, and VMS images were calculated between 40 and 190 keV. The artefact sizes were measured volumetrically by semiautomatic selection of regions of interest (ROIs), considering the VMS energies and the polychromatic spectres. Moreover, density and image noise within the pellets were measured. All three phantoms exhibit artefact size reduction as energy increases from 40 to 190 keV. Titanium exhibited a stronger reduction than chrome-cobalt and stainless steel. The artefacts were dependent on the diameter of the stem. Image quality increases with higher energies on VMS with a better depiction of surrounding structures. Monoenergetic energies 70 keV and 140 keV demonstrate superior image quality to those produced by spectral energies 80 kVp and 140 kVp.

Optimize non-contrast head CT imaging tasks using multiple virtual monochromatic image sets in dual-energy spectral CT.

To demonstrate the value of optimizing non-contrast head imaging tasks by using the multiple virtual monochromatic spectral imaging (VMSI) sets in dual-energy spectral computed tomography (CT) and determine the optimal energy levels for various tasks in imaging head. This retrospective study includes 55 patients (29 women and 26 men, average age of 54.5±12.3years) who underwent non-contrast head CT in spectral imaging mode. For each patient, 21 VMSI sets from 40 to 140 keV at 5 keV intervals and 120 kVp-like image were reconstructed. Signal-to-noise ratio (SNR) for gray matter (GM) and white matter (WM), contrast-to-noise ratio (CNR) between GM and WM, subcalvarial artifact index (SAI) and posterior fossa artifact index (PFAI) were measured by placing regions-of-interest (ROIs) in nine areas of the brain. Two radiologists subjectively rated the image quality in terms of GM-WM differentiation, beam hardening artifacts in the subcalvarial space, and posterior fossa. The overall image noise was evaluated using a 5-point Likert scale. Measurement data were then statistically analyzed. The optimal energy level for viewing the supratentorial brain and reducing beam hardening artifacts in the subcalvarial space and posterior fossa was 65 keV and 75 keV, respectively. All corresponding measurements at these energy levels were significantly better than those measured at other energy levels (all P < 0.05). Dual-energy spectral CT imaging provides a set of virtual monochromatic spectral imaging and can be selected on-demand to optimize the imaging tasks in non-contrast head CT. VMSI reconstruction of dual-energy unenhanced head CT scans at 65-75 keV enables to maximize image quality.

Virtualmonochromatic spectral imaging versus linearly blended dual-energy and single-energy imaging during CT-guided biopsy needle positioning: Optimization of keV settings and impact on image quality.

ObjectivesTo compare image quality and metal artifact reduction between virtual monochromatic spectral imaging (VMSI), linearly blended dual-energy (DE) and single-energy (SE) images, each with and without dedicated iterative metal artifact reduction (iMAR) for CT-guided biopsy.Materials and methodsA biopsy trocar was positioned in the liver of six pigs. DE (Sn140/100kVp) and SE (120kVp/200mAs) acquisitions were performed with equivalent dose. From dual-energy datasets DE Q30-3 images and VMSI between 40–180 keV in steps of 20 keV were generated. From SE datasets I30-3 images were reconstructed. All images were reconstructed with and without iMAR. Objective image quality was analyzed applying density measurements at standardized positions (e.g. trocar tip and liver parenchyma adjacent to the trocar tip) and semi-automated threshold based segmentation. Subjective image quality was performed using semi-quantitative scores. Analyses were performed by two observers.ResultsAt the trocar tip quantitative image analysis revealed significant difference in CT numbers between reconstructions with iMAR compared to reconstructions without iMAR for VMSI at lower keV levels (80 and 100 keV; p = 0.03) and DE (p = 0.03). For liver parenchyma CT numbers were significantly higher in VMSI at high keV compared to low keV (p≤0.01). VMSI at high keV also showed higher CT numbers compared to DE and SE images, though not the level of statistical significance. The best signal-to-noise ratio for VMSI was at 80 keV and comparable to DE and SE. Noise was lowest at 80 keV and lower than in DE and SE. Subjective image quality was best with VMSI at 80 keV regardless of the application of iMAR. iMAR significantly improved image quality at levels of 140 keV and 160 keV. Interreader-agreement was good for quantitative and qualitative analysis.ConclusioniMAR improved image quality in all settings. VMSI with iMAR provided metal artifact reduction and better image quality at 80 keV and thus could improve the accurate positioning in CT-guided needle biopsy. In comparison, DE imaging did not improve image quality compared to SE.

Value of virtual monochromatic spectral image of dual-layer spectral detector CT with noise reduction algorithm for image quality improvement in obese simulated body phantom

BackgroundDual-layer spectral detector CT (SDCT) may provide several theoretical advantages over pre-existing DECT approaches in terms of adjustment-free sampling number and dose modulation, beam hardening correction, and production spectral images by post-processing. In addition, by adopting noise reduction algorithm, high contrast resolution was expected even in low keV level. We surmised that this improvement would be beneficial to obese people. Therefore, our aim of study is to compare image quality of virtual monochromatic spectral images (VMI) and polychromatic images reconstructed from SDCT with different body size and radiation dose using anthropomorphic liver phantom.MethodsOne small and one large size of body phantoms, each containing eight (four high- and four low-contrast) simulated focal liver lesions (FLLs) were scanned by SDCT (at 120 kVp) using different Dose Right Indexes (DRIs). VMI were reconstructed from spectral base images from 40 keV to 200 keV. Hybrid iterative reconstruction (iDose4) was used for polychromatic image reconstruction. Image noise and contrast to noise ratio (CNR) were compared. Five radiologists independently rated lesion conspicuity, diagnostic acceptability and subjective noise level in every image sets, and determined optimal keV level in VMI.ResultsCompare with conventional polychromatic images, VMI showed superior CNR at low keV level regardless of phantom size at every examined DRIs (Ps < 0.05). As body size increased, VMI had more gradual CNR decrease and noise increase than conventional polychromatic images. For low contrast FLLs in large phantom, lesion conspicuities at low radiation dose levels (DRI 16 and 19) were significantly increased in VMI (Ps < 0.05). Subjective image noise and diagnostic acceptabilities were significantly improved at VMI in both phantom size.ConclusionsVMI of dual-layer spectral detector CT with noise reduction algorithm provides improved CNR, noise reduction, and better subjective image quality in imaging of obese simulated liver phantom compared with polychromatic images. This may hold promise for improving detection of liver lesions and improved imaging of obese patients.

Influence of virtual monochromatic spectral image at different energy levels on motion artifact correction in dual-energy spectral coronary CT angiography.

To investigate the influence of virtual monochromatic spectral (VMS) CT images at different energy levels on the effectiveness of a motion correction technique (SSF) in dual-energy Spectral coronary CT angiography (CCTA). 29 cases suspected of or diagnosed with coronary artery disease underwent Spectral CCTA using a prospective ECG triggering with 250ms padding time. SSF was applied to the determined least-motion phase to generate 6 additional sets of VMS images with energy levels from 40 to 100keV. CT value and standard deviation (SD) in the aortic root and epicardial adipose tissue were measured. Image quality of the RCA, LAD and LCX was evaluated on a per-vessel basis in each patient. Two reviewers evaluated the artery using the score of the segment. The low energy VMS images increased CT value and image noise compared with higher-energy VMS images, except 90keV and 100keV. The CNR of 40-70keV were higher than those of 80-100keV (P < 0.05). The image quality scores for images at 50-80keV were higher than those of 40, 90, and 100keV (P < 0.05), and the VMS image quality at 50keV and 60keV with SSF was the highest. SSF can effectively reduce the motion artifacts when coronary vessels have suitable contrast enhancement which can be achieved by adjusting energy levels of VMS images.

Value of virtual monochromatic spectral images with metal artifact reduction algorithm in dual-energy computed tomography-guided microcoil localization of pulmonary nodules.

To evaluate the clinical value of virtual monochromatic spectral (VMS) images with metal artifact reduction (MAR) algorithm in dual-energy computed tomography (DECT)-guided microcoil localization of pulmonary nodules.Fifty-one patients underwent DECT after placement of microcoils on small pulmonary nodules before video-assisted thoracoscopic surgery (VATS). Optimal energy level (in keV) was defined as the level at which CT values of nodules were equivalent to those of 120 kVp images and with no serious metal artifacts. VMS images at optimal keV and at 50, 90,110, and 140 keV with and without MAR were reconstructed. Image quality was scored using a 3-point scale: 1 = excellent, minimal artifacts; 2 = good, mild artifacts; and 3 = poor, extensive artifacts. Image quality scores between the VMS-only and VMS + MAR groups were compared;74 keV was found to be the optimal level for VMS images. The image quality of the VMS + MAR images at 74 keV were significantly better than VMS-only images (1.35 ± 0.59 vs 2.11 ± 0.87, P = .005). There was no difference in image quality score among VMS + MAR images at 74 keV and higher energy levels.VMS images from DECT at 74 keV with MAR can reduce artifacts from microcoils and improve image quality for microcoil localization of pulmonary nodules.

Dual energy CT angiography in peripheral arterial stents: optimal scanning protocols with regard to image quality and radiation dose.

To determine the optimal scanning protocols of dual energy computed tomography angiography (DECTA) in terms of radiation dose and image quality assessment at different keV levels, and compare it with conventional computed tomography angiography (CTA) in patients treated with peripheral arterial stents. Twenty-nine patients with previous stent placement in peripheral arteries were evaluated with DECTA. Images were reconstructed with virtual monochromatic spectral imaging (VMS) at 65, 68, 70 and 72 keV and adaptive statistical iterative reconstruction (ASIR) at 50% compared with CTA. Image quality comprising image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed, and radiation dose was compared. Effects of different type of peripheral arterial stents on image quality were also evaluated. Fifty-six uniquely identified stents that were located in common iliac arteries (CIA), external iliac arteries (EIA) and superficial femoral arteries (SFA) were evaluated. Within subjects, the results showed that DECTA images (VMS) had less noise than the CTA images for CIA, EIA and SFA stents, with the lowest noise at 72 keV. Also, the VMS images had greater SNR than the CTA images for the EIA stents (P<0.05); and the VMS images had greater CNR than the CTA images for CIA, EIA, and SFA stents (P<0.001). Also, on CT attenuation, VMS continued to outperform CTA, but to a lesser extent. Between subjects, average VMS noise varied significantly with the type of the stent used (P=0.025) for CIA stents. Radiation dose was highly significant between DECTA and conventional CTA scans (6.98 vs. 7.40 mSv, P=0.047). We conclude that an optimal scanning protocol consisting of 72 keV and 50% ASIR leads to better image quality for DECTA in peripheral arterial stenting when compared to conventional CTA.

Reduction of metal artifacts from unilateral hip arthroplasty on dual-energy CT with metal artifact reduction software.

Background The evaluation of hip arthroplasty is a challenge in computed tomography (CT). The virtual monochromatic spectral (VMS) images with metal artifact reduction software (MARs) in spectral CT can reduce the artifacts and improve the image quality. Purpose To evaluate the effects of VMS images and MARs for metal artifact reduction in patients with unilateral hip arthroplasty. Material and Methods Thirty-five patients underwent dual-energy CT. Four sets of VMS images without MARs and four sets of VMS images with MARs were obtained. Artifact index (AI), CT number, and SD value were assessed at the periprosthetic region and the pelvic organs. The scores of two observers for different images and the inter-observer agreement were evaluated. Results The AIs in 120 and 140 keV images were significantly lower than those in 80 and 100 keV images. The AIs of the periprosthetic region in VMS images with MARs were significantly lower than those in VMS images without MARs, while the AIs of pelvic organs were not significantly different. VMS images with MARs improved the accuracy of CT numbers for the periprosthetic region. The inter-observer agreements were good for all the images. VMS images with MARs at 120 and 140 keV had higher subjective scores and could improve the image quality, leading to reliable diagnosis of prosthesis-related problems. Conclusion VMS images with MARs at 120 and 140 keV could significantly reduce the artifacts from hip arthroplasty and improve the image quality at the periprosthetic region but had no obvious advantage for pelvic organs.

Image quality of virtual monochromatic images obtained using 320-detector row CT: A phantom study evaluating the effects of iterative reconstruction and body size

ObjectivesTo compare the image quality between virtual monochromatic spectral (VMS) images obtained using 320-row detector CT and polychromatic 120-kVp images reconstructed with or without iterative reconstruction using various phantom sizes. Materials and methodsTorso phantoms simulating three patient sizes and containing four syringes filled with water or different contrast media (5, 10, 15mgI/mL15mgI/ml) were used. The phantoms were scanned using dual-energy (80/135-kVp) and single-energy (120-kVp) protocols at different settings (20mGy, 12mGy, and 6mGy). VMS images were generated at 1-keV intervals (range, 35–135keV). Both the VMS images and the single-energy 120-kVp images were reconstructed using filtered back projection (FBP) and adaptive iterative dose reduction 3D (AIDR-3D). The signal-to-noise ratio (SNR), and the contrast-to-noise ratio (CNR) were assessed. ResultsUsing FBP reconstruction, the SNR and CNR of the VMS images were lower than or similar to those of the 120-kVp images for most dose settings. Using AIDR-3D reconstruction, however, the 70-keV VMS images had higher SNRs and CNRs than the 120-kVp images at most settings. ConclusionsThe image quality of VMS images with FBP reconstruction tended to be lower than that of the 120-kVp images. With the use of AIDR-3D, however, approximately 70-keV VMS images had a higher image quality than the 120-kVp images.

Fast kVp-switching dual energy contrast-enhanced thorax and cardiac CT: A phantom study on the accuracy of iodine concentration and effective atomic number measurement.

To assess the effect of vessel diameter and exposure parameters on the estimation accuracy of concentration and effective atomic number (Zeff ) of iodine (I) in contrast-enhanced thorax and cardiac dual-energy CT using a modern fast kVp-switching CT scanner. A standard semi-anthropomorphic cardiac CT phantom devised to simulate the human chest at three different body habitus i.e., medium-sized, large-sized, and obese, was scanned using a fast kVp-switching Revolution-GSI GE CT scanner. Five cylindrical, 10 mm diameter, vials were filled with solutions prepared by diluting I contrast at five concentrations (2.5, 5, 10, 15, and 20 mg I/ml). To simulate small vessels, pipette tips with a diameter ranging from 5 mm to 0.5 mm were employed. The vials and pipette tips were accommodated within the semi-anthropomorphic phantom. CT acquisitions were performed in the fast kVp-switching dual-energy mode at six different CTDIw values. Acquisitions were also performed at 80, 100, 120, and 140 kVp. Images were acquired at 64 × 0.625 mm beam collimation and reconstructed at 2.5 mm using all available reconstruction filter kernels. Virtual monochromatic spectral (VMS) images, iodine concentration (IMeas ), and Zeff maps were reconstructed. Hounsfield unit as a function of energy (HUkeV ) in VMS and single-kVp (HUkVp ), IMeas and Zeff were measured at each CTDIw . The effect of vessel diameter on IMeas and Zeff was investigated. Measured HUkeV and Zeff were compared to theoretically estimated values and IMeas were compared to nominal (INom ) values. In 10 mm diameter vessels, HUkeV values were accurate to 18% for the medium-sized, 22% for the large-sized and 39% for the obese phantoms. IMeas was underestimated by up to 10% for the medium-sized, 26% for the large-sized and 33% for the obese phantom. IMeas error decreased with increasing CTDIw from ±0.799 mg/ml at 8.61 mGy to ±0.082 mg/ml at 32.01 mGy. The percentage difference between measured and theoretically estimated Zeff ranged from -3.9% to -14.5%. In pipette tip vessels, IMeas was found to depend on the kernel employed. At the standard kernel, IMeas , for INom = 20 mg/ml, was reduced with vessel diameter from 19.25 ± 0.39 mg/ml, at 10 mm, to 2.52 ± 0.31 mg/ml, at 1 mm. Linear regression between IMeas and INom resulted in IMeas /INom factors of 0.925 for 5 mm, 0.815 for 4 mm, 0.651 for 3 mm, 0.377 for 2 mm, and 0.129 for 1 mm vessel diameter. Measured Zeff values were underestimated when vessel diameter was decreased from 5 mm to 1 mm by 27% for the 20 mg I/ml and 21% for the 2.5 mg I/ml. HUkeV , IMeas , and Zeff depend on several parameters such as body size, vessel size, exposure parameters, and reconstruction kernel. The limiting spatial resolution of the CT system results in considerable underestimation of HUkVp , IMeas , and Zeff in vessels smaller than 5 mm diameter. The underestimation of I uptake may be experimentally corrected, if the diameter of the investigated vessel is measured and the correction factors produced in this study are employed.

Virtual monochromatic spectral imaging for the evaluation of vertebral inconspicuous osteoblastic metastases from lung.

Background The diagnosis of inconspicuous osteoblastic metastases (OBMs) is a challenge in computed tomography (CT) images. The virtual monochromatic spectral (VMS) image of spectral CT is useful for the detection of the low-contrast lesions. Purpose To select the optimal monochromatic level for VMS images of spectral CT for detecting and diagnosing inconspicuous OBMs of the vertebra from lung cancer. Material and Methods Thirty-five patients underwent spectral CT for chest or abdomen. The CT number and standard deviation (SD) of lesions and adjacent normal bone and the SD value of subcutaneous fat were measured on the conventional polychromatic image (140 kVp) and 40-140 keV VMS images. The contrast-to-noise ratio (CNR) was compared among the 11 VMS images and 140 kVp images. The scores of two observers for different images and the inter-observer agreement were evaluated. The diameter and CNR of the detected and missed lesions were assessed. Results The lowest image noise was distributed in 70 and 140 keV images and the highest CNR was noted in 70 keV images. Good and moderate inter-observer agreement were identified for the evaluation of diagnostic ability, and the subjective scores of two observers for 60 and 70 keV images were increased compared with 140 kVp images ( P < 0.05). The diameter had no significant difference between the detected and missed lesions. The CNR of the missed lesions was reduced compared with detected lesions. Conclusion VMS images at 70 keV may be optimal for detecting and diagnosing inconspicuous OBMs from lung cancer.

Tomografía Computada de doble Energía: Nueva tecnología para la reducción de artefactos de metal. [Dual Energy Computed Tomography: New technology for metal artifacts reduction.

&lt;p&gt;&lt;strong&gt;Objetivos:&lt;/strong&gt; Explorar la utilidad de la tomografía computada de doble energía (TCDE) mediante tecnología de imágenes espectrales &lt;em&gt;gemstone&lt;/em&gt; (GSI) y de un software dedicado a la reducción de artefactos de metal (MARS), para la evaluación de tejidos periprotésicos e interpretabilidad diagnóstica de patologías relacionadas con implantes.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Materiales y Métodos:&lt;/strong&gt; Se estudió la densidad ósea, partes blandas y grasa en el tejido periprotésico comparado con tejido control sin implante, utilizando un escáner de alta definición de TCDE-GSI tanto en imágenes policromáticas convencionales (PI) y monocromáticas virtuales (VMSI) con MARS en 80 pacientes con prótesis metálicas en diversas regiones musculo-esqueléticas. Se valoró también la calidad de imagen y la interpretabilidad diagnóstica mediante escala de Likert.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Resultados:&lt;/strong&gt; Con PI se observaron diferencias significativas entre el área periprotésica en los tres tipos de tejidos evaluados respecto a los controles (p&amp;lt;0.0001); sin diferencias significativas utilizando VMSI-MARS (p=0.053 hueso, p=0.32 partes blandas, y p=0.13 grasa), demostrando mayor similitud con el tejido normal. Además, los niveles de ruido de las imágenes (DS) fueron significativamente mayores con PI (p&amp;lt;0.0001) que con VMSI-MARS. Todas las regiones periprotésicas se consideraron no interpretables utilizando PI comparado con 11 (9%) utilizando VMSI-MARS. No hubo diferencias significativas en la dosis de radiación comparado con un grupo control pareado por sexo y edad (p= 0.21).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusiones: &lt;/strong&gt;La tecnología TCDE tiene la capacidad de reducir los artefactos periprotésicos, logrando un significativo incremento en la capacidad de identificación de tejidos e interpretabilidad diagnóstica de posibles patologías relacionadas con implantes.&lt;/p&gt;