Virtual Monochromatic Spectral 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.

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.

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.

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.

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.

Image quality evaluation of virtual monoenergetic spectral images obtained in two types of dual energy CT based on noise level

Objective To investigate the image quality difference of the virtual monochromatic spectral(VMS) images synthesized from fast kilovoltage switching and dual-source dual-energy CT for a given radiation dose. Methods A plurality of disposable syringes containing 15 mg/ml iodine contrast agent and saline were placed on the surface of the male anthropomorphic phantom consisting ofhead neck and torso, GE HD750 gemstone spectral imaging and Siemens Somatom Definition Flash dual energy CT protocols were performed on the phantom for a same dose(volume CT dose index 6.52 mGy), and VMS images (40, 60, 70, 80, 100, 120, 140 keV) were reconstructed and obtained(VMSkV switching and VMSdual-source image), respectively. The objective image noise, iodine signal noise ratio(SNR), iodine contrast noise ratio (CNR) and CT values were measured. The results were analyzed using the paired t test and ANOVA. Results All VMS iodine CT values were gradually decreased with the increasing of keV, and iodine CT values on VMSdual-source images were greater than on VMSkV switching images(P<0.05), VMSkV switching iodine CT values in descending order from the head, chest, abdomen at less than 100 keV,while most VMSdual-source iodine CT values were highest on chest(P<0.05). VMSdual-source and VMSkV switching image noise were highest at 40 keV and successively raised from the head, chest, abdomen. VMSkV switching image noise gradually decreased with the increase of keV in the range of 40 to 70 keV, gradually increased up to the trough after 70 keV from 80 keV gradually decreased, while VMSdual-source image noise was lowest at 70 keV or 80 keV, and then with the keV increased gradually increased. Image noise on VMSkV switching images in the range of 40 to 100 keV were higher than that on VMSdual-source images and lower in the range of 100 to 140 keV at most part(P<0.05). VMSdual-source and VMSkV switching iodine SNR were highest at 40 keV or 60 keV, SNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head and abdomen(P<0.05). VMSdual-source and VMSkV switching iodine CNR were highest at 60 keV, CNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head 100 keV and 120 keV on abdomen(P<0.05).SNR and CNR decreased from the head, chest, abdomen (P<0.05). Conclusion VMS images synthesized from fast kilovoltage switching and dual-source dual-energy CT have different image quality performance at most keV and body parts, but VMS imaging at approximately 70 keV yielded lower image noise, and at approximately 60 keV yielded highest SNR and CNR. Key words: Tomography, X-ray computed; Comparative study; Virtual monochromatic spectral

Reduction of Metal Artifact with Dual-Energy CT: Virtual Monospectral Imaging with Fast Kilovoltage Switching and Metal Artifact Reduction Software.

Imaging of patients with metal implants is a common activity for radiologists, and overcoming metal artifacts during computed tomography (CT) is still a challenge. Virtual monochromatic spectral (VMS) imaging with dual-energy CT has been reported to reduce beam-hardening metal artifact effectively. Dual-energy CT allows the synthesis of VMS images. Monochromatic images depict how the imaged object would look if the X-ray source produced X-ray photons at only a single-energy level. For this reason, VMS imaging improve image quality by reducing beam-hardening artifacts. Additional metal artifact reduction postprocessing such as metal artifact reduction software can be applied to improve the visualization of the bone-prosthesis interface, periprosthetic areas, and soft tissue near and far from the metal implant. This article summarizes how virtual monochromatic images are synthesized from dual-energy CT, and it describes and illustrates our clinical experience with a single-source dual-energy scanner with fast kilovoltage switching to reduce beam hardening in patients with metal implants.

Complementary contrast media for metal artifact reduction in dual-energy computed tomography.

Metal artifacts have been a problem associated with computed tomography (CT) since its introduction. Recent techniques to mitigate this problem have included utilization of high-energy (keV) virtual monochromatic spectral (VMS) images, produced via dual-energy CT (DECT). A problem with these high-keV images is that contrast enhancement provided by all commercially available contrast media is severely reduced. Contrast agents based on higher atomic number elements can maintain contrast at the higher energy levels where artifacts are reduced. This study evaluated three such candidate elements: bismuth, tantalum, and tungsten, as well as two conventional contrast elements: iodine and barium. A water-based phantom with vials containing these five elements in solution, as well as different artifact-producing metal structures, was scanned with a DECT scanner capable of rapid operating voltage switching. In the VMS datasets, substantial reductions in the contrast were observed for iodine and barium, which suffered from contrast reductions of 97% and 91%, respectively, at 140 versus 40keV. In comparison under the same conditions, the candidate agents demonstrated contrast enhancement reductions of only 20%, 29%, and 32% for tungsten, tantalum, and bismuth, respectively. At 140 versus 40keV, metal artifact severity was reduced by 57% to 85% depending on the phantom configuration.

Role of dual energy CT with adjusted radiation dose in accurate assessment of electrode position in pediatric cochlear implant

Background and purposePostoperative imaging of cochlear implant needs to provide detailed information on the position of individual electrodes; the aim of this study was to evaluate visualization of individual electrodes and measurement of the electrode–modiolus distance (EMD) using dual energy CT (DECT) – with low radiation dose using virtual monochromatic spectral (VMS) imaging comparing the images quality and radiation dose with those by using multidetector CT (MDCT). Materials and methods25 pediatric patients who underwent cochlear implantation were imaged using DECT (15 patients) and MDCT (10 patients), and the image quality and radiation dose of DECT were compared to those of MDCT. Measurement of EMD was done for 5 electrodes and the results were correlated with neural response telemetry (NRT) and behavioural mapping levels. ResultsA statistically significant difference between the radiation dose of DECT and MDCT was confirmed (p=0.002) without a statistically significant difference in images quality (weighted K=−0.129 and PABAK=0.533).Statistically significant correlations were found between EMD and NRT threshold, T (threshold) and C (maximum comfortable) levels with p=<0.01. ConclusionDECT accurately detects the electrode position with low radiation dose which helps in CI fitting.

The Value of Nonenhanced Single-Source Dual-Energy CT for Differentiating Metastases From Adenoma in Adrenal Glands

To evaluate the value of the nonenhanced single-source dual-energy computed tomography (ssDECT) in differentiating metastases from adenomas in adrenal glands. This retrospective study was approved by our Institutional Review Board, and written informed consent was waived. One hundred twelve patients (66 men:46 women; mean age, 58 years) with 63 adrenal metastases (AMs) and 64 adrenal adenomas (AAs) underwent a plain dual-energy spectral CT imaging from August 2011 to December 2013 were included. The fat (water) density (DFa [Wa]) from the material decomposition (MD) images and CT number and effective atomic number (eff-Z) from the virtual monochromatic spectral (VMS) image sets were measured for the AMs and AAs. The spectral Hounsfield unit (HU) curve (CT number as a function of photon energy from 40 to 140 keV) was generated, and its slope (K) was calculated. The difference of these parameters between AMs and AAs was statistically compared by the Wilcoxon rank sum test. Receiver operating characteristic curve (ROC) curves were used to compare the diagnostic efficacies of these measures in the identification of AAs and AMs. The distribution of spectral HU curve was analyzed using the chi-square test in terms of its slope K: ascending (K > 0.1), straight (-0.1 ≤ K ≤ 0.1), and descending (K < -0.1). 1) 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). 2) The fat concentration of metastases (-177.37, 296.38 mg/mL) was statistically lower than that of adenomas (126.73, 328.07 mg/mL; P < .05). 3) The eff-Z of metastases (7.76, 0.23) was significantly higher than that of adenomas (7.42, 0.32; P < .05). 4) With CT number of VMS image at 40 keV of 21.78 HU as a threshold, the sensitivity and specificity for differentiating metastases from adenomas was 92.1% and 76.6%, respectively, and the area under the ROC curve was 0.90. 5) The spectral curve types included 3.2% (2 of 63) ascending, 20.6% (13 of 63) straight, and 76.2% (48 of 63) descending for the metastases, whereas the corresponding numbers were 60.9% (39 of 64), 21.9% (14 of 64), and 17.2% (11 of 64) for the adenomas. The difference was statistically significant (X(2) = 56.63; P < .05). The nonenhanced ssDECT enables a multiparametric approach to provide an excellent sensitivity for identifying AMs from AAs.

Renal cyst pseudoenhancement: intraindividual comparison between virtual monochromatic spectral images and conventional polychromatic 120-kVp images obtained during the same CT examination and comparisons among images reconstructed using filtered back projection, adaptive statistical iterative reconstruction, and model-based iterative reconstruction.

The purpose of this study was to compare renal cyst pseudoenhancement between virtual monochromatic spectral (VMS) and conventional polychromatic 120-kVp images obtained during the same abdominal computed tomography (CT) examination and among images reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR).Our institutional review board approved this prospective study; each participant provided written informed consent. Thirty-one patients (19 men, 12 women; age range, 59–85 years; mean age, 73.2 ± 5.5 years) with renal cysts underwent unenhanced 120-kVp CT followed by sequential fast kVp-switching dual-energy (80/140 kVp) and 120-kVp abdominal enhanced CT in the nephrographic phase over a 10-cm scan length with a random acquisition order and 4.5-second intervals. Fifty-one renal cysts (maximal diameter, 18.0 ± 14.7 mm [range, 4–61 mm]) were identified. The CT attenuation values of the cysts as well as of the kidneys were measured on the unenhanced images, enhanced VMS images (at 70 keV) reconstructed using FBP and ASIR from dual-energy data, and enhanced 120-kVp images reconstructed using FBP, ASIR, and MBIR. The results were analyzed using the mixed-effects model and paired t test with Bonferroni correction.The attenuation increases (pseudoenhancement) of the renal cysts on the VMS images reconstructed using FBP/ASIR (least square mean, 5.0/6.0 Hounsfield units [HU]; 95% confidence interval, 2.6–7.4/3.6–8.4 HU) were significantly lower than those on the conventional 120-kVp images reconstructed using FBP/ASIR/MBIR (least square mean, 12.1/12.8/11.8 HU; 95% confidence interval, 9.8–14.5/10.4–15.1/9.4–14.2 HU) (all P < .001); on the other hand, the CT attenuation values of the kidneys on the VMS images were comparable to those on the 120-kVp images.Regardless of the reconstruction algorithm, 70-keV VMS images showed a lower degree of pseudoenhancement of renal cysts than 120-kVp images, while maintaining kidney contrast enhancement comparable to that on 120-kVp images.

Differential diagnosis of osteoblastic metastases from bone islands in patients with lung cancer by single-source dual-energy CT: Advantages of spectral CT imaging

ObjectivesTo evaluate the diagnostic efficacy of spectral CT for the differentiation of osteoblastic metastases (OBMs) from bone islands (BIs) in patients with lung cancer. MethodsIn 94 patients with lung cancer who underwent spectral CT, focal hyperdense lesions in vertebral bodies were diagnosed as OBMs or BIs. Regions of interest were placed within each lesion to measure the mean CT value and its standard deviation (SD) on polychromatic single-energy CT (SECT) at 140kVp and dual-energy virtual monochromatic spectral (VMS) images. The mean bone (Dbone(wa)) and water densities (Dwa(bone)) of each lesion were also measured. The slope (k) of the spectral curve was calculated. Independent-sample t-test was used to compare those values between OBMs and BIs. Receiver operator characteristic analysis was performed to compare the area under curve (AUC) for the differentiation of OBMs from BIs. ResultsA total of 79 OBMs and 43 BIs were confirmed. The CT and SD values on SECT at 140kVp and VMS images at 50–130keV, k value, and Dbone(wa) for OBMs were significantly lower than for BIs; Dwa(bone) was significantly higher for OBMs than for BIs (p<0.05 for all). The AUC for the SD value at 110keV was the highest among those parameters. The optimal cut-off value for this differentiation was 68.6HU for the SD value on VMS images at 110keV with sensitivity of 93.0% and specificity of 93.3%. ConclusionSpectral CT is helpful for the differentiation of OBMs from BIs in patients with lung cancer, particularly using SD of the CT value on high-energy VMS images.

Abdominal CT: An intra-individual comparison between virtual monochromatic spectral and polychromatic 120-kVp images obtained during the same examination

ObjectivesTo compare quantitative and subjective image quality between virtual monochromatic spectral (VMS) and conventional polychromatic 120-kVp imaging performed during the same abdominal computed tomography (CT) examination. Materials and methodsOur institutional review board approved this prospective study; each participant provided written informed consent. 51 patients underwent sequential fast kVp-switching dual-energy (80/140kVp, volume CT dose index: 12.7mGy) and single-energy (120-kVp, 12.7mGy) abdominal enhanced CT over an 8cm scan length with a random acquisition order and a 4.3-s interval. VMS images with filtered back projection (VMS-FBP) and adaptive statistical iterative reconstruction (so-called hybrid IR) (VMS-ASIR) (at 70keV), as well as 120-kVp images with FBP (120-kVp-FBP) and ASIR (120-kVp-ASIR), were generated from dual-energy and single-energy CT data, respectively. The objective image noises, signal-to-noise ratios and contrast-to-noise ratios of the liver, kidney, pancreas, spleen, portal vein and aorta, and the lesion-to-liver and lesion-to-kidney contrast-to-noise ratios were measured. Two radiologists independently and blindly assessed the subjective image quality. The results were analyzed using the paired t-test, Wilcoxon signed rank sum test and mixed-effects model with Bonferroni correction. ResultsVMS-ASIR images were superior to 120-kVp-FBP, 120-kVp-ASIR and VMS-FBP images for all the quantitative assessments and the subjective overall image quality (all P<0.001), while VMS-FBP images were superior to 120-kVp-FBP and 120-kVp-ASIR images (all P<0.004). ConclusionsVMS images at 70keV have a higher image quality than 120-kVp images, regardless of the application of hybrid IR. Hybrid IR can further improve the image quality of VMS imaging.

Optimal Monochromatic Energy Levels in Spectral CT Pulmonary Angiography for the Evaluation of Pulmonary Embolism

BackgroundThe aim of this study was to determine the optimal monochromatic spectral CT pulmonary angiography (sCTPA) levels to obtain the highest image quality and diagnostic confidence for pulmonary embolism detection.MethodsThe Institutional Review Board of the Shanghai Jiao Tong University School of Medicine approved this study, and written informed consent was obtained from all participating patients. Seventy-two patients with pulmonary embolism were scanned with spectral CT mode in the arterial phase. One hundred and one sets of virtual monochromatic spectral (VMS) images were generated ranging from 40 keV to 140 keV. Image noise, clot diameter and clot to artery contrast-to-noise ratio (CNR) from seven sets of VMS images at selected monochromatic levels in sCTPA were measured and compared. Subjective image quality and diagnostic confidence for these images were also assessed and compared. Data were analyzed by paired t test and Wilcoxon rank sum test.ResultsThe lowest noise and the highest image quality score for the VMS images were obtained at 65 keV. The VMS images at 65 keV also had the second highest CNR value behind that of 50 keV VMS images. There was no difference in the mean noise and CNR between the 65 keV and 70 keV VMS images. The apparent clot diameter correlated with the keV levels.ConclusionsThe optimal energy level for detecting pulmonary embolism using dual-energy spectral CT pulmonary angiography was 65–70 keV. Virtual monochromatic spectral images at approximately 65–70 keV yielded the lowest image noise, high CNR and highest diagnostic confidence for the detection of pulmonary embolism.