Optimization of window settings for standard and advanced virtual monoenergetic imaging in abdominal dual-energy CT angiography

Optimal CT windowing on low-monoenergetic images using a simplex algorithm-based approach for abdominal inflammatory processes

BACKGROUND

OBJECTIVES: To determine optimal window settings for conspicuity of abdominal inflammatory processes on 50 keV low-monoenergetic images derived from dual-energy spectral CT (DECT).

METHODS

A retrospective study of 30 patients with clinically proven pancreatitis (15/30) or pyelonephritis (15/30) with inflammatory lesions visible on DECT scans were selected to serve as reference populations. 50 keV low-monoenergetic images in the portal venous phase were iteratively evaluated by 6 abdominal radiologists in twenty-one different windows (7-350HU center; 120-580HU width), selected using a simplex optimization algorithm. Each reader graded the conspicuity of the parenchymal hypodense lesions and image background quality. Three-dimensional contour maps expressing the relationship between overall reader grade and window center and width were constructed and used to find the ideal window for inflammatory pancreatic and renal processes and the image background quality. Finally, 15 appendicitis cases were reviewed on optimal pancreas and kidney windows and the manufacturer recommended conventional abdominal window settings for conventional imaging.

RESULTS

Convergence to optimal windowing was achieved based upon a total of 3,780 reads (21 window settings × 6 readers × 15 cases for pancreas and kidney). Highest conspicuity grade (>4.5 ± 0.0) for pancreas inflammatory lesions was seen at 116HU/430HU, whereas hypodense pyelonephritis had highest conspicuity at 290HU/570HU. This rendered an ideal "compromise" window (>4 ± 0.2) of 150HU/450HU which differed substantially from conventional manufacturer recommended settings of 50HU/380HU (2.1 ± 1.0, p = 0.00001). Appendix mucosal enhancement was best visualized at manufacturer settings.

CONCLUSIONS

Optimal visualization of inflammatory processes in abdominal organs on 50 keV low-monoenergetic images may require tailored refinement of window settings.

Advances for Pulmonary Functional Imaging: Dual-Energy Computed Tomography for Pulmonary Functional Imaging

Dual-energy computed tomography (DECT) can improve the differentiation of material by using two different X-ray energy spectra, and may provide new imaging techniques to diagnostic radiology to overcome the limitations of conventional CT in characterizing tissue. Some techniques have used dual-energy imaging, which mainly includes dual-sourced, rapid kVp switching, dual-layer detectors, and split-filter imaging. In iodine images, images of the lung's perfused blood volume (PBV) based on DECT have been applied in patients with pulmonary embolism to obtain both images of the PE occluding the pulmonary artery and the consequent perfusion defects in the lung's parenchyma. PBV images of the lung also have the potential to indicate the severity of PE, including chronic thromboembolic pulmonary hypertension. Virtual monochromatic imaging can improve the accuracy of diagnosing pulmonary vascular diseases by optimizing kiloelectronvolt settings for various purposes. Iodine images also could provide a new approach in the area of thoracic oncology, for example, for the characterization of pulmonary nodules and mediastinal lymph nodes. DECT-based lung ventilation imaging is also available with noble gases with high atomic numbers, such as xenon, which is similar to iodine. A ventilation map of the lung can be used to image various pulmonary diseases such as chronic obstructive pulmonary disease.

Photon-counting detector CT improves quality of arterial phase abdominal scans: A head-to-head comparison with energy-integrating CT

PURPOSE

Photon-counting detector (PCD)-CT is expected to have a substantial impact on oncologic abdominal imaging. We compared subjective and objective image quality between PCD-CT and conventional energy-integrating detector (EID-)CT arterial phase abdominal scans.

METHODS

This study included 84 patients undergoing both types of abdominal CT. EID-CT scans were acquired with a tube voltage of 100 kVp. With PCD-CT, acquired with 120-kVp, we reconstructed polychromatic T3D images and virtual monoenergetic images (VMIs) in 10-keV intervals from 40 to 90 keV. Quantitative image analysis included noise and contrast-to-noise ratio (CNR) of hepatic vessels, kidney cortex, and hypervascular liver lesions to liver parenchyma. Three raters used a 5-point Likert scale for qualitative image analysis of image noise and contrast, lesion conspicuity, and overall image quality. Radiation dose exposure (CT dose index) was compared between the two CT types.

RESULTS

Mean CT dose index and effective dose were respectively 18 % and 26 % lower with PCD-CT versus EID-CT. Compared with EID-CT, CNRs of kidney cortex and vessel to liver parenchyma were significantly higher in PCD-CT VMIs at energies ≤ 60 keV and in polychromatic T3D images (p < 0.004). Overall image quality of PCD-CT VMIs at 50 and 60 keV was rated as significantly better (p < 0.01) than the EID-CT images (inter-reader agreement alpha = 0.80). Lesion conspicuity was significantly better in low-keV VMIs (p < 0.03) and worse in > 70-keV VMIs.

CONCLUSIONS

With low-keV VMI, PCD-CT yields significantly improved objective and subjective quality of arterial phase oncological imaging compared with EID-CT. This advantage may translate into higher diagnostic confidence and lower radiation dose protocols.

Dual-Energy CT of the Heart: A Review

Dual-energy computed tomography (DECT) represents an emerging imaging technique which consists of the acquisition of two separate datasets utilizing two different X-ray spectra energies. Several cardiac DECT applications have been assessed, such as virtual monoenergetic images, virtual non-contrast reconstructions, and iodine myocardial perfusion maps, which are demonstrated to improve diagnostic accuracy and image quality while reducing both radiation and contrast media administration. This review will summarize the technical basis of DECT and review the principal cardiac applications currently adopted in clinical practice, exploring possible future applications.

Initial Investigation of Clinical Value of Noise-Optimized Virtual Monoenergetic Images Derived From Dual-Energy Computed Tomography Angiography in Preoperative Perforator Planning of Anterolateral Thigh Flap Transplantation

OBJECTIVE

To objectively and subjectively assess the image characteristics of noise-optimized virtual monoenergetic images [MEI (+)] and polyenergetic images (PEIs) from dual-energy computed tomography angiography and then to explore the clinical value of the optimal MEI (+) in preoperative perforator planning of anterolateral thigh (ALT) flap transplantation.

METHODS

Sixteen patients (32 thighs) who underwent lower extremity run-off dual-energy computed tomography angiography for planning ALT flap transplantation were enrolled. One standard PEI and 5 MEI (+) in 10-keV intervals (range, 40-80 keV) were reconstructed. First, we compared the image quality subjectively (branch order, image quality, and vascular network continuity) and objectively (vascular attenuation, image noise, signal-to-noise ratio, and the contrast-to-noise ratio). Then, we compared the clinical value (number, type, source artery, pedicle length, caliber, and location of all sizable perforators) between the optimal MEI (+) and PEI groups.

RESULTS

The 40-keV MEI (+) was rated superior subjective and objective image quality metrics to PEI (all P < 0.001). Compared with PEI, 40 keV MEI (+) increased the number of visible perforators, the percentage of perforators with identifiable types, and the measurable length of perforator pedicle (all P < 0.001).

CONCLUSIONS

We recommend 40 keV MEI (+) for the visualization of perforators and their contribution to the selection and location of suitable perforators in preoperative planning for ALT flaps.

Noise-optimized virtual monoenergetic imaging technology of the third-generation dual-source computed tomography and its clinical applications

The third-generation dual-source computed tomography (DSCT) is among the most advanced imaging methods. It employs noise-optimized virtual monoenergetic imaging (VMI+) technology. It uses the frequency-split method to extract high-contrast image information from low-energy images and low-noise information from images reconstructed at an optimal energy level, combining them to obtain the final image with improved quality. This review is the first to summarize the results of clinical studies that primarily and recently evaluated the VMI+ technique based on tumor, blood vessel, and other lesion classification. We aim to assist radiologists in quickly selecting the appropriate energy level when performing image reconstruction for superior image quality in clinical work and providing several ideas for future scientific research of the VMI+ technique. Presently, VMI+ reconstruction is mostly used for images of various tumors or blood vessels, including coronary plaques, coronary stents, deep vein thromboses, pulmonary embolisms (PEs), active arterial hemorrhages, and endoleaks after endovascular aneurysm repair. In addition, VMI+ has been used for imaging children's heads, liver lesions, pancreatic lacerations, and reducing metal artifacts. Regarding the reconstruction at the optimal energy level, the VMI+ technique yielded a higher image quality than the pre-optimized virtual monoenergetic imaging (VMI) technique and single-energy CT. Moreover, either low concentrations of contrast medium or low iodine injection rates can be applied before VMI+ reconstruction at a low-energy level to reduce contrast agent-related kidney injury risk. After reconstructing an image at the optimal energy level, both the image's window width and level can also be adjusted to improve the image effect's reach and diagnosis suitability. To improve image quality and lesion-imaging clarity and reduce the use of contrast agents, VMI+ reconstruction technology has been applied clinically, in which the selection of energy level is the key to the whole reconstruction process. Our review summarizes these optimal levels for radiologists' reference and suggests new ideas for the direction of future VMI+ research.

Generally applicable window settings of low-keV virtual monoenergetic reconstructions in dual-layer CT-angiography of the head and neck

Background

Increased vessel contrast in low-keV virtual monoenergetic images (VMI) in spectral detector CT angiography of the head and neck requires adaption of window settings. Aim of this study was to define generally applicable window settings of low-keV VMI.

Methods

Two radiologists determined ideal subjective window settings for VMI_{40-70 keV} in 54 patients. To obtain generally applicable window settings, center and width values were modeled against the attenuation of the internal carotid artery (HUICA). This modeling was performed with and without respect to keV. Subsequently, image quality of VMI_{40-70 keV} was assessed using the model-based determined window settings.

Results

With decreasing keV values, HUICA increased significantly in comparison to conventional images (CI) (P<0.05 for 40-60 keV). No significant differences between modelled and individually recorded window settings were found confirming validity of the obtained models (P values: 0.2-1.0). However, modelling with respect to keV was marginally less precise.

Conclusions

Window settings of low-keV VMI can be semi-automatically determined in dependency of the ICA attenuation in spectral detector CTA of the head and neck. The reported models are a promising tool to leverage the improved image quality of these images in clinical routine.

Visibility of bronchial arteries using virtual and advanced virtual monoenergetic imaging

BACKGROUND

The utility of virtual monoenergetic imaging (VMI) for fine arteries has not been well clarified.

PURPOSE

To assess bronchial artery visualization using VMI and noise-optimized advanced VMI (VMI+).

MATERIAL AND METHODS

Eighty-seven patients with esophageal cancer underwent computed tomography (CT) using a third-generation dual-source system before surgery. Tube voltages were set to 90 kVp and 150 kVp, respectively. Images were reconstructed using VMI and VMI+ with energy levels of 40-120 keV (in 10-keV increments); composite images equivalent to CT images at 105 kVp were also generated. The CT attenuation value and contrast-to-noise ratio (CNR) of bronchial arteries using VMI and VMI+ were compared with those obtained using composite imaging. Two radiologists subjectively analyzed bronchial artery visualization with reference to the composite image.

RESULTS

CT attenuation values for bronchial arteries using VMI at 40-60 keV and VMI+ at 40 keV and 50 keV were significantly higher than those obtained using composite imaging (P < 0.05). CNR using VMI at 40-60 keV was significantly higher than that obtained using composite imaging (P < 0.05), whereas no differences were noted for values obtained using composite imaging between VMI+ at 40 keV and 50 keV. In the subjective analysis, VMI at 40 keV and 50 keV yielded significantly better visibility of bronchial arteries than VMI+ (P < 0.05).

CONCLUSION

VMI and VMI+ at low voltages (40-50 keV) may be useful for bronchial artery visualization. VMI+ may be less effective for fine vessels as bronchial artery visualization.

Visceral fat shows the strongest association with the need of intensive care in patients with COVID-19

BACKGROUND

Obesity was recently identified as a major risk factor for worse COVID-19 severity, especially among the young. The reason why its impact seems to be less pronounced in the elderly may be due to the concomitant presence of other comorbidities. However, all reports only focus on BMI, an indirect marker of body fat.

AIM

To explore the impact on COVID-19 severity of abdominal fat as a marker of body composition easily collected in patients undergoing a chest CT scan.

METHODS

Patients included in this retrospective study were consecutively enrolled among those admitted to an Emergency Department in Rome, Italy, who tested positive for SARS-Cov-2 and underwent a chest CT scan in March 2020. Data were extracted from electronic medical records.

RESULTS

150 patients were included (64.7% male, mean age 64 ± 16 years). Visceral fat (VAT) was significantly higher in patients requiring intensive care (p = 0.032), together with age (p = 0.009), inflammation markers CRP and LDH (p < 0.0001, p = 0.003, respectively), and interstitial pneumonia severity as assessed by a Lung Severity Score (LSS) (p < 0.0001). Increasing age, lymphocytes, CRP, LDH, D-Dimer, LSS, total abdominal fat as well as VAT were found to have a significant univariate association with the need of intensive care. A multivariate analysis showed that LSS and VAT were independently associated with the need of intensive care (OR: 1.262; 95%CI: 1.0171-1.488; p = 0.005 and OR: 2.474; 95%CI: 1.017-6.019; p = 0.046, respectively).

CONCLUSIONS

VAT is a marker of worse clinical outcomes in patients with COVID-19. Given the exploratory nature of our study, further investigation is needed to confirm our findings and elucidate the mechanisms underlying such association.

Virtual Monoenergetic Images (VMI+) in Dual-Source Dual-Energy CT Venography (DSDE-CTV) of the Lower Extremity Prior to Coronary Artery Bypass Graft (CABG): A Feasibility Study

RATIONALE AND OBJECTIVES

To evaluate the image quality and suitability of Dual-Source Dual-Energy CT venography (DSDE-CTV) with asynchronous virtual monoenergetic images (VMI+) of the entire lower extremity in the context of pre-surgical assessment of complex cases prior to coronary bypass graft as a feasibility study.

MATERIALS AND METHODS

Fifteen consecutive patients, consisting of 5 females and 10 males with an average age of 52 ± 17 years underwent DSDE-CTV from the pubic symphysis to the ankles after intravenous injection of an iodinated contrast medium. DSDE-CTV was acquired with tube voltages of 80 kVp and sn140 kVp. Single spectrum images (A - 80 kVp; B - 140 kVp) as well as a linearly blended mixed data set (M_0.6) were reconstructed. By postprocessing, an VMI+ dataset at 40 keV was generated. Objective image quality parameters of the deep and superficial veins of thigh, knee, and calves were measured separately for each location. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Additionally, subjective image quality was assessed independently by two radiologists.

RESULTS

Mean vascular attenuation was 73.9 ± 17.8 HU at B, 113.7 ± 42.2 HU at M_0.6, 119.4 ± 45.5 HU at A, and 201.0 ± 89.7 HU at VMI+. Mean CNR was 6.7 ± 2.0 at 140 keV, 9.25 ± 2.3 in the M_0.6 datasets, 8.7 ± 3.0 at 80 keV, and 12.9 ± 4.3 at 40 keV. Attenuation values were approximately doubled when compared to the reference standard (M_0.6) with significantly improved SNR and CNR (p < 0.05). Subjective image quality scores were highest for VMI+ datasets (4.1 ± 0.5) and lowest for B datasets (2.3 ± 0.37), however differences between VMI+ datasets and M_0.6 datasets did not reach statistical significance.

CONCLUSION

Postprocessing of dual-energy CTV with VMI+ significantly increases attenuation of veins and markedly improves SNR and CNR values, thereby improving the diagnostic quality of CTV for the evaluation of deep and superficial veins of the entire lower limb prior to coronary bypass graft.

Carotid and cerebrovascular dual-energy computed tomography angiography: Optimization of window settings for virtual monoenergetic imaging reconstruction

PURPOSE

Dedicated post-processing of dual-energy computed tomography angiography (DE-CTA) datasets has been shown to allow for increased vascular contrast. The goal of our study was to define optimal window settings for displaying virtual monoenergetic images (VMI) reconstructed from dual-energy carotid and cerebrovascular DE-CTA.

METHODS

Fifty-seven patients who underwent clinically-indicated carotid and cerebrovascular third-generation dual-source DE-CTA were retrospectively evaluated. Standard linearly-blended (M_0.6), 70-keV traditional VMI (M70), and 40-keV noise-optimized VMI (M40+) reconstructions were analyzed. For M70 and M40+ datasets, the subjectively best window setting (width and level, B-W/L) was independently determined by two observers and subsequently related with aortic arch attenuation to calculate optimized values (O-W/L) using linear regression. Subjective evaluation of image quality (IQ) between W/L settings were assessed by two additional readers. Repeated measures analysis of variance were performed to compare W/L settings and IQ indices between M_0.6, M70, and M40 + .

RESULTS

B-W/L and O-W/L for M70 were 580/210 and 560/200, and for M40+ were 1630/570 and 1560/550, respectively, higher than standard DE-CTA W/L settings (450/100). Highest subjective scores were observed for M40+ regarding overall IQ (all p < 0.001).

CONCLUSION

Application of O-W/L settings is mandatory to optimize subjective IQ of VMI reconstructions of DE-CTA.

Virtual mono-energetic images and iterative image reconstruction: abdominal vessel imaging in the era of spectral detector CT

AIM

To compare the quality of virtual mono-energetic (VMI) and polychromatic images reconstructed with hybrid iterative (PCI_HIR) or model-based reconstruction (PCI_MBR) derived from dual-layer spectral detector computed tomography (SDCT) in arterial phase images to visualise the aorta and abdominal main branches.

MATERIAL AND METHODS

A retrospective review of 50 patients with abdominal arterial phase scans was undertaken. Attenuation, intraluminal noise, and signal-/contrast-to-noise ratio (S-/CNR) were assessed in the PCI_HIR, PCI_MBR and VMI_40keV, VMI_70keV, and VMI_100keV images. Contrast, noise, and visualization of soft-plaque, and macro-/micro-calcifications were scored in a blinded reading by two radiologists.

RESULTS

VMI_40keV yielded highest S-/CNR (p≤0.001). VMI_70keV and PCI_MBR showed comparable SNR (p≥0.999) and yielded higher SNR than PCI_HIR. VMI_70keV yielded higher CNR than PCI_HIR (p<0.001) and PCI_MBR (p<0.045). VMI_100keV yielded lowest CNR (p≤0.001) and SNR (p≥0.104). In the subjective analysis, VMI_40keV outperformed PCI_MBR for contrast and noise, PCI_MBR scored better than VMI_70keV, and the latter scored better than PCI_HIR for these categories (all p<0.001). PCI_MBR was superior for depiction of soft-plaque and micro-calcifications (p<0.001). VMI_100keV visualized micro-calcifications second best (p<0.001) and matched PCI_MBR for the depiction of macro-calcifications (p>0.999), while VMI_40keV scored second best for depiction of soft-plaque (p<0.020).

CONCLUSIONS

VMI_40keV and VMI_70keV yield better S-/CNR than PCI_HIR and PCI_MBR; however, PCI_MBR visualized arteriosclerotic plaques best, followed by VMI_40keV for depiction of soft-plaque and VMI_100keV for macro- and micro-calcification. Based on the present findings, PCI_MBR on conventional CT and VMI_40keV supplemented by VMI_100keV on SDCT are recommended for the diagnostic assessment of abdominal arteries.

Computed tomography pulmonary angiograms using a novel dual-layer spectral detector: Adjusted window settings are essential for diagnostic image quality

OBJECTIVE

The aim of this study was to determine optimal window settings for conventional polyenergetic and virtual monoenergetic images derived from computed tomography pulmonary angiogram (CTPA) examinations of a novel dual-layer spectral detector computed tomography system (DLCT).

METHODS

Monoenergetic (40 keV) and polyenergetic images of 50 CTPA examinations were calculated and the best individual window width and level (W/L) values were manually assessed. Optimized values were obtained afterwards based on regression analysis. Diameters of standardized pulmonary artery segments and subjective image quality parameters were evaluated and compared.

RESULTS

Attenuation and contrast-to-noise values were higher in monoenergetic than in polyenergetic images (P≤.001). Averaged best individual W/L for polyenergetic and monoenergetic were 1020/170 and 2070/480 HU, respectively.All adjusted W/L-settings varied significantly compared to standard settings (700/100 HU) and obtained higher subjective image quality scores. A systematic overestimation of artery diameters for standard window settings in monoenergetic images was observed.

CONCLUSIONS

Appropriate W/L-settings are required to assess polyenergetic and monoenergetic CTPA images of a novel DLCT. W/L-settings of 1020/170 HU and 2070/480 HU were found to be the best averaged values for polyenergetic and monoenergetic CTPA images, respectively.

Dual energy computed tomography virtual monoenergetic imaging: technique and clinical applications

Dual energy CT (DECT) has evolved into a commonly applied imaging technique in clinical routine due to its unique post-processing opportunities for improved evaluation of all body areas. Reconstruction of virtual monoenergetic imaging (VMI) series has shown beneficial effects for both non-contrast and contrast-enhanced DECT due to the flexibility to calculate low-keV VMI reconstructions to increase contrast and iodine attenuation, or to compute high-keV VMI reconstructions to reduce beam-hardening artefacts. The goal of this review article is to explain the technical background of VMI and noise-optimized VMI+ algorithms and to give an overview of useful clinical applications of the VMI technique in DECT of various body regions.

Spectral Detector Computed Tomography Pulmonary Angiography: Improved Diagnostic Assessment and Automated Estimation of Window Settings Angiography of Pulmonary Arteries From Novel Spectral Detector Computed Tomography Provides Improved Image Quality if Settings are Adjusted

OBJECTIVE

This study aimed to evaluate image quality (IQ) of virtual monoenergetic images (VMIs) from novel spectral detector computed tomography angiography of the pulmonary arteries and to identify appropriate window settings for each kiloelectron volt level.

MATERIALS

Forty consecutive patients were included in this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study.Signal- and contrast-to-noise ratios were calculated within the pulmonary trunk, and pulmonary/lobar/segmental arteries were calculated. The IQ and diagnostic certainty were rated by 2 radiologists on 5-point scales. In addition, they recorded appropriate window settings (center/width) that were linearly modeled against attenuation within the pulmonary trunk to generate generable results.

RESULTS

Signal- and contrast-to-noise ratios, IQ, and diagnostic certainty are significantly increased in low-kiloelectron volt VMIs (≤60 keV). Interrater agreement was excellent (ĸ = 0.89). We developed 2 linear models (R: 0.91-0.97 and R: 0.43-0.91, respectively, P ≤ 0.01), that suggest appropriate window settings.

CONCLUSIONS

The VMIs from spectral detector computed tomography improve objective and subjective IQ in angiography of the pulmonary arteries, if window settings are adjusted; they can be automatically estimated using reported linear models.

Virtual Monoenergetic Images for Diagnostic Assessment of Hypodense Lesions Within the Liver: Semiautomatic Estimation of Window Settings Using Linear Models

OBJECTIVE

The aim of the study was to establish the reference window settings for display of virtual monoenergetic images (VMIs) from spectral detector computed tomography when assessing hypodense liver lesions.

METHODS

In patients with cysts (n = 24) or metastases (n = 26), objective (HU, signal-to-noise ratio [SNR]) and subjective (overall image quality, lesion conspicuity and noise) were assessed. Furthermore, 2 readers determined optimal window center/width (C/W) for conventional images (CIs) and VMIs of 40 to 120 keV. Center/width were modeled against HUliv with and without respect to the keV level (models A and B).

RESULTS

Attenuation and SNR were significantly higher in low-keV VMIs and improved overall image quality and lesion conspicuity (P ≤ 0.05). Model B provided valid estimations of C/W, whereas model A was slightly less accurate.

CONCLUSIONS

The increase in attenuation and SNR on low-keV VMIs requires adjustment of C/W, and they can be estimated in dependency of HUliv using linear models. Reference values for standard display of VMIs of 40 to 120 keV are reported.

Evaluation of Virtual Monoenergetic Images on Pulmonary Vasculature Using the Dual-Layer Detector-Based Spectral Computed Tomography

OBJECTIVE

To evaluate the ability of retrospectively generated virtual monoenergetic images (VMIs) from the detector-based spectral computed tomography (SDCT) to augment pulmonary artery enhancement in CT and if iodine map can predict the optimal monoenergetic level.

METHODS

The study included 79 patients with contrast-enhanced chest CT scans on an SDCT scanner. Conventional 120-kVp images and VMI from 40 to 80 keV were generated. Attenuation, noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured at 7 different locations in the pulmonary arterial system. The iodine concentration (in milligrams per milliliter) was calculated using the iodine-density images. The overall image quality was subjectively graded on a 5-point scale, with 1 being the worst and 5 the best. Fifty-four patients with suboptimal pulmonary enhancement (<200 Hounsfield units [HU]) were then identified. From the VMIs, an ideal set was chosen that maintained mean vascular attenuation greater than 200 HU while maintaining at least diagnostically acceptable quality (ie, IQ score ≥3). At this ideal energy level, quantitative and qualitative parameters were compared with the standard 120-kVp polyenergetic study. Average iodine concentrations were correlated with the optimal keV levels used for salvaging suboptimal studies.

RESULTS

The mean attenuation of all the measured pulmonary arterial regions in the suboptimal cases was 136.1 ± 18.1 HU in conventional 120-kVp images. Attenuations of the VMIs at 40, 50, and 60 keV were significantly higher than conventional images measuring 357.5 ± 19.5, 243.6 ± 16.7, and 176.6 ± 15.0 HU, respectively (P < 0.001). Similar results were seen with SNR and CNR. In total, 50 studies can be salvaged, with 50 keV being the optimal energy for 21, 60 keV optimal for 17, and 40 keV optimal for 12 studies. At the optimal energy level, there were improvements of attenuation, SNR, and CNR by 71%, 63%, and 137% compared with conventional images. There was a positive correlation between iodine value and optimal reconstruction energy with a linear equation y = 5.9539x + 27.434 and R = 0.8093.

CONCLUSIONS

Suboptimal enhanced pulmonary arterial CT studies can be salvaged using low-energy VMI generated from the SDCT scanner. There were significant improvements of attenuation, SNR, and CNR at the optimal monoenergetic level.

Utility of virtual monoenergetic images derived from a dual-layer detector-based spectral CT in the assessment of aortic anatomy and pathology: A retrospective case control study

OBJECTIVES

To evaluate the ability of the retrospectively generated virtual monoenergetic images (VMIs) from a dual-layer detector-based spectral computed tomography (SDCT) to augment aortic enhancement for the evaluation of aortic anatomy and pathology.

METHODS

98 patients with suboptimal aortic enhancement (≤200 HU) were retrospectively identified from SDCT scans. VMI from 40 to 80 keV were generated. Attenuation, noise, SNR, and CNR were measured at seven levels in the aorta. Image quality was graded on a 5-point scale, 5 being the best. From the VMI, an ideal set was chosen with mean vascular attenuation above 200 HU while maintaining diagnostic quality. Image parameters and quality of this ideal-set were compared to the standard 120-kVp images.

RESULTS

The mean attenuation of all seven measured anatomical regions was 156.6 ± 61.7 HU in the 120-kVp images. Attenuation of the VMI from 40 to 70 keV were higher than the 120-kVp image, measuring 439.2 ± 215.3 HU, 298.5 ± 140.6 HU, 213.4 ± 94.3 HU, and 164.7 ± 90.2 HU, for 40 keV, 50 keV, 60 keV, and 70 keV, respectively (p value <0.01 for 40, 50, 60 keV; 0.07 for 70 keV). SNR and CNR showed similar trends. The 50 keV VMI had the best image quality (4.48 ± 0.84 vs. 2.24 ± 0.92 on 120-kVp images, p < 0.001). Attenuation, CNR, and SNR increased by 90.6%, 85.0%, and 108.1% at 50 keV compared to 120-kVp.

CONCLUSIONS

A contrast-enhanced CT study can be optimized for the assessment of the aorta by using low-energy VMI obtained using SDCT. At the optimal monoenergetic level, attenuation, SNR, CNR and image quality were significantly higher than that of conventional polyenergetic images.

Dual-energy CT of the heart current and future status

Several applications utilizing dual-energy cardiac CT (DECT) have recently transitioned from the realm of research into clinical workflows. DECT acquisition techniques and subsequent post-processing can provide improved qualitative analysis, allow quantitative imaging, and have the potential to decrease requisite radiation and contrast material doses. Additionally, several experimental DECT techniques are pending further investigation and may improve the diagnostic accuracy of cardiac CT and/or provide evaluation of emerging imaging biomarkers in the future. This review article will summarize the major applications utilizing DECT in diagnosis of cardiovascular disease, including both the clinically used and investigational techniques examined to date.

Virtual Monoenergetic Images From a Novel Dual-Layer Spectral Detector Computed Tomography Scanner in Portal Venous Phase: Adjusted Window Settings Depending on Assessment Focus Are Essential for Image Interpretation

OBJECTIVE

We aimed to determine optimal window settings for conventional polyenergetic (PolyE) and virtual monoenergetic images (MonoE) derived from abdominal portal venous phase computed tomography (CT) examinations on a novel dual-layer spectral-detector CT (SDCT).

METHODS

From 50 patients, SDCT data sets MonoE at 40 kiloelectron volt as well as PolyE were reconstructed and best individual window width and level values manually were assessed separately for evaluation of abdominal arteries as well as for liver lesions. Via regression analysis, optimized individual values were mathematically calculated. Subjective image quality parameters, vessel, and liver lesion diameters were measured to determine influences of different W/L settings.

RESULTS

Attenuation and contrast-to-noise values were significantly higher in MonoE compared with PolyE. Compared with standard settings, almost all adjusted W/L settings varied significantly and yielded higher subjective scoring. No differences were found between manually adjusted and mathematically calculated W/L settings.

CONCLUSIONS

PolyE and MonoE from abdominal portal venous phase SDCT examinations require appropriate W/L settings depending on reconstruction technique and assessment focus.

Assessment of an advanced virtual monoenergetic reconstruction technique in cerebral and cervical angiography with third-generation dual-source CT: Feasibility of using low-concentration contrast medium

OBJECTIVES

To investigate the feasibility of low-concentration contrast media (LC-CM) in cerebral and cervical dual-energy CT angiography (DE-CTA) using an advanced monoenergetic (Mono+) reconstruction technique.

METHODS

Sixty-five consecutive patients prospectively selected to undergo cerebral and cervical DE-CTA were randomised into two groups: 32 patients (63.7 ± 9.7 years) in the high-concentration contrast medium (HC-CM) group with iopromide 370 and 33 patients (60.7 ± 10.8 years) in the low-concentration contrast medium (LC-CM) group with iodixanol 270. Traditional monoenergetic (Mono) and Mono+ images from 40 to 100 keV levels (at 10-keV intervals) and the standard mixed (Mixed, 120 kVp equivalent) images were reconstructed. Subjective image quality parameters included the contrast-to-noise ratio (CNR) and objective image quality parameters were evaluated and compared between the two groups.

RESULTS

The 40-keV Mono+ images in the LC-CM group showed comparable objective CNR (common carotid arteries: 83.7 ± 24.5 vs. 78.1 ± 23.2; internal carotid arteries: 82.2 ± 26.8 vs. 76.8 ± 24.1; middle cerebral arteries: 72.5 ± 24.6 vs. 70.6 ± 19.2; all p > 0.05) and subjective image scores (3.95 ± 0.19 vs. 3.83 ± 0.35; p > 0.05) compared with Mixed images in the HC-CM group.

CONCLUSION

The Mono+ reconstruction technique could reduce the concentration of iodinated CM in the diagnosis of cerebral and cervical angiography.

KEY POINTS

• Mono+ shows decreased noise and superior CNR compared with Mono. • The 40-keV Mono+ images show the highest CNR in the LC-CM group. • The Mono+ reconstruction technique could reduce the concentration of iodinated CM.

Poly-energetic and virtual mono-energetic images from a novel dual-layer spectral detector CT: optimization of window settings is crucial to improve subjective image quality in abdominal CT angiographies

PURPOSE

We aimed to determine optimal window settings for poly-energetic (PolyE) and virtual mono-energetic images (MonoE) derived from abdominal angiographic studies on a novel dual-layer spectral detector CT (SDCT) system.

METHODS

From 50 patients, SDCT datasets PolyE and MonoE at 70 and 40 keV levels were reconstructed and best individual window width and level (BI-W/L) manually assessed. Through regression analysis, the so-called optimized individual (OI-W/L) values were obtained. Subjective image quality parameters and vessel diameters were measured to determine influences of different W/L settings.

RESULTS

Image noise was lower and attenuation and contrast-to-noise ratio were higher in MonoE compared to PolyE (all p ≤ 0.002). Mean BI-W/L values for PolyE, 70, and 40 keV were 637/284, 647/291, and 1568/691, respectively. Mean OI-W/L values were 631/276, 628/286, and 1516/667, respectively. Compared to standard settings, all adjusted W/L settings varied significantly and yielded higher subjective scoring. No between-group differences were found between manually adjusted and mathematically calculated W/L settings.

CONCLUSION

PolyE and MonoE from abdominal angiographic SDCT studies require appropriate W/L settings especially at low energy reconstruction levels. Individual adjustment reaches the best image quality but is time consuming. From our data, predefined W/L settings of 640/280 (PolyE/MonoE 70 keV) and 1570/690 (MonoE 40 keV) as a non-individualized starting point for abdominal angiographic studies from the novel SDCT system are suggested.