Imaging of acute pulmonary embolism using a dual energy CT system with rapid kVp switching: Initial results

Dual-layer dual-energy CT-derived pulmonary perfusion for the differentiation of acute pulmonary embolism and chronic thromboembolic pulmonary hypertension

OBJECTIVES

To evaluate dual-layer dual-energy computed tomography (dlDECT)-derived pulmonary perfusion maps for differentiation between acute pulmonary embolism (PE) and chronic thromboembolic pulmonary hypertension (CTEPH).

METHODS

This retrospective study included 131 patients (57 patients with acute PE, 52 CTEPH, 22 controls), who underwent CT pulmonary angiography on a dlDECT. Normal and malperfused areas of lung parenchyma were semiautomatically contoured using iodine density overlay (IDO) maps. First-order histogram features of normal and malperfused lung tissue were extracted. Iodine density (ID) was normalized to the mean pulmonary artery (MPA) and the left atrium (LA). Furthermore, morphological imaging features for both acute and chronic PE, as well as the combination of histogram and morphological imaging features, were evaluated.

RESULTS

In acute PE, normal perfused lung areas showed a higher mean and peak iodine uptake normalized to the MPA than in CTEPH (both p < 0.001). After normalizing mean ID in perfusion defects to the LA, patients with acute PE had a reduced average perfusion (IDmean,LA) compared to both CTEPH patients and controls (p < 0.001 for both). IDmean,LA allowed for a differentiation between acute PE and CTEPH with moderate accuracy (AUC: 0.72, sensitivity 74%, specificity 64%), resulting in a PPV and NPV for CTEPH of 64% and 70%. Combining IDmean,LA in the malperfused areas with the diameter of the MPA (MPAdia) significantly increased its ability to differentiate between acute PE and CTEPH (sole MPAdia: AUC: 0.76, 95%-CI: 0.68-0.85 vs. MPAdia + 256.3 * IDmean,LA - 40.0: AUC: 0.82, 95%-CI: 0.74-0.90, p = 0.04).

CONCLUSION

dlDECT enables quantification and characterization of pulmonary perfusion patterns in acute PE and CTEPH. Although these lack precision when used as a standalone criterion, when combined with morphological CT parameters, they hold potential to enhance differentiation between the two diseases.

CLINICAL RELEVANCE STATEMENT

Differentiating between acute PE and CTEPH based on morphological CT parameters is challenging, often leading to a delay in CTEPH diagnosis. By revealing distinct pulmonary perfusion patterns in both entities, dlDECT may facilitate timely diagnosis of CTEPH, ultimately improving clinical management.

KEY POINTS

• Morphological imaging parameters derived from CT pulmonary angiography to distinguish between acute pulmonary embolism and chronic thromboembolic pulmonary hypertension lack diagnostic accuracy. • Dual-layer dual-energy CT reveals different pulmonary perfusion patterns between acute pulmonary embolism and chronic thromboembolic pulmonary hypertension. • The identified parameters yield potential to enable more timely identification of patients with chronic thromboembolic pulmonary hypertension.

Utility of Dual-Energy Computed Tomography in Clinical Conundra

Advancing medical technology revolutionizes our ability to diagnose various disease processes. Conventional Single-Energy Computed Tomography (SECT) has multiple inherent limitations for providing definite diagnoses in certain clinical contexts. Dual-Energy Computed Tomography (DECT) has been in use since 2006 and has constantly evolved providing various applications to assist radiologists in reaching certain diagnoses SECT is rather unable to identify. DECT may also complement the role of SECT by supporting radiologists to confidently make diagnoses in certain clinically challenging scenarios. In this review article, we briefly describe the principles of X-ray attenuation. We detail principles for DECT and describe multiple systems associated with this technology. We describe various DECT techniques and algorithms including virtual monoenergetic imaging (VMI), virtual non-contrast (VNC) imaging, Iodine quantification techniques including Iodine overlay map (IOM), and two- and three-material decomposition algorithms that can be utilized to demonstrate a multitude of pathologies. Lastly, we provide our readers commentary on examples pertaining to the practical implementation of DECT's diverse techniques in the Gastrointestinal, Genitourinary, Biliary, Musculoskeletal, and Neuroradiology systems.

Dual-Energy CT in Cardiothoracic Imaging: Current Developments

This article describes the technical principles and clinical applications of dual-energy computed tomography (DECT) in the context of cardiothoracic imaging with a focus on current developments and techniques. Since the introduction of DECT, different vendors developed distinct hard and software approaches for generating multi-energy datasets and multiple DECT applications that were developed and clinically investigated for different fields of interest. Benefits for various clinical settings, such as oncology, trauma and emergency radiology, as well as musculoskeletal and cardiovascular imaging, were recently reported in the literature. State-of-the-art applications, such as virtual monoenergetic imaging (VMI), material decomposition, perfused blood volume imaging, virtual non-contrast imaging (VNC), plaque removal, and virtual non-calcium (VNCa) imaging, can significantly improve cardiothoracic CT image workflows and have a high potential for improvement of diagnostic accuracy and patient safety.

Dual-energy computed tomography as a lower radiation dose alternative to perfusion computed tomography in tumor viability assessment

To present the utility of dual-energy computed tomography (DECT) in the assessment of angiogenesis of focal lesions as an example of a solitary pulmonary nodule (SPN). This prospective study comprised 28 patients with SPN who underwent DECT and perfusion computed tomography (CTP), according to a proprietary protocol. Two radiologists independently analyzed four perfusion parameters, namely blood flow (BF), blood volume (BV), the time to maximum of the tissue residue function (Tmax), permeability surface area product (PS) from CTP, in addition to the iodine concentration (IC) and normalized iodine concentration (NIC) of the SPN from DECT. We used the Pearson R correlation and interclass correlation coefficients (ICC_s). Statistical significance was assumed at p < 0.05. The mean tumor size was 23.5 ± 6.5 mm. We observed good correlations between IC and BF (r = 0.78, p < 0.000) and NIC and BF (r = 0.71, p < 0.000) as well as between IC and BV (r = 0.73, p < 0.000) and NIC and BV (r = 0.73, p < 0.000) and poor correlation between IC and PS (r = 0.38, p = 0.044).There was no correlation between NIC and PS (r = 0.35, p = 0.064), IC content and Tmax (r = - 0.28, p = 0.147) and NIC and Tmax (r = - 0.21, p = 0.266). Inter-reader agreement on quantitative parameters at CTP (ICC_PS = 0.97, ICC_Tmax = 0.96, ICC_BV = 0.98, and ICC_BF = 0.99) and DECT (ICC_IC = 0.98) were excellent. The radiation dose was significantly lower in DECT than that in CTP (4.84 mSv vs. 9.07 mSv, respectively). DECT is useful for the functional assessment of oncological lesions with less exposure to radiation compared to perfusion computed tomography.

A Computer-based Analysis for Identification and Quantification of Small Airway Disease in Lung Computed Tomography Images: A Comprehensive Review for Radiologists

Computed tomography (CT) imaging is being increasingly used in clinical practice for detailed characterization of lung diseases. Respiratory diseases involve various components of the lung, including the small airways. Evaluation of small airway disease on CT images is challenging as the airways cannot be visualized directly by a CT scanner. Small airway disease can manifest as pulmonary air trapping (AT). Although AT may be sometimes seen as mosaic attenuation on expiratory CT images, it is difficult to identify diffuse AT visually. Computer technology advances over the past decades have provided methods for objective quantification of small airway disease on CT images. Quantitative CT (QCT) methods are being rapidly developed to quantify underlying lung diseases with greater precision than subjective visual assessment of CT images. A growing body of evidence suggests that QCT methods can be practical tools in the clinical setting to identify and quantify abnormal regions of the lung accurately and reproducibly. This review aimed to describe the available methods for the identification and quantification of small airway disease on CT images and to discuss the challenges of implementing QCT metrics in clinical care for patients with small airway disease.

Role of Dual-energy Computed Tomography in Diagnosis of Acute Pulmonary Emboli, a Review

Prompt diagnosis of pulmonary embolism is essential to avert morbidity and mortality. There are a number of diagnostic options for identification of a pulmonary embolism, including laboratory and imaging investigations. While computed tomography pulmonary angiography (CTPA) has largely supplanted nuclear medicine ventilation/perfusion studies, there remain significant limitations in the optimal performance of CTPA. Dual-energy computed tomography has the ability to overcome many of the limitations of standard of care CTPA, including rescue of poor contrast boluses and the ability to evaluate pulmonary perfusion defects.

Pilot study for comparative assessment of dual-energy computed tomography and single-photon emission computed tomography V/Q scanning for lung perfusion evaluation in infants

OBJECTIVE

To evaluate clinical applications of dual-energy computed tomography (DECT) in pediatric-specific lung diseases and compare ventilation and perfusion findings with those from single-photon emission computed tomography (SPECT-CT) V/Q.

METHODS

All patients at our institution who underwent exams using both techniques within a 3-month period were included in this study. Two readers independently described findings for DECT, and two other readers independently analyzed the SPECT-CT V/Q scan data. All findings were compared between readers and disagreements were reassessed and resolved by consensus. Inter-modality agreements are described throughout this study.

RESULTS

Eight patients were included for evaluation. The median age for DECT scanning was 3.5 months (IQR = 2). Five of these patients were scanned for both DECT and SPECT-CT V/Q studies the same day, and three had a time gap of 7, 65, and 94 days between studies. The most common indications were chronic lung disease (5/8; 63%) and pulmonary hypertension (6/8; 75%). DECT and SPECT-CT V/Q identified perfusion abnormalities in concordant lobes in most patients (7/8; 88%). In one case, atelectasis limited DECT perfusion assessment. Three patients ultimately underwent lobectomy with corresponding perfusion abnormalities identified by all reviewers on both DECT and SPECT-CT V/Q in all resected lobes.

CONCLUSION

DECT is a feasible technique that could be considered as an alternative for SPECT-CT V/Q for lung perfusion evaluation in infants.

Evaluation Of a New Reconstruction Technique for Dual-Energy (DECT) Lung Perfusion: Preliminary Experience In 58 Patients

PURPOSE

To compare dual-energy (DE) lung perfused blood volume generated by subtraction of virtual monoenergetic images (Lung Mono) with images obtained by three-compartment decomposition (Lung PBV).

MATERIAL AND METHODS

The study included 58 patients (28 patients with and 30 patients without PE) with reconstruction of Lung PBV images (i.e., the reference standard) and Lung Mono images. The inter-technique comparison was undertaken at a patient and segment level.

RESULTS

The distribution of scores of subjective image noise (patient level) significantly differed between the two reconstructions (p<0.0001), with mild noise in 58.6% (34/58) of Lung Mono images vs 25.9% (15/58) of Lung PBV images. Detection of perfusion defects (segment level) was concordant in 1104 segments (no defect: n=968; defects present: n=138) and discordant in 2 segments with a PE-related defect only depicted on Lung Mono images. Among the 28 PE patients, the distribution of gradient of attenuation between perfused areas and defects was significantly higher on Lung Mono images compared to Lung PBV (median= 73.5 HU (QI=65.0; Q3=86.0) vs 24.5 HU (22.0; 30.0); p<0.0001). In all patients, fissures were precisely identified in 77.6% of patients (45/58) on Lung Mono images while blurred (30/58; 51.7%) or not detectable (28/58; 48.3%) on Lung PBV images.

CONCLUSION

Lung Mono perfusion imaging allows significant improvement in the overall image quality and improved detectability of PE-type perfusion defects.

Dual-energy spectral CT imaging of pulmonary embolism with Mycoplasma pneumoniae pneumonia in children

BACKGROUND

Pulmonary embolism (PE) associated with Mycoplasma pneumoniae pneumonia (MPP) in children has already attracted more attention. CT pulmonary angiography (CTPA) has been the preferred method for diagnosing PE, but it has some limitations, especially for children. Dual-energy spectral CT has been used in diagnosing PE in adults.

PURPOSE

To evaluate the application of dual-energy spectral CT in diagnosing PE in children with MPP.

MATERIALS AND METHODS

Eighty-three children with MPP and highly suspected PE, underwent CTPA with spectral imaging mode, 25 children were diagnosis with PE. Noise, clot-to-artery contrast-to-noise ratio, image quality and diagnosis confidence were calculated and assessed on nine monochromatic image sets (40 to 80 keV). CTPA images were observed for the presence, localization and embolic degrees of PE. Clots were divided into intra- and extra-consolidation clots. For extra-consolidation clots, iodine concentration (IC) of perfusion defects and normal lung, perfusion defects of four children before and after the treatment were measured and compared. For intra-consolidation clots, IC of consolidation areas with clots and consolidation areas without clot were measured and compared.

RESULTS

The optimal energy level for detecting PE in children was 55 keV. 116 clots (29 extra-consolidations) were found, IC of defect regions was 0.69 ± 0.28 mg/mL (extra-consolidations) and 0.90 ± 0.23 mg/mL (intra-consolidations), both significantly lower than the 2.76 ± 0.45 mg/mL in normal lungs and 10.25 ± 1.76 mg/mL in consolidations without clots (P < 0.001). Significant difference was found in the presence or absence of perfusion defects between occlusive clots and nonocclusive clots (P < 0.001). IC of the perfusion defects significantly increased after treatment (P < 0.001).

CONCLUSIONS

In dual-energy spectral CTPA, 55 keV images optimize PE detection for children, and MD images quantify pulmonary blood flow of PE, and may help to detect small clots and quantify embolic degrees.

Dual-Energy CT for Pulmonary Embolism: Current and Evolving Clinical Applications

Pulmonary embolism (PE) is a potentially fatal disease if the diagnosis or treatment is delayed. Currently, multidetector computed tomography (MDCT) is considered the standard imaging method for diagnosing PE. Dual-energy CT (DECT) has the advantages of MDCT and can provide functional information for patients with PE. The aim of this review is to present the potential clinical applications of DECT in PE, focusing on the diagnosis and risk stratification of PE.

Canadian Society of Thoracic Radiology/Canadian Association of Radiologists Best Practice Guidance for Investigation of Acute Pulmonary Embolism, Part 2: Technical Issues and Interpretation Pitfalls

The investigation of acute pulmonary embolism is a common task for radiologists in Canada. Technical image quality and reporting quality must be excellent; pulmonary embolism is a life-threatening disease that should not be missed but overdiagnosis and unnecessary treatment should be avoided. The most frequently performed imaging investigation, computed tomography pulmonary angiogram (CTPA), can be limited by poor pulmonary arterial opacification, technical artifacts and interpretative errors. Image quality can be affected by patient factors (such as body habitus, motion artifact and cardiac output), intravenous (IV) contrast protocols (including the timing, rate and volume of IV contrast administration) and common physics artifacts (including beam hardening). Mimics of acute pulmonary embolism can be seen in normal anatomic structures, disease in non-vascular structures and pulmonary artery filling defects not related to acute pulmonary emboli. Understanding these pitfalls can help mitigate error, improve diagnostic quality and optimize patient outcomes. Dual energy computed tomography holds promise to improve imaging diagnosis, particularly in clinical scenarios where routine CTPA may be problematic, including patients with impaired renal function and patients with altered cardiac anatomy.

Dual-energy CT angiography reveals high prevalence of perfusion defects unrelated to pulmonary embolism in COVID-19 lesions

BACKGROUND

Lung perfusion defects (PDs) have been described in COVID-19 using dual-energy computed tomography pulmonary angiography (DE-CTPA). We assessed the prevalence and characteristics of PDs in COVID-19 patients with suspected pulmonary embolism (PE) and negative CTPA.

METHODS

This retrospective study included COVID-19 and non-COVID-19 pneumonia groups of patients with DE-CTPA negative for PE. Two radiologists rated the presence of PD within the lung opacities and analyzed the type of lung opacities and PD pattern (i.e. homogeneous or heterogeneous). The clinical, biological, radiological characteristics including time from first symptoms and admission to DE-CTPA, oxygen requirements, CRP, D-dimer levels, duration of hospital admission and death were compared within the COVID-19 group between patients with (PD +) or without PD (PD-).

RESULTS

67 COVID-19 and 79 non-COVID-19 patients were included. PDs were more frequent in the COVID-19 than in the non-COVID-19 group (59.7% and 26.6% respectively, p < 0.001). Patterns of PDs were different, with COVID-19 patients exhibiting heterogenous PDs (38/40, 95%) whereas non-COVID-19 patients showed mostly homogeneous perfusion defects (7/21 heterogeneous PDs, 33%), p < 0.001. In COVID-19 patients, most consolidations (9/10, 90%) exhibited PDs while less than a third of consolidations (19/67, 28%) had PDs in non-COVID-19 patients. D-dimer, oxygen levels and outcome were similar between COVID-19 PD + and PD- patients; however, time between admission and DE-CTPA was longer in PD + patients (median [IQR], 1 [0-7] and 0 [0-2]; p = 0.045).

CONCLUSION

Unlike in bacterial pneumonia, heterogeneous PDs within lung opacities are a frequent feature of COVID-19 pneumonia in PE-suspected patients.

Dual-energy CT performance in acute pulmonary embolism: a meta-analysis

OBJECTIVES

To evaluate the diagnostic performance of dual-energy computed tomography (DECT) with regard to its post-processing techniques, namely linear blending (LB), iodine maps (IM), and virtual monoenergetic (VM) reconstructions, in diagnosing acute pulmonary embolism (PE).

METHODS

This meta-analysis was conducted according to PRISMA. A systematic search on MEDLINE and EMBASE was performed in December 2019, looking for articles reporting the diagnostic performance of DECT on a per-patient level. Diagnostic performance meta-analyses were conducted grouping study parts according to DECT post-processing methods. Correlations between radiation or contrast dose and publication year were appraised.

RESULTS

Seventeen studies entered the analysis. Only lobar and segmental acute PE were considered, subsegmental acute PE being excluded from analysis due to data heterogeneity or lack of data. LB alone was assessed in 6 study parts accounting for 348 patients, showing a pooled sensitivity of 0.87 and pooled specificity of 0.93. LB and IM together were assessed in 14 study parts accounting for 1007 patients, with a pooled sensitivity of 0.89 and pooled specificity of 0.90. LB, IM, and VM together were assessed in 2 studies (for a total 144 patients) and showed a pooled sensitivity of 0.90 and pooled specificity of 0.90. The area under the curve for LB alone, and LB together with IM was 0.93 (not available for studies using LB, IM and VM because of paucity of data). Radiation and contrast dose did not decrease with increasing year of publication.

CONCLUSIONS

Considering the published performance of single-energy CT in diagnosing acute PE, either dual-energy or single-energy computed tomography can be comparably used for the detection of acute PE.

KEY POINTS

• Dual-energy CT displayed pooled sensitivity and specificity of 0.87 and 0.93 for linear blending alone, 0.89 and 0.90 for linear blending and iodine maps, and 0.90 and 0.90 for linear blending iodine maps, and virtual monoenergetic reconstructions. • The performance of dual-energy CT for patient management is not superior to that reported in literature for single-energy CT (0.83 sensitivity and 0.96 specificity). • Dual-energy CT did not yield substantial advantages in the identification of patients with acute pulmonary embolism compared to single-energy techniques.

From Early Morphometrics to Machine Learning-What Future for Cardiovascular Imaging of the Pulmonary Circulation?

Imaging plays a cardinal role in the diagnosis and management of diseases of the pulmonary circulation. Behind the picture itself, every digital image contains a wealth of quantitative data, which are hardly analysed in current routine clinical practice and this is now being transformed by radiomics. Mathematical analyses of these data using novel techniques, such as vascular morphometry (including vascular tortuosity and vascular volumes), blood flow imaging (including quantitative lung perfusion and computational flow dynamics), and artificial intelligence, are opening a window on the complex pathophysiology and structure-function relationships of pulmonary vascular diseases. They have the potential to make dramatic alterations to how clinicians investigate the pulmonary circulation, with the consequences of more rapid diagnosis and a reduction in the need for invasive procedures in the future. Applied to multimodality imaging, they can provide new information to improve disease characterization and increase diagnostic accuracy. These new technologies may be used as sophisticated biomarkers for risk prediction modelling of prognosis and for optimising the long-term management of pulmonary circulatory diseases. These innovative techniques will require evaluation in clinical trials and may in themselves serve as successful surrogate end points in trials in the years to come.

Differential diagnosis of chromophobe renal cell carcinoma and papillary renal cell carcinoma with dual-energy spectral computed tomography

BACKGROUND

Computed tomography (CT) image features of chromophobe renal cell carcinoma (ChRCC) and papillary renal cell carcinoma (PRCC) are, occasionally, sometimes difficult to identify. However, spectral CT might provide quantitative parameters to differentiate them.

PURPOSE

To differentiate between ChRCC and PRCC with quantitative parameters using spectral CT.

MATERIAL AND METHODS

Forty cases of RCC confirmed with pathological tests were analyzed retrospectively (27 cases of PRCC and 13 cases of ChRCC). All patients underwent non-enhanced CT and dual-phase contrast-enhanced CT scans. For each lesion, the CT value of monochromatic images as well as iodine and water concentrations were measured, and the slope of spectrum curve was calculated. Data were analyzed using Student's t-test. Sensitivity and specificity of the quantitative parameters were analyzed using the receiver operating characteristic (ROC) curve.

RESULTS

During the cortex phase (CP) and parenchyma phase (PP), the CT value and slope of spectrum curve of ChRCC were higher than those of PRCC, and significant differences were observed at low energy levels (40-70 keV). Normalized iodine concentration of ChRCC and that of PRCC was significantly different during CP and PP (P < 0.05). The water (iodine) concentrations of ChRCC and PRCC in CP and PP were not statistically different (P > 0.05). All the ROCs for parameters were above the reference line.

CONCLUSION

Spectral CT may help increase the diagnostic accuracy of differentiating PRCC from ChRCC using a quantitative analysis.

CT imaging of pulmonary embolism in patients with COVID-19 pneumonia: a retrospective analysis

Objectives

To describe imaging and laboratory findings of confirmed PE diagnosed in COVID-19 patients and to evaluate the characteristics of COVID-19 patients with clinical PE suspicion. Characteristics of patients with COVID-19 and PE suspicion who required admission to the intensive care unit (ICU) were also analysed.

Methods

A retrospective study from March 18, 2020, until April 11, 2020. Inclusion criteria were patients with suspected PE and positive real-time reverse-transcription polymerase chain reaction (RT-PCR) for SARS-CoV-2. Exclusion criteria were negative or inconclusive RT-PCR and other chest CT indications. CTPA features were evaluated and severity scores, presence, and localisation of PE were reported. d-dimer and IL-6 determinations, ICU admission, and previous antithrombotic treatment were registered.

Results

Forty-seven PE suspicions with confirmed COVID-19 underwent CTPA. Sixteen patients were diagnosed with PE with a predominant segmental distribution. Statistically significant differences were found in the highest d-dimer determination in patients with PE and ICU admission regarding elevated IL-6 values.

Conclusion

PE in COVID-19 patients in our series might predominantly affect segmental arteries and the right lung. Results suggest that the higher the d-dimer concentration, the greater the likelihood of PE. Both assumptions should be assessed in future studies with a larger sample size.

Key Points

• On CT pulmonary angiography, pulmonary embolism in COVID-19 patients seems to be predominantly distributed in segmental arteries of the right lung, an assumption that needs to be approached in future research.

• Only the highest intraindividual determination ofd-dimer from admission to CT scan seems to differentiate patients with pulmonary embolism from patients with a negative CTPA. However, interindividual variability calls for future studies to establish cut-off values in COVID-19 patients.

• Further studies with larger sample sizes are needed to determine whether the presence of PE could increase the risk of intensive care unit (ICU) admission in COVID-19 patients.

Diagnostic Accuracy of Dual-Energy CT in Detection of Acute Pulmonary Embolism: A Systematic Review and Meta-Analysis

PURPOSE

In this systematic review and meta-analysis, we aimed to investigate the accuracy of dual-energy computed tomography (DECT) in the detection of acute pulmonary embolism (PE).

METHODS

We searched Medline (via PubMed), EBSCO, Web of Science, Scopus, and the Cochrane Library for relevant published studies. We selected studies assessing the accuracy of DECT in the detection of PE. Quality assessment of bias and applicability was conducted using the Quality of Diagnostic Accuracy Studies-2 tool. Meta-analysis was performed to calculate mean estimates of sensitivity, specificity, positive likelihood ratio (PLR), and negative likelihood ratio (NLR). The summary receiver operating characteristic (sROC) curve was drawn to get the Cochran Q-index and the area under the curve (AUC).

RESULTS

Seven studies were included in our systematic review. Of the 182 patients included, 108 patients had PEs. The pooled analysis showed an overall sensitivity and specificity of 88.9% (95% confidence interval [CI]: 81.4%-94.1%) and 94.6% (95% CI: 86.7%-98.5%), respectively. The pooled PLR was 8.186 (95% CI: 3.726-17.986), while the pooled NLR was 0.159 (95% CI: 0.093-0.270). Cochran-Q was 0.8712, and AUC was 0.935 in the sROC curve.

CONCLUSION

Dual-energy computed tomography shows high sensitivity, specificity, and diagnostic accuracy in the detection of acute PE. The high PLR highlights the high clinical importance of DECT as a prevalence-independent, rule-in test. Studies with a larger sample size with standardized reference tests are still needed to increase the statistical power of the study and support these findings.

Acquisition time, radiation dose, subjective and objective image quality of dual-source CT scanners in acute pulmonary embolism: a comparative study

OBJECTIVES

To compare the scan acquisition time, radiation dose, subjective and objective image quality of two dual-source CT scanners (DSCT) for detection of acute pulmonary embolism.

METHODS

Two hundred twenty-one scans performed on the 2nd-generation DSCT and 354 scans on the 3rd-generation DSCT were included in this large retrospective study. In a randomized blinded design, two radiologists independently reviewed the scans using a 5-point Likert scale. Radiation dose and objective image quality parameters were calculated.

RESULTS

Mean acquisition time was significantly lower in the 3rd-generation DSCT (2.81 s ± 0.1 in comparison with 9.7 s ± 0.15 [mean ± SD] respectively; p < 0.0001) with the 3rd generation 3.4 times faster. The mean subjective image quality score was 4.33/5 and 4/5 for the 3rd- and 2nd-generation DSCT respectively (p < 0.0001) with strong interobserver reliability agreement. DLP, CTDI_vol, and ED were significantly lower in the 3rd than the 2nd generation (175.6 ± 63.7 mGy cm; 5.3 ± 1.9 mGy and 2.8 ± 1.2 mSv in comparison with 266 ± 255 mGy.cm; 7.8 ± 2.2 mGy and 3.8 ± 4.3 mSv). Noise was significantly lower in the 3rd generation (p < 0.01). Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM), a dose-insensitive index for CNR, were significantly higher in the 3rd-generation DSCT (33.5 ± 23.4; 29.0 ± 21.3 and 543.7 ± 1037 in comparison with 23.4 ± 17.7; 19.4 ± 16.0 and 170.5 ± 284.3).

CONCLUSION

Objective and subjective image quality are significantly higher on the 3rd-generation DSCT with significantly lower mean acquisition time and radiation dose.

KEY POINTS

• The 3rd-generation DSCT scanner provides an improved image quality, less perceived artifacts, and lower radiation dose in comparison with the 2nd-generation DSCT, when operating in dual-energy (DE) mode. • The 3.4-times-faster 3rd-generation DSCT scanner can be of particular value in patients with chronic lung diseases or breathing difficulties that prevent adequate breathhold.

Influence of Monoenergetic Images at Different Energy Levels in Dual-Energy Spectral CT on the Accuracy of Computer-Aided Detection for Pulmonary Embolism

PURPOSE

To investigate the influence of monoenergetic images of different energy levels in spectral computed tomography (CT) on the accuracy of computer aided detection (CAD) for pulmonary embolism (PE).

MATERIALS AND METHODS

CT images of 20 PE patients who underwent spectral CT pulmonary angiography were retrospectively analyzed. Nine sets of monochromatic images from 40 to 80 keV at 5 keV interval were reconstructed and then independently analyzed for detecting PE using a commercially available CAD software. Two experienced radiologists reviewed all images and recorded the number of emboli manually, which was used as the reference standard. The CAD findings for the number of PE at different energies were compared with the reference standard to determine the number of true positives and false positives with CAD and to calculate the sensitivity and false positive rate at different energies.

RESULT

There were 120 true emboli. The total numbers of CAD-detected PE at 40-80 keV were 48, 67, 63, 87, 106, 115, 138, 157, and 226. Images at low energies had low sensitivities and low false positive rates; images at high energies had high sensitivities and high false positive rates. At 60 keV and 65 keV, CAD achieved sensitivity at 81.67% and 84.17%, respectively and false positive rate at 7.55% and 12.17%, respectively to provide the optimum combination of high sensitivity and low false positive rate.

CONCLUSION

Monochromatic images of different energies in dual-energy spectral CT affect the accuracy of CAD for PE. The combination of CAD with images at 60-65 keV provides the optimum combination of high sensitivity and low false positive rate in detecting PE.

Diagnostic accuracy of lamellar body count as a predictor of fetal lung maturity: A systematic review and meta-analysis

Objective

This study aimed to synthesize evidence from published studies about the diagnostic accuracy of lamellar body count (LBC) as a predictor of fetal lung maturity.

Study design

We searched Medline (via PubMed), EBSCO, Web of Science, Scopus and the Cochrane Library for relevant published studies assessing the accuracy of LBC as a predictor of fetal lung maturity. Studies were classified according to the counting essays, centrifugation protocols, and the reported optimum cut off values. Data of the true positive, true negative, false positive, and false negative were extracted and analyzed to calculate the overall sensitivity and specificity of the LBC.

Results

Thirty-one studies were included in the final analysis. Fourteen studies reported data for centrifuged amniotic fluid (AF) samples, 13 studies reported data for uncentrifuged samples, and four studies did not have enough information about whether centrifugation was done. LBC showed an area under the curve >80% in diagnosing lung immaturity with variable cut off values. Pooled analysis showed that LBC a 100% specificity to exclude respiratory distress syndrome (RDS) at a cut off value of 15,000 and 100% sensitivity to diagnose RDS at a cut off value of 55,000.

Conclusion

Cases with LBC < 15,000 are considered to have lung immaturity while cases with LBC > 45,000 in centrifuged AF samples or >55,000 in uncentrifuged AF samples are likely to have mature lungs. Cases with LBC ranging between these maturity and immaturity limits should be considered for further evaluation by other lung maturity tests.

Fast kilovoltage-switching dual-energy CT offering lower x-ray dose than single-energy CT for the chest: a quantitative and qualitative comparison study of the two methods of acquisition

PURPOSE

We aimed to compare the size-specific dose estimates (SSDE), computed tomography (CT) dose indices and image quality parameters of the chest CTs obtained with fast kilovoltage-switching (FKS) dual-energy (DE) CT versus those with single-energy (SE) CT.

METHODS

Patients who had chest SECT within the last 6 months were prospectively scanned with chest FKS-DECT. Quantitative comparison was made by calculating the mean SSDE, CTDIvol, contrast, noise, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) for both acquisitions. Two radiologists evaluated the chest SECT and DECT images qualitatively blinded to the technique used. The paired Student's t test was utilized for comparing the quantitative and qualitative data. Inter- and intraobserver agreement were also assessed.

RESULTS

A total of 42 patients were included. The mean SSDE, CTDIvol, contrast, noise, CNR, and SNR for SECT versus DECT were 12.7±2.2 mGy vs. 9.3±1.2 mGy (P = 0.001), 10.9±2.4 mGy vs. 8±1.2 mGy (P < 0.001), 211.9±44.7 vs. 216.3±59 (P = 0.350), 12.9±2.4 vs. 13.9±3.7 (P = 0.086), 13.5±5.2 vs. 13.3±8.4 (P = 0.548) and 12±3.5 vs. 11.5±3.4 (P = 0.774), respectively. Interobserver reproducibility was high for contrast, noise, CNR, and SNR (ICC = 0.89, 0.85, 0.93, and 0.82, respectively; all P < 0.05). Intraobserver reproducibility was high for contrast, noise, CNR, and SNR (ICC = 0.80, 0.77, 0.85, and 0.88, respectively; all P < 0.05).

CONCLUSION

The mean SSDE of the chest CTs obtained with FKS-DECT were 26.8% lower than those with SECT with significant difference for the objective assessment and there was no significant difference for the subjective assessment of the image qualities, in this series.

Spectral Computed Tomography Imaging in the Differential Diagnosis of Lung Cancer and Inflammatory Myofibroblastic Tumor

OBJECTIVE

The aim of this study was to explore the value of spectral computed tomography (CT) imaging in differentiating lung cancer from inflammatory myofibroblastic tumor (IMT).

METHODS

One hundred twelve patients with 96 lung cancers and 16 IMTs underwent spectral CT during arterial phase (AP) and venous phase (VP). The normalized iodine concentration in AP (NICAP) and VP (NICVP), slope of spectral Hounsfield unit curve in AP (λAP) and VP (λVP), and normalized iodine concentration difference between AP and VP (ICD) were calculated. The 2-sample t test compared quantitative parameters. Two readers qualitatively assessed lesion types according to imaging features. Receiver operating characteristic curves were generated to calculate sensitivity and specificity. Sensitivity and specificity of the qualitative and quantitative studies were compared.

RESULTS

The patients with IMT had significantly higher NICAP, NICVP, λAP, λVP, and ICD than did the patients with lung cancer (P < 0.05). The threshold NICVP of 0.425 would yield the highest sensitivity and specificity of 92.7% and 81.3%, respectively, for differentiating lung cancer from IMT. The logistic regression model produced from combining quantitative parameters NICAP, NICVP, λAP, and λVP provided a sensitivity and specificity of 100% and 81.3%, respectively, for differentiating lung cancer from IMT.

CONCLUSIONS

Spectral CT imaging with the quantitative analysis may help to increase the accuracy of differentiating lung cancer from IMT.

Dual-Energy CT Angiography for Detection of Pulmonary Emboli: Incremental Benefit of Iodine Maps

Purpose To determine if there is added benefit of using iodine maps from dual-energy (DE) CT in addition to conventional CT angiography images to diagnose pulmonary embolism (PE). Materials and Methods In this retrospective analysis, 1144 consecutive dual-energy CT angiography examinations performed from January through September 2014 at an oncologic referral center to evaluate for PE were reviewed. The 1144 examinations included 1035 patients (mean age, 58.7 years; range, 15-99 years). First, the location, level, and type (occlusive vs nonocclusive) of PEs on conventional CT angiograms were recorded. Iodine maps were then reviewed for defects suggestive of PE. Last, CT angiograms were rereviewed to detect additional PEs suggested by the iodine map. Consensus reviews were performed for examinations with PEs. The confidence interval of percentages was calculated by using the Clopper-Pearson method. Results On 147 of 1144 (12.8%) CT angiograms, a total of 372 PEs were detected at initial review. After review of the DE CT iodine map, 27 additional PEs were found on 26 of 1144 CT angiograms (2.3%; 95% confidence interval [CI]: 1.5%, 3.3%). Of the 27 additional PEs, six (22.2%) were segmental, 21 (77.8%) were subsegmental, 24 (88.9%) were occlusive, and three (11.1%) were nonocclusive. Eleven of 1144 (1.0%; 95% CI: 0.5%, 1.7%) CT angiograms had a new diagnosis of PE after review of the DE CT iodine maps. Conclusion Dual-energy CT iodine maps show a small incremental benefit for the detection of occlusive segmental and subsegmental pulmonary emboli. © RSNA, 2018.

Comparison of the effect of radiation exposure from dual-energy CT versus single-energy CT on double-strand breaks at CT pulmonary angiography

PURPOSE

To compare the effect of dual-source dual-energy CT versus single-energy CT on DNA double-strand breaks (DSBs) in blood lymphocytes at CT pulmonary angiography (CTPA).

METHODS AND MATERIALS

Sixty-two patients underwent either dual-energy CTPA (Group 1: n = 21, 80/Sn140 kVp, 89/38 mAs; Group 2: n = 20, 100/Sn140 kVp, 89/76 mAs) or single-energy CTPA (Group 3: n = 21, 120 kVp, 110 mAs). Blood samples were obtained before and 5 min after CTPA. DSBs were assessed with fluorescence microscopy and Kruskal-Walls tests were used to compare DSBs levels among groups. Volume CT dose index (CTDIvol), dose length product (DLP) and organ radiation dose were compared using ANOVA.

RESULTS

There were increased excess DSB foci per lymphocyte 5 min after CTPA examinations in three groups (Group 1: P = .001; Group 2: P = .001; Group 3: P = .006). There were no differences among groups regarding excess DSB foci/cell and percentage of excess DSBs (Group 1, 23%; Group 2, 24%; Group 3, 20%; P = .932). CTDIvol, DLP and organ radiation dose in Group 1 were the lowest among the groups (all P < .001).

CONCLUSION

DSB is increased following dual-source and single-source CTPA, while dual-source dual-energy CT protocols do not increase the estimated radiation dose and also do not result in a higher incidence of DNA DSBs in patients undergoing CTPA.

Preliminary Results: Can Dual-Energy Computed Tomography Help Distinguish Cardiogenic Pulmonary Edema and Acute Interstitial Lung Disease?

OBJECTIVE

We compared iodine concentration in pulmonary ground-glass opacity on iodine density images of contrast-enhanced chest dual-energy computed tomography (DECT) between patients with cardiogenic pulmonary edema (CPE) and acute interstitial lung disease (AILD).

METHODS

Five of 12 patients who underwent contrast-enhanced chest DECT to exclude pulmonary embolism were clinically diagnosed with CPE and 7, with AILD. We compared the mean CT value on monochromatic images at 65 keV and iodine concentration on iodine density images between the affected and normal areas.

RESULTS

The mean iodine concentrations were comparable between the affected and normal areas (P = 0.3048) in patients with CPE and were significantly higher in the affected than in the normal areas in those with AILD (P < 0.0001).

CONCLUSIONS

Measurement of iodine concentration in pulmonary ground-glass opacity of contrast-enhanced chest DECT has the potential to help distinguish CPE and AILD.

Spectral CT in evaluating the therapeutic effect of transarterial chemoembolization for hepatocellular carcinoma: A retrospective study

This study aimed to investigate the value of computed tomographic (CT) spectral imaging in evaluating the effect of transarterial chemoembolization (TACE).The records of 67 patients with hepatocellular carcinoma (HCC) who had undergone dynamic spectral CT before treatment were selected for the study. Iodine concentrations pretreatment in liver parenchyma, the HCC lesion(s), portal vein, and aorta were measured from the decomposition images. The normalized iodine concentrations (NIC) were calculated. All of them underwent plain scan or contrast-enhanced CT post-treatment (approximately 4-6 weeks after TACE).The values of arterial phase normalized iodine concentrations (AP NIC) before TACE correlated with the grades of lipiodol deposition in tumors (r = 0.76, P < .001). However, there was no relationship between normalized iodine concentrations in the portal venous phase (PVP NIC) before TACE and the grade of lipiodol deposition (r = 0.17, P = .17). Values of AP NIC in residual tumors pre-TACE were significantly lower than those in partial lesions with deposition of iodized oil. The threshold AP NIC of 0.18 yielded an AUC of 0.895, 83.33% sensitivity, 81.03% specificity, 83.33% positive predictive value (PPV), and 82.76% negative predictive value, respectively. The survival probability in patients with AP NIC values pre-TACE ≥ 0.18 was higher than those whose AP NIC values pre-TACE were < 0.18 (P = .028).Spectral CT with quantitative analysis of AP NIC may help to evaluate the utility and predict the therapeutic effect of TACE. Values of AP NIC had high sensitivity and specificity for differentiating partial tumors with lipiodol deposition from those without lipiodol deposition.

Systemic Thrombolysis for Pulmonary Embolism: Who and How

Anticoagulation has been shown to improve mortality in acute pulmonary embolism (PE). Initiation of anticoagulation should be considered when PE is strongly suspected and the bleeding risk is perceived to be low, even if acute PE has not yet been proven. Low-risk patients with acute PE are simply continued on anticoagulation. Severely ill patients with high-risk (massive) PE require aggressive therapy, and if the bleeding risk is acceptable, systemic thrombolysis should be considered. However, despite clear evidence that parenteral thrombolytic therapy leads to more rapid clot resolution than anticoagulation alone, the risk of major bleeding including intracranial bleeding is significantly higher when systemic thrombolytic therapy is administered. It has been demonstrated that right ventricular dysfunction, as well as abnormal biomarkers (troponin and brain natriuretic peptide) are associated with increased mortality in acute PE. In spite of this, intermediate-risk (submassive) PE comprises a fairly broad clinical spectrum. For several decades, clinicians and clinical trialists have worked toward a more aggressive, yet safe solution for patients with intermediate-risk PE. Standard-dose thrombolysis, low-dose systemic thrombolysis, and catheter-based therapy which includes a number of devices and techniques, with or without low-dose thrombolytic therapy, have offered potential solutions and this area has continued to evolve. On the basis of heterogeneity within the category of intermediate-risk as well as within the high-risk group of patients, we will focus on the use of systemic thrombolysis in carefully selected high- and intermediate-risk patients. In certain circumstances when the need for aggressive therapy is urgent and the bleeding risk is acceptable, this is an appropriate approach, and often the best one.

Contrast-enhanced CT- and MRI-based perfusion assessment for pulmonary diseases: basics and clinical applications

Assessment of regional pulmonary perfusion as well as nodule and tumor perfusions in various pulmonary diseases are currently performed by means of nuclear medicine studies requiring radioactive macroaggregates, dual-energy computed tomography (CT), and dynamic first-pass contrast-enhanced perfusion CT techniques and unenhanced and dynamic first-pass contrast enhanced perfusion magnetic resonance imaging (MRI), as well as time-resolved three-dimensional or four-dimensional contrast-enhanced magnetic resonance angiography (MRA). Perfusion scintigraphy, single-photon emission tomography (SPECT) and SPECT fused with CT have been established as clinically available scintigraphic methods; however, they are limited by perfusion information with poor spatial resolution and other shortcomings. Although positron emission tomography with 15O water can measure absolute pulmonary perfusion, it requires a cyclotron for generation of a tracer with an extremely short half-life (2 min), and can only be performed for academic purposes. Therefore, clinicians are concentrating their efforts on the application of CT-based and MRI-based quantitative and qualitative perfusion assessment to various pulmonary diseases. This review article covers 1) the basics of dual-energy CT and dynamic first-pass contrast-enhanced perfusion CT techniques, 2) the basics of time-resolved contrast-enhanced MRA and dynamic first-pass contrast-enhanced perfusion MRI, and 3) clinical applications of contrast-enhanced CT- and MRI-based perfusion assessment for patients with pulmonary nodule, lung cancer, and pulmonary vascular diseases. We believe that these new techniques can be useful in routine clinical practice for not only thoracic oncology patients, but also patients with different pulmonary vascular diseases.

Dual-Energy Spectral CT: Various Clinical Vascular Applications

Single-source dual-energy (DE) computed tomography (CT) with fast switching of tube voltage allows projection-based image reconstruction, substantial reduction of beam-hardening effects, reconstruction of accurate monochromatic images and material decomposition images (MDIs), and detailing of material composition by using x-ray spectral information. In vascular applications, DE CT is expected to overcome limitations of standard single-energy CT angiography, including patient exposure to nephrotoxic contrast medium and carcinogenic radiation, insufficient contrast vascular enhancement, interference from metallic and beam-hardening artifacts and severe vessel calcification, and limited tissue characterization and perfusion assessment. Acquisition of low-energy monochromatic images and iodine/water MDIs can reasonably reduce contrast agent dose and improve vessel enhancement. Acquisition of virtual noncontrast images, such as water/iodine MDIs, can reduce overall radiation exposure by replacing true noncontrast CT in each examination. Acquisition of monochromatic images by using metal artifact reduction software or acquisition of iodine/water MDIs can reduce metal artifacts with preserved or increased vessel contrast, and subtraction of monochromatic images between two energy levels can subtract coils composed of dense metallic materials. Acquisition of iodine/calcium (ie, hydroxyapatite) MDIs permits subtraction of vessel calcification and improves vessel lumen delineation. Sensitive detection of lipid-rich plaque can be achieved by using fat/water MDIs, the spectral Hounsfield unit curve (energy level vs CT attenuation), and a histogram of effective atomic numbers included in an image. Various MDIs are useful for accurate differentiation among materials with high attenuation values, including contrast medium, calcification, and fresh hematoma. Iodine/water MDIs are used to assess organ perfusion, such as in the lungs and myocardium. Understanding these DE CT techniques enhances the value of CT for vascular applications. (©)RSNA, 2016.

Single source dual energy CT: What is the optimal monochromatic energy level for the analysis of the lung parenchyma?

OBJECTIVE

To determine the optimal monochromatic energy level for lung parenchyma analysis in spectral CT.

METHODS

All 50 examinations (58% men, 64.8±16yo) from an IRB-approved prospective study on single-source dual energy chest CT were retrospectively included and analyzed. Monochromatic images in lung window reconstructed every 5keV from 40 to 140keV were independently assessed by two chest radiologists. Based on the overall image quality and the depiction/conspicuity of parenchymal lesions, each reader had to designate for every patient the keV level providing the best diagnostic and image quality.

RESULTS

72% of the examinations exhibited parenchymal lesions. Reader 1 picked the 55keV monochromatic reconstruction in 52% of cases, 50 in 30% and 60 in 18%. Reader 2 chose 50keV in 52% cases, 55 in 40%, 60 in 6% and 40 in 2%. The 50 and 55keV levels were chosen by at least one reader in 64% and 76% of all patients, respectively. Merging 50 and 55keV into one category results in an optimal setting selected by reader 1 in 82% of patients and by reader 2 in 92%, with a 74% concomitant agreement.

CONCLUSION

The best image quality for lung parenchyma in spectral CT is obtained with the 50-55keV monochromatic reconstructions.

[GSI Quantitative Parameters: Preoperative Diagnosis of Metastasis Lymph Nodes in Lung Cancer]

背景与目的

肺癌淋巴结转移是重要的生存预后因素，准确的纵隔淋巴结分期可以使患者最大程度地受益于手术。本研究旨在探讨宝石能谱计算机断层扫描（computed tomography, CT）定量参数在术前诊断非小细胞肺癌（non-small cell lung cancer, NSCLC）患者淋巴结转移的价值。

方法

收集48例NSCLC患者，连续进行宝石能谱CT成像（gemstone spectral imaging, GSI）模式肺增强扫描和手术治疗。重建GSI数据，测量淋巴结的大小、动脉期和静脉期的CT值、能谱曲线的斜率、标准化碘浓度以及水浓度。采用独立样本的t检验，并进行受试者工作特征曲线（receiver operating characteristic, ROC）分析，确定诊断的最佳阈值及效能。

结果

转移性淋巴结与非转移性淋巴结短轴直径、动脉期和静脉期的CT值、能谱曲线的斜率、标准化碘浓度均有统计学差异。当确定动脉期能谱曲线斜率的最佳临界值为2.75，其诊断的敏感性、特异性及总体的准确性分别为88.2%、88.4%、87.0%。

结论

能谱CT的GSI模式定量参数较传统CT在术前诊断转移性淋巴结方面有更高的诊断效能。

Dual-Energy CT: Spectrum of Thoracic Abnormalities

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

Dual Energy Spectral CT Imaging for Colorectal Cancer Grading: A Preliminary Study

Objectives

To assess the diagnostic value of dual energy spectral CT imaging for colorectal cancer grading using the quantitative iodine density measurements in both arterial phase (AP) and venous phase (VP).

Methods

81 colorectal cancer patients were divided into two groups based on their pathological findings: a low grade group including well (n = 13) and moderately differentiated cancer (n = 24), and a high grade group including poorly differentiated (n = 42) and signet ring cell cancer (n = 2). Iodine density (ID) in the lesions was derived from the iodine-based material decomposition (MD) image and normalized to that in the psoas muscle to obtain normalized iodine density (NID). The difference in ID and NID between AP and VP was calculated.

Results

The ID and NID values of the low grade cancer group were, 14.65±3.38mg/mL and 1.70±0.33 in AP, and 21.90±3.11mg/mL and 2.05± 0.32 in VP, respectively. The ID and NID values for the high grade cancer group were 20.63±3.72mg/mL and 2.95±0.72 in AP, and 26.27±3.10mg/mL and 3.51±1.12 in VP, respectively. There was significant difference for ID and NID between the low grade and high grade cancer groups in both AP and VP (all p<0.001). ROC analysis indicated that NID of 1.92 in AP provided 70.3% sensitivity and 97.7% specificity in differentiating low grade cancer from high grade cancer.

Conclusions

The quantitative measurement of iodine density in AP and VP can provide useful information to differentiate low grade colorectal cancer from high grade colorectal cancer with NID in AP providing the greatest diagnostic value.

Pancreatic ductal adenocarcinoma and chronic mass-forming pancreatitis: Differentiation with dual-energy MDCT in spectral imaging mode

OBJECTIVE

To investigate the value of dual-energy MDCT in spectral imaging in the differential diagnosis of chronic mass-forming chronic pancreatitis (CMFP) and pancreatic ductal adenocarcinoma (PDAC) during the arterial phase (AP) and the pancreatic parenchymal phase (PP).

MATERIALS AND METHODS

Thirty five consecutive patients with CMFP (n=15) or PDAC (n=20) underwent dual-energy MDCT in spectral imaging during AP and PP. Iodine concentrations were derived from iodine-based material-decomposition CT images and normalized to the iodine concentration in the aorta. The difference in iodine concentration between the AP and PP, contrast-to-noise ratio (CNR) and the slope K of the spectrum curve were calculated.

RESULTS

Normalized iodine concentrations (NICs) in patients with CMFP differed significantly from those in patients with PDAC during two double phases (mean NIC, 0.26±0.04 mg/mL vs. 0.53±0.02 mg/mL, p=0.0001; 0.07±0.02 mg/mL vs. 0.28±0.04 mg/mL, p=0.0002, respectively). There were significant differences in the value of the slope K of the spectrum curve in two groups during AP and PP (K(CMFP)=3.27±0.70 vs. K(PDAC)=1.35±0.41, P=0.001, and K(CMFP)=3.70±0.17 vs. K(PDAC)=2.16±0.70, p=0.003, respectively). CNRs at low energy levels (40-70 keV) were higher than those at high energy levels (80-40 keV).

CONCLUSION

Individual patient CNR-optimized energy level images and the NIC can be used to improve the sensitivity and the specificity for differentiating CMFP from PDAC by use of dual-energy MDCT in spectral imaging with fast tube voltage switching.

Differentiation of low-attenuation intracranial hemorrhage and calcification using dual-energy computed tomography in a phantom system

OBJECTIVES

Calcific and hemorrhagic intracranial lesions with attenuation levels of less than 100 Hounsfield units (HUs) cannot currently be reliably differentiated by single-energy computed tomography (SECT). The proper differentiation of these lesion types would have a multitude of clinical applications. A phantom model was used to test the ability of dual-energy CT (DECT) to differentiate such lesions.

MATERIALS AND METHODS

Agar gel-bound ferric oxide and hydroxyapatite were used to model hemorrhage and calcification, respectively. Gel models were scanned using SECT and DECT and organized into SECT attenuation-matched pairs at 16 attenuation levels between 0 and 100 HU. Dual-energy CT data were analyzed using 3-dimensional (3D) Gaussian mixture models (GMMs), as well as a simplified threshold plane metric derived from the 3D GMM, to assign voxels to hemorrhagic or calcific categories. Accuracy was calculated by comparing predicted voxel assignments with actual voxel identities.

RESULTS

We measured 6032 voxels from each gel model, for a total of 193,024 data points (16 matched model pairs). Both the 3D GMM and its more clinically implementable threshold plane derivative yielded similar results, with higher than 90% accuracy at matched SECT attenuation levels of 50 HU and greater.

CONCLUSIONS

Hemorrhagic and calcific lesions with attenuation levels between 50 and 100 HU were differentiable using DECT in a clinically relevant phantom system with higher than 90% accuracy. This method warrants further testing for potential clinical applications.

Iodine Distribution Map in Dual-Energy Computed Tomography Pulmonary Artery Imaging with Rapid kVp Switching for the Diagnostic Analysis and Quantitative Evaluation of Acute Pulmonary Embolism

RATIONALE AND OBJECTIVES

To assess the diagnostic value of dual-energy (DE) computed tomography pulmonary angiography (CTPA) for acute pulmonary embolism (PE) using a helical DE scan mode with rapid kVp switching.

MATERIALS AND METHODS

Seventy-six patients with suspected acute PE underwent DE CTPA. Two readers independently assessed and measured the iodine maps. CTPA images were assessed for the presence, location, and degree of PE as the standard of reference. Iodine maps were used to identify the perfusion defect (PD), and the diagnostic accuracy of iodine maps was calculated. The iodine concentrations of PDs and normal lung parenchyma were also measured and compared.

RESULTS

A per-patient analysis showed the 84.6% sensitivity and 96.0% specificity of iodine map for PE, and on per-segment analysis, the sensitivity and specificity for PE were 82.9% and 99.6%, respectively. Intraobserver and interobserver variability correlations were excellent, with k values from 0.806 to 1.000. Quantitative analysis showed there was a significant difference for iodine concentration between circumscribed/patchy PDs or wedge-shaped PDs consistent with PE and normal lung parenchyma (P < .05). The intraobserver reliability of reader 1 was from 0.928 to 0.997, and reader 2 was from 0.912 to 0.995. And, the interobserver reliability between two readers was from 0.967 to 0.999.

CONCLUSIONS

CTPA based on DE scanning with rapid kVp switching can provide both morphologic analysis and quantitative evaluation of PD related to acute PE in addition to standard CTPA data. Quantification of iodine concentration may be helpful for identifying the presence or absence of PE.

Chronic thromboembolic pulmonary arterial hypertension: a review of the literature and novel therapeutic approaches

Chronic thromboembolic pulmonary hypertension is defined as pulmonary hypertension (PH) caused by single or recurrent pulmonary emboli and is characterized by chronic obstruction of the pulmonary arteries leading to increased vascular resistance and PH. Also, progressive remodeling may occur in occluded and nonoccluded territories. Better understanding of the underlying mechanisms and risk factors could improve diagnosis and allow appropriate interventions. Pulmonary endarterectomy is an established approach and is considered the definitive treatment for chronic PH, resulting from thromboembolic disease. Furthermore, percutaneous transluminal pulmonary angioplasty is technically feasible, especially for those with peripheral-type of the disease. In addition, several agents, including prostanoids, endothelin receptor antagonists and phosphodiesterase type-5 inhibitors, have been tested in selected patients yielding promising results. Several novel agents are under investigation, and extensive research is currently in progress aiming to resolve uncertainties in the understanding and treatment of the disease.

Differentiation of lung cancers from inflammatory masses with dual-energy spectral CT imaging

RATIONALE AND OBJECTIVES

To investigate the value of dual-energy spectral computed tomography (DESCT) in the quantitative differentiation between pulmonary malignant masses and inflammatory masses.

MATERIALS AND METHODS

This study was an institutional review board-approved study, and written informed consent was obtained from all patients. Sixty patients with 35 lung cancers and 25 inflammatory masses underwent DESCT scan during arterial phase (AP) and venous phase (VP). CT numbers of net enhancement in 70 keV monochromatic images in central and peripheral regions of masses and their differences (dCT) were measured. Iodine concentrations in the two regions were measured and normalized to the aorta as normalized iodine concentrations (NICs). The slopes of spectral attenuation curves (λHU) in the two regions were also calculated. The two-sample t test was used to compare quantitative parameters. Receiver operating characteristic (ROC) curves were generated to calculate sensitivity and specificity.

RESULTS

CT numbers of net enhancement and NICs in central regions, and λHU values both in the central and peripheral region of lung cancers were significantly lower than those of inflammatory masses during AP and VP. On the other hand, the dCT values of lung cancers were higher than that of inflammatory masses. NIC value in the central regions in VP had the highest sensitivity (86%) and specificity (100%) in differentiating malignant masses from inflammatory masses.

CONCLUSIONS

DESCT imaging with quantitative parameters such as CT numbers of 70 keV monochromatic images, NIC, and λHU may be a new method for differentiating lung cancers from inflammatory masses.

Spectral CT imaging in the differential diagnosis of necrotic hepatocellular carcinoma and hepatic abscess

AIM

To explore the value of CT spectral imaging in the differential diagnosis of necrotic hepatocellular carcinoma (nHCC) and hepatic abscess (HA) during the arterial phase (AP) and portal venous phase (PP).

MATERIALS AND METHODS

Sixty patients with 36 nHCCs and 24 HAs underwent spectral CT during AP and PP. Iodine or water concentration were measured and the normalized iodine concentration (NIC) and lesion-normal parenchyma iodine concentration ratio (LNR) were calculated. The two-sample t-test was used to compare quantitative parameters. Two readers qualitatively assessed lesion types according to imaging features. Sensitivity and specificity were compared between the qualitative and quantitative studies.

RESULTS

NIC and LNR in the AP for the wall of nHCC (0.14 ± 0.04 mg/ml; 2.77 ± 0.74) were higher than those of HA (0.13 ± 0.02 mg/ml; 1.4 ± 0.9). NIC and LNR in the PP for the wall of HA (0.66 ± 0.05 mg/ml; 1.2 ± 0.2) were higher than those of nHCC (0.5 ± 0.11 mg/ml; 0.94 ± 0.12). The differences in NIC in the AP were not significant but the differences in LNR in AP, and NIC and LNR in the PP were significant. The best quantitative parameter was LNR in AP, and a threshold of 1.52 would yield a sensitivity and specificity of 100% and 91.7%, respectively, for differentiating nHCC from HA.

CONCLUSION

CT spectral imaging with quantitative iodine concentration analysis may help to increase the accuracy of differentiating nHCC from HA.

Quantitative material decomposition using spectral computed tomography with an energy-resolved photon-counting detector

Dual-energy computed tomography (CT) techniques have been used to decompose materials and characterize tissues according to their physical and chemical compositions. However, these techniques are hampered by the limitations of conventional x-ray detectors operated in charge integrating mode. Energy-resolved photon-counting detectors provide spectral information from polychromatic x-rays using multiple energy thresholds. These detectors allow simultaneous acquisition of data in different energy ranges without spectral overlap, resulting in more efficient material decomposition and quantification for dual-energy CT. In this study, a pre-reconstruction dual-energy CT technique based on volume conservation was proposed for three-material decomposition. The technique was combined with iterative reconstruction algorithms by using a ray-driven projector in order to improve the quality of decomposition images and reduce radiation dose. A spectral CT system equipped with a CZT-based photon-counting detector was used to implement the proposed dual-energy CT technique. We obtained dual-energy images of calibration and three-material phantoms consisting of low atomic number materials from the optimal energy bins determined by Monte Carlo simulations. The material decomposition process was accomplished by both the proposed and post-reconstruction dual-energy CT techniques. Linear regression and normalized root-mean-square error (NRMSE) analyses were performed to evaluate the quantitative accuracy of decomposition images. The calibration accuracy of the proposed dual-energy CT technique was higher than that of the post-reconstruction dual-energy CT technique, with fitted slopes of 0.97-1.01 and NRMSEs of 0.20-4.50% for all basis materials. In the three-material phantom study, the proposed dual-energy CT technique decreased the NRMSEs of measured volume fractions by factors of 0.17-0.28 compared to the post-reconstruction dual-energy CT technique. It was concluded that the proposed dual-energy CT technique can potentially be used to decompose mixtures into basis materials and characterize tissues according to their composition.

Dual-energy CT for differentiating acute and chronic pulmonary thromboembolism: an initial experience

The purpose of this study was to prospectively evaluate the diagnostic capability of single-phase dual-energy CT (DECT) angiography to differentiate acute and chronic pulmonary thromboembolism (APTE, CPTE). We prospectively enrolled 26 patients (M:F = 9:17; mean age, 61 years old) with a filling defect in the pulmonary artery on DECT angiography. They were divided into two groups-APTE and CPTE-based on the clinical criteria. Two investigators quantitatively measured the following parameters at the embolism and main pulmonary artery: CT attenuation density [Hounsfield unit (HU) values], iodine-related HU value (IHU), and iodine concentration (IC, mg/ml). These parameters of the embolism and their ratio divided by those of the main pulmonary artery were compared between APTE and CPTE groups. Among 26 patients, 15 were categorized into the APTE group and 11 into the CPTE group. The mean HU, IHU, and IC values of emboli were significantly different between the APTE and CPTE groups (32.2 ± 17.0 vs. 52.1 ± 13.6 HU; P = 0.016, 7.2 ± 2.8 vs. 27.3 ± 12.7 HU; P < 0.001, and 0.57 ± 0.23 vs. 1.56 ± 0.67; P < 0.001). The mean HU, IHU, and IC ratios between emboli and main pulmonary arteries were also significantly different between the two groups (0.085 ± 0.046 vs. 0.156 ± 0.064 HU; P = 0.003, 0.023 ± 0.013 vs. 0.099 ± 0.053; P < 0.001, and 0.048 ± 0.035 vs. 0.130 ± 0.064; P = 0.001). DECT angiography using a quantitative analytic methodology can be used to differentiate between APTE and CPTE.

Thoracic dual energy CT: acquisition protocols, current applications and future developments

Thanks to a simultaneous acquisition at high and low kilovoltage, dual energy computed tomography (DECT) can achieve material-based decomposition (iodine, water, calcium, etc.) and reconstruct images at different energy levels (40 to 140keV). Post-processing uses this potential to maximise iodine detection, which elicits demonstrated added value for chest imaging in acute and chronic embolic diseases (increases the quality of the examination and identifies perfusion defects), follow-up of aortic endografts and detection of contrast uptake in oncology. In CT angiography, these unique features are taken advantage of to reduce the iodine load by more than half. This review article aims to set out the physical basis for the technology, the acquisition and post-processing protocols used, its proven advantages in chest pathologies, and to present future developments.

Development of quantitative computed tomography lung protocols

The purpose of this review article is to review the process of developing optimal computed tomography (CT) protocols for quantitative lung CT (QCT). In this review, we discuss the following important topics: QCT-derived metrics of lung disease; QCT scanning protocols; quality control; and QCT image processing software. We will briefly discuss several QCT-derived metrics of lung disease that have been developed for the assessment of emphysema, small airway disease, and large airway disease. The CT scanning protocol is one of the most important elements in a successful QCT. We will provide a detailed description of the current move toward optimizing the QCT protocol for the assessment of chronic obstructive pulmonary disorder and asthma. Quality control of CT images is also a very important part of the QCT process. We will discuss why it is necessary to use CT scanner test objects (phantoms) to provide frequent periodic checks on the CT scanner calibration to ensure precise and accurate CT numbers. We will discuss the use of QCT image processing software to segment the lung and extract the desired QCT metrics of lung disease. We will discuss the practical issues of using this software. The data obtained from the image processing software are then combined with those from other clinical examinations, health status questionnaires, pulmonary physiology, and genomics to increase our understanding of obstructive lung disease and improve our ability to design new therapies for these diseases.

Differentiating hepatocellular carcinoma from angiomyolipoma of the liver with CT spectral imaging: a preliminary study

AIM

To investigate the value of computed tomography (CT) spectral imaging in differentiating hepatocellular carcinoma (HCC) from angiomyolipoma (AML) during the arterial phase (AP) and portal venous phase (PP).

MATERIALS AND METHOD

Fifty-three patients underwent spectral CT during the AP and PP. Forty-five patients had 45 HCC and eight patients had eight AML. Iodine concentrations in the lesions were normalized to those of the aorta. The normalized iodine concentrations (NIC) and the lesion-normal parenchyma iodine concentration ratio (LNR) were calculated. The two-sample t-test was performed to compare quantitative parameters. Two readers qualitatively assessed lesion types on the basis of imaging features. Sensitivity and specificity were compared between the qualitative and quantitative studies.

RESULTS

NICs and LNRs in patients with HCC differed significantly from those in patients with AML: mean NICs were 0.25 ± 0.06 mg/ml versus 0.59 ± 0.03 mg/ml, respectively, during the AP and 0.52 ± 0.12 mg/ml versus 0.78 ± 0.03 mg/ml, respectively, during the PP. Mean LNRs were 2.97 ± 0.42 versus 5.85 ± 0.43, respectively, during the AP and 0.99 ± 0.17 versus 1.36 ± 0.05, respectively, during the PP. The NICs and LNRs for HCC were lower than those of AML during the AP and PP. The differences were significant (p < 0.05). The threshold NIC and LNR had high sensitivity and specificity in differentiating HCC from AML.

CONCLUSION

CT spectral imaging with the quantitative analysis of iodine concentration may help increase the accuracy of differentiating HCC from AML.