Can dual-energy CT evaluate contrast enhancement of ground-glass attenuation? Phantom and preliminary clinical studies

Dual-Energy Computed Tomography Applications in Lung Cancer

This article examines the intrathoracic applications for dual-energy computed tomography (DECT), focusing on lung cancer. The topics covered include the image data sets, methods for iodine quantification, and clinical applications. The applications of DECT are to differentiate benign and malignant lung nodules, determining the grade of lung cancer and expression of ki-67 expression. Iodine quantification has role in assessment of treatment response in both the primary tumor and nodal metastases.

Quantitative parameters of enhanced dual-energy computed tomography for differentiating lung cancers from benign lesions in solid pulmonary nodules

Objectives

This study aimed to investigate the ability of quantitative parameters of dual-energy computed tomography (DECT) and nodule size for differentiation between lung cancers and benign lesions in solid pulmonary nodules.

Materials and Methods

A total of 151 pathologically confirmed solid pulmonary nodules including 78 lung cancers and 73 benign lesions from 147 patients were consecutively and retrospectively enrolled who underwent dual-phase contrast-enhanced DECT. The following features were analyzed: diameter, volume, Lung CT Screening Reporting and Data System (Lung-RADS) categorization, and DECT-derived quantitative parameters including effective atomic number (Zeff), iodine concentration (IC), and normalized iodine concentration (NIC) in arterial and venous phases. Multivariable logistic regression analysis was used to build a combined model. The diagnostic performance was assessed by area under curve (AUC) of receiver operating characteristic curve, sensitivity, and specificity.

Results

The independent factors for differentiating lung cancers from benign solid pulmonary nodules included diameter, Lung-RADS categorization of diameter, volume, Zeff in arterial phase (Zeff_A), IC in arterial phase (IC_A), NIC in arterial phase (NIC_A), Zeff in venous phase (Zeff_V), IC in venous phase (IC_V), and NIC in venous phase (NIC_V) (all P < 0.05). The IC_V, NIC_V, and combined model consisting of diameter and NIC_V showed good diagnostic performance with AUCs of 0.891, 0.888, and 0.893, which were superior to the diameter, Lung-RADS categorization of diameter, volume, Zeff_A, and Zeff_V (all P < 0.001). The sensitivities of IC_V, NIC_V, and combined model were higher than those of IC_A and NIC_A (all P < 0.001). The combined model did not increase the AUCs compared with IC_V (P = 0.869) or NIC_V (P = 0.633).

Conclusion

The DECT-derived IC_V and NIC_V may be useful in differentiating lung cancers from benign lesions in solid pulmonary nodules.

Pulmonary nodule enhancement in subtraction CT and dual-energy CT: A comparison study

OBJECTIVE

To compare nodule enhancement on subtraction CT iodine maps to that on dual-energy CT iodine maps using CT datasets acquired simultaneously.

METHODS

A previously-acquired set of lung subtraction and dual-energy CT maps consisting of thirty patients with 95 solid pulmonary nodules (≥4 mm diameter) was used. Nodules were annotated and segmented on CT angiography, and mean nodule enhancement in the iodine maps calculated. Three radiologists scored nodule visibility with both techniques on a 4-point scale.

RESULTS

Mean nodule enhancement was higher (p < 0.001) at subtraction CT (34.9 ± 12.9 HU) than at dual-energy CT (25.4 ± 21.0 HU). Nodule enhancement at subtraction CT was judged more often to be "highly visible" for each observers (p < 0.001) with an area under the curve of 0.81.

CONCLUSIONS

Subtraction CT is able to depict iodine enhancement in pulmonary nodules better than dual-energy CT.

Dual-Energy Computed Tomography Lung in patients of Pulmonary Tuberculosis

Objectives

The objective of this study was to characterize findings of high-resolution computed tomography (HRCT) and dual-energy CT (DECT) (80 keV, 140 keV, and mixed) in pulmonary tuberculosis (TB) patients and to compare and correlate HRCT and DECT findings.

Material and Methods

This cross-sectional study was conducted on 67 patients of 18-65 years of age who were suspected cases of pulmonary TB with signs and symptoms of cough, fever, hemoptysis, sputum, night sweats, and weight loss with positive sputum AFB examinations/bronchoalveolar lavage. All the patients subjected to HRCT scan and followed with DECT scan. Comparison of various imaging techniques (DECT 80 keV, DECT 140 keV, and DECT mixed) with HRCT was done for detecting lung findings and data so obtained were subjected to statistical analysis.

Results

On comparing the various imaging techniques with HRCT for detecting consolidation, tree in bud pattern, cavitary lesions, ground-glass opacity, bronchiectasis, atelectasis, nodules, granuloma, peribronchial thickening, and fibrosis, the maximum agreement of HRCT was found with DECT 80 keV and minimum agreement was found with DECT 140 keV.

Conclusion

The study concluded that DECT 80 keV monochromatic reconstructions among 80 keV, mixed, and 140 keV monochromatic reconstructions in lung parenchyma window settings are a faster and better analytical tool for the assessment of findings of pulmonary TB when compared with HRCT.

Extra-abdominal dual-energy CT applications: a comprehensive overview

Unlike conventional computed tomography, dual-energy computed tomography is a relatively novel technique that exploits ionizing radiations at different energy levels. The separate radiation sets can be achieved through different technologies, such as dual source, dual layers or rapid switching voltage. Body tissue molecules vary for their specific atomic numbers and electron density, and the interaction with different sets of radiations results in different attenuations, allowing to their final distinction. In particular, iodine recognition and quantification have led to important information about intravenous contrast medium delivery within the body. Over the years, useful post-processing algorithms have also been validated for improving tissue characterization. For instance, contrast resolution improvement and metal artifact reduction can be obtained through virtual monoenergetic images, dose reduction by virtual non-contrast reconstructions and iodine distribution highlighting through iodine overlay maps. Beyond the evaluation of the abdominal organs, dual-energy computed tomography has also been successfully employed in other anatomical districts. Although lung perfusion is one of the most investigated, this evaluation has been extended to narrowly fields of application, such as musculoskeletal, head and neck, vascular and cardiac. The potential pool of information provided by dual-energy technology is already wide and not completely explored, yet. Therefore, its performance continues to raise increasing interest from both radiologists and clinicians.

Translation of Quantitative Imaging Biomarkers into Clinical Chest CT

Quantitative imaging has been proposed as the next frontier in radiology as part of an effort to improve patient care through precision medicine. In 2007, the Radiological Society of North America launched the Quantitative Imaging Biomarkers Alliance (QIBA), an initiative aimed at improving the value and practicality of quantitative imaging biomarkers by reducing variability across devices, sites, patients, and time. Chest CT occupies a strategic position in this initiative because it is one of the most frequently used imaging modalities, anatomically encompassing the leading causes of mortality worldwide. To date, QIBA has worked on profiles focused on the accurate, reproducible, and meaningful use of volumetric measurements of lung lesions in chest CT. However, other quantitative methods are on the verge of translation from research grounds into clinical practice, including (a) assessment of parenchymal and airway changes in patients with chronic obstructive pulmonary disease, (b) analysis of perfusion with dual-energy CT biomarkers, and (c) opportunistic screening for coronary atherosclerosis and low bone mass by using chest CT examinations performed for other indications. The rationale for and the key facts related to the application of these quantitative imaging biomarkers in cardiothoracic chest CT are presented. ^©RSNA, 2019 See discussion on this article by Buckler (pp 977-980).

Invasive Pulmonary Adenocarcinomas Versus Preinvasive Lesions Appearing as Pure Ground-Glass Nodules: Differentiation Using Enhanced Dual-Source Dual-Energy CT

OBJECTIVE. The objective of our study was to investigate the potentials of enhanced dual-source dual-energy CT (DECT) and three-planar measurements for differentiating invasive pulmonary adenocarcinomas (IPAs) from preinvasive lesions appearing as pure ground-glass nodules (pGGNs). MATERIALS AND METHODS. Thirty-nine patients with 53 pGGNs who underwent enhanced dual-source DECT were included in this retrospective study. All pGGNs were pathologically confirmed and categorized into two groups: preinvasive lesions or IPAs. The traditional CT features of the pGGNs were evaluated on unenhanced images. Quantitative parameters were measured on iodine-enhanced images of dual-source DECT in three planes, and both intra- and interobserver reproducibility analyses were performed to assess the measurement reproducibility of quantitative parameters. To identify significant factors for differentiating IPAs from preinvasive lesions, we performed logistic regression analysis and ROC curve analysis. RESULTS. For traditional CT features, only lesion size and unenhanced CT attenuation value showed significant differences between preinvasive lesions and IPAs (p < 0.05). Preinvasive lesions and IPAs exhibited significant differences in attenuation on virtual images, so-called "virtual HU" or "VHU," and the modified normalized iodine concentration (NIC) (p < 0.05), and both intra- and interobserver agreement for the quantitative measurements were excellent. Multivariate logistic regression analysis revealed that larger lesion size (adjusted odds ratio [OR], 3.65) and higher modified NIC (adjusted OR, 19.01) were significant differentiators of IPAs from preinvasive lesions (p < 0.05). ROC curve analysis revealed that modified NIC showed excellent performance (AUC, 0.924) and significantly higher performance than lesion size (AUC, 0.711) for differentiating IPAs from preinvasive lesions. CONCLUSION. In pGGNs, a lesion with a modified NIC value of more than 0.29 can be a very specific discriminator of IPAs from preinvasive lesions, and IPAs can be accurately and reliably differentiated from preinvasive lesions using enhanced dual-source DECT and three-planar measurements.

Can spectral computed tomography imaging improve the differentiation between malignant and benign pulmonary lesions manifesting as solitary pure ground glass, mixed ground glass, and solid nodules?

BACKGROUND

This study quantitatively assessed the efficacy of spectral computed tomography (CT) imaging parameters for differentiating the malignancy and benignity of solitary pulmonary nodules (SPNs) manifesting as ground glass nodules (GGNs) and solid nodules (SNs).

METHODS

The study included 114 patients with SPNs (61 GGNs, and 53 SNs) who underwent CT plain and enhanced scans in the arterial (a) and venous (v) phases using the spectral imaging mode. The spectral CT imaging parameters included: iodine concentrations (IC) of lesions in the arterial (ICLa) and venous (ICLv) phases; normalized IC (NICa/NICv, normalized to the IC in the aorta); the slope of the spectral Hounsfield unit (HU) curve (λHUa/λHUv); and monochromatic CT number (CT40keVa/v, CT70keVa/v) enhancement on 40 and 70 keV images. The two-sample Mann-Whitney U test was used to compare quantitative parameters between malignant and benign SPNs, SNs, and GGNs.

RESULTS

Pathology revealed 75 lung cancer cases, 3 metastatic nodules, 14 benign nodules, and 22 inflammatory nodules. Among the 53 SNs there were 37 malignant and 16 benign nodules. Among the 61 GGNs there were 41 malignant and 20 benign nodules. Overall, the CT40keVa, λHUa, CT40keVv, λHUv, and ICLv of benign SPNs were all greater than those of malignant SPNs (all P < 0.05). For GGNs, CT40keVa/v, CT70keVa/v, λHUa/λHUv, and ICLv of malignant GGNs were all lower than those of benign GGNs.

CONCLUSION

Spectral CT imaging is a more promising method for distinguishing malignant from benign nodules, especially in nodules manifesting as GGNs in contrast-enhanced scanning.

Identification of epidermal growth factor receptor mutations in pulmonary adenocarcinoma using dual-energy spectral computed tomography

OBJECTIVES

To explore the role of dual-energy spectral computed tomography (DESCT) quantitative characteristics for the identification of epidermal growth factor receptor (EGFR) mutation status in a cohort of East Asian patients with pulmonary adenocarcinoma.

MATERIALS AND METHODS

Patients with lung adenocarcinoma who underwent both DESCT chest examination and EGFR test were retrospectively selected from our institution's database. The DESCT visual morphological features and quantitative parameters, including the CT number at 70 keV, normalized iodine concentration (NIC), normalized water concentration, and slopes of the spectral attenuation curves (slope λ HU [Hounsfield unit]), were evaluated or calculated. The patients were divided into two groups: the EGFR mutation group and EGFR wild-type group. Statistical analyses were performed to identify the DESCT quantitative parameters for diagnosis of EGFR mutation status.

RESULTS

EGFR mutations were detected in 66 (55.0%) of the 120 enrolled patients. The univariate analysis revealed that sex, smoking history, CT texture, NIC, and slope λ HU were significantly associated with EGFR mutation status (p = 0.037, 0.001, 0.047, 0.010, and 0.018, respectively). The multivariate logistic analysis revealed that smoking history (odds ratio [OR] = 3.23, p = 0.005) and NIC (OR = 58.026, p = 0.049) were the two significant predictive factors associated with EGFR mutations. Based on this analysis, the smoking history and NIC were combined to determine the predictive value for EGFR mutations with the area under the curve of 0.702.

CONCLUSIONS

NIC may be a potential quantitative DESCT parameter for predicting EGFR mutations in patients with pulmonary adenocarcinoma.

KEY POINTS

• DESCT can provide multiple quantitative image parameters compared to conventional CT. • Identification of the radio-genomic relation between DESCT and EGFR status can help to define molecular subcategories of lung adenocarcinoma, which is valuable for personalized clinical targeted therapy. • NIC may be a potential DESCT quantitative parameter for predicting EGFR mutations in pulmonary adenocarcinoma.

Assessing the Blood Supply Status of the Focal Ground-Glass Opacity in Lungs Using Spectral Computed Tomography

Objective

To exploit material decomposition analysis in dual-energy spectral computed tomography (CT) to assess the blood supply status of the ground-glass opacity (GGO) in lungs.

Materials and Methods

This retrospective study included 48 patients with lung adenocarcinoma, who underwent a contrast-enhanced dual-energy spectral CT scan before treatment (53 GGOs in total). The iodine concentration (IC) and water content (WC) of the GGO, the contralateral and ipsilateral normal lung tissues were measured in the arterial phase (AP) and their differences were analyzed. IC, normalized IC (NIC), and WC values were compared between the pure ground-glass opacity (pGGO) and the mixed ground-glass opacity (mGGO), and between the group of preinvasive lesions and the minimally invasive adenocarcinoma (MIA) and invasive adenocarcinoma (IA) groups.

Results

The values of pGGO (IC = 20.9 ± 6.2 mg/mL and WC = 345.1 ± 87.1 mg/mL) and mGGO (IC = 23.8 ± 8.3 mg/mL and WC = 606.8 ± 124.5 mg/mL) in the AP were significantly higher than those of the contralateral normal lung tissues (IC = 15.0 ± 4.9 mg/mL and WC = 156.4 ± 36.8 mg/mL; IC = 16.2 ± 5.7 mg/mL and WC = 169.4 ± 41.0 mg/mL) and ipsilateral normal lung tissues (IC = 15.1 ± 6.2 mg/mL and WC = 156.3 ± 38.8 mg/mL; IC = 15.9 ± 6.0 mg/mL and WC = 174.7 ± 39.2 mg/mL; all p < 0.001). After normalizing the data according to the values of the artery, pGGO (NIC = 0.1 and WC = 345.1 ± 87.1 mg/mL) and mGGO (NIC = 0.2 and WC = 606.8 ± 124.5 mg/mL) were statistically different (p = 0.049 and p < 0.001, respectively), but not for the IC value (p = 0.161). The WC values of the group with preinvasive lesions and MIA (345.4 ± 96.1 mg/mL) and IA (550.1 ± 158.2 mg/mL) were statistically different (p < 0.001).

Conclusion

Using dual-energy spectral CT and material decomposition analysis, the IC in GGO can be quantitatively measured which can be an indicator of the blood supply status in the GGO.

Analysis of pulmonary pure ground-glass nodule in enhanced dual energy CT imaging for predicting invasive adenocarcinoma: comparing with conventional thin-section CT imaging

Background

To investigate the value of dual energy computed tomography (DECT) parameters (including iodine concentration and monochromatic CT numbers) for predicting pure ground-glass nodules (pGGNs) of invasive adenocarcinoma (IA).

Methods

A total of 55 resected pGGNs evaluated with both unenhanced thin-section CT (TSCT) and enhanced DECT scans were included. Correlations between histopathology [adenocarcinoma in situ (AIS), minimally IA (MIA), and IA] and CT scan characteristics were examined. CT scan and clinicodemographic data were investigated by univariate and multivariate analysis to identify features that helped distinguish IA from AIS or MIA.

Results

Both normalized iodine concentration (NIC) of IA and slope of spectral curve [slope(k)] were not significantly different between IA and AIS or MIA. Size, performance of pleural retraction and enhanced monochromatic CT attenuation values of 120-140 keV were significantly higher for IA. In multivariate regression analysis, size and enhanced monochromatic CT number of 140 keV were independent predictors for IA. Using the two parameters together, the diagnostic capacity of IA could be improved from 0.697 or 0.635 to 0.713.

Conclusions

DECT could help demonstrate blood supply and indicate invasion extent of pGGNs, and monochromatic CT number of higher energy (especially 140 keV) would be better for diagnosing IA than lower energies. Together with size of pGGNs, the diagnostic capacity of IA could be better.

Quality Improvement of Dual-Energy Lung Perfusion Image by Reduction of Low-Energy X-Ray Spectrum: An Evaluation on Clinical Images

Background

The effects of the reduction of low-energy X-ray spectrum on lung perfusion images created by dual-energy CT have not been well evaluated. The aim of this study is to investigate the reliability of lung perfusion blood volume (PBV) images created by dual-energy CT (DECT) equipped with or without a tin filter, focusing on its accuracy adjacent to high-attenuation areas.

Material/Methods

Among 176 patients who underwent DECT for suspicion of pulmonary embolism, 38 patients (mean age, 64; range, 16 to 83 years) without apparent evidence of pulmonary embolism were evaluated in this study. They underwent DECT at 100/140 kVp with a tin filter on 140 kVp tube (Group A; n=18) or at 80/140 kVp without the filter (Group B; n=20). On the lung PBV images, the degrees of artifacts – pulmonary enhancement defect (PED) and pseudo-enhancement in the trachea (PTE) adjacent to the vena cava were evaluated using a four-point scale (0=minimal to 3=prominent).

Results

The mean degrees of artifact in Group A were significantly lower than those in Group B (0.8 vs. 1.9; P<0.0001 for PED, respectively, and 1.1 vs. 2.2; P<0.0001 for TPE, respectively). The mean CTDIvols were 4.90±1.14 and 12.98±3.15 mGy (P<0.0001) for Group A and Group B, respectively.

Conclusions

The quality and accuracy of dual-energy lung perfusion image will be improved by using the tin filter technique.

Prognostic impact of average iodine density assessed by dual-energy spectral imaging for predicting lung tumor recurrence after stereotactic body radiotherapy

The purpose of this study was to investigate the prognostic significance of average iodine density as assessed by dual-energy computed tomography (DE-CT) for lung tumors treated with stereotactic body radiotherapy (SBRT). From March 2011 to August 2014, 93 medically inoperable patients with 74 primary lung cancers and 19 lung metastases underwent DE-CT prior to SBRT of a total dose of 45-60 Gy in 5-10 fractions. Of these 93 patients, nine patients had two lung tumors. Thus, 102 lung tumors were included in this study. DE-CT was performed for pretreatment evaluation. Regions of interest were set for the entire tumor, and average iodine density was obtained using a dedicated imaging software and evaluated with regard to local control. The median follow-up period was 23.4 months (range, 1.5-54.5 months). The median value of the average iodine density was 1.86 mg/cm(3) (range, 0.40-9.27 mg/cm(3)). Two-year local control rates for the high and low average iodine density groups divided by the median value of the average iodine density were 96.9% and 75.7% (P = 0.006), respectively. Tumors with lower average iodine density showed a worse prognosis, possibly reflecting a hypoxic cell population in the tumor. The average iodine density exhibited a significant impact on local control. Our preliminary results indicate that iodine density evaluated using dual-energy spectral CT may be a useful, noninvasive and quantitative assessment of radio-resistance caused by presumably hypoxic cell populations in tumors.

Dual-Energy Computed Tomography Virtual Monoenergetic Imaging of Lung Cancer: Assessment of Optimal Energy Levels

OBJECTIVE

The aim of the study was to evaluate objective and subjective image qualities of virtual monoenergetic imaging (VMI) in dual-source dual-energy computed tomography (DECT) and optimal kiloelectron-volt (keV) levels for lung cancer.

METHODS

Fifty-nine lung cancer patients underwent chest DECT. Images were reconstructed as VMI series at energy levels of 40, 60, 80, and 100 keV and standard linear blending (M_0.3) for comparison. Objective and subjective image qualities were assessed.

RESULTS

Lesion contrast peaked in 40-keV VMI reconstructions (2.5 ± 2.9) and 60 keV (1.9 ± 3.0), which was superior to M_0.3 (0.5 ± 2.7) for both comparisons (P < 0.001). Compared with M_0.3, subjective ratings were highest for 60-keV VMI series regarding general image quality (4.48 vs 4.52; P = 0.74) and increased for lesion demarcation (4.07 vs 4.84; P < 0.001), superior to all other VMI series (P < 0.001). Image sharpness was similar between both series. Image noise was rated superior in the 80-keV and M_0.3 series, followed by 60 keV.

CONCLUSIONS

Virtual monoenergetic imaging reconstructions at 60-keV provided the best combination of subjective and objective image qualities in DECT of lung cancer.

Dual-energy CT after radiofrequency ablation of liver, kidney, and lung lesions: a review of features

Early detection of residual tumour and local tumour progression (LTP) after radiofrequency (RF) ablation is crucial in the decision whether or not to re-ablate. In general, standard contrast-enhanced computed tomography (CT) is used to evaluate the technique effectiveness; however, it is difficult to differentiate post-treatment changes from residual tumour. Dual-energy CT (DECT) is a relatively new technique that enables more specific tissue characterisation of iodine-enhanced structures because of the isolation of iodine in the imaging data. Necrotic post-ablation zones can be depicted as avascular regions by DECT on greyscale- and colour-coded iodine images. Synthesised monochromatic images from dual-energy CT with spectral analysis can be used to select the optimal keV to achieve the highest contrast-to-noise ratio between tissues. This facilitates outlining the interface between the ablation zone and surrounding tissue. Post-processing of DECT data can lead to an improved characterisation and delineation of benign post-ablation changes from LTP. Radiologists need to be familiar with typical post-ablation image interpretations when using DECT techniques. Here, we review the spectrum of changes after RF ablation of liver, kidney, and lung lesions using single-source DECT imaging, with the emphasis on the additional information obtained and pitfalls encountered with this relatively new technique.

Teaching Points

•Technical success of RF ablation means complete destruction of the tumour.

•Assessment of residual tumour on contrast-enhanced CT is hindered by post-ablative changes.

•DECT improves material differentiation and may improve focal lesion characterisation.

•Iodine maps delineate the treated area from the surrounding parenchyma well.

Diagnostic efficiency of split-bolus dual-energy computed tomography for patients with suspected urinary stones

OBJECTIVE

The objective of this study was to evaluate the efficiency of virtual noncontrast image (VNCI) generated from dual-energy split-bolus computed tomographic urography (DE-SBCTU) for urinary stones detection.

METHODS

Three hundred fifty-six patients underwent true noncontrast image (TNCI) and DE-SBCTU. Two radiologists evaluated opacification scores of DE-SBCTU as well as iodine subtractions and image noise on VNCI. Diagnostic performance of the VNCI was evaluated using TNCI as a reference standard, according to diameter and image quality. The results were compared between patient groups with body mass index of less than 25 and 25 kg/m2 or greater.

RESULTS

Agreements for opacification, iodine subtraction, and image noise between the radiologists were excellent, and there were no significant difference in the 2 patients groups. A total of 499 stones were detected on VNCI, with a sensitivity and diagnostic accuracy of 95.1% (468/492) and 92.9% (499/537). Mean (SD) diameter was significantly smaller on VNCI (3.6 [2.3] mm) than on TNCI (4.4 [2.0] mm) (P = 0.01). The stone diameter with false interpretation was less than 4 mm in 48 of 51 patients. The diameter and image quality on VNCI had no significant difference between the 2 patients groups.

CONCLUSIONS

Virtual noncontrast image displays high accuracy for detecting urinary stones, regardless of body mass index.

Oncological applications of dual-energy computed tomography imaging

Dual-energy computed tomography (DECT) imaging is a promising method used in oncology for accurate detection/diagnosis of malignant and benign lesions. Use of dual-energy spectral, weighted average, color-coded map, and virtual unenhanced images provides increased visual detection and easy lesion delineation. Lesion detectability, sensitivity, and conspicuity are significantly improved using DECT. Material characterization and decomposition are promising using DECT. Both anatomical and functional information related to oncology can be provided by DECT using single contrast-enhanced CT.

Correlation between tumor size and blood volume in lung tumors: a prospective study on dual-energy gemstone spectral CT imaging

The purpose of this study was to investigate the relationship between tumor size and blood volume for patients with lung tumors, using dual-energy computed tomography (DECT) and a gemstone spectral imaging (GSI) viewer. During the period from March 2011 to March 2013, 50 patients with 57 medically inoperable lung tumors underwent DECT before stereotactic body radiotherapy (SBRT) of 50-60 Gy in 5-6 fractions. DECT was taken for pretreatment evaluation. The region-of-interest for a given spatial placement of the tumors was set, and averages for CT value, water density and iodine density were compared with tumor size. The average values for iodine density in tumors of ≤ 2 cm, 2-3 cm, and >3 cm maximum diameter were 24.7, 19.6 and 16.0 (100 µg/cm(3)), respectively. The average value of the iodine density was significantly lower in larger tumors. No significant correlation was detected between tumor size and average CT value or between tumor size and average water density. Both the average water density and the average CT value were affected by the amount of air in the tumor, but the average iodine density was not affected by air in the tumor. The average water density and the average CT value were significantly correlated, but the average iodine density and the average CT value showed no significant correlation. The blood volume of tumors can be indicated by the average iodine density more accurately than it can by the average CT value. The average iodine density as assessed by DECT might be a non-invasive and quantitative assessment of the radio-resistance ascribable to the hypoxic cell population in a tumor.

Radiotherapy treatment planning with contrast-enhanced computed tomography: feasibility of dual-energy virtual unenhanced imaging for improved dose calculations

Background

In radiotherapy treatment planning, intravenous administration of an iodine-based contrast agent during computed tomography (CT) improves the accuracy of delineating target volumes. However, increased tissue attenuation resulting from the high atomic number of iodine may result in erroneous dose calculations because the contrast agent is absent during the actual procedure. The purpose of this proof-of-concept study was to present a novel framework to improve the accuracy of dose calculations using dual-energy virtual unenhanced CT in the presence of an iodine-based contrast agent.

Methods

Simple phantom experiments were designed to assess the feasibility of the proposed concept. By utilizing a “second-generation” dual-source CT scanner equipped with a tin filter for improved spectral separation, four CT datasets were obtained using both a water phantom and an iodine phantom: “true unenhanced” images with attenuation values of 2 ± 11 Hounsfield Units (HU), “enhanced” images with attenuation values of 274 ± 23 HU, and two series of “virtual unenhanced” images synthesized from dual-energy scans of the iodine phantom, each with a different combination of tube voltages. Two series of virtual unenhanced images demonstrated attenuation values of 12 ± 29 HU (with 80 kVp/140 kVp) and 34 ± 10 HU (with 100 kVp/140 kVp) after removing the iodine component from the contrast-enhanced images. Dose distributions of the single photon beams calculated from the enhanced images and two series of virtual unenhanced images were compared to those from true unenhanced images as a reference.

Results

The dose distributions obtained from both series of virtual unenhanced images were almost equivalent to that from the true unenhanced images, whereas the dose distribution obtained from the enhanced images indicated increased beam attenuation caused by the high attenuation characteristics of iodine. Compared to the reference dose distribution from the true unenhanced images, the dose distribution pass rates from both series of virtual unenhanced images were greater than 90%, while those from the enhanced images were less than approximately 50–60%.

Conclusions

Dual-energy virtual unenhanced CT improves the accuracy of dose distributions in radiotherapy treatment planning by removing the iodine component from contrast-enhanced images.

Accuracy of iodine removal using dual-energy CT with or without a tin filter: an experimental phantom study

BACKGROUND

The effects of a tin filter on virtual non-enhanced (VNE) images created by dual-energy CT have not been well evaluated.

PURPOSE

To compare the accuracy of VNE images between those with and without a tin filter.

MATERIAL AND METHODS

Two different types of columnar phantoms made of agarose gel were evaluated. Phantom A contained various concentrations of iodine (4.5-1590 HU at 120 kVp). Phantom B consisted of a central component (0, 10, 25, and 40 mgI/cm(3)) and a surrounding component (0, 50, 100, and 200 mgI/cm(3)) with variable iodine concentration. They were scanned by dual-source CT in conventional single-energy mode and dual-energy mode with and without a tin filter. CT values on each gel at the corresponding points were measured and the accuracy of iodine removal was evaluated.

RESULTS

On VNE images, the CT number of the gel of Phantom A fell within the range between -15 and +15 HU under 626 and 881 HU at single-energy 120 kVp with and without a tin filter, respectively. With attenuation over these thresholds, iodine concentration of gels was underestimated with the tin filter but overestimated without it. For Phantom B, the mean CT numbers on VNE images in the central gel component surrounded by the gel with iodine concentrations of 0, 50, 100, and 200 mgI/cm(3) were in the range of -19-+6 HU and 21-100 HU with and without the tin filter, respectively.

CONCLUSION

Both with and without a tin filter, iodine removal was accurate under a threshold of iodine concentration. Although a surrounding structure with higher attenuation decreased the accuracy, a tin filter improved the margin of error.

Dual-energy CT imaging of thoracic malignancies

Computed tomography (CT) plays a pivotal role in the detection, characterization, and staging of lung cancer and other thoracic malignancies. Since the introduction of clinically viable dual-energy CT techniques, substantial evidence has accumulated on the use of this modality for imaging chest malignancies. This article describes the principles of dual-energy CT along with suitable image acquisition, reconstruction, and postprocessing strategies for oncologic applications in the chest. The potential of dual-energy CT techniques for the detection, characterization, staging, and surveillance of chest malignancy, as well as the limitations of this modality are discussed.

Dual-energy CT of the lung

OBJECTIVE

The introduction of dual-energy CT (DECT) has ushered in the ability of material differentiation and tissue characterization beyond the traditional CT attenuation scale. This quality has been exploited for visualizing and quantifying the specific tissue content using radiographic contrast agents, such as iodine-based contrast media or inhaled xenon gas. Applications of this paradigm in the thorax include characterization of the pulmonary blood pool in the setting of acute or chronic pulmonary embolism (PE) and characterization of diseases of the lung parenchyma. Selective xenon detection is being explored for imaging of lung ventilation. In addition, the usefulness of DECT-based selective iodine uptake measurements has been described for the diagnosis and surveillance of thoracic malignancies. This article reviews the current applications of DECT-based imaging techniques in the chest with an emphasis on the diagnosis and characterization of pulmonary thromboembolic disorders.

CONCLUSION

DECT can provide both anatomic and functional information about the lungs in a variety of pulmonary disease states based on a single contrast-enhanced CT examination. This quality has been shown to improve the diagnosis of acute and chronic PEs, other vascular disorders, lung malignancies, and parenchymal diseases. Further developments in DECT techniques and CT scanner technology will further foster and enhance the utility of this application and open new avenues in lung imaging.

Dual-energy CT can evaluate both hilar and mediastinal lymph nodes and lesion vascularity with a single scan at 60 seconds after contrast medium injection

RATIONALE AND OBJECTIVES

The aim of this study was to investigate whether 80-kVp and weighted-average 120-kVp computed tomographic (CT) images scanned at 60 seconds after contrast material injection using a dual-source CT scanner could substitute for conventional 120-kVp images obtained at 30 and 100 seconds.

MATERIALS AND METHODS

Eighty-three consecutive patients with suspected lung cancer were enrolled. Images were obtained in dual-energy mode (80 and 140 kVp) at 60 seconds and conventional 120-kVp mode at 30 and 100 seconds after contrast injection. The CT numbers of the pulmonary artery, pulmonary vein, hilar zone lymph nodes, and pulmonary lesions were measured. Contrasts between the pulmonary artery/pulmonary vein and lymph nodes and beam-hardening artifacts were visually evaluated using five-point and four-point scales, respectively. The degree of enhancement was evaluated on 30-second 120-kVp, 100-second 120-kVp, and 60-second weighted-average 120-kVp images.

RESULTS

The mean differences in attenuation between the pulmonary artery/pulmonary vein and lymph nodes on the 30-second 120-kVp, 60-second 80-kVp, and 60-second weighted-average 120-kVp images were 184/155, 130/140, and 84/92 Hounsfield units, respectively (all P values <.001). The mean contrast scores for the hilar/mediastinal lymph nodes were 4.5/4.7, 3.7/4.2, 3.3/3.6, and 2.4/2.5 for these three and for 100-second 120-kVp images, respectively (all P values <.01). The mean artifact scores of the four images were 1.2, 3.4, 3.6, and 4.0, respectively. On 60-second weighted-average 120-kVp images, 55 of 60 lesions (92%) showed higher enhancement than on 100-second conventional 120-kVp images.

CONCLUSIONS

Dual-energy CT images scanned 60 seconds after contrast injection show excellent vessel-lymph node contrast and enhancement of lesions and can replace dual-phase scan protocols.

Split-bolus CT-urography using dual-energy CT: feasibility, image quality and dose reduction

PURPOSE

To prospectively evaluate the feasibility of dual-energy (DE) split-bolus CT-urography (CTU) and the quality of virtual non-enhanced images (VNEI) and DE combined nephrographic-excretory phase images (CNEPI), and to estimate radiation dose reduction if true non-enhanced images (TNEI) could be omitted.

PATIENTS AND METHODS

Between August and September 2011, 30 consecutive patients with confirmed or suspected urothelial cancer or with hematuria underwent DE CT. Single-energy TNEI and DE CNEPI were obtained. VNEI was reconstructed from CNEPI. Image quality of CNEPI and VNEI was evaluated using a 5-point scale. The attenuation of urine in the bladder on TNEI and VNEI was measured. The CT dose index volume (CTDI (vol)) of the two scans was recorded.

RESULTS

The mean image quality score of CNEPI and VNEI was 4.7 and 3.3, respectively. The mean differences in urine attenuation between VNEI and TNEI were 14±15 [SD] and -16±29 in the anterior and posterior parts of the bladder, respectively. The mean CTDI (vol) for TNEI and CNEPI was 11.8 and 10.9 mGy, respectively. Omission of TNEI could reduce the total radiation dose by 52%.

CONCLUSION

DE split-bolus CTU is technically feasible and can reduce radiation exposure; however, an additional TNEI scan is necessary when the VNEI quality is poor or quantitative evaluation of urine attenuation is required.