Dual-Energy CT in Emergency Neuroimaging: Added Value and Novel Applications

Change in Emergency Department Length of Stay following Routine Adoption of Dual-Energy CT to Differentiate Intracranial Hemorrhage from Calcification

BACKGROUND AND PURPOSE

Dual-energy CT (DECT) is an advanced CT technique that has been shown to improve accuracy in distinguishing between intracranial hemorrhage and calcification, which is often challenging on conventional CT and therefore may warrant repeat imaging in the emergency department (ED) to document stability and exclude enlarging intracranial hemorrhage. We hypothesized that implementation of a DECT head protocol in the ED would decrease the need for repeat imaging and therefore reduce overall ED length of stay (LOS).

MATERIALS AND METHODS

This is a retrospective study comparing ED LOS over a 1-year period before (July 1, 2016 to June 30, 2017) and after (July 1, 2018 to June 30, 2019) implementing a DECT head protocol, for patients scanned for headache, trauma, or fall who were found to have indeterminate intracranial hyperdensities on conventional images, and were subsequently discharged home from the ED (excluding patients who were admitted, taken to the operating room, or left against medical advice). Additional clinical information regarding ED time course and management were also reviewed, including data on time to CT scan, CT report, and if applicable, time to repeat head CT and neurosurgical consultation.

RESULTS

There was no significant difference in patient demographics and CT indications between the pre-DECT and post-DECT cohorts. There was a small but statistically significant difference in mean baseline ED LOS in the initial cohorts of 20 minutes (P = .002). After the inclusion of only intracranial indeterminate hyperdensities, there was a larger statistically significant difference in ED LOS, with mean pre-DECT LOS of 421 minutes and mean post-DECT LOS of 272 minutes, resulting in mean LOS reduction of 149 minutes (P = .003). The increased ED LOS correlated with increased frequency of neurosurgical consultation and repeat head CT for the findings of indeterminate intracranial hyperdensities.

CONCLUSIONS

ED LOS was significantly longer in the pre-DECT cohort, which was partly attributable to neurosurgical consultation and repeat head CT performed for indeterminate intracranial hyperdensities.

Dual-energy CT angiography in detecting underlying causes of intracerebral hemorrhage: an observational cohort study

BACKGROUND

CT angiography (CTA) is often used to detect underlying causes of acute intracerebral hemorrhage (ICH). Dual-energy CT (DECT) is able to distinguish materials with similar attenuation but different compositions, such as hemorrhage and contrast. We aimed to evaluate the diagnostic yield of DECT angiography (DECTA), compared to conventional CTA in detecting underlying ICH causes.

METHODS

All non-traumatic ICH patients who underwent DECTA (both arterial as well as delayed venous phase) at our center between January 2014 and February 2020 were analyzed. Conventional CTA acquisitions were reconstructed ('merged') from DECTA data. Structural ICH causes were assessed on both reconstructed conventional CTA and DECTA. The final diagnosis was based on all available diagnostic and clinical findings during one-year follow up.

RESULTS

Of 206 included ICH patients, 30 (14.6%) had an underlying cause as final diagnosis. Conventional CTA showed a cause in 24 patients (11.7%), DECTA in 32 (15.5%). Both false positive and false negative findings occurred more frequently on conventional CTA. DECTA detected neoplastic ICH in all seven patients with a definite neoplastic ICH diagnosis, whereas conventional CTA only detected four of these cases. Both developmental venous anomalies (DVA) and cerebral venous sinus thrombosis (CVST) were more frequently seen on DECTA. Arteriovenous malformations and aneurysms were detected equally on both imaging modalities.

CONCLUSIONS

Performing DECTA at clinical presentation of ICH may be of additional diagnostic value in the early detection of underlying causes, especially neoplasms, CVST and DVAs.

The Impact of Weighting Factors on Dual-Energy Computed Tomography Image Quality in Non-Contrast Head Examinations: Phantom and Patient Study

Background: This study aims to evaluate the impact of various weighting factors (WFs) on the quality of weighted average (WA) dual-energy computed tomography (DECT) non-contrast brain images and to determine the optimal WF value. Because they simulate standard CT images, 0.4-WA reconstructions are routinely used. Methods: In the initial phase of the research, quantitative and qualitative analyses of WA DECT images of an anthropomorphic head phantom, utilizing WFs ranging from 0 to 1 in 0.1 increments, were conducted. Based on the phantom study findings, WFs of 0.4, 0.6, and 0.8 were chosen for patient analyses, which were identically carried out on 85 patients who underwent non-contrast head DECT. Three radiologists performed subjective phantom and patient analyses. Results: Quantitative phantom image analysis revealed the best gray-to-white matter contrast-to-noise ratio (CNR) at the highest WFs and minimal noise artifacts at the lowest WF values. However, the WA reconstructions were deemed non-diagnostic by all three readers. Two readers found 0.6-WA patient reconstructions significantly superior to 0.4-WA images (p < 0.001), while reader 1 found them to be equally good (p = 0.871). All readers agreed that 0.8-WA images exhibited the lowest image quality. Conclusions: In conclusion, 0.6-WA reconstructions demonstrated superior image quality over 0.4-WA and are recommended for routine non-contrast brain DECT.

Mobile photon counting detector CT with multi material decomposition methods for neuroimaging of patients in intensive care unit

The photon-counting detector computed tomography (PCD-CT) is a promising new technology that provides more spectral information in medical imaging. PCD-CT enables bedside imaging in the neuro intensive care unit (neuro ICU) for patients with life-threatening conditions such as brain hemorrhage and ischemic stroke. The primary purpose of this study is to evaluate a multi-material decomposition algorithm available on PCD-CT, dubbed MD Plus, to differentiate between contrast agent and hemorrhage in hyperdense lesions. A certified multi-energy phantom was used to validate its performance with various x-ray exposure conditions and locations of contrast agent. The results from the quantitative analysis of multi-energy phantoms and the clinical cases of patients in the ICU demonstrated that MD Plus can accurately differentiate between the contrast agent and the hemorrhage. The extended MD Plus algorithm, including virtual non-contrast (VNC) and bone removal, was also validated for various clinical applications.

Dual-Energy Computed Tomography in the Evaluation and Management of Subarachnoid Hemorrhage, Intracranial Hemorrhage, and Acute Ischemic Stroke

Dual-energy computed tomography (DECT) has emerged as a valuable imaging modality in the diagnosis and management of various cerebrovascular pathologies, including subarachnoid hemorrhage, intracranial hemorrhage, and acute ischemic stroke. This article reviews the principles of DECT and its applications in the evaluation and management of these conditions. The authors discuss the advantages of DECT over conventional computed tomography, as well as its limitations, and provide an overview of current research and future directions in the field.

Neuroradiology Applications of Dual and Multi-energy Computed Tomography

Computed tomography (CT) imaging has become an essential diagnostic tool for most emergent clinical conditions, owing to its speed, accuracy, cost, and few contraindications, compared with MR imaging cross-sectional imaging. Spectral CT, which includes dual, multienergy, and photon-counting CT, is superior to conventional single-energy CT (SECT) in many respects. Spectral information enables differentiation between materials with similar Hounsfield Unit attenuations on SECT; examples include but are not limited to "virtual noncontrast," "virtual noncalcium," and most notably for neuro applications, "hemorrhage versus iodine." This article expands on the many possible benefits of spectral CT in neuroimaging.

Leveraging Dual-Energy Computed Tomography to Improve Emergency Radiology Practice

Dual-energy computed tomography affords emergency radiologists with important tools to aid in the detection and discrimination of commonly encountered ED pathologies. In doing so, it can increase the speed of diagnosis and diagnostic certainty while sparing patients potentially unnecessary downsteam workups and radiation exposure. This article demonstrates these clinical benefits through a case-based approach.

Vascular Applications of Dual-Energy Computed Tomography

Dual- or multi-energy CT imaging provides several advantages over conventional CT in the context of vascular imaging. Specific advantages include the use of low-energy virtual monoenergetic images (VMIs) to boost iodine attenuation to salvage suboptimal enhanced studies, perform low-contrast material dose studies, and increase conspicuity of small vessels and lesions. Alternatively, high-energy VMIs reduce artifacts caused by some metals, endoprosthesis, calcium blooming, and beam hardening. Virtual non-contrast (VNC) images reduce radiation dose by eliminating the need for a true non-contrast acquisition in multiphasic CT studies. Iodine maps can be used to evaluate perfusion of tissues and lesions.

Dual-Energy Computed Tomography in Stroke Imaging : Value of a New Image Acquisition Technique for Ischemia Detection after Mechanical Thrombectomy

OBJECTIVE

To assess if a new dual-energy computed tomography (DECT) technique enables an improved visualization of ischemic brain tissue after mechanical thrombectomy in acute stroke patients.

MATERIAL AND METHODS

The DECT head scans with a new sequential technique (TwinSpiral DECT) were performed in 41 patients with ischemic stroke after endovascular thrombectomy and were retrospectively included. Standard mixed and virtual non-contrast (VNC) images were reconstructed. Infarct visibility and image noise were assessed qualitatively by two readers using a 4-point Likert scale. Quantitative Hounsfield units (HU) were used to assess density differences of ischemic brain tissue versus healthy tissue on the non-affected contralateral hemisphere.

RESULTS

Infarct visibility was significantly better in VNC compared to mixed images for both readers R1 (VNC: median 1 (range 1-3), mixed: median 2 (range 1-4), p < 0.05) and R2 (VNC: median 2 (range 1-3), mixed: 2 (range 1-4), p < 0.05). Qualitative image noise was significantly higher in VNC compared to mixed images for both readers R1 (VNC: median 3, mixed: 2) and R2 (VNC: median 2, mixed: 1, p < 0.05, each). Mean HU were significantly different between the infarcted tissue and the reference healthy brain tissue on the contralateral hemisphere in VNC (infarct 24 ± 3) and mixed images (infarct 33 ± 5, p < 0.05, each). The mean HU difference between ischemia and reference in VNC images (mean 8 ± 3) was significantly higher (p < 0.05) compared to the mean HU difference in mixed images (mean 5 ± 4).

CONCLUSION

TwinSpiral DECT allows an improved qualitative and quantitative visualization of ischemic brain tissue in ischemic stroke patients after endovascular treatment.

Virtual monoenergetic images by spectral detector computed tomography may improve image quality and diagnostic ability for ischemic lesions in acute ischemic stroke

BACKGROUND

Acute ischemic lesions are challenging to detect by conventional computed tomography (CT). Virtual monoenergetic images may improve detection rates by increased tissue contrast.

PURPOSE

To compare the ability to detect ischemic lesions of virtual monoenergetic with conventional images in patients with acute stroke.

MATERIAL AND METHODS

We included consecutive patients at our center that underwent brain CT in a spectral scanner for suspicion of acute stroke, onset <12 h, with or without (negative controls) a confirmed cortical ischemic lesion in the initial scan or a follow-up CT or magnetic resonance imaging. Attenuation was measured in predefined areas in ischemic gray (guided by follow-up exams), normal gray, and white matter in conventional images and retrieved in spectral diagrams for the same locations in monoenergetic series at 40-200 keV. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Visual assessment of diagnostic measures was performed by independent review by two neuroradiologists blinded to reconstruction details.

RESULTS

In total, 29 patients were included (January 2018 to July 2019). SNR was higher in virtual monoenergetic compared to conventional images, significantly at 60-150 keV. CNR between ischemic gray and normal white matter was higher in monoenergetic images at 40-70 keV compared to conventional images. Virtual monoenergetic images received higher scores in overall image quality. The sensitivity for diagnosing acute ischemia was 93% and 97%, respectively, for the reviewers, compared to 55% of the original report based on conventional images.

CONCLUSION

Virtual monoenergetic reconstructions of spectral CIs may improve image quality and diagnostic ability in stroke assessment.

Clinical applications of dual-energy computed tomography in neuroradiology

Dual-energy computed tomography (DECT) has developed into a robust set of techniques with increasingly validated clinical applications in neuroradiology. We review some of the most common applications in neuroimaging along with demonstrative case examples that showcase the use of this technology in intracranial hemorrhage, stroke imaging, trauma imaging, artifact reduction, and tumor characterization.

Dual-Energy Parathyroid 4D-CT: Improved Discrimination of Parathyroid Lesions from Thyroid Tissue Using Noncontrast 40-keV Virtual Monoenergetic Images

BACKGROUND AND PURPOSE

In parathyroid CT, a noncontrast phase aids discrimination of parathyroid lesions (not iodine-containing) from thyroid tissue (iodine-containing). When thyroid iodine is pathologically diminished, this differentiation is difficult with standard CT. Because the attenuation of an element is maximal near its K-edge (iodine  = 33.2 keV), we hypothesized that dual-energy CT 40-keV virtual monoenergetic images will accentuate thyroid iodine relative to standard images, improving the differentiation of thyroid from parathyroid lesions. Our purpose was to test this hypothesis through quantitative assessment of Hounsfield unit attenuation and contrast-to-noise on dual-energy CT standard (70-keV) and 40-keV noncontrast images.

MATERIALS AND METHODS

For this retrospective study including 20 dual-energy parathyroid CTs, we used an ROI-based analysis to assess the attenuation of thyroid tissue, parathyroid lesions, and sternocleidomastoid muscle as well as corresponding contrast-to-noise on standard and 40- keV noncontrast images. Wilcoxon signed rank tests were performed to compare differences between 70  and 40 keV.

RESULTS

Absolute and percentage increases in attenuation at 40 keV were significantly greater for thyroid gland than for parathyroid lesions and sternocleidomastoid muscle (P < .001 for all). Significant increases in the contrast-to-noise of thyroid relative to parathyroid lesions (median increase, 0.8; P < .001) and relative to sternocleidomastoid muscle (median increase, 1.3; P < .001) were observed at 40 keV relative to 70 keV.

CONCLUSIONS

Forty-kiloelectron volt virtual monoenergetic images facilitate discrimination of parathyroid lesions from thyroid tissue by significantly increasing thyroid attenuation and associated contrast-to-noise. These findings are particularly relevant for parathyroid lesions that exhibit isoattenuation to the thyroid on parathyroid CT arterial and venous phases and could, therefore, be missed without the noncontrast phase.

Image Quality of Virtual Monochromatic Reconstructions of Noncontrast CT on a Dual-Source CT Scanner in Adult Patients

RATIONALE AND OBJECTIVES

To evaluate the image quality of virtual monochromatic images (VMI) reconstructed from dual-energy dual-source noncontrast head CT with different reconstruction kernels.

MATERIALS AND METHODS

Twenty-five consecutive adult patients underwent noncontrast dual-energy CT. VMI were retrospectively reconstructed at 5-keV increments from 40 to 140 keV using quantitative and head kernels. CT-number, noise levels (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) in the gray and white matter and artifacts using the posterior fossa artifact index (PFAI) were evaluated.

RESULTS

CT-number increased with decreasing VMI energy levels, and SD was lowest at 85 keV. SNR was maximized at 80 keV and 85 keV for the head and quantitative kernels, respectively. CNR was maximum at 40 keV; PFAI was lowest at 90 (head kernel) and 100 (quantitative kernel) keV. Optimal VMI image quality was significantly better than conventional CT.

CONCLUSION

Optimal image quality of VMI energies can improve brain parenchymal image quality compared to conventional CT but are reconstruction kernel dependent and depend on indication for performing noncontrast CT.

Principles and Applications of Dual Energy Computed Tomography in Neuroradiology

Dual-energy computed tomography (DE CT) is a promising tool with many current and evolving applications. Available DE CT scanners usually consist of one or two tubes, or use layered detectors for spectral separation. Most DE CT scanners can be used in single energy or dual-energy mode, except for the layered detector scanners that always acquire data in dual-energy mode. However, the layered detector scanners can retrospectively integrate the data from two layers to obtain conventional single energy images. DE CT mode enables generation of virtual monochromatic images, blended images, iodine quantification, improving conspicuity of iodinated contrast enhancement, and material decomposition maps or more sophisticated quantitative analysis not possible with conventional SE CT acquisition with an acceptable or even lower dose than the SE CT. This article reviews the basic principles of dual-energy CT and highlights many of its clinical applications in the evaluation of neurological conditions.

Advantages of Colour-Coded Dual-Energy CT Venography in Emergency Neuroimaging

The objective of this Pictorial Review is to describe the use of colour-coded Dual-Energy CT (DECT) to aid in the interpretation of CT Venography (CTV) of the head for emergent indications. We describe a DE CTV acquisition and post-processing technique that can be readily incorporated into clinical workflow. Colour-coded DE CTV may aid the identification and characterization of dural venous sinus abnormalities and other cerebrovascular pathologies, which can improve diagnostic confidence in emergent imaging settings.

Diagnostic accuracy of dual-energy computed tomography to differentiate intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke: systematic review and meta-analysis

OBJECTIVES

To assess whether dual-energy computed tomography (DECT), using conventional computed tomography or magnetic resonance imaging as a reference standard, is sufficiently accurate to differentiate intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke.

METHODS

On January 20, 2021, we searched the PubMed Medline, Embase, Web of Science, and Cochrane Library databases. QUADAS-2 was used to assess the risk of bias and applicability. Meta-analyses were performed using a bivariate random-effects model. To explore sources of heterogeneity, meta-regression analyses were performed. Deeks' funnel plot asymmetry test was used to assess publication bias.

RESULTS

A total of 7 studies (269 patients, 269 focal areas) were included. The pooled mean sensitivity, specificity, and accuracy of DECT in identifying intracerebral hemorrhage from contrast extravasation after mechanical thrombectomy for acute ischemic stroke were 0.77 (95% confidence interval (CI) 0.29 to 0.96), 1 (95% CI 0.86 to 1), and 0.99 (95% CI 0.98 to 1), respectively. This evidence was of moderate certainty due to the risk of bias. Higgin's I-squared for study heterogeneity was observed for the pooled sensitivity (I² = 78.88%) and pooled specificity (I² = 82.12%). Moreover, Deeks' funnel plot asymmetry test revealed no publication bias (p = 0.38).

CONCLUSION

DECT shows excellent accuracy and specificity in differentiating intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke. Nevertheless, there was substantial and moderate heterogeneity among the studies. Future large-scale, prospective cohort studies are warranted to validate our findings.

KEY POINTS

• Dual-energy computed tomography shows excellent accuracy and specificity in differentiating intracerebral hemorrhage from contrast extravasation after endovascular thrombectomy for acute ischemic stroke. • Via meta-regression analysis, we found various possible covariates, including the publication date, image analysis, index test time, time of follow-up imaging, and reference standard judgment, that had an important effect on the heterogeneity. • There were no concerns regarding applicability in any of the included studies.

Initial experience with dual-layer detector spectral CT for diagnosis of blood or contrast after endovascular treatment for ischemic stroke

PURPOSE

To determine whether spectral detector CT (SDCT) with a plain non-enhanced monochromatic CT, a water-weighted image after iodine removal, an iodine map, and Mono energetic images changes the diagnosis and classification of intracranial hemorrhage based on single energy CT after endovascular treatment (EVT) for ischemic stroke.

METHODS

Two readers evaluated single energy and SD CT data collected from 63 patients within one week after EVT. They diagnosed ICH or contrast staining, and graded ICH according to the Heidelberg and Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST) classification. Differences in diagnosis between single energy and SD CT were tested with Pearson's chi-squared test. Diagnostic values of single energy CT were calculated. Interrater agreement was based on Cohen's Kappa.

RESULTS

When spectral data were added to single energy CT, the diagnosis of ICH changed in 8 CT scans (13%): in 4, the diagnosis of ICH was rejected and in 4, initially undetected ICH was diagnosed. In an additional 3 patients, the ICH grade was modified. CT alone had 88% sensitivity, 87% specificity, 88% positive diagnostic value, 87% negative diagnostic value, and 87% overall accuracy for ICH compared to SDCT. Interreader agreement on the presence of ICH was 0.84 (95% CI 0.51-0.86) for spectral CT and 0.84 (95% CI 0.73-0.97) for single energy CT.

CONCLUSION

SD CT after endovascular treatment contributes to the distinction between intracranial hemorrhage and contrast staining.

Dual-Energy CT Angiography Improves Accuracy of Spot Sign for Predicting Hematoma Expansion in Intracerebral Hemorrhage

Background and Purpose

Spot sign (SS) on computed tomography angiography (CTA) is associated with hematoma expansion (HE) and poor outcome after intracerebral hemorrhage (ICH). However, its predictive performance varies across studies, possibly because differentiating hyperdense hemorrhage from contrast media is difficult. We investigated whether dual-energy-CTA (DE-CTA), which can separate hemorrhage from iodinated contrast, improves the diagnostic accuracy of SS for predicting HE.

Methods

Primary ICH patients undergoing DE-CTA (both arterial as well as delayed venous phase) and follow-up computed tomography were prospectively included between 2014 and 2019. SS was assessed on both arterial and delayed phase images of the different DE-CTA datasets, i.e., conventional-like mixed images, iodine images, and fusion images. Diagnostic accuracy of SS for prediction of HE was determined on all datasets. The association between SS and HE, and between SS and poor outcome (modified Rankin Scale at 3 months ≥3) was assessed with multivariable logistic regression, using the dataset with highest diagnostic accuracy.

Results

Of 139 included patients, 47 showed HE (33.8%). Sensitivity of SS for HE was 32% (accuracy 0.72) on conventional-like mixed arterial images which increased to 76% (accuracy 0.80) on delayed fusion images. Presence of SS on delayed fusion images was independently associated with HE (odds ratio [OR], 17.5; 95% confidence interval [CI], 6.14 to 49.82) and poor outcome (OR, 3.84; 95% CI, 1.16 to 12.73).

Conclusions

Presence of SS on DE-CTA, in particular on delayed phase fusion images, demonstrates higher diagnostic performance in predicting HE compared to conventional-like mixed imaging, and it is associated with poor outcome.

The feasibility of dual-energy CT to predict the probability of symptomatic intracerebral haemorrhage after successful mechanical thrombectomy

AIM

To study the ability of dual-energy computed tomography (DECT) after successful mechanical thrombectomy (MT) to predict symptomatic intracerebral haemorrhage (sICH) in anterior circulation acute ischaemic stroke (AIS).

MATERIALS AND METHODS

From June 2018 to February 2020, 102 AIS patients with DECT performed immediately after successful MT were enrolled prospectively. According to the presence of iodine contrast media extravasation (ICME) on DECT and subsequent sICH development, patients were classified into four groups. The neurological outcome was compared among groups. Imaging parameters, together with clinical factors, were investigated for sICH prediction based on a linear logistic regression model after class-imbalance resolved by Synthetic Minority Sampling Technique (SMOTE) method.

RESULTS

Among 102 patients, patients (14.7%, 15/102) with the presence of sICH experienced worse outcomes than others without sICH (p<0.001). No case without ICME was observed with sICH development (0/102). The parameters derived from DECT have excellent performance for sICH prediction after successful MT, which is better than clinical predictive model boosted data (area under the curve [AUC]: DECT 0.87 versus clinical prediction 0.65), cross-validation results (AUC: DECT 0.87 versus clinical prediction 0.65), and original data (AUC: DECT 0.85 versus clinical prediction 0.68). By combining clinical and radiological parameters, the predictive performance for sICH could be further improved with an AUC of 0.90 (95% CI: 0.85-0.96).

CONCLUSIONS

Based on DECT parameters acquired immediately after successful MT, the present model was more efficient than the clinical model for accurate prediction of sICH. Rho and ICME volume appeared to be the best parameters for predicting sICH using DECT.

Dual-energy computed tomography in acute ischemic stroke: state-of-the-art

Abstract

Dual-energy computed tomography (DECT) allows distinguishing between tissues with similar X-ray attenuation but different atomic numbers. Recent studies demonstrated that this technique has several areas of application in patients with ischemic stroke and a potential impact on patient management. After endovascular stroke therapy (EST), hyperdense areas can represent either hemorrhage or contrast staining due to blood-brain barrier disruption, which can be differentiated reliably by DECT. Further applications are improved visualization of early infarctions, compared to single-energy computed tomography, and prediction of transformation into infarction or hemorrhage in contrast-enhancing areas. In addition, DECT allows detection and evaluation of the material composition of intra-arterial clots after EST. This review summarizes the clinical state-of-the-art of DECT in patients with stroke, and features some prospects for future developments.

Key points

• Dual-energy computed tomography (DECT) allows differentiation between tissues with similar X-ray attenuation but differentatomic numbers.

• DECT has several areas of application in patients with ischemic stroke and a potential impact on patient management.

• Prospects for future developments in DECT may improve treatment decision-making.

Radiation doses and image quality of abdominal CT scans at different patient sizes using spectral detector CT scanner: a phantom and clinical study

PURPOSE

To compare radiation dose and image quality for abdominal CTs performed on a spectral detector CT (SDCT) and a comparable single-energy conventional CT scanner for patients of different sizes.

METHODS

Four semi-anthropomorphic phantoms were scanned on an SDCT (IQon, Philips Healthcare) and a comparable single-energy CT (iCT 256, Philips Healthcare) under matched scan parameters. Image noise and radiation dose were compared. For the HIPAA-compliant, IRB-approved retrospective cohort patient study, radiation dose was compared after adjusting for patient water equivalent diameter. Difference in subjective and objective image quality was assessed on a subset of 50 patients scanned on both scanners by two readers.

RESULTS

CTDIvol and noise from SDCT were higher than conventional CT for all phantoms, with a relative difference of 7.8% (range 5.3-14%) for radiation dose and average difference of 9.0% (range 5.5-11%) for noise. 718 SDCT and 937 conventional CT patients were included in the patient study. CTDIvol for SDCT patients tends to be lower for smaller patients (- 2%, 95% confidence interval (- 5%, - 0.2%) for 200 mm water equivalent diameter) and higher for larger patients compared to conventional CT (8%, (6%, 11%) for 400 mm). No difference was seen for subjective image quality, SNR, CNR, or image noise between the two scanners, except for higher image noise in the portal vein and higher signal in the aorta on SDCT.

CONCLUSION

Radiation dose for abdominal CT performed on SDCT is similar to the dose on a conventional CT for average size patients, lower for smaller patients, and slightly higher for larger patients. Image quality is similar between the two scanners.

Principal Component Analysis in Projection and Image Domains-Another Form of Spectral Imaging in Photon-Counting CT

OBJECTIVE

We explore the feasibility of principal component analysis (PCA) as a form of spectral imaging in photon-counting CT.

METHODS

Using the data acquired by a prototype system and simulated by computer, we investigate the feasibility of spectral imaging in photon-counting CT via PCA for feature extraction and study the impacts made by data standardization and de-noising on its performance.

RESULTS

The PCA in the projection domain maintains the data consistence that is essential for tomographic image reconstruction and performs virtually the same as that in the image domain. The first three primary components account for more than 99.99% covariance of the data. Within anticipation, the contrast-to-noise ratio (CNR) between the target and background in the first principal component image can be larger than that in the image generated from the data acquired in each energy bin. More importantly, the CNR in the first principal component image may be larger than that in the image formed by the summed data acquired in all energy bins (i.e., the conventional polychromatic CT image). In addition, de-noising can not only reduce the noise in images but also improve the effectiveness/efficiency of PCA in feature extraction.

CONCLUSION

The PCA in either projection or image domain provides another form of spectral imaging in photon-counting CT that fits the essential requirements on spectral imaging in true color.

SIGNIFICANCE

The verification of PCA's feasibility in CT as a form spectral imaging and observation of its potential superiority in CNR over conventional polychromatic CT are meaningful in theory and practice.

Virtual monochromatic dual-energy CT reconstructions improve detection of cerebral infarct in patients with suspicion of stroke

Purpose

Early infarcts are hard to diagnose on non-contrast head CT. Dual-energy CT (DECT) may potentially increase infarct differentiation. The optimal DECT settings for differentiation were identified and evaluated.

Methods

One hundred and twenty-five consecutive patients who presented with suspected acute ischemic stroke (AIS) and underwent non-contrast DECT and subsequent DWI were retrospectively identified. The DWI was used as reference standard. First, virtual monochromatic images (VMI) of 25 patients were reconstructed from 40 to 140 keV and scored by two readers for acute infarct. Sensitivity, specificity, positive, and negative predictive values for infarct detection were compared and a subset of VMI energies were selected. Next, for a separate larger cohort of 100 suspected AIS patients, conventional non-contrast CT (NCT) and selected VMI were scored by two readers for the presence and location of infarct. The same statistics for infarct detection were calculated. Infarct location match was compared per vascular territory. Subgroup analyses were dichotomized by time from last-seen-well to CT imaging.

Results

A total of 80–90 keV VMI were marginally more sensitive (36.3–37.3%) than NCT (32.4%; p > 0.680), with marginally higher specificity (92.2–94.4 vs 91.1%; p > 0.509) for infarct detection. Location match was superior for VMI compared with NCT (28.7–27.4 vs 19.5%; p < 0.010). Within 4.5 h from last-seen-well, 80 keV VMI more accurately detected infarct (58.0 vs 54.0%) and localized infarcts (27.1 vs 11.9%; p = 0.004) than NCT, whereas after 4.5 h, 90 keV VMI was more accurate (69.3 vs 66.3%).

Conclusion

Non-contrast 80–90 keV VMI best differentiates normal from infarcted brain parenchyma.

Electronic supplementary material

The online version of this article (10.1007/s00234-020-02492-y) contains supplementary material, which is available to authorized users.

CT for Treatment Selection in Acute Ischemic Stroke: A Code Stroke Primer

CT is the primary imaging modality used for selecting appropriate treatment in patients with acute stroke. Awareness of the typical findings, pearls, and pitfalls of CT image interpretation is therefore critical for radiologists, stroke neurologists, and emergency department providers to make accurate and timely decisions regarding both (a) immediate treatment with intravenous tissue plasminogen activator up to 4.5 hours after a stroke at primary stroke centers and (b) transfer of patients with large-vessel occlusion (LVO) at CT angiography to comprehensive stroke centers for endovascular thrombectomy (EVT) up to 24 hours after a stroke. Since the DAWN and DEFUSE 3 trials demonstrated the efficacy of EVT up to 24 hours after last seen well, CT angiography has become the operational standard for rapid accurate identification of intracranial LVO. A systematic approach to CT angiographic image interpretation is necessary and useful for rapid triage, and understanding common stroke syndromes can help speed vessel evaluation. Moreover, when diffusion-weighted MRI is unavailable, multiphase CT angiography of collateral vessels and source-image assessment or perfusion CT can be used to help estimate core infarct volume. Both have the potential to allow distinction of patients likely to benefit from EVT from those unlikely to benefit. This article reviews CT-based workup of ischemic stroke for making tPA and EVT treatment decisions and focuses on practical skills, interpretation challenges, mimics, and pitfalls.^©RSNA, 2019.

Added value of color-coded virtual non-calcium dual-energy CT in the detection of acute knee fractures in non-radiology inexpert readers

PURPOSE

To evaluated the added value of dual-energy CT (DECT) virtual non-calcium (VNCa) protocol on conventional CT in the detection of acute knee fractures in non-radiology inexpert readers.

METHOD

One hundred fifty-six patients (mean age, 51.97 years; age range, 17-86 years) with knee trauma, who underwent DECT and MRI within 3 days between April 2017 and October 2018, were retrospectively analyzed. Three readers (intern, 1st-year general surgery resident, 1st-year emergency medicine resident) independently analyzed CT alone and then with the additional color-coded DECT VNCa for fractures. A board-certified radiologist, analyzed CT and MRI series to define the reference standard. Sensitivity, specificity, and AUC were compared between the two reading sessions.

RESULTS

Fifty-seven patients had acute fractures and 99 had no fractures. Thirteen of 57 fractures were nondisplaced. The additional use of VNCa images significantly increased the mean AUC (reader 1: 0.813 vs. 0.919; reader 2: 0.842 vs. 0.930; reader 3: 0.837 vs. 0.921; P < 0.05). When only nondisplaced fractures included, the mean AUC was more increased in the combined analysis of CT and DECT VNCa (reader 1: 0.521 vs. 0.916; reader 2: 0.542 vs. 0.926; reader 3: 0.575 vs. 0.926; P <  .01). Sensitivity increased by 15 %-20 % in total fracture group and by 69 %-77 % in nondisplaced fracture group over that with CT alone when both CT and DECT VNCa were used. Specificity did not differ significantly.

CONCLUSIONS

The additional use of color-coded DECT VNCa protocol to conventional CT improved diagnostic performance in detecting acute knee fractures for inexperienced non-radiology readers.

Dual energy CT in clinical routine: how it works and how it adds value

Dual energy computed tomography (DECT), also known as spectral CT, refers to advanced CT technology that separately acquires high and low energy X-ray data to enable material characterization applications for substances that exhibit different energy-dependent x-ray absorption behavior. DECT supports a variety of post-processing applications that add value in routine clinical CT imaging, including material selective and virtual non-contrast images using two- and three-material decomposition algorithms, virtual monoenergetic imaging, and other material characterization techniques. Following a review of acquisition and post-processing techniques, we present a case-based approach to highlight the added value of DECT in common clinical scenarios. These scenarios include improved lesion detection, improved lesion characterization, improved ease of interpretation, improved prognostication, inherently more robust imaging protocols to account for unexpected pathology or suboptimal contrast opacification, length of stay reduction, reduced utilization by avoiding unnecessary follow-up examinations, and radiation dose reduction. A brief discussion of post-processing workflow approaches, challenges, and solutions is also included.

Single-source dual-energy computed tomography for the detection of bone marrow lesions: impact of iterative reconstruction and algorithms

PURPOSE

To compare the diagnostic performance of different reconstruction algorithms of single-source dual-energy computed tomography (DECT) for the detection of bone marrow lesions (BML) in patients with vertebral compression fracture using MRI as the standard of reference.

MATERIAL AND METHODS

Seventeen patients with an age over 50 who underwent single-source DECT of the spine were included. The raw data (RD) were reconstructed using filtered back-projection (FBP) and iterative reconstruction (IR) with three iteration levels (IR1-IR3). Bone marrow images were generated using a three-material decomposition (3MD) and a two-material decomposition (2MD) algorithm and an RD-based approach. Three blinded readers scored the images for image quality and the presence of bone marrow lesions (BML). Only vertebrae with height loss were included. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The different reconstructions were compared using Dunn's multiple comparison test.

RESULTS

Thirty-nine vertebrae were included. IR(1-3) showed superior sensitivity (87.5%) compared to FBP (75%) using 3MD but was comparable to RD (83.3%). All 2MD images were inferior (sensitivity < 38%). The image quality score was significantly higher for 3MD-IR(1-3) compared to 3MD-FBP (p < 0.0001) and all 2MD data sets (p < 0.03). This pattern was also supported by the SNR and CNR measurements. RD showed no significant improvement compared to IR.

CONCLUSION

The image quality of bone marrow images acquired with DECT can be improved by using IR compared with FBP. RD-based reconstruction does not offer significant improvement over image data-based reconstruction. 2MD algorithms are not suitable for BML detection.

Dual energy CT: a step ahead in brain and spine imaging

OBJECTIVE

The purpose of this pictorial essay is to illustrate the utility of dual energy CT as an adjunct or alternative to routine single energy CT (SECT) scan of the brain and spine in emergency neuroradiology practice.

CONCLUSION

Dual energy CT can be used as a problem-solving tool in brain and spine imaging. It enables one to make a confident and accurate diagnosis for a variety of clinical conditions thereby impacting patient management.

Technical Principles of Dual-Energy Cone Beam Computed Tomography and Clinical Applications for Radiation Therapy

PURPOSE

Medical imaging is an indispensable tool in radiotherapy for dose planning, image guidance and treatment monitoring. Cone beam CT (CBCT) is a low dose imaging technique with high spatial resolution capability as a direct by-product of using flat-panel detectors. However, certain issues such as x-ray scatter, beam hardening and other artifacts limit its utility to the verification of patient positioning using image-guided radiotherapy.

METHODS AND MATERIALS

Dual-energy (DE)-CBCT has recently demonstrated promise as an improved tool for tumor visualization in benchtop applications. It has the potential to improve soft-tissue contrast and reduce artifacts caused by beam hardening and metal. In this review, the practical aspects of developing a DE-CBCT based clinical and technical workflow are presented based on existing DE-CBCT literature and concepts adapted from the well-established library of work in DE-CT. Furthermore, the potential applications of DE-CBCT on its future role in radiotherapy are discussed.

RESULTS AND CONCLUSIONS

Based on current literature and an investigation of future applications, there is a clear potential for DE-CBCT technologies to be incorporated into radiotherapy. The applications of DE-CBCT include (but are not limited to): adaptive radiotherapy, brachytherapy, proton therapy, radiomics and theranostics.

Dual-Energy CT to Differentiate Small Foci of Intracranial Hemorrhage from Calcium

Background Diagnostic uncertainty in CT of possible intracranial hemorrhage requires short-interval follow-up imaging, resulting in reduced efficiency of care and higher costs. Purpose To quantify the diagnostic performance of dual-energy CT versus simulated single-energy CT in the differentiation of small foci of intracranial hemorrhage from calcium. Materials and Methods Images from consecutive unenhanced dual-energy CT of the head in patients from a single emergency department obtained from December 2014 to April 2016 were reviewed retrospectively for hyperattenuating intracranial foci. Ground truth was established from reference standard comparison CT or MRI. Foci were divided into development and test sets. Development set foci regions of interest were used to derive candidate CT attenuation thresholds for virtual noncalcium (VNCa) and calcium images. Test set foci were used for threshold validation, and diagnostic performance and confidence were evaluated for two readers blinded to final diagnosis. Statistical comparisons were made with exact binomial tests or repeated-measures analysis of variance. Results The study included 137 patients (65 years ± 17; 70 men) with 146 foci. Foci were divided into a development set (n = 105) and a test set (n = 41). Quantitative analysis of the development set produced candidate thresholds of 44 HU for VNCa images and 7 HU for calcium-only images, yielding diagnostic accuracies for the test set of 88% (36 of 41 foci; 95% confidence interval [CI]: 78%, 98%) and 95% (39 of 41 foci; 95% CI: 88%, 100%), respectively. Dual-energy CT improved reader accuracy from 90% (reader 1, 37 of 41 foci; 95% CI: 81%, 99%) and 93% (reader 2, 38 of 41 foci; 95% CI: 85%, 100%) to 100% (both readers, 41 of 41 foci; 95% CI: 100%, 100%). Diagnostic confidence (classifications rated as "certain") increased from 71% (29 of 41 foci; 95% CI: 57%, 85%) to 90% (37 of 41 foci; 95% CI: 81%, 99%) for reader 1 (P = .019) and from 46% (19 of 41 foci; 95% CI: 31%, 62%) to 85% (35 of 41 foci; 95% CI: 75%, 96%) for reader 2 (P = .0001). Conclusion Dual-energy CT showed high diagnostic performance in the differentiation of small foci of intracranial hemorrhage from calcium and improved diagnostic accuracy and confidence in the initial evaluation of suspected hemorrhage. © RSNA, 2019 See also the editorial by Kotsenas in this issue.

Dual-Energy Computed Tomography Imaging of Head: Virtual High-Energy Monochromatic (190 keV) Images Are More Reliable Than Standard 120 kV Images for Detecting Traumatic Intracranial Hemorrhages

High-energy monochromatic (190 keV) images may be more reliable than standard 120 kV Images for detecting intracranial hemorrhages. We aimed to retrospectively compare virtual high monochromatic (190 keV) and standard 120 kV images from dual-energy computed tomography (CT; DECT) for the diagnosis of intracranial hemorrhages in traumatic brain injury (TBI). We analyzed admission CT studies in 100 trauma patients. Three radiologists independently reviewed four image sets: 120 kV and 190 keV (thin [1 mm] and thick [5 mm] section) images for the presence of various types of intracranial hemorrhages. The proportions of positive variables were compared and differences calculated by McNemar test and sensitivities determined by contingency tables. Randomly selected hemorrhagic lesions were analyzed for contrast index (CI). Thin-section 190 keV images were superior in the detection of subdural hematomas (SDH) (p < 0.0001), supratentorial contusions (p < 0.0001), and epidural hematomas (EDH) (p = 0.014), when compared with standard 120 kV images. However, 190 keV images were inferior to standard 120 kV images in diagnosis of subarachnoid hemorrhage (SAH) (thin-sections, p = 0.059; thick-sections, 0.0075). The 190 keV images yielded moderate increase in CI of contusions (Cohen's d > 0.53) and a large increase in CI of extra-axial hematomas (Cohen's d > 0.86). Our results indicate that virtual high monochromatic (190 keV, thin-section) images combined with standard 120 kV images may provide optimal diagnostic performance for evaluation of patients suspected of TBI.

Dual-layer spectral detector CT monoenergetic reconstruction improves image quality of non-contrast cerebral CT as compared with conventional single energy CT

PURPOSE

To investigate and compare image quality of monoenergetic reconstructions from spectral NCCT to conventional 120 kVp images acquired at a similar dose.

MATERIALS AND METHODS

Patients undergoing NCCT on a dual-layer spectral detector CT (n = 30) and a conventional CT (n = 30) were enrolled in the study. The spectral detector CT data was reconstructed at monoenergetic images from 40 to 140 keV in 5-keV increments and 65-70 keV in 1-keV increments (Group A1) and using single energy CT equivalent reconstruction (Group A2). The reference conventional 120kVp images (Group B) were acquired using a standard-of-care protocol with the same radiation dose. We evaluated the image quality of monoenergetic images and determined the optimal keV level using HU attenuation, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), artifact evaluation in posterior fossa by placing region-of-interest (ROI) and subjective image score by 2 radiologists independently using a 4-point scale (1-excellent, 4-undiagnostic).

RESULTS

The SNR and subjective image score were optimal at 66-70keV, while monoenergetic 68 keV images with a higher SNR (18.48 ± 1.94, 15.55 ± 1.56 and 14.33 ± 1.38 for Group 68keV, A2 and B respectively, p < 0.001), CNR (4.09 ± 0.65, 3.43 ± 0.56 and 3.52 ± 0.55 for Group 68keV, A2 and B respectively, p < 0.001) and a lower noise (1.80 ± 0.19, 2.11 ± 0.19 and 2.25 ± 0.25 for Group 68keV, A2 and B respectively, p < 0.001).

CONCLUSION

Spectral NCCT monoenergetic reconstructions at 68 keV improve image quality and reduce artifact compared to conventional single energy CT without radiation dose penalty.

Dual-Energy CT in Hemorrhagic Progression of Cerebral Contusion: Overestimation of Hematoma Volumes on Standard 120-kV Images and Rectification with Virtual High-Energy Monochromatic Images after Contrast-Enhanced Whole-Body Imaging

BACKGROUND AND PURPOSE

In patients with hemorrhagic contusions, hematoma volumes are overestimated on follow-up standard 120-kV images obtained after contrast-enhanced whole-body CT. We aimed to retrospectively determine hemorrhagic progression of contusion rates on 120-kV and 190-keV images derived from dual-energy CT and the magnitude of hematoma volume overestimation.

MATERIALS AND METHODS

We retrospectively analyzed admission and follow-up CT studies in 40 patients with hemorrhagic contusions. After annotating the contusions, we measured volumes from admission and follow-up 120-kV and 190-keV images using semiautomated 3D segmentation. Bland-Altman analysis was used for hematoma volume comparison.

RESULTS

On 120-kV images, hemorrhagic progression of contusions was detected in 24 of the 40 patients, while only 17 patients had hemorrhagic progression of contusions on 190-keV images (P = .008). Hematoma volumes were systematically overestimated on follow-up 120-kV images (9.68 versus 8 mm³; mean difference, 1.68 mm³; standard error, 0.37; P < .001) compared with 190-keV images. There was no significant difference in volumes between admission 120-kV and 190-keV images. Mean and median percentages of overestimation were 29% (95% CI, 18-39) and 22% (quartile 3 - quartile 1 = 36.8), respectively.

CONCLUSIONS

The 120-kV images, which are comparable with single-energy CT images, significantly overestimated the hematoma volumes, hence the rate of hemorrhagic progression of contusions, after contrast-enhanced whole-body CT. Hence, follow-up of hemorrhagic contusions should be performed on dual-energy CT, and 190-keV images should be used for the assessment of hematoma volumes.

Dual-Energy CT in Enhancing Subdural Effusions that Masquerade as Subdural Hematomas: Diagnosis with Virtual High-Monochromatic (190-keV) Images

BACKGROUND AND PURPOSE

Extravasation of iodinated contrast into subdural space following contrast-enhanced radiographic studies results in hyperdense subdural effusions, which can be mistaken as acute subdural hematomas on follow-up noncontrast head CTs. Our aim was to identify the factors associated with contrast-enhancing subdural effusion, characterize diffusion and washout kinetics of iodine in enhancing subdural effusion, and assess the utility of dual-energy CT in differentiating enhancing subdural effusion from subdural hematoma.

MATERIALS AND METHODS

We retrospectively analyzed follow-up head dual-energy CT studies in 423 patients with polytrauma who had undergone contrast-enhanced whole-body CT. Twenty-four patients with enhancing subdural effusion composed the study group, and 24 randomly selected patients with subdural hematoma were enrolled in the comparison group. Postprocessing with syngo.via was performed to determine the diffusion and washout kinetics of iodine. The sensitivity and specificity of dual-energy CT for the diagnosis of enhancing subdural effusion were determined with 120-kV, virtual monochromatic energy (190-keV) and virtual noncontrast images.

RESULTS

Patients with enhancing subdural effusion were significantly older (mean, 69 years; 95% CI, 60-78 years; P < .001) and had a higher incidence of intracranial hemorrhage (P = .001). Peak iodine concentration in enhancing subdural effusions was reached within the first 8 hours of contrast administration with a mean of 0.98 mg/mL (95% CI, 0.81-1.13 mg/mL), and complete washout was achieved at 38 hours. For the presence of a hyperdense subdural collection on 120-kV images with a loss of hyperattenuation on 190-keV and virtual noncontrast images, when considered as a true-positive for enhancing subdural effusion, the sensitivity was 100% (95% CI, 85.75%-100%) and the specificity was 91.67% (95% CI, 73%-99%).

CONCLUSIONS

Dual-energy CT has a high sensitivity and specificity in differentiating enhancing subdural effusion from subdural hematoma. Hence, dual-energy CT has a potential to obviate follow-up studies.