Utility of Dual-Energy Computed Tomography in Clinical Conundra

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

Dual-Energy Computed Tomography in Cardiac Imaging

Dual-energy computed tomography (DECT) acquires images using two energy spectra and offers a variation of reconstruction techniques for improved cardiac imaging. Virtual monoenergetic images decrease artifacts improving coronary plaque and stent visualization. Further, contrast attenuation is increased allowing significant reduction of contrast dose. Virtual non-contrast reconstructions enable coronary artery calcium scoring from contrast-enhanced scans. DECT provides advanced plaque imaging with detailed analysis of plaque components, indicating plaque stability. Extracellular volume assessment using DECT offers noninvasive detection of myocardial fibrosis. This review aims to outline the current cardiac applications of DECT, summarize recent literature, and discuss their findings.

Non-Contrast and Contrast-Enhanced Cardiac Computed Tomography Imaging in the Diagnostic and Prognostic Evaluation of Coronary Artery Disease

In recent decades, cardiac computed tomography (CT) has emerged as a powerful non-invasive tool for risk stratification, as well as the detection and characterization of coronary artery disease (CAD), which remains the main cause of morbidity and mortality in the world. Advances in technology have favored the increasing use of cardiac CT by allowing better performance with lower radiation doses. Coronary artery calcium, as assessed by non-contrast CT, is considered to be the best marker of subclinical atherosclerosis, and its use is recommended for the refinement of risk assessment in low-to-intermediate risk individuals. In addition, coronary CT angiography (CCTA) has become a gate-keeper to invasive coronary angiography (ICA) and revascularization in patients with acute chest pain by allowing the assessment not only of the extent of lumen stenosis, but also of its hemodynamic significance if combined with the measurement of fractional flow reserve or perfusion imaging. Moreover, CCTA provides a unique incremental value over functional testing and ICA by imaging the vessel wall, thus allowing the assessment of plaque burden, composition, and instability features, in addition to perivascular adipose tissue attenuation, which is a marker of vascular inflammation. There exists the potential to identify the non-obstructive lesions at high risk of progression to plaque rupture by combining all of these measures.

High-pitch, high temporal resolution, multi-energy cardiac imaging on a dual-source photon-counting-detector CT

OBJECTIVE

To measure the accuracy of material decomposition using a dual-source photon-counting-detector (DS-PCD) CT operated in the high-pitch helical scanning mode and compare the results against dual-source energy-integrating-detector (DS-EID) CT, which requires use of a low-pitch value in dual-energy mode.

METHODS

A DS-PCD CT and a DS-EID CT were used to scan a cardiac motion phantom consisting of a 3-mm diameter iodine cylinder. Iodine maps were reconstructed using DS-PCD in high-pitch mode and DS-EID in low-pitch mode. Image-based circularity, diameter, and iodine concentration of the iodine cylinder were calculated and compared between the two scanners. With institutional review board approval, in vivo exams were performed with the DS-PCD CT in high-pitch mode. Images were qualitatively compared against patients with similar heart rates that were scanned with DS-EID CT in low-pitch dual-energy mode.

RESULTS

On iodine maps, the mean circularity was 0.97 ± 0.02 with DS-PCD in high-pitch mode and 0.95 ± 0.06 with DS-EID in low-pitch mode. The mean diameter was 2.9 ± 0.2 mm with DS-PCD and 3.1 ± 0.2 mm with DS-EID, both of which are close to the 3 mm ground truth. For DS-PCD, the mean iodine concentration was 9.6 ± 0.8 mg/ml and this was consistent with the 9.4 ± 0.6 mg/ml value obtained with the cardiac motion disabled. For DS-EID, the concentration was 12.7 ± 1.2 mg/ml with motion enabled and 11.7 ± 0.5 mg/ml disabled. The background noise in the iodine maps was 15.1 HU with DS-PCD and 14.4 HU with DS-EID, whereas the volume CT dose index (CTDIvol ) was 3 mGy with DS-PCD and 11 mGy with DS-EID. On comparison of six patients (three on PCD, three on EID) with similar heart rates, DS-PCD provided iodine maps with well-defined coronaries even at a high heart rate of 86 beats per minute. Meanwhile, there were substantial motion artifacts in iodine maps obtained with DS-EID for patients with similar heart rates.

CONCLUSION

In a cardiac motion phantom, DS-PCD CT can perform accurate material decomposition in high-pitch mode, providing iodine maps with excellent geometric accuracy and robustness to motion at approximately 38% of the dose for similar noise as DS-EID CT.

Dual-Energy CT of the Heart: A Review

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

Dual-Energy Imaging of the Chest

Dual-energy computed tomography (DECT) is a contemporary development by which the tissue can be characterized beyond conventional computed tomography. It improves tissue differentiation by exploiting the X-ray absorptive property of the tissues. Although still in its early stages, DECT utilization in pulmonary and cardiovascular pathologies is emerging. It includes applications such as pulmonary embolism, pulmonary hypertension, myocardial perfusion, and coronary artery assessment. This article discusses DECT principles and their current and emerging applications in thoracic imaging.

Narrative review of cardiac computed tomography perfusion: insights into static rest perfusion

Cardiac or left ventricular perfusion performed with cardiac computed tomography (CCT) is a developing method that may have the potential to complete in a very straight forward way the assessment of ischemic heart disease by means of CT. Myocardial CT perfusion (CTP) can be achieved with a single static scan during the first-pass of the iodinate contrast agent, with the monoenergetic or dual-energy acquisition, or as a dynamic, time-resolved scan during stress by using coronary vasodilator agents. Several methods can be performed, and we focused on static perfusion. CTP may serve as a useful adjunct to coronary CT angiography (CTA) to improve specificity of detecting myocardial ischemia. Technological advances will reduce the radiation dose of myocardial CTP, such as low tube voltage imaging or new reconstruction algorithms, making it a more viable clinical option. The advantages of static first-pass non-stress perfusion are several; the main one is that it can be done to each and every patient who undergoes CCT for the assessment of coronary artery tree. Future advances in CTP will likely improve the diagnostic accuracy of CTP + CTA, and will better estimate the severity of ischemia Therefore, it is simple and comprehensive. However, it has several limitations. In this review we will discuss the technique with its advantages and limitations.

[Possibilities of Stress Computed Tomography Myocardial Perfusion Imaging in the Diagnosis of Ischemic Heart Disease]

Computed tomography angiography (CT-angiography, CTA) allows noninvasive visualization of coronary arteries (CA). This method is highly sensitive in detecting coronary atherosclerosis. However, standard CTA does not allow evaluation of the hemodynamic significance of found CA stenoses, which requires additional functional tests for detection of myocardial ischemia. This review focuses on possibilities of clinical use, limitations, technical aspects, and prospects of a combination of CT-angiography and CT myocardial perfusion imaging in diagnostics of ischemic heart disease.

Functional cardiac CT-Going beyond Anatomical Evaluation of Coronary Artery Disease with Cine CT, CT-FFR, CT Perfusion and Machine Learning

The aim of this review is to provide an overview of different functional cardiac CT techniques which can be used to supplement assessment of the coronary arteries to establish the significance of coronary artery stenoses. We focus on cine-CT, CT-FFR, CT-myocardial perfusion and how developments in machine learning can supplement these techniques.

Role of DECT in coronary artery disease: a comparative study with ICA and SPECT

PURPOSE

Earlier imaging techniques for coronary artery disease (CAD) focused primarily on either morphological or functional assessment of CAD. However, dual-energy computed tomography (DECT) can be used to assess myocardial blood supply both morphologically and functionally. We aimed to evaluate the diagnostic accuracy of DECT in detecting morphological and functional components of CAD, using invasive coronary angiography (ICA) and single photon emission computed tomography (SPECT) as reference standards.

METHODS

Twenty-five patients with known or suspicious CAD and scheduled for ICA were investigated by DECT and SPECT. DECT was performed during the resting state using retrospective electrocardiography (ECG) gating. CT coronary angiography and perfusion images were generated from the same raw data. All patients were evaluated for significant stenosis (≥50%) on both ICA and DECT coronary angiography, and for myocardial perfusion defects on SPECT and DECT perfusion. Comparison was done between ICA and DECT coronary angiography for detection of significant stenosis and between SPECT and DECT perfusion for detecting myocardial perfusion defects.

RESULTS

Using ICA as reference standard, sensitivity, specificity, and accuracy of DECT coronary angiography in detecting ≥50% stenosis of coronary artery lumen were 81.6%, 97.8%, and 95.0%, respectively, by segment-based analysis and 92.1%, 96.1%, and 93.7%, respectively, by vessel-based analysis. Using SPECT as the reference standard, the sensitivity, specificity, and accuracy of DECT perfusion in detecting myocardial perfusion defects were 70.4%, 86.4%, and 80.6%, respectively, on per-segment analysis and 90.7%, 66.6%, and 84.7%, respectively, on per-territorial basis.

CONCLUSION

DECT accurately detected coronary artery stenosis and myocardial ischemia using ICA and SPECT as reference standards. In the same scan, DECT can accurately provide integrative imaging of coronary artery morphology and myocardial perfusion.

Computed tomography for myocardial characterization in ischemic heart disease: a state-of-the-art review

This review provides an overview of the currently available computed tomography (CT) techniques for myocardial tissue characterization in ischemic heart disease, including CT perfusion and late iodine enhancement. CT myocardial perfusion imaging can be performed with static and dynamic protocols for the detection of ischemia and infarction using either single- or dual-energy CT modes. Late iodine enhancement may be used for the analysis of myocardial infarction. The accuracy of these CT techniques is highly dependent on the imaging protocol, including acquisition timing and contrast administration. Additionally, the options for qualitative and quantitative analysis and the accuracy of each technique are discussed.

Dual-Energy Computed Tomography in Cardiothoracic Vascular Imaging

Dual energy computed tomography is becoming increasingly widespread in clinical practice. It can expand on the traditional density-based data achievable with single energy computed tomography by adding novel applications to help reach a more accurate diagnosis. The implementation of this technology in cardiothoracic vascular imaging allows for improved image contrast, metal artifact reduction, generation of virtual unenhanced images, virtual calcium subtraction techniques, cardiac and pulmonary perfusion evaluation, and plaque characterization. The improved diagnostic performance afforded by dual energy computed tomography is not associated with an increased radiation dose. This review provides an overview of dual energy computed tomography cardiothoracic vascular applications.

Clinical Impact of Rest Dual-energy Computed Tomography Myocardial Perfusion in Patients with Coronary Artery Disease

BACKGROUND/AIM

To evaluate the hypothesis that patients with suspected coronary artery disease (CAD) assessed using rest dual-energy computed tomography-derived myocardial perfusion imaging (DECT-P), could have fewer invasive coronary angiographies (ICA), showing non-obstructive CAD.

MATERIALS AND METHODS

Patients who had undergone coronary computed tomography angiography (cCTA), rest DECT-P and ICA were analyzed.

RESULTS

We evaluated 51 patients (62.7% males, mean age 51.6±12.8 years). Rest DECT-P identified perfusion defects in three (10.7%) of the 28 patients with cCTA negative for luminal stenosis and in 10 (43.5%) of the 23 patients with cCTA positive for luminal stenosis. In total, 21 patients underwent both cCTA and ICA, of which seven (33.3%) showed obstructive CAD. Rest DECT-P revealed false-negative results in four cases (19.1%) and false-positive results in six cases (28.6%).

CONCLUSION

Adding rest DECT-P to cCTA has no incremental diagnostic value over cCTA alone, to exclude haemodynamically significant CAD. Therefore, a rest-stress-DECT-P protocol or a CT-based FFR calculation might be a promising concept to improve diagnostic accuracy in a real clinical setting.

Dual-energy CT of the heart current and future status

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

Functional Information in Coronary Artery Disease: The Case of Computed Tomography Myocardial Perfusion

PURPOSE OF REVIEW

To review methodological and logistical aspects of CT myocardial perfusion, current clinical evidence and possible future directions, with specific focus on use in patients with coronary artery disease (CAD).

RECENT FINDINGS

CT myocardial perfusion imaging may be performed as an add-on to standard coronary CT angiography (CCTA), to identify regions of myocardial hypoperfusion, at rest and during adenosine stress. The principle of measurement is well-validated in animal experimental models, and CT myocardial perfusion imaging has a high degree of concordance with already clinically available perfusion imaging methods. Combining CCTA and CT myocardial perfusion imaging increases the diagnostic accuracy to identify patients with CAD associated with ischemia. In patients suspected of CAD, CCTA frequently detects coronary atherosclerotic lesions, in which revascularization could be clinically beneficial. CT myocardial perfusion imaging may be helpful to identify coronary lesions associated with myocardial ischemia, and thus potentially suitable for coronary intervention.

Myocardial ischemia testing with computed tomography: emerging strategies

Although cardiac computed tomography (CT) has high negative predictive value to exclude obstructive coronary artery disease (CAD), particularly in the low to intermediate risk population, it has low specificity in the diagnosis of ischemia-inducing lesions. This inability to predict hemodynamically significant stenosis hampers the ability of CT to be an effective gatekeeper for invasive angiography and to guide appropriate revascularization. Recent advances in CT technology have resulted in the development of multiple techniques to provide hemodynamic information and detect lesion-specific ischemia, namely CT perfusion (CTP), CT-derived fractional flow reserve (CT-FFR) and coronary transluminal attenuation gradient (TAG). In this article, we provide a perspective on these emerging CT techniques in the evaluation of myocardial ischemia.

Improved Discrimination of Myocardial Perfusion Defects at Low Energy Levels Using Virtual Monochromatic Imaging

OBJECTIVES

The aim of this study was to explore the diagnostic performance of dual-energy computed tomography perfusion (DE-CTP) at different energy levels.

METHODS

Patients with known or suspected coronary artery disease underwent stress and rest DE-CTP and single-photon emission computed tomography. Images were evaluated using monochromatic data, and perfusion defects were initially identified in a qualitative manner and subsequently confirmed using attenuation levels.

RESULTS

Thirty-six patients were included. Sensitivity, specificity, positive predictive value, and negative predictive value of DE-CTP for the identification of perfusion defects were 84.1%, 94.2%, 77.3%, and 96.2%, respectively. Perfusion defects showed significantly lower attenuation than normal segments, with the largest differences among low energy levels (sensitivity of 96% and specificity of 98% using a cutoff value ≤ 153 Hounsfield units at 40 keV), progressively declining at the higher levels (P < 0.001).

CONCLUSIONS

Dual-energy CTP at the lowest energy levels allowed improved discrimination of perfusion defects compared with higher energy levels.

Myocardial CT perfusion imaging for ischemia detection

Coronary computed tomography angiography (CCTA) plays an important role in many specific scenarios such as in symptomatic patients with intermediate pretest of coronary artery disease (CAD), as well as in the triage of patients with acute chest pain with TIMI risk ≤2. However, it cannot detect the presence of associated ischemia, which is critical for clinical decision making among patients with moderate to severe stenosis. Although functional information can be obtained with different non-invasive tools, cardiac CT is the unique modality that can perform a comprehensive evaluation of coronary anatomy plus the functional significance of lesions. Myocardial CT perfusion (CTP) can be performed with different approaches such as static and dynamic CTP. In addition, static CTP can be performed using single energy CT (SECT) or dual energy CT (DECT). In this review, we will discuss the technical parameters and the available clinical evidence of static CTP using both SECT and DECT.

Delayed enhancement cardiac computed tomography for the assessment of myocardial infarction: from bench to bedside

A large number of studies support the increasingly relevant prognostic value of the presence and extent of delayed enhancement (DE), a surrogate marker of fibrosis, in diverse etiologies. Gadolinium and iodinated based contrast agents share similar kinetics, thus leading to comparable myocardial characterization with cardiac magnetic resonance (CMR) and cardiac computed tomography (CT) at both first-pass perfusion and DE imaging. We review the available evidence of DE imaging for the assessment of myocardial infarction (MI) using cardiac CT (CTDE), from animal to clinical studies, and from 16-slice CT to dual-energy CT systems (DECT). Although both CMR and gadolinium agents have been originally deemed innocuous, a number of concerns (though inconclusive and very rare) have been recently issued regarding safety issues, including DNA double-strand breaks related to CMR, and gadolinium-associated nephrogenic systemic fibrosis and deposition in the skin and certain brain structures. These concerns have to be considered in the context of non-negligible rates of claustrophobia, increasing rates of patients with implantable cardiac devices, and a number of logistic drawbacks compared with CTDE, such as higher costs, longer scanning times, and difficulties to scan patients with impaired breath-holding capabilities. Overall, these issues might encourage the role of CTDE as an alternative for DE-CMR in selected populations.

Static and dynamic assessment of myocardial perfusion by computed tomography

Recent developments in computed tomography (CT) technology have fulfilled the prerequisites for the clinical application of myocardial CT perfusion (CTP) imaging. The evaluation of myocardial perfusion by CT can be achieved by static or dynamic scan acquisitions. Although both approaches have proved clinically feasible, substantial barriers need to be overcome before its routine clinical application. The current review provides an outline of the current status of CTP imaging and also focuses on disparities between static and dynamic CTPs for the evaluation of myocardial blood flow.

Dual-Energy Computed Tomography: Advantages in the Acute Setting

The aim of this article is to inform and update emergency radiologists in respect of the clinically relevant benefits that dual-energy computed tomography (CT) contributes over conventional single-energy CT in the emergency setting using practical imaging examples. Particular emphasis will be placed on acute gout, bone marrow edema, acute renal colic, acute cardiovascular and neurovascular emergencies aswell as characterization of abdominal incidentalomas. The relevant scientific literature will be summarized and limitations of the technique also will be emphasized to provide the reader with a rounded concept of the current state of technology.

Technical prerequisites and imaging protocols for dynamic and dual energy myocardial perfusion imaging

Coronary CT angiography (CCTA) is an established imaging technique used for the non-invasive morphological assessment of coronary artery disease. As in invasive coronary angiography, CCTA anatomical assessment of coronary stenosis does not adequately predict hemodynamic relevance. However, recent technical improvements provide the possibility of CT myocardial perfusion imaging (CTMPI). Two distinct CT techniques are currently available for myocardial perfusion assessment: static CT myocardial perfusion imaging (sCTMPI), with single- or dual-energy modality, and dynamic CT myocardial perfusion imaging (dCTMPI). The combination of CCTA morphological assessment and CTMPI functional evaluation holds promise for achieving a comprehensive assessment of coronary artery anatomy and myocardial perfusion using a single image modality.

Beyond stenosis detection: computed tomography approaches for determining the functional relevance of coronary artery disease

Coronary computed tomography angiography (CCTA) is an established imaging technique for the noninvasive assessment of coronary arteries. However, CCTA remains a morphologic technique with the same limitations as invasive coronary angiography in evaluating the hemodynamic significance of coronary stenosis. Different computed tomography (CT) techniques for the functional analysis of coronary lesions have recently emerged, including static and dynamic CT myocardial perfusion imaging and CT-based fractional flow reserve and transluminal attenuation gradient methods. These techniques hold promise for achieving a comprehensive appraisal of anatomic and functional aspects of coronary heart disease with a single modality.