Detection of Hemodynamically Significant Coronary Artery Stenosis: Incremental Diagnostic Value of Dynamic CT-based Myocardial Perfusion Imaging

Personalized coronary and myocardial blood flow models incorporating CT perfusion imaging and synthetic vascular trees

Computational simulations of coronary artery blood flow, using anatomical models based on clinical imaging, are an emerging non-invasive tool for personalized treatment planning. However, current simulations contend with two related challenges - incomplete anatomies in image-based models due to the exclusion of arteries smaller than the imaging resolution, and the lack of personalized flow distributions informed by patient-specific imaging. We introduce a data-enabled, personalized and multi-scale flow simulation framework spanning large coronary arteries to myocardial microvasculature. It includes image-based coronary anatomies combined with synthetic vasculature for arteries below the imaging resolution, myocardial blood flow simulated using Darcy models, and systemic circulation represented as lumped-parameter networks. We propose an optimization-based method to personalize multiscale coronary flow simulations by assimilating clinical CT myocardial perfusion imaging and cardiac function measurements to yield patient-specific flow distributions and model parameters. Using this proof-of-concept study on a cohort of six patients, we reveal substantial differences in flow distributions and clinical diagnosis metrics between the proposed personalized framework and empirical methods based purely on anatomy; these errors cannot be predicted a priori. This suggests virtual treatment planning tools would benefit from increased personalization informed by emerging imaging methods.

Imaging biomarkers in cardiac CT: moving beyond simple coronary anatomical assessment

Cardiac computed tomography angiography (CCTA) is considered the standard non-invasive tool to rule-out obstructive coronary artery disease (CAD). Moreover, several imaging biomarkers have been developed on cardiac-CT imaging to assess global CAD severity and atherosclerotic burden, including coronary calcium scoring, the segment involvement score, segment stenosis score and the Leaman-score. Myocardial perfusion imaging enables the diagnosis of myocardial ischemia and microvascular damage, and the CT-based fractional flow reserve quantification allows to evaluate non-invasively hemodynamic impact of the coronary stenosis. The texture and density of the epicardial and perivascular adipose tissue, the hypodense plaque burden, the radiomic phenotyping of coronary plaques or the fat radiomic profile are novel CT imaging features emerging as biomarkers of inflammation and plaque instability, which may implement the risk stratification strategies. The ability to perform myocardial tissue characterization by extracellular volume fraction and radiomic features appears promising in predicting arrhythmogenic risk and cardiovascular events. New imaging biomarkers are expanding the potential of cardiac CT for phenotyping the individual profile of CAD involvement and opening new frontiers for the practice of more personalized medicine.

Evaluation of stable angina by coronary computed tomographic angiography versus standard of care: A systematic review and meta-analysis

INTRODUCTION

There is limited data comparing Coronary Computed Tomography Angiography (CCTA) versus the usual Standard of care (SOC) in patients with suspected stable coronary artery disease (CAD). We aimed to perform a systematic review and meta-analysis to compare CCTA versus SOC in patients with stable CAD.

METHODS

We searched multiple databases for randomized controlled trials (RCTs) comparing CCTA with SOC, which included various functional testing approaches for evaluating stable CAD. We used a random-effects model to calculate risk ratios (RRs) with 95 % confidence intervals (CIs). Outcomes included all-cause mortality, myocardial infarction (MI), hospitalization for unstable angina (UA), invasive angiography, revascularization, percutaneous coronary intervention (PCI), and coronary artery bypass grafting (CABG).

RESULTS

We identified 6 RCTs with 19,881 patients with stable CAD, of which 9995 underwent CCTA, and 9886 underwent SOC. There were no significant differences between CCTA and SOC in terms of all-cause mortality (RR: 0.91; 95 % CI: 0.70-1.19; p = 0.50), MI (RR: 0.78; 95 % CI: 0.58-1.05; p = 0.11), hospitalizations for UA (RR: 1.20; 95 % CI: 0.95-1.51;p = 0.12), invasive angiography (RR: 0.71; 95 % CI: 0.32-1.61; p = 0.42), revascularization (RR:1.25; 95 % CI: 0.83-1.89; p = 0.29), PCI (RR: 1.20; 95 % CI: 0.78-1.85; p = 0.40), and CABG rates (RR: 0.89; 95 % CI: 0.530-1.49; p = 0.65).

CONCLUSION

In patients with stable CAD, CCTA is associated with similar outcomes compared to the usual Standard of care. Given its potential to quickly rule out severe obstructive disease, its ability to provide non-invasive physiology and identify non-obstructive CAD with plaque information makes it an attractive addition to the available armamentarium to evaluate chest pain.

Dynamic CT Myocardial Perfusion: The Role of Functional Evaluation in the Diagnosis of Coronary Artery Disease

Coronary computed tomography angiography (CTA) is a widely accepted, non-invasive diagnostic modality for the evaluation of patients with suspected coronary artery disease (CAD). However, a limitation of CTA is its inability to provide information on the hemodynamic significance of the coronary lesion. The recently developed stress dynamic CT perfusion technique has emerged as a potential solution to this diagnostic challenge. Dynamic CT myocardial perfusion provides information on the hemodynamic consequences of coronary stenosis and is used to detect myocardial ischemia. The combination of stress dynamic CT myocardial perfusion with CTA provides a comprehensive assessment that integrates anatomical and functional information. CT myocardial perfusion has been validated in several clinical studies and has shown comparable accuracy to Positron Emission Tomography (PET) and stress magnetic resonance imaging (MRI) in the diagnosis of hemodynamically significant coronary stenosis and superior performance to Single Photon Emission Computed Tomography (SPECT). More importantly, CTP-derived myocardial perfusion has been shown to have a strong correlation with FFR, and the use of CTP results in a reduction of negative catheterizations. In the context of suspected stable coronary artery disease, the CT protocol with dynamic perfusion imaging combined with CTA eliminates the need for additional testing, making it a convenient "one-stop-shop" method and an effective gatekeeper to an invasive approach.

Personalized coronary and myocardial blood flow models incorporating CT perfusion imaging and synthetic vascular trees

Computational simulations of coronary artery blood flow, using anatomical models based on clinical imaging, are an emerging non-invasive tool for personalized treatment planning. However, current simulations contend with two related challenges - incomplete anatomies in image-based models due to the exclusion of arteries smaller than the imaging resolution, and the lack of personalized flow distributions informed by patient-specific imaging. We introduce a data-enabled, personalized and multi-scale flow simulation framework spanning large coronary arteries to myocardial microvasculature. It includes image-based coronary models combined with synthetic vasculature for arteries below the imaging resolution, myocardial blood flow simulated using Darcy models, and systemic circulation represented as lumped-parameter networks. Personalized flow distributions and model parameters are informed by clinical CT myocardial perfusion imaging and cardiac function using surrogate-based optimization. We reveal substantial differences in flow distributions and clinical diagnosis metrics between the proposed personalized framework and empirical methods based on anatomy; these errors cannot be predicted a priori. This suggests virtual treatment planning tools would benefit from increased personalization informed by emerging imaging methods.

Comprehensive Computed Tomography Imaging of Vessel-specific and Lesion-specific Myocardial Ischemia

Coronary computed tomographic angiography (CCTA) has emerged as a fast and robust tool with high sensitivity and excellent negative predictive value for the evaluation of coronary artery disease, but is unable to estimate the hemodynamic significance of a lesion. Advances in computed tomography (CT)-based diagnostic techniques, for example, CT-derived fractional flow reserve and CT perfusion, have helped transform CCTA primarily from an anatomic assessment tool to a technique that is able to provide both anatomic and functional information for a stenosis. With the results of the ISCHEMIA trial published in 2019, these advanced techniques can elevate CCTA into the role of a better gatekeeper for decision-making and can help guide referral for invasive management. In this article, we review the principles, limitations, diagnostic performance, and clinical utility of these 2 functional CT-based techniques in the evaluation of vessel-specific and lesion-specific ischemia.

Adenosine vs. regadenoson for stress induction in dynamic CT perfusion scan of the myocardium: A single‑center retrospective comparison

Cardiac computed tomography (CT) angiography offers several approaches to determine the hemodynamic severity of coronary artery obstruction. Dynamic myocardial perfusion is based on serial CT imaging of contrast flow into the myocardium and calculation of absolute myocardial perfusion rates. East-Slovak Institute of Cardiovascular Diseases has been the first center in Slovakia intensively using this modern technique to increase the quality level of non-invasive diagnosis of symptomatic patients with a low to moderate pre-test probability of ischemic heart disease. The present study included 46 patients with a mean age of 64 years (33 men and 13 women). Prior to the CT study, myocardial stress was pharmacologically (adenosine, n=15 and regadenoson, n=31) induced by vasodilatation of the coronary arteries. Hemodynamic parameters (myocardial blood flow) were evaluated in all patients following successful CT perfusion without complications, allergic reaction or other severe side effects. The present study revealed that regadenoson increased the heart rate following infusion with a higher magnitude compared with adenosine. Moreover, the effect of regadenoson was independent of patient's body mass index and was associated with a lower incidence of mild adverse effects. The present study provided further clinical evidence for a more wider use of regadenoson over adenosine.

A Novel CT Perfusion-Based Fractional Flow Reserve Algorithm for Detecting Coronary Artery Disease

Background: The diagnostic accuracy of fractional flow reserve (FFR) derived from coronary computed tomography angiography (CCTA) (FFR-CT) needs to be further improved despite promising results available in the literature. While an innovative myocardial computed tomographic perfusion (CTP)-derived fractional flow reserve (CTP-FFR) model has been initially established, the feasibility of CTP-FFR to detect coronary artery ischemia in patients with suspected coronary artery disease (CAD) has not been proven. Methods: This retrospective study included 93 patients (a total of 103 vessels) who received CCTA and CTP for suspected CAD. Invasive coronary angiography (ICA) was performed within 2 weeks after CCTA and CTP. CTP-FFR, CCTA (stenosis ≥ 50% and ≥70%), ICA, FFR-CT and CTP were assessed by independent laboratory experts. The diagnostic ability of the CTP-FFR grouped by quantitative coronary angiography (QCA) in mild (30–49%), moderate (50–69%) and severe stenosis (≥70%) was calculated. The effect of calcification of lesions, grouped by FFR on CTP-FFR measurements, was also assessed. Results: On the basis of per-vessel level, the AUCs for CTP-FFR, CTP, FFR-CT and CCTA were 0.953, 0.876, 0.873 and 0.830, respectively (all p < 0.001). The sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) of CTP-FFR for per-vessel level were 0.87, 0.88, 0.87, 0.85 and 0.89 respectively, compared with 0.87, 0.54, 0.69, 0.61, 0.83 and 0.75, 0.73, 0.74, 0.70, 0.77 for CCTA ≥ 50% and ≥70% stenosis, respectively. On the basis of per-vessel analysis, CTP-FFR had higher specificity, accuracy and AUC compared with CCTA and also higher AUC compared with FFR-CT or CTP (all p < 0.05). The sensitivity and accuracy of CTP-FFR + CTP + FFR-CT were also improved over FFR-CT alone (both p < 0.05). It also had improved specificity compared with FFR-CT or CTP alone (p < 0.01). A strong correlation between CTP-FFR and invasive FFR values was found on per-vessel analysis (Pearson’s correlation coefficient 0.89). The specificity of CTP-FFR was higher in the severe calcification group than in the low calcification group (p < 0.001). Conclusions: A novel CTP-FFR model has promising value to detect myocardial ischemia in CAD, particularly in mild-to-moderate stenotic lesions.

One-stop patient-specific myocardial blood flow quantification technique based on allometric scaling law

Establishing a patient-specific and non-invasive technique to derive blood flow as well as coronary structural information from one single cardiac CT imaging modality. 336 patients with chest pain or ST segment depression on electrocardiogram were retrospectively enrolled. All patients underwent adenosine-stressed dynamic CT myocardial perfusion imaging (CT-MPI) and coronary computed tomography angiography (CCTA) in sequence. Relationship between myocardial mass (M) and blood flow (Q), defined as log(Q) = b · log(M) + log(Q₀), was explored based on the general allometric scaling law. We used 267 patients to obtain the regression results and found strong linear relationship between M (gram) and Q (mL/min) (b = 0.786, log(Q₀) = 0.546, r = 0.704; p < 0.001). We Also found this correlation was applicable for patients with either normal or abnormal myocardial perfusion (p < 0.001). Datasets from the other 69 patients were used to validate this M-Q correlation and found the patient-specific blood flow could be accurately estimated from CCTA compared to that measured from CT-MPI (146.480 ± 39.607 vs 137.967 ± 36.227, r = 0.816, and 146.480 ± 39.607 vs 137.967 ± 36.227, r = 0.817, for the left ventricle region and LAD-subtended region, respectively, all unit in mL/min). In conclusion, we established a technique to provide general and patient-specific myocardial mass-blood flow correlation obeyed to allometric scaling law. Blood flow information could be directly derived from structural information acquired from CCTA.

Perspectives in noninvasive imaging for chronic coronary syndromes

Both the latest European guidelines on chronic coronary syndromes and the American guidelines on chest pain have underlined the importance of noninvasive imaging to select patients to be referred to invasive angiography. Nevertheless, although coronary stenosis has long been considered the main determinant of inducible ischemia and symptoms, growing evidence has demonstrated the importance of other underlying mechanisms (e.g., vasospasm, microvascular disease, energetic inefficiency). The search for a pathophysiology-driven treatment of these patients has therefore emerged as an important objective of multimodality imaging, integrating "anatomical" and "functional" information. We here provide an up-to-date guide for the choice and the interpretation of the currently available noninvasive anatomical and/or functional tests, focusing on emerging techniques (e.g., coronary flow velocity reserve, stress-cardiac magnetic resonance, hybrid imaging, functional-coronary computed tomography angiography, etc.), which could provide deeper pathophysiological insights to refine diagnostic and therapeutic pathways in the next future.

Improved Functional Assessment of Ischemic Severity Using 3D Printed Models

Objective

To develop a novel in vitro method for evaluating coronary artery ischemia using a combination of non-invasive coronary CT angiograms (CCTA) and 3D printing (FFR_3D).

Methods

Twenty eight patients with varying degrees of coronary artery disease who underwent non-invasive CCTA scans and invasive fractional flow reserve (FFR) of their epicardial coronary arteries were included in this study. Coronary arteries were segmented and reconstructed from CCTA scans using Mimics (Materialize). The segmented models were then 3D printed using a Carbon M1 3D printer with urethane methacrylate (UMA) family of rigid resins. Physiological coronary circulation was modeled in vitro as flow-dependent stenosis resistance in series with variable downstream resistance. A range of physiological flow rates (Q) were applied using a peristaltic steady flow pump and titrated with a flow sensor. The pressure drop (ΔP) and the pressure ratio (P_d/P_a) were assessed for patient-specific aortic pressure (P_a) and differing flow rates (Q) to evaluate FFR_3D using the 3D printed model.

Results

There was a good positive correlation (r = 0.87, p < 0.0001) between FFR_3D and invasive FFR. Bland-Altman analysis revealed a good concordance between the FFR_3D and invasive FFR values with a mean bias of 0.02 (limits of agreement: −0.14 to 0.18; p = 0.2).

Conclusions

3D printed patient-specific models can be used in a non-invasive in vitro environment to quantify coronary artery ischemia with good correlation and concordance to that of invasive FFR.

A Novel Quantitative Parameter for Static Myocardial Computed Tomography: Myocardial Perfusion Ratio to the Aorta

We evaluated the feasibility of myocardial perfusion ratio to the aorta (MPR) in static computed tomography perfusion (CTP) for detecting myocardial perfusion abnormalities assessed by single-photon emission computed tomography (SPECT). Twenty-five patients with suspected coronary artery disease who underwent dynamic CTP and SPECT were retrospectively evaluated. CTP images scanned at a sub-optimal phase for detecting myocardial perfusion abnormalities were selected from dynamic CTP images and used as static CTP images in the present study. The diagnostic accuracy of MPR derived from static CTP was compared to those of visual assessment and conventional quantitative parameters such as myocardial CT attenuation (HU) and transmural perfusion ratio (TPR). The area under the curve of MPR (0.84; 95% confidence interval [CI], 0.76−0.90) was significantly higher than those of myocardial CT attenuation (0.73; 95% CI, 0.65−0.79) and TPR (0.76; 95% CI, 0.67−0.83) (p < 0.05). Sensitivity and specificity were 67% (95% CI, 54−77%) and 90% (95% CI, 86−92%) for visual assessment, 51% (95% CI, 39−63%) and 86% (95% CI, 82−89%) for myocardial CT attenuation, 63% (95% CI, 51−74%) and 84% (95% CI, 80−88%) for TPR, and 78% (95% CI, 66−86%) and 84% (95% CI, 80−88%) for MPR, respectively. MPR showed higher diagnostic accuracy for detecting myocardial perfusion abnormality compared with myocardial CT attenuation and TPR.

Knowledge of Hyperemic Myocardial Blood Flow in Healthy Subjects Helps Identify Myocardial Ischemia in Patients With Coronary Artery Disease

Backgrounds

Dynamic CT myocardial perfusion imaging (CT-MPI) allows absolute quantification of myocardial blood flow (MBF). Although appealing, CT-MPI has not yet been widely applied in clinical practice, partly due to our relatively limited knowledge of CT-MPI. Knowledge of distribution and variability of MBF in healthy subjects helps in recognition of physiological and pathological states of coronary artery disease (CAD).

Objectives

To describe the distribution and normal range of hyperemic MBF in healthy subjects obtained by dynamic CT-MPI and validate whether it can accurately identify functional myocardial ischemia when the cut-off value of hyperemia MBF is set to the lower limit of the normal range.

Materials and Methods

Fifty-one healthy volunteers (age, 38 ± 12 years; 15 men) were prospectively recruited. Eighty patients (age, 58 ± 10 years; 55 men) with suspected or known CAD who underwent interventional coronary angiography (ICA) examinations were retrospectively recruited. Comprehensive CCTA + dynamic CT-MPI protocol was performed by the third – generation dual-source CT scanner. Invasive fractional flow reserve (FFR) measurements were performed in vessels with 30–90% diameter reduction. ICA/FFR was used as the reference standard for diagnosing functional ischemia. The normal range for the hyperemic MBF were defined as the mean ± 1.96 SD. The cut-off value of hyperemic MBF was set to the lower limit of the normal range.

Results

The global hyperemic MBF were 164 ± 24 ml/100 ml/min and 123 ± 26 ml/100 ml/min for healthy participants and patients. The normal range of the hyperemic MBF was 116–211 ml/100 ml/min. Of vessels with an ICA/FFR result (n = 198), 67 (34%) were functionally significant. In the per-vessel analysis, an MBF cutoff value of <116 ml/100 ml/min can identify myocardial ischemia with a diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of 85.9% (170/198), 91.0% (61/67), 83.2 % (109/131), 73.5% (61/83), and 94.8% (109/115). CT-MPI showed good consistency with ICA/FFR in diagnosing functional ischemia, with a Cohen's kappa statistic of 0.7016 (95%CI, 0.6009 – 0.8023).

Conclusion

Recognizing hyperemic MBF in healthy subjects helps better understand myocardial ischemia in CAD patients.

Diagnostic Performance of Dynamic Myocardial Perfusion Imaging Using Dual-Source Computed Tomography

BACKGROUND

Single-center studies indicated a high diagnostic accuracy of dynamic computed tomography perfusion (CTP) imaging in the diagnosis of coronary artery disease (CAD).

OBJECTIVES

This prospective multicenter study determined the diagnostic performance of combined coronary computed tomography angiography (CTA) and CTP for detecting hemodynamically significant CAD defined by invasive coronary angiography (ICA) with fractional flow reserve (FFR).

METHODS

Seven centers enrolled 174 patients with suspected or known CAD who were clinically referred for ICA. CTA and dynamic CTP were performed using dual-source CT before ICA. FFR was done as part of ICA in the case of 26% to 90% coronary diameter stenosis. Hemodynamically significant stenosis was defined as FFR of <0.8 or >90% stenosis on ICA.

RESULTS

The study protocol was completed in 157 participants, and hemodynamically significant stenosis was detected in 76 of 157 patients (48%) and 112 of 442 vessels (25%). According to receiver-operating characteristic curve analysis, adding dynamic CTP to CTA significantly increased the area under the curve from 0.65 (95% CI: 0.57-0.72) to 0.74 (95% CI: 0.66-0.81; P = 0.011) on the patient level, with decreased sensitivity (93% vs 72%; P < 0.001), improved specificity (36% vs 75%; P < 0.001), and improved overall accuracy (64% vs 74%; P < 0.001).

CONCLUSIONS

In this prospective multicenter study on dynamic CTP, the combination of anatomic assessment with coronary CTA and functional evaluation with dynamic CTP allowed more accurate identification of hemodynamically significant CAD compared with CTA alone. However, the clinical significance of this approach needs to be further investigated, including its usefulness in improving prognosis. (Assessment of Myocardial Perfusion Linked to Infarction and Fibrosis Explored With Dual-Source CT [AMPLIFiED]; UMIN000016353).

Hyperemic myocardial blood flow in patients with atrial fibrillation before and after catheter ablation: A dynamic stress CT perfusion study

BACKGROUND

Atrial fibrillation (AF) patients without coronary artery stenosis often show clinical evidence of ischemia. However myocardial perfusion in AF patients has been poorly studied. The purposes of this study were to investigate altered hyperemic myocardial blood flow (MBF) in patients with AF compared with risk-matched controls in sinus rhythm (SR), and to evaluate hyperemic MBF before and after catheter ablation using dynamic CT perfusion.

METHODS

Hyperemic MBF was quantified in 87 patients with AF (44 paroxysmal, 43 persistent) scheduled for catheter ablation using dynamic CT perfusion, and compared with hyperemic MBF in 87 risk-matched controls in SR. Follow-up CT after ablation was performed in 49 AF patients.

RESULTS

Prior to ablation, hyperemic MBF of patients in AF during the CT (1.29 ± 0.34 ml/mg/min) was significantly lower than in patients in SR (1.49 ± 0.26 ml/g/min, p = 0.002) or matched controls (1.65 ± 0.32 ml/g/min, p < 0.001); no significant difference was seen between patients in SR during the CT and matched controls (vs. 1.50 ± 0.31 ml/g/min, p = 0.815). In patients in AF during the pre-ablation CT (n = 24), hyperemic MBF significantly increased after ablation from 1.30 ± 0.35 to 1.53 ± 0.17 ml/g/min (p = 0.004); whereas in patients in SR during the pre-ablation CT (n = 25), hyperemic MBF did not change significantly after ablation (from 1.46 ± 0.26 to 1.49 ± 0.27 ml/g/min, p = 0.499).

CONCLUSION

In the current study using stress perfusion CT, hyperemic MBF in patients with AF during pre-ablation CT was significantly lower than that in risk-matched controls, and improved significantly after restoration of SR by catheter ablation, indicating that MBF abnormalities in AF patients are caused primarily by AF itself.

Clinical Validation of the Accuracy of Absolute Myocardial Blood Flow Quantification with Dual-Source CT Using 15O-Water PET

PURPOSE

To determine the fitting equation that can correct for the underestimation of myocardial blood flow (MBF) measurement by using dynamic CT perfusion (CTP) with dual-source CT (MBFCT), using MBF with oxygen 15-labeled water (15O-water) PET (MBFPET) as a reference, and to determine the accuracy of corrected MBFCT (MBFCT-corrected) compared with MBFPET in a separate set of participants.

MATERIALS AND METHODS

In this prospective study (reference no. 2466), 34 participants (mean age, 70 years ± 8 [standard deviation]; 27 men) known or suspected to have coronary artery disease underwent dynamic stress CTP and stress 15O-water PET between January 2014 and December 2018. The participants were randomly assigned to either a pilot group (n = 17), to determine the fitting equation on the basis of the generalized Renkin-Crone model that can explain the relation between MBFCT and MBFPET, or to a validation group (n = 17), to validate MBFCT-corrected compared with MBFPET. The agreement between MBFCT-corrected and MBFPET was evaluated by intraclass correlation and Bland-Altman analysis.

RESULTS

In the pilot group, MBFCT was lower than MBFPET (1.24 mL/min/g ± 0.28 vs 2.51 mL/min/g ± 0.89, P < .001) at the segment level. The relationship between MBFCT and MBFCT-corrected was represented as MBFCT = MBFCT-corrected × {1-exp[-(0.11 × MBFCT-corrected + 1.54)/MBFCT-corrected]}. In the validation group, MBFCT-corrected was 2.66 mL/min/g ± 1.93, and MBFPET was 2.68 mL/min/g ± 1.87 at the vessel level. MBFCT-corrected showed an excellent agreement with MBFPET (intraclass correlation coefficient = 0.93 [95% CI: 0.87, 0.96]). The measurement bias of MBFCT-corrected and MBFPET was -0.02 mL/min/g ± 0.74.

CONCLUSION

Underestimation of MBF by CT was successfully corrected with a correction method that was based on contrast kinetics in the myocardium.Keywords: CT, CT-Perfusion, PET, Cardiac, Heart Supplemental material is available for this article. © RSNA, 2021.

A Novel Computed Tomography-Based Imaging Approach for Etiology Evaluation in Patients With Acute Coronary Syndrome and Non-obstructive Coronary Angiography

Objective: This study sought to investigate the diagnostic value of dynamic CT myocardial perfusion imaging (CT-MPI) combined with coronary CT angiography (CCTA) in acute coronary syndrome (ACS) patients without obstructive coronary angiography. Methods: Consecutive ACS patients with normal or non-obstructive coronary angiography findings who had cardiac magnetic resonance (CMR) contraindications or inability to cooperate with CMR examinations were prospectively enrolled and referred for dynamic CT-MPI + CCTA + late iodine enhancement (LIE). ACS etiology was determined according to combined assessment of coronary vasculature by CCTA, quantified myocardial blood flow (MBF) and presence of LIE. Results: Twenty two patients were included in the final analysis. CCTA revealed two cases of side branch occlusion and one case of intramural hematoma which were overlooked by invasive angiography. High risk plaques were observed in 6 (27.3%) patients whereas myocardial ischemia was presented in 19 (86.4%) patients with varied extent and severity. LIE was positive in 13 (59.1%) patients and microvascular obstruction was presented in three cases with side branch occlusion or spontaneous intramural hematoma. The specific etiology was identified in 20 (90.9%) patients, of which the most common cause was cardiomyopathies (41%), followed by microvascular dysfunction (14%) and plaque disruption (14%). Conclusion: Dynamic CT-MPI + CCTA was able to reveal the potential etiologies in majority of patients with ACS and non-obstructive coronary angiography. It may be a useful alternative to CMR for accurate etiology evaluation.

Dynamic Myocardial Perfusion CT for the Detection of Hemodynamically Significant Coronary Artery Disease

OBJECTIVES

In this international, multicenter study, using third-generation dual-source computed tomography (CT), we investigated the diagnostic performance of dynamic stress CT myocardial perfusion imaging (CT-MPI) in addition to coronary CT angiography (CTA) compared to invasive coronary angiography (ICA) and invasive fractional flow reserve (FFR).

BACKGROUND

CT-MPI combined with coronary CTA integrates coronary artery anatomy with inducible myocardial ischemia, showing promising results for the diagnosis of hemodynamically significant coronary artery disease in single-center studies.

METHODS

At 9 centers in Europe, Japan, and the United States, 132 patients scheduled for ICA were enrolled; 114 patients successfully completed coronary CTA, adenosine-stress dynamic CT-MPI, and ICA. Invasive FFR was performed in vessels with 25% to 90% stenosis. Data were analyzed by independent core laboratories. For the primary analysis, for each coronary artery the presence of hemodynamically significant obstruction was interpreted by coronary CTA with CT-MPI compared to coronary CTA alone, using an FFR of ≤0.80 and angiographic severity as reference. Territorial absolute myocardial blood flow (MBF) and relative MBF were compared using C-statistics.

RESULTS

ICA and FFR identified hemodynamically significant stenoses in 74 of 289 coronary vessels (26%). Coronary CTA with ≥50% stenosis demonstrated a per-vessel sensitivity, specificity, and accuracy for the detection of hemodynamically significant stenosis of 96% (95% CI: 91–100), 72% (95% CI: 66–78), and 78% (95% CI: 73–83), respectively. Coronary CTA with CT-MPI showed a lower sensitivity (84%; 95% CI: 75–92) but higher specificity (89%; 95% CI: 85–93) and accuracy (88%; 95% CI: 84–92). The areas under the receiver-operating characteristic curve of absolute MBF and relative MBF were 0.79 (95% CI: 0.71–0.86) and 0.82 (95% CI: 0.74–0.88), respectively. The median dose-length product of CT-MPI and coronary CTA were 313 mGy·cm and 138 mGy·cm, respectively.

CONCLUSIONS

Dynamic CT-MPI offers incremental diagnostic value over coronary CTA alone for the identification of hemodynamically significant coronary artery disease. Generalized results from this multicenter study encourage broader consideration of dynamic CT-MPI in clinical practice. (Dynamic Stress Perfusion CT for Detection of Inducible Myocardial Ischemia [SPECIFIC]; NCT02810795)

Spatio-temporal multi-task network cascade for accurate assessment of cardiac CT perfusion

The assessment of myocardial perfusion has become increasingly important in the early diagnosis of coronary artery disease. Currently, the process of perfusion assessment is time-consuming and subjective. Although automated methods by threshold processing have been proposed, they cannot obtain an accurate perfusion assessment. Thus, there is a great clinical demand to obtain a rapid and accurate assessment of myocardial perfusion through a standard procedure using an automated algorithm. In this work, we present a spatio-temporal multi-task network cascade (ST-MNC) to provide an accurate and robust assessment of myocardial perfusion. The proposed network captures patch-based spatio-temporal representations for each pixel through a spatio-temporal encoder-decoder network. Then the multi-task network cascade uses spatio-temporal representations as shared features to predict various perfusion parameters and myocardial ischemic regions. Extensive experiments on CT images of 232 subjects demonstrate ST-MNC could produce a good approximation for perfusion parameters and an accurate classification for ischemic regions. These results show that our proposed method can provide a fast and accurate assessment of myocardial perfusion.

CT Assessment of Myocardial Perfusion and Fractional Flow Reserve in Coronary Artery Disease: A Review of Current Clinical Evidence and Recent Developments

Coronary computed tomography angiography (CCTA) is routinely used for anatomical assessment of coronary artery disease (CAD). However, invasive measurement of fractional flow reserve (FFR) is the current gold standard for the diagnosis of hemodynamically significant CAD. CT-derived FFRCT and CT perfusion are two emerging techniques that can provide a functional assessment of CAD for risk stratification and clinical decision making. Several clinical studies have shown that the diagnostic performance of concomitant CCTA and functional CT assessment for detecting hemodynamically significant CAD is at least non-inferior to that of other routinely used imaging modalities. This article aims to review the current clinical evidence and recent developments in functional CT techniques.

Motion compensation combining with local low rank regularization for low dose dynamic CT myocardial perfusion reconstruction

Dynamic CT myocardial perfusion imaging (DCT-MPI) is a reliable examination tool for the assessment of myocardium and vascular, while its special scan protocol may result in excessive radiation exposure to patients and inevitable inter-frame motion. Lowering the tube current is a simple way to reduce radiation exposure. However, low mAs will certainly cause severe image noise, thus may further impact the accuracy of functional hemodynamic parameters, which are used for the assessment of blood supply. In this work, we present a novel scheme applying motion compensation and local low rank regularization (MC-LLR) for obtaining high quality motion compensated DCT-MPI images. Specifically, motion compensation by using robust data decomposition registration (RDDR) was introduced. Robust principal component analysis coupled with optical flow-based registration algorithm were used in RDDR. Then, the local low rank constraint on the motion compensated time series images was applied for the DCT-MPI reconstruction. One healthy mini pig and two patient datasets were used to evaluate the proposed MC-LLR algorithm. Results show that the present method achieved satisfactory image quality with higher CNRs, smaller rRMSEs, and more accurate hemodynamic parameter maps.

Myocardial perfusion imaging using computed tomography: Current status, clinical value and prognostic implications

Combined anatomical and functional evaluation of coronary artery disease (CAD) using computed tomography (CT) has recently emerged as an accurate, robust, and non-invasive tool for the evaluation of ischemic heart disease. Cardiac CT has become a one-stop-shop imaging modality that allows the simultaneous depiction, characterization, and quantification of coronary atherosclerosis and the assessment of myocardial ischemia. Advancements in scanner technology (improvements in spatial and temporal resolution, dual-energy imaging, wide detector panels) and the implementation of iterative reconstruction algorithms enables the detection of myocardial ischemia in both qualitative and quantitative fashion using low-dose scanning protocols. The addition of CT perfusion (CTP) to standard coronary CT angiography is a reliable tool to improve diagnostic accuracy. CTP using static first-pass imaging enables qualitative assessment of the myocardial tissue, whereas dynamic perfusion imaging can also provide quantitative information on myocardial blood flow. Myocardial tissue assessment by CTP holds the potential to refine risk in stable chest pain or microvascular dysfunction. CTP can aid the detection of residual ischemia after coronary intervention. Comprehensive evaluation of CAD using CTP might therefore improve the selection of patients for aggressive secondary prevention therapy or coronary revascularization with high diagnostic certainty. In addition, prognostic information provided by perfusion CT imaging could improve patient outcomes by quantifying the ischemic burden of the left ventricle. The current review focuses on the clinical value of myocardial perfusion imaging by CT, current status of CTP imaging and the use of myocardial CTP in various patient populations for the diagnosis of ischemic heart disease.

Temporal feature prior-aided separated reconstruction method for low-dose dynamic myocardial perfusion computed tomography

Dynamic myocardial perfusion computed tomography (DMP-CT) is an effective medical imaging technique for coronary artery disease diagnosis and therapy guidance. However, the radiation dose received by the patient during repeated CT scans is a widespread concern of radiologists because of the increased risk of cancer. The sparse few-view CT scanning protocol can be a feasible approach to reduce the radiation dose of DMP-CT imaging; however, an advanced reconstruction algorithm is needed. In this paper, a temporal feature prior-aided separated reconstruction method (TFP-SR) for low-dose DMP-CT images reconstruction from sparse few-view sinograms is proposed. To implement the proposed method, the objective perfusion image is divided into the baseline fraction and the enhancement fraction introduced by the arrival of the contrast agent. The core of the proposed TFP-SR method is the utilization of the temporal evolution information that naturally exists in the DMP-CT image sequence to aid the enhancement image reconstruction from limited data. The temporal feature vector of an image pixel is defined by the intensities of this pixel in the pre-reconstructed enhancement sequence, and the connection between two related features is calculated via a zero-mean Gaussian function. A prior matrix is constructed based on the connections between the extracted temporal features and used in the iterative reconstruction of the enhancement images. To evaluate the proposed method, the conventional filtered back-projection algorithm, the total variation regularized PWLS (PWLS-TV) and the prior image constrained compressed sensing are compared in this paper based on studies on a digital extended cardiac-torso (XCAT) thoracic phantom and a preclinical porcine DMP-CT data set that take image misregistration into account. The experimental results demonstrate that the proposed TFP-SR method has superior performance in sparse DMP-CT images reconstruction in terms of image quality and the analyses of the time attenuation curve and hemodynamic parameters.

The Incremental Role of Coronary Computed Tomography in Chronic Coronary Syndromes

In the context of chronic coronary syndromes (CCS), coronary computed tomography angiography (CCTA) has gained broad acceptance as a noninvasive anatomical imaging tool with ability of excluding coronary stenosis with strong negative predictive value. Atherosclerotic plaque lesions are independent predictors of cardiovascular outcomes in high risk patients with known coronary artery disease (CAD). Calcium detection is commonly expressed through the coronary artery calcium score (CACS), but further research is warranted to confirm the powerness of a CACS-only strategy in both diagnosis and prognosis assessment. Recent studies evidence how defined plaque composition characteristics effectively relate to the risk of plaque instabilization and the overall ischemic burden. Fractional flow reserve from CCTA (FFR-CT) has been demonstrated as a reliable method for noninvasive functional evaluation of coronary lesions severity, while the assessment of perfusion imaging under stress conditions is growing as a useful tool for assessment of myocardial ischemia. Moreover, specific applications in procedural planning of transcatheter valve substitution and follow-up of heart transplantation have gained recent importance. This review illustrates the incremental role of CCTA, which can potentially revolutionize the diagnosis and management pathway within the wide clinical spectrum of CCS.

Cardiac CT perfusion and FFRCTA: pathophysiological features in ischemic heart disease

Cardiac computed tomography (CCT) has rapidly evolved, becoming a powerful integrated tool for the evaluation of coronary artery disease (CAD), and being superior to other noninvasive methods due to its high accuracy and ability to simultaneously assess both lumen stenosis and atherosclerotic plaque burden. Furthermore, CCT is regarded as an effective gatekeeper for coronary angiography, and carries independent important prognostic information. In the last decade, the introduction of new functional CCT applications, namely CCT perfusion (CCTP) imaging and CT-derived fractional flow reserve (FFR_CTA), has opened the door for accurate assessment of the haemodynamic significance of stenoses. These new CCT technologies, thus, share the unique advantage of assessing both myocardial ischemia and patient-specific coronary artery anatomy, providing an integrated anatomical/functional analysis. In the present review, starting from the pathophysiology of myocardial ischemia, we evaluate the existing evidence for functional CCT imaging and its value in relation to alternative, well-established, non-invasive imaging modalities and invasive indices of ischemia (currently the gold-standard). The knowledge of clinical applications, benefits, and limitations of these new CCT technologies will allow efficient and optimal use in clinical practice in the near future.

Stent evaluation by coronary computed tomography angiography: a comparison between Iopamidol-370 and Ioversol-320 hypo-osmolar iodine concentration contrasts

OBJECTIVE

Qualitative and quantitative image analysis between Iopamidol-370 and Ioversol-320 in stents´ evaluation by coronary computed tomography angiography (CTA).

METHODS

Sixty-five patients with low-risk stable angina undergoing stent follow-up with coronary CTA were assigned to Iopamidol I-370 (n = 33) or Ioversol I-320 (n = 32) in this prospective, double-blind, non-inferiority, randomized trial. Stent lumen image quality was graded by 5-point Likert Scale. Lumen mean attenuation was measured at native coronary segments: pre-stent, post-stent, distal segments and at coronary plaques. Lumen attenuation increase (LAI) ratio was calculated for all stents. Heart rate (HR) variation, premature heart beats (PHB), heat sensation (HS), blooming and beam hardening were also assessed.

RESULTS

Image quality was similar between groups, with no significant difference (Likert score 4.48 ± 0.75 vs 4.54 ± 0.65, p = 0.5). There were similarities in LAI ratio between I-370 and I-320 (0.39 ± 0.42 vs 0.48 ± 0.44 HU, p = 0.08). Regarding lumen mean attenuation at native coronary segments, a significant difference was observed, with I-320 presenting lower values, including contrast mean attenuation in distal segments. After statistical multivariate analysis, three variables correlated with stent image quality: 1) stent diameter, 2) HR variation and 3) stent lumen LAI ratio.

CONCLUSIONS

There was no significant difference between Iopamidol-370 mgI ml^-1 and Ioversol-320 mgI ml^-1 contrasts regarding overall stent lumen image quality, which was mainly influenced by stent diameter, HR and LAI ratio.Advances in knowledge:Coronary CTA allows adequate stents' visualization and image quality is influenced by stent diameter, HR variation and LAI ratio.Stents' image quality showed no difference between different concentration contrasts (I-370 vs. I-320); however, higher concentration contrasts may provide an improved overall visualization, especially regarding coronary distal segments.

CCTA in the diagnosis of coronary artery disease

The world of cardiac imaging is proposing to physicians an ever-increasing spectrum of options and tools with the disadvantages of patients presently submitted to multiple, sequential, time-consuming, and costly diagnostic procedures and tests, sometimes with contradicting results. In the last two decades, the CCTA has evolved into a valuable diagnostic test in today's patient care, changing the official existing guidelines and clinical practice with a pivotal role to exclude significant CAD, in the referral of patients to the Cath-Lab, in the follow-up after coronary revascularization, and finally in the cardiovascular risk stratification.

Diagnostic performance of quantitative, semi-quantitative, and visual analysis of dynamic CT myocardial perfusion imaging: a validation study with invasive fractional flow reserve

OBJECTIVES

To investigate the diagnostic performance of absolute myocardial blood flow (MBF), MBF_ratio, and visual analysis of dynamic CT myocardial perfusion imaging (CT-MPI) for the detection of hemodynamically significant coronary stenosis.

METHODS

Consecutive patients with chest pain and intermediate-to-high pre-test probability of obstructive coronary artery disease were prospectively enrolled. All patients were referred for dynamic CT-MPI and fractional flow reserve (FFR) measurements within 4 weeks. Absolute MBF, MBF_ratio (mean MBF of stenosis-subtended territories versus that of reference territories), and visually identified perfusion defect were tested for the diagnostic performance with reference to FFR.

RESULTS

Sixty-two patients with 95 target vessels were included for final analysis. The mean radiation dose for dynamic CT-MPI was 3.0 (2.2-4.0) mSv. The mean lesion-based absolute MBF value was significantly lower in ischemic segments than that in non-ischemic segments (78.0 (65.0-86.0) mL/min/100 mL vs. 133.0 (117.5-163.8) mL/min/100 mL, p < 0.001). Similarly, the lesion-based MBF_ratio was also markedly lower in territories with positive FFR results (0.52 (0.44-0.64) vs. 0.93 (0.91-0.97), p < 0.001). According to per-lesion ROC curve analysis, MBF and MBF_ratio had a similar area under the curve (AUC) for detecting hemodynamically significant lesions (AUC = 0.942 vs. 0.956, p = 0.413), which were larger than that of visual analysis (AUC = 0.802, both p < 0.01). The vessel-based sensitivity, specificity, and diagnostic accuracy were 84.3%, 97.7%, and 90.5% for MBF and 96.1%, 93.2%, and 94.7% for MBF_ratio.

CONCLUSIONS

Absolute MBF and MBF_ratio had similarly excellent diagnostic performance with reference to FFR. In addition, these two parameters outperformed visual analysis for the detection of myocardial ischemia.

KEY POINTS

• The mean MBF and MBF_ratio were significantly lower in ischemic segments than those in non-ischemic segments. • Absolute MBF and MBF_ratio had similar AUCs for the detection of hemodynamically significant lesions (AUC = 0.942 vs. 0.956, p = 0.413), which were larger than that of visual analysis (AUC = 0.802, both p < 0.01). • The vessel-based sensitivity, specificity, and diagnostic accuracy were 84.3%, 97.7%, and 90.5% for absolute MBF and 96.1%, 93.2%, and 94.7% for MBF_ratio.

Dynamic CT Myocardial Perfusion Imaging in Patients without Obstructive Coronary Artery Disease: Quantification of Myocardial Blood Flow according to Varied Heart Rate Increments after Stress

OBJECTIVE

The present study aimed to investigate the association between myocardial blood flow (MBF) quantified by dynamic CT myocardial perfusion imaging (CT-MPI) and the increments in heart rate (HR) after stress in patients without obstructive coronary artery disease.

MATERIALS AND METHODS

We retrospectively included 204 subjects who underwent both dynamic CT-MPI and coronary CT angiography (CCTA). Patients with more than minimal coronary stenosis (diameter ≥ 25%), history of myocardial infarction/revascularization, cardiomyopathy, and microvascular dysfunction were excluded. Global MBF at stress was measured using hybrid deconvolution and maximum slope model. Furthermore, the HR increments after stress were recorded.

RESULTS

The median radiation dose of dynamic CT-MPI plus CCTA was 5.5 (4.5-6.8) mSv. The median global MBF of all subjects was 156.4 (139.8-180.4) mL/100 mL/min. In subjects with HR increment between 10 to 19 beats per minute (bpm), the global MBF was significantly lower than that of subjects with increment between 20 to 29 bpm (153.3 mL/100 mL/min vs. 171.3 mL/100 mL/min, p = 0.027). This difference became insignificant when the HR increment further increased to ≥ 30 bpm.

CONCLUSION

The global MBF value was associated with the extent of increase in HR after stress. Significantly higher global MBF was seen in subjects with HR increment of ≥ 20 bpm.

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.

Deep Learning Analysis of Coronary Arteries in Cardiac CT Angiography for Detection of Patients Requiring Invasive Coronary Angiography

In patients with obstructive coronary artery disease, the functional significance of a coronary artery stenosis needs to be determined to guide treatment. This is typically established through fractional flow reserve (FFR) measurement, performed during invasive coronary angiography (ICA). We present a method for automatic and non-invasive detection of patients requiring ICA, employing deep unsupervised analysis of complete coronary arteries in cardiac CT angiography (CCTA) images. We retrospectively collected CCTA scans of 187 patients, 137 of them underwent invasive FFR measurement in 192 different coronary arteries. These FFR measurements served as a reference standard for the functional significance of the coronary stenosis. The centerlines of the coronary arteries were extracted and used to reconstruct straightened multi-planar reformatted (MPR) volumes. To automatically identify arteries with functionally significant stenosis that require ICA, each MPR volume was encoded into a fixed number of encodings using two disjoint 3D and 1D convolutional autoencoders performing spatial and sequential encodings, respectively. Thereafter, these encodings were employed to classify arteries using a support vector machine classifier. The detection of coronary arteries requiring invasive evaluation, evaluated using repeated cross-validation experiments, resulted in an area under the receiver operating characteristic curve of 0.81 ± 0.02 on the artery-level, and 0.87 ± 0.02 on the patient-level. The results demonstrate the feasibility of automatic non-invasive detection of patients that require ICA and possibly subsequent coronary artery intervention. This could potentially reduce the number of patients that unnecessarily undergo ICA.

Myocardial Coverage and Radiation Dose in Dynamic Myocardial Perfusion Imaging Using Third-Generation Dual-Source CT

OBJECTIVE

Third-generation dual-source computed tomography (3rd-DSCT) allows dynamic myocardial CT perfusion imaging (dynamic CTP) with a 10.5-cm z-axis coverage. Although the increased radiation exposure associated with the 50% wider scan range compared to second-generation DSCT (2nd-DSCT) may be suppressed by using a tube voltage of 70 kV, it remains unclear whether image quality and the ability to quantify myocardial blood flow (MBF) can be maintained under these conditions. This study aimed to compare the image quality, estimated MBF, and radiation dose of dynamic CTP between 2nd-DSCT and 3rd-DSCT and to evaluate whether a 10.5-cm coverage is suitable for dynamic CTP.

MATERIALS AND METHODS

We retrospectively analyzed 107 patients who underwent dynamic CTP using 2nd-DSCT at 80 kV (n = 54) or 3rd-DSCT at 70 kV (n = 53). Image quality, estimated MBF, radiation dose, and coverage of left ventricular (LV) myocardium were compared.

RESULTS

No significant differences were observed between 3rd-DSCT and 2nd-DSCT in contrast-to-noise ratio (37.4 ± 11.4 vs. 35.5 ± 11.2, p = 0.396). Effective radiation dose was lower with 3rd-DSCT (3.97 ± 0.92 mSv with a conversion factor of 0.017 mSv/mGy·cm) compared to 2nd-DSCT (5.49 ± 1.36 mSv, p < 0.001). Incomplete coverage was more frequent with 2nd-DSCT than with 3rd-DSCT (1.9% [1/53] vs. 56% [30/54], p < 0.001). In propensity score-matched cohorts, MBF was comparable between 3rd-DSCT and 2nd-DSCT in non-ischemic (146.2 ± 26.5 vs. 157.5 ± 34.9 mL/min/100 g, p = 0.137) as well as ischemic myocardium (92.7 ± 21.1 vs. 90.9 ± 29.7 mL/min/100 g, p = 0.876).

CONCLUSION

The radiation increase inherent to the widened z-axis coverage in 3rd-DSCT can be balanced by using a tube voltage of 70 kV without compromising image quality or MBF quantification. In dynamic CTP, a z-axis coverage of 10.5 cm is sufficient to achieve complete coverage of the LV myocardium in most patients.

Prevalence of Decreased Myocardial Blood Flow in Symptomatic Patients with Patent Coronary Stents: Insights from Low-Dose Dynamic CT Myocardial Perfusion Imaging

OBJECTIVE

To study the prevalence and clinical characteristics of decreased myocardial blood flow (MBF) quantified by dynamic computed tomography (CT) myocardial perfusion imaging (MPI) in symptomatic patients without in-stent restenosis.

MATERIALS AND METHODS

Thirty-seven (mean age, 71.3 ± 10 years; age range, 48-88 years; 31 males, 6 females) consecutive symptomatic patients with patent coronary stents and without obstructive de novo lesions were prospectively enrolled to undergo dynamic CT-MPI using a third-generation dual-source CT scanner. The shuttle-mode acquisition technique was used to image the complete left ventricle. A bolus of contrast media (50 mL; iopromide, 370 mg iodine/mL) was injected into the antecubital vein at a rate of 6 mL/s, followed by a 40-mL saline flush. The mean MBF value and other quantitative parameters were measured for each segment of both stented-vessel territories and reference territories. The MBF_ratio was defined as the ratio of the mean MBF value of the whole stent-vessel territory to that of the whole reference territory. An MBF_ratio of 0.85 was used as the cut-off value to distinguish hypoperfused from non-hypoperfused segments.

RESULTS

A total of 629 segments of 37 patients were ultimately included for analysis. The mean effective dose of dynamic CT-MPI was 3.1 ± 1.2 mSv (range, 1.7-6.3 mSv). The mean MBF of stent-vessel territories was decreased in 19 lesions and 81 segments. Compared to stent-vessel territories without hypoperfusion, the mean MBF and myocardial blood volume were markedly lower in hypoperfused stent-vessel territories (77.5 ± 16.6 mL/100 mL/min vs. 140.4 ± 24.1 mL/100 mL/min [p < 0.001] and 6.4 ± 3.7 mL/100 mL vs. 11.5 ± 4 mL/100 mL [p < 0.001, respectively]). Myocardial hypoperfusion in stent-vessel territories was present in 48.6% (18/37) of patients. None of clinical parameters differed statistically significantly between hypoperfusion and non-hypoperfusion subgroups.

CONCLUSION

Decreased MBF is commonly present in patients who are symptomatic after percutaneous coronary intervention, despite patent stents and can be detected by dynamic CT-MPI using a low radiation dose.

Diagnostic Accuracy of Perfusional Computed Tomography in Moderate Coronary Stenosis: Comparison With Fractional Flow Reserve

Coronary computed tomography with myocardial perfusion imaging (CCTA-MPI) provides data on coronary anatomy and perfusion and may be useful in the assessment of ischemic coronary artery disease (CAD). Management of angiographically intermediate coronary lesions is challenging, and coronary fractional flow reserve (FFR) evaluation is recommended to assess whether these lesions are functionally significant. Our aim was to evaluate the diagnostic accuracy of CCTA-MPI in patients with stable CAD and at least 1 angiographically intermediate coronary lesion submitted to FFR. In this single-center prospective study, patients with stable CAD and at least 1 moderate coronary stenosis (50%-70% by visual estimation) were referred for CCTA-MPI (64-row multidetector) assessment before coronary FFR evaluation. Patients with severe coronary obstructions (≥70%) were excluded. The significance level adopted for all tests was 5%. Twenty-eight patients (mean age 60 ± SD years, 54% women) with 33 intermediate coronary obstructions were enrolled. Ten patients (30%) had functionally significant coronary obstructions characterized by FFR ≤0.8. The sensitivity, specificity, and accuracy of CCTA-MPI for the detection of functionally significant coronary obstructions were 30%, 100%, and 78.8%, respectively. CCTA-MPI positive predictive value was 100%, whereas negative predictive value was 76.7%. Correlation coefficient between tests was 0.48 (P = 0.005). On a novel approach to evaluate intermediate coronary lesions, accuracy of CCTA-MPI was 78.8%. The positive predictive value of an abnormal CCTA-MPI on this population was 100%, suggesting that CCTA-MPI may have a role in the assessment of patients with anatomically identified intermediate coronary lesions.

Clinical Outcomes of Dynamic Computed Tomography Myocardial Perfusion Imaging Combined With Coronary Computed Tomography Angiography Versus Coronary Computed Tomography Angiography–Guided Strategy

Background:

Dynamic computed tomography (CT) myocardial perfusion imaging (MPI) provides quantitative myocardial blood flow for the precise assessment of myocardial ischemia. However, compared with coronary CT angiography (CCTA), whether this functional imaging modality can reduce invasive coronary angiography without revascularization remains unknown. We aimed to determine the clinical outcomes of a dynamic CT-MPI+CCTA-guided versus CCTA-guided strategy in patients with suspected coronary artery disease.

Methods:

Consecutive patients with intermediate pretest probability of coronary artery disease were prospectively enrolled and randomized to dynamic CT-MPI+CCTA-guided or CCTA-guided workup. The primary end point was the rate of invasive coronary angiography without revascularization within 3 months. The secondary end point was a composite of major adverse cardiac event at the 3-month, 6-month, and 1-year follow-up.

Results:

A total of 240 patients (mean age, 69.01±11.2 years; 173 men) were included. The total radiation dose and contrast media usage within 90 days were higher in the CT-MPI+CCTA group than in the CCTA group (10.3 versus 7.1 mSv, P =0.031; 134.5±40.6 versus 108.1±48.2 mL, P <0.0001). Compared with the CCTA-guided group, the CT-MPI+CCTA-guided group had significantly lower rates of invasive coronary angiography within 90 days (48.3% [58/120] versus 30.8% [37/120], P =0.006) and invasive coronary angiography without revascularization (50.0% [29/58] versus 10.8% [4/37], P <0.0001). There were no significant differences regarding the frequency of major adverse cardiac event between the 2 groups at the 3-month, 6-month, and 1-year follow-up.

Conclusions:

In patients with intermediate pretest probability of coronary artery disease, CT-MPI+CCTA-guided patient management may be preferred over the CCTA-guided strategy as an approach to reduce unnecessary invasive procedures.

Evaluation of Myocardial Perfusion by Computed Tomography - Principles, Technical Background and Recommendations

Coronary computed tomography angiography (CCTA) has gained a prominent role in the evaluation of coronary artery disease. However, its anatomical nature does not allow the evaluation of the functional repercussion of coronary obstructions. It has been made possible to evaluate Myocardial computed tomography perfusion (Myocardial CTP) recently, based on myocardial contrast changes related to coronary stenoses. Several studies have validated this technique against the anatomical reference method (cardiac catheterization) and other functional methods, including myocardial perfusion scintigraphy and fractional flow reserve. The Myocardial CTP is performed in conjunction with the CCTA, a combined analysis of anatomy and function. The stress phase (with assessment of myocardial perfusion) can be performed before or after the resting phase (assessment of resting perfusion and coronary arteries), and different acquisition parameters are proposed according to the protocol and type of equipment used. Stressors used are based on coronary vasodilation (e.g. dipyridamole, adenosine). Image interpretation, similar to other perfusion assessment methods, is based on the identification and quantification of myocardial perfusion defects. The integration of both perfusion and anatomical findings is fundamental for the examination interpretation algorithm, allowing to define if the stenoses identified are hemodynamically significant and may be related to myocardial ischemia.

Detection of Hemodynamically Significant Coronary Stenosis: CT Myocardial Perfusion versus Machine Learning CT Fractional Flow Reserve

Background Direct intraindividual comparison of dynamic CT myocardial perfusion imaging (MPI) and machine learning (ML)-based CT fractional flow reserve (FFR) has not been explored for diagnosing hemodynamically significant coronary artery disease. Purpose To investigate the diagnostic performance of dynamic CT MPI and ML-based CT FFR for functional assessment of coronary stenosis. Materials and Methods Between January 2, 2017, and October 17, 2018, consecutive participants with stable angina were prospectively enrolled. All participants underwent dynamic CT MPI coronary CT angiography and invasive conventional coronary angiography (CCA) FFR within 2 weeks. Receiver operating characteristic (ROC) curve analysis was used to assess diagnostic performance. Results Eighty-six participants (mean age, 67 years ± 12 [standard deviation]; 67 men) with 157 target vessels were included for final analysis. The mean radiation doses for dynamic CT MPI and coronary CT angiography were 3.6 mSv ± 1.1 and 2.7 mSv ± 0.8, respectively. Myocardial blood flow (MBF) was lower in ischemic segments compared with nonischemic segments and reference segments (defined as the territory of vessels without stenosis) (75 mL/100 mL/min ± 20 vs 148 mL/100 mL/min ± 22 and 169 mL/100 mL/min ± 34, respectively, both P < .001). Similarly, CT FFR was also lower for hemodynamically significant lesions than for hemodynamically nonsignificant lesions (0.68 ± 0.1 vs 0.83 ± 0.1, respectively, P < .001). MBF had the largest area under the ROC curve (AUC) (using 99 mL/100 mL/min as a cutoff) among all parameters, outperforming ML-based CT FFR (AUC = 0.97 vs 0.85, P < .001). The vessel-based specificity and diagnostic accuracy of MBF were higher than those of ML-based CT FFR (93% vs 68%, P < .001 and 94% vs 78%, respectively, P = .04) whereas the sensitivity of both methods was similar (96% vs 88%, respectively, P = .11). Conclusion Dynamic CT myocardial perfusion imaging was able to help accurately evaluate the hemodynamic significance of coronary stenosis using a reduced amount of radiation. In addition, the myocardial blood flow derived from dynamic CT myocardial perfusion imaging outperformed machine learning-based CT fractional flow reserve for identifying lesions causing ischemia. © RSNA, 2019 Online supplemental material is available for this article.See also the editorial by Loewe in this issue.

Dynamic CT myocardial perfusion imaging

Cardiac CT offers several approaches to establish the hemodynamic severity of coronary artery obstructions. Dynamic myocardial perfusion CT (MPI_CT) is based on serial CT imaging to measure the inflow of contrast medium into the myocardium and calculate absolute measures of myocardial perfusion. This review describes the MPI_CT acquisition protocol, post-image acquisition processing and calculation of quantitative parameters, the diagnostic performance of MPI_CT and the potential incremental value of this technique in comparison to alternative approaches. Further technical innovation using different scanner platforms and establishment of reproducible diagnostic thresholds to differentiate significant coronary artery disease will be crucial in the path to broader clinical implementation.

Dynamic Stress Computed Tomography Perfusion With a Whole-Heart Coverage Scanner in Addition to Coronary Computed Tomography Angiography and Fractional Flow Reserve Computed Tomography Derived

OBJECTIVES

The aims of the study were to test the diagnostic accuracy of integrated evaluation of dynamic myocardial computed tomography perfusion (CTP) on top of coronary computed tomography angiography (cCTA) plus fractional flow reserve computed tomography derived (FFR_CT) by using a whole-heart coverage computed tomography (CT) scanner as compared with clinically indicated invasive coronary angiography (ICA) and invasive fractional flow reserve (FFR).

BACKGROUND

Recently, new techniques such as dynamic stress computed tomography perfusion (stress-CTP) emerged as potential strategies to combine anatomical and functional evaluation in a one-shot scan. However, previous experiences with this technique were associated with high radiation exposure.

METHODS

Eighty-five consecutive symptomatic patients scheduled for ICA were prospectively enrolled. All patients underwent rest cCTA followed by stress dynamic CTP with a whole-heart coverage CT scanner (Revolution CT, GE Healthcare, Milwaukee, Wisconsin). FFR_CT was also measured by using the rest cCTA dataset. The diagnostic accuracy to detect functionally significant coronary artery disease (CAD) in a vessel-based model of cCTA alone, cCTA+FFR_CT, cCTA+CTP, or cCTA+FFR_CT+CTP were assessed and compared by using ICA and invasive FFR as reference. The overall effective dose of dynamic CTP was also measured.

RESULTS

The prevalence of obstructive CAD and functionally significant CAD was 77% and 57%, respectively. The sensitivity and specificity of cCTA alone, cCTA+FFR_CT, and cCTA+CTP were 83% and 66%, 86% and 75%, and 73% and 86%, respectively. Both the addition of FFR_CT and CTP improves the area under the curve (AUC: 0.876 and 0.878, respectively) as compared with cCTA alone (0.826; p < 0.05). The sequential strategy of cCTA+FFR_CT+CTP showed the highest AUC (0.919; p < 0.05) as compared with all other strategies. The mean effective radiation dose (ED) for cCTA and stress CTP was 2.8 ± 1.2 mSv and 5.3 ± 0.7 mSv, respectively.

CONCLUSIONS

The addition of dynamic stress CTP on top of cCTA and FFR_CT provides additional diagnostic accuracy with acceptable radiation exposure.