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Current Evidence in Cardiothoracic Imaging

Computed Tomography–derived Fractional Flow Reserve in Stable Chest Pain

Schwartz, Fides R., MD*; Koweek, Lynne M., MD*; Nørgaard, Bjarne L., MD, PhD

doi: 10.1097/RTI.0000000000000369
Current Evidence in Cardiothoracic Imaging

High-accuracy diagnostic imaging is needed to diagnose and manage coronary artery disease as well as to allow risk stratification for future events. Advancements in multidetector computed tomography and image postprocessing allow for routine computed tomography coronary angiography to provide anatomic luminal assessment similar to invasive coronary angiography, and, similarly, computational fractional flow reserve derived from computed tomography facilitates determination of hemodynamically relevant stenosis comparable to invasive fractional flow reserve. In this review article, we describe the diagnostic performance and the potential impact of fractional flow reserve derived from computed tomography in clinical practice.

*Department of Radiology, Duke University Medical Center, Durham, NC

Department of Cardiology, Aarhus University Hospital Skejby, Aarhus, Denmark

B.L.N. and L.M.K. have received institutional research support from Edwards Lifesciences, Siemens, and HeartFlow.

The authors declare no conflicts of interest.

Correspondence to: Fides R. Schwartz, MD, Department of Radiology, Duke University Medical Center, P.O. Box 3808, Durham, NC 27710 (e-mail:

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  • In patients with stable chest pain, fractional flow reserve derived from computed tomography (FFRCT) has a high diagnostic performance when compared with invasive fractional flow reserve (FFR) without exposing patients to additional radiation doses or the risk of an invasive procedure.
  • Coronary computed tomography angiography (CCTA) with selective FFRCT testing may improve the management of patients with stable chest pain by identifying functionally relevant coronary disease in one noninvasive diagnostic imaging procedure.
  • Imaging strategies using FFRCT may have a positive economic profile compared with routine care.
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During the last decade, CCTA has undergone tremendous scanner advances and clinical validation with improved image quality and significant reductions in radiation dose. Accordingly, noninvasive imagers are increasingly involved in the diagnosis and management of patients with suspected coronary artery disease (CAD). The diagnostic and prognostic value of CCTA has been documented in multiple studies.1,2 Its negative predictive value for detection of CAD is close to 100%, and CCTA is unique in its ability to detect and quantify atherosclerosis in both nonobstructive diffuse as well as obstructive CAD, providing clinicians with information on the risk that may better guide preventive and therapeutic interventions than routine care.3–5 Accordingly, recent meta-analyses, large-scale registry studies, and randomized trials have shown improved clinical outcomes in stable CAD following initial testing with CCTA when compared with noninvasive functional testing such as stress electrocardiography and radionuclide studies.4–10 Moreover, the US National Cardiovascular Data Registry demonstrated in >400,000 patients that only 45% were correctly identified as having >50% stenosis at invasive coronary angiography (ICA) following traditional functional testing while for CCTA the proportion was 70%.11 Vavalle et al12 demonstrated that, on the other end of the spectrum, 74% of patients with typical angina and a negative stress-test result subsequently had obstructive CAD on ICA.

Accordingly, the updated National Institute for Health and Care Excellence (NICE) stable chest pain guideline (CG95) recommends CCTA in lieu of functional testing as the first-line test strategy in patients without known CAD and atypical or classical angina.13,14 Advanced image analysis algorithms such as FFRCT further expand the imager’s role in the diagnosis and management of CAD by providing information on lesion-specific ischemia.

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Coronary artery CTA has a reported high sensitivity (90%; range: 86% to 93%) and high negative predictive value (98.7%; 95% confidence interval, 97.9%-99.4%), but lower specificity and positive predictive value of 60% and 64%, respectively, for the diagnosis of an obstructive CAD.15 Major limitations are the inaccurate evaluation of vessel lumen in areas of severely calcified disease as well as motion artifacts hampering vessel definition. Thus, in general, CCTA overestimates stenosis severity. Moreover, similar to ICA, CCTA remains a strictly anatomic test and, as such, it is often discordant with measures of lesion-specific ischemia determined by invasive FFR, which is the established gold standard for decision-making in the catheterization laboratory.16,17 Even in seemingly clear-cut cases with low-grade or high-grade stenosis, anatomic imaging alone can be incorrect in characterizing the hemodynamic significance of lesions.18,19 Accordingly, when compared with traditional functional test modalities, CCTA is associated with increasing downstream ICA and revascularization utilization. To overcome these limitations, new diagnostic strategies for assessment of the physiological relevance of stenoses determined by CCTA have been proposed.

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Traditionally, adjudication of lesion-specific ischemia is performed invasively by FFR, which assesses the ratio of flow across a stenosis during maximum vasodilatation. FFR is associated with the clinical outcome in a continuous manner and has been shown in multiple randomized trials to guide revascularization in a cost-effective manner.20,21 While FFR is a robust tool for the adjudication of the hemodynamic significance of a stenosis, it is limited by its invasiveness and costs; hence, in real-world practice, it is used for coronary revascularization decision-making in only a minority of patients.22 Recent advances in image postprocessing with the integration of computational fluid dynamics and quantitative anatomic and physiological modeling now enable simulation of patient-specific hemodynamic parameters including blood velocity, pressure, pressure gradients, and FFRCT from standard acquired CCTA data sets without the need for additional procedural planning, medication, or radiation.23 FFRCT testing requires offsite computer processing (HeartFlow, Redwood City, CA) requiring 2 to 6 hours.23–26 However, significantly faster FFRCT processing times resulting from software improvements are expected in the near future. Recently, there has been renewed interest in past generations of reduced order computational fluid modeling versions that are less computationally intense and, when coupled with less comprehensive anatomic modeling than for FFRCT, enable on-site analysis with reduced analysis times (<1 h). While noninvasive on-site CT-derived FFR has shown interesting results in small, single-center, retrospective studies,27–29 further investigations in prospective multicenter trials are needed in order to determine the actual diagnostic performance of these techniques.30

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The diagnostic performance of FFRCT in patients with proven or suspected stable CAD has been tested in 3 prospective multicenter trials.24–26 A total of 609 patients and 1050 vessels have been investigated. An overview of the study design, populations, and estimates of FFRCT diagnostic performance in these 3 trials is presented in Table 1. Overall, FFRCT revealed both high per-patient and per-vessel discrimination for the presence of ischemia with blinded comparison with invasively measured FFR. Moreover, the diagnostic performance of FFRCT was superior when compared with anatomic interpretation alone. In the most recent trial (NXT), which used an updated FFRCT analysis software, a marked increase of 34% to 79% on a per-patient and 60% to 86% on a per-vessel basis was shown in diagnostic specificity when moving from stenosis (>50%) to physiological assessment by FFRCT (≤0.80).26 Thus, on a per-patient level, FFRCT correctly reclassified 68% of CCTA false positives to true negatives. Of note, in the NXT trial, >90% of the coronary lesions were in the intermediate range (30% to 70%), in which the discrepancy between anatomical and physiological assessment is most profound. Relevant patient examples are shown in Figure 1.





In the NXT trial, there was a good direct per-vessel FFRCT to FFR correlation (Pearson correlation coefficient 0.82).26 Moreover, it has been demonstrated that FFRCT has high diagnostic performance in the presence of coronary calcification. In an NXT trial substudy, there was no difference in diagnostic accuracy, sensitivity, or specificity of FFRCT across Agatston score quartiles, including the highest quartile of patients with Agatston scores ranging between 416 and 3599.31 No prospective head-to-head comparisons between the diagnostic performance of FFRCT and traditional noninvasive functional modalities against FFR have been published. In a recent meta-analysis by Danad and colleagues, FFRCT demonstrated higher sensitivity than stress echocardiography (90% vs. 77%), ICA (90% vs. 69%), and SPECT (90% vs. 70%), while showing equal sensitivity to cardiac MRI (both 90%). The specificity of FFRCT (71%) was similar to stress echocardiography (75%), ICA (74%), and SPECT (78%) but significantly lower than MRI (94%).15

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The impact of noninvasive coronary imaging on patient management and outcome has implications for best practice use and appropriate resource investments.

Recently, we have seen FFRCT advance from diagnostic testing to the realm of clinical utility (Table 2). The prospective, multicenter PLATFORM trial examined the clinical impact of FFRCT to guide patient management compared with usual care.32–34 The primary endpoint was the rate of finding no obstructive stenosis (≥50%) among those with planned ICA. A total of 584 patients with new-onset chest pain, no prior history of CAD, and an intermediate pretest likelihood of obstructive CAD were enrolled. In patients scheduled for ICA, 73% of usual care patients had no obstructive CAD compared with only 12% of patients guided by FFRCT, an 83% reduction (P<0.0001). Although clinicians in the PLATFORM study were not protocol driven to utilize FFRCT test results, in 61% of patients with planned ICA, the angiogram was cancelled after receiving FFRCT results. In a recent prospective study by Jensen et al34 of 774 patients with stable chest pain, a diagnostic strategy of first-line CCTA with selective FFRCT testing in intermediate range CAD, ICA was deferred in 91% versus 75% in patients with low-intermediate and high pretest probability of CAD, respectively. In an observational analysis from real-world practice of 3500 patients with intermediate stenosis on CCTA by Nørgaard et al35, it was shown that replacing an adjunctive test strategy of myocardial perfusion imaging with FFRCT led to lower downstream ICA utilization, an improved diagnostic yield of ICA, and improved physiological guidance of revascularization. Moreover, the potential clinical utility of FFRCT has been evaluated in 2 retrospective studies. The RIPCORD-FFRCT study demonstrated that 30% of the subgroup of patients planned for coronary revascularization based on the CCTA result after FFRCT could be managed with medical treatment.36 In addition, the target vessels for coronary interventions were adjusted from the CCTA-based management plan in 18% of patients after FFRCT data were made available. In a substudy of the PROMISE cohort by Lu et al37 it was demonstrated that reserving ICA for patients with FFRCT≤0.80 would reduce the proportion of ICA procedures with the finding of no obstructive disease by 44%, and increase the proportion of ICA, leading to revascularization by 24%. Importantly, all data on the clinical utility of FFRCT have been derived from patients with stable chest pain. At this point, no data have been published to support the use of FFRCT in patients with acute coronary syndromes.38



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In the PLATFORM trial, clinical outcomes for patients in whom ICA was deferred on the basis of FFRCT were favorable with a 1-year risk of all-cause death, myocardial infarction, or unplanned hospitalization with urgent revascularization of 1%.33 This finding is in accordance with a recent single-center real-world study of 110 consecutive patients with stable chest pain, moderate CAD, and deferral of ICA in those with FFRCT≥0.80, among whom no adverse cardiac events occurred over a median of 12 months’ follow-up.39 In the Lu PROMISE FFRCT substudy, “blinded” FFRCT≤0.80 was predictive of subsequent revascularization and major adverse cardiac events with a significantly higher hazard ratio than CCTA stenosis assessment alone (hazard ratio, 4.3 vs. 2.9; P=0.033).37 Historical cost simulation analyses indicate that FFRCT guidance for selection of ICA and decision-making on coronary revascularization may reduce costs in stable CAD.40,41 In the PLATFORM trial, among patients with planned ICA, the mean costs were 32% lower in the FFRCT group than in the usual care group.32 The ongoing prospective multicenter multinational longitudinal “Assessing Diagnostic value of Non-Invasive FFRCT in Coronary Care” (ADVANCE) registry will further delineate the clinical utility, prognostic aspects, and cost-effectiveness of FFRCT-guidance in 5000 patients with or without known CAD.42

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Incorporation of cardiac CTA and FFRCT into routine clinical use requires these examinations to provide accurate means of classification and high confidence for interpretation. Significant CT imaging artifacts such as motion, low contrast, or blooming may impair the diagnostic performance of CCTA and thus of FFRCT. However, these issues can be minimized by adhering to CCTA image acquisition guidelines, particularly by administration of heart-rate–lowering medication and sublingual nitrates before image acquisition.43,44 In recent studies from real-world practice, it was demonstrated that a conclusive FFRCT result was obtainable in >95% of consecutive stable chest pain patients with intermediate range lesions.35,39

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The impact of FFRCT for next-step patient management is evolving. Standardized criteria on the clinical utility and interpretation of FFRCT have not been published. However, at this point, FFRCT testing seems to be a valuable gatekeeper to the catheterization laboratory for physiological assessment of intermediate-range lesions determined by CCTA in patients with stable chest pain. Currently, preservation of 80% of flow across a lesion is considered not flow limiting for both FFRCT and FFR. Luminal narrowing associated with a drop of flow between 75% and 80% is considered indeterminate for lesion-specific ischemia.39 Further understanding of the downstream management of patients following FFRCT testing as well as the impact of other CT-derived measures associated with flow obstruction such as coronary plaque volume and characteristics19 and ratio of blood volume to myocardial mass45 are yet to be determined. Moreover, further studies are needed to assess the relative cost-efficiency in the clinical practice of CCTA-FFRCT versus conventional noninvasive functional testing.

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FFRCT is a novel noninvasive method using computational fluid dynamics for the calculation of FFR from patient-specific modeling derived from CCTA data sets. During the last 5 years, FFRCT has undergone remarkable advancements in technology and clinical validation, challenging conventional ischemia testing as the adjunctive test strategy in patients with moderate CAD determined by CCTA. These trends in combination with continued technical developments and emerging data supporting the clinical utility and safety of FFRCT will move imagers to the forefront of early anatomic and physiological assessment of CAD for an ever-growing patient population.

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1. Min JK, Dunning A, Lin FY, et al. Age- and sex-related differences in all-cause mortality risk based on coronary computed tomography angiography findings: results from the International Multicenter CONFIRM (Coronary CT Angiography Evaluation for Clinical Outcomes: An International Multicenter Registry) of 23,854 patients without known coronary artery disease. J Am College Cardiol. 2011;58:849–860.
2. Hadamitzky M, Taubert S, Deseive S, et al. Prognostic value of coronary computed tomography angiography during 5 years of follow-up in patients with suspected coronary artery disease. Eur Heart J. 2013;34:3277–3285.
3. Chow BJ, Small G, Yam Y, et al. Prognostic and therapeutic implications of statin and aspirin therapy in individuals with nonobstructive coronary artery disease: results from the CONFIRM (COronary CT Angiography EvaluatioN For Clinical Outcomes: An InteRnational Multicenter registry) registry. Arterioscler Thromb Vasc Biol. 2015;35:981–989.
4. Williams MC, Hunter A, Shah ASV, et al. Use of coronary computed tomographic angiography to guide management of patients with coronary disease. J Am Coll Cardiol. 2016;67:1759–1768.
5. Jorgensen ME, Andersson C, Norgaard BL, et al. Functional testing or coronary computed tomography angiography in patients with stable coronary artery disease. J Am Coll Cardiol. 2017;69:1761–1770.
6. Nielsen LH, Ortner N, Norgaard BL, et al. The diagnostic accuracy and outcomes after coronary computed tomography angiography vs. conventional functional testing in patients with stable angina pectoris: a systematic review and meta-analysis. Eur Heart J Cardiovasc Imaging. 2014;15:961–971.
7. SCOT-HEART Investigators. CT coronary angiography in patients with suspected angina due to coronary heart disease (SCOT-HEART): an open-label, parallel-group, multicentre trial. Lancet. 2015;385:2383–2391.
8. Foy AJ, Dhruva SS, Peterson B, et al. Coronary computed tomography angiography vs functional stress testing for patients with suspected coronary artery disease: a systematic review and meta-analysis. JAMA Intern Med. 2017;177:1623–1631.
9. Hoffmann U, Ferencik M, Udelson JE, et al. Prognostic value of noninvasive cardiovascular testing in patients with stable chest pain: insights from the PROMISE Trial (Prospective Multicenter Imaging Study for Evaluation of Chest Pain). Circulation. 2017;135:2320–2332.
10. Fordyce CB, Douglas PS, Roberts RS, et al. Identification of patients with stable chest pain deriving minimal value from noninvasive testing: the PROMISE minimal-risk tool, a secondary analysis of a randomized clinical trial. JAMA Cardiol. 2017;2:400–408.
11. Patel MR, Peterson ED, Dai D, et al. Low diagnostic yield of elective coronary angiography. N Engl J Med. 2010;362:886–895.
12. Vavalle JP, Shen L, Broderick S, et al. Effect of the presence and type of angina on cardiovascular events in patients without known coronary artery disease referred for elective coronary angiography. JAMA Cardiol. 2016;1:232–234.
13. National Institute of Health and Clinical Excellence. Chest pain of recent onset: assessment and diagnosis of recent onset chest pain or discomfort of suspected cardiac origin. Clinical guideline CG95. 2016. Available at: Accessed January 30, 2018.
14. Moss AJ, Williams MC, Newby DE, et al. The updated NICE guidelines: cardiac ct as the first-line test for coronary artery disease. Curr Cardiovasc Imaging Rep. 2017;10:15.
15. Danad I, Szymonifka J, Twisk JWR, et al. Diagnostic performance of cardiac imaging methods to diagnose ischaemia-causing coronary artery disease when directly compared with fractional flow reserve as a reference standard: a meta-analysis. Eur Heart J. 2017;38:991–998.
16. Tonino PA, Fearon WF, De Bruyne B, et al. Angiographic versus functional severity of coronary artery stenoses in the FAME study fractional flow reserve versus angiography in multivessel evaluation. J Am Coll Cardiol. 2010;55:2816–2821.
17. De Bruyne B, Pijls NHJ, Kalesan B, et al. Fractional flow reserve–guided PCI versus medical therapy in stable coronary disease. N Engl J Med. 2012;367:991–1001.
18. Curzen N, Rana O, Nicholas Z, et al. Does routine pressure wire assessment influence management strategy at coronary angiography for diagnosis of chest pain?: the RIPCORD study. Circ Cardiovasc Interv. 2014;7:248–255.
19. Ahmadi A, Leipsic J, Ovrehus K, et al. P876Lesion-specific and vessel-related determinants of FFR. Eur Heart J. 2017;38 (suppl_1):521–530.
20. Fearon WF, Bornschein B, Tonino PA, et al. Economic evaluation of fractional flow reserve-guided percutaneous coronary intervention in patients with multivessel disease. Circulation. 2010;122:2545–2550.
21. Johnson NP, Johnson DT, Kirkeeide RL, et al. Repeatability of fractional flow reserve despite variations in systemic and coronary hemodynamics. JACC Cardiovasc Interv. 2015;8:1018–1027.
22. Morris PD, Ryan D, Morton AC, et al. Virtual fractional flow reserve from coronary angiography: modeling the significance of coronary lesions: results from the VIRTU-1 (VIRTUal Fractional Flow Reserve From Coronary Angiography) study. JACC Cardiovasc Interv. 2013;6:149–157.
23. Taylor CA, Fonte TA, Min JK. Computational fluid dynamics applied to cardiac computed tomography for noninvasive quantification of fractional flow reserve: scientific basis. J Am Coll Cardiol. 2013;61:2233–2241.
24. Koo BK, Erglis A, Doh JH, et al. Diagnosis of ischemia-causing coronary stenoses by noninvasive fractional flow reserve computed from coronary computed tomographic angiograms. Results from the prospective multicenter DISCOVER-FLOW (Diagnosis of Ischemia-Causing Stenoses Obtained Via Noninvasive Fractional Flow Reserve) study. J Am Coll Cardiol. 2011;58:1989–1997.
25. Min JK, Leipsic J, Pencina MJ, et al. Diagnostic accuracy of fractional flow reserve from anatomic CT angiography. JAMA. 2012;308:1237–1245.
26. Norgaard BL, Leipsic J, Gaur S, et al. Diagnostic performance of noninvasive fractional flow reserve derived from coronary computed tomography angiography in suspected coronary artery disease: the NXT trial (Analysis of Coronary Blood Flow Using CT Angiography: Next Steps). J Am Coll Cardiol. 2014;63:1145–1155.
27. Renker M, Schoepf UJ, Wang R, et al. Comparison of diagnostic value of a novel noninvasive coronary computed tomography angiography method versus standard coronary angiography for assessing fractional flow reserve. Am J Cardiol. 2014;114:1303–1308.
28. Coenen A, Lubbers MM, Kurata A, et al. Coronary CT angiography derived fractional flow reserve: methodology and evaluation of a point of care algorithm. J Cardiovasc Comput Tomogr. 2016;10:105–113.
29. Ko BS, Cameron JD, Munnur RK, et al. Noninvasive CT-derived FFR based on structural and fluid analysis: a comparison with invasive FFR for detection of functionally significant stenosis. JACC Cardiovasc Imaging. 2017;10:663–673.
30. Norgaard BL, Leipsic J. From newton to the coronaries: computational fluid dynamics has entered the clinical scene. JACC Cardiovasc Imaging. 2016;9:700–702.
31. Norgaard BL, Gaur S, Leipsic J, et al. Influence of coronary calcification on the diagnostic performance of CT angiography derived FFR in coronary artery disease: a substudy of the NXT trial. JACC Cardiovasc Imaging. 2015;8:1045–1055.
32. Hlatky MA, De Bruyne B, Pontone G, et al. Quality-of-life and economic outcomes of assessing fractional flow reserve with computed tomography angiography: PLATFORM. J Am Coll Cardiol. 2015;66:2315–2323.
33. Douglas PS, De Bruyne B, Pontone G, et al. 1-Year outcomes of FFRCT-guided care in patients with suspected coronary disease: the PLATFORM study. J Am Coll Cardiol. 2016;68:435–445.
34. Jensen JM, Bøtker HE, Mathiassen ON, et al. Computed tomography derived fractional flow reserve testing in stable patients with typical angina pectoris: influence on downstream rate of invasive coronary angiography. Eur Heart J Cardiovasc Imaging. 2018;19:405–414.
35. Nørgaard BL, Gormsen LC, Botker HE, et al. Myocardial perfusion imaging versus computed tomography angiography-derived fractional flow reserve testing in stable patients with intermediate-range coronary lesions: influence on downstream diagnostic workflows and invasive angiography findings. J Am Heart Assoc. 2017;6:8.
36. Curzen NP, Nolan J, Zaman AG, et al. Does the routine availability of CT-derived FFR influence management of patients with stable chest pain compared to CT angiography alone?: The FFRCT RIPCORD Study. JACC Cardiovasc Imaging. 2016;9:1188–1194.
37. Lu MT, Ferencik M, Roberts RS, et al. Noninvasive FFR derived from coronary CT angiography: management and outcomes in the PROMISE trial. JACC Cardiovasc Imaging. 2017;10:1350–1358.
38. Gaur S, Taylor CA, Jensen JM, et al. FFR derived from coronary CT angiography in nonculprit lesions of patients with recent STEMI. JACC Cardiovasc Imaging. 2017;10:424–433.
39. Norgaard BL, Hjort J, Gaur S, et al. Clinical use of coronary CTA-derived FFR for decision-making in stable CAD. JACC Cardiovasc Imaging. 2017;10:541–550.
40. Hlatky MA, Saxena A, Koo BK, et al. Projected costs and consequences of computed tomography-determined fractional flow reserve. Clin Cardiol. 2013;36:743–748.
41. Kimura T, Shiomi H, Kuribayashi S, et al. Cost analysis of non-invasive fractional flow reserve derived from coronary computed tomographic angiography in Japan. Cardiovasc Interv Ther. 2015;30:38–44.
42. Chinnaiyan KM, Akasaka T, Amano T, et al. Rationale, design and goals of the HeartFlow assessing diagnostic value of non-invasive FFRCT in Coronary Care (ADVANCE) registry. J Cardiovasc Comput Tomogr. 2017;11:62–67.
43. Leipsic J, Yang TH, Thompson A, et al. CT angiography (CTA) and diagnostic performance of noninvasive fractional flow reserve: results from the Determination of Fractional Flow Reserve by Anatomic CTA (DeFACTO) study. AJR Am J Roentgenol. 2014;202:989–994.
44. Abbara S, Blanke P, Maroules CD, et al. SCCT guidelines for the performance and acquisition of coronary computed tomographic angiography: a report of the society of Cardiovascular Computed Tomography Guidelines Committee: Endorsed by the North American Society for Cardiovascular Imaging (NASCI). J Cardiovasc Comput Tomogr. 2016;10:435–449.
45. Taylor CA, Gaur S, Leipsic J, et al. Effect of the ratio of coronary arterial lumen volume to left ventricle myocardial mass derived from coronary CT angiography on fractional flow reserve. J Cardiovasc Comput Tomogr. 2017;11:429–436.

coronary computed tomography angiography; fractional flow reserve; computational fluid dynamics; stable chest pain; coronary artery disease; noninvasive cardiac imaging; noninvasive diagnostic testing

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