European Radiology

, Volume 25, Issue 8, pp 2282–2290 | Cite as

Fractional flow reserve derived from coronary CT angiography in stable coronary disease: a new standard in non-invasive testing?

Cardiac

Abstract

Fractional flow reserve (FFR) measured during invasive coronary angiography is the gold standard for lesion-specific decisions on coronary revascularization in patients with stable coronary artery disease (CAD). Current guidelines recommend non-invasive functional or anatomic testing as a gatekeeper to the catheterization laboratory. However, the “holy grail” in non-invasive testing of CAD is to establish a single test that quantifies both coronary lesion severity and the associated ischemia. Most evidence to date of such a test is based on the addition of computational analysis of FFR to the anatomic information obtained from standard-acquired coronary CTA data sets at rest (FFRCT). This review summarizes the clinical evidence for the use of FFRCT in stable CAD in context to the diagnostic performance of other non-invasive testing modalities.

Key Points

The process of selecting appropriate patients for invasive coronary angiography is inadequate

Invasive fractional flow reserve is the standard for assessing coronary lesion-specific ischemia

Fractional flow reserve may be derived from standard coronary CT angiography (FFRCT)

FFRCTprovides high diagnostic performance in stable coronary artery disease

Keywords

Coronary artery disease Coronary CT angiography Fractional flow reserve Invasive coronary angiography Non-invasive imaging 

Abbreviations

AUC

Area under the receiver operating characteristic curve

CAD

Coronary artery disease

CTA

Computed tomography angiography

CTP

Computed tomography perfusion

CMR

Magnetic resonance myocardial perfusion imaging

FFR

Fractional flow reserve

FFRCT

Fractional flow reserve derived from coronary computed tomography angiography

ICA

Invasive coronary angiography

NPV

Negative predictive value

PPV

Positive predictive value

SPECT

Single photon emission computed tomography

TAG

Transluminal attenuation gradient

Introduction

Invasive coronary angiography (ICA) remains the gold standard for the accurate assessment of coronary anatomy. However, The Clinical Outcomes Utilizing Revascularization and Aggressive Drug Evaluation (COURAGE) trial supplied evidence that anatomic assessment by ICA alone does not improve prognosis [1]. Moreover, several studies have demonstrated a poor correlation between angiographic stenosis severity as assessed by ICA and ischemia [2, 3].

In patients with suspected stable coronary artery disease (CAD), the presence of myocardial ischemia is associated with a poor prognosis [4, 5]. Moreover, there may be a threshold in the ischemic continuum beyond which coronary revascularization imparts a survival benefit [4, 5]. Therefore, in patients suspected of CAD, current guidelines recommend non-invasive functional imaging testing (NIFT) as the first-line strategy for identifying regional differences in myocardial blood flow supply (e.g., single photon emission computed tomography [SPECT] or cardiac magnetic resonance [CMR]), or left ventricular wall motion abnormalities (e.g., stress echocardiography) [6]. In meta-analyses, NIFT modalities have shown high diagnostic performances for the detection or exclusion of obstructive CAD, with sensitivities and specificities around 80 % [6, 7, 8]. However, these estimates are based on a wide array of measures, and thus may not reflect real-world practice. In fact, large-scale registry data indicate that up to 60 % of patients referred for ICA on suspicion of CAD do not have obstructive disease, despite prior NIFT having been performed in four of five patients [9]. In addition, patients with a positive NIFT result are only slightly more likely to have obstructive CAD on ICA than those who do not undergo testing [10]. Furthermore, NIFT may misclassify a significant proportion of patients with significant CAD as low risk [11]. Several explanations may account for the disconnect between NIFT diagnostic performance in contemporary practice and in the literature. The specificity of a diagnostic test may decline with time as the test is implemented in less experienced laboratories and applied to a wider spectrum of patients [12]. The presence of referral bias or refusal to publish negative reports may have inflated the perceived diagnostic accuracy of tests. It should also be acknowledged that, originally, the diagnostic performance of NIFT was established using ICA stenosis severity as the reference standard [6, 7, 8]. Thus, the use of NIFT as a “gold standard” for anatomic assessment by ICA seems highly problematic, since the diagnostic performance of the “gold standard” was, in fact, derived from ICA [13].

Coronary computed tomography angiography (CTA) is a rapidly evolving technology with excellent diagnostic sensitivity and negative predictive value for ruling out obstructive CAD [14, 15]. Moreover, the absence of CAD on coronary CTA is associated with an excellent clinical outcome [16]. However, because of limitations associated with spatial resolution and the presence of coronary calcification, coronary CTA tends to overestimate the severity of CAD, and hence its diagnostic specificity is only modest [2, 14, 15]. Furthermore, coronary CTA, like ICA, has a poor ability to determine the hemodynamic significance of a stenosis [2]. This has led to concern that widespread use of coronary CTA may lead to an increase in unneeded downstream diagnostic and therapeutic procedures [17]. According to guidelines, coronary CTA is best applied as an alternative to NIFT for ruling out CAD among symptomatic individuals with low to intermediate pretest probability of disease [6].

Both anatomical and functional information is essential for guiding the optimal treatment strategy for patients with suspected CAD [5, 6, 18, 19]. However, the field of cardiac imaging presents the clinician with a bewildering array of test choices, with the inherent risk of submitting patients to multiple and costly diagnostic tests [6]. Therefore, the “holy grail” in non-invasive assessment of CAD has been to develop a single test with the ability to both quantify coronary lesion severity and determine the hemodynamic significance of these lesions. Three such methods have the potential to be optimal less-invasive imaging modalities for the diagnosis of CAD: 1) myocardial CT perfusion (CTP) imaging [20, 21, 22], 2) the transluminal attenuation gradient (TAG) method [23, 24], and 3) computational analysis of fractional flow reserve (FFR) from coronary CTA (FFRCT) [25, 26, 27]. This review summarizes the clinical evidence for the use of FFRCT in stable CAD in context to the diagnostic performance of existing non-invasive functional testing modalities.

Fractional flow reserve

Fractional flow reserve assesses the ratio of flow across a stenosis to putative flow in the absence of stenosis. FFR is measured during ICA using a pressure-sensitive catheter placed across the stenotic lesion after maximal hyperaemia is established using a vasodilating agent such as adenosine. Coronary lesions with FFR < 0.75 are almost always functionally significant, whereas stenosis with FFR > 0.80 are rarely associated with ischemia [28, 29]. The Fractional Flow Reserve Versus Angiography for Multivessel Evaluation (FAME) study added to the findings of the COURAGE trial by showing improved clinical outcomes following FFR versus anatomically guided coronary intervention [29]. To date, FFR is the only tool whose use in large prospective randomized trials has been shown to improve clinical outcomes as well as reduce healthcare costs [29, 30, 31]. While FFR is thus considered the current gold standard for quantification of CAD and guiding coronary revascularization [32], in the real world it is not used for coronary revascularization decision-making in many patients [33, 34]. This is most likely due to drawbacks associated with the instrumentation of the coronary arteries as well as cost. These issues underscore the need for accurate non-invasive gatekeeping to the catheterization laboratory.

Combined anatomic and physiologic assessment of coronary artery disease

Previous single-centre studies have shown promising results regarding the diagnostic performance of coronary CTA in patients with suspected CAD through the addition of stress CTP imaging [20, 22]. In one prospective multi-centre trial including 320 patients, the specificity of coronary CTA in identifying ≥ 50 % stenosis alone versus ≥ 50 % stenosis and a CTP perfusion defect (summed stress score of 4) in predicting ≥ 50 % stenosis on ICA with a corresponding SPECT perfusion defect increased from 51 % to 74 % [21]. One major limitation of the latter diagnostic strategy, however, is that it, like other stress imaging tests, consist of two scans (rest and pharmacological stress contrast imaging), which adds to procedural complexity, cost, and radiation burden. Two non-invasive methods based on standard acquired coronary CTA data sets at rest, without the need for additional patient preparation, radiation, contrast, or medication, have been investigated for evaluation of coronary anatomy and physiology. The TAG method assesses the contrast gradient of vessel stenosis on coronary CTA as a surrogate of coronary flow [23, 24]. In one study of 53 patients with known or suspected CAD, FFRCT provided better diagnostic performance for the diagnosis of lesion-specific ischemia compared to coronary CTA stenosis and TAG [23]. No larger studies on the diagnostic performance of TAG as applied to different scanner platforms and heterogeneous patient cohorts have been reported. The diagnostic performance of FFRCT has been rigorously validated in three prospective multi-centre studies using directly measured FFR as the reference standard [25, 26, 27].

Non-invasive fractional flow reserve computed from standard acquired coronary CTA

Computation of non-invasive FFRCT from coronary CTA image data acquired using standard acquisition protocols requires the generation of a physiologic model of coronary blood flow. The physiologic model is based on three underlying principles that have been described in detail by Taylor et al. [35]. The first principle asserts that the total resting coronary blood flow can be quantified relative to the myocardial mass as assessed by CT. The second principle states that microcirculatory vascular resistance at rest is inversely proportional to the size of the coronary arteries supplying the myocardium. And the third principle maintains that the vasodilatory response of the coronary microcirculation to adenosine infusion is predictable, allowing computational modeling of the maximal hyperaemic state. Integration of these patient-specific mathematical models of coronary physiology to three-dimensional computational models enables computation of coronary flow and pressure at each point in the coronary tree under hyperaemic conditions. Thus, FFRCT is calculated in the same manner as when it is directly measured during ICA. A schematic representation of the FFRCT analytic process is shown in Fig. 1.
Fig. 1

Schematic Presentation of the FFRCT Analysis (adapted from Nørgaard et al. [26], with permission). (a) Routine coronary computed tomography angiography data are received. (b) Generation of a 3-dimensional anatomic model of the aortic root and coronary arteries. (c) Constructing a patient-specific physiologic model of the coronary circulation by incorporating the direct relationship of total resting coronary blood flow to myocardial mass and the inverse relationship of microvascular resistance to coronary artery size, and then simulating maximal hyperaemia by reducing microvascular resistance. (d) Application of computational fluid dynamics to compute pressure and flow simultaneously at all points in the coronary tree. (e) Fractional flow reserve is calculated as the distal coronary pressure divided by the aortic pressure under conditions of maximal hyperaemic flow at each point in the coronary tree, and a colour map is displayed with the lowest FFRCT value in each major territory identified

Non-invasive fractional flow reserve—clinical evidence

The diagnostic performance of FFRCT in identifying lesion-specific ischemia in known or suspected CAD has been evaluated in three trials comprising a total of 609 patients and 1050 vessels, with blinded comparison of FFRCT to FFR (Table 1) [25, 26, 27]. A blinded "integration core laboratory" was used in each case to select the FFRCT value in the model corresponding to the location of the FFR measurement.
Table 1

Studies with comparison of FFRCT diagnostic performance using FFR as the reference standard

Study

Design

Population

Accuracy

95 % CI

Sensitivity

95 % CI

Specificity

95 % CI

PPV

95 % CI

NPV

95 % CI

AUC

95 % CI

DISCOVER-FLOW

Koo B-K et al., 2011 [24]

● Statistically powered on a per vessel basis

● 4 centres

● Prospective

● Obstructive CAD: Coronary stenosis >50 %

● Ischemia: FFR or FFRCT ≤0.80

● Blinded FFRCT core-lab analyses

● Patients with suspected or known CAD who underwent coronary CTA, ICA and FFR. All patients had at least one stenosis ≥50 % in a major vessel at coronary CTA

● 159 vessels (103 patients)

● Mean age, 63 years

● Male gender, 74 %

● Proportion of vessels with FFR ≤0.80: 56 %

● Proportion of FFR values directly measured: 100 %

84 %

(78–90)

88 %

(77–95)

82 %

(73–89)

74 %

(62–84)

92

(85–97)

0.90

(0.85–0.96)

De-FACTO

Min J et al., 2012 [25]

● Statistically powered on a per-patient basis

● 17 centres

● Prospective

● Obstructive CAD: Coronary stenosis >50 %

● Ischemia: FFR or FFRCT ≤0.80

● Blinded FFRCT core-lab analyses

● Patients with suspected or known CAD who underwent clinically indicated non-emergent ICA after coronary CTA (<60 days), and with at least one ICA stenosis 30–90 %

● 252 patients (408 vessels)

● Mean age, 63 years

● Male gender, 71 %

● Proportion of patients with FFR ≤0.80: 53 %

● Proportion of FFR values directly measured: 100 %

73 %

(67–78)

90 %

(84–95)

54 %

(46–83)

67 %

(60–74)

84 %

(74–90)

0.81

(0.75–0.86)

NXT

Norgaard B et al., 2014 [26]

● Statistically powered on a per-patient basis

● 10 centres

● Prospective

● Coronary CTA acquisition protocols according to societal guidelines

● Image quality independently evaluated using a predefined scoring system

● Obstructive CAD: Coronary stenosis >50 %

● Ischemia: FFR or FFRCT ≤0.80

● Blinded FFRCT core-lab analyses using an updated FFRCT analysis software

● Blinded FFR core-lab analyses

● Patients suspected of CAD who underwent coronary CTA and ICA within <60 days

● 254 patients (484 vessels)

● Mean age, 64 years

● Male gender, 64 %

● Proportion of patients with FFR ≤0.80: 32 %

● Proportion of FFR values directly measured: 97 %

81 %

(76–85)

86 %

(77–92)

79 %

(72–84)

65 %

(56–74)

93 %

(87–96)

0.90

(0.87–0.94)

AUC area under curve of the receiver operating characteristics curve, CAD coronary artery disease, CI confidence interval, CTA CT angiography, FFR fractional flow reserve, FFRCT fractional flow reserve calculated from coronary CTA, ICA invasive coronary angiography, PPV positive predictive value, NPV negative predictive value

The FFRCT "proof of concept" was documented in the Diagnosis of Ischemia-Causing Coronary Stenoses by Noninvasive Fractional Flow Reserve Computed from Coronary Computed Tomographic Angiograms (DISCOVER-FLOW) trial, which included 103 patients and 159 vessels [25]. The primary endpoint of the study was met with a per-vessel diagnostic accuracy of 84 % for FFRCT compared to 59 % for coronary CTA alone, arising from an increase in specificity from 40 % for coronary CTA to 82 % for FFRCT. Moreover, the ability of FFRCT to discriminate ischemia was significantly improved, with an increase in the area under the receiver operating characteristics curve (AUC) as compared to coronary CTA of 0.90 versus 0.75 (p < 0.001). The second study, Determination of Fractional Flow Reserve by Anatomic Computed Tomographic Angiography (DeFACTO) included 252 patients (407 vessels) and showed improved per-patient diagnostic accuracy for FFRCT (73 %) compared to coronary CTA (64 %) [26]. However, the pre-specified primary endpoint of the study was not met, as the lower limit of the 95 % confidence interval (67–-78 %) for diagnostic accuracy of FFRCT did not exceed 70 %. However, FFRCT demonstrated superior per-patient and per-vessel discrimination of ischemia compared to coronary CTA, with AUCs of 0.81 versus 0.68 (p < 0.001) and 0.81 versus 0.75 (p < 0.001), respectively. The most recent study, the Analysis of Coronary Blood Flow Using CT Angiography, Next Steps (NXT) trial, included 254 patients and 484 vessels and incorporated learnings from the previous two trials, including the latest generation of FFRCT analysis software [27, 36]. The primary endpoint in the NXT study was met, with improved discrimination of per-patient ischemia, with an AUC for FFRCT of 0.90 versus 0.81 for coronary CTA (p < 0.001). Similarly, on a per-vessel basis, FFRCT had higher discriminatory power in detecting ischemia than coronary CTA, with AUCs of 0.93 versus 0.79, respectively (p <0.0001). The per-patient diagnostic performance of FFRCT was higher than that of coronary CTA, with improved accuracy (81 % vs. 53 %, p < 0.001) and specificity (79 % vs. 34 %, p < 0.001), and comparable sensitivity. Even in comparison to ICA stenosis severity ≥ 50 %, FFRCT tended to increase per-patient accuracy (81 % vs. 77 %, p = 0.09), arising from an increase in sensitivity (64 % vs. 86 %, p < 0.001), with no sacrifice in specificity. Notably, the NXT trial cohort pretest probability of significant CAD was in the intermediate range, thus representing patients in whom non-invasive imaging is best employed [6]. The improved diagnostic performance of FFRCT in the NXT versus DeFACTO trials, particularly with regard to specificity, reflects substantial refinements in FFRCT technology and physiologic modeling, as well as increased focus on coronary CTA image quality [27, 36]. Accordingly, preliminary data indicate that employing the latest generation of FFRCT computation technology (as used in the NXT trial) and standardized CT image metrics on the DeFACTO CT data set resulted in diagnostic performance of FFRCT comparable to that of the NXT trial [37]. The impact of coronary CTA image quality on the diagnostic performance of both coronary CTA and FFRCT is well established [38, 39, 40]. The diagnostic performance of coronary CTA and FFRCT have been shown to improve with the adherence to best practice guidelines for image acquisition, particularly regarding heart rate control and use of pre-scan nitroglycerin [39, 40]. In contrast to previous trials, strict adherence to these guidelines in the NXT trial was mandatory.

In the setting of coronary calcification, coronary CTA interpretation is particularly challenging, with decreasing diagnostic specificity in relation to increasing coronary calcification [14]. In the NXT trial, among 55 patients (28 %) with an Agatston score of less than 400, the accuracy, sensitivity, and specificity of FFRCT were 75 %, 88 %, and 69 %, respectively [27]. Accuracy among these patients was significantly improved compared to coronary CTA (44 %), arising from a threefold increase in specificity, from 23 % with coronary CTA to 69 % with FFRCT.

Coronary stenosis in the intermediate range represents a particular challenge in clinical practice, since the relationship between coronary CTA or ICA stenosis severity and ischemia is very poor [2]. In the DISCOVER-FLOW, DeFACTO, and NXT trials, among patients with intermediate stenosis, the diagnostic performance of FFRCT versus coronary CTA mirrored overall study results [25, 26, 27, 41]. Of note, more than 90 % of patients in the NXT study had intermediate coronary stenosis ranging between 30 % and 70 % [27].

Based on the clinical evidence regarding the diagnostic performance of FFRCT, as well as guidelines on the management of stable CAD [6, 25, 26, 27, 41], FFRCT seems most appropriately applied as a gatekeeper to the catheterization laboratory in symptomatic patients with a lower intermediate range pretest probability of CAD and with one or more intermediate-range coronary stenoses on coronary CTA (Fig. 2). In the future, however, with improvements in CT spatial resolution and/or the FFRCT technology, it may be possible to apply coronary CTA for assessment of higher-risk patients. Accordingly, FFRCT appears to significantly improve the diagnostic specificity of coronary CTA in the event of relatively high levels of coronary calcification.
Fig. 2

Case example of a 63-year-old female patient with chest pain (courtesy of Andrejs Erglis, MD, Riga, Latvia). Coronary CTA demonstrates a calcified > 50 % stenosis in the mid RCA and a non-calcified > 70 % stenosis in the LAD (red arrows). The FFRCT computational model reveals that lesions are not hemodynamically significant, with FFRCT values > 0.80. Coronary angiography with measurement of FFR confirms that stenoses do not induce ischemia with FFR values > 0.80 in either RCA or LAD. In real-world practice, symptomatic patients with > 50 % intermediate-range stenosis on coronary CTA would typically be referred for additional testing with either non-invasive functional imaging or invasive coronary angiography (with fractional flow reserve measurement). FFRCT analysis applied to the standard coronary CTA data set can differentiate patients with ischemia-producing lesions from those with non-functional stenoses, and thus avoid the need for further testing, including invasive coronary angiography. CTA CT angiography, FFR fractional flow reserve, FFRCT fractional flow reserve calculated from coronary CTA, LAD left anterior descending artery, RCA right coronary artery

There is a good direct per-vessel correlation between FFRCT and FFR, with Pearson’s correlation coefficients ranging from 0.63 to 0.82, with a systematic slight underestimation of FFRCT (mean difference of 0.019-0.058) [25, 26, 27]. A recent study found high reproducibility with repeated FFRCT analyses, with a within-subject coefficient of variation of 3.4 % [42].

Non-invasive fractional flow reserve—limitations

Since FFRCT is derived from coronary CTA imaging data, significant CT imaging artefacts such as motion, low contrast, or blooming from coronary calcification may impair its diagnostic performance. These issues can be minimized by adhering to coronary CTA image acquisition guidelines, particularly by the administration of heart rate-lowering medication and sublingual nitrates before image acquisition [37, 38, 39, 40]. As FFRCT computation is based on global coronary and myocardial information, this modality may be inherently less susceptible to single artefacts than coronary CTA. Accordingly, It has been shown that even at lower levels of coronary CTA image quality, FFRCT continues to provide significant diagnostic improvement compared to coronary CTA [43]. Moreover, it is anticipated that further refinements in CT technology and the FFRCT analysis process may reduce the impact of CT imaging artefacts.

The diagnostic performance of FFRCT may be affected by a patient-specific microcirculatory response to vasodilatation and physiologic conditions that can affect fluid viscosity. Viscosity is assumed from the hematocrit/haemoglobin concentration, and in the normal range, it has minimal influence on FFRCT. The potential influence of severe anaemia on FFRCT is not known. To date, the diagnostic performance of FFRCT has been studied only in patients with suspected stable CAD, and thus the generalizability of FFRCT to other patient cohorts (e.g., with acute coronary syndromes or previous coronary intervention) is unknown. Currently, FFRCT requires offsite computer processing, with a 24-hour response time. Reduced order models for FFRCT computation may allow for onsite FFRCT assessment in the future [44], but further investigation in prospective multi-centre trials is needed in order to determine the diagnostic performance of these techniques. As for other non-invasive testing modalities, prospective data assessing the cost effectiveness of FFRCT in clinical practice are lacking. However, simulation analyses based on historical data indicate that the use of FFRCT to guide the selection of ICA and coronary revascularization could reduce costs and improve outcomes for patients with stable CAD [45, 46]. The ongoing multi-centre Prospective Longitudinal Trial of FFRCT: Outcome and Resource Impacts (PLATFORM) trial (ClinicalTrials.gov Identifier: NCT01943903) compares the effect of FFRCT-guided versus standard functional diagnostic evaluation on clinical outcomes, resource utilization, and costs in patients with suspected CAD.

Comparison of diagnostic performance of non-invasive functional tests using FFR as reference standard

In view of the emergence of the use of measured FFR rather than visual assessment by by ICA for interventional decision-making [3, 28, 29, 30, 31, 32], NIFT modalities are increasingly being evaluated using measured FFR as the reference standard. However, the published studies are small and single-centre-based, and employ local site-reads of both NIFT and FFR results. In many of these studies, when FFR was not or could not be measured, values were assigned to vessels, and accordingly to vascular perfusion territories, on the basis of the angiographic findings. For example, in a recent meta-analysis of 12 studies reporting the diagnostic performance of CMR in stable CAD using FFR as the reference standard, on a coronary territory basis, pooled sensitivity was 88 % and pooled specificity was 89 %, suggesting high diagnostic accuracy of CMR for detection of flow-limiting stenosis [47]. Among the studies, however, the rate of actual FFR measurements in vessels included in analysis varied from 12 % to 100 %, with fewer than 75 % of vessels undergoing direct FFR interrogation in 10 of the studies [47, 48, 49]. This may lead to significant error, since it is well known that patients with < 50 % stenosis on ICA may have functionally significant stenosis (FFR ≤ 0.80) [50], and that patients with stenosis severity > 50 %, or even > 70 %, often have FFR values > 0.80 [2, 3]. Thus it is likely that studies that include a significant proportion of assigned rather than measured FFR values may not be meaningfully different from those using ICA as reference standard. Figure 3 shows a comparison of studies reporting the diagnostic performance (sensitivity and specificity) of stress echocardiography [51], SPECT [52], CMR [48, 49], coronary CTA [2, 24, 25, 26, 27], FFRCT [25, 26, 27], and TAG [23, 24] for identifying hemodynamically significant CAD using FFR (threshold, 0.80) as the reference standard, in which more than 75 % of the FFR values used for analysis were directly interrogated.
Fig. 3

Per-vessel/myocardial territory diagnostic performance (sensitivity and specificity) of non-invasive functional testing modalities for identifying hemodynamically significant coronary artery disease using FFR (threshold, 0.80) as the reference standard. Only data from studies in which more than 75 % of the FFR values used for analysis were directly interrogated are shown. Numbers refer to references. The open circle in the upper right corner indicates the reference standard, FFR. CMR cardiac magnetic resonance, CTA CT angiography, FFRCT fractional flow reserve calculated from coronary CTA, SPECT single photon emission computed tomography, TAG transluminal attenuation gradient

Conclusions

FFRCT derived from standard coronary CTA image data sets using FFR as the reference standard shows high diagnostic performance in patients with stable CAD, and may encourage the use of coronary CTA with FFRCT as a "one-stop shop", providing high diagnostic sensitivity for anatomic evaluation of CAD and high specificity for ischemia. FFRCT may thus enhance the potential of coronary CTA as a gatekeeper to the catheterization laboratory. Studies regarding the most appropriate clinical use (e.g., patient selection) and cost-effectiveness of FFRCT relative to conventional NIFT are ongoing.

Notes

Acknowledgments

The scientific guarantor of this publication is Hans Erik Botker (heb@dadlnet.dk). The authors of this manuscript declare relationships with the following companies: GE Healthcare, HeartFlow, Siemens, and Edwards Lifesciences. The authors state that this work has not received any funding. No complex statistical methods were necessary for this paper. Institutional Review Board approval and written informed consent was not required for this study because this was a retrospective review. Some study subjects or cohorts have been previously reported. Methodology: review.

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Copyright information

© European Society of Radiology 2015

Authors and Affiliations

  1. 1.Department of Cardiology BAarhus University Hospital SkejbyAarhus NDenmark
  2. 2.Department RadiologySt. Paul’s HospitalVancouverCanada

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