Several imaging technologies have become available for diagnostic cardiac imaging, such as single photon emission computed tomography (SPECT) [1–7], positron emission tomography (PET) [8], magnetic resonance imaging (MRI) [9–13], and coronary computed tomography angiography (CTA) [14–38]. These techniques individually offer unique advantages, but also suffer from specific limitations. CTA mainly provides anatomical information, MRI offers anatomical and functional information, whereas SPECT and PET offer metabolic and functional information. In particular gated SPECT provides functional information as this modality can be applied during conventional stress and allows the calculation of left ventricular volumes and ejection fraction. Software techniques have been developed to combine cardiac images from different modalities and generate composite multimodality images, allowing better diagnosis than obtained from images analyzed separately. Hybrid scanners (SPECT/CT and PET/CT) have also been proposed for integrated cardiac imaging.

However, several studies have claimed that CTA as a stand-alone imaging modality may provide useful and practical information in patients with suspected and known coronary artery disease (CAD) [37–41]. Gaemperli et al. [39] showed that CTA offers a valuable alternative for the diagnosis of CAD but its value in the detection of functionally relevant coronary stenoses remains uncertain. The authors compared the accuracy of 64-slice CTA with that of myocardial perfusion imaging using perfusion SPECT as the gold standard for the detection of functionally CAD in 100 consecutive patients. Using a cut-off value of >75% area stenosis, CTA yielded a sensitivity of 75%, a specificity of 95%, a negative predictive value of 93%, a positive predictive value of 50% and an accuracy of 94%, respectively. It was concluded that CTA is a reliable tool to rule out functionally relevant CAD in a non-selected population with an intermediate pretest likelihood of disease. However, an abnormal CTA proved to be a poor predictor of myocardial ischemia.

Min et al. [40] assessed the costs and clinical outcomes in individuals without known CAD who underwent CTA compared with those in matched patients who underwent myocardial perfusion SPECT. One-year CAD costs (additional diagnostic coronary testing, CAD hospitalization, and coronary procedural and revascularization costs) and clinical outcomes were examined in individuals without known CAD who underwent CTA (n = 1,647) compared with those who underwent myocardial perfusion SPECT (n = 6,588). The CTA group was less likely to undergo coronary angiography than the myocardial perfusion SPECT group. Adjusted CAD costs in the CTA group were 25.9% lower than in the myocardial perfusion SPECT group. Consequently, individuals without known CAD who underwent CTA as an initial diagnostic test compared with those who underwent SPECT incurred lower health care costs with similar rates of myocardial infarction and CAD-related hospitalization.

In the present issue of the International Journal of Cardiovascular Imaging, Haramati et al. [41] evaluated the utility of CTA for demonstrating CAD in inner-city outpatients. CTA was prospectively compared with stress SPECT myocardial perfusion imaging in 61 patients in an ethnically diverse, gender-balanced population. A luminal stenosis of >70% on CTA was considered positive. Results were compared with SPECT perfusion defects and correlated with clinical endpoints (hospital admissions, cardiovascular events, coronary interventions and deaths). There was moderate global agreement of 79% between CTA and SPECT (kappa 0.483). With SPECT as the reference standard, CTA had a sensitivity of 73%, a specificity of 80%, a negative predictive value of 90%, and a positive predictive value of 55%. Eleven patients (18%) underwent subsequent cardiac catheterization, which proved to be positive in 91% of patients. Compared with catheterization, CTA and SPECT had positive predictive values of 90% and 83%, respectively.

The current study supports the value of CTA as an alternative modality for the evaluation of CAD in an ethnically diverse, gender balanced inner-city outpatient population, whereby CTA had a high negative predictive value of 90% in comparison with SPECT. Reported limitations of the study were the rather small study population, the small portion of diabetes patients (10%), the low number of invasive angiograms (18%), the relatively short follow-up period of 9 months, and the low event rate. Furthermore, in comparing CTA with SPECT one has to realize that SPECT perfusion imaging and CTA provide different and complementary information on CAD, namely detection of ischemia versus detection of atherosclerosis. This might explain the discordant findings in 13 patients i.e. 46 had a normal SPECT and 33 patients a normal CTA. Either a non-critical stenosis (i.e. normal CTA) may still give rise to a perfusion defect (certainly in case of a cut-off value of 70% for a critical stenosis), or a normal SPECT may occur with anatomically significant—but hemodynamically insignificant—atherosclerosis. In addition, seven patients could not be evaluated by CTA. Lastly, as the mean pretest-likelihood was rather low (30%), the number of false positives tend to increase which may affect specificity. Nevertheless, the study of Haramati et al. [41] is a very valuable contribution to the early identification of coronary atherosclerosis in an ethnically heterogeneous group of inner-city outpatients.