CONTINUING EDUCATION

Myocardial Perfusion Imaging Versus CT Coronary : When to Use Which?

Balaji Tamarappoo and Rory Hachamovitch

Section of Cardiovascular Imaging, Department of Cardiovascular Medicine, Cleveland Clinic, Cleveland, Ohio

Learning Objectives: On successful completion of this activity, participants should be able to describe (1) the various types of noninvasive tests and how the results of each are utilized; (2) recent advances in CT coronary angiography, PET myocardial perfusion imaging, and SPECT myocardial perfusion imaging of ; and (3) the clinical use of anatomic versus physiologic tests in symptomatic patients with known or suspected coronary artery disease. Financial Disclosure: The authors of this article have indicated no relevant relationships that could be perceived as a real or apparent conflict of interest. CME Credit: SNM is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to sponsor continuing education for physicians. SNM designates each JNM continuing education article for a maximum of 1.0 AMA PRA Category 1 Credit. Physicians should claim only credit commensurate with the extent of their participation in the activity. For CE credit, participants can access this activity through the SNM Web site (http://www.snm.org/ce_online) through June 2012. suspected coronary artery disease (CAD). The results of Both anatomy- and physiology-based approaches to patient these tests are used for patient risk stratification, evaluation management have advantages and limitations. Compared of myocardial ischemia as a cause of symptoms, and assess- with the latter, the former has a superior ability to exclude ment of ongoing disease management. Stress myocardial disease and does not miss high-risk coronary artery disease (CAD). However, it is limited by a possibility of overestimating perfusion imaging (MPI) with SPECT is a well-established the severity of CAD and of potentially failing to determine modality capable of quantifying relative stress and rest myo- which posttest therapeutic approach optimizes treatment cardial perfusion and left ventricular function with estab- benefit. On the other hand, although a physiology-based lished diagnostic accuracies and prognostic performance approach could potentially identify optimal therapeutic strate- characteristics. More recently, perfusion imaging with gies, the possibility of both false-positive and false-negative PET has been shown to have similar diagnostic accuracy findings is a concern. This review incorporates some of the more recent advances in CT coronary angiography and for detection of CAD, with the added advantage of en- myocardial perfusion imaging (MPI), including PET MPI, into hanced image quality and the potential to quantify absolute a discussion of anatomic versus physiologic imaging and myocardial blood flow. The introduction of noninvasive CT provides our perspective on how an anatomy-based testing coronary angiography as part of routine patient care al- strategy centered in CT coronary angiography versus a lowed anatomic characterization of coronary arteries with physiology-based testing strategy with MPI may be clinically outstanding accuracy for detecting the presence of ana- used for the evaluation of known or suspected CAD in symptomatic patients. tomic obstructions secondary to CAD. More recently, eval- uation of the prognostic value of this test has been reported Key Words: CT coronary angiography; myocardial perfusion; review by several centers. Interestingly, the availability of CT J Nucl Med 2011; 52:1079–1086 coronary angiography has brought to the forefront the long- DOI: 10.2967/jnumed.110.081133 standing question of assessing CAD on the basis of anatomic criteria (CT coronary angiography) versus physiologic crite- ria (MPI). The role of coronary calcium score, CT coronary angiography, and MPI for the evaluation of asymptomatic intermediate- to high-risk patients and symptomatic patients Noninvasive cardiac imaging tests are often the first step has previously been discussed by Berman et al. in a compre- in the assessment of coronary anatomy, myocardial perfu- hensive review (1). The goal of this current review is to sion, or left ventricular function in patients with known or incorporate some of the more recent advances in CT coronary angiography and MPI, including PET MPI, into this discus- sion of anatomic versus physiologic imaging and to provide our perspective on how an anatomy-based testing strategy Received Jan. 28, 2011; revision accepted May 16, 2011. centered in CT coronary angiography versus a physiology- For correspondence or reprints contact: Rory Hachamovitch, Section of Cardiovascular Imaging, Department of Cardiovascular Medicine, Cleveland based testing strategy with MPI may be clinically used for the Clinic, 9500 Euclid Ave., Desk J1-5, Cleveland, OH 44195. evaluation of known or suspected CAD in symptomatic pa- E-mail: [email protected] COPYRIGHT ª 2011 by the Society of , Inc. tients.

MPI VERSUS CT CORONARY ANGIOGRAPHY • Tamarappoo and Hachamovitch 1079 ANATOMY-BASED APPROACH: CT CORONARY by SPECT MPI showed that at the extremes of luminal ANGIOGRAPHY stenosis severity (,50% [negative predictive value, 98%] Diagnostic Value and $90% [positive predictive value, 74%]), CT coronary A recent review of advanced cardiovascular imaging angiography capably predicted the absence or presence of summarized the published studies examining the diagnostic ischemia (8). In contrast, there was wide variability in the accuracy of CT coronary angiography. The weighted sen- prevalence of ischemia among patients with a luminal sitivity and specificity of these studies were relatively high stenosis severity of 50%–90%. All these studies demonstra- (per patient, 94% and 77%, respectively; per segment, 83% ted that the absence of plaque on CT coronary angiography and 92%, respectively) (2). Methodologically, these studies can be an extremely useful finding in ruling out CAD in were based on the recruitment of stable patients referred symptomatic patients; however, in almost 50% of low- to for elective catheterization and for a research CT coronary intermediate-likelihood patients with stenosis greater than angiography study. Not surprisingly, in light of this source of 50% on CT coronary angiography, a second noninvasive patient recruitment, the prevalence of CAD was relatively imaging test may be necessary to definitively diagnose high (62%), thus affecting both positive predictive value ischemia as the cause of symptoms. and negative predictive value (per patient, 84% and 87%, respectively). CT coronary angiography is unlikely to be Prognostic Value applied in practice to populations with this high a prevalence The prognostic literature supporting the use of CT cor- of CAD. If recalculated for a CAD prevalence of 15% (more onary angiography has been greatly expanded over the past likely to be seen in practice), the positive and negative pre- 5 years, and several important points emerge from the dictive values become 46% and 98%, respectively. current literature. First, there is little doubt that a normal A more realistic assessment of CT coronary angiography CT coronary angiography study, particularly in the absence of any evidence of atherosclerosis, is associated with both a was obtained by the ACCURACY trial (Assessment by very high negative predictive value for the occurrence of Coronary Computed Tomographic Angiography of Individ- adverse events and a low likelihood of obstructive CAD. A uals Undergoing Invasive Coronary Angiography), a pro- recent metaanalysis of 18 studies evaluating 9,592 patients spective, multicenter study enrolling 230 patients with a with a 20-mo median follow-up revealed a 0.15%/y rate of low to intermediate pretest likelihood of CAD who under- death or and a 0.17% rate of death, went both CT coronary angiography and invasive coronary myocardial infarction, or (major adverse angiography (3). In that study, although observed sensitivity coronary event) (9). Thus, the risk of adverse cardiovascu- and specificity were very good to excellent (93.8% and lar events after a completely normal CT coronary angiog- 81.8%, respectively, for detecting stenosis .70%) and neg- raphy result is comparable to the baseline risk of a healthy ative predictive value was outstanding (98.8%), the positive patient. Further, significant risk stratification is achieved by predictive value of CT coronary angiography was only the results of CT coronary angiography in that among the 47.6%. This study illustrated that CT coronary angiogra- 2,772 patients with obstructive CAD, the authors reported phy, although able to exclude obstructive CAD with con- annualized rates of 8.8% for a major adverse coronary fidence, misidentifies disease in approximately half of event, 2.2% for death, and 2.1% for myocardial infarction. patients with positive test results. In patients with a CT These results suggest an efficient stratification, with an ab- coronary angiography–based stenosis of more than 50%, normal study indicating a relative risk more than 40 times there is still a wide margin of error in the grading of steno- that of a normal study. sis severity, reducing the accuracy of identifying individu- Further, as has been shown with MPI, the risk of adverse als whose symptoms may be attributed to myocardial events is closely associated with the extent and severity of ischemia. In the nonacute setting, CT coronary angiography underlying CAD. In a study of 1,127 low- to intermediate- is extremely valuable in ruling out CAD but varies widely risk symptomatic patients referred for 16-slice CT coronary in the ability to identify the exact severity of luminal steno- angiography for the diagnosis of stable chest pain syndrome, sis and, therefore, its hemodynamic relevance. Min et al. demonstrated that during a 15-mo follow-up, the Subsequently, several studies have examined the rela- risk of death increased with the number of vessels that had tionship between assessment of coronary artery stenosis on atherosclerotic plaque and with the severity of stenosis. CT coronary angiography and assessment of myocardial Further, risk was greatest in patients who had plaque in the ischemia on SPECT MPI and PET MPI. These retrospec- left main coronary artery or the proximal left anterior de- tive studies showed that only 30%–50% of all individuals scending coronary artery (10). with a maximal stenosis of more than 50% exhibited myo- To evaluate whether CT coronary angiography has incre- cardial ischemia on MPI (4–7). In the subgroup of individ- mental prognostic value over MPI, a recent study followed uals with a maximal stenosis of 50%–75%, the prevalence 541 patients at intermediate risk for CAD (defined as 15%– of ischemia was even lower, ranging from 16% to 20%. A 85%) who underwent both CT coronary angiography and more recent study of 292 patients comparing luminal steno- SPECT MPI. Luminal stenosis greater than 50% was sis by CT coronary angiography and myocardial ischemia detected by CT coronary angiography in 31% of study

1080 THE JOURNAL OF NUCLEAR MEDICINE • Vol. 52 • No. 7 • July 2011 patients, and abnormal myocardial perfusion (summed stress obstructive CAD may be considered candidates for a more score $ 4) was observed in 33%. After adjustment for clin- aggressive course of treatment and are more likely to be re- ical risk factors, both obstructive plaque on CT coronary ferred for invasive assessment. angiography and abnormal results on SPECT MPI were independent predictors of late events, and the combined IMAGING IN A POST-COURAGE WORLD use of the 2 modalities significantly enhanced the prediction The results of the COURAGE trial (Clinical Outcomes of major adverse cardiac events, including all-cause mortal- Utilizing Revascularization and Aggressive Drug Evaluation) ity, revascularization, and infarction (11). indicated that survival benefit was not enhanced—nor quality Unlike invasive coronary angiography, CT coronary of life improved—when percutaneous coronary intervention angiography can assess atherosclerotic plaque location, (PCI) was added to a strategy of aggressive medical therapy morphology, and composition (2). It is likely that with time, in patients with documented obstructive CAD (13). Although the prognostic and therapeutic implications of this informa- the implications of this trial for the use of revascularization tion will be used to further enhance prognostication and its procedures are well appreciated, the implications for the application to clinical practice (12). Similarly, a normal MPI imaging community are often overlooked. In most patients result, although excluding obstructive CAD, cannot deter- currently referred for stress MPI or CT coronary angiography mine whether the disease process has already started, thus in the United States, the referral is for the purpose of assess- differentiating between the need for primary versus secon- ing known or suspected CAD. If, as suggested by COUR- dary prevention (2). On the other hand, CT coronary angiog- AGE, neither survival nor quality of life will benefit from raphy is similar to invasive coronary angiography, in that it revascularization, the routine use of noninvasive imaging to has several significant limitations. Neither modality can reli- detect possible ischemia and identify possible revasculariza- ably measure the functional significance of coronary stenosis tion candidates is unnecessary. In a future world shaped by (2). Also similar to invasive angiography, CT coronary COURAGE, the use of imaging in the assessment of ische- angiography is ineffective in determining which individual mic disease will be limited to evaluation of those plaque is likely to be the site of a future acute coronary event patients suspected of having left main CAD. (2,12). The COURAGE trial was performed on patients with documented obstructive CAD. Many of these patients may Posttest Management Strategy have had either limited or no inducible ischemia or extensive In Figure 1, we outline an anatomy-based posttest man- prior myocardial infarction. Although the COURAGE trial agement strategy for a stable, symptomatic patient with an does suggest a lack of revascularization benefit in patients intermediate to high likelihood of 50%–85% (1). An anat- identified on anatomic grounds, data support a possible role omy-based approach in a patient with unstable angina would for assessment of ischemia or flow reserve in the identi- most likely comprise invasive coronary angiography. In pa- fication of patients who may benefit from revascularization. tients with normal findings on CT coronary angiography, The use of fractional flow reserve—defined as the ratio both obstructive CAD and atherosclerosis are effectively of pressure proximal and distal to a stenotic lesion during excluded, and the patient is thus a candidate for primary pre- vasodilator-induced hyperemia—to measure the physiologic vention. In patients showing nonobstructive lesions (,50% significance of anatomic lesions at the time of invasive stenosis) on CT coronary angiography, there is no need for angiographic studies has been shown to play a significant further noninvasive assessment with SPECT MPI or for inva- role in identifying revascularization candidates. In patients sive assessment. However, this result still indicates a diag- with a fractional flow reserve greater than 0.75, PCI can nosis of CAD, and secondary prevention would thus be the be deferred without increased patient risk, despite the an- best subsequent course. In patients showing mild obstructive giographic appearance of a significant stenosis (14). Further- lesions (50%–70% stenosis) on CT coronary angiography, more, cardiac event rates during a 5-y follow-up were lower secondary prevention would still be the required clinical in patients with a fractional flow reserve greater than 0.75 course. However, the presence of limiting symptoms, limited without PCI than with PCI (15,16). Even in the setting of left functional capacity, or other issues resulting in recurrent main CAD, these investigators found that a fractional flow patient presentation would justify a noninvasive imaging reserve greater than 0.75 was associated with an excellent strategy with SPECT MPI or PET MPI to rule out myocar- 3-y survival rate and freedom from major adverse cardio- dial ischemia. Finally, in patients with results suggestive of vascular events (17). Conversely, event rates increased high-risk CAD (left main lesion or proximal left anterior when lesions with a fractional flow reserve lower than descending lesion) on CT coronary angiography, it is gener- 0.75 were not revascularized (18). Finally, FAME (Frac- ally agreed that referral for invasive assessment in conjunc- tional Flow Reserve Versus Angiography for Multivessel tion with secondary prevention measures is an appropriate Evaluation), a prospective multicenter randomized trial, clinical course. Many centers perform gated CT studies, thus compared a fractional flow reserve–guided versus angiog- permitting assessment of left ventricular ejection fraction raphy-based revascularization strategy in 1,005 patients and wall motion as part of routine studies. Patients found with multivessel CAD (19). At 1 y, the fractional flow to have left ventricular dysfunction in conjunction with reserve–guided strategy reduced the rate of a composite

MPI VERSUS CT CORONARY ANGIOGRAPHY • Tamarappoo and Hachamovitch 1081 FIGURE 1. Potential testing algorithm based on use of CT coronary angiography. endpoint (death, myocardial infarction, repeated PCI, and revascularization or medical therapy in that study was not coronary artery bypass grafting) by 30% (P 5 0.02). Fur- based on the extent of ischemia. The COURAGE nuclear ther, the rate of mortality and myocardial infarction at 1 y substudy compared optimal medical therapy, versus revascu- was reduced by 34% (P 5 0.04). Thus, a strategy of phys- larization plus optimal medical therapy, in 314 patients who iologic assessment of coronary lesions before revasculari- underwent noninvasive MPI before and 6–18 mo after ran- zation may identify a subgroup of patients who may benefit domization (25). That substudy demonstrated that, compared from revascularization. However, fractional flow reserve with optimal medical therapy alone, revascularization in addi- measurements are not routinely used across all centers per- tion to optimal medical therapy led to decreased ischemia forming PCI before revascularization. with an associated decrease in adverse cardiac events. The This approach can be extended to the use of an MPI- above-mentioned studies suggest that knowledge of the extent based decision-making approach in identifying candidates of ischemia may be valuable in guiding clinical management for revascularization versus medical therapy. Hachamovitch by allowing us to identify the treatment strategy—medical et al. demonstrated a survival benefit with medical therapy versus revascularization—that would confer a mortality benefit. for patients showing mild or no ischemia on MPI, compared with similar patients who underwent revascularization; how- PHYSIOLOGY-BASED APPROACH: MPI ever, revascularization produced a survival benefit over med- Prognostic Value ical therapy in patients with moderate to severe ischemia An extensive body of literature supports the ability of (20). Similarly, in a subsequent study, these authors found stress MPI to successfully risk-stratify a variety of patient that the relative benefits of revascularization over medical groups (26). A normal exercise MPI result in patients who therapy were seen for ischemia but not for ejection fraction are able to attain more than 85% of maximal predicted heart (21). These results were extended to asymptomatic diabetic rate, or a normal pharmacologic stress MPI result, can patients in a subsequent study from the Mayo Clinic group identify patients at low risk for future cardiac events (27). that again found the presence of inducible ischemia to be A metaanalysis of 19 studies (n 5 39,173 patients) found associated with improved survival in the setting of revascu- that a normal- or low-risk stress MPI result was associated larization (22). In contrast, Tarakji et al., from the Cleveland with an annual cardiac event rate of only 0.6% (25th–75th Clinic, found no such survival benefit using a stress PET and percentiles, 0.5%–0.9%) (28). Even in the presence of 18F-FDG protocol in a cohort of patients with advanced angiographically documented CAD, a normal stress MPI CAD; however, these patients had more severe and extensive result still defines a group with only a 1% annual risk of CAD than patients in previous studies (23). Indeed, in a cardiac events (29). On the other hand, perfusion abnormal- recent study, the mortality benefit of a perfusion-guided ities of increasing extent and severity are closely associated approach was found to also apply to patients with a previous with increasing patient risk (26). These findings have been history of CAD as long as significant scarring (.10% of shown in multiple patient subgroups, using multiple radio- myocardium) was absent (24). isotopes, as well as several different stress agents. Although the COURAGE study called into question the use Although this risk-based approach to the use of cardio- of a revascularization strategy, assignment of patients to either vascular imaging has dominated thinking for several years,

1082 THE JOURNAL OF NUCLEAR MEDICINE • Vol. 52 • No. 7 • July 2011 basing patient management on the results of risk stratification on the basis of the data presented here, patients with scarring in no way ensures improvement and patient well-being or of more than 10%–15% of the myocardium may not be can- survival. In light of increasing calls for a value-based health didates for revascularization and may therefore be candidates care system, we will need to demonstrate that patients can for a preventive strategy. benefit from the use of these expensive imaging modalities. Thus, despite the past emphasis on risk-based testing, a newer PET MPI paradigm of benefit-based testing is slowly emerging (26). Compared with SPECT MPI, PET MPI has several distinct advantages. First, the increased sensitivity of this SPECT MPI technique, along with superior spatial and temporal reso- A post–SPECT MPI patient management strategy fo- lution, provides better diagnostic accuracy (2,12,30). Further, cusing on the identification of potential revascularization because stress images are obtained during infusion of a vaso- candidates is shown in Figure 2. Patients with abnormal dilator, the results of stress gated PET represent peak stress SPECT studies showing more than 10%–15% of the myo- wall motion. Although vasodilator-stress gated images are cardium ischemic are candidates for referral for invasive not the equivalent of exercise gated images, investigators assessment with an eye to possible revascularization. On have found that the failure to show an increased ejection the other hand, patients whose SPECT result is normal, fraction on stress gated PET images compared with rest abnormal but with slight ischemia (,10%–15% of myocar- images is strongly associated with the presence of extensive dium), or abnormal but with no inducible ischemia are not CAD (31). This ejection fraction reserve has also been candidates for catheterization and would be considered for shown to be prognostically significant (32). Finally, the abil- preventive treatment only. The exception to this approach ity to quantify absolute myocardial blood flow (2,33,34)with in these 3 groups of patients is when underestimation of stress PET MPI permits identification of patients in whom ischemia is a concern. Some patients with angiographically the relative regional distribution of tracer may appear normal significant CAD may manifest a normal SPECT result because of a balanced reduction of blood flow. because of balanced ischemia due to the relative nature of The ability to quantify myocardial blood flow with 82Rb perfusion defect assessment. When there is an equivocal PET has been shown to be useful in identifying 3-vessel SPECT result, a normal SPECT result but recurrent or lim- CAD (35). Furthermore, mean flow rate has been shown to iting symptoms, or discordance between clinical findings serve as a useful prognostic marker for adverse cardiac during stress and findings on stress SPECT, CT coronary an- events. Herzog et al. demonstrated that in the setting of a giography may be appropriate (1). In the subgroup of patients normal MPI result, a preserved mean flow rate of more than with significant stress-induced ischemic 2.0 may provide a warranty period of 3 y versus a reduced changes, stress-induced symptoms, serious stress-induced mean flow rate (36). Also, mean flow rate results were found ventricular arrhythmias, and unequivocal transient ischemic to stratify patients—both those with normal and those with dilation or other ancillary SPECT findings, there may be abnormal stress perfusion—with respect to their risk of ad- reasonable grounds for referral for catheterization despite verse cardiovascular events. PET MPI in combination with the absence of extensive SPECT-identified ischemia. Finally, quantification of regional myocardial blood flow or regional

FIGURE 2. Potential testing algorithm based on use of stress cardiac SPECT MPI.

MPI VERSUS CT CORONARY ANGIOGRAPHY • Tamarappoo and Hachamovitch 1083 mean flow rate may therefore improve our ability to identify HYBRID APPROACH patients who might benefit from revascularization and may Recently, an attempt has been made to perform physio- provide better prognostic estimates of future cardiac events. logic and anatomic imaging simultaneously with a hybrid Although mean flow rate measurements may be obtainable PET MPI/CT coronary angiography technique (37). In their from PET-based perfusion imaging, potential sources of study of 104 patients who underwent both the hybrid tech- errors in measurement, including the effect of high driving nique and invasive coronary angiography, Kajander et al. pressure and high resting flow rates, are still being charac- found that, using invasive coronary angiography as the gold terized. Furthermore, still unexplored is how mean flow rate standard, the hybrid technique had a higher positive pre- may differentiate between patients who have epicardial dictive value than either technique alone (81% for CT, 86% stenoses and patients who have abnormalities with subendo- for PET, and 100% for the hybrid technique) and a similarly cardial microvascular perfusion. higher specificity (87%, 91%, and 100%, respectively). That Figure 3 outlines a potential post–PET MPI patient man- study also showed that an absolute myocardial blood flow of agement approach based on the use of ejection fraction less than 2.5 mL/min/g was the optimal cutoff between nor- reserve and flow quantification. Patients with a normal mal and abnormal perfusion and that a myocardial blood flow PET result can be referred directly for a preventive strat- of less than 2 mL/min/g was unequivocally abnormal. The egy, because normal is defined on the basis of perfusion, mean radiation dose in most of their patients was 9.3 mSv ejection fraction reserve, and coronary flow reserve. when prospective triggering was used, and this value was Patients with abnormal PET perfusion and extensive comparable to a mean estimated radiation dose of 7 mSv for . myocardial ischemia ( 10%–15% of myocardium) are invasive angiography. Thus, further advances in technology may potential candidates for revascularization and would be enable simultaneous assessment of both anatomy and physiol- referred for invasive assessment. The remaining patients, ogy, resulting in an even better diagnostic modality with the those with slight inducible ischemia or those with slight added benefit of providing prognostic information. The major scarring without inducible ischemia, would be referred limitation of the hybrid technique is not only radiation exposure for a preventive strategy unless there is other evidence of but also increased cost. Before widespread acceptance, it will be extensive ischemia, such as a compromised ejection frac- central to identify in which patient subsets testing strategies can tion reserve or a significant global reduction in coronary be enhanced by the use of this hybrid technique. flow reserve. It is likely that patients with extensive scar- ring may not be eligible for revascularization. To date, there have been no published studies demonstrating a SEQUENTIAL APPROACH survival benefit with revascularization on the basis of Finally, it is possible that these 2 technologies are best used PET results. However, such a benefit has been shown by integrating anatomy- and physiology-based imaging in the with SPECT MPI and is likely to exist with PET MPI appropriate setting, thereby maximally utilizing the strengths as well. of each. With a high negative predictive value, CT coronary

FIGURE 3. Potential testing algorithm based on use of stress cardiac PET MPI. EF 5 ejection fraction; CFR 5 coronary flow reserve.

1084 THE JOURNAL OF NUCLEAR MEDICINE • Vol. 52 • No. 7 • July 2011 angiography qualifies as an excellent initial test to exclude the Tomographic Angiography of Individuals Undergoing Invasive Coronary An- giography) trial. J Am Coll Cardiol. 2008;52:1724–1732. presence of CAD. On the other hand, the quantification of 4. Di Carli MF, Dorbala S, Curillova Z, et al. Relationship between CT coronary inducible ischemia by MPI enhances our ability to identify angiography and stress perfusion imaging in patients with suspected ischemic heart the optimal therapeutic approach: medical therapy versus disease assessed by integrated PET-CT imaging. J Nucl Cardiol. 2007;14:799–809. possible revascularization. Regardless of which diagnostic 5. Gaemperli O, Schepis T, Koepfli P, et al. Accuracy of 64-slice CT angiography for the detection of functionally relevant coronary stenoses as assessed with myo- test is chosen first, an equivocal or a borderline result may cardial perfusion SPECT. 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1086 THE JOURNAL OF NUCLEAR MEDICINE • Vol. 52 • No. 7 • July 2011