Original Article
Quantitative assessment of myocardial perfusion abnormality on SPECT myocardial perfusion imaging is more reproducible than expert visual analysis

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Abstract

Background

Current guidelines of Food and Drug Administration for the evaluation of SPECT myocardial perfusion imaging (MPI) in clinical trials recommend independent visual interpretation by multiple experts. Few studies have addressed whether quantitative SPECT MPI assessment would be more reproducible for this application.

Methods and Results

We studied 31 patients (age 68 ± 13, 25 male) with abnormal stress MPI who underwent repeat exercise (n = 11) or adenosine (n = 20) MPI within 9-22 months (mean 14.9 ± 3.8 months) and had no interval revascularization or myocardial infarction and no change in symptoms, stress type, rest or stress ECG, or clinical response to stress on the second study. Visual interpretation per FDA Guidance used 17-segment, 5-point scoring by two independent expert readers with overread of discordance by a third expert, and percent myocardium abnormal was derived from normalized summed scores. The quantitative magnitude of perfusion abnormality was assessed by the total perfusion deficit (TPD), expressing stress, rest, and ischemic perfusion abnormality. High linear correlations were observed between visual and quantitative size of stress, rest, and ischemic defects (R = 0.94, 0.92, 0.84). Correlations of two tests were higher by quantitative than by visual methods for stress (R = 0.97 vs R = 0.91, P = 0.03) and rest defects (R = 0.94 vs R = 0.82, P = 0.03), respectively, and statistically similar for ischemic defects (R = 0.84 vs R = 0.70, P = ns).

Conclusions

In stable patients having serial SPECT MPI, quantification is more reproducible than visual for magnitude of perfusion abnormality, suggesting its superiority for use in randomized clinical trials and monitoring the effects of therapy in an individual patient.

Introduction

Serial studies of SPECT myocardial perfusion imaging (MPI) are increasingly being employed in randomized clinical trials (RCTs) for assessing effects of treatment. In recent years, these trials have increasingly relied on quantitative approaches to myocardial perfusion assessment.1, 2, 3, 4 Nonetheless, current guidelines of Food and Drug Administration (FDA) for evaluation of SPECT MPI in clinical trials recommend independent visual interpretation by multiple experts.5 Due to the subjective nature of visual interpretation, however, the visual approach is likely to have lower repeatability than objective quantitative measurements. Danias et al, for example, reported intraobserver agreement of only 65-80% for visual assessment of normal and abnormal SPECT MPI.6 On the other hand, the reproducibility of quantitatively analyzed SPECT MPI has been reported to be excellent (96%).6 Although it is recognized that quantification of myocardial perfusion images enhanced reliability and reproducibility of interpretation,7 few studies have compared reproducibility between visual and quantitative assessments of SPECT MPI for this application—the subject of the present study.

Section snippets

Study Population

We retrospectively identified all patients in our database who met the following criteria: free of known nonischemic cardiomyopathy or valvular heart disease, referred for clinically indicated rest thallium (Tl)-201/stress gated Tc-99m sestamibi SPECT MPI with exercise (n = 11) or adenosine stress (n = 20) on two separate occasions within two years between March 2000 and March 2006 with no intervening cardiac event [myocardial infarction (MI), cardiac hospitalization, or revascularization],

Clinical Characteristics

Patient characteristics at study 1 and study 2 are illustrated in Table 1. By study design, there was no difference in the numbers of patients with prior MI or revascularization at the time of the two studies. There were high frequencies of diabetes, hypertension, hypercholesterolemia, angina symptoms, and abnormal resting ECG. All variables at study 2 are same as or similar to study 1 (P = ns) except older age (P < 0.001). In one patient, digoxin was no longer a medication at the time of the

Discussion

The intent of this study was to compare the repeatability of quantitative and visual analyses of myocardial perfusion. As a group, in these patients with stable coronary artery disease (CAD) selected for lack of interval change in clinical parameters, serial SPECT MPI studies over a 9-22 month interval showed no statistically significant change in quantitative or visual assessments of myocardial perfusion. Correlations of the magnitude of stress and rest perfusion abnormality between the serial

Conclusion

The present study demonstrates that defect extent by visual and quantitative analysis is highly correlated. In patients with stable CAD having serial SPECT MPI, quantitative assessment is more reproducible than visual interpretation for magnitude of MPI abnormality, suggesting its superiority for use in randomized clinical trials.

Acknowledgments

This work was supported in part by grants from Bristol-Meyers-Squibb Medical Imaging, Inc. Billerica, Massachusetts, and Astellas Healthcare, Inc. Deerfield, Illinois. This research was supported in part by R01HL089765-01 from the NHLBI/NIH (PI: Piotr Slomka). Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NHLBI.

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See related editorial, doi:10.1007/s12350-008-9020-6

This study was presented in part at the Society of Nuclear Medicine 55th Annual Meeting, New Orleans, Louisiana, June 14-18, 2008.

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