Reply: Simplified Quantification of Myocardial Flow Reserve with ¹⁸F-Flurpiridaz: Validation with Microspheres in a Pig Model

REPLY: We appreciate the thoughtful letter from Drs. Johnson and Gould expressing their concerns with an extrapolation from our study that the ratio of standardized uptake values from stress and rest studies could serve as an index of myocardial flow reserve when a physical stress test is used (1). Consistent with remarks by Drs. Johnson and Gould, in human studies at 30 min after flurpiridaz injection, myocardial standardized uptake value was found to be 5.2, 10.8, and 5.5 at rest, pharmacologic stress, and exercise stress, respectively (2). Consequently, we fully agree that a noninvasive assessment of the arterial input function to estimate myocardial blood flow is the appropriate strategy for this stress condition. Furthermore, studies in humans under different stress conditions are necessary to evaluate whether simplified acquisition and analysis schemes are applicable.

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