Fantastic voyage: Catheter-based quantification of tracer distribution on a miniature scale
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Department of Nuclear Medicine, Hannover Medical School, Hannover, Germany
Received Sep 7, 2020; accepted Sep 8, 2020 doi:10.1007/s12350-020-02379-8
See related article: https://doi.org/10.10 07/s12350-020-02317-8. The expansion of the nuclear cardiology armamentarium to encompass a wider range of tracers targeted to specific molecular processes offers opportunities for precise monitoring of disease progression and guidance of therapy.1 While some processes affect the global myocardium, many such as post-ischemic inflammation, infection, or fibroblast activation tend to be regional.2,3 Particularly subtle disease may also be below the detection limit of conventional imaging techniques. Moreover, localized pathology poses challenges to delivery of targeted cell, gene, or drug therapy, which may require precise targeting to evoke optimal benefit. As such, the limitations of resolution, regional heterogeneity, and mixed cellular substrates complicate interpretation of conventional radionuclide images, and raise the question whether other strategies could more precisely quantify regional tracer distribution. In the current issue of the Journal of Nuclear Cardiology, Stendahl and colleagues describe a novel diagnostic device for minimally invasive tissue-level detection of tracer distribution in the myocardium, with a vision toward guided regional therapeutic intervention.4 The miniature plastic scintillator effectively discriminates b? and b- activity over c-radiation, which could precisely pinpoint the spatial binding of a positron-emitting tracer. In a pig heart after ballooninduced myocardial infarction, heterogeneous uptake 18 F-fluorodeoxyglucose (18F-FDG) was observed by ex vivo PET imaging, thought to reflect regional
Reprint requests: James T. Thackeray, PhD, Department of Nuclear Medicine, Hannover Medical School, Carl Neuberg Str 1, Hannover30625, Germany; [email protected] J Nucl Cardiol 1071-3581/$34.00 Copyright Ó 2020 The Author(s)
inflammatory cell infiltration to the infarct and border zone territories. The regional disparity in signal was confirmed by spatial mapping using the b-detection catheter, providing a matrix distribution of activity content. Segment-to-segment activity established reasonable correlations between ex vivo PET, gamma well counting, and catheter-based measurements supporting the accuracy of the latter. The strength of the manuscript lies in the ingenuity of the approach, which tackles the challenge of regional tracer uptake heterogeneity using a minimally invasive local measurement. While the analysis is limited to only two animals and selected areas in these infarct hearts, validation by conventional (albeit ex vivo) PET and well counting indicates the capacity of the b-detector catheter to define spatial disparities of tracer accumulation. However, it is disappointing that this potential is not explored further, e.g., by confirmation of cellular substrate by histopathology. Indeed, while typical investigation requires alignment of adjacent tissue sections for ex
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