Variability in bone-seeking tracers and imaging protocols for the diagnosis of cardiac amyloidosis: The more the merrier
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Department of Nuclear Medicine, Rambam Health Care Campus, Haifa, Israel Department of Medical Biophysics and Nuclear Medicine, Hadassah University Hospital and Hebrew University, Jerusalem, Israel Institute of Nuclear Medicine, University College London and UCL Hospitals NHS Trust, London, UK
Received Jul 28, 2020; accepted Jul 28, 2020 doi:10.1007/s12350-020-02330-x
See related article, https://doi.org/10.10 07/s12350-020-02239-5 Cardiac amyloidosis (CA) is a hot topic in nuclear cardiology and molecular imaging has become an important tool in the management of CA due to the unique capability to diagnose transthyretin CA (ATTR) noninvasively. The diagnosis of ATTR that was based in the past on invasive myocardial biopsy can be obtained with high sensitivity (95-100%) and near perfect specificity (97-99%), provided plasma cell disease is excluded,1,2 by myocardial scintigraphy with three 99m bone-seeking tracers, Tc-3,3-diphosphono-1,2propanodicarboxylic acid (DPD), 99mTc-Pyrophosphate (PYP) and 99mTc-Hydroxymethylene diphosphonate (HMDP). The three tracers perform equally well in the diagnosis of ATTR but not light chain CA (AL),1 likely due to calcium binding.3 Recently, three new drugs were approved by the US Food and Drug Administration for the treatment of ATTR with clinical studies underway that will likely expand the use of molecular imaging in the diagnosis and management of CA. In this issue of the Journal of Nuclear Cardiology, Santarelli et al. have retrospectively assessed HMDP studies of 38 patients who underwent a multi-step imaging protocol, designed to detect the earliest time Reprint requests: Simona Ben-Haim, MD, DSc, Department of Medical Biophysics and Nuclear Medicine, Hadassah University Hospital and Hebrew University, Ein Kerem, Jerusalem 9112001, Israel; [email protected] J Nucl Cardiol 1071-3581/$34.00 Copyright 2020 American Society of Nuclear Cardiology.
point to diagnose ATTR with high sensitivity and specificity.4 Dynamic imaging for as little as 4.5 min, as well as static images as early as 3.5 min after injection, both performed as well as late imaging, 1 to 3 h after injection. These early images were not subjected to visual interpretation. Rather, regions of interest (ROI) were drawn around structures representing uptake in the blood pool, the heart, skeleton and background. Timeactivity curves (TAC) of heart uptake divided by bone uptake (TACHeart/Bone) for time [ 6 min and a retention index derived from these data (RIheart-bone) for time[10 min distinguished between patients with ATTR and controls with a good intra- and inter-observer consistency.4 The results of this study suggest that early planar HMDP scintigraphy, either static or dynamic, may replace late imaging in patients with suspected cardiac amyloidosis. This would be good news to patients, who would benefit from the shortened time in the clinic. However, the altered protocol will require additional validation. The number of patients in present study is small and the study population is selective. None o
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