Letter to the editor: Lassen et al. 3D PET/CT 82 Rb PET myocardial blood flow quantification: comparison of half-dose an
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LETTER TO THE EDITOR
Letter to the editor: Lassen et al. 3D PET/CT 82Rb PET myocardial blood flow quantification: comparison of half-dose and full-dose protocols Jennifer M. Renaud 1 & Jonathan B. Moody 1 & Edward P. Ficaro 1 Received: 23 June 2020 / Accepted: 1 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Dear Sir, We read with interest the article by Lassen et al. [1], in which the authors evaluated the frequency of system saturation for fixed dose 82Rb 3D PET dynamic imaging, and the impact on myocardial blood flow (MBF) estimation. This study is topical as MBF quantification is gaining more widespread clinical use; however, we would like to provide additional context to some of the statements made by the authors. In this study, a small number of patients (N = 20) underwent repeat rest imaging with fixed 82Rb doses of 1500 MBq (fulldose; FD) and 750 MBq (half-dose; HfD). The authors stated that their FD acquisition protocol “was based on the most recent joint positions in North America and Europe.” However, the most current position statement [2] recommends a typical dose of 1100 MBq with patient-specific adjustment for body weight, body mass index, or attenuation, in contrast to the fixed dose of 1500 MBq considered here. PET system saturation effects were identified in this study via visual evaluation of image-derived blood input functions and sinogram data. Using this method, the authors reported 20% saturation frequency with the FD protocol, which was eliminated using HfD. However, after excluding FD scans with saturation, Lassen et al. still observed a significant difference in MBF for FD versus HfD. One possible explanation not discussed by the authors could be the presence of residual saturation in the retained FD scans which was not identified by their visual criteria. More objective quantitative criteria for saturation include empirical thresholds of count rate and dead time factor as we previously demonstrated [3]. For example, This article is part of the Topical Collection on Letter to the Editor * Jennifer M. Renaud [email protected] 1
INVIA Medical Imaging Solutions, Ann Arbor, MI, USA
for the TruePoint scanner used by Lassen et al., a peak singles rate threshold of 56 Mcps (based on results from a similar scanner) could be used in real-time during patient scanning to immediately identify saturation and ensure acquisition of quantitatively accurate images. In referring to our previous work [3], the authors incorrectly interpreted our results by indicating that the calibration between the PET camera and 82Rb delivery system could “introduce non-conformities of the dose-deliveries with a bias of up to 68%.” The quoted value of 68% represents the adjustment of the apparent phantom weight used to derive the maximum activity/body weight dose, based on patient scans for one particular injection system and PET scanner combination, highlighting the importance of validating weight-based dosing limits in patients. The authors also stated that weight-based protocols incre
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