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. 2021 May 1;203(9):1186–1187. doi: 10.1164/rccm.202007-2944IM

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Copyright © 2021 by the American Thoracic Society

This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (https://creativecommons.org/licenses/by-nc-nd/4.0/). For commercial usage and reprints, please contact Diane Gern (dgern@thoracic.org).

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Figure 1. — (A–C) Axial (A), left sagittal (B), and coronal (C) slices from computed tomography (CT) (left), ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET)/CT (center), and lung perfusion single-photon-emission CT (SPECT)/CT (right). Note normal or increased lung perfusion in most hypermetabolic areas detected by PET/CT (solid arrows) compared with the apparently unaffected lung. The inflammatory abnormalities have a clear predominance in the posterior lung fields and included all consolidations or ground-glass opacities on CT images. In general, the denser the lung parenchyma on CT images, the greater the ¹⁸F-FDG uptake on PET images. Hypoperfusion (preserved vasoconstriction) is present in a few areas of ¹⁸F-FDG uptake (dashed arrows). (D) Corresponding segmented coronal slices, representative of the volumetric quantification, are shown. The segmented lungs obtained from CT images have a total volume of 2,560 cm³ (pulmonary contour in D; left). The maximal standardized uptake value of the ¹⁸F-FDG PET/CT images is 11.8. The volume of ¹⁸F-FDG uptake, representing total lung inflammation, was segmented using the mediastinal blood pool as the threshold (standardized uptake value = 1.8) and measures 1,009 cm³ (blue area in D; center). This corresponds to 39% of the total anatomic lung volume (right lung: 23%, left lung: 16%). The mask of the segmented volume of ¹⁸F-FDG uptake was transferred to the SPECT volume (green area in D; right). The counts within this mask were divided by the total counts of the SPECT image. This resulted in 59% of the total counts of lung perfusion occurring in inflamed lung tissue (right lung: 37%, left lung: 22%). Accordingly, 61% of the normal (noninflamed) lungs, which ideally should receive 100% of lung perfusion, receive only 41% of it. Therefore, this quantification estimates the total loss of hypoxic vasoconstriction in this patient. This right-to-left shunt could partially explain the severe hypoxemia of this patient. See the details of the image acquisition and quantification in the online supplement.