PMC5954667_01
Coronal slice of the MRI-derived attenuation maps (AM; a) and attenuation-corrected [18F]FDG PET images (AC PET; b) demonstrating misidentification of liver tissue as lungs and artificially suppressed tracer uptake in the liver (arrows). Native data are shown on the left side while manually-corrected attenuation map and resulting PET data are shown on the right side
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Fig1
Inspection of the determined AM demonstrated that most parts of the liver (approximately 82% as determined by volumetric analysis of MR and AM images) had not been identified as water-like soft tissue (with assigned linear absorption coefficients of 0.1000 cm-1), but as lung tissue (0.0224 cm-1) (Fig. 1a). This in turn led to highly suppressed PET activity values of the liver in the reconstructed images with an apparent SUVmean of the liver amounting to 0.6, far outside a typical reference range of 1.4-3.2 (Boktor et al.,) (Fig. 1b). Manual segmentation of the lung-liver border in the AM along the visible border in the Dixon water image (Fig. 2b), assigning a soft-tissue value of 0.1000 cm-1 (Fig. 1a), and reconstructing the PET data with this modified AM resulted in PET images with visually typical [18F]FDG uptake in the liver (Fig. 1b, Fig. 3).
Coronal slice of in-phase and out-of-phase Dixon MR images (a) and determined fat and water images (b). The in-phase image demonstrates markedly low MR signals of the liver (arrow)
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Fig2
The acquired Dixon sequence-based in-phase image (Fig. 2a) demonstrated markedly reduced signal intensities of the liver, similar to those of lung tissue. This translated into comparatively low values in the calculated water image (Fig. 2b). Manual segmentation of the lung-liver border in the AM along the visible border in the Dixon water image (Fig. 2b), assigning a soft-tissue value of 0.1000 cm-1 (Fig. 1a), and reconstructing the PET data with this modified AM resulted in PET images with visually typical [18F]FDG uptake in the liver (Fig. 1b, Fig. 3).
Maximum intensity projections of native (left) and corrected whole-body PET (right), demonstrating elevated tracer uptake levels in the rectum, the sigmoid colon, as well as the ascending and descending colon
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Fig3
PET images revealed elevated tracer uptake levels in the rectum, the sigmoid colon, as well as the ascending and descending colon (Fig. 3), indicative of GVHD in accordance with a study by Stelljes et al. (Stelljes et al.,). Manual segmentation of the lung-liver border in the AM along the visible border in the Dixon water image (Fig. 2b), assigning a soft-tissue value of 0.1000 cm-1 (Fig. 1a), and reconstructing the PET data with this modified AM resulted in PET images with visually typical [18F]FDG uptake in the liver (Fig. 1b, Fig. 3).