Blanching Defects at Pressure Points: Observations from Dynamic Total-Body PET/CT Studies

Abstract

Total-body PET/CT allows simultaneous acquisition of all body parts at a single bed position during the radiotracer uptake phase. Dynamic imaging protocols using total-body PET might demonstrate findings that may not have been previously visualized or described using conventional PET/CT scanners. We examined the characteristics of blanching defects—areas of markedly reduced (partial defect) or absent (complete defect) radiotracer uptake seen at the skin and subcutaneous tissues opposite the bony prominences at pressure points. Methods: In this observational study, 77 participants underwent dynamic total-body PET/CT imaging using ¹⁸F-FDG (group 1, n = 47, 60-min dynamic, arms down, divided into 3 subgroups according to the injected dose) or ¹⁸F-fluciclovine (group 2, n = 30, 25-min dynamic, arms up). Forty of the 47 participants in group 1 were reimaged at 90 min after being allowed off the scanning table. Blanching defects, partial or complete, were characterized opposite the bony prominences at 7 pressure points (the skull, scapula, and calcaneus bilaterally, as well as the sacrum). The association of the blanching defects with different clinical and technical characteristics was analyzed using uni- and multivariate analyses. Results: In total, 124 blanching defects were seen in 68 of the 77 (88%) participants at one or more pressure points. Blanching defects were higher, on average, in group 2 (3.5 ± 1.7) than in group 1 (2.1 ± 1.4; P < 0.001) but did not vary within group 1 for different ¹⁸F-FDG dose subgroups. All defects resumed a normal pattern on delayed static (90-min) images, except for 14 partial defects. No complete blanching defects were seen on the 90-min images. By multivariate analysis, arm positioning above the head was associated with skull defects; scapular and sacral defects were significantly more common in men and in those with a lower body mass index, whereas calcaneal defects were not associated with any factor. Conclusion: Blanching defects opposite the bony pressure points are common on dynamic total-body PET/CT images using different radiopharmaceuticals and injection doses. Their appearance should not be immediately interpreted as an abnormality. The current findings warrant further exploration in a prospective setting and may be used to study various mechanopathologic conditions, such as pressure ulcers.