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 5 47, 60-min dynamic, arms down, divided into 3 subgroups according to the injected dose) or 18F-fluciclovine (group 2, n 5 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 6 1.7) than in group 1 (2.1 6 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.