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18F-FDG PET/CT lung ‘focalities’ without coregistered CT findings: an interpretative clinical dilemma

Chondrogiannis, Sotirios; Marzola, Maria Cristina; Grassetto, Gaia; Zorzi, Alessio; Milan, Elisa; Rampin, Lucia; Rubello, Domenico; Colletti, Patrick M.

Nuclear Medicine Communications: April 2015 - Volume 36 - Issue 4 - p 334–339
doi: 10.1097/MNM.0000000000000261

Aim The aim of the study was to assess the prevalence of focal fluorine-18 fluorodeoxyglucose (18F-FDG) activity in the lungs using 18F-FDG PET/computed tomography (CT) without matching CT findings.

Materials and methods A total of 10 500 consecutive 18F-FDG PET/CT records over 4 years were reviewed for focal incongruence between PET and CT, potentially indicating an artifact 18F-FDG (2.2 MBq/kg) was injected through a butterfly needle, followed by a 10 ml saline flush. Non-contrast-enhanced low-dose CT (140 kV and 40–80 mA) was coregistrated with PET.

Results Sixteen patients (12 men and four women; mean age 63 years, range 44–83) had focal pulmonary areas of high 18F-FDG activity [mean maximum standardized uptake value (SUVmax) 15.8; range 3.5–81.0], typically peripheral, with a mean maximum diameter of 1.3 cm (range 0.5–2.2 cm) on PET. 18F-FDG focality was singular in 14 patients, whereas two patients had two foci each. None had corresponding CT abnormalities. Identification of these ‘focalities’ during the acquisition phase led to late respiratory gated thoracic PET acquisitions in eight patients at 2 h with no significant changes in the location or size of the ‘focalities’. Five PET/CTs repeated at 48 h did not confirm the ‘focalities’. Five had negative follow-up contrast-enhanced CT. 18F-FDG-positive ‘focalities’ at PET/CT without anatomical correlation findings were considered as ‘artefactual accumulation’ of the tracer.

Conclusion In the absence of morphological abnormality, focal pulmonary 18F-FDG activity is very rare (1.5 cases/1000 PET scans) but potentially very ‘dangerous’. Artefact identification during acquisition can lead to late respiratory gated images for more confident interpretation, avoiding erroneous reports or further imaging procedures.

aDepartment of Nuclear Medicine, PET/CT Centre, ‘Santa Maria della Misericordia Hospital’, Rovigo, Italy

bDepartment of Radiology, University of Southern California, Los Angeles, California, USA

Correspondence to Sotirios Chondrogiannis, MD, Department of Nuclear Medicine, PET/CT Centre, ‘Santa Maria della Misericordia’ Hospital’, via Tre Martiri 140; 45100 Rovigo, Italy Tel: +39 0425 394432; fax: +39 0425 384434; e-mail:

Received December 7, 2014

Received in revised form December 7, 2014

Accepted December 7, 2014

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