18 F-FDG PET/CT in Detecting Metastatic Infection in Children Ilse J.E. Kouijzer, MD,* Gijsbert J. Blokhuis, MD,† Jos M.T. Draaisma, MD, PhD,‡ Wim J.G. Oyen, MD, PhD,† Lioe-Fee de Geus-Oei, MD, PhD,†§|| and Chantal P. Bleeker-Rovers, MD, PhD* Purpose of the Report: Metastatic infection is a severe complication of bacteremia with high morbidity and mortality. The aim of this study was to investigate the diagnostic value of 18 F-FDG PET combined with CT (FDG PET/CT) in children suspected of having metastatic infection. Methods: The results of FDG PET/CT scans performed in children be- cause of suspected metastatic infection from September 2003 to June 2013 were analyzed retrospectively. The results were compared with the final clin- ical diagnosis. Results: FDG PET/CT was performed in 13 children with suspected meta- static infection. Of the total number of FDG PET/CT scans, 38% were clin- ically helpful. Positive predictive value of FDG PET/CT was 71%, and negative predictive value was 100%. Conclusions: FDG PET/CT appears to be a valuable diagnostic technique in children with suspected metastatic infection. Prospective studies of FDG PET/CT as part of a structured diagnostic protocol are needed to assess the exact additional diagnostic value. Key Words: FDG PET/CT, metastatic infection, bacteremia, children (Clin Nucl Med 2016;41: 278–281) O ne of the main complications of bacteremia is secondary metastatic infection caused by spreading of the microorgan- isms to distant sites, especially in case of Staphylococcus aureus and Streptococcus species bacteremia and candidemia. 1 Reported incidence of these metastatic foci varies between 16% and 36%. 2–8 Early detection and treatment of metastatic foci are important be- cause morbidity and mortality are higher in patients with metastatic infectious disease, probably due to incomplete eradication during initial treatment. 6 To date, conventional radiologic techniques such as CT, MRI, and ultrasonography are often used to detect focal infectious disease. These techniques require the presence of guiding symp- toms because usually only a fixed part of the body is visualized. However, metastatic foci are often asymptomatic. Vos et al 2 re- ported in 2012 that only 41% of the cases had symptoms guiding the attending physician in the diagnostic workup. 18 F-FDG PET combined with CT (FDG PET/CT) is increasingly utilized in infec- tious diseases and has proven its effectiveness in diagnosing infec- tious foci and has shown great results in fever of unknown origin. 9 Also, FDG PET/CT proved to be a valuable imaging technique in adult patients at high risk of metastatic infectious disease, even when the results of other diagnostic procedures are normal. In a ret- rospective study of 40 adult patients with bacteremia and a high risk of complications, FDG PET was used to diagnose a clinically rele- vant new focus in 45% of cases, while on average 4 conventional diagnostic tests had already been performed previously. 1 A pro- spective study on the value of FDG PET/CT in 115 adult patients with gram-positive bacteremia and at least 1 risk factor for meta- static infectious disease showed that routine FDG PET/CT is a cost- effective tool to reduce morbidity and mortality. 10 Because no comparable studies have been performed in children, the aim of this study was to assess the diagnostic value of FDG PET/CT to detect metastatic infectious foci in children with bacteremia. MATERIAL AND METHODS Patients All children (aged 0–17 years) who underwent FDG PET/CT because of suspected metastatic infection after bacteremia between September 2003 and June 2013 were identified using the database of the Nuclear Medicine Department of Radboud University Medi- cal Center. Metastatic infection was suspected when there were signs of infection more than 48 hours before initiation of appropri- ate treatment, fever more than 72 hours after initiation of appropri- ate treatment, or positive blood cultures more than 48 hours after initiation of appropriate treatment. According to the Dutch law, this study was exempt from approval by an ethics committee, because of the retrospective character of this study and the anonymous storage of data. FDG PET/CT FDG PET/CT scans were performed on an integrated PET/ CT scanner (Siemens Biograph until 2012 and after 2012 Siemens Biograph mCT, Knoxville, Tenn). Prior to FDG injection, patients fasted for at least 6 hours. Intake of sugar-free liquids was per- mitted. In all patients, glucose levels were checked and were less than 10 mmol/L. Immediately prior to the procedure, patients were hydrated with an amount of water adapted to age up to 500 mL. If drinking was not possible, the patient was well hydrated with in- travenous normal saline solution. The dose of FDG (Mallinckrodt Medical [Petten, the Netherlands] or IBA [Amsterdam, the Netherlands]) was calculated using the following formula: 6:4  body weight kg ð Þ minutes per bed position MBq with a minimum of 20 MBq. The attending physician individually determined the necessity and dose of furosemide injection. One hour after intravenous injection of FDG and furosemide, emission images of the whole body were acquired. Images were corrected for attenuation using a low-dose CT scan for FDG PET/CT. The low-dose CT images were also used for anatomic correlation. Im- ages were reconstructed using the ordered subsets-expectation max- imization algorithm. Received for publication July 9, 2015; revision accepted November 26, 2015. From the Departments of *Internal Medicine, †Radiology and Nuclear Medicine, and ‡Pediatrics, Radboud University Medical Center, Nijmegen; §Depart- ment of Nuclear Medicine, Leiden University Medical Center, Leiden; and ‖MIRA Institute for Biomedical Technology and Technical Medicine, Biomedical Photonic Imaging Group, University of Twente, Enschede, the Netherlands. Conflicts of interest and sources of funding: none declared. Correspondence to: Ilse J. E. Kouijzer, MD, Department of Internal Medicine, Radboud University Medical Center, PO Box 9101, 6500 HB, Nijmegen, the Netherlands. E-mail: ilsekouijzer@gmail.com. Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved. ISSN: 0363-9762/16/4104–0278 DOI: 10.1097/RLU.0000000000001119 ORIGINAL ARTICLE 278 www.nuclearmed.com Clinical Nuclear Medicine • Volume 41, Number 4, April 2016 Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.