Page 112 - ARNM-3-1

Advances in Radiotherapy
& Nuclear Medicine 18 F-FDG PET & unexplained inflammatory syndromes

etiologies of unexplained inflammatory syndromes include Measured activity within the
vasculitis, neoplastic processes, granulomatous diseases, MBq
and infections affecting the cardiovascular, gastrointestinal, volume of interest ( mL )
and pulmonary systems. SUV max = Injected dose of1 8F (I)
2. Methods −FDG (MBq)
Patient’s body weight (g)
2.1. Patient recruitment
This retrospective study included 25 consecutive The ensure accuracy and reliability in SUV measurements,
patients with unexplained inflammatory syndrome who a rigorous in-house quality control program was
underwent F-FDG PET/CT at our institution between implemented. This program included weekly calibrations
18
18
January 2019 and December 2024. Inflammatory conducted by the service team. It involved radioactive F-
syndrome was defined as a persistent elevation of FDG PET/CT sources, calibration phantoms, standardized
C-reactive protein beyond the normal range for a protocols, detailed result analysis, and regular staff training
minimum duration of 3 weeks. All patients presented to maintain optimal equipment performance and reliable
18
with febrile syndrome and had negative morphological imaging results. On PET/CT images, sites of abnormal F-
findings on conventional imaging. FDG uptake were documented based on uptake intensity
and anatomical location. These findings were further
2.2. F-FDG PET/CT evaluated by comparing the intensity of abnormal intake to
18
18
All F-FDG PET/CT scans were performed using an that of physiological F-FDG uptake in the liver.
18
integrated PET/CT scanner (GE Discovery STE8, GE 2.3. Histopathological and descriptive analyses
Healthcare, USA). Patients fasted for at least 8 h before
imaging, without any premedication. Blood glucose levels Histopathological examination was considered the gold
and body weight were measured before F-FDG injection, standard for confirming the etiology of inflammatory
18
ensuring that all patients had blood glucose levels below syndrome. Biopsy was performed in patients with accessible
6.27 mmol/L. A net dose of 3 MBq/kg of F-FDG was pathological 18 F-FDG uptake. Descriptive analyses,
18
administered intravenously, with an average uptake time including patient age, sex, PET value, and histological
of 45 – 60 min. Based on patient body weights ranging confirmation, are represented in Table 1.
from 50 to 80 kg, and after accounting for residual syringe 3. Results
activity, the mean net injected dose was 193 MBq. Image
acquisition began 45 min post-injection, covering the region A total of 25 patients with suspected unexplained
from the head to the upper thighs, with a scan duration of inflammatory syndrome were included in this study.
3 min per bed position. PET images were reconstructed The mean age at the time of F-FDG PET/CT imaging
18
using vendor-provided algorithms that applied ordered was 55 years (range: 11 – 82 years). There was a male
subset expectation maximization, employing two predominance, with 15 males (60%) and 10 females (40%),
iterations, 28 subsets, and a 128 × 128 reconstruction resulting in a sex ratio of 1.5. Among the study population,
matrix. Attenuation correction was achieved using CT 9 patients (9/25; 36%) presented with unexplained long-
18
data acquired during the same session. CT imaging was term fever (≥38.5°C for at least 3 weeks). F-FDG PET/CT
performed from the skull base to the upper thighs, with was positive in 15 patients (60%) and negative in 10 patients
imaging parameters set at 120 mA current, 140 kV voltage, (40%). Patients with a positive PET/CT result subsequently
and a table speed of 13.5 mm/rotation. Axial CT images underwent biopsy confirmation whenever possible.
were reconstructed with a slice thickness of 3.75 mm. However, two patients had inaccessible uptake, precluding
All PET/CT studies were independently reviewed by two morphological confirmation (Table 1). In this study, the
18
nuclear physicians. These experts analyzed PET-only, specificity and sensitivity of F-FDG PET/CT for diagnosing
CT-only, and fused PET/CT images in combined sessions. inflammatory syndrome were 81% and 93%, respectively.
Fused PET/CT images were primarily used to localize The positive and negative predictive values (NPV) were 86%
lesions and differentiate pathological F-FDG uptake from and 90%, respectively, while the false-positive and false-
18
physiological uptake in adjacent organs. Metabolic activity negative rates were 7% and 19%, respectively (Table 2).
at abnormal F-FDG uptake sites was assessed qualitatively
18
and semi-quantitatively. The maximum standardized 4. Discussion
uptake value (SUVmax) within the volume of interest was Inflammatory syndrome can manifest in two phases: acute
calculated using Equation I: or chronic, depending on its duration. Acute inflammation

Volume 3 Issue 1 (2025) 104 doi: 10.36922/arnm.5895