P251. Correlation of FDG PET scanning with clinical and laboratory markers of activity in patients with Crohn's disease
E. Russo1, S. Khan2, A. Brown3, N. Keat3, W. Hallett3, R. Janisch3, R. Gunn3, E. Rabiner3, P. Matthews1, T. Orchard1, 1Imperial College London, Medicine, London, United Kingdom, 2Imperial College Healthcare NHS Trust, Radiology, London, United Kingdom, 3Imanova, Imaging, London, United Kingdom
Several studies have investigated the value of 18F-Fluoro-deoxy-glucose Positron Emission Tomography (FDG-PET) in the assessment of disease activity in adult and paediatric Crohn's disease (CD) in recent years . It is hypothesised that inflammatory foci have higher local metabolic rates, and therefore increased glucose and FDG uptake compared to background tissue.
15 patients with an established diagnosis of CD underwent FDG-PET scanning at our institution. Following a 6-hour fast, patients received 185MBq of intravenous FDG followed by 800ml of oral 2.5% mannitol ingested gradually, over 45 minutes. A low dose CT scan of the abdomen was performed (130KV, 30mAs, pitch 1.5, 6 slice x 3 mm collimation). Subsequently, PET emission data from the whole of the GI tract were acquired in 3-dimensional model on a Biograph-6 PET/CT scanner. A maximum of 3 bed positions (10 minutes per bed position) were performed.
For the purposes of the analysis, the gut was split into 6 segments on CT (terminal ileum, ascending, transverse, descending and sigmoid colon and rectum). A segment was deemed positive if its FDG signal had a maximum Standardised Uptake Value (SUV-MAX) higher than the SUV-MEAN of liver parenchyma, i.e. an intestine-to-liver SUV ratio (SUV-ITL) >1. Regions of Interest (ROI) consisting of voxels with an SUV-ITL >1.0 were created for each abnormal segment and their mean SUV, and Volume in cm3 were calculated. We defined as Segmental Inflammatory Volume (SIV):
SIV = ROI SUV-MEAN/Liver SUV-MEAN × ROI Volume,
and as Total Inflammatory Volume (TIV):
TIV = Sum of SIVs.
TIV is a composite endpoint of both extent and severity of disease in each patient. We also assessed the SUV-MAX in the GI tract as a marker of disease severity.
TIV and SUV-MAX were correlated with the Harvey–Bradshaw Index (HBI), C-Reactive Protein (CRP) and Faecal Calprotectin (FC) measurements obtained on the same day, using Spearman's rank correlation coefficient.
PET data, Clinical scores and CRP were obtained in 15 patients and calprotectin was obtained in 14 patients with active CD.
|SUV-MAX||ρ = 0.20 (P = 0.48)||ρ = 0.35 (P = 0.22)||ρ = 0.21 (P = 0.46)|
|TIV||ρ = 0.33 (P = 0.23)||ρ = 0.25 (P = 0.38)||ρ = 0.31 (P = 0.26)|
At best, FDG PET parameters are not strongly correlated with clinical and laboratory markers of activity. Potential explanations include a large physiological or non-specific component of the signal, or FDG accumulation in segments of subclinical disease which do not contribute to symptomatology or increases in other biomarkers.
1. Shyn PB, (2012), 18F-FDG positron emission tomography: potential utility in the assessment of Crohn's disease, Abdom Imaging.