Estimation of the most Appropriate Threshold for Lesion Delineation and Volumetric Quantification in 18F-FDG PET

Abstract

Abstract Purpose Function formulation to estimate the most appropriate threshold for automatic lesion delineation in PET scan. Materials and Methods The phantom consists of two parts: A hollow cylinder with set of spheres. The sphere assembly contains 4 spheres of different volumes. The phantom was filled with water containing 18F-Fluorodeoxyglucose (18F-FDG) forming the sphere versus background activity concentration (μCi/ml) ratios 3:1, 5:1, 8:1, 10:1, 12:1, 14:1 and15:1. Graphs were plotted, of standardized uptake value threshold versus lesion-size at different sphere/background ratio. There was a logarithmic decrease in threshold with an increase in lesion size. The most appropriate SUV threshold for each lesion at different contrast ratio was estimated from the plotted graphs. Four tests were used to generate a 3D general function to estimate threshold using the contrast ratio and lesion volume as inputs and the other three tests were used for the function validation. The Normalized mean square error (NMSE) is used to measure the convergence between estimated and measured data set. Results The created logarithmic functions offer an easy and simple way to estimate the percentage value of SUVmax as a threshold using the lesion/background ratio and sphere volume(or Diameter) from CT images as inputs to be used for lesion delineation and volume determination in PET images that was verified and the NMSE=6.2 Conclusion: The created formula is a useful and easy to estimate the most appropriate SUV threshold for automatically definite lesion volume.