Comparison between Two Different Scanners for the Evaluation of the Role of 18F-FDG PET/CT Semiquantitative Parameters and Radiomics Features in the Prediction of Final Diagnosis of Thyroid Incidentalomas

Abstract

The aim of this study was to compare two different tomographs for the evaluation of the role of semiquantitative PET/CT parameters and radiomics features (RF) in the prediction of thyroid incidentalomas (TIs) at ¹⁸F-FDG imaging. A total of 221 patients with the presence of TIs were retrospectively included. After volumetric segmentation of each TI, semiquantitative parameters and RF were extracted. All of the features were tested for significant differences between the two PET scanners. The performances of all of the features in predicting the nature of TIs were analyzed by testing three classes of final logistic regression predictive models, one for each tomograph and one with both scanners together. Some RF resulted significantly different between the two scanners. PET/CT semiquantitative parameters were not able to predict the final diagnosis of TIs while GLCM-related RF (in particular GLCM entropy_log2 e GLCM entropy_log10) together with some GLRLM-related and GLZLM-related features presented the best predictive performances. In particular, GLCM entropy_log2, GLCM entropy_log10, GLZLM SZHGE, GLRLM HGRE and GLRLM HGZE resulted the RF with best performances. Our study enabled the selection of some RF able to predict the final nature of TIs discovered at ¹⁸F-FDG PET/CT imaging. Classic semiquantitative and volumetric PET/CT parameters did not reveal these abilities. Furthermore, a good overlap in the extraction of RF between the two scanners was underlined.

Keywords: 18F-FDG; PET/CT; positron emission tomography; radiomics; texture analysis; thyroid cancer; thyroid incidentalomas.

Figure 1

(A): Axial CT, axial PET and axial fused PET/CT images demonstrating the presence of TI revealed as intense focal uptake of ¹⁸F-FDG on the right lobe of thyroid. The lesion had a SUVmax of 44.47, an MTV of 0.7 and a TLG of 18.1 and subsequent cytological exam revealed no malignancy (TIR2). (B): Axial CT, axial PET and axial fused PET/CT images of another scan demonstrating again the presence of TI as a faint uptake on the right lobe of thyroid. The values of SUVmax, MTV and TLG of the lesion were 2.64, 6.9 and 10.3, respectively. Cytological evaluation (TIR5) and subsequent total thyroidectomy revealed the presence of papillary carcinoma.

Figure 2

Correlation maps for first and second order RF between the two scanners. Scanner 1 (Discovery 690) is presented on the left, while scanner 2 (Discovery STE) is presented on the right. Blue means high positive correlation; red means high negative correlation; white means no correlation.

Figure 3

Visual representations of the three combinations ((A) GLCM Entropy_log10+GLZLM_SZHGE, (B) GLCM Entropy_log2+GLZLM:SZHGE; (C) GLCM Entropy_lo10+GLRLM_HGRE) with best performances at bivariate analysis for both scanners considered together.