Dual-time-point 18F-FDG-PET/CT imaging in the assessment of suspected malignancy

Introduction (purpose of the study): The objective of this study was to assess whether dual-time-point F-18-fluoro-2-deoxyglucose (F-18-FDG)-PET/CT imaging improved the evaluation of suspected malignancy and if there was any resulting change in management. Methods: A total of 53 patients with suspected malignancy were investigated by performing two static acquisitions started at mean times t = 64 and t = 155 min after the tracer injection. The total number of malignant lesions was 133 and the total number of benign lesions was 61. Visual and semi-quantitative analysis was performed on both the early and delayed images. Results: Overall, there was a significant improvement (P < 0.001) in the sensitivity of delayed imaging (94%) compared with early imaging (77%) in detecting malignant lesions, without a reduction in specificity. In 10 patients, 13 malignant lesions were undetected on early imaging alone but detected on delayed imaging. In seven patients, 10 malignant lesions were incorrectly classified as 'likely benign' on early imaging but correctly reported as 'likely malignant' on delayed imaging. Management was altered in 2 out of 17 patients. Overall, delayed imaging altered management in 2 out of 53 studied patients. Dual-time-point (18)FDG-PET/CT imaging was useful in differentiating malignant from benign intra-abdominal lesions but did not improve the evaluation of pulmonary lesions. Conclusions: F-18-FDG-PET/CT imaging should be performed as late as reasonably possible after tracer administration in order to increase tumour-tobackground contrast and thereby improve the sensitivity of demonstrating additional sites of disease. Dual-time-point (18)FDG-PET/CT may be of benefit in the evaluation of intra-abdominal lesions but does not improve the overall evaluation of pulmonary lesions.