Objective: The study compares the utility of dual-time point (early and delayed imaging) versus standard single-time (early imaging alone) ¹⁸F-FDG PET in the evaluation of suspected malignancy.

Methods: Thirty-four patients with known or suspected malignancy were examined twice: initial and delayed whole-body ¹⁸F-FDG PET imaging at 1 hour and 2.5 hours.
After visual interpretation, regions of interest were overlaid onto lesions to calculate the SUV_early and SUV_delayed for each lesion.

Results: Surgical pathology and follow-up revealed 30 patients with 81 malignant tumours, whereas 4 patients only had benign lesions. The tumour SUVs (mean +/- SD) were 5.2+/-0.9 (early scan) and 6.7+/-1.3 (delayed scan) (29% increase; P< 0.01). Benign lesions had SUVs of 2.5+/-0.3 (early scan) and 2.6+/-0.4 (delayed scan) (P= not significant). In 5 patients, 7 malignant lesions (3 mediastinal lymph nodes, 3 liver metastases and 1 para-aortic lymph node) were only seen in the delayed images. Two of these patients were upstaged and their management (radiotherapy field) altered. In 3 patients, 4 malignant lesions (1 mediastinal lymph node, 1 supraclavicular lymph node, 1 lung and 1 pancreatic lesion) classified as benign or equivocal on visual analysis in the early images were reported as malignant on delayed imaging. Management was altered in the patient with pancreatic lesion who went on to have surgery. Histology confirmed carcinoma in the head of pancreas.

Conclusion: Dual-time point ¹⁸F-FDG PET imaging has the potential to improve the accuracy, staging and management in the evaluation of suspected malignant tumours.