Time of Flight compared to standard iterative acquisition and reconstruction for assessment of pulmonary nodules.

Objectives To determine if assessment of pulmonary nodules based on activity compared to mediastinal blood pool differs significantly with time of flight compared to standard iterative reconstructions.

Methods Over a 2 year period, 90 18FDG-PET/CT scans were performed using both time of flight (TOF) and standard (ST) iterative acquisition and reconstruction techniques for evaluation of pulmonary nodules in a high risk population with high risk of malignancy for nodules of 80%. From these exams, 57 nodules were assessed that also had pathologic or 2 year CT follow up data available. These nodules were divided based on size criteria.

Results Nine of 13 nodules measuring 0-7mm were malignant and activity above the blood pool was present in 44% on TOF and 11% using ST. Benign lesions showed activity above blood pool in 25% (TOF) and 0% (ST). Five nodules showed activity greater than mediastinal blood pool on TOF and 80% were malignant. One nodule had activity greater than blood pool on ST and it was malignant. Thirteen of 27 pulmonary nodules measuring 8-15 mm were malignant. Activity greater than blood pool was 54% TOF and 23% ST for malignant nodules and 50% TOF and 14% ST for benign nodules. Fifteen nodules showed activity greater than blood pool on TOF, 47% of which were malignant. Five nodules had activity over blood pool on ST 23% of which malignant. Five of the 17 nodules larger than 15mm were malignant. Activity greater than the blood pool was seen in 80% (TOF) and 60% (ST) for malignant nodules and 83% (TOF) and 25% (ST) for benign lesions. Fourteen nodules showed activity greater than mediastinal blood pool on TOF and 29% of these were malignant. Six nodules had activity greater than blood pool on ST and 50% were malignant.

Conclusions Despite increased activity on time of flight, there is not improvment of differentiation between benign and malignant pulmonary nodules based on nodule to blood pool activity. However, the impact of hight incidence of malignancy in this population may have negatively affected the outcome.