Usefulness of high-definition PET reconstruction in pulmonary nodules

Objectives High-Definition PET Reconstruction (HD) is a new image reconstruction approach based on the point spread function system. We evaluated the usefulness of HD compared to the conventional ordered subsets expectation maximization (OSEM) in pulmonary nodules.

Methods FDG-PET/CT scans of 120 patients with known or suspected malignant pulmonary nodules were retrospectively evaluated. Scanning was performed at 90 minutes after the intravenous injection of 3.7MBq 18F-FDG per kilogram of body weight, and scanning time was 2 min per bed position for PET. Standardized uptake values (SUVs) and diameters of pulmonary nodules were measured using TrueD of syngo MM Workplace (Siemens) with HD images and OSEM images.

Results Visually, the noise in HD images was significantly lower on comparison with in OSEM images, and FDG uptake of pulmonary nodules is clearer and the margin of uptake is more sharp in HD images than in OSEM images. Despite the respiratory motion, FDG uptake of nodules in HD images is clearly seen both upper lung lesions and lower lung lesions. Maximum SUVs (SUVmax) of pulmonary nodules in HD images were significantly higher than SUVmax in OSEM images. And no significant difference is present between upper lung lesions and lower lung lesions. When the outer border of lesion was defined by an isocontour representing 45% of SUVmax, diameters of nodules in HD images were smaller than that in OSEM images. And diameters of nodules in HD images were similar to that in CT images. The ratio of dimeters in OSEM images and in CT images was tend to become large in lower lung lesions, compare to in upper lung lesions. The ratio of diameters in HD images and in CT images didn't show such tendency.

Conclusions HD PET reconstruction images have an excellent image quality and show good contrast of FDG uptake of pulmonary nodules even the lesions exist in lower lung. We consider that HD PET reconstruction is very useful for clinical diagnosis of pulmonary nodules