Background - In PET/CT imaging the amount of 18 F-FDG activity injected to patient is mainly based on the patient body weight (BW) or on body mass index (BMI). Imaging overweight and obese patients using standard protocols results quite often in poor diagnostic images. The purpose of this study was to optimise BMI-based whole body 18 F-FDG PET images obtained from overweight and obese patients and assess the added value in terms of image quality, quantitative accuracy and radiation dose in comparison to BW-based images.
Methods - The NEMA-IEC-body phantom was scanned on the mCT 128 slices scanner (Siemens Healthineers). The spheres and background were filed with F-18 activity. Spheres-to-background (2.1kBq/mL) ratio was 4:1. Data was reconstructed using the OSEM-TOF-PSF routine reconstruction (2 iterations, 21 subsets, 3mm Gaussian filter). The optimisation was performed by varying number of iterations, number of subsets, filter’s size and type and matrix size. The phantom images were assessed using contrast recovery coefficients (CRCs). The optimised reconstruction was applied to 17 overweight and obese patients. The optimised BMI-based images and BW-based images were compared visually and using signal-to-noise ratio (SNR), SUVmax and SUVpeak measurements.
Results- The visual assessment of the optimised phantom images using 1 iteration, 21 subsets, 3mm Hamming filter showed better image quality and CRC values compared to the routine reconstruction. On patient data, the optimised BMI-based images provided better image quality compared to BW-based images in 87.5% of the overweight cases and 66.7% for obese cases. Compared to BW-based images, the optimised BMI-based images resulted in reduction of 18.6% in SUVmax, 10.6% in SUVpeak and 59% in radiation dose for overweight patients. Similar trends were observed in obese patients. SNR improvement on BMI optimised images over BW images was 55% and 59% on overweight and obese patients, respectively.
Conclusions - The optimised BMI-based approach using 1 iteration, 21 subsets, 3mm Hamming filter improves image quality, reduces radiation dose and provides, at least, similar quantitative accuracy compared to the BW-based approach for both overweight and obese patients. These findings are compelling enough support to conducting a full assessment of the approach on a large patient population.