Effect of amplitude-based respiratory gating on image quantification

Objectives Respiratory motion causes blurring of lesions, underestimation of radionuclide uptake and overestimation of lesion volumes. Amplitude-based respiratory gating divides the respiratory cycle into different amplitude ranges and reconstructs images based on the range which corresponds to the smallest amount of respiratory motion. It thus reduces motion induced image blurring and improves quantification. This study sought to investigate the effect of a specific type of amplitude-based gating termed HD·Chest (HD) on image quantification¹.

Methods Whole body FDG-PET/CT was performed in 100 patients with lung lesions using a Siemens mCT scanner. Respiratory gating was performed using HD with images reconstructed with 35% of acquired PET data. The maximum standardized uptake value (SUV_max) and peak SUV (SUV_peak) of lung lesions were defined on gated and non-gated images. Lesions were grouped according to their anatomical location and histology. Differences in SUV_max and SUV_peak between gated and non-gated images were calculated and assessed using rank sign testing (Wilcoxon).

Results With HD, SUV_max increased 14.4% (± 21.1) for all lesions, 10% (± 10.0) for lesions located in the upper lobes, and 20% (± 28.6%) for lesions located in the lower and middle lobes. SUV_peak increased by 8.3% (± 14.4) for all lesions with an average of 4.3% (± 5.8) increase in upper lobe and 13.5% (± 13.5) increase in lower and middle lobe lesions (p<0.05). HD increased measured FDG-uptake to a greater degree in lesions located in the lower and middle lobes compared to upper lobes (p<0.05). With HD, SUV_max increased similarly across tissue types. Adenocarcinomas demonstrated significantly lower SUV_max (11.3 ± 6.9) than squamous (16.4 ± 9.0) and small cell (20.0 ± 11.9) cancers consistent with previous reports^2,3.

Conclusions HD is a viable approach to correct the effect of respiratory motion on FDG PET image quantification with potential impact on diagnosis, response monitoring and radiation therapy planning.