Accuracy of amplitude-based respiratory gating for PET/CT in irregular respirations

We evaluated the accuracy of amplitude gating PET (AG-PET) compared with phase gating PET (PG-PET) in relation to respiratory motion patterns based on a phantom analysis. We used a NEMA IEC body phantom filled with an ¹⁸F solution with a 4:1 sphere-to-background radioactivity ratio (12.6 and 2.97 kBq/mL). PET/CT scans were acquired in a motionless and moving state on a Biograph mCT. The respiratory movements were simulated by four different waveform patterns consisting of ideal breathing, breathing with a pause period, breathing with a variable amplitude and breathing with a changing baseline. AG-PET selects the narrow bandwidth containing 20% of the respiratory cycle. PG-PET was reconstructed with five gates. The image quality was physically assessed using the percent contrast (Q_H,10mm), background variability (N_10mm) recovery coefficient (RC), and sphere volumes. In regular motion patterns with ideal breathing and breathing with a pause period, the Q_H,10mm RC and sphere volumes were not different between AG-PET and PG-PET. In the variable amplitude pattern, the Q_H,10mm of AG-PET was higher than that of PG-PET (35.8 vs 28.2%), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.4 vs 8.6 mL). In the changing baseline pattern, the Q_H,10mm of AG-PET was higher than that of PG-PET (42.4 vs 16.7%), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.2 vs 9.8 mL). The N_10mm did not differ between AG-PET and PG-PET, irrespective of the motion pattern. Amplitude gating PET is considered to be more accurate than phase gating PET for examining unstable respiratory motion patterns, such as those involving a variable amplitude or changing baseline. (author)