Low dose interpolated average CT for PET/CT attenuation correction using an active breathing controller (ABC)

While the complexity of implementation hampers the use of 4D PET/CT in the clinics, previously we developed and evaluated an interpolated average CT (IACT) method for attenuation correction (AC) in PET/CT. This study aims to evaluate the clinical implementation of IACT using an active breathing controller (ABC). This system consists of a spirometer for monitoring respiratory cycle and an airway-sealing unit. Real time detection of the change of flow volume and air flow direction by a flow sensor was used to determine the end-inspiration and end-expiration phases, while the valve of the ABC was closed for ~6 s to suspend the patients breathing and the helical CT (HCT) scans were manually turned on. To demonstrate the clinical feasibility of this system, two subjects were recruited for the PET/CT scans. Thoracic PET scans were acquired 1 hr after 328 MBq and 406 MBq ¹⁸F-FDG injections for each subject respectively, using 3 mins per bed position for 2 bed positions. The PET sinograms were reconstructed with AC using: (i) standard HCT (120 kV, smart mA (30-150 mA), 0.984:1 pitch); (ii) IACT obtained from 2 end-inspiration and end-expiration breath-hold HCTs (120 kV, 10 mA) using ABC to assure that the captured phases represented the free-breathing state as in PET acquisition. For IACT, multi-resolution B-spline registration algorithm and nonlinear interpolation were used to generate the interpolated phases between the two extreme phases. The final IACT was obtained by averaging the original and interpolated phases. The PET reconstructed image quality was assessed by visual observation and image profiles. Results showed that PET images using HCT for AC had severe artifacts near the diaphragm comparing to IACT, as confirmed by the image profiles. The IACT reduced ~87% radiation dose as compared to HCT. We conclude that IACT provides improved PET reconstructed image quality as compared to HCT with reduced radiation dose. IACT for PET AC is feasible and robust i- clinical practice with the aid of ABC.