Background: Respiratory gating in positron emission tomography (PET) is used to improve detection of small tumors in the lower lung regions and in the liver, and to obtain a better estimate of the standardized uptake value (SUV).
Purpose: To develop a time-efficient method for acquisition of respiratory-gated PET/CT that would produce one single high quality image volume corresponding to a breath-hold state.
Material and methods: An instrument was developed that displayed to the patient either red or green numbers, counting down from a chosen maximum to one at a rate of one dial per second. The patient was instructed to repeatedly hold the breath in moderate inspiration when red numbers were displayed and to breathe freely during display of green numbers. PET data were acquired in list mode and trigger signals were sent to the scanner and inserted into the list file each time the color of the countdown numbers switched from green to red. Data acquired during breath-holds were used to create one single image volume.
Results: High quality breath-hold images were obtained from 10 min data acquisition at one bed position. Improved image quality compared to standard whole-body PET was demonstrated by a significant reduction of noise (standard deviation) in regions of normal liver tissues.
Conclusion: The instruction to perform repeated breath-holds was well understood by patients and they cooperated satisfactorily. When the new procedure is used the duration of the data acquisition may typically be reduced by a factor of 4 compared to conventional respiratory-gated protocols where the patient breathes freely.
Keywords: PET/CT respiratory phase matching; Respiratory-gated PET; liver; lung; repeated breath-holds.