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Shifting To Free Breathing CT For Attenuation Correction of Q-Freeze PET/CT Elastic Respiratory Motion Correction

O Mawlawi1 , J Meier2*, (1) MD Anderson Cancer Ctr., Houston, TX, (2) UT MD Anderson Cancer Center, Houston, TX


(Monday, 7/30/2018) 1:15 PM - 1:45 PM

Room: Exhibit Hall | Forum 9

Purpose: Q-Freeze is an elastic respiratory motion correction algorithm in PET/CT which uses all of the acquired PET data, improving image quality in comparison to Q-Static which uses data only from the end of expiration. Typically for PET attenuation correction(AC), a free breathing 3DCT is acquired. For AC of Q-Freeze, the vendor recommends a phase matched 4DCT, limiting its implementation. Our aim is to determine the impact of using free breathing CT for AC of Q-Freeze, Q-Static, and STATIC(no motion correction).

Methods: A retrospective analysis was performed on 5 patients with lung or liver lesions of diameter between 1-3 cm acquired on a GE Discovery 690 PET/CT. Decreasing times of 12, 7.5, 5, and 3(clinical acquisition) minutes were unlisted from each patient’s 12 minute PET acquisition. For the Q-Freeze reconstruction, 6 gates were used. For Q-Static, the PET data was selected from phase range 35-75%, retaining 40% of the data. For STATIC, all data was used with no motion correction. End expiration CT was used for PET AC. For each patient, motion compensation method, and acquisition time, we measured tumor SUVmax and the SUV standard deviation in the healthy liver.

Results: Across all acquisition times, for the 7 tumors analyzed, SUVmax changed negligibly. The mean SUVmax(% change relative to STATIC) was 6.58, 8.91(35.5%), and 8.50(29.2%) for STATIC, Q-Static, and Q-Freeze. For the 12, 7.5, 5, and 3 minute acquisitions, the percent change in liver SUV standard deviation relative to STATIC was 25.7%, 37.2%, 48.0%, and 62.8% for Q-Static,and 20.8%, 28.4%, 35.2%, 42.7% for Q-Freeze.

Conclusion: When using a free breathing CT for AC, Q-Freeze and Q-Static showed similar increases in SUVmax in comparison to STATIC PET. For the same acquisition times, Q-Freeze image noise was lower than Q-Static suggesting that Q-Freeze can replace Q-Static if a single CT is acquired.

Funding Support, Disclosures, and Conflict of Interest: Research Agreement with Siemens Healthineers


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