Program Information
Range of Quantitative Uncertainty in PET/CT Quiescent Phase Respiratory Gating When Using Free Breathing Helical CT
J Meier*, O Mawlawi , MD Anderson Cancer Ctr., Houston, TX
Presentations
WE-F-201-6 (Wednesday, August 2, 2017) 1:45 PM - 3:45 PM Room: 201
Purpose: Quiescent Phase Gating (QPG) is the most commonly used motion correction algorithm in PET/CT. This approach uses PET data acquired in End Expiration, but does not have a matched CT for attenuation correction (CTAC). Our aim is to determine the range of quantitative uncertainty when using free breathing CT for attenuation correction of QPG PET.
Methods: 37 patients with lung or liver tumors of 1-3 cm in size affected by respiratory motion were scanned on a GE Discovery 690 PET/CT. A 7 minute acquisition was gated using GE Q.Static QPG algorithm with a phase offset and width of 35% and 40%, resulting in 3 minutes of PET data (clinical standard). 9 different CTAC maps were used for attenuation correction: a free breathing CT (CT_3D), and an 8 phase 4DCT (CT_4D) representing all phases the CT_3D could be acquired in. PET reconstructions used 3D OSEM, 2 IT, 24 SS, 6.4 mm Gaussian filtration, 192 x 192 matrix, TOF, and PSF. The range and % difference of SUVbw_max between the CT_3D and CT_4D reconstructions was determined for each tumor. Additionally we determined which reconstructions had the highest value of SUVbw_max. Finally, we determined the frequency of CT_3D that are acquired within the QPG phase (35%-75%).
Results: 34 tumors in 27 patients were analyzed. The mean, standard deviation, maximum, and minimum of the SUVbw_max range (%difference) between the CT_3D and CT_4D reconstructions of all tumors was 1.3 (-7.5%), 1.8 (23.1%), 8.9 (100%), and 0.1 (-128.5%) respectively. In 23/34 tumors, the end expiration phase reconstruction had the highest SUVbw_max. In 6/34 tumors, the 3D_CT reconstruction had the highest SUVbw_max. For 10/28 tumors, the CT_3D was acquired during the QPG phase.
Conclusion: QPG SUVbw_max values can change significantly when using free breathing CTAC, suggesting the need for a QPG phase matched CTAC.
Funding Support, Disclosures, and Conflict of Interest: General Electric Siemens
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