Influence of region-of-interest determination on measurement of signal-to-noise ratio in liver on PET images.

OBJECTIVE: On 18 F-fluoro-2-deoxy-D-glucose (18 F-FDG) positron emission tomography (PET), signal-to-noise ratio in the liver (SNRliver ) is used as a metric to assess image quality. However, some regions-of-interest (ROIs) are used when measuring the SNRliver . The purpose of this study is to examine the different ROIs and volumes of interest (VOIs) to obtain a reproducible SNRliver .

METHODS: This study included 108 patients who underwent 18 F-FDG-PET/CT scans for the purpose of cancer screening. We examined four different ROIs and VOIs; a 3-cm-diameter and a 4-cm-diameter circular ROI and a 3-cm-diameter and a 4-cm-diameter spherical VOI on the right lobe of the patients' livers. The average of SUV (SUVmean ), standard deviation (SD) of SUV (SUVSD ), SNRliver and SD of the SNRliver obtained using ROIs and VOIs were then compared.

RESULTS: Although the SUVmean was not different among the ROIs and VOIs, the SUVSD was small with a 3-cm-diameter ROI. The largest SUVSD was obtained with a 4-cm-diameter spherical VOI. The SNRliver and the SD of the SNRliver with a 4-cm-diameter spherical VOI were the smallest, while those with a 3-cm-diameter circular ROI were the largest. These results suggest that a small ROI may be placed on a relatively homogeneous region not representing whole liver unintentionally.

CONCLUSION: The SNRliver varied according to the shape and size of ROIs or VOIs. A 4-cm-diameter spherical VOI is recommended to obtain stable and reproducible SNRliver .