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Reducing motion artifacts on abdominal PET/MR images1Radiology, University of California, San Francisco, San Francisco, CA, United States, 2Research, Stanford University, Palo Alto, CA, United States, 3PET/MR Clinical Development, GE Healthcare, Waukesha, WI, United States
Synopsis
Motion can pose a significant challenge for positron emission tomography (PET) reconstructions. A block sequential regularized expectation maximization reconstruction algorithm (Q.Clear, GE Healthcare) is used to increase the signal-to-noise ratio (SNR) of PET images. Respiratory motion compensation Quiescent Phase Gating (QPG), also called Q.Static, is used to reduce motion-induced artifacts by extracting data from the quiescent period. Q.Static performed without Q.Clear increases image noise as only ~50% of the counts are utilized for image reconstruction. However, Q.Static performed with Q.Clear improves image quality for whole-body PET without increasing the scan time.
Background
Block sequential regularized expectation maximization reconstruction algorithm1 (Q.Clear, GE Healthcare) can be used to increase the signal-to-noise ratio (SNR) of PET images. By incorporating prior knowledge about the image quality into the reconstruction through discouraging differences in neighboring image voxel values, Q.Clear reaches full convergence while controlling image noise. To reduce motion artifacts and blurring due to subject’s breathing, PET images over the abdominal area were reconstructed with Q.Static. Since most patients spend more breathing time dwelling at the end-expiration quiescent period2, extracting the data at this time will reduce the motion artifacts and blurring in reconstructed PET images. However, this results in loss of ~50% of all counts for PET image reconstruction resulting in increased image noise. To compensate for this, Q.Clear is applied along with Q.Static to decrease image noise without increasing the scan time.Teaching Point
We perform respiratory motion compensation Quiescent Phase Gating (QPG) also called Q.Static on patients to improve image quality by reducing motion-induced artifacts. However, the Q.Static method routinely uses only ~50% of the total counts, which results in noisy image texture unless there is increased scan time . We propose leveraging the technique Q.Clear to maintain acceptable image noise without increasing acquisition time.Summary
To improve image quality, Q.Static is used for PET reconstruction by reducing motion-induced artifacts. However, using Q.Static without Q.Clear increases image noise due to using only 50% of the counts for image reconstruction. Using Q.Static with Q.Clear allows for improved image quality for whole-body PET without increasing the scan time.Acknowledgements
We would like to thank Sharmila Majumdar, PhD. for her guidance and support on this project.References
- Ahn S, Fessler JA. Globally convergent image reconstruction for emission tomography using relaxed ordered subsets algorithms. IEEE Trans Med Imaging. 2003;22:613–626.
- C. Liu, A. Alessio, et al. “Quiescent period respiratory gating for PET/CT,” Med. Phys., vol. 379, pp. 5037–5043, 2010.
Figures
Figure 1: Comparing PET image reconstruction on a subject using Q.Static with and without Q.Clear.
Top row images (1a & 1b) show the coronal maximum intensity projections.
Bottom row image shows the same axial slice with only Q.Static (1c), and with Static and Q.Clear (1d).
The image blurriness is improved by using Q.Static and Q.Clear helps to improve SNR.