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A Comparison of the Uniformity Requirements for SPECT Image Reconstruction Using FBP and OSEM Techniques

Section of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, Minnesota

Objective: Gamma camera nonuniformity can result in the presence of ring artifacts in reconstructed SPECT images. The objective of this study is to compare the relationship between ring artifact magnitude and image noise in tomographic images reconstructed using FBP and OSEM.

Methods: A cylindrical phantom was filled with water and ^99mTc. Seven tomographic acquisitions were performed, with total counts per acquisition ranging from 1.5 Mcts to 100 Mcts. All acquisitions were reconstructed using both FBP and OSEM. Ring artifacts were generated in the transaxial data by introducing defects at a given location in each planar image. The modified acquisitions were again reconstructed using both FBP and OSEM. The ring artifacts were isolated by the subtraction of the uncorrupted datasets from the corrupted datasets. The magnitude of the ring artifacts in the corrupted reconstructions was measured and compared to the mean counts and noise level in the uncorrupted data.

Results: Ring magnitude in OSEM-reconstructed images is approximately one third that of FBP images. However, there is a corresponding reduction in image noise with OSEM and the ratio of ring magnitude-to-image noise was relatively similar for both OSEM and FBP. Rings generated with OSEM fell off more rapidly with distance from the image center, and reached a plateau at a higher magnitude at large distances. The visibility of rings with OSEM relative to FBP will depend on the location of the causative defect in the planar data and the number of iterations performed with OSEM. Differences between the 2 algorithms are subtle.

Conclusion: Our results would indicate that the uniformity requirements for SPECT are similar for FBP and OSEM reconstruction algorithms.

Key Words: SPECT; FBP; OSEM; ring artifacts; uniformity

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