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This Article Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Watson, C. Articles by Bendriem, B. PubMed Articles by Watson, C. Articles by Bendriem, B.

Prompt gamma correction for improved quantification in ⁸²Rb PET

¹ Siemens Molecular Imaging, Knoxville, Tennessee

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Objectives: The positron emitter ⁸²Rb also emits a 777 keV prompt gamma (PG) in 14% of its β⁺ decays. This produces a true coincidence background, distinct from scatter, which, if left uncompensated, will lead to quantitative errors in cardiac perfusion images. These errors may exist in both 2D and 3D PET and are more important the poorer the system energy resolution is. We have implemented and validated a correction for this PG background.

Methods: Because the PGs are uncorrelated in angle with the annihilation photons, the ⁸²Rb PG background has a spatial distribution similar to random coincidences. We estimate a randoms sinogram from measured single event rates. This PG model is combined with a scatter sinogram estimated by the SSS algorithm, and the total background model is scaled to fit the tails of the measured data.

Results: Because the PG background differs in shape from scatter, a background correction that includes only a scatter model, when fitted to the data, can be unstable, cause over-scaling of the scatter, and result in quantitative inaccuracies in the resulting image. However, we find ⁸²Rb thorax phantom studies with the combined PG+scatter correction show quantitative accuracy comparable to conventional ¹⁸F studies. In six ⁸²Rb cardiac patients scans on a Siemens Biograph PET/CT, PG fractions were 6-12%, while scatter fractions were 30-42%. The PG correction (PGC) was also robust for independently reconstructed gated cardiac studies.

Conclusions: PGC improves quantitative accuracy in ⁸²Rb cardiac studies and may reduce the potential for spurious uptake variations as well. For these reasons, PGC could be important for both quantitative and semi-quantitative CAD diagnosis, and should be employed for images in the normals database as well as for the clinical patient scans.

Research Support: Data courtesy of Emory Crawford Long Hospital and Cardiovascular Imaging Technologies.

This Article Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Watson, C. Articles by Bendriem, B. PubMed Articles by Watson, C. Articles by Bendriem, B.