Impact of Using Uniform Attenuation Coefficients for Heterogeneously Dense Breasts in a Dedicated Breast PET/X-ray Scanner.

We investigated PET image quantification when using a uniform attenuation coefficient (μ) for attenuation correction (AC) of anthropomorphic density phantoms derived from high-resolution breast CT scans. A breast PET system was modeled with perfect data corrections except for AC. Using uniform μ for AC resulted in quantitative errors roughly proportional to the difference between μ used in AC (μ AC) and local μ, yielding approximately ± 5% bias, corresponding to the variation of μ for 511 keV photons in breast tissue. Global bias was lowest when uniform μ AC was equal to the phantom mean μ (μ mean). Local bias in 10-mm spheres increased as the sphere μ deviated from μ mean, but remained only 2-3% when the μ sphere was 6.5% higher than μ mean. Bias varied linearly with and was roughly proportional to local μ mismatch. Minimizing local bias, e.g., in a small sphere, required the use of a uniform μ value between the local μ and the μ mean. Thus, biases from using uniform-μ AC are low when local μ sphere is close to μ mean. As the μ sphere increasingly differs from the phantom μ mean, bias increases, and the optimal uniform μ is less predictable, having a value between μ sphere and the phantom μ mean.