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

• Published in: IEEE transactions on radiation and plasma medical sciences Vol. 4; no. 5; pp. 585 - 593
• Main Authors: MacDonald, Lawrence R., Lo, Joseph Y., Sturgeon, Gregory M., Zeng, Chengeng, Harrison, Robert L., Kinahan, Paul E., Segars, William Paul
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.09.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Attenuation; Attenuation coefficients; Attenuation correction (AC); Bias; Breast; breast PET; Breasts; Computed tomography; Phantoms; Photons; Positron emission; Positron emission tomography; quantitative PET; Simulation; Tomography; X-rays; Simulation; Attenuation correction; Quantitative PET; Breast PET; Positron Emission Tomography
• ISSN: 2469-7311; 2469-7303
• DOI: 10.1109/TRPMS.2020.2991120

We investigated PET image quantification when using a uniform attenuation coefficient (<inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>) 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 <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> for AC resulted in quantitative errors roughly proportional to the difference between <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> used in AC (<inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ AC}} </tex-math></inline-formula>) and local <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>, yielding approximately ± 5% bias, corresponding to the variation of <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> for 511-keV photons in breast tissue. Global bias was lowest when uniform <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ AC}} </tex-math></inline-formula> was equal to the phantom mean <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>). Local bias in 10-mm spheres increased as the sphere <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> deviated from <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>, but remained only 2%-3% when the <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ sphere}} </tex-math></inline-formula> was 6.5% higher than <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>. Bias varied linearly with and was roughly proportional to local <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> mismatch. Minimizing local bias, e.g., in a small sphere, required the use of a uniform <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> value between the local <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> and the <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>. Thus, biases from using uniform-<inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> AC are low when local <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ sphere}} </tex-math></inline-formula> is close to <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>. As the <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ sphere}} </tex-math></inline-formula> increasingly differs from the phantom <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>, bias increases, and the optimal uniform <inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula> is less predictable, having a value between <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ sphere}} </tex-math></inline-formula> and the phantom <inline-formula> <tex-math notation="LaTeX">\mu _{\mathrm{ mean}} </tex-math></inline-formula>.