Assessment of dedicated brain PET designs with different geometries

We compared the geometrical efficiencies and parallax errors of three different conceptual dedicated brain PETs, including a spherical cap design (R=18cm), a dodecahedron design (inscribed sphere radius = 15cm) and a cylindrical design (30cm in height and 30 cm in diameter) with their conventional whole body counterpart (a cylinder 20cm in height and 76 cm in diameter) by calculating the Solid Angle Fractions (SAF) and Average Gamma-ray Incident Angles (AGIA). The results show that spherical cap and dodecahedron have an identical SAF that is 58.4% higher than that of 30cm diameter cylinder, and 5.44 times higher than that of 76cm diameter cylinder. The 76cm diameter cylinder has the lowest AGIA. The spherical cap has an AGIA 16.2% lower than that of the 30cm cylinder, and 33.5% lower than that of dodecahedron in brain phantom simulation. In a region around the geometric center, the dodecahedron and the 30cm cylinder have similar parallax error. We conclude that the spherical cap is a better geometry for brain imaging compared to 30cm or 76cm cylinder. The dodecahedral PET consisting of 11 flat detector faces and an opening face, is a reasonable approximation of the spherical cap PET.