Comparison of profiles for one LOR-PDF with different radionuclides and surrounding medium: γγ in air, 18F in water and 15O in water. Each profile was scaled to its own maximum. The LOR group is φ = [−2.5°,2.5°], b =12, and θ = [−5.5°, 5.5°] . The PDF’s depth index along LOR is 4 out of a total of 9 segments (central bin). The location of the profile is shown in the top-middle image in Figure 5. The PDF sample sizes for in air and 18F in γγ water are 0.16 mm, it is 0.32 mm for 15O in water to accommodate its broader spread.