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Table 2 Relationship among ILO standard grades for rounded opacities and the size in mm, size in pixels and range in frequency

From: Recent multiscale AM-FM methods in emerging applications in medical imaging

Type of rounded opacities Range in mm Range in pixels Range in lowest frequency content
P Up to 1.5 Up to 18 [π/9, π]
q 1.5-3 18-36 [π/18, π/9]
r 3-10 36-120 [π/36, π/18]
  1. Relationships are based on a scanning rate of 12 pixels per mm. Frequency range refers to the cut-off frequencies that can be used to characterize an opacity [67].