Fig. 3
From: Image quality of 4D in-treatment CBCT acquired during lung SBRT using FFF beam: a phantom study
Illustration of the contrast-to-noise ratio (CNR) calculation for the spherical moving target in the XSight lung tracking phantom. On the a axial and b sagittal cuts that intersect with the target center, two circles are displayed, which represent the boundaries of the target (sphere) and background (spherical shell). The resulting CNR was 5.6 for the 0-phase (end of exhalation) pretreatment CBCT image