The X-Ray Projection Pixel Calibration Macro defines the attributes needed to completely describe the specific inputs and results from projection image pixel calibration based on isocenter reference. The attributes are provided to allow usage of calibration result as well as recalibration. The below included figures illustrate the relationship of the attributes.
In these figures, the object of interest of size D (in mm) is projected on the stored image over a distance of #Px (in pixels). The pixel spacing on the stored image is called (Px . The “Source to Isocenter Distance” is called ISO . The “Source Image Receptor Distance” is called SID . The shortest distance from the tabletop plane to the Isocenter and to the object of interest are called respectively TH and TO . The angle between the X-Ray beam and the axis perpendicular to the tabletop plane is called Beam Angle . Finally, the distance from the X-Ray source to the object of interest in the direction of the X-Ray beam is called SOD and is calculated from the other distances.
(Px: Imager Pixel Spacing (0018,1164)
ISO : Source Isocenter Distance (0018,9402)
SID : Distance Source to Detector (0018,1110)
TH : Table Height (0018,1130)
TO : Distance Object to Table Top (0018,9403)
Beam Angle: Beam Angle (0018,9449)
Note: The equipment related Beam Angle attribute (0018,9449) shall be consistent with the patient oriented Positioner Primary Angle (0018,1510) and Positioner Secondary Angle (0018,1511) together with the patient orientation on the table specified in Patient Orientation Code Sequence (0054,0410) attributes.
The Figures C.8.19.6-1 and C.8.19.6-2 illustrate the usage of the attributes under the conditions laid out above.
Figure C.8.19.6-1Project Calibration without angulation of the X-Ray beam (Beam Angle = 0)
Figure C.8.19.6-2Project Calibration with angulation of the X-Ray beam (Beam Angle not equal 0)