Table C.8.19.6-9 specifies the Attributes of the X-Ray Projection Pixel Calibration Macro.
Table C.8.19.6-9. X-Ray Projection Pixel Calibration Macro Attributes
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A Sequence that describes the geometrical position of the patient relative to the equipment. |
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Distance between the anatomic region of interest of observation and table top in mm. |
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Physical distance within the anatomic region of interest in the center of the beam and perpendicular to the beam between the center of each pixel, specified by a numeric pair adjacent row spacing (delimiter) adjacent column spacing in mm. See Section C.8.19.6.9.2. See Section 10.7.1.3 for further explanation of the order of the Values. Required if Distance Object to Table Top (0018,9403) is not empty. |
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The distance of the top of the patient table to the center of rotation of the source (i.e., the isocenter) in mm. A positive value indicates that the tabletop is below the isocenter. Required if Image Type (0008,0008) Value 1 is ORIGINAL, may be present otherwise. |
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The equipment related angle in degrees of the X-Ray beam relative to the perpendicular to the tabletop plane. An angle from 0 to +90 degrees indicates that the X-Ray source is below the table. The valid range is 0 to +180 degrees. Required if Image Type (0008,0008) Value 1 is ORIGINAL, may be present otherwise. |
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. Figure C.8.19.6-1 and Figure C.8.19.6-2 illustrate the relationship of the Attributes.
In Figure C.8.19.6-1 and Figure C.8.19.6-2, 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 DPx. 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.
DPx: Imager Pixel Spacing (0018,1164)
ISO: Source Isocenter Distance (0018,9402)
SID: Distance Source to Detector (0018,1110)
TO: Distance Object to Table Top (0018,9403)
Beam Angle: Beam Angle (0018,9449)
Note
The equipment related Beam Angle (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).
Figure C.8.19.6-1 and Figure C.8.19.6-2 illustrate the usage of the Attributes under the conditions laid out above.
Figure C.8.19.6-2. Projection Calibration With Angulation of the X-Ray Beam (Beam Angle Not Equal to 0)
The value provided for Beam Angle (0018,9449) shall correspond to the other Attribute Values within this Module and according to the mathematic terms listed in Section C.8.19.6.9.1.
The terms listed will result in infinite result when used with 90-degree beam angles.
It is outside the scope of this Standard to define reasonable limits for single input values in the above-mentioned terms, or to define the mathematical accuracy of applications using those terms.