Phantom Laboratory Catphan 503 - Patient Alignment System Check

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Patient alignment system check
The laser, optical, and mechanical patient alignment system can be checked for accuracy.
Align the white dots on the phantom housing with the alignment lights as discussed
in Initial phantom positioning. The scanned image should show good alignment as
discussed in Phantom position verication.
For measuring the z axis alignment accuracy, measure from the center of the ramp image
to the part of the ramp which aligns with the center of the phantom and sensitometry
samples. Multiply the distance A by 0.42 to determine the z axis alignment light
accuracy. To evaluate x and y accuracy, measure from the center of the phantom to the
center of the scan eld by use of the grid function or knowledge of the central pixel
location.
The accuracy of the localizer, pilot or scout view can be checked. To check this function
perform a localization scan of the phantom. Align an axial scan at the crossing point of
the wire ramps. Scan this axial cut and check the misalignment as discussed above.