The relationship between the quantity (C/2b) and tan (c/2b) used to determine
the tomographic exposure angle A and tomographic exposure half angles A
and A. To use this graph, calculate the value of the quantity (C/2b) and find
its position along the x-axis. Then determine the tan (C/2b) value along the y-
axis, which would correspond to this.
NOTE:
The exposure angle measured by using this technique should agree with the
indicated exposure angle to within plus or minus 4 degrees. The symmetry of
the exposure angle, about midline, should be within plus or minus 2 degrees.
On the test results, the image of the long diagonal wire will appear as two
blurred triangles. The apex of each triangle will appear in sharp focus at the
level of the cut. In the above example the apex will appear sharp at 12.5 cm.
6-11. PREVENTIVE MAINTENANCE
As with the other tests, preventive maintenance is extremely important in order to
spot trouble, if there is any, before overexposure to your patients and yourself can
occur.
a. Perform routinely at six-month intervals.
b. Perform after any service work has been done involving the mechanical
aspects of the drive systems.
6-12. CORRECTIVE MAINTENANCE
a. Always perform a retest to confirm or deny the first test results.
b. Call a qualified service representative or engineer if the retest confirms the
problem.
Section III. UNIFORMITY OF TOMOGRAPHIC EXPOSURE TEST
6-13. PURPOSE
The uniformity exposure test determines the uniformity of the exposures.
6-14. EQUIPMENT/MATERIAL
a. Plexiglas spacer block 5 cm thick.
b. Lead aperture plate with a hole in the middle (see figure 6-4).
MD0062
6-8
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