Simulated sectional phantoms can be used to qualitatively evaluate a system’s
performance.
For fluoroscopy systems, additional tests have to be performed to check the
performance of the Image Intensifier (I.I.) and the camera and TV systems. These
include:
(a)
Patient entrance exposure rate:
Patient entrance exposure rates are measured by using ionisation chamber and
dosemeter. The minimum Source-I.I. Distance (SID) should be used. Perspex
of size 30 x 30 cm, 20 cm thickness is placed near the I.I. to simulate a
patient. The chamber is put on top of the phantom at 30 cm from the I.I. The
exposures are recorded for every field size and mode of operation. For
maximum entrance exposure, the I.I. is cover with at least 3 mm lead to boost
the kVp and mA to maximum.
Regulation requires that the maximum exposure shall not exceed 10 R per
minute.
(b)
Automatic brightness control:
Different thicknesses of perspex is placed near the source, activate screening
and observed if brightness on the monitor image is maintained. The kVp and
mA should be recorded.
(c)
High contrast resolution:
Use low kVp (40-60), high input exposure rate, a line pair phantom is placed
on the surface of the I.I. and screen. Count the group of line pair that can just
be resolved.
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