(c)
Beam quality, HVL
The beam quality is measured by means of Half Value Layer (HVL). A set of
pure aluminium filters (type 1100 aluminium) of different thicknesses from
0.1 mm to 1 mm is used:
An ionisation chamber is placed in the X-ray beam at about 100 cm from the
X-ray source. The exposure parameters are fixed to 80 kVp, 100 mAs. The
exposures are measured both without filter and by adding filters. The
thickness of aluminium that is required to cut the output to half is the HVL.
(d)
X-ray wave form analysis
The kV waveforms for various generator system are as shown below on the
left:
Waveforms for different generators
Typical 3 phase generator waveform
They can be measured by means of a voltage divider connected to an
oscilloscope, which is an invasive technique. Typical output from the
oscilloscope is as shown above on the right.
(e)
Collimation
Maximum symmetrical radiation field:
Aluminum filters
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