System information

HVLs for Units With Manual Exposure Rate Controls
Fluoroscopic systems
with manual exposure
rate
controls allow use of Test Method I in Section I-7-A with
some minor geometry changes. The image intensifier
should be set at its maximum SID on under table x-ray
tube systems. The added Aluminum test filters are put on
the table top while the ion chamber is placed halfway
between the table top and spotfilm device.
(On over
table x-ray tube
systems,
the geometry
suggested in
Section i-7-A does
not
require change.) Fluoroscopy can
be used to center the dosimeter, filters, and x-ray beam
and to minimize the x-ray field size.
An exposure rate
measurement during routine fluoroscopy (set kV and mA) or
an integrated exposure measurement
using
the spot film
mode (set kVp, mA, and time) can be used.
HVLs for Units Without Manual Exposure Rate Controls
Changing the thickness of test filtration
in the
primary beam of most Automatic Exposure Rate Controlled
systems (AERC) results in a change in the kVp which
changes the HVL.
Therefore, in the
AERC mode of
operation, the total thickness
of added
filtration
between the focal spot and image intensifier must remain
constant.
HVL Test Method I: Noninvasive, 80 kVp Test Point
1) Extend the imaging chain tower to its
2)
3)
4)
5)
6)
maximum SID.
Place the ionization chamber halfway between
the spot film device and tabletop on undertable
x-ray tube systems.
Place it halfway
between the tabletop and focal spot on
overtable x-ray tube systems.
Tape two or three 0.8 mm (0.03") copper sheets
and 4-5 mm 1100 alloy Aluminum sheets onto
the underneath side of the image inten-
sifier tower for undertable systems.
Place these attenuators on the tabletop
on overtable systems.
Adjust the collimator during fluoroscopy
to minimize the x-ray field size at the
ionization chamber.
Add or subtract Copper until 80-85 kVp
is obtained during fluoroscopy.
adjustment in
kVp can be achieved by
reducing the SID.
(77-83
kVp is ac-
ceptable for this measurement.)
Record the exposure rate; this
is the 0 mm Al data point.
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