The typical IVU examination at our
institution consists of one posteroanterior
and four anteroposterior views, each
of which involves a 14 3 17-inch screenfilm
combination acquired at 70 kVp and
64 mAs. The skin entrance exposure values
for these views were calculated for an
average-sized patient by using the radiation
output data of the x-ray installation.
The exposure in air without backscatter
was measured at 90 cm from the focal
spot by using a recently calibrated ionization
chamber and dosimeter (Model
35055; Keithley Instruments, Cleveland,
Ohio). The x-ray beam quality used during
the procedure was assessed by measuring
the beam half-value layer at 80 kVp.
The entrance exposure in air without
backscatter was calculated by using the
output data and knowledge of the technique
used, with the inverse square law
and an appropriate skin-to-focus distance
taken into account (7). An appropriate
area of the x-ray beam at the skin entrance
was used to calculate the exposurearea
product for each view, and the energy
imparted to the patient was determined
by extrapolating data from that of Shrimpton
et al (8) for an appropriate x-ray beam
quality