A breathing technique is planned for a right anterior oblique (RAO) sternum radiograph. The
intended exposure is 50 milliampere-seconds (mAs) at 75 kilovolts peak (kVp) at 100 centimeter
source to image receptor distance (SID). Which milliampere (mA) station is preferred, assuming the
radiographer ensures exposure occurs during the act of inspiration?
A. 10
B. 25
C. 50 CORRECT ANSWER
D. 100
An exposure time of 1 second is optimal for breathing technique, provided the radiographer ensures
exposure occurs during the act of inspiration. To obtain 50 mAs at an exposure time of 1 second
means use of the 50 mA station. 10 mA is too small, as this would cause an exposure time of 5
seconds...a virtual guarantee of sternal motion on the image. Even 25 (B) mA is too small as this
means 2 seconds of exposure, again producing likely motion. 100 mA is too large, as the exposure
time is 0.5 second, too short to be useful at blurring ribs and lung markings.
This is not as hard as it may seem. A breathing technique requires the patient to take
short, shallow breaths while you increase the exposure time to about 1 second (1
second is optimal though our book tells us that a breathing technique should be
anywhere from 1-3 seconds) to cause blurring of ribs and lung markings.
The question is saying that an RAO sternum (which requires a breathing technique)
should use 50 mAs to complete the exposure. Knowing that the exposure time should
be increased to about 1 second for a breathing techniques would make us realize that
we need to take the total mAs (50 mAs) and divide it by the mA stations that are given in
the multiple choice. (Remeber that mAs/mA=time)
A.
10 (50 mAs/10 mA= 5 seconds; this is much too long for a breathing technique and will cause an
excessive amount of blur)
B. 25 (50 mAs/25 mA= 2 seconds; this is closer to an appropriate amount of time for a breathing
technique exposure, but still too long)
C. 50 (50 mAs/50 mA= 1 second; this is perfect amount of exposure time for a breathing
technique)
D. 100 (50 mAs/100 mA= 0.5 seconds; this is not long enough of an exposure to cause the desired blur
of lung markings)