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role in putting the ALARA principle into effect.
Numerous variables affect the output data that forms the basis of the provided information.
These variables include mass, body size, location of the bone relative to the focal point,
attenuation in the body, and ultrasound exposure time. Among these, exposure time is the
variable that one must pay the most attention to. For, unlike other variables, exposure time is
entirely controlled by the operator of the ultrasound system.
▌ Applying ALARA
The system-imaging mode used depends upon the information needed. 2D-mode and M-
mode imaging provide anatomical information, while Doppler, Power, and Color imaging
provide information about blood flow. Scanned modes like 2D-mode, Power, or Color,
disperse or scatter the ultrasonic energy over an area, while unscanned modes like M-mode
or Doppler concentrate ultrasonic energy. Understanding the nature of the imaging mode
being used allows the sonographer to apply the ALARA principle with informed judgment. The
probe frequency, system set-up values, scanning techniques, and operator experience aid the
sonographer in meeting the definition of the ALARA principle. The decision as to the amount
of acoustic output is, in the final analysis, up to the system operator. This decision must be
based on the following factors: type of patient, type of exam, patient history, ease or difficulty
of obtaining diagnostically useful information, and the potential localized heating of the patient
due to probe surface temperatures. Prudent use of the system occurs when patient exposure
is limited to the lowest index reading for the shortest amount of time necessary to achieve
acceptable diagnostic results.
Although a high index reading does not necessarily mean that a bioeffect is occurring, it
should still be taken seriously. Every effort should be made to reduce the possible effects of a
high index reading. Limiting exposure time is an effective way to accomplish this goal.
There are several system controls that the operator can use to adjust the image quality and
limit the acoustic intensity. These controls are related to the techniques that an operator might
use to implement ALARA. These controls can be divided into three categories: direct, indirect,
and receiver controls.
▌ Direct Controls
Application selection and the output intensity control directly affect acoustic intensity. There
are different ranges of allowable intensity or output based on your selection. Selecting the
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