Chapter 1 Safety 1 - 25
▐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 an unscanned mode, like M-mode or Doppler, concentrate the 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 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 mean that a biological effect is actually occurring, it should 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 and can be divided into three categories: direct, indirect, and receiver control.
▐Direct Controls
Application selection and the output intensity control directly affect acoustic intensity. There are different
ranges of allowable intensity or output depending on your selection. Selecting the correct range of
acoustic intensity for the application is one of the first things required during any exam. For example,
peripheral vascular intensity levels are not recommended for fetal exams. Some systems automatically
select the proper range for a particular procedure, while others require manual selection. Ultimately, the
user bears the responsibility for proper clinical use. Samsung Medison systems provide both
automatic and user-definable settings.
Output has direct impact on acoustic intensity. Once the application has been established, the output
control can be used to increase or decrease the output intensity. The output control allows you to select
intensity levels less than the defined maximum. Prudent use dictates that you select the lowest output
intensity consistent with good image quality.
▐Indirect Controls
The indirect controls are those that have an indirect effect on acoustic intensity. These controls affect
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