Philips EPIQ 7 User Manual page 51

Biological Safety Safety
The ability of the user to abide by the ALARA principle is important. Advances in diagnostic
ultrasound, not only in the technology but in the applications of that technology, have resulted
in the need for more and better information to guide the user. The output display indices are
designed to provide that important information.
There are a number of variables which affect the way in which the output display indices can be
used to implement the ALARA principle. These variables include index values, body size,
location of the bone relative to the focal point, attenuation in the body, and ultrasound
exposure time. Exposure time is an especially useful variable, because it is controlled by the
user. The ability to limit the index values over time supports the ALARA principle.
Applying ALARA
The system imaging mode used depends upon the information needed. 2D and M‑mode
imaging provide anatomical information, while Doppler, Color Power Angio (CPA), and Color
imaging provide information about blood flow. A scanned mode, like 2D or Color, disperses or
scatters the ultrasonic energy over an area, while an unscanned mode, like M‑mode or Doppler,
concentrates ultrasonic energy. Understanding the nature of the imaging mode being used
allows the sonographer to apply the ALARA principle with informed judgment. Additionally, the
transducer frequency, system setup values, scanning techniques, and operator experience
allow the sonographer to meet 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 transducer 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 bioeffect is actually occurring, a high index
reading 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. These controls can be divided into three categories: direct, indirect,
and receiver controls.
EPIQ 7 User Manual 4535 617 25341 51