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.
Acoustic Output Limits
This ultrasound system maintains acoustic output below the appropriate limits
for each application, as listed here. The significant difference in magnitude
emphasizes the need to select the correct application and remain in that
application, so the correct application limits are in use for the appropriate
application.
Limits for Non-Ophthalmic Applications
• I
spta.3
≤ 720 mW/cm
2
• MI ≤ 1.9
• TI ≤ 6.0
Limits for Ophthalmic Applications
• I
spta.3
≤ 50 mW/cm
2
• MI ≤ 0.23
• TI ≤ 1.0
Direct Controls
Application selection and the output-power control directly affect acoustic
intensity. There are different ranges of allowable intensity or output based on
your selection. Selecting the correct range of acoustic intensity for the application
is one of the first things that occurs in any exam. For example, peripheral vascular
intensity levels are not recommended for fetal exams. Some systems automatically
49
iU22 User Manual
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2
Safety
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