FujiFilm VisualSonics Vevo MD, Руководство пользователя

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ALARA principle
ALARA is the guiding principle for the use of diagnostic ultrasound. Sonographers and
other qualified ultrasound users, using good judgment and insight, determine the
exposure that is “as low as reasonably achievable.” There are no set rules to
determine the correct exposure for every situation. The qualified ultrasound user
determines the most appropriate way to keep exposure low and bio effects to a
minimum, while obtaining a diagnostic examination.
A thorough knowledge of the imaging modes, transducer capability, system setup and
scanning technique is necessary. The imaging mode determines the nature of the
ultrasound beam. A stationary beam results in a more concentrated exposure than a
scanned beam, which spreads that exposure over that area. The transducer capability
depends upon the frequency, penetration, resolution, and field of view. The default
system presets are reset at the start of each new patient. It is the scanning technique
of the qualified ultrasound user along with patient variability that determines the
system settings throughout the exam.
The variables which affect the way the qualified ultrasound user implements the
ALARA principle include patient 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 the qualified ultrasound user can control it. The
ability to limit the exposure over time supports the ALARA principle.
Applying the ALARA principle
The system imaging mode selected by the qualified ultrasound user is determined by
the diagnostic information required. 2D imaging provides anatomical information;
Color Doppler Mode imaging provides information about the energy or amplitude
strength of the Doppler signal over time at a given anatomical location and is used for
detecting the presence of blood flow. Understanding the nature of the imaging mode
used allows the qualified ultrasound user to apply the ALARA principle.
Prudent use of ultrasound means limiting ultrasound to situations in which it is
medically useful and limiting patient exposure to the lowest ultrasound output for the
shortest time necessary to achieve acceptable diagnostic results. Although there are
no direct user controls for acoustic output, users can indirectly control output by
378 Appendices