Acoustic Output; Alara Principle; Applying The Alara Principle; Direct Controls - FujiFilm SonoSite Edge II Manual De Instrucciones

Acoustic output

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; CPD 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; Color 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, velocity, and direction of blood flow; Tissue Harmonic Imaging (THI) uses higher received
frequencies to reduce clutter, artifact, and improve resolution on the 2D image. Understanding the nature of
the imaging mode used allows the qualified ultrasound user to apply the ALARA principle.
Prudent use of ultrasound requires that patient exposure to ultrasound be limited to the lowest ultrasound
output for the shortest time necessary to achieve acceptable diagnostic results. Decisions that support
prudent use are based on the type of patient, exam type, patient history, ease or difficulty of obtaining
diagnostically useful information, and potential localized heating of the patient due to transducer surface
temperature.
The system has been designed to ensure that temperature at the face of the transducer will not exceed the
limits established in IEC 60601-2-37: Particular requirement for the safety of ultrasound medical diagnostic
"Transducer surface temperature rise"
and monitoring equipment. See on page 10-9. In the event of a
device malfunction, there are redundant controls that limit transducer power. This is accomplished by an
electrical design that limits both power supply current and voltage to the transducer.
The sonographer uses the system controls to adjust image quality and limit ultrasound output. The system
controls are divided into three categories relative to output: controls that directly affect output, controls that
indirectly affect output, and receiver controls.

Direct controls

2
The system does not exceed a spatial peak temporal average intensity (ISPTA) of 720 mW/cm for all
imaging modes. (For either the Ophthalmic or Orbital exam, the acoustic output is limited to the following
2
values: ISPTA does not exceed 50 mW/cm ; TI does not exceed 1.0, and MI does not exceed 0.23.) The
mechanical index (MI) and thermal index (TI) may exceed values greater than 1.0 on some transducers in
some imaging modes. One may monitor the MI and TI values and adjust the controls to reduce these values.
"Guidelines for reducing MI and TI"
See on page 10-3. Additionally, one means for meeting the ALARA
principle is to set the MI or TI values to a low index value and then modifying this level until a satisfactory
image or Doppler mode is obtained. For more information on MI and TI, refer to Medical Ultrasound Safety,
AIUM (a copy is included with each system) and IEC 60601-2-37 Annex "Guidance on the interpretation of
TI and MI to be used to inform the operator."
32 ALARA principle