Applying Alara; Direct Controls; Indirect Controls - FujiFilm SonoSite M-Turbo User Manual

Applying ALARA

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 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 Section 42 of EN 60601‐2‐37: Particular requirement for the
safety of ultrasound medical diagnostic and monitoring equipment. See "Transducer surface
temperature rise" on page 120. 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

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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
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limited to the following 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. See "Guidelines for reducing MI and TI"
on page 115. 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, see BS EN 60601‐2‐37:2001: Annex HH.

Indirect controls

The controls that indirectly affect output are controls affecting imaging mode, freeze, and
depth. The imaging mode determines the nature of the ultrasound beam. Tissue attenuation is
directly related to transducer frequency. The higher the PRF (pulse repetition frequency), the
more output pulses occur over a period of time.
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