User guide

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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 125. 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
The system does not exceed a spatial peak temporal average intensity (ISPTA) of 720 mW/cm
2
for all imaging modes. (For either the Ophthalmic or Orbital exam, the acoustic output is limited to
the following values: ISPTA does not exceed 50 mW/cm
2
; 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 121.
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.
Receiver controls
The receiver controls are the gain controls. Receiver controls do not affect output. They should be
used, if possible, to improve image quality before using controls that directly or indirectly affect
output.
Acoustic artifacts
An acoustic artifact is information, present or absent in an image, that does not properly indicate
the structure or flow being imaged. There are helpful artifacts that aid in diagnosis and those that
hinder proper interpretation. Examples of artifacts include:
•Shadowing
• Through transmission
•Aliasing
• Reverberations