The Alara Principle; Guidelines For Reducing Ti - SonoSite 180PLUS Guide D'utilisation

a. Field strengths from fixed transmitters such as base stations for radio (cellular/cordless) telephones and land mobile
radios, amateur radio, AM and FM radio broadcast and TV broadcast cannot be predicted theoretically with accuracy.
To assess the electromagnetic environment due to fixed RF transmitters, an electromagnetic site survey should be
considered. If the measured field strength in the location in which the SonoSite ultrasound system is used exceeds the
applicable RF compliance level above, the SonoSite ultrasound system should be observed to verify normal operation.
If abnormal performance is observed, additional measures may be necessary, such as re-orienting or relocating the
SonoSite ultrasound system.
b. Over the frequency range 150 kHz to 80 MHz, field strengths should be less than 3 V/m.

The ALARA Principle

The information below is excerpted and edited from the SonoSite Ultrasound System User Guide. See
the user guide for complete text.
Applying ALARA
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
on page 9. If the power monitor protection circuit senses an over-current condition, then the drive
current to the transducer is shut off immediately, preventing over-heating of the transducer surface.
Validation of the power monitor protection circuit is performed under normal system operation.
Direct Controls
The system does not exceed a spatial peak temporal average intensity (ISPTA) of 720 mW/cm
imaging modes. The thermal index (TI) may exceed values greater than 1.0 on some transducers in
some imaging modes. The system does not exceed an MI of 1.0 for all exam types, and MI is not
displayed. One means for meeting the ALARA principle is to set the 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 TI, see BS EN 60601-2-37:2001: Annex HH.

Guidelines for Reducing TI

The following are general guidelines for reducing TI. If multiple parameters are given then the best
results may be achieved by minimizing these parameters simultaneously. In some modes changing
these parameters will not affect TI. Changes to other parameters may also result in TI reductions.
Please note the 'TI' read out on the right side of the LCD screen.
"↓" means to decrease or lower setting of parameter to reduce TI. "↑" means to raise or increase
setting of parameter to reduce TI. When the indicated setting is blank, then no consistent way was
determined to change TI for that parameter.
6 Chapter 2: Safety
"Transducer Surface Temperatures"
2
for all