Simpli Series System Instructions for Use
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01-5034-00 R1
Display of Indices
The calculated Mechanical Index and Thermal Index can be viewed on the main display screen and can
be monitored by the operator. By monitoring these displayed values as the acoustic power, depth, and
frequency are adjusted, the operator can achieve the lowest possible values of the indices that still
enables them to acquire the desired image. Proper ALARA principles direct you to move through the
exam quickly and ensure that the indices are kept to a minimum. The resolution of displayed Mechanical
and Thermal Indices is 0.1. Displayed values are relative values based on acoustic power testing and
change in frequency, transmit power, and focal depth. Mechanical and Thermal indices are calculated
values. They cannot be measured and as such should be only used as input to properly practice the
ALARA principles of keeping the acoustic power exposure to a minimum.
Thermal Index Display
There are three thermal indices. The TIB informs the user of potential heating near the focus after the
ultrasound has transitioned through fluid or soft tissue. TIC informs the user of potential heating of bone
at or near the surface. TIS is used to indicate any heating effect in soft homogenous tissue. If the
ultrasound device is not capable of exceeding a thermal index of 1.0 in any mode, then the thermal
index is not displayed.
Adjusting Image Controls to Minimize the Indices
As acoustic power is minimized you will see the Mechanical and Thermal indices values changing. When
using color mode with standard 2D mode, the system will display the Indices for the color or 2D,
whichever is greater. Biological effects are also dependent on pulse frequency. Higher pulse frequencies
have lower biological effects. Therefore, use the highest pulse frequency that still allows you to obtain
the desired image.
As displayed depth is changed the transmit focal point and frame rate are adjusted automatically for the
user. If the new depth and focal point affect the indices, the user will see the displayed indices change.
ALARA Resources
Medical Ultrasound Safety, Third Edition, AIUM 2014
American Institute of Ultrasound in Medicine Bioeffects Consensus Report Vol. 27, Issue 4, April 2008
AIUM Consensus Report on Potential Bioeffects and Safety of Diagnostic Ultrasound." January 1993
