Acoustic Output 17-3
TIB: Thermal index for applications, such as fetal (second and third trimester) or
neonatal cephalic (through the fontanel), in which the ultrasound beam passes
through soft tissue and a focal region is in the immediate vicinity of bone.
TIC: Thermal index for applications, such as pediatric and adult cranial
applications, in which the ultrasound beam passes through bone near the beam
entrance into the body.
Although the output power is automatically controlled for the selected applications, high TI
values should be kept to a minimum or avoided in obstetric applications. WFUMB (World
Federation for Ultrasound in Medicine and Biology) guidelines: state that temperature
increase of 4 degree C for 5 min or more should be considered as potentially hazardous to
embryonic and fetal tissue.
The smaller the MI/TI values, the lower the bioeffects.
17.4.2 MI/TI Display
TI and MI values are displayed in real time in the upper part of the screen. The operator
should monitor these index values during examinations and ensure that exposure time
and output values are maintained at the minimum amounts needed for effective diagnosis.
Under different operating conditions, once there is a situation that a MI value is greater
than 1.0; the start point of displaying MI values is 0.4.
In the same way, once there is a situation that a TI value is greater than 1.0, the TI value
will be displayed and the start point is 0.4.You can set which TI item is to be displayed in
the. Open the B/THI page in [Image Preset] screen, and the acoustic output setups appear,
as shown in the figure below:
Here you can set TIC, TIB or TIS to be displayed, as well as the level of acoustic power.
Generally speaking, when a cranial exam is performed, TIC is set to be displayed only.
NOTE:
If there is a value of MI or TI exceeds 1.0, you must be careful to practice the
ALARA principle.
The display precision is 0.1.
17.5 Acoustic Power Setting
Acoustic power adjustment
Click [A. power] in the soft menu or the menu to adjust the acoustic power percentage,
and its value is displayed on the corresponding item as well as at the top of the screen.
The greater the acoustic power percentage, the greater the current acoustic output.
When the image is frozen, the system stops transmitting acoustic power.
Default setting of acoustic power
Selection of diagnostic applications is the most important factor for controlling ultrasound
output.
The permissible level of intensity of ultrasound differs depending on the region of interest.
For fetal examinations, in particular, much care must be exercised.
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