Acoustic Output
22-3
z 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.
z 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.
2. MI/TI
The smaller the MI/TI values, the lower the bioeffects.
22.4.2 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 insure that exposure time
and output values are maintained at the minimum amounts needed for effective
diagnosis.
You can set which TI item is to be displayed in the screen. Open the [B/THI] page in
[Image Preset] dialog box, 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.
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.
22.5 Acoustic Power Setting
Acoustic power adjustment
Use the soft menu control for [A. Power] in the soft menu to adjust the acoustic power
percentage, and its value is displayed on the soft menu 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.
To Next Page
Loading...
