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24.2.2 MI/TI display description
(1) Definition of MI
Mechanical Index (MI) is the peak-rarefactional acoustic pressure P
considering the tissue attenuation) divided by the square root of the center
frequency f
MI =
(2) Definition of TI
Thermal Index (TI) is the ratio of total acoustic power to the acoustic power
required to raise tissue temperature by 1 degree centigrade under defined
assumptions.
TIS (Thermal Index Soft Tissue) is related to heating in abdominal, cardiac and
peripheral vascular applications.
TIB (Thermal Index Bone) is related to bone heating, which may be of particular
importance in fetal applications.
TIC (Thermal Index Cranial) is related to heating in adult cephalic applications.
(3) Displayed MI/TI values
Accuracy
The MI and TI values are mean values that are determined and displayed based
on the measured acoustic power data.
The displayed label names have "m" as the last character (such as MIm and TISm).
The system also has other index values. They are called global maximum values
and internally control the ultrasound output. They are determined statistically,
based on the variation due to the following factors.
* Measurement error in acoustic power measurement
* Variation in the characteristics of the system and transducer
* Ultrasound propagation characteristics
Display Precision is rounded in units of 0.1.
The MI and TI values are displayed only when the value is 0.4 or higher.
(unit: MHz) and can be expressed as follows:
c
P
.3
f
c
No. 2B771-004EN*M
24-11
(calculated
.3
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