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24.1.2 MI/TI display description
(1) Definition of MI
Mechanical Index (MI) is the peak-rarefactional acoustic pressure P
considering the tissue attenuation; = 0.3 dB/cm/MHz) divided by the square root
of the acoustic working frequency f
MI =
f
awf
where C
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 determined and displayed based on the measured
acoustic power data. The displayed values contain errors 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.
P
,
r,
C
MI
= 1 (MPa / MHz )
No. 2B771-004EN*M
24-3
(unit: MHz) and can be expressed as follows:
awf
(calculated
r,
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