User's Manual

2
2 enin
Understanding the MI/TI Display
InnoSight Ultrasound System
P6992-4, EN, 16/12/6
De-rating factor R
F
for the various distances and frequencies with attenuation coefficient 3 dB cm
-1
MHz
-
1
in homogeneous soft tissue is listed in the following table An example is if the operator uses  MHz
frequency, the power will be attenuated by  at  cm, or 3 x  x   -112 dB The De-rated
Intensity is also referred to as 3’ at the end (eg I
spta3
)
Distance (cm)
Frequency (MHz)
1 3 5 7.5
1 9332 12  9
2 1 66 12 34
3 12 3 34 2113
4 6 436 212 129
  34 1 
6 66 24 129 44
7 6166 2344 91 266
 4 193 631 1
Tale 5
I’  I  R
F
Where I’ is the intensity in soft tissue, I is the time-averaged intensity measured in water
TI
TI is defined as the ratio of the In Situ acoustic power (W3) to the acoustic power required to raise tissue
temperature by 1C (W
deg
),
TI  W3 / W
deg
Three TIs corresponding to soft tissue (TIS) for abdominal bone (TIB) for fetal and neonatal cephalic and
cranial bone (TIC) for pediatric and adult cephalic, have been developed for applications in different exams
An estimate of the acoustic power in milliwatts necessary to produce a 1C temperature elevation in soft
tissue is:
W
deg
 21 / fc
For model 1 to 4, where fc is the center frequency in MHz
W
deg
 4    D
For model  and 6, where  (beam shape factor) is 1, D is the aperture diameter in cm at the depth of
interest
MI
Cavitation is more likely to occur at high pressures and low frequencies in pulse ultrasound wave in the
tissue, which contains a bubble or air pocket (for instance, the lung, intestine, or scan with gas contrast
agents) The threshold under optimum conditions of pulsed ultrasound is predicted by the ratio of the peak
pressure to the square root of the frequency
MI  Pr’ / sqrt(fc)
Pr’ is the de-rated (3) peak rare-fractional pressure in Mpa at the point where PII is the maximum, and
fc is the center frequency in MHz PII is the Pulse Intensity Integral that the total energy per unit area
carried by the wave during the time duration of the pulse The peak rare-fractional pressure is measured in
hydrophone maximum negative voltage normalized by the hydrophone calibration parameter