ECO 6 Digital Color Doppler Ultrasound System
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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 (Wdeg), TI = W.3/Wdeg.
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 milli-watts necessary to produce a 1°C temperature elevation in soft
tissue is:
Wdeg = 210/fc,for model 1 to 4, where fc is the center frequency in MHz.
Wdeg = 40 K Dfor model 5 and 6, where K (beam shape factor) is 1.0, 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 the 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 ration of the peak pressure to the
square root of the frequency.
MI = Pr’ / sqrt(fc)
Pr’ is the de-rated (0.3) 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.
Display Guideline:
For different operation modes, different indices must be displayed. However, only one index needs to be
shown at a time. Display is not required if maximum MI is less than 1.0 for any setting of the operating mode,
or if maximum TI is less than 1.0 for any setting of the operating mode. For TI, if the TIS and TIB are both
greater than 1.0, the scanners need not be capable of displaying both indices simultaneously. If the index falls
below 0.4, no display is needed. The display increments are no greater than 0.2 for index value less than one
and no greater than 1.0 for index values greater than one (e.g. 0.4, 0.6, 0.8, 1, 2, and 3).
Display and Report
Located on the upper middle section of the system display monitor, the acoustic output display provides the
operator with real-time indication of acoustic levels being generated by the system.
For Scan
Only display and report MI, and start from 0.4 if maximum MI > 1.0, display in increments of 0.2.
Below is a simple guideline for the user when TI exceeds one limit exposure time to 4(6-TI) minutes based on
the ‘National Council on Radiation Protection. Exposure Criteria for Medical Diagnostic Ultrasound: I.
Criteria Based on Thermal Mechanisms. Report No.113 1992’.
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