Safety Information
T3300 Diagnostic Ultrasound System | 20 | B00601-010 4/10/17
Track-3 follows the Output Display Standard for systems which include fetal Doppler applications.
The acoustic output will not be evaluated on an application-specific basis, but the global maximum
de-rated I
spta
must be 720 mW/cm
2
and either the global maximum MI must be 1.9, or the global
maximum derated Isppa must be 190 W/cm
2
. An exception is for ophthalmic use, in which case
the TI=max (TIS) is not to exceed 1.0; I
spta
.3 50 mW/CM
2
, and MI 0.23. Track-3 gives the
operator the freedom to increase the output acoustic power for a specific exam, and still limit output
acoustic power within the global maximum de-rated I
spta
720 mW/cm
2
under an Output Display
Standard.
The system design allows full software control of the acoustic output, entry of new patient
identification data or change from a non-foetal to a foetal application, and the system may switch to
an appropriate default setting upon powering on. These default setting levels are established before
shipping and may be reconfigured by the operator.
For any ultrasound systems, Track-3 provides an Output Indices Display Standard. The ultrasound
system and its Basic Operating Instructions contain the information regarding an ALARA (As Low As
Reasonably Achievable) education program from the clinical end-user and the acoustic output
indices, MI and TI. The MI describes the likelihood of cavitation, and the TI offers the predicted
maximum temperature rise in tissue as a result of the diagnostic examination. In general, a
temperature increase of 2.5°C must be present consistently at one spot for 2 hours to cause
possible fetal abnormalities. Avoiding a local temperature rise above 1°C should ensure that no
thermally induced biologic effect occurs. When referring to the TI for potential thermal effect, a TI
equal to 1 does not mean the temperature will rise 1°C. It only means an increased potential for
thermal effects can be expected as the TI increases. A high index does not mean that bioeffects are
occurring, but only that the potential exists and there is no consideration in the TI for the scan
duration, so minimizing the overall scan time will reduce the potential for effects. These operator
control and display features move the safety responsibility from the manufacturer to the operator. So
it is very important to have the ultrasound systems display the acoustic output indices correctly and
the well-educated operator to interpret the value appropriately.
R
F
: De-rating factor
In Situ intensity and pressure cannot currently be measured. Therefore, the acoustic power
measurement is normally done in the water tank, and when soft tissue replaces water along the
ultrasound path, a decrease in intensity is expected. The fractional reduction in intensity caused by
attenuation is denoted by the derating factor (R
F
),
R
F
= 10
(-0.1 a.f.z)
Where a is the attenuation coefficient in dB cm
-1
MHz
-1
, f is the transducer center frequency, and z
is the distance along the beam axis between the source and the point of interest.
De-rating factor R
F
for the various distances and frequencies with attenuation coefficient 0.3 dB cm
-
1
MHz
-1
in homogeneous soft tissue is listed in the following table. An example is if the operator uses
Triplex V V
CW Doppler
Table 10 MI/TI generating from applicable transducer/mode combinations
Mode /
Transducer
P42B6 Phased
Array 64 elements
2-4 MHz
C62B Curved
Linear Array 2-
6 MHz
L154BH Linear
Array 4-12 MHz
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