Q9 Digital Color Doppler Ultrasound System
11
results. In obstetric examinations, TIS (soft tissue thermal index) should be monitored during scans carried
out in the first eight weeks after gestation, and TIB (bone thermal index) thereafter. In applications where the
probe is very close to bone (e.g. trans-cranial applications), TIC (cranial bone thermal index) should be
monitored.
MI> 0.3
There is a possibility of minor damage to neonatal lung or intestine. If such exposure is
necessary, reduce the exposure time as much as possible.
MI> 0.7
There is a risk of cavitations if an ultrasound contrast agent containing gas micro-
spheres is being used. There is a theoretical risk of cavitations without the presence of
ultrasound contrast agents. The risk increases with MI values above this threshold.
TI> 0.7
The overall exposure time of an embryo or fetus should be restricted in accordance with
Table 2-2 below as a reference:
TI
Maximum exposure
time (minutes)
0.7
60
1.0
30
1.5
15
2.0
4
2.5
1
Table 2-2 Maximum recommended exposure times for an embryo or fetus
Non-diagnostic use of ultrasound equipment is not generally recommended. Examples of non-diagnostic uses
of ultrasound equipment include repeated scans for operator training, equipment demonstration using normal
subjects, and the production of souvenir pictures or videos of a fetus. For equipment of which the safety
indices are displayed over their full range of values, the TI should always be less than 0.5 and the MI should
always be less than 0.3. Avoid frequent repeated exposure of any subject. Scans in the first trimester of
pregnancy should not be carried out for the sole purpose of producing souvenir videos or photographs, nor
should their production involve increasing the exposure levels or extending the scan times beyond those
needed for clinical purposes.
Diagnostic ultrasound has the potential for both false positive and false negative results. Misdiagnosis is far
more dangerous than any effect that might result from the ultrasound exposure. Therefore, diagnostic
ultrasound system should be performed only by those with sufficient training and education.
2.6.2
Understanding the MI/TI Display
Track-3 follows the Output Display Standard for systems that include fetal Doppler applications. The acoustic output
will not be evaluated on an application-specific basis, but the global maximum de-rated Ispta must be
≤
720 mW/cm
2
and either the global maximum MI must be
≤
1.9 or the global maximum de-rated Isppa must be
≤
190 W/cm
2
. An
exception is for ophthalmic use, in which case the TI = max (TIS_as, TIC) is not to exceed 1.0; Ispta.3
≤
50mW/cm
2
,