Digital Color Doppler Palm Ultrasound System
11
an embryo less than eight weeks after gestation; or the head, brain or spine of any fetus or neonate.
Operators should continually monitor the on-screen thermal index (TI) and mechanical index (MI) values
and use control settings that keep these settings as low as possible while still achieving diagnostically
useful 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.
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 cavitation if an ultrasound contrast agent containing gas micro-spheres is
being used. There is a theoretical risk of cavitation 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 Ispta
must be ≤ 190 W/cm
2
. An exception is for ophthalmic
use, in which case the TI = max (
TIS_as
) is not to exceed 1.0; Ispta.3 ≤50mW/cm
2
, and MI ≤ 0.2
3.
