11
(e.g. during transcranial applications), the TIC (thermal index in cranial bone) must be monitored.
MI> 0.3 There is the possibility of minor damage to the lungs or intestine of the neonate. If such
exposure is necessary, reduce the exposure time to the degree necessary.
MI> 0.7 There is a risk of cavitation when using an ultrasound contrast agent with micro gas bubbles.
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 total exposure time of an embryo or fetus must be restricted in accordance with
Table 2-2 below:
TI
Max. 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 generally not recommended. Examples of non-diagnostic uses of ultra-
sound equipment include repeated scans for operator training, the demonstration of equipment using normal subjects,
and creation of souvenir pictures or videos of a fetus. For equipment where 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 in any patient. Scans in the first trimester of pregnancy should not be carried out for the sole pur-
pose of producing souvenir videos or photographs, nor should their creation 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 dan-
gerous than any effect that might result from the ultrasound exposure. The diagnostic ultrasound system should there-
fore only be operated by those with sufficient training and experience.
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 is not
evaluated in an application-specific way, but the global maximum derating ISPTA must be ≤ 720 mW/cm2, and either the
global maximum MI must be ≤ 1.9 or the global maximum derating Isppa must be ≤ 190 W/cm2. An exception applies to
ophthalmic use, where the TI = max (TIS_as, TIC) and must not exceed 1.0; ISPTA.3 ≤ 50 mW/cm2 and MI ≤ 0.23.
Track-3 gives the user the freedom to increase the acoustic output power for a specific examination while still limiting the
acoustic output power to a global maximum de-rated ISPTA of 720 mW/cm2 under an output display standard.
Track-3 offers standardised output displays for all diagnostic ultrasound systems. The diagnostic ultrasound systems
and their instructions for use contain information regarding an ALARA (As Low As Reasonably Achievable) training
programme for the clinical user, as well as information on the MI and TI acoustic output indexes. The MI describes
the probability of occurrence of cavitations and the TI represents the predicted maximum temperature increase in the
tissue due to diagnostic examination. In general, a temperature increase of 2.5°C must exist at one specific spot
for two hours in order to cause fetal abnormalities. Avoiding a local temperature increase of more than 1°C should
ensure that no thermally induced biological effect occurs. When referring to the TI for possible thermal effect, a TI
equal to 1 does not mean that the temperature will rise by 1 degree C. This only means that an increased potential