Basic Overview of Possible Effects & Possible safety measures based on ALARA Principle.

1. SAFETY OF DIAGNOSTIC
ULTRASOUND IN FETAL
SCANNING
Aqib Umair
MID

2. This is a very short overview of possible effects
of ultrasound and safe approach in fetal
scanning.
Information provided is based on
“The Fetal Medicine Foundation” Data.

3. Possible Effects of Ultrasound on
Tissue
1. Thermal Effects:
Heating of tissue as ultrasound is absorbed by
tissue. Heat is also produced at the transducer
surface.
2. Cavitation:
Formation of gas bubbles at high negative pressure.
3. Mechanical Effects:
mechanical radiation forces leading to streaming in
fluids and stress at tissue interfaces.

4. Current Regulations on Effects
Thermal Index:
TI is ratio of the power used to that required to
cause a maximum temperature increase of
1°C. Thermal Index of 1 indicates a power
causing a temperature increase of 1C.
Subdivision: In subdivision of thermal index most
important in fetal scanning is
TIB: thermal index with bone at focus.

5. Current Regulations on Effects
Mechanical Index:
MI is estimate of the maximum amplitude of
the pressure pulse in tissue. It gives an
indication as to the relative risk of mechanical
effects (streaming & cavitation).
FDA regulations allow a mechanical index of up
to 1.9 to be used for all applications except
ophthalmic(maximum 0.23).

6. Practical Approach to Safe Fetal
Scanning
ALARA (As Low As Reasonably Achievable).
Power Outputs should be lowered and increase it as necessary.
B-mode(grayscale) has the lowest output and intensity.
M-mode, Color Doppler, Specteral Doppler have higher outputs
which can cause more heating at the site of examination.
The examination Should begin with B-mode and use color and
spectral Doppler only when necessary.

7. Practical Approach to Safe Fetal
Scanning
Special Care Should be taken in Febrile patients
since ultrasound heating will cause additional
heating to the fetus.
Do not scan for longer than is necessary to
obtain the diagnostic information.

8. Thanks