Diagnostic ultrasound ( PDFDrive )

CHAPTER
29
Bioeffects and Safety of Ultrasound
in Obstetrics
Jacques S. Abramowicz
SUMMARY OF KEY POINTS
• Obstetric ultrasound should only be performed with a clear
indication, with calibrated machines, and by proicient
professionals.
• Know the speciic machine being used (what causes
increase in output power).
• Keep the examination as short as possible and use the
lowest possible output power but compatible with arriving
at the correct diagnosis (as low as reasonably achievable
[ALARA] principle).
• Keep track of the onscreen thermal index (TI) and
mechanical index (MI).
• Keep the TI under 1.
• Keep the MI under 1.
• Start the scan at low power output and increase power
only if necessary.
• It is preferable to use gain compensation over increasing
output power.
• Be very cautious when using Doppler in the irst trimester
or in the immediate vicinity of bone.
CHAPTER OUTLINE
INSTRUMENT OUTPUTS
Scanning Mode
System Setup
Dwell Time
THERMAL EFFECTS
MECHANICAL EFFECTS
BIOEFFECTS OF ULTRASOUND
Animal Research
Human Studies
Birth Weight
Delayed Speech
Dyslexia
Nonright-Handedness
Neurologic Development and
Behavioral Issues
Congenital Malformations
Childhood Malignancies
IS DOPPLER DIFFERENT?
SAFETY GUIDELINES
CONCLUSION
More than half a century of extensive use in clinical obstetric
and radiologic practice has shown that diagnostic ultrasound
does not cause major abnormalities in the fetus. Ultrasound,
however, is a form of energy and clinicians must consider whether
subtle efects are possible when such energy penetrates living
tissues. Although some efects have been described in animals,
no immediate human correlation can be made. Conversely, “no
efects detected so far” does not necessarily means “no efect.”
Only large, epidemiologic studies can solve this problem. In the
United States, most women who receive prenatal care are referred
for at least one ultrasound scan; in many other countries, almost
100% of these women are exposed to ultrasound. In reproductive
endocrinology, numerous scans are performed on the ovaries
(and the follicles) and the very early developing embryo or fetus. 1
Furthermore, multiple examinations are oten performed during
pregnancy, with or without clear indication. Because of this
near-universal exposure of pregnant women and their unborn
children to ultrasound, given its tremendous diagnostic value, 2
the issues of possible efects and safety need to be addressed.
he issue of whether short-term or long-term adverse bioefects
to the fetus may result from exposure to ultrasound has been
raised since the beginning of the clinical use of this
modality. 3,4
It is well established that under certain conditions, ultrasound
can have undesirable side efects. his and the issue of safety
have been discussed extensively in the literature. 3,5-24 Two conlicting
points need clariication: (1) to date, no evidence has been
found of harmful efects of ultrasound in humans at clinical
exposure levels, but (2) all available published epidemiologic
data are from before 1992. Since then, acoustic output of diagnostic
systems for fetal use was increased by a factor of almost
8, from 94 mW/cm 2 to 720 mW/cm 2 , and, in reality, a factor of
16 (from 46 mW/cm 2 ) based on earlier regulations. 25 Additional
concerns follow:
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