Diagnostic ultrasound ( PDFDrive )

CHAPTER 29 Bioeffects and Safety of Ultrasound in Obstetrics 1041
external factors such as ultrasound could afect this process. 152
In another study, only 2 of 123 variables were found to be disturbed
at birth, but not at 1 year of age, in children exposed in
utero; these variables are grasp relex and tonic neck relex. 153
he signiicance was not elaborated, and some doubts exist
regarding statistical validity. Stark et al. 125 reported that vision
and intelligence scores were identical among 425 exposed infants
and 381 controls. A large report found no association between
routine exposure to prenatal ultrasound and school performance
(deicits in attention, motor control, perception, vision, and
hearing). 154 In more than 4900 children age 15 to 16 years, no
diferences were found in school performance between exposed
and nonexposed children, except for a lower score for exposed
boys in physical education. 155
Behavioral changes may be a more sensitive marker of subtle
brain damage than obvious structural alterations. 156 Such changes
have been described in animals, 84,105 although oten transient. 97
An interesting study in mice was recently published. 157 As detailed
earlier, there may be male preponderance of nonright-handedness
ater in utero ultrasound exposure. Furthermore, an increased
prevalence of autism exists in males and there are reports of
excess nonright-handedness in this population. Pregnant mice
were exposed to 30 minutes of diagnostic ultrasound at embryonic
day 14.5. Social behavior of their male pups was analyzed 3
weeks ater birth. Ultrasound-exposed pups were signiicantly
(P < .01) less interested in social interaction than sham-exposed
pups and demonstrated signiicantly (P < .05) more activity
relative to the sham-exposed pups (only in the presence of an
unfamiliar mouse). hese results suggest that social behavior in
young mice was altered by in utero exposure to diagnostic
ultrasound. he authors’ conclusions are that this may be relevant
for autism but that major diferences between the exposure of
diagnostic ultrasound of mice and humans preclude conclusions
regarding human exposure and require further studies. Indeed,
no such changes have been reported in humans. In particular,
schizophrenia and other psychoses have not been found to be
associated with prenatal ultrasound exposure. 158 he question
has been raised about the increased rate of autism observed over
the past few years and its relation to the greatly increased use
of ultrasound in obstetrics. Although a major upsurge in both
have occurred, there is no cause and efect demonstrable between
the two. 159
Congenital Malformations
In humans, prenatal ultrasound has not been shown to result in
an increased incidence of congenital anomalies, as found in
animals.
Childhood Malignancies
No association has been found between ultrasound exposure in
utero and the later development of leukemia 160,161 or solid tumors
in children. 128,162-166
Again, although some of these studies were published in 2007
or 2008, the populations studied were exposed to ultrasound in
utero 20 to 30 years ago, that is, with instruments generating
lower outputs and with minimal or no information available on
exposure conditions.
IS DOPPLER DIFFERENT?
Spectral (pulsed) Doppler uses high pulse repetition frequencies,
generating greater temporal average intensities and powers than
B- or M-mode, and hence greater heating potential (see “hermal
Efects”). 75 Adequate diagnostic information may be obtained
with low output levels (as documented by values of the TI), as
demonstrated in Fig. 29.1. his has been reported in the literature,
speciically for Doppler, the mode with the highest output, both
in early and later pregnancy. 167,168 In fact, under pressure from
bioefects and safety committees of various professional organizations
(American Institute of Ultrasound in Medicine [AIUM],
European Federation of Societies of Ultrasound in Medicine and
Biology [EFSUMB], International Society for Ultrasound in
Obstetrics and Gynecology [ISUOG], and World Federation for
Ultrasound in Medicine and Biology [WFUMB]), several
manufacturers have changed their default settings, speciically
for pulsed Doppler in fetal mode, from very high (as it was
originally, presumably in an attempt to obtain better images) to
very low, with the end user capable of raising the output, if
desired. Because acoustic output is high in Doppler, special
precaution is recommended, particularly in early gestation. 169
SAFETY GUIDELINES
It is diicult to issue precise safety recommendations because
of the multitude of ultrasound instruments, each with a selection
of transducers and used in a variety of applications. Patient
characteristics further complicate the task. 170 Safety guidelines
are very important, however, given the very low level of knowledge
about bioefects and safety of ultrasound among clinical end
users. In a questionnaire distributed to ultrasound active end
users (of which 82% were obstetricians), only 17.7% gave the
correct answer of the deinition of the TI. Approximately 96%
did not know the proper deinition for MI. Almost 80% of
respondents did not know the correct answer to the multiple
choice question of where to ind the acoustic indices; answer
options were the machine documentation, a textbook, a complicated
calculation or in real time on the ultrasound monitor
(the correct answer). 171 Similar results were recorded in surveys
abroad, performed in Europe, Asia, or the Middle East, 172-174
indicating that clinical end users worldwide show poor knowledge
regarding safety issues of ultrasound during pregnancy. 30 More
recently, knowledge among residents in obstetrics and gynecology
was also found to be grossly lacking. 175 Similar results were
obtained in a survey of sonographers, and years of experience
made no diference. 176
In another study, compliance with the ALARA (as low as
reasonably achievable) principle by practitioners seeking credentialing
for nuchal translucency (NT) measurement between
11 and 14 weeks’ gestation was evaluated. Only 5% of the providers
used the correct TI type (TIB) at lower than 0.5 for all submitted
images, 6% at lower than 0.7, and 12% at 1.0 or lower. A TI (TIB
or TIS) higher than 1.0 was used by almost 20% of the providers.
Proiciency in NT measurement and educational background
(physician or sonographer) did not inluence compliance with
ALARA. he authors concluded that clinicians seeking