sonography/ultrasound protocol and safety standards
TRANSCRIPT
Page 1 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
Sonography/Ultrasound Protocol and Safety Standards
A senior research projected submitted in partial requirement for the degree Doctorate of Chiropractic.
Logan University
Sterling Foster
Advisor: Mary Unger-Boyd, DC, DICS, CACCP
December 2013
Page 2 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
Abstract:
The evolution of the diagnosis and management of women who are pregnant has been a medical success over the past years. Pregnancy confirmation was once determined by amenorreaic symptoms in the presence sexual activity accompanied by a feeling of “morning sickness.” It progressed into a pregnancy test that has reached a level of sensitivity and specificity which is unlikely to be surpassed either by better tests or alternative technology.22 currently, confirmation of pregnancy is being achieved through visualization of the fetus with sonography. The biophysical effects of the ultrasound are damaging to energy sensitive structures of the fetus if >1.5 TI or MI is exceeded. User incompetence is identified through poor knowledge of safety standards on sonography equipment through questionnaires. These factors must be acknowledged when discussing routine, low-risk ultrasoundography.
Methods: A comprehensive review of the literature is performed. Information was inserted in Cochrane database of Systematic Review, PubMed, and Google Scholar in an attempt to identify the presence of specific practice guidelines when performing prenatal ultrasounds/sonography.
Conclusion: ODS safety standards issued by the FDA exceed levels that may be harmful too the developing fetus, especially the first trimester, when sonography is used improperly by the end user. Further research is needed in regards to regulation standards for ultrasound technicians.
Keywords: sonography, ultrasound, safety, efficacy, complication, protocol and procedure.
Page 3 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
Introduction:
The evolution of the diagnosis and management of women who are pregnant has been a
medical success over the past years. Pregnancy confirmation was once determined by
amenorreaic symptoms in the presence of sexual activity accompanied by a feeling of “morning
sickness.” It progressed into a pregnancy test that has reached a level of sensitivity and
specificity which is unlikely to be surpassed either by better tests or alternative technology.22
Currently, confirmation of pregnancy is being achieved through visualization of the fetus with
sonography. The complications of the first two remain minimal, however evidence regarding the
safety of the latter is rarely, if ever, reviewed or questioned. Modern sophisticated
ultrasonographic equipment is capable of delivering substantial levels of acoustic energy into
the body when used at maximum outputs.20 Establishing the boundaries for obstetrical
intervention is important for the health of the mother and child during the gestational period.
Identifying key factors for neonatal mortality are important, but routine ultrasound does not
increase these chances. The New England Journal of Medicine reported screening
ultrasonography did not improve prenatal outcome as compared with the selective use of
ultrasonography on the basis of clinician judgment.1 With such similarity existing between the
two groups it should become even more important to thoroughly analyze the safety of emitting
routine ultrasonography to a developing fetus without first evaluating the potential for harm.
High-energy ultrasound can induce biophysical effects when passing through tissue, for
example, thermal effects and mechanical stress, causing cavitations. Standard ultrasound
protocols and procedures should be in place to prevent abuse or harm to the fetus and
Page 4 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
regulation should strictly adhered to. This literature review evaluates the potential side effects
of ultrasound, diagnostic usage, and safety protocols of the end-user.
Page 5 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
Discussion:
Biophysical Effects: The FDA mandates that machines capable of producing higher outputs be
able to display to the diagnostician some indication of the relative potential for ultrasound-
induced bioeffects. This regulation is known as the Standard for Real-Time Display of Thermal
and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment, more commonly
known as the output display standard (ODS).15 The ODS indicators comprise two types of
biophysical index: the thermal index (TI) and mechanical index (MI)10 The ODS supplies on
screen, in real time, numerical displays that provide information about the potential for
temperature increases (TI) and mechanical damage (MI).14 These indices are calculated for the
given machine settings on the basis of tissue models and their acoustic properties.
The TI is an estimate of the tissue temperature rise in degrees centigrade (°C). For
particular examination situations, three types of TI have been defined: soft tissue (TIS), bone
tissue (TIB) thermal index, and for cranial examinations (TIC). The presence of bone within the
ultrasound beam greatly increases the likelihood of a temperature rise due to direct absorption
in the bone itself and conduction of heat from bone to adjacent tissues.16 A temperature
elevation less than 1.5°C likely does not present a bioeffects risk to the embryo, although there
has been some debate on the threshold nature of thermal effects. A temperature elevation
greater than 4°C for 5 minutes can present a bioeffects risk to the embryo. Biologically
significant temperature increases can occur at or near to bone in the fetus from the second
trimester, if the beam is held stationary for more than 30 s in some pulsed Doppler
applications.21 Velocity, power, and pulsed spectral Doppler ultrasound all have the potential to
Page 6 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
reach these levels. The TI provides a guide for the sonographer and sonologist regarding the
magnitude of the temperature increase.17
The MI attempts to indicate the probability of non-thermal effects occurring within the
tissue. Cavitation is the phenomenon where bubbles form in a liquid material when the local
pressure falls below the vapor pressure of the liquid sufficient to pull the material apart.
Cavitation generally falls into 2 types: (1) inertial or transient cavitation, in which the newly
formed bubble rapidly collapses, producing a shock wave that can be capable of biological
effects and (2) non-inertial cavitations, in which the bubble oscillates in the acoustic field and
appears to be less likely to produce biological effects.16 The MI and TI are only rough estimates
of possible effects and should not be understood as giving more than guidance to the operator.
Nevertheless, the ODS is considered at present to be the best way of providing safety
information.9
According to the ODS, for equipment that can at certain machine settings produce
output energy giving TI or MI ≥ 1.0, the indices should be displayed if they exceed 0.4.16
Sonography Protocol: Cochrane database of Systematic Review (CDSR) produced no results
found with the keyword search “sonography” AND “safety, efficacy, complication, protocol and
procedure.” The same lack of results was found with the keyword “ultrasound” AND “safety,
efficacy, complication, protocol and procedure.”
There were a total of 2 results found in the CDSR when the word “sonography” was used alone
in conjunction with the “Protocol” type result. They are reported as Second-line, post-docetaxel
Page 7 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
therapy for advanced, androgen deprivation-refractory prostate cancer; and Transcranial
Doppler sonography for detecting stenosis or occlusion of intracranial arteries people with
acute ischemic stroke. No sonography protocols for prenatal management were identified under
the CDSR.
There were a total of 9 results found in the CDSR when the word “ultrasound” was used
in conjunction with the “Protocol” type result. The studies were as followed:
1. Dimercaptosuccinic acid scan versus ultrasound in screening for vesicoureteral reflux
among children with urinary tract infections. 2. Doppler ultrasound, CT angiography, MR
angiography, and contrast-enhanced MR angiography versus intra-arterial angiography for
moderate and severe carotid stenosis in symptomatic patients. 3. Therapeutic ultrasound for
chronic low-back pain. 4. Therapeutic ultrasound for soft-tissue injuries of the elbow. 5.
Therapeutic ultrasound for soft-tissue injuries of the knee. 6. Traditional landmark versus
ultrasound guidance for central vein catheterization. 7. Transient ultrasound elastography and
magnetic resonance elastography for the diagnosis of oesophageal varices in patients with
chronic liver disease or portal vein thrombosis. 8. Ultrasound-guided transvaginal ovarian
needle drilling for clomiphene-resistant polycystic ovarian syndrome in subfertile women. 9. Use
of endoanal ultrasound for reducing the risk of complications related to anal sphincter injury
after vaginal birth.
No ultrasound protocols for prenatal management were present in the CDSR.
Protocols for sonography have not been systematically reviewed by the CDSR.
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LITERATURE STUDY: One study found exposure to multiple prenatal ultrasound examinations
from 18 weeks' gestation onwards might be associated with a small effect on fetal growth but is
followed in childhood by growth and measures of developmental outcome similar to those in
children who had received a single prenatal scan.3 That same study also states that there were
no significant differences indicating deleterious effects of multiple ultrasound studies at any age
as measured by standard tests of childhood speech, language, behavior, and neurological
development.3
Another study suggests that diagnostic US has no adverse effect on embryogenesis or fetal
growth. However, although B and M mode are safe during the first trimester, color, pulsed or
power Doppler should be performed with caution. The US effects are mainly due to cavitation.4
However, this Mechanism has been determined mainly in animal models. Thermal effect, which
was thought to be hazardous, probably does not influence fetal development.4
A similar study suggest children that were exposed to ultrasound in utero showed evidence that
prenatal ultrasound examination does not cause adverse effects with regard to malformations,
childhood malignancy, neurological abnormalities or abnormal growth. 7
Obstetric ultrasound should only be done for medical reasons, and exposure should be
kept as low as reasonably achievable (ALARA) because of the potential for tissue heating. Higher
energy is of particular concern for pulsed Doppler, color flow, first trimester ultrasound with a
long transvesical path (> 5 cm), second or third trimester exams when bone is in the focal zone,
as well as when scanning tissue with minimal perfusion (embryonic) or in patients who are
febrile.5 Operators should minimize risk by limiting dwell time and limiting exposure to critical
Page 9 Sonography/Ultrasound Protocol and Safety Standard. By: Sterling Foster
structures. Critical structures can be classified as places such as the retina and visual cortex and
the cochlea of the inner ears.21 these places become compromised because of one-to-one cell
connections. Even the eye lens is a sensitive organ because of the lack of continuous blood
circulation, so a rise in temperature caused by ultrasound cannot be counteracted.21
consequently, minor visual or hearing losses could be possible results of ultrasound exposure in
fetal life.
The following equipment generated exposure information is recommended by
Diagnostic Imaging Committee of Health Canada.
Recommendations:
1. Obstetric ultrasound should only be used when the potential medical benefit outweighs any
theoretical or potential risk.
2. Obstetric ultrasound should not be used for nonmedical reasons, such as sex determination,
producing nonmedical photos or videos, or for commercial purposes.
3. Ultrasound exposure should be as low as reasonably achievable (ALARA) because of the
potential for tissue heating when the thermal index exceeds 1. Exposure can be reduced
through the use of output control and (or) by reducing the amount of time the beam is focused
on one place (dwell time).
4. All diagnostic ultrasound devices should comply with the output display standards (MI and
TI).
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5. When ultrasound is done for research or teaching purposes, exposed individuals should be
informed if either the MI or TI is greater than 1 and how this exposure compares to that found
in normal diagnostic practice.
6. While imaging the fetus in the first trimester, Doppler and color Doppler should be avoided.5
A contradictory study promotes the use of Doppler ultrasound in identifying the pulsatile index
of veins of the ductos venosus as early as 10-14 weeks. Ductus venosus Doppler studies can
substantially improve Down syndrome screening efficiency.25 Violation of safety protocol
procedures by early use of Doppler ultrasound in the first trimester may affect future fetal
development negatively.
DAMAGE: Mammalian tissues have differing sensitivities to damage by physical agents such as
ultrasound.21 Ultrasound may damage human tissue by a rise in temperature or cavitations.
Local cell death or cell membrane damage, which in turn affects cell differentiation, might be
the result of ultrasound exposure. Hyperthermia is considered teratogenic in human fetuses,
especially during organogenesis in the first trimester.27 Actively dividing cells of the embryonic
and fetal central nervous system are most readily disturbed.21 As a diagnostic ultrasound beam
envelopes a small volume of tissue, it is possible that the effects of mild disturbance may not be
detected unless major neural pathways are involved. Identifying the disturbances is difficult to
calculate in the prenatal period. It has been shown that the output intensities of commercially
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available equipments have significantly increased over the years and that they can reach levels
many times higher than those used years ago.11 Increased acoustic output levels, as expressed
by TI levels, are reached during obstetric Doppler studies.24 Evidence demonstrates that maybe
the intent of prevention might be the source of causalgia due to the increase in energy output
of sonography equipment.
USER INCOMPETANCE: One study identifies the profound incompetence and poor quality
control of the end-user. Only 32.2% of the participants were familiar with the term thermal
index, only 17.7% actually gave the correct answer to the question on the nature of the thermal
index. Only 22% were familiar with the term mechanical index, but only 3.8% described it
properly. Almost 80% of end users did not know where to find the acoustic indices. Only 20.8%
were aware that they are displayed on the monographic monitor during the examinations.14
A second study showed 13.4% of residents and 20.9% of maternal-fetal medicine fellows knew
how to find or use the output display standard, and 10.9% of residents and 22.7% of fellows
reported use of the output display standard during their ultrasound examinations. Overall, 37%
to 46% of residents and fellows reported no limitations to the use of obstetric ultrasound and
22% to 39% reported no limitations to the use of Doppler ultrasound in the first, second, and
third trimesters. Only 34.8% of third-year fellows reported use of the output display standard.19
About one-third of the ultrasound experts were able to define the abbreviations TI and MI. For
the subclasses of the TI, the correct answer was found in only 3–8% of cases. Of those who
knew what the TI and MI meant, only two-thirds and one-third of respondents, respectively,
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were able to give a simple explanation of the indices.19 In 49% of questionnaires, the Doppler
modes were correctly ranked as generally producing higher ultrasound exposure than the
imaging modes (B-mode, 3D). Some 28% of the respondents correctly indicated where on their
own machine the information on safety indices is displayed. However, not all of them knew how
to control the output energy level. For all items in the questionnaire there were no significant
differences in the results between the three categories of respondents (i.e. physicians,
sonographers and midwives).19
The results of these studies were anything but encouraging and they indicated that the
users, who are supposed to be responsible for controlling exposure of the fetus to ultrasound,
had a very poor knowledge of the basic safety aspects of ultrasound. This was surprising
because the people who are lacking the knowledge of safety are the ones performing the fetal
imaging. It can be presumed that the level of knowledge is still lower among clinicians without
special interest in diagnostic ultrasounds that are routinely using ultrasound for examinations of
pregnant women.
NON DIAGNOSTIC USE: Nondiagnostic uses of ultrasound equipment should be avoided. First-
trimester fetal scans should not use color and power Doppler modes and should not be
performed for the sole purpose of producing souvenir videos or photographs. Production of
fetal souvenir photographs or videos during diagnostic clinical studies should not increase
exposure levels or extend scan times beyond those needed for clinical purposes.18 Operators
should follow safe scanning guidelines and ALARA principles. The FDA considers the promotion,
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selling, or leasing of ultrasound equipment for making “keepsake fetal videos” that are not part
of a medical diagnostic procedure to be an unapproved use of a medical device; thus, the use of
diagnostic ultrasound system for these purposes, without a physician’s order, may be in
violation of state laws or regulations.18 Previous studies state 30% of the ultrasound
professionals actually approved of keepsake ultrasound examinations without any clinical
indication. The discrepancy represents the need for stricter regulation in performing ultrasound
for non diagnostic use.
DIAGNOSTIC USE: Routine ultrasound in early pregnancy appears to enable better gestational
age assessment, earlier detection of multiple pregnancies and earlier detection of clinically
unsuspected fetal malformation at a time when termination of pregnancy is possible.2 Of
course, high-risk pregnancy warrant ultrasound exposure at clinician’s discretion. It is more
likely to exceed the ODS safety measure when longer dwell times and needed for diagnoses. In a
study recording the levels of safety indices and their time course during standard examinations
of high-risk pregnancies, including examinations of the uterine and fetal circulation with
Doppler ultrasound, the TI values were found to exceed 1.5 and even 2.0 on several occasions
during the examination.12 Some believe the use of ultrasound as a screening tool is effective
diagnostic use. A high proportion of abdominal wall defects are associated with concurrent
malformations, syndromes or chromosomal abnormalities, stressing the need for the
introduction of repeated detailed ultrasound examination as a standard procedure.26
One study of small sample size reported proper regulation of ODS safety standards. MI and TI
levels never exceeded 1.5.22
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Conclusion:
Standard ultrasound protocols and procedures should be in place to prevent abuse or harm to
the fetus. Ultrasound usage continues daily under the impression of zero side-effects; however
evidence demonstrates the potential for tissue heating and cellular destruction through
cavitations if the ultrasound exceeds safety limits. With such a large part of obstetrical
healthcare being prenatal based, it is important to further research efforts to ensure safety
requirements are constantly being evaluated.
The purpose of the ODS was to provide the capability for end users of diagnostic
ultrasound to operate their machines at higher levels to increase diagnostic capabilities. The
ODS does not specify any upper limits and it is up to the end user, whether obstetrician or
sonographer, to be competent enough to follow safety regulations. Obstetricians and
sonographers should be familiar with the output energy, how to control it, and, accordingly,
how to use the machine in a safe manner. More studies of the biophysical effects of cellular
interaction occurring from ultrasound energy need to be performed along with proper end-user
training programs.
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References:
1. Ewigman, B. G., Crane, J. P., Frigoletto, F. D., LeFevre, M. L., Bain, R. P., & McNellis, D. (1993). Effect of prenatal ultrasound screening on perinatal outcome. New England journal of medicine, 329(12), 821-827.
2. Neilson, J. P. (1998). Ultrasound for fetal assessment in early pregnancy. Cochrane Database Syst Rev,
3. Newnham, J. P., Doherty, D. A., Kendall, G. E., Zubrick, S. R., Landau, L. L., & Stanley, F. J. (2004). Effects of repeated prenatal ultrasound examinations on childhood outcome up to 8 years of age: follow-up of a randomised controlled trial. The Lancet, 364(9450), 2038-2044.
4. Hershkovitz, R., Sheiner, E., & Mazor, M. (2002). Ultrasound in obstetrics: a review of safety. European Journal of Obstetrics & Gynecology and Reproductive Biology, 101(1), 15-18.
5. Bly, S., & Van den Hof, M. C. (2005). Obstetric ultrasound biological effects and safety. Journal of obstetrics and gynaecology Canada: JOGC= Journal d'obstétrique et gynécologie du Canada: JOGC, 27(6), 572.
6. Barnett, S. B., Ter Haar, G. R., Ziskin, M. C., Rott, H. D., Duck, F. A., & Maeda, K. (2000). International recommendations and guidelines for the safe use of diagnostic ultrasound in medicine. Ultrasound in medicine & biology, 26(3), 355-366.
7. Salvesen KA, Eik-Nes SH. Ultrasound during pregnancy and birthweight, childhood malignancies and neurological development. Ultrasound Med Biol 1999; 25: 1025–1031.
8. Salvesen KA, Eik-Nes SH. Ultrasound during pregnancy and subsequent childhood non righthandedness: a meta-analysis. Ultrasound Obstet Gynecol 1999; 13: 241–246.
9. Maršál, K. (2005). The output display standard: has it missed its target?. Ultrasound in Obstetrics & Gynecology, 25(3), 211-214.
10. European Committee for Ultrasound Radiation Safety. EFSUMB tutorial paper: thermal and mechanical indices. Eur J Ultrasound 1996; 4: 145–150.
11. Whittingham TA. The acoustic output of diagnostic machines. In The Safe Use of Ultrasound in Medical Diagnosis, ter HaarG, DuckFA (eds). British Medical Ultrasound Society/British Institute of Radiology: London, UK, 2000; 16–31.
12. Deane C, Lees C. Doppler obstetric ultrasound: a graphical display of temporal changes in safetyindices. Ultrasound Obstet Gynecol 2000; 15: 418–423.
13. Mole R.Possible hazards of imaging and Doppler ultrasound in obstetrics. Birth1986; 13: 29–37.
14. Sheiner, E., Shoham-Vardi, I., & Abramowicz, J. S. (2007). What do clinical users know regarding safety of ultrasound during pregnancy?. Journal of ultrasound in medicine, 26(3), 319-325.
15. American Institute of Ultrasound in Medicine. How to interpret the ultrasound output display standard for higher acoustic output diagnostic ultrasound devices: version 2[technical bulletin]. J Ultrasound Med 2004; 23:723–726
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16. Nelson, T. R., Fowlkes, J. B., Abramowicz, J. S., & Church, C. C. (2009). Ultrasound biosafety considerations for the practicing sonographer and sonologist. Journal of Ultrasound in Medicine, 28(2), 139.
17. World Federation for Ultrasound in Medicine and Biology.WFUMB Symposium on Safety of Ultrasound in Medicine.Conclusions and recommendations on thermal and nonthermal mechanisms for biological effects of ultrasound;Kloster-Banz, Germany; 14–19 April, 1996. Ultrasound Med Biol 1998; 24(suppl 1):i–xvi, S1–S58.
18. Rados C. FDA cautions against ultrasound “keepsake”images. FDA Consumer 2004; January-February. http://www.fda.gov/fdac/features/2004/104_images.html.
19. Houston, L. E., Allsworth, J., & Macones, G. A. (2011). Ultrasound is safe... right? Resident and maternal-fetal medicine fellow knowledge regarding obstetric ultrasound safety. Journal of Ultrasound in Medicine, 30(1), 21-27.
20. Barnett, S. B., Ter Haar, G. R., Ziskin, M. C., Rott, H. D., Duck, F. A., & Maeda, K. (2000). International recommendations and guidelines for the safe use of diagnostic ultrasound in medicine. Ultrasound in medicine & biology, 26(3), 355-366.
21. Barnett, S. B., Rott, H. D., ter Haar, G. R., Ziskin, M. C., & Maeda, K. (1997). The sensitivity of biological tissue to ultrasound. Ultrasound in medicine & biology, 23(6), 805-812.
22. Chard, T. (1992). REVIEW: Pregnancy tests: a review. Human Reproduction, 7(5), 701-710. 23. Sheiner, E., Freeman, J., & Abramowicz, J. S. (2005). Acoustic output as measured by
mechanical and thermal indices during routine obstetric ultrasound examinations. Journal of ultrasound in medicine, 24(12), 1665-1670.
24. Sheiner, E., Shoham-Vardi, I., Pombar, X., Hussey, M. J., Strassner, H. T., & Abramowicz, J. S. (2007). An increased thermal index can be achieved when performing Doppler studies in obstetric sonography. Journal of ultrasound in medicine, 26(1), 71-76.
25. Borrell, A., Gonce, A., Martinez, J. M., Borobio, V., Fortuny, A., Coll, O., & Cuckle, H. (2005). First‐trimester screening for Down syndrome with ductus venosus Doppler studies in addition to nuchal translucency and serum markers. Prenatal diagnosis, 25(10), 901-905.
26. Barisic, I., Clementi, M., Haeusler, M., Gjergja, R., Kern, J., & Stoll, C. (2001). Evaluation of prenatal ultrasound diagnosis of fetal abdominal wall defects by 19 European registries. Ultrasound in obstetrics & gynecology, 18(4), 309-316.
27. Cavicchi TJ, O’Brien WD Jr. Heat generated by ultrasound in an absorbing medium. J Acoust Soc Am 1984; 70: 1244–1245