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Conclusions Regarding Epidemiology for Obstetric Ultrasound (Approved 3/27/2010)

Based on the epidemiologic data available and on current knowledge of interactive mechanisms, there is insufficient justification to warrant conclusion of a causal relationship between diagnostic ultrasound and recognized adverse effects in humans. Some studies have reported effects of exposure to diagnostic ultrasound during pregnancy, such as low birth weight, delayed speech, dyslexia, and non-right-handedness. Other studies have not demonstrated such effects. The epidemiologic evidence is based primarily on exposure conditions prior to 1992, the year in which acoustic limits of ultrasound machines were substantially increased for fetal/obstetric applications.

Statement on Mammalian In Vivo Ultrasonic Biological Effects (Approved 11/8/2008)

Information from experiments using laboratory mammals has contributed significantly to our understanding of ultrasonically induced biological effects and the mechanisms that are most likely
responsible. The following statement summarizes observations relative to specific diagnostic ultrasound parameters and indices. In the low-megahertz frequency range there have been no independently confirmed adverse biological effects in mammalian tissues exposed in vivo under experimental ultrasound conditions, as follows:

1. Thermal Mechanisms No effects have been observed for an unfocused beam having free-field spatial-peak temporal-average (SPTA) intensities* below 100 mW/cm², or a focused** beam having intensities below 1 W/cm², or thermal index values of less than 2. 
   For fetal exposures, no effects have been reported for a temperature increase above the normal physiologic temperature, ΔT, when ΔT < 4.5 – (log10t/0.6), where t is exposure time ranging from 1 to 250 minutes, including off time for pulsed exposure (Miller et al, 2002).
   For postnatal exposures producing temperature increases of 6°C or less, no effects have been reported when ΔT < 6 – (log10t/0.6), including off time for pulsed exposure. For example, for temperature increases of 6.0°C and 2.0°C, the corresponding limits for the exposure durations t are 1 and 250 minutes (O'Brien et al, 2008).
   For postnatal exposures producing temperature increases of 6°C or more, no effects have been reported when ΔT < 6 – (log10t/0.3), including off time for pulsed exposure. For example, for a temperature increase of 9.6°C, the corresponding limit for the exposure duration is 5 seconds (=0.083 minutes) (O'Brien et al, 2008).
2. Nonthermal Mechanisms
   In tissues that contain well-defined gas bodies, eg, lung, no effects have been observed for in situ peak rarefactional pressures below approximately 0.4 MPa or mechanical index values less than approximately 0.4.
   In tissues that do not contain well-defined gas bodies, no effects have been reported for peak rarefactional pressures below approximately 4.0 MPa or mechanical index values less than approximately 4.0 (Church et al, 2008).

*Free-field SPTA intensity for continuous wave and pulsed exposures.

**Quarter-power (–6-dB) beam width smaller than 4 wavelengths or 4 mm, whichever is less at the exposure frequency.

Safety in Training and Research (Approved 4/1/2012)

Diagnostic ultrasound has been in use since the late 1950s. There are no confirmed adverse biological effects on patients resulting from this usage. Although no hazard has been identified that would preclude the prudent and conservative use of diagnostic ultrasound in education and research, experience from normal diagnostic practice may or may not be relevant to extended exposure times and altered exposure conditions. It is therefore considered appropriate to make the following recommendation: When examinations are carried out for purposes of training or research, ultrasound exposures should be as low as reasonably achievable (ALARA) within the goals of the study/training. In addition, the subject should be informed of the anticipated exposure conditions and how these compare with normal diagnostic practice. Repetitive and prolonged exposures on a single subject should be justified and consistent with prudent and conservative use.

Prudent Use and Clinical Safety (Approved 4/1/2012)

Diagnostic ultrasound has been in use since the late 1950s. Given its known benefits and recognized efficacy for medical diagnosis, including use during human pregnancy, the American Institute of Ultrasound in Medicine herein addresses the clinical safety of such use: No independently confirmed adverse effects caused by exposure from present diagnostic ultrasound instruments have been reported in human patients in the absence of contrast agents. Biological effects (such as localized pulmonary bleeding) have been reported in mammalian systems at diagnostically relevant exposures but the clinical significance of such effects is not yet known. Ultrasound should be used by qualified health professionals to provide medical benefit to the patient. Ultrasound exposures during examinations should be as low as reasonably achievable (ALARA).

Safety in Diagnostic Ultrasound Educational Activities Using Nonpregnant Participants (Approved: 05/19/2020)

Background: The American Institute of Ultrasound in Medicine has long advocated the prudent use of medical ultrasound and has developed safety recommendation statements. These include the following: (1) ultrasound should be used by qualified health professionals to provide medical benefit to patients¹; (2) ultrasound exposures should be as low as reasonably achievable (ALARA) within the goals of the study^2,3; (3) the participant should be informed of the anticipated exposure conditions and how these compare with normal diagnostic practice²; (4) repetitive and prolonged exposures on a single participant should be justified and consistent with prudent and conservative use²; and (5) infection control policies and procedures must be followed.^4,5
Statement: Ultrasound examinations conducted for the purpose of education and training require adherence to prudent and conservative use guidelines. Specifically, the guidelines below should be followed:

1. Demonstration scans on live, nonpregnant participants should be performed in a manner consistent with the ALARA principle, including limiting the thermal index (TI; (≤0.7 for neonatal transcranial and neonatal spinal examinations, ≤1.0 for ophthalmic examinations, or ≤1.5 for all other examinations)^3,6 and mechanical index (MI; ≤0.23 for 
   ophthalmic examinations, <0.4 specifically for contrast-aided and lung examinations, ≤1.4 for intestine examinations, and ≤1.9 for other examinations such as liver ultrasound). ^4,6–8
2. If higher exposure conditions or contrast agents are needed for the training, then either
   1. a tissue-mimicking phantom should be used, or 
   2. the live participant should only be scanned once per day similar to the exposures experienced during clinical practice. The use of contrast agents should be in accordance with the product label and recommendations of relevant professional organizations, and dosage should be the minimum required to produce diagnostic-quality images. ^9–12 In some cases, this might be considerably less than the dose specified in the product label.
3. All participants should provide appropriate informed consent for the ultrasound study after a discussion of the risks and benefits, including safety and potential biological
   effects. If an injectable contrast agent is used, the discussion and consent should also include details about vascular access, possible adverse reactions such as cardiopulmonary reactions consistent with labeling, and possible bioeffects of contrast imaging.⁶ Female participants should provide a statement to the best of their knowledge that they are not pregnant.
4. All equipment must be used in a manner consistent with its US Food and Drug Administration (FDA)-cleared indications for use. In particular, only equipment that has been FDA-cleared for ophthalmic indications should be used to scan the eye during training due to the sensitivity of the eye to heating, as reflected by lower FDA- recommended maximum output levels (MI ≤0.23 and TI ≤1.0).⁴ 

As Low As Reasonably Achievable (ALARA) Principle (Approved: 05/19/2020)

The potential benefits and risks of each examination should be considered. The as low as reasonably achievable (ALARA) principle should be observed when adjusting controls that affect the acoustic output and by considering both the transducer dwell time and overall scanning time. Practicing ALARA requires that users do all of the following:

1. Apply correct examination presets if built into the diagnostic ultrasound device. The review of manufacturer default presets for appropriateness is encouraged.
2. Adjust the power to the lowest available setting that provides diagnostic-quality images. If appropriate, reduce power at the end of each examination so the next user will start with the lowest acoustic output setting.
3. Monitor the mechanical index (MI) and thermal index (TI). Know the recommended upper limit of the MI, TI, and related duration limitations for the type of examination being
   performed. ^1,2
4. Move/lift the transducer when stationary imaging is not necessary to reduce the dwell time on a particular anatomic structure. When possible, avoid fields of view that include
   sensitive tissues such as the eye, gas-filled tissues (lung and intestines), and fetal calcified structures (skull and spine).
5. Minimize the overall scanning time to that needed to obtain the required diagnostic information.

Official statements of the AIUM may be viewed at
Reviewed 2025