Acoustic Output 15-1
15 Acoustic Output
This section of the operator’s manual applies to the overall system including the main unit, probes,
accessories and peripherals. This section contains important safety information for operators of the
device, pertaining to acoustic output and how to control patient exposure through use of the ALARA (as
low as reasonably achievable) principle. Also this section contains information regarding the acoustic
output testing and the real-time output display.
Read this information carefully before using the system.
15.1 Concerns with Bioeffects
Diagnostic ultrasound is recognized as being safe. In fact, there have been no reports of injuries to
patients caused by diagnostic ultrasound.
It cannot be stated categorically that ultrasound is 100% safe. Studies have revealed that ultrasound
with extremely high intensity is harmful to body tissues.
Diagnostic ultrasound technology has made a great leap forward during the last several years. This
rapid advance has generated concerns about the potential risk of bioeffects when new applications or
diagnostic technologies become available.
15.2 Prudent Use Statement
Although there are no confirmed biological effects on patients caused by exposures from present
diagnostic ultrasound instruments, the possibility exists that such biological effects may be identified in
the future. Thus ultrasound should be used in a prudent manner to provide medical benefit to the
patient. High exposure levels and long exposure times should be avoided while acquiring necessary
clinical information.
15.3 ALARA Principle (As Low As Reasonably
Achievable)
It is required to practice ALARA when using ultrasound energy. Practicing ALARA ensures that the total
energy level is controlled below a low enough level at which bioeffects are not generated while
diagnostic information is being accumulated. The total energy is controlled by output intensity and total
radiation time. The output intensity necessary for examinations differs depending on the patient and the
clinical case.
Not all examinations can be performed with an extremely low level of acoustic energy. Controlling the
acoustic level at an extremely low level leads to low-quality images or insufficient Doppler signals,
adversely affecting the reliability of the diagnosis. However, increasing the acoustic power more than
necessary does not always contribute to an increase in quality of information required for diagnosis,
rather increasing the risk of generating bioeffects.
Users must take responsibility for the safety of patients and utilize ultrasound deliberately. Deliberate
use of ultrasound means that output power of ultrasound must be selected based on ALARA.
Additional information regarding the concept of ALARA and the possible bioeffects of Ultrasound is
available in a document from the AIUM (American Institute of Ultrasound Medicine) title “Medical
Ultrasound Safety”.
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