SAEVO EVUS 8, Руководство пользователя

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1 Safety
4 Basic User Manual
1�3�1 Biological Safety
Diagnostic ultrasound is recognized as being safe, but the possibility of biological effects exists when using it in
high exposure levels and long exposure times. Thus ultrasound should be used in a prudent manner to provide
medical benefit to the patient.
1�3�2 ALARA
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.
The operator must take responsibility for the safety of the patient and utilize the ultrasound deliberately. Deliberate
use of the ultrasound means that output power of the 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”.
1�3�3 Mechanical and Thermal Indices
The display of the ultrasound system consists of two parts: Thermal Index (TI) and Mechanical Index(MI).
■ MI/TI Explanation
In October 1987, the American Institute of Ultrasound in Medicine (AIUM) ratified a report prepared by its
Bioeffects Committee (Bioeffects Considerations for the Safety of Diagnostic Ultrasound, J Ultrasound Med.,Sept.
1988: Vol. 7, No. 9 Supplement), sometimes referred to as the StoweReport, which reviewed available data on
possible effects of ultrasound exposure. Another report “Bioeffects and Safety of Diagnostic Ultrasound” dated
January28, 1993, provides more current information.
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Mechanical Index (MI)
Mechanical bioeffects are threshold phenomena that occur when a certain level of output is exceeded. The
threshold level varies, however, with different types of tissue. The potential mechanical bioeffects varies with
peak pressure and ultrasound frequency. The MI accounts for these two factors. The higher the MI value,
the greater the likelihood of mechanical bioeffects occurring. There is no specific MI value that means that
a mechanical effect is actually occurring. The MI should be used as a guide for implementing the ALARA
principle.
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Thermal Index (TI)
The TI value informs the operator about the conditions that might lead to an increase in temperature on the
surface of the body, within the body tissue, or at the point of focus of the ultrasound beam on bone. That
is, the TI value informs the operator about the potential temperature rise in body tissue. It is an estimate of
temperature increase in body tissue with specific properties. The actual amount of any temperature rise is
influenced by factors such as tissue type, vascularity, mode of operation and others. The TI value should be
used as a guide for implementing the ALARA principle.
Depending on the examination and type of tissue involved, TI could be one of three types:
− Soft Tissue Thermal Index (TIS) is used when imaging soft tissue only, it provides an estimate of potential
temperature rise in soft tissue.
− Bone Thermal Index (TIB) is used when bone is near the focus of the image as in the trimester, it provides
an estimate of potential temperature rise in the bone or adjacent soft tissue.
− Cranial Bone Thermal Index (TIC) is used when bone is near the skin surface as in transcranial examination,
it provides an estimate of potential temperature rise in the bone or adjacent soft tissue.