MediSono P25 EXP, Руководство пользователя

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1 Safety
Basic User Manual 7
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3 Mechanical and Thermal Indices
The display of the 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:
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Soft Tissue Thermal Index (TIS) is used when imaging soft tissue only, it provides
an estimate of potential temperature rise in soft tissue.
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Bone Thermal Index (TIB) is used when bone is near the focus of the image as in
the third trimester, it provides an estimate of potential temperature rise in the bone
or adjacent soft tissue.
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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.