Konica Minolta SONIMAGE HS2 - 9.1 Basic Knowledge of MI;TI

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MI/TI are an indication of the potential for biological e󰀨ects induced by the acoustic output of clinical ultrasound sys-
tems.
• MI: Stands for Mechanical Index.
• TI: Stands for Thermal Index.
(1) Concerns with bioe󰀨ects
Diagnostic ultrasound is recognized as being safe. However, it cannot be stated categorically that ultrasound is
100 % safe. Studies have revealed that ultrasound with extremely high intensity is harmful to body tissues.
This rapid advance has generated concerns about the potential risk of bioe󰀨ects when new applications or diag-
nostic technologies become available.
(2) Mechanical e󰀨ects and thermal e󰀨ects
Studies have revealed that two di󰀨erent kinds of ultrasound characteristics a󰀨ect human bodies: one is the me-
chanical effect due to cavitation generated when the negative pressure of ultrasound exceeds a certain limit
(generation/destruction of air bubbles), and the other is the e󰀨ect due to thermal energy generated when tissues
absorb ultrasound.
The levels of these two kinds of e󰀨ects are represented by indices: the MI (Mechanical Index) and the TI (Thermal
Index), respectively.
(3) MI/TI values
The smaller the MI/TI values are, the less the bioe󰀨ects are.
(4) Controlling the ultrasound output
In 1976, the FDA in the U.S.A. established limits to the acoustic output level for diagnostic ultrasound equipment
(Track 1), along with the rapid advance in diagnostic ultrasound technology and the versatile proliferation of its
applications, with the aim of ensuring the safety of patients.
Thereinafter, manufacturers were required to control the acoustic output level below the limits when releasing
new diagnostic ultrasound systems on the market.
<Note>
I
spta.3
may be represented as follows:
I
zpta,α
(α=0.3 dB/cm/MHz) (IEC 60601-2-37 (2001), Amd.1, Amd.2)
I
spta,α
(α=0.3 dB/cm/MHz) (IEC 60601-2-37 (2007))
Maximum acoustic power specied by FDA (Track 1)
Application I
spta.3
(mW/cm
2
) I
sppa.3
(W/cm
2
) MI
Peripheral blood vessels 720 190 1.9
Cardiovascular systems 430 190 1.9
Fetal and others 94 190 1.9
Eyes 17 28 0.23
9.1 Basic Knowledge of MI/TI