Samsung MYSONO U6 Bedienungsanleitung PDF herunterladen (Seite 45)

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Chapter 1 Safety

6. Information for Manufacturer Seeking Marketing Clearance of Diagnostic Ultrasound Systems and

Transducers. FDA. September 1997. FDA.

7. Standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic

Ultrasound Equipment. (Revision 1, AIUM, NEMA. 1998)

8. WFUMB. Symposium on Safety of Ultrasound in Medicine: Conclusions and Recommendations on

Thermal and Non-Thermal Mechanisms for Biological Eects of Ultrasound, Ultrasound in Medicine

and Biology, 1998: Vol. 24, Supplement1.

In Situ, Derated, and Water Value Intensities

All intensity parameters are measured in water. Since water does not absorb acoustic energy, these

water measurements represent a worst case value. Biological tissue does not absorb acoustic energy.

The true value of the intensity at any point depends on the amount and type of tissue and the

frequency of the ultrasound that passes through the tissue. The intensity value in the tissue and the In

Situ value have been estimated by using the following formula:

In Situ = Water [

- (0,23 alf)

]

where: In Situ = In Situ Intensity Value

Water = Water Value Intensity

e = 2.7183

a = Attenuation Factor

Tissue a(dB/cm-MHz)

Brain .53

Heart .66

Kidney .79

Liver .43

Muscle .55

l = skin line to measurement depth (cm)

f = Center frequency of the transducer/system/mode combination(MHz)

Since the ultrasonic path during an examination is likely to pass through varying lengths and types of

tissue, it is dicult to estimate the true In Situ intensity. An attenuation factor of 0.3 is used for general

reporting purposes. Therefore, the In Situ value which is commonly reported uses the following

formula:

In Situ (derated) = Water [

-(0,069 lf)

]

Since this value is not the true In Situ intensity, the term “derated” is used.

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