Samsung ACCUVIX XG Manual de usuario descargar pdf (Pagina 51)

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Chapter 1 Safety

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 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, In Situ, has been

estimated 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 difficult to estimate the true In Situ intensity. An attenuation factor of 0.3 is used for general

reporting purpose; therefore, the In Situ value which is commonly reported uses the formula:

In Situ (derated) = Water [

-(0.069 lf)

]

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

The maximum derated and the maximum water values do not always occur at the same operating

condition; therefore, the reported maximum water and derated values may not be related to the In

Situ (derated) formula. Take for example a multi-zone array transducer that has maximum water value

intensities in its deepest zone: the same transducer may have its largest derated intensity in one if its

shallowest focal zones.

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Samsung ACCUVIX XG Manual de usuario Pagina 51