Samsung PT60A Manual do Utilizador descarregar pdf (Página 48)

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Operation Manual

The Acoustic output for this system has been measured and calculated in accordance with the

Standard for Real-Time Display of Thermal and Mechanical Acoustic Output Indices On Diagnostic

Ultrasound Equipment (AIUM / NEMA, 2004) and the Acoustic Output Measurement Standard for

Diagnostic Ultrasound Equipment (AIUM / NEMA, 2004)

 In Situ, De-rated, and Water Value Intensities

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

water measurements represent the largest possible value. Biological tissue absorbs 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 dicult to estimate the true in situ intensity. A de-rating factor of 0.3 is used for general

reporting purposes; 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 “de-rated” is used.

The maximum de-rated and maximum water values do not always occur under the same operating

conditions. Therefore, the reported maximum water and de-rated values may not be related to the

In Situ (de-rated) formula. For example, a multi-zone array transducer has the greatest water value

intensities in its deepest zone. The same transducer may have its largest de-rated intensity in one of

its shallowest focal zones.

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Samsung PT60A Manual do Utilizador Página 48