GE Voluson 730, Инструкция по эксплуатации

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Safety
In some cases the max. Recalculated value and the max. Value in water do not occur under the same
operating conditions. Therefore the max. Values in water and recalculated max. Values mentioned in
reports may not be related according to the above mentioned formula.
For example: An array probe with multiple focusing, whose max. Intensity values in water are lying in
the deepest focal zone; for this zone, however, the smallest recalculating factor is valid. With the same
probe the highest recalculated intensity can be lying in one of the focal zones closest to the surface.
The FDA has laid down limits for the max. recalculated intensity values (see following section).
Therefore the recalculated intensities are brought to the highest possible value with the help of the
system controls when the output power is tested. Under all operating conditions the point of the max.
Recalculated intensity can be closer to the probe than the point of the max. Intensity in water; it will
never be further away from the transducer.
2.13.3 Derivation and Meaning of the thermal and mechanical Indices
The Standard for real-time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic
Ultrasound Equipment, ©1992 by the American Institute of Ultrasound in Medicine (AIUM) and the
National Electrical Manufacturers Association (NEMA), defines Thermal and Mechanical Indices as
follows. Please refer to this standard to get further information on this matter.
Thermal Index (TI) is a quantity related to calculated or estimated temperature rise under certain
defined assumptions. The Thermal Index is the ratio of total acoustic power to the power required to
raise tissue temperature by 1°C under defined assumptions. In the calculation of all Thermal Indices in
the "Standard for real-time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic
Ultrasound Equipment", of the AIUM and NEMA, the average ultrasonic attenuation is assumed to be
0.3 dB/cm-MHz along the beam axis in the body.
Soft Tissue Thermal Index (TIS) is the Thermal Index related to soft tissues.
Bone Thermal Index (TIB) is the thermal index for applications, such as fetal (second and third
trimester) or neonatal cephalic (through the fontanel), in which the ultrasound beam passes through
soft tissue and a focal region is the immediate vicinity of bone.
Cranial Bone Thermal Index (TIC) is the Thermal Index for applications, such as pediatric and adult
cranial applications, in which the ultrasound beam passes through bone near the beam entrance into
the body.
Mechanical Index (MI) formula is the spatial-peak value of the peak rare factional pressure, derated
by 0.3 dB/cm-MHz at each point along the beam axis, divided by the square root of the center
frequency. To make the MI unitless, the right-hand side of the equation below is multiplied by [(1
MHz)0.5/(1 Mpa)].
Scanned
mode (auto-scanning) is the electronic or mechanical steering of successive ultrasonic pulses
or series of pulses, through at least two dimensions.
Unscanned
mode (nonautoscanning) is the emission of ultrasonic pulses in a single direction, where
scanning in more than one direction would require moving the transducer assembly manually.
Voluson
®
730 - Instruction Manual
2-12
105838 Rev. 3