Terason t3000, Руководство пользователя

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Chapter 12 - System Safety and Maintenance Acoustic Output Indices
Terason t3000 / Echo Ultrasound System User Guide 268
Acoustic Output Indices
The Terason Ultrasound System complies with the Standard for Real-Time Display of
Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment
(UD3-98). When the relevant output index is below 1.0, the index value is not displayed.
When operating in any mode with the Freeze function disabled, the window displays the
acoustic output indices relevant to the currently- active transducer and operating mode.
As described in this User Guide, minimizing the real-time displayed index values allows
the practice of the ALARA principle (exposure of the patient to ultrasound energy at a
level that is As Low As Reasonably Achievable).
General Description of Indices
For a detailed explanation of the clinical significance and proper use of the real-time
acoustic output indices displayed on the Terason image display, consult relevant literature
and educational materials available from industry and professional organizations
concerned with medical ultrasound. To help understand how adjustment of the controls
may affect the display of indices during an exam, read the following overview.
In general, indexes are described in terms of the following factors.
• Potential bioeffect of concern: Mechanical (cavitation or other non-thermal
mechanical effects), or thermal (heating of tissue through absorption of the ultrasound
energy) -for all indices, an index value less than 1.0 indicates relatively low risk for
harm to the patient when the index is applied properly.
• Type of operating mode: Generally, mechanical effects are a greater concern during
2D-only operation, while thermal effects are a greater concern during any non-2D
operation. Thermal effects of non-scanned modes (M-Mode and Pulsed-Wave Doppler
modes) are calculated separately from effects of scanned modes (Color Doppler and
Power Doppler modes).
• Type of and location of tissue of concern: Bone or soft tissue, located either at the
tissue surface nearest the transducer, or at or near the beam focus.
• Measured acoustic parameters: Ultrasound power, time average intensity, or
instantaneous peak pressure used in calculating the index value. All calculations assume
an attenuation (or “derating”) rate of
0.3 dB/cm/MHz.
Warning: Ultrasound procedures should be used for valid reasons, for the
shortest period of time, and at the lowest mechanical/thermal
index setting necessary to produce clinically acceptable images.
The ultrasound system incorporates an output display of
Mechanical and Thermal Indices to allow you to monitor, and to
limit, the amount of ultrasound energy that is transferred to the
patient.
Note: For systems distributed in the United States of America,
refer to the Medical Ultrasound Safety ultrasound education
program brochure produced by the AIUM.