BC Biomedical USP-100A Manual de usuario descargar pdf (Pagina 8)

Water as a Measurement Medium*

The measurements are to be performed in water because ultrasound propagation in

water closely approximates that in tissues. The ultrasonic attenuation in water can be

taken as a lower limit on the attenuation that will be encountered in the body. Large

areas in the body can consist of low attenuating material such as urine and amniotic

fluid. The use of water prevents measurements in a more highly attenuating material,

such as liver equivalent gels, from representing the highest possible intensities that

might be encountered in the body.

* Ultrasound propagation in water closely approximates human tissue and degassed water is the generally accepted

test medium for ultrasound transducers (see AIUM/NEMA Standards Publication #UL-1-1981, SAFETY STANDARD

FOR DIAGNOSTIC ULTRASOUND EQUIPMENT).

Degassed Water

Ultrasound Power measurement accuracy is affected if the water contains more than

5-10 PPM of air. To degas, boil distilled water for 30 minutes, then seal the container

tightly and place it in a refrigerator. An alternate method of degassing water is to heat

the water to the boiling point, then pull a vacuum on it for five to ten minutes. The

degassed water storage container should be made of glass or plastic. Polystyrene

containers should not be used since they allow oxygen to permeate and degrade the

water quality.

Before testing, pour water into tilted test tank with minimum amount of turbulence. The

test tank water surface will absorb oxygen, therefore a change of degassed water is

recommended before each test. Water temperature affects accuracy, so it is

TEST SETUP

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BC Biomedical USP-100A Manual de usuario Pagina 8