Samsung SONOACE R5 Manual do Utilizador descarregar pdf (Página 37)

1-21

Chapter 1 Safety

to the focal point, attenuation in the body, and ultrasound exposure time. Exposure time is an especially

useful variable, because the user controls it. The ability to limit the index values over time support the

ALARA principle.

Applying ALARA

The system-imaging mode used depends upon the information needed. 2D-mode and M-mode

imaging provide anatomical information, while Doppler, Power, and Color imaging provide information

about blood ow. Scanned modes, like 2D-mode, Power, or Color, disperse or scatter the ultrasonic

energy over an area, while an unscanned mode, like M-mode or Doppler, concentrates ultrasonic

energy. Understanding the nature of the imaging mode being used allows the sonographer to apply

the ALARA principle with informed judgment. The probe frequency, system set-up values, scanning

techniques, and operator experience aid the sonographer in meeting the denition of the ALARA

principle.

The decision as to the amount of acoustic output is, in the nal analysis, up to the system operator. This

decision must be based on the following factors: type of patient, type of exam, patient history, ease

or diculty of obtaining diagnostically useful information, and the potential localized heating of the

patient due to probe surface temperatures. Prudent use of the system occurs when patient exposure

is limited to the lowest index reading for the shortest amount of time necessary to achieve acceptable

diagnostic results.

Although a high index reading does not mean that a bioeect is actually occurring, a high index

reading should be taken seriously. Every eort should be made to reduce the possible eects of a high

index reading. Limiting exposure time is an eective way to accomplish this goal.

There are several system controls that the operator can use to adjust the image quality and limit

the acoustic intensity. These controls are related to the techniques that an operator might use to

implement ALARA. These controls can be divided into three categories: direct, indirect, and receiver

control.

Direct Controls

Application selection and the output intensity control directly aect acoustic intensity. There are

dierent ranges of allowable intensity or output based on your selection. Selecting the correct range

of acoustic intensity for the application is one of the rst things required during any exam. For example,

peripheral vascular intensity levels are not recommended for fetal exams. Some systems automatically

select the proper range for a particular procedure, while others require manual selection. Ultimately,

the user bears the responsibility for proper clinical use. The Samsung Medison system provides both

automatic and user-denable settings.

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Samsung SONOACE R5 Manual do Utilizador Página 37