Samsung SONOACE R5 Manual do Utilizador descarregar pdf (Página 39)

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Chapter 1 Safety

Indirect Controls

The indirect controls are those that have an indirect eect on acoustic intensity. These controls aect

imaging mode, pulse repetition frequency, focus depth, pulse length, and probe selection.

The choice of imaging mode determines the nature of the ultrasound beam. 2D-mode is a scanning

mode, Doppler is a stationary or unscanned mode. A stationary ultrasound beam concentrates energy

on a single location. A moving or scanned ultrasound beam disperses the energy over a wide area and

the beam is only concentrated on a given area for a fraction of the time necessary in unscanned mode.

Pulse repetition frequency or rate refers to the number of ultrasound bursts of energy over a specic

period of time. The higher the pulse repetition frequency, the more pulses of energy in a given period

of time. Several controls aect pulse repetition frequency: focal depth, display depth, sample volume

depth, color sensitivity, number of focal zones, and sector width controls.

Focus of the ultrasound beam aects the image resolution. To maintain or increase resolution at a

dierent focus requires a variation in output over the focal zone. This variation of output is a function

of system optimization. Dierent exams require dierent focal depths. Setting the focus to the proper

depth improves the resolution of the structure of interest.

Pulse length is the time during which the ultrasonic burst is turned on. The longer the pulse, the greater

the time-average intensity value. The greater the time-average intensity, the greater the likelihood of

temperature increase and cavitations. Pulse length or burst length or pulse duration is the output

pulse duration in pulsed Doppler. Increasing the Doppler sample volume increases the pulse length.

Probe selection aects intensity indirectly. Tissue attenuation changes with frequency. The higher

the probe operating frequency, the greater the attenuation of the ultrasonic energy. Higher probe

operating frequencies require higher output intensity to scan at a deeper depth. To scan deeper at

the same output intensity, a lower probe frequency is required. Using more gain and output beyond

a point, without corresponding increases in image quality, can mean that a lower frequency probe is

needed.

Receiver Controls

Receiver controls are used by the operator to improve image quality. These controls have no eect on

output. Receiver controls only aect how the ultrasound echo is received. These controls include gain,

TGC, dynamic range, and image processing. The important thing to remember, relative to output, is

that receiver controls should be optimized before increasing output. For example; before increasing

output, optimize gain to improve image quality.

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Samsung SONOACE R5 Manual do Utilizador Página 39