Samsung PT60A User Manual download pdf (Page 41)

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Chapter 1 Safety

 Indirect Controls

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

aect the 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 scanned

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.

The 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.

The focus of the ultrasound beam aects the image resolution. Maintaining or increasing the

resolution at a dierent focal zone involves the adjustment of numerous outputs from the focal

zone. This output adjustment is one of the system’s optimization features. 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 cavitation. Pulse length, burst length, and pulse duration

refer to the output pulse duration in pulsed Doppler mode. In addition, 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 greater 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

concerning output is that the receiver controls should be optimized before increasing it. For

example; before increasing output, gain should be optimized to improve image quality.

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Samsung PT60A User Manual Page 41