FujiFilm Sonosite PX System, Руководство по обслуживанию

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Chapter 4: System Overview 33
Front End Overview
The Front End is designed to support various imaging modalities such as 2D, M-Mode, Spectral Doppler
and Color Doppler. From the Front End's perspective, all modes can be grouped into a few basic types:
Single mode, simultaneous modes and triggered modes. All of these modes are built from similar basic
transmit and receive sequences controlled within the Front End. A generic top level block diagram of a
typical Front End is shown below in
Figure 4.2 on page 33
Figure 4.2 Generic Front End Block Diagram
The transmit section consists of a waveform generator, delay block, and high power high voltage driver to
excite the transducer element. Multiple elements are driven with delays determined by the time of flight in
the medium from the elements to the point in space where the beam is to be focused. The longer the time
of flight is to the focal point the smaller the delay is for a given transmit element to allow all to arrive at the
focal point at the same time. The number of elements driven is determined by element sensitivity off axis
and depth of field considerations. The waveform is selected to drive the transducer at a certain center
frequency, bandwidth, and power and is optimized for the given mode.
The receive section consists of a transmit/receive switch to protect the receiver from the transmit voltage, a
variable gain receiver to amplify and condition the return echoes, an A/Dconverter to digitize the data, a
delay block to focus the return signals and a weight block to scale the return echoes for each channel. All
Continuous Wave
Doppler Audio
Output The system provides for audio output of the CW velocity information. This can
be presented as stereo information, with flow moving towards the transducer
on one channel and flow away on the other, or as a mono output with the single
audio output representing the summation of the flow directions.
Pulsed Wave
Doppler Audio
Output The system provides for audio output of the PW velocity information. This can
be presented as stereo information, with flow moving towards the transducer
on one channel and flow away on the other, or as a mono output with the single
audio output representing the summation of the flow directions.
Receive Section
X
T/R Sw
TGC Amplifier
A/D Delay
Weight
Pulser
Waveform
Delay
X
T/R Sw
TGC Amplifier
A/D Delay
Weight
Pulser
Waveform
Delay
Beamformed
Data
Transducer
Transmit Section
Control