SonoSite M-Turbo, Service Manual

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Chapter 2: System Overview 7
Additional System Feature Performances
Pulsed Wave
(PW) Doppler PW provides a real-time representation of blood flow and is displayed as a
velocity-versus-time sweeping output. Velocity (or frequency) is presented as the vertical
axis with time along the horizontal axis. The magnitude of the detected signal is represented
as different gray scale values. The ultrasound data is derived from a single area, the sample
volume, on a stationary beam.
PW Doppler mode provides the clinician with the ability to obtain blood flow velocities
about a spatial sample volume. A burst of ultrasound with a known spectrum is transmitted
by the system; on the receive side, the transducer receive echoes are amplified and range
gated at the appropriate depth. The signal is analyzed by a quadrature phase detector that
establishes two receive channels to allow detection of flow direction. These two channels are
then analyzed by a fast complex Fourier transform (FFT) circuit to establish the spectrum of
frequencies present in the echoes. The data are displayed as spectrum frequencies with
respect to time.
PW can be used alone but is normally used in conjunction with a 2D image for spatial
reference. The 2D image has a graphical line (D-line) superimposed on the 2D image
indicating where the M-mode beam is located. The sample volume position (depth) and size
are also indicated on the D-Line.
Broadband Imaging This ultrasound acquisition system uses high resolution broadband technology in
the transmit pulsers, transducer, and receivers. The receive path can capture and
process signals over a wide spectrum, from below 2.0 MHz to beyond 10 MHz. For
each application, the transmit pulse is designed to produce an appropriate
bandwidth. For example, in 2D grayscale imaging, a wide band pulse is used to
support good axial resolution. For Doppler modes, a narrower band pulse is used,
which improves the spectral resolution of the detected Doppler signal.
In addition to transmit pulse control, programmable digital signal processing is used
in the receive path to further refine the bandwidth used to produce the final image.
Digital filters are applied to the digitized received signal to limit and shape the
spectral bandwidth used to generate the displayed output.
Tissue Specific
Imaging In this feature, parameters for signal and image processing are optimized to
maximize the image quality or to obtain the best compromise of resolution and
penetration for different specific clinical applications. These parameters include: the
order of received filters, the bandwidth, the dynamic range, the compression curve,
the gain setting and parameters for compounding frequency band, etc. For
example, different system parameter setups are used for abdominal or peritoneal
scanning. This feature is for ease of use for the operator by automatically setting up
system control parameters rather than manually adjusting settings for best
performance.
Biopsy Guidance The system can display a pair of biopsy guidelines that represent the anticipated
path of the biopsy needle. The image of an anatomical target, biopsy guidelines, a
scan plane marker, and a biopsy needle are displayed to assist in guiding the biopsy
needle to the target. The system also provides needle guidance for vascular access
procedures. For additional information, see the biopsy user guides.
Measurement and
Calculation
Capabilities The system offers a variety of measurements and calculations, specific to exam type
and transducer. A list of them , and author references, are in the system user guide.
Measurement accuracy is also discussed.