GE HEALTHCARE - KRETZTECHNIK VOLUSON® 730EXPERT (BT03)
D
IRECTION 105899, REVISION 3 DRAFT (APRIL 29, 2008) SERVICE MANUAL
Chapter 5 - Components and Functions (Theory) 5-7
5-2-1-3-2 Power Doppler
A real-time two dimensional cross-section of blood flow is displayed. The 2D cross-section may be
presented as a rectangle, parallelogram, trapezoid, sector, or a full circle, depending on the particular
transducer used. The 2D cross-section is presented as a full color display, with various colors being
used to represent the power in blood flow echoes. Often, to provide spatial orientation, the full color
blood flow cross-section is overlaid on top of the gray scale cross-section of soft tissue structure (2D
echo). For each pixel in the overlay, the decision of whether to display color (Doppler power), gray scale
(echo) information or a blended combination is based on the relative strength of return echoes from the
soft-tissue structures and from the red blood cells. A high pass filter (wall filter) is used to remove the
signals from stationary or slowly moving structures.
Tissue motion is discriminated from blood flow by assuming that blood is moving faster than the
surrounding tissue, although additional parameters may also be used to enhance the discrimination.
The power in the remaining signal after wall filtering is then averaged over time (persistence) to present
a steady state image of blood flow distribution. Power Doppler can be used in combination with 2D and
Spectral Doppler modes as well as with 3D mode.
5-2-1-3-3 Tissue Doppler
The Tissue Color Doppler Imaging is used for color encoded evaluation of heart movements.
The TD image provides information about tissue motion direction and velocity.
5-2-1-4 Pulsed (PW) Doppler
PW Doppler processing is one of two spectral Doppler modalities, the other being CW Doppler. In
spectral Doppler, blood flow is presented as a scrolling display, with flow velocity on the Y-axis and time
on the X-axis. The presence of spectral broadening indicates turbulent flow, while the absence of
spectral broadening indicates laminar flow. PW Doppler provides real time spectral analysis of pulsed
Doppler signals. This information describes the Doppler shifted signal from the moving reflectors in the
sample volume. PW Doppler can be used alone but is normally used in conjunction with a 2D image
with an M-line and sample volume marker superimposed on the 2-D image indicating the position of the
Doppler sample volume. The sample volume size and location are specified by the operator. Sample
volume can be overlaid by a flow direction cursor which is aligned, by the operator, with the direction of
flow in the vessel, thus determining the Doppler angle. This allows the spectral display to be calibrated
in flow velocity (m/sec.) as well as frequency (Hz). PW Doppler also provides the capability of
performing spectral analysis at a selectable depth and sample volume size. PW Doppler can be used
in combination with 2D and Color Flow modes.
5-2-2 3D Imaging
The Voluson® 730Expert Ultrasound System will be used to acquire multiple, sequential 2D images
which can be combined to reconstruct a three dimensional image. These 3D images are useful in
visualizing three-dimensional structures, and in understanding the spatial or temporal relationships
between the images in the 2D sequence. The 3D image is presented using standard visualization
techniques, such as surface or volume rendering.
5-2-2-1 3D Data Collection and Reconstruction
2D gray scale images including Color Flow or Power Doppler information may be reconstructed.
The acquisition of volume data sets is performed by sweeping 2D-scans with special transducers
(called 3D-transducers) designed for the 2D-scans and the 3D-sweep.
Images are spatially registered, using internal probe position sensing and a position control to ensure
geometric accuracy of the 3D data.
2D ultrasound imaging modes are used to view a two dimensional cross-sections of parts of the body.
For example in 2D gray scale imaging, a 2 dimensional cross-section of a 3-dimensional soft-tissue
structure such as the heart is displayed in real time. Typically, the user of an ultrasound machine
manipulates the position and orientation of this 2D cross-section in real time during an ultrasound exam.
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