Computer graphics processing and selective visual display system – Display peripheral interface input device
Reexamination Certificate
1996-10-25
2001-01-23
Luu, Matthew (Department: 2778)
Computer graphics processing and selective visual display system
Display peripheral interface input device
C600S441000
Reexamination Certificate
active
06177923
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an imaging modality displaying signals containing both velocity and energy information derived from echoes of ultrasound signals from fluid flow or tissue motion, where the signals are represented by display features obtained from the energy and velocity information according to two-dimensional display feature maps. As used in the description herein below, the term “velocity” means the mean velocity and the terms “velocity” and “mean velocity” are used interchangeably, such as in the case of the velocity (i.e., mean velocity) of fluid flow and tissue motion.
Conventional Methods
Color Doppler imaging has been in use for more than a decade. The conventional color Doppler modalities are briefly described as follows:
I. Color Doppler velocity imaging
This is the most common color Doppler imaging mode where only the velocity component of the received Doppler signal is shown.
FIG. 1A
is a typical color map which is used to show flow velocities and directions. The upper and lower color bars in
FIG. 1A
may be composed of varying intensities and hues of color to show different velocity flow components. The upper and lower bars may be constructed from different color combinations to distinguish positive and negative flows. A baseline with no color is usually included to inhibit the representation of the lowest velocity flow states where the ultrasound system is not as reliable in detecting directional flows, or to remove stationary clutter signals.
II. Color Doppler Velocity and Variance Imaging
In this imaging mode, both the variance and velocity components of the received Doppler signal are estimated. The color map for color Doppler velocity and variance imaging is similar to the one in
FIG. 1A
, except that the top and bottom right corners of the color map are used to show flow variance while flow velocity is color-coded using the rest of the color map. This mode is especially useful for illustrating turbulent Doppler flow since flow turbulence is usually characterized by high flow velocities and variances.
III. Color Doppler Energy Imaging
Color Doppler energy imaging is recently recognized as an important color Doppler mode for perfusion imaging. In this mode, only the energy (or squared modulus) component of a received Doppler signal is shown. While the rotating phase of a Doppler signal is used to estimate its velocity and variance components, the squared modulus of the same signal is used for calculating the signal energy or power. Since phase detection is less accurate than square modulus detection especially in the case where signal-to-noise ratios (SNR) are low, the same Doppler system provides more sensitivity in energy imaging compared to velocity and variance imaging. Color Doppler energy imaging thus becomes a dominant mode for perfusion imaging where the perfusion signal is usually weak and may easily be submerged by noise.
FIG. 1B
is a typical color map for energy imaging in which only the energy components are color-coded.
IV. Color Doppler Energy and Velocity Imaging
In the early days of medical ultrasound imaging, people had unsuccessfully attempted a combined energy and velocity imaging mode. In this conventional combined mode, typically the top and bottom right comers of the color map are used to show flow energy while flow velocity is color-coded using the rest of the color map. This mode is not useful for perfusion imaging because only the high energy levels are shown; the low energy levels (perfusion signals) are not color-coded. While this mode was available on early color Doppler imaging systems, it was not adopted by clinical users and has since been removed from most, if not all, of the current color Doppler systems.
Disadvantages of the Above Conventional Methods
One clinical objective of this disclosure is to provide a color Doppler imaging mode which is capable of tissue perfusion imaging and providing flow velocities and directions at the same time. From the discussion in the previous section, it is clear that neither color Doppler velocity nor velocity/variance imaging can provide the necessary sensitivity desired for tissue perfusion imaging. Similarly, the above-described conventional color Doppler energy and velocity imaging mode is unsuitable for perfusion imaging.
Although color Doppler energy imaging provides the desired sensitivity, it is unable to distinguish flow directions and velocities. For example, in the diagnosis of liver cirrhosis, it is clinically significant to be able to observe liver perfusion in the tissue and flow directions in the larger blood vessels simultaneously.
From the above, none of the conventional methods is entirely satisfactory. It is therefore desirable to provide a new and improved imaging modality with improved information display capabilities.
SUMMARY OF THE INVENTION
While the term “velocity” is used in this application, it should be understood that the quantity “velocity” processed here can be derived from the Doppler frequency shift, and the mean Doppler frequency or wavelength estimate is converted to a mean velocity estimate by use of the well-known Doppler equation:
v=f
D
c/
2
f
o
cos&thgr;
where f
D
is the Doppler frequency shift, c is the speed of sound, f
o
is the transmitted frequency and &thgr; is the Doppler angle or the angle subtended by the ultrasound beam and the direction of flow. Therefore, it will be understood that whenever “mean velocity” is referred to in the application, “mean frequency” or “mean wavelength” may be used instead; such variations are within the scope of the invention. For simplicity, the term “mean velocity related parameter” of a signal in this application will mean “mean velocity”, “mean frequency” and/or “mean wavelength” of the signal. Similarly, instead of processing energy of the Doppler information or time shift signals, it is possible to process the power or amplitude of such signals instead; where power is the energy of such signals per unit time, and amplitude is proportional to the square root of power. For simplicity, again the term “energy related parameter” of a signal in this application will mean “energy” and/or “power” and/or “amplitude” of the signal and the last three terms in quotations are used interchangeably.
The invention of this application involves a system where a number of signals are supplied that contain information including velocity and energy of fluid flow or tissue motion. The information on velocity and energy of fluid flow or tissue motion is then coded into display features, and the display feature is displayed on the display medium. The system includes a subsystem for coding according to a coding scheme the velocity and energy information of the signals as the display features to be displayed. Therefore, whenever an aspect of the invention is set forth below as directed to an overall system including signal acquisition and display of display features, a separate aspect of the invention is directed to the coding scheme of the subsystem. In the preferred embodiment, the display features to be displayed are the colors selected as functions of the signals.
One aspect of the invention is directed towards a method for displaying information comprising the following steps. A plurality of signals are supplied containing information including mean velocity and energy of fluid flow or tissue motion. A boundary is provided in a two variable, two-dimensional display feature space, said variables being a mean velocity related parameter and an energy related parameter, each of the magnitude of mean velocity related parameter and energy related parameter having a minimum value for said plurality of signals at a point defining an origin in the space. The boundary divides the space into a first and a second region, said first region containing the origin. For each signal, a display feature is obtained that is a function only of the energy related parameter when the energy related and mean velocity related parameters of the information in such signal correspond to a point in the first re
Arenson James W.
Chim Stanley S. C.
Guracar Ismayil M.
Marshall Janice L.
Maslak Samuel H.
Acuson Corporation
Luu Matthew
Morrison & Foerster / LLP
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