Image analysis – Applications – Biomedical applications
Reexamination Certificate
1999-04-07
2002-04-09
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
Biomedical applications
Reexamination Certificate
active
06370264
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improved methods and apparatus for ultrasonic imaging of color flow data representing, for example, the flow of blood in the chambers of a heart and, in particular, to an improved method and apparatus for ultrasonic color flow imaging wherein flow velocity data is generated by separately processing the velocity vector phase information and the velocity vector magnitude information and wherein three forms of image data, the velocity data derived from phase components of the autocorrelation vectors, the compressed amplitude of autocorrelation vectors, and two dimensional (2D) image amplitude information, are provided for generating segmented images on a pixel by pixel basis wherein segmentation is the process of displaying velocity information or anatomical 2D information at a specific location.
BACKGROUND ART
Ultrasonic transducers and imaging systems are used in many medical applications and, in particular, for the non-invasive acquisition of images of cross sections of organs and conditions within a patient, typical examples being the ultrasound imaging of fetuses and the heart. Such systems commonly use a phased array transducer having multiple transmitting and receiving elements to transmit and receive narrowly focused and “steerable” beams, or “lines”, of ultrasonic energy into and from the body. The transmitted beams, or lines, are reflected from the body's internal structures and received as beams, or lines, that contain information that is used to generate images of the body's internal structures.
In a typical application, such as cardiac scanning, a number of beams or lines are transmitted and received along a plurality of angles forming a sector, that is, a wedge of finite thickness, wherein the angular width of a sector may be the full range of angles that the transducer is capable of generating and receiving, or a selected portion of that range. A volume is interrogated, rather than a plane, due to the transmit and receive beam having a finite elevation thickness. The lines of a sector are typically then organized into “frames” wherein each frame contains data representing a volume of interest, that is, a sector, and may be further processed or viewed to extract or present the information of interest, such as an image of the volume of interest over a part or the whole of a cardiac cycle.
One important application of ultrasonic imaging is color flow mapping wherein doppler information is extracted from the returning signals, that is, scan lines, to generate images, or maps, of blood flow velocity in, for example, the chambers of a heart. Color flow mapping, however, requires more data acquisitions than does anatomic 2D imaging of a volume of interest of a heart and more extensive and complex processing of the input data, that is, the scan lines.
As a consequence, the color flow mapping systems of the prior art have generally required complex and expensive hardware to perform the color flow data processing operations, thereby increasing the cost of color flow mapping and limiting the use of color flow mapping.
In addition, the methods of the prior art for processing color flow data to generate color flow images have frequently resulted in inherent errors in or degradation of the color flow mapping images because of unwanted effects from the processing methods themselves. For example, a typical method for color flow mapping involves determining the autocorrelation vectors from the real and imaginary components of the complex samples taken at an array of locations in the region of interest and the subsequent complex scan conversion of the real and imaginary components of the autocorrelation vectors to generate the components of the color flow map. Each resultant autocorrelation sum, or velocity vector, represents the direction and magnitude of motion of an “object” wherein these “objects” may be a collection of red blood cells or moving tissue. As a consequence of the autocorrelation, the velocity vectors are typically scan converted from the input polar coordinate space to an x-y cartesian space. Since the real and imaginary components must be converted to velocity using trigonometric relationships, the full dynamic range of the components must be preserved through scan conversion, thereby creating a significant design issue in preserving the dynamic range of the components within an acceptable number of data bits.
In the prior art, segmentation may be done prior to scan conversion in order to alleviate the need to carry the magnitude of the autocorrelation vector through scan conversion, thereby enabling scan conversion of unit autocorrelation vectors only. The segmentation done prior to scan conversion would use the amplitude and phase of the autocorrelation vectors along with the two dimensional amplitude to decide on a sample by sample basis whether to keep the autocorrelation value, and ultimately the flow velocity, or keep the two dimensional sample. After segmentation, the autocorrelation vectors may be converted to unit amplitude vectors for subsequent scan conversion, thereby eliminating the dynamic range problem. The problem with segmentation at the sample level is that each decision affects many pixels after scan conversion, resulting in large flow voids scattered throughout the image. Solving the dynamic range scan conversion in this way causes unnecessarily large flow voids.
The present invention provides a solution to these and other problems of the prior art.
SUMMARY OF THE INVENTION
The present invention is directed to a flow velocity processor for use in a color flow imaging system having reduced dynamic range requirements for subsequent scan conversion of velocity image information, and the method for processing flow velocity information to provide reduced dynamic range requirements. In addition, an improved segmentation method based on a pixel by pixel decision after scan conversion using three components, the velocity data derived from the autocorrelation vector after conversion to a unit vector, a compressed magnitude of the autocorrelation vector, and the two dimensional magnitude information.
The ultrasonic flow imaging system typically includes an ultrasonic scan array of transducer elements for transmitting and receiving scan lines, a beamformer for forming transmitting and receiving scan lines, and a scan line signal processor for detecting received scan lines and generating two dimensional acoustic samples and complex samples representing image flow information wherein each complex sample conveys both amplitude and phase information.
According to one embodiment of the present invention, the flow velocity processor includes an autocorrelation vector processor for generating autocorrelation vectors between pairs of complex samples of at least one input set of N complex samples wherein N is at least two and wherein each autocorrelation vector includes both amplitude and phase information. The flow velocity processor further includes a unit vector convertor for generating a corresponding unity amplitude autocorrelation vector for each processed input set of N complex samples. The phase of each unit amplitude autocorrelation vector is the same as the resultant autocorrelation vector. The two components of the unit amplitude autocorrelation vector are inputted to a scan convertor for subsequent calculation of the velocity and segmentation into a final color flow image.
The flow velocity processor may also include an autocorrelation vector magnitude information processing path for extracting the amplitude component of each autocorrelation vector, generating compressed autocorrelation vector amplitude information, and providing the compressed vector amplitude information to the scan convertor for generation of a final segmented image.
The color flow imaging system may further include a two dimensional image data processing path for extracting two dimensional image data from the received scan lines and providing the two dimensional image data to the scan convertor for the generation of a fina
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