Abstract:
An ultrasound survey frame (SF) is processed in order to determine the portions representing fluid flow. An assembly ( 20 ) again rescans only the portions of a subject represented by the portions of the survey frame in which fluid flow was found. Target frames (TF) then are created from the rescanning and are processed in order to provide a color flow image restricted to the portions of the survey frame in which fluid flow is indicated.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to ultrasound color flow imaging, and more particularly relates to such imaging based on a portion of a subject in which fluid flow is identified. 
     A conventional ultrasound system typically interleaves B-mode imaging with color flow imaging. The color flow vectors from the color flow imaging are formed over the entire color flow region of interest (ROI) for every acoustic frame. These color flow vectors typically are contained in several interleave groups across the ROI. Every vector position in the color flow ROI is sampled and processed for every acoustic frame before display. As a result, a large amount of processing is required in order to produce a color flow image of the entire region of interest. In addition, a large amount of memory is normally required and a substantial reduction in frame rate may occur. This invention addresses these problems and provides a solution. 
     BRIEF SUMMARY OF THE INVENTION 
     The preferred embodiment is useful in an ultrasound imaging system for displaying a color flow image representing at least a portion of a subject being studied. In such an environment, the preferred embodiment transmits ultrasound waves toward a first portion of the subject and receives first reflected ultrasound waves from the first portion. The transmitting and receiving preferably are accomplished with a transducer assembly. A first set of signals is generated having first values related to the velocity components of the fluid flow in the first portion of the subject in response to the first reflected ultrasound waves. The first values are analyzed to identify flow data representing a region of fluid flow within the first portion of the subject. The generating and analyzing preferably is accomplished with a processor. Ultrasound waves are transmitted toward a second portion of the subject and second reflected ultrasound waves are received from the second portion such that the second portion of the subject is smaller than the first portion and includes at least some of the region of fluid flow. The transmitting toward the second portion preferably is accomplished with the transducer assembly. A second set of signals is generated having second values related to velocity components of the fluid flow in the second portion of the subject in response to the second reflected ultrasound waves. The second scan values are processed to generate processed color flow data for display as a color flow image. The generating of the second set of signals and the processing preferably are done with the processor. A color flow image is displayed in response to the processed color flow data. 
     By using the foregoing techniques, the tissue interrogation and/or color flow processing required in a clinical examination may be substantially reduced. A reduction in interrogation and/or processing may be used in various ways to increase the average acoustic frame rate, improve color flow sensitivity and resolution, reduce processing and memory loads and increase color flow regions of interest without unduly sacrificing frame rate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of a preferred form of apparatus made in accordance with the present invention. 
     FIG. 2 is a schematic block diagram showing in more detail a portion of the apparatus as shown in FIG.  1 . 
     FIG. 3 is a schematic diagram illustrating the division of a survey frame over a region of interest and target frames which contain data indicative of fluid flow. 
     FIG. 4 is a schematic diagram illustrating a reduction in the number of target frames compared to the illustration of FIG.  3 . 
     FIG. 5 is a schematic illustration of a target frame with adjacent buffer vectors and regions. 
     FIG. 6 is a schematic illustration of a target frame in which only regions including flow data are subjected to color flow processing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a preferred form of the invention comprises an imaging system  10  for displaying a color flow image of a subject S being studied. System  10  includes a transducer and agile beam former assembly  20  of the type described in U.S. Pat. No. 5,653,236 (Miller, issued Aug. 5, 1997) (the “&#39;236 Patent”). Assembly  20  transmits ultrasound waves toward a controllable portion of subject S along an axis  36  and receives reflected ultrasound waves from the portion along the same axis  36  in the manner described in the &#39;236 Patent. Assembly  20  generates signals in response to the reflected ultrasound waves which are transmitted over a bus  40  to an adaptive color flow processing module  70 . The direction of axis  36  is controlled by control signals received over a bus  50  from an adaptive scan sequencer controller  60 . Controller  60  controls the angle of axis  36  in the manner described in the &#39;236 Patent. 
     Referring to FIGS. 1 and 2, processing module  70  comprises a processor unit  74  which may include one or more individual processors. For example, processor unit  74  may include a survey frame processor  80  comprising an arithmetic unit  82 , FIFO units  84  and  86  and a memory  88  connected as shown. Processor unit  74  also may comprise a target frame processor  90  comprising an arithmetic unit  92 , FIFO units  94  and  96  and a memory  98  connected as shown. Processor unit  74  also may include other processors, such as processors  100  and  110 , which are identical to processor  80 . Each of processors  80 ,  90 ,  100 , and  110  may comprise a digital signal processor, such as model TMS 320C6201 manufactured by Texas Instruments. The processors shown in FIG. 2 are interconnected by communication busses  120 - 122 , and processor  110  communicates with a standard logic 700 slave VME interface (I/F)  130  over a communication bus  132 . 
     Processor unit  74  receives data over an input bus  140  from an input control and scan bus interface (I/F)  150  which comprises a field programmable gate array (FPGA). Interface  130  communicates with interface  150  over a communication bus  160 . In addition, interface  130  provides output signals over a bus  164  to controller  60  (FIG.  1 ). 
     Processor unit  74  provides output data on an output bus  170  to an output control unit  180  which comprises a field programmable gate array (FPGA). Control unit  180  communicates with interface  130  over a communication bus  190  reads and writes data to and from an SRAM memory  200  over busses  202  and  204 . Control unit  180  provides color flow data for display over an output bus  210  to a conventional scan conversion and display processing unit  220  (FIG.  1 ). The color flow data is converted to a corresponding image created on a display  230 . 
     Referring to FIGS. 1-3, processor  80  issues a command which results in a signal transmitted over bus  164  to controller  60  that results in assembly  20  transmitting ultrasound waves toward a region of interest (ROI) of subject S and receiving reflected ultrasound waves from the ROI. The reflected waves are processed by processor  80  into a survey frame SF 1  (FIG. 3) which includes four equally sized interleaved groups of data G 1 -G 4  stored in memory  88 . Processor  80  processes the data in groups G 1 -G 4  and determines that only the data in groups G 2  and G 3  result from fluid flow in the ROI. As a result, processor  80  issues another command which results in a second signal transmitted over bus  164  to controller  60  that causes assembly  20  to again transmit a second group of ultrasound waves toward the portions of subject  80  that resulted in data groups G 2  and G 3  in frame SF 1 . 
     As can be seen from FIG. 3, the portion of the subject scanned by the second group of ultrasound waves is substantially smaller than the ROI portion of the subject indicated in frame SF 1 . The data resulting from the second group of reflected ultrasound waves is transmitted to the target frame processor  90  which color flow processes only the data resulting from groups G 2  and G 3  as shown in FIG.  3 . As shown in FIG. 3, target frames TF 1 -TF 3  include only data groups G 2  and G 3 , whereas survey frame SF 1  includes not only data groups G 2  and G 3 , but also data groups G 1  and G 4 . 
     Processor  90  processes the data on bus  140  resulting from the second group of reflected ultrasound waves to form target frame groups G 2  and G 3  which include a set of signals having values related to the velocity components of the fluid flow in the portion of subject S represented by data groups G 2  and G 3 . Data in groups G 2  and G 3  is color flow processed by processor  90  to generate color flow data which is transmitted over output bus  170  to control unit  180  which, in turn, transmits color flow data over bus  210  to scan conversion and display processing unit  220 . By well known means, unit  220  displays the resulting color flow images on display unit  230 . Since only the portion of the ROI represented by data groups G 2  and G 3  are scanned by assembly  20  and processed by processor  90 , they&#39;re typically is time for more target frames than survey frames. As a result, FIG. 3 shows target frames TF 1 -TF 3  resulting from a single survey frame SF 1 . 
     If all four frames, SF 1  and TF 1 -TF 3 , were scanned and processed in their entirety according to conventional color flow techniques, the scanning and processing load would be 100%. However, with the example shown in FIG. 3, only half of the vectors in each target frame need to be scanned, sampled and processed. This corresponds to a scanning and processing load of only 62.5% for a potential savings of 37.5%. The extra frame rate achieved by the technique shown in FIG. 3, could be accepted or the packet size and/or vector density could be increased to achieve more color flow sensitivity and resolution. The survey and target frames shown in FIG. 3 are continuously repeated during scanning of subject S as long as the described conditions remain the same. 
     Referring to FIG. 4, if the average acoustic frame rate were significantly lower, or if the flow state were changing significantly faster than in the FIG. 3 example, the number of target frames may need to be reduced to, for example, only a single target frame TF 1  as shown in FIG.  4 . For the case shown in FIG. 4, the scanning and processing load would be reduced to 75%, for a potential savings of 25%. 
     The examples of FIGS. 3 and 4 illustrate an ideal situation in which fluid flow corresponds exactly to the vectors within interleave groups G 2  and G 3 . In the most general implementation of the preferred embodiment, the target frame firing decisions could be made on a vector-by-vector basis. In the examples of FIGS. 3 and 4, the target frame scanning decisions are constrained to interleave groups (e.g., either scan and process an interleave group, such as group G 2 , or none of the group). Scanning and processing limited to entire interleave groups (e.g., group G 2 ) would be easier to implement, but would not, in general, yield significant improvements as often as decisions made on a vector-by-vector basis. 
     Referring to FIG. 5, buffer flow vectors may be added in buffer regions, such as BR 1  and BR 2 , in order to make the preferred embodiment more robust and less sensitive to motion. For example, in a region of interest including data groups G 1 , G 2 , and G 3  as shown in FIG. 5, buffer regions BR 1  and BR 2  may lie on either side of a region R in which fluid flow occurs. More generally, for every vector determined to have flow on a survey frame, some number, b, of adjacent buffer vectors might also be fired and sampled on target frames. This procedure minimizes the reduced sampling benefit on a given target frame, but improves over-all imaging performance. As shown in FIG. 5, buffer vectors are illustrated on either side of the fluid flow region R to create two buffer regions BR 1  and BR 2  of extra vectors that are scanned, sampled and processed in a target frame consisting of group G 2  by processor  90 . As shown in FIG. 5, the target frame would include only a data group G 2  and buffer regions BR 1  and BR 2 . 
     Referring to FIG. 6, according to the preferred embodiment, the efficiency of the system may be further improved by selectively processing only those vector range samples in which flow is known to exist. In this way, the survey frame provides range intervals over which flow is detected, and the target frame provides adaptive color flow processing for only those range intervals. Such a procedure does not increase the frame rate, but reduces the color flow processing load in the range dimension as well as in the lateral dimension, as a function of the amount of flow in the ROI. This reduced processing load can be traded off against reduced hardware costs, covering a wider ROI, or using the processing hardware assets of the imager to provide improved color flow performance (e.g., better detection, better resolution, etc.). 
     Still referring to FIG. 6, processor  80  processes survey frame SF 2  with a color flow processing algorithm which identifies pixels having valid color flow information and sets up a region around these pixels on which parameter estimation and other color flow processing functions are performed on subsequent target frames. Pixel location in R-theta space is managed for subsequent scan version. In addition, an adequate buffer area, such as buffer regions BR 1  and BR 2  shown in FIG. 5, may be incorporated into the regions to be processed in FIG. 6 for the purpose of making the mechanization less sensitive to motion. 
     Still referring to FIG. 6, the entire region of interest (ROI) is scanned by assembly  20  and the resulting reflected ultrasound waves are processed by processor  80  in order to form a survey frame SF 2 . Processor  80  identifies regions R 2  and R 3  as the only regions in which fluid flow data exists. As a result, processor  80  sends a signal over bus  164  to controller  60  that causes assembly  20  to again scan the subject only in regions R 2  and R 3 . The resulting reflected ultrasound waves from regions R 2  and R 3  are processed by processor  90  into corresponding target frames. Adaptive color flow processing is only performed on the data resulting from regions R 2  and R 3  so that only regions R 2  and R 3  result in a color flow image on display  230 . However, since regions R 2  and R 3  are much smaller than the entire region of interest, additional target frames may be processed for each survey frame or the data may be manipulated in the ways previously described in order to take advantage of the reduced processing time required for regions R 2  and R 3 . 
     Those skilled in the art will recognize that only the preferred embodiments have been described in connection with FIGS. 1-6, and that those embodiments may be altered and modified without departing from the true spirit and scope of the invention as defined in the accompanying claims. For example, processors  80  and  90  may be combined into a single processor, such as a single digital signal processor or microprocessor. In addition, all of the processors  80 ,  90 ,  100  and  110  may be combined into a single processor, such as a digital signal processor or a microprocessor.