Abstract:
A system for measuring intramuscular fat in live cattle uses an ultrasound device to produce ultrasound image of an interior muscle portion. The image contains speckle caused by the scattering of ultrasound waves by the intramuscular fat. Image data representative of the speckle are analyzed in terms of pixel grey areas in the computer to produce measures of intramuscular fat including partial autocorrelation, correlation in a co-occurrence matrix and nonspeckle area.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns the measurement of intramuscular fat, i.e., marbling, in cattle using ultra-sound to produce an image of an interior portion of a muscle and then to analyze data representative of that image to produce a measurement of marbling. 
     2. Description of the Prior Art 
     The grading systems for beef carcasses emphasize leanness in terms of yield grades and palatability in terms of quality grades, i.e., intramuscular fat or marbling. Marbling is considered an indicator of favorable ogano-leptic properties such as juiciness, flavor and tenderness. The yield and quality grades of beef are determined after slaughter. If these grades could be determined accurately in live cattle, producers would have the ability to cluster live cattle during the feedlot phases on the basis of anticipated grades to satisfy packer and consumer specifications. Additionally, this would enable cattle breeders to select breeding stock on the basis of the desirable grading traits. 
     Ultrasound techniques have been used with some success for determining anticipated yield grades in cattle. A smooth tissue boundary such as that between subcutaneous fat and muscle results in a specular reflection of the ultrasound that produces a congruent image on the ultrasound monitor. Because of this, ultrasound produces a fairly accurate image of backfat and other attributes predictive of yield grade. 
     The ultrasound techniques have not been successful, however, in producing images representative of marbling. This is because the intramuscular fat deposits of varying sizes and shapes present discontinuities that cause sound waves to scatter rather than echo back to the ultrasound probe. This scattering causes constructive and destructive interference at the probe in a manner analogous to acoustical noise and produces a graininess or mottling in the ultrasound images known as &#34;speckle.&#34; Additionally, as marbling increases, the degree of scatter increases. 
     In the prior art, various attempts have been made to use the speckle itself as an indicator of marbling. For example, in one prior art technique, the speckle in ultrasound images is analyzed visually. With sufficient experience and training, this technique has provided encouraging results, but requires subjective judgment by an individual; subjective judgment in the grading of beef has been a problem in the prior art because it leads to inconsistent results over time and from individual to individual. 
     SUMMARY OF THE INVENTION 
     The present invention solves the prior art problems discussed above and provides a distinct advance in the state of the art. In particular, the system enables the objective measurement of marbling in the muscular tissue of live cattle. 
     In the preferred embodiment, an ultrasound device is used to produce image data from the muscle tissue in live cattle wherein the image data is in the form of pixels having respective grey levels. The image data is then analyzed in a computer to produce a value or score representative of marbling. In preferred forms, the marbling score is determined as a function of pixel value correlation in a co-occurrence matrix, partial autocorrelation and nonspeckle area. Other preferred aspects of the present invention are set forth hereinbelow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the preferred apparatus in accordance with the present invention shown in use; 
     FIG. 2 is a photographic illustration of an ultra-sonic echogram correlated with a grade of USDA Low Select; 
     FIG. 3 is a photographic illustration of an ultra-sonic echogram correlated with a grade of USDA High Choice; 
     FIG. 4A is a graph representing a score of actual carcass marbling versus predicted carcass marbling using multiple regression analysis in accordance with the present invention; and 
     FIG. 4B is a graph representing scores of actual carcass marbling versus predicted marbling scores using neural network analysis in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates preferred apparatus 10 including ultrasound device 12, video cassette recorder (VCR) 14 and computer 16. Device 12 is preferably Aloka model 210 distributed by Corometrics Medical Systems, Inc., of Wallingford, Conn. operable in real time in the so-called B-mode for producing a two dimensional echogram with pixel brightness indicating signal strength and having a refresh rate of 30 times per second. Images are stored in a four bit format providing 16 levels of grey scale. Device 12 includes signal processor 18 coupled with probe 20, which is preferably Aloka model UST-5021 that operates as a phased array probe with a 3.5 MHz central frequency and a 125 mm window. 
     VCR 14 is a conventional unit such as a Sharp VC-A5630 or preferably a Sony SLV-757VC coupled with signal processor 18 for receiving and recording about 30 seconds of real time imaging from ultrasound device 12. Computer 16 is preferably a Zenith A-386/25 personal computer equipped with Sony Trinitron monitor. Computer 16 includes a Targa M8 image capture board available from Truevision of Indianapolis, Ind., coupled with VCR 14 for receiving and digitizing images therefrom. 
     In use, probe 20 is placed on the surface 22 of live stock 24. More particularly, the insonation site is moistened with mineral oil as a couplant between probe 20 and surface 22 to minimize ultrasound attenuation. The preferred probe site is over the twelfth rib 26 beginning at the juncture of the rib and the spinous process at the vertebrae in order to develop a cross sectional image of the longissimus dorsi, i.e., ribeye, muscle 28 near the region where the carcass is to be cut into quarters. In this way, the image is of the same site presented to the grader for marbling classification. The gain of ultra-sound device 12 is set at maximum in order to provide an image completely through longissimus muscle 28. 
     Probe 20 is manipulated laterally so that it follows the curvature of rib 26 until a full tomogram of muscle 28 comes into view on display 30 of signal processor 18, bracketed between backfat layer 32 and rib 26. In preferred practice, it is desired to record about 30 seconds of images from ultrasound device 12 to VCR 14. 
     FIGS. 2 and 3 are photographic illustrations of ultrasonic images produced by device 12 as presented on display 30 and as recorded by VCR 14. As illustrated in these images, and with reference to FIG. 1, the upper layer depicts backfat layer 32 and the curved portion in the lower right of each image shows rib 26 with the area inbetween being muscle 28. As illustrated, the area of muscle 28 shows white patches known as speckle. Intramuscular fat in this area causes random scattering of the ultrasound waves and because of this, the marbling itself is not imaged. Instead, it is the scattering caused by the marbling that results in signal noise that is imaged as the white patches in the area of muscle 28 in FIGS. 2 and 3. A comparison of these two figures illustrates that the higher level of marbling in FIG. 3 produces the higher level of signal noise known as &#34;speckle&#34; in the region near backfat layer 32. 
     After the image recordation process is complete as described above, three to five representative frames are selected, digitized and stored in computer 16 as image data representative of the ultrasound image as pixels with eight bits defining 256 grey level values. Ultra-sound device 12, however, only portrays 16 grey levels and the digitizer maps these values to eight bits. Computer 16 includes Java video analysis software available from Jandel Scientific of Cote Madera, Calif., which is used to manipulate the computer monitor cursor for outlining and defining a selected region of interest of about 3 to 4 cm square presenting a resolution of about 27 pixels per centimeter of tissue with about 8,000 to 10,000 pixels total in the region. 
     The region of interest is selected to be centered between backfat layer 32 and rib 26 within muscle 28, and to present a uniform pattern while avoiding acoustical shadows. The region of interest is located in the sector of the longissimus that is distal from the midline of the animal because that area is more likely to present a more consistent pattern of speckle and random specular echoes. The image data of the region of interest of each captured frame are processed for the statistical features which are then averaged for further analysis. The image data are initially stored as a TIF file and then converted to an ASCII format so that the data is amenable to image analysis. The pixel values in the stored array are initially preprocessed by using statistical regression to adjust for signal attenuation remaining after gain compensation adjustments of the ultrasound signal processor 12. 
     As those skilled in the art will appreciate, a vast array of mathematical techniques are available for analyzing images. In the development of the present invention, about 500 different techniques were investigated. For example, it was found that conventional first order statistics such as mean pixel values as well as the second, third and fourth moments of those values were insufficient. As a result, second order statistics are used to evaluate the relationships among the pixel grey level values of the region of interest, primarily involving co-occurrence and run-length matrices. None of the standard procedures were found to be adequate for measuring intramuscular fat. 
     Accordingly, three variables were developed for building a multiple regression model. These image texture variables include partial autocorrelation, correlation in a co-occurrence matrix and nonspeckle area. These were calculate along pixel vectors that were in the dimension axial to beam transmission. Appendix I incorporated as part of the disclosure hereof illustrates the preferred program written in Fortran for analyzing the image data in computer 16. 
     The partial autocorrelation variable is a time series analysis used to analyze the pixel grey level values along a row in the time domain. More particularly, the preferred partial autocorrelation is the regression of a pixel value with the pixel value two steps behind it, independent of the values of the intervening pixels. This is obtained from a formula involving two autocorrelations of a pixel with the pixel at lag 1 and lag 2. The specific formula is: 
     
         AR2.1=(AR2-AR1.sup.2)/(1-AR1.sup.2) 
    
     where AR2.1 is the partial autocorrelation of the grey level value on the pixel at lag 2 independent of the pixel at lag 1, AR2 is the autocorrelation of lag 2 and lag 0, and AR1 is the autocorrelation of lag 1 and lag 0. 
     The data are normalized to a mean of 0 so that the autocorrelation values are the same as autoregressions. This was performed on values in an eight bit format and across all rows as if they were one continuous vector. The values are negative and usually in the range of -0.65 to -0.75 with the values nearest 0 associated with the higher level of marbling. 
     For the correlation variable, a co-occurrence matrix is built by mapping a pixel value (grey level) with that of a neighbor at a designated distance, that is, from row vectors across the data set and with eight bit formatting. The matrix is made symmetrical by placing values both above and below the diagonal. The correlation statistic is calculated from the regression of matrix values to the column (or row) values so that a high correlation indicates a predominance along the trace (diagonal) of the matrix and measures the similarity of a pixel value with its designated neighbor. A high co-occurrence correlation is associated with a high degree of marbling and relates to an image with uniform visual texture. 
     The nonspeckle area variable measures the lack of speckle in the image and is inversely related to marbling. This variable is developed from the run length grey level matrix by assessing the length of runs of the same grey level value along a row in the matrix. Initially the pixel grey level values are mapped to the four bit level because the eight bit resolution is too fine for meaningful run-length intonation. The abscissa values of the run length matrix are normalized so that the mean and standard deviation of the run length are the same as grey level value. 
     The nonspeckle area is calculated by summing the cell values in the matrix multiplied by the square of the normalized run length and dividing by the square of the corresponding grey level: 
     
         Nonspeckle area=(Summation P(i,j)/N*J.sup.2 /I.sub.2)-1 
    
     where P(i,j) is the element in the matrix, N is the total number of runs (this normalizes the procedure so that it is independent of the size of the region of interest), J is the normalized run length that corresponds to the cell, and I is the corresponding grey level. The value of &#34;1&#34; is subtracted to increase the dynamic range. The nonspeckle area is inversely related to marbling because it measures the predominance of long, low grey levels, which characterizes an image with low speckle and thus, low marbling. 
     While each of the variables discussed above relates to marbling, each presents a different relationship between the pixel grey levels and marbling. In order to enhance the utility of the measurement, these variables are used in a multiple regression model to develop a marbling score. In the preferred embodiment, the marbling score (MS) is formulated as: MS=17.91342+2.890843 * Correlation-5643.7574 * Nonspeckle Area+13.58639 * Partial Autocorrelation. Those skilled in the art will appreciate that the coefficients of the marbling score formula can vary as the calibration set of data expands. 
     FIG. 4A is a graph of actual carcass marbling scores as determined by inspection grading after slaughter versus marbling scores (MS) developed from the ultrasound image analysis discussed above. The straight line in the graph is the isopach line for perfect correspondence. As illustrated, the average deviation from isopach is 0.43. 
     In another embodiment of the present invention, neural computing software such as Neuralworks Explorer by NeuralWare of Pittsburgh, Penn., was used to process the three marbling variables discussed above to develop a neural network score (NNS). This software was used in place of the marbling score (MS) formula. The results of this analysis are shown in FIG. 4B which is a graph of actual carcass marbling scores versus the neural network score. As illustrated, the average isopach deviation is 0.27. 
     As those skilled in the art will appreciate, the present invention encompasses many variations in the preferred embodiments described herein. For example, the output from ultrasound device 12 can be provided directly to computer 16 thereby eliminating the need for VCR 14. Additionally, each of the three marbling variables provide an independent measure of marbling from the ultrasound image and could be used singly or in combination with two in some circumstances. In addition, other techniques can be developed for developing marbling scores from the image texture variables. ##SPC1##