CA1214286A - Multiple measurement noise reducing system using artifact edge identification and selective signal processing - Google Patents
Multiple measurement noise reducing system using artifact edge identification and selective signal processingInfo
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- CA1214286A CA1214286A CA000447734A CA447734A CA1214286A CA 1214286 A CA1214286 A CA 1214286A CA 000447734 A CA000447734 A CA 000447734A CA 447734 A CA447734 A CA 447734A CA 1214286 A CA1214286 A CA 1214286A
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
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Abstract
ABSTRACT
Disclosed is a multiple measurement multiple energy x-ray imaging system in which a plurality of measurements are processed to provide a first image signal representing a desired parameter of an object and in which the plurality of measurements are processed to provide a second processed image signal having greater signal-to-noise ratio than the first processed image signal but in which extraneous arti-facts may be introduced into the signal. The spatial location of edges of the extraneous artifacts are determined.
The first processed image signal and the second processed image signal are combined to provide an improved image signal except at the spatial locations of the extraneous artifacts where the first processed image signal is used for the image signal thereby eliminating the extraneous artifact from the displayed image.
Disclosed is a multiple measurement multiple energy x-ray imaging system in which a plurality of measurements are processed to provide a first image signal representing a desired parameter of an object and in which the plurality of measurements are processed to provide a second processed image signal having greater signal-to-noise ratio than the first processed image signal but in which extraneous arti-facts may be introduced into the signal. The spatial location of edges of the extraneous artifacts are determined.
The first processed image signal and the second processed image signal are combined to provide an improved image signal except at the spatial locations of the extraneous artifacts where the first processed image signal is used for the image signal thereby eliminating the extraneous artifact from the displayed image.
Description
28~
MULTIPLE MEASUREMENT NOISE REDUCING SYSTEM USING ARTIFACT
EDGE IDE~TIFI(~ATION AND SELECTIVE SIGNAL PROCESSING
This invention relates generally to imaging systems such as x-ray systems, and more particularly the invention relates to the processing of images derived from a plurality of measurements In many imaging application areas, images are constructed as a weighted sum of a plurality of measurements. A prime example are the recent new developments in x-ray imaging.
- 10 Here measurements are made at different energies and/or at different times These measurements are then combined to provide selective images representing specific materials.
One example is that of temporal subtraction techniques using digital radiography as described in the publication by C. A.
Mistreat and A. B. Crummy, "Diagnosis of Cardiovascular Disease by digital Subtraction Angiography," in Science, Vol. 214, pp. 761-65, 1981. Here measurements taken before and after the administration of iodine into blood vessels are subtracted to provide an image of vessels alone. Another I example is that of energy-selective radiography as described in the publication by L. A. Lehman, et at., generalized Image Combinations in Dual KVP Digital Radiography," in Medical Physics, Vol. 8, pp. 659-67, 1981. Here measurements made at different energies axe combined to enhance or elm-Nate specific materials. A third example is energy-selective computerized tomography as described in the publication by
MULTIPLE MEASUREMENT NOISE REDUCING SYSTEM USING ARTIFACT
EDGE IDE~TIFI(~ATION AND SELECTIVE SIGNAL PROCESSING
This invention relates generally to imaging systems such as x-ray systems, and more particularly the invention relates to the processing of images derived from a plurality of measurements In many imaging application areas, images are constructed as a weighted sum of a plurality of measurements. A prime example are the recent new developments in x-ray imaging.
- 10 Here measurements are made at different energies and/or at different times These measurements are then combined to provide selective images representing specific materials.
One example is that of temporal subtraction techniques using digital radiography as described in the publication by C. A.
Mistreat and A. B. Crummy, "Diagnosis of Cardiovascular Disease by digital Subtraction Angiography," in Science, Vol. 214, pp. 761-65, 1981. Here measurements taken before and after the administration of iodine into blood vessels are subtracted to provide an image of vessels alone. Another I example is that of energy-selective radiography as described in the publication by L. A. Lehman, et at., generalized Image Combinations in Dual KVP Digital Radiography," in Medical Physics, Vol. 8, pp. 659-67, 1981. Here measurements made at different energies axe combined to enhance or elm-Nate specific materials. A third example is energy-selective computerized tomography as described in the publication by
- 2 -R. E. Alvarez and A. Macovski, "Energy-Selective Reconstructions in X-ray Computerized Tomography," in Physics in Medicine &
Biology, Vol. 21, pp. 733-744, 1976. Here sets of measurements are made at two energy spectra and distortion free reconstructions are made which delineate the average atomic number and density of each region. A fourth example is hybrid subtraction described in the publication by W. R. Broody, "Hybrid Subtraction for Improved Intravenous Arteriography." in Radiology, Vol. 141, pp. 828-831, 1981. Here dual energy measurements are made before and after the administration of iodine. Each dual energy pair is used to eliminate soft tissue. In this way the resultant subtracted vessel images are immune to soft tissue motion.
In each case, where a number of measurements are combined to select specific material properties, the resultant S NO ( Signal-Tunis ratio) is reduced as compared to the non-selective image.
Therefore, these various processing techniques which improve the visualization of disease processes by selecting specific materials have the disadvantage of a reduction in SIR. This reduced SIR
can interfere with the ability to visualize regions of disease.
A system to improve the SIR of the hybrid subtraction and other multiple measurement systems has been developed by A. Macovski. An array of measurements are taken of an object under different conditions. These are combined to select a specific aspect of the object. The same measurements are then combined in different weighting to provide a lower-noise image, without the desired selectivity. The improved selective image is formed by combining -the selective image with the lower-noise image using the lower frequency components of the former and the ~",.~.
Biology, Vol. 21, pp. 733-744, 1976. Here sets of measurements are made at two energy spectra and distortion free reconstructions are made which delineate the average atomic number and density of each region. A fourth example is hybrid subtraction described in the publication by W. R. Broody, "Hybrid Subtraction for Improved Intravenous Arteriography." in Radiology, Vol. 141, pp. 828-831, 1981. Here dual energy measurements are made before and after the administration of iodine. Each dual energy pair is used to eliminate soft tissue. In this way the resultant subtracted vessel images are immune to soft tissue motion.
In each case, where a number of measurements are combined to select specific material properties, the resultant S NO ( Signal-Tunis ratio) is reduced as compared to the non-selective image.
Therefore, these various processing techniques which improve the visualization of disease processes by selecting specific materials have the disadvantage of a reduction in SIR. This reduced SIR
can interfere with the ability to visualize regions of disease.
A system to improve the SIR of the hybrid subtraction and other multiple measurement systems has been developed by A. Macovski. An array of measurements are taken of an object under different conditions. These are combined to select a specific aspect of the object. The same measurements are then combined in different weighting to provide a lower-noise image, without the desired selectivity. The improved selective image is formed by combining -the selective image with the lower-noise image using the lower frequency components of the former and the ~",.~.
3~2~
higher frequency components of the latter. To assure the proper amplitude of the higher frequency components, the components are weighted such as with the ratio of the derivative of the selective image to the derivative of the Lorraine image. Nonlinear thresholds are used for those cases where this ratio becomes an unreliable indicator of the correct amplitude of the high frequency components. one limitation of the Macovski system is the introduction of extraneous signals (herein termed "artifacts") by the low noise signal.
The present invention is directed to an improvement in tile Macovski system. The improvements eliminate severe artifact edges which may not otherwise be suppressed in the Macovski system.
Briefly, the locations of the artifact edges in the image signal are identified and -the display signal is switched from the Macovski noise-reducing system (NRS) signal to the initial selective signal, S, or a signal derived therefrom. In a preferred embody-mint, the artifact edges are identified by passing an artifact image signal through a plurality of derivative operators in the horizontal and vertical directions to provide the two components of the spatial gradient vector, then taking the magnitude of the gradient at each point. This magnitude is then applied to a threshold detector. Since severe edges are of interest, a relatively large threshold is used. When the -threshold is exceeded, thereby indicating a severe artifact-- edge in the NRS
signal, the selective signal, S, or a signal derived therefrom is applied to the display.
Accordingly, an object of the present invention is a multiple measurement noise reducing system in which severe 12~Z86 artifacts are eliminated.
According to one aspect of the invention there is provided in an imaging system, appear r US for reducing extraneous image signals in a processed image signal of an object representing a desired parameter derived from a plurality of measurements comprising: first processing means for processing said plurality of measurements and producing a first processed image signal represent-in said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, third processing means interconnected with said first processing means and said second processing means for receiving and combining said first processed image signal and said second processed image signal and producing a third processed image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said third processed image signal to a signal based on said first processed image signal when edges of extraneous images are detected.
According to another aspect of the invention there is provided in an imaging system, apparatus for refacing extraneous image signals in a processed image signal of an object represent-in a desired parameter derived from a plurality of measurements comprising: first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio - 3b -from said first processed image signal, first filter means for receiving and low pass filtering said first processed image signal, second filter means for receiving and high pass filtering said second processed image signal, means for combining said filtered first processed image signal and said filtered second processed image signal to produce a combined image signal, means for deter-mining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said combined image signal to a signal based on said first processed image signal in response to detection of edges of extraneous images.
According to a further aspect of the invention there is provided for use in a X-ray imaging system in which a plurality of measurements are made, a method of reducing extraneous signals in a processed image signal comprising the steps of:
processing said plurality of measurements to provide a first processed image signal representing a desired parameter of an ox-jet, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifact images, combining said first and second processed image signals and thereby providing a third processed image signal, determining the spatial location of edges of said artifacts in said second processed signal, and switching from said third processed image signal to said first processed image signal at the spatial location of said artifacts.
According to another aspect of the invention there is provided for use in an imaging system in which a plurality of measurements are made, a method of reducing extraneous signals - 3c -~:14~
in a processed image signal of an object comprising thy steps of:
processing said plurality of measurements to provide a first processed image representing a desired parameter of said object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifacts, low pass filtering said first processed image signal to reduce its noise, high pass filtering said second processed image signal, said high pass filtering being complementary to said low pass filtering, lo combining said filtered first processed image and said filtered second processed image to provide an improved processed image signal, determining the spatial location of edges of said anti-facts, and selectively switching from said improved processed image signal to a signal based on said first processed image signal at the spatial locations of artifacts.
The invention and objects and features thereof will be most readily apparent from the following description and appended 8;
claims when taken with the drawings, in which:
Figure 1 is a block diagram of an x-ray system for acquiring signals useful in the invention.
Figure 2 is a block diagram of an x-ray system in accordance ' with the prior art.
Figure 3 is a functional block diagram of an x-ray signal processing system in accordance with the present invention.
Figure 4 is a functional block diagram of edge detection circuitry useful with the system of Figure 3.
10 Referring now to the drawings, Figure 1 is a block diagram of an x-ray system which includes an x-ray tube 8 supplied by variable voltage power Source 3. The x-rays are trays-milted through object 1, normally the human anatomy. The transmitted rays are received my x-ray detector 4, such as 15 an image intensifier and television camera, or a one- or two-dimensional array of centiliters, eta. The image signal 5 is applied to storage system 6 where a plurality of images 9, 10, 11, 12, etc., can be stored.
In temporal subtraction a first image g is stored. Following 20 administration of a contrast agent using syringe 2, a second image 10 it stored. These are then used in the subsequent processing systems. In energy selective systems, images 9, 10, 11, 12, etc., are stored at different values of beam energy corresponding different anode voltages 3. In 25 dual-energy systems two voltages are used. In addition different x-ray beam filters, not shown, can be added.
In the Broody hybrid subtraction system previously described, measurements at two voltages are taken prior to the ad mini-striation of contrast material. These are stored as 9 and 30 10. Following administration of the contrast agent, two additional measurements at the same two voltages are taken and stored as 11 and 12. These four measurements are then 28~i --s--processed to obtain a low-noise image of the vessels opus-fled by the contrast material from syringe 2.
Referring now to Figure 2, the lines 9, 10, 11 and 12 repro-setting an array of x-ray measurements of an object, are processed in accordance with the Macovski system described above. These signal could be obtained, for example, from the output of the television camera in a fluoroscopic system where an array of images are formed and stored, for example, on a magnetic disc or in a solid-state frame memory. These signals can represent x-ray images taken with different photon energy spectra or taken before and after the ad mini-striation of a contrast agent.
In general the multiple measurements are taken so as to provide the isolation or elimination of specific materials.
One simple example involves the isolation of vessel images by subtracting measurements taken before and after the administration of an iodinated contrast agent. Other exam-pies include measurements at different x-ray photon energy spectra which are then combined to eliminate or enhance specific materials.
Weighted summer 13 takes the measurements and provides selective signal 17, containing the desired material pro-parties. Unfortunately, however, signal 17 often has relatively poor SIR. The weighted sum usually involves negative weights which diminish the signal. The noise variances of each independent measurement and, however, to provide a large variance, hence a low SIR. This SIR it considerably improved using low pass filter 15 which seduces the bandwidth. This noise reduction, however, is accom-polished at the price of reduced resolution. primary objective of this invention it to restore the resolution using a source of high frequency information with reduced noise.
Signals 9, 10, 11 and 12 are also applied to weighted sum-mint structure 14. These weights can be chosen to maximize the signal-ts-noise ratio for a particular component of the image. For example, for vessel imaging they can be chosen to maximize the signal-to-noise ratio for the iodinated contrast agent. This is in sharp distinction to weighted summing structure I where the weights are chosen to isolate iodine and eliminate the various tissue components. Ideally, the weight which maximize the SIR will vary in different portions of the image, depending on the intervening tissue.
Thus, the weights can be varied as the signals are scanned.
However, for simplicity, the weights can be fixed to maximize the average SIR with relatively small degradation in per-pheromones.
The high SIR weighted-sum signal, 18, is applied to high pass filter 16 which extracts the high frequency components.
A preferred embodiment of this high pass filter is the complement of low pass filter 15. Thus the sum of the normalized transmissions equals unity within the frequencies of interest. These filters can either be implemented in the frequency domain or as convolution functions.
- 20 Combiner 21 combines the low frequency image or signal 19 with the high frequency image or signal 20 to obtain the processed image 22 which is displayed in display 23. Since signal 19 is low noise because of the filtering, and signal 20 is low noise because of the weighings, the processed signal 22 is a low noise version of the desired signal, having the full bandwidth or resolution.
The degree of artifacts in the image can depend on the nature of the combiner 21. For simplicity, the combiner 21 can simply be an adder. were the desired selected image will have the required low noise and high resolution.
However, signal 20 contains the high frequency components of undesired structures. For example, in vessel images, signal 20 contains the edges ox undesired structures such as bone and various soft tissue organs and motion artifacts. Since US these are only edges, however, a trained radiologist can ignore them and concentrate on the vessels.
I
This system is particularly applicable to top prosily-described hybrid subtraction scheme. Assume summer 13 weights the four signals to eliminate everything but iodine, while also subtracting soft tissue motion artifacts.
5 Summer 14 can, for example, weight the signals to provide a low noise temporal subtraction, without concern about soft tissue motion artifacts. This can ye accomplished by using a large positive weight for the low energy signal before iodine is administered, and a smaller positive weight for the high energy signals since it contains less of the iodine component. These weights are reversed for the measurements taken after the iodine administration to provide a temporal subtraction of everything except iodine.
In this case, in the absence of motion, when lo and 20 are added, the desired isolated vessel signal will be formed having its full resolution. In the presence of soft tissue motion, signal 19 will be immune and continue to be vessels only, as described in the previously referenced application on hybrid subtraction. Low noise signal 20, however, will 20 contain motion artifacts. Thus when they are added in combiner 21, the edges of these artifacts will be present.
In accordance with the present invention, the multiple measurement noise reducing system of Macovski is modified whereby severe artifacts, which may not be reliably pro-vented in the Macovski system, are eliminated by switching to the parameter selective signal or a signal derived therefrom in the image regions where the severe artifact edge is present.
Apparatus in accordance with the invention is illustrated in the block diagram of Figure 3. The selective signal, S, 17 and the low noise signal, M, 18 are applied to the NRS
filter and combiner shown generally at 30 and which cores-pond to the functional elements 15, 16, and 21 in Figure 2.
The low noise signal, M, or a signal, D, which is the difference (M - S) or any other signal which includes the artifact edges, is applied to an edge detection operator 32 which identities artifact edges and generates a signal, I, in response thereto. The signal E is applied to a switch 36 whereby the signal from the NRS filter and combiner 30 it overridden upon detection of an artifact edge, and the 5 selective signal, S, or a spatially filtered version thereof derived from the spatial filter 34, is applied as the output image signal, S. Accordingly, in the region of the artifact edge, as identified by the edge detection operator, the artifact generated in the NRS filter and combiner 30 it 10 eliminated by disconnecting the NRS filter and combiner.
Figure 4 is a functional block diagram of one embodiment of an edge detector operator 32 of Figure 3 and includes a plurality of derivative operators ion other edge filters) 40, 41, and 42, each receiving the input image signal, D or 15 M, in the horizontal and vertical directions to provide the two components of the spatial gradient Hector. The mahogany-tune of the gradient vector at each point in the image signal as derived by the point operator 44 is then compared with a threshold. Other edge map techniques can be employed such as template filters known in the art to detect edge orientation and strength.
There has been described an improved multiple measurement noise reducing system in which the presence of severe anti-facts is eliminated by detecting the presence of artifacts and selectively overriding the noise reduction system (NRS).
By detecting the edges of an artifact through use of spatial operators and then selecting between the NRS signal and a higher noise or slightly distorted signal without artifacts, an improved image it provided. While the invention has been described with reference to a specific embodiment, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modify-cations and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims
higher frequency components of the latter. To assure the proper amplitude of the higher frequency components, the components are weighted such as with the ratio of the derivative of the selective image to the derivative of the Lorraine image. Nonlinear thresholds are used for those cases where this ratio becomes an unreliable indicator of the correct amplitude of the high frequency components. one limitation of the Macovski system is the introduction of extraneous signals (herein termed "artifacts") by the low noise signal.
The present invention is directed to an improvement in tile Macovski system. The improvements eliminate severe artifact edges which may not otherwise be suppressed in the Macovski system.
Briefly, the locations of the artifact edges in the image signal are identified and -the display signal is switched from the Macovski noise-reducing system (NRS) signal to the initial selective signal, S, or a signal derived therefrom. In a preferred embody-mint, the artifact edges are identified by passing an artifact image signal through a plurality of derivative operators in the horizontal and vertical directions to provide the two components of the spatial gradient vector, then taking the magnitude of the gradient at each point. This magnitude is then applied to a threshold detector. Since severe edges are of interest, a relatively large threshold is used. When the -threshold is exceeded, thereby indicating a severe artifact-- edge in the NRS
signal, the selective signal, S, or a signal derived therefrom is applied to the display.
Accordingly, an object of the present invention is a multiple measurement noise reducing system in which severe 12~Z86 artifacts are eliminated.
According to one aspect of the invention there is provided in an imaging system, appear r US for reducing extraneous image signals in a processed image signal of an object representing a desired parameter derived from a plurality of measurements comprising: first processing means for processing said plurality of measurements and producing a first processed image signal represent-in said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, third processing means interconnected with said first processing means and said second processing means for receiving and combining said first processed image signal and said second processed image signal and producing a third processed image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said third processed image signal to a signal based on said first processed image signal when edges of extraneous images are detected.
According to another aspect of the invention there is provided in an imaging system, apparatus for refacing extraneous image signals in a processed image signal of an object represent-in a desired parameter derived from a plurality of measurements comprising: first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio - 3b -from said first processed image signal, first filter means for receiving and low pass filtering said first processed image signal, second filter means for receiving and high pass filtering said second processed image signal, means for combining said filtered first processed image signal and said filtered second processed image signal to produce a combined image signal, means for deter-mining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said combined image signal to a signal based on said first processed image signal in response to detection of edges of extraneous images.
According to a further aspect of the invention there is provided for use in a X-ray imaging system in which a plurality of measurements are made, a method of reducing extraneous signals in a processed image signal comprising the steps of:
processing said plurality of measurements to provide a first processed image signal representing a desired parameter of an ox-jet, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifact images, combining said first and second processed image signals and thereby providing a third processed image signal, determining the spatial location of edges of said artifacts in said second processed signal, and switching from said third processed image signal to said first processed image signal at the spatial location of said artifacts.
According to another aspect of the invention there is provided for use in an imaging system in which a plurality of measurements are made, a method of reducing extraneous signals - 3c -~:14~
in a processed image signal of an object comprising thy steps of:
processing said plurality of measurements to provide a first processed image representing a desired parameter of said object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifacts, low pass filtering said first processed image signal to reduce its noise, high pass filtering said second processed image signal, said high pass filtering being complementary to said low pass filtering, lo combining said filtered first processed image and said filtered second processed image to provide an improved processed image signal, determining the spatial location of edges of said anti-facts, and selectively switching from said improved processed image signal to a signal based on said first processed image signal at the spatial locations of artifacts.
The invention and objects and features thereof will be most readily apparent from the following description and appended 8;
claims when taken with the drawings, in which:
Figure 1 is a block diagram of an x-ray system for acquiring signals useful in the invention.
Figure 2 is a block diagram of an x-ray system in accordance ' with the prior art.
Figure 3 is a functional block diagram of an x-ray signal processing system in accordance with the present invention.
Figure 4 is a functional block diagram of edge detection circuitry useful with the system of Figure 3.
10 Referring now to the drawings, Figure 1 is a block diagram of an x-ray system which includes an x-ray tube 8 supplied by variable voltage power Source 3. The x-rays are trays-milted through object 1, normally the human anatomy. The transmitted rays are received my x-ray detector 4, such as 15 an image intensifier and television camera, or a one- or two-dimensional array of centiliters, eta. The image signal 5 is applied to storage system 6 where a plurality of images 9, 10, 11, 12, etc., can be stored.
In temporal subtraction a first image g is stored. Following 20 administration of a contrast agent using syringe 2, a second image 10 it stored. These are then used in the subsequent processing systems. In energy selective systems, images 9, 10, 11, 12, etc., are stored at different values of beam energy corresponding different anode voltages 3. In 25 dual-energy systems two voltages are used. In addition different x-ray beam filters, not shown, can be added.
In the Broody hybrid subtraction system previously described, measurements at two voltages are taken prior to the ad mini-striation of contrast material. These are stored as 9 and 30 10. Following administration of the contrast agent, two additional measurements at the same two voltages are taken and stored as 11 and 12. These four measurements are then 28~i --s--processed to obtain a low-noise image of the vessels opus-fled by the contrast material from syringe 2.
Referring now to Figure 2, the lines 9, 10, 11 and 12 repro-setting an array of x-ray measurements of an object, are processed in accordance with the Macovski system described above. These signal could be obtained, for example, from the output of the television camera in a fluoroscopic system where an array of images are formed and stored, for example, on a magnetic disc or in a solid-state frame memory. These signals can represent x-ray images taken with different photon energy spectra or taken before and after the ad mini-striation of a contrast agent.
In general the multiple measurements are taken so as to provide the isolation or elimination of specific materials.
One simple example involves the isolation of vessel images by subtracting measurements taken before and after the administration of an iodinated contrast agent. Other exam-pies include measurements at different x-ray photon energy spectra which are then combined to eliminate or enhance specific materials.
Weighted summer 13 takes the measurements and provides selective signal 17, containing the desired material pro-parties. Unfortunately, however, signal 17 often has relatively poor SIR. The weighted sum usually involves negative weights which diminish the signal. The noise variances of each independent measurement and, however, to provide a large variance, hence a low SIR. This SIR it considerably improved using low pass filter 15 which seduces the bandwidth. This noise reduction, however, is accom-polished at the price of reduced resolution. primary objective of this invention it to restore the resolution using a source of high frequency information with reduced noise.
Signals 9, 10, 11 and 12 are also applied to weighted sum-mint structure 14. These weights can be chosen to maximize the signal-ts-noise ratio for a particular component of the image. For example, for vessel imaging they can be chosen to maximize the signal-to-noise ratio for the iodinated contrast agent. This is in sharp distinction to weighted summing structure I where the weights are chosen to isolate iodine and eliminate the various tissue components. Ideally, the weight which maximize the SIR will vary in different portions of the image, depending on the intervening tissue.
Thus, the weights can be varied as the signals are scanned.
However, for simplicity, the weights can be fixed to maximize the average SIR with relatively small degradation in per-pheromones.
The high SIR weighted-sum signal, 18, is applied to high pass filter 16 which extracts the high frequency components.
A preferred embodiment of this high pass filter is the complement of low pass filter 15. Thus the sum of the normalized transmissions equals unity within the frequencies of interest. These filters can either be implemented in the frequency domain or as convolution functions.
- 20 Combiner 21 combines the low frequency image or signal 19 with the high frequency image or signal 20 to obtain the processed image 22 which is displayed in display 23. Since signal 19 is low noise because of the filtering, and signal 20 is low noise because of the weighings, the processed signal 22 is a low noise version of the desired signal, having the full bandwidth or resolution.
The degree of artifacts in the image can depend on the nature of the combiner 21. For simplicity, the combiner 21 can simply be an adder. were the desired selected image will have the required low noise and high resolution.
However, signal 20 contains the high frequency components of undesired structures. For example, in vessel images, signal 20 contains the edges ox undesired structures such as bone and various soft tissue organs and motion artifacts. Since US these are only edges, however, a trained radiologist can ignore them and concentrate on the vessels.
I
This system is particularly applicable to top prosily-described hybrid subtraction scheme. Assume summer 13 weights the four signals to eliminate everything but iodine, while also subtracting soft tissue motion artifacts.
5 Summer 14 can, for example, weight the signals to provide a low noise temporal subtraction, without concern about soft tissue motion artifacts. This can ye accomplished by using a large positive weight for the low energy signal before iodine is administered, and a smaller positive weight for the high energy signals since it contains less of the iodine component. These weights are reversed for the measurements taken after the iodine administration to provide a temporal subtraction of everything except iodine.
In this case, in the absence of motion, when lo and 20 are added, the desired isolated vessel signal will be formed having its full resolution. In the presence of soft tissue motion, signal 19 will be immune and continue to be vessels only, as described in the previously referenced application on hybrid subtraction. Low noise signal 20, however, will 20 contain motion artifacts. Thus when they are added in combiner 21, the edges of these artifacts will be present.
In accordance with the present invention, the multiple measurement noise reducing system of Macovski is modified whereby severe artifacts, which may not be reliably pro-vented in the Macovski system, are eliminated by switching to the parameter selective signal or a signal derived therefrom in the image regions where the severe artifact edge is present.
Apparatus in accordance with the invention is illustrated in the block diagram of Figure 3. The selective signal, S, 17 and the low noise signal, M, 18 are applied to the NRS
filter and combiner shown generally at 30 and which cores-pond to the functional elements 15, 16, and 21 in Figure 2.
The low noise signal, M, or a signal, D, which is the difference (M - S) or any other signal which includes the artifact edges, is applied to an edge detection operator 32 which identities artifact edges and generates a signal, I, in response thereto. The signal E is applied to a switch 36 whereby the signal from the NRS filter and combiner 30 it overridden upon detection of an artifact edge, and the 5 selective signal, S, or a spatially filtered version thereof derived from the spatial filter 34, is applied as the output image signal, S. Accordingly, in the region of the artifact edge, as identified by the edge detection operator, the artifact generated in the NRS filter and combiner 30 it 10 eliminated by disconnecting the NRS filter and combiner.
Figure 4 is a functional block diagram of one embodiment of an edge detector operator 32 of Figure 3 and includes a plurality of derivative operators ion other edge filters) 40, 41, and 42, each receiving the input image signal, D or 15 M, in the horizontal and vertical directions to provide the two components of the spatial gradient Hector. The mahogany-tune of the gradient vector at each point in the image signal as derived by the point operator 44 is then compared with a threshold. Other edge map techniques can be employed such as template filters known in the art to detect edge orientation and strength.
There has been described an improved multiple measurement noise reducing system in which the presence of severe anti-facts is eliminated by detecting the presence of artifacts and selectively overriding the noise reduction system (NRS).
By detecting the edges of an artifact through use of spatial operators and then selecting between the NRS signal and a higher noise or slightly distorted signal without artifacts, an improved image it provided. While the invention has been described with reference to a specific embodiment, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modify-cations and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims
Claims (14)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an imaging system, apparatus for reducing extraneous image signals in a processed image signal of an object representing a desired parameter derived from a plurality of measurements comprising:
first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, third processing means interconnected with said first pro-cessing means and said second processing means for receiving and combining said first processed image signal and said second processed image signal and producing a third processed image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said third processed image signal -to a signal based on said first processed image signal when edges of extraneous images are detected.
first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, third processing means interconnected with said first pro-cessing means and said second processing means for receiving and combining said first processed image signal and said second processed image signal and producing a third processed image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said third processed image signal -to a signal based on said first processed image signal when edges of extraneous images are detected.
2. Apparatus as defined by claim 1 wherein said means for determining the spatial location of edges includes differential means for determining the components of the spatial gradient signal vector of the difference between the said first processed image signal and said second processed image signal.
3. In an imaging system, apparatus for reducing extraneous image signals in a processed image signal of an object representing a desired parameter derived from a plurality of measurements comprising:
first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, first filter means for receiving and low pass filtering said first processed image signal, second filter means for receiving and high pass filtering said second processed image signal, means for combining said filtered first processed image signal and said filtered second processed image signal to produce a combined image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said combined image signal to a signal based on said first processed image signal in response to detection of edges of extraneous images.
first processing means for processing said plurality of measurements and producing a first processed image signal representing said desired parameter, second processing means for processing said plurality of measurements and producing a second processed image signal having a greater signal-to-noise ratio from said first processed image signal, first filter means for receiving and low pass filtering said first processed image signal, second filter means for receiving and high pass filtering said second processed image signal, means for combining said filtered first processed image signal and said filtered second processed image signal to produce a combined image signal, means for determining the spatial location of edges of extraneous images in said second processed image signal, and means for switching from said combined image signal to a signal based on said first processed image signal in response to detection of edges of extraneous images.
4. Apparatus as defined by claim 3 wherein said means for determining the spatial location of edges includes differential means for determining the components of the spatial gradient signal vector of the difference between said first processed image signal and said second processed image signal.
5. Apparatus as defined by claim 3 wherein said first filter means and said second filter means are complementary in frequency.
6. Apparatus as defined by claim 3 wherein said first pro-cessed image signal is derived from a first weighted sum of said measurements and said second processed image signal is derived from a second weighted sum of said measurements.
7. Apparatus as defined by claim 6 wherein said imaging system comprises an X-ray system and said measurements are at different X-ray energies.
8. Apparatus as defined by claim 6 wherein said imaging system comprises an X-ray system and said measurements are at different times.
9. For use in an X-ray imaging system in which a plurality of measurements are made, a method of reducing extraneous signals in a processed image signal comprising the steps of:
processing said plurality of measurements to provide a first processed image signal representing a desired parameter of an object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifact images, combining said first and second processed image signals and thereby providing a third processed image signal, determining the spatial location of edges of said artifacts in said second processed signal, and switching from said third processed image signal to said first processed image signal at the spatial location of said artifacts.
processing said plurality of measurements to provide a first processed image signal representing a desired parameter of an object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifact images, combining said first and second processed image signals and thereby providing a third processed image signal, determining the spatial location of edges of said artifacts in said second processed signal, and switching from said third processed image signal to said first processed image signal at the spatial location of said artifacts.
10. For use in an imaging system in which a plurality of measurements are made, a method of reducing extraneous signals in a processed image signal of an object comprising the steps of:
processing said plurality of measurements to provide a first processed image representing a desired parameter of said object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifacts, low pass filtering said first processed image signal to reduce its noise, high pass filtering said second processed image signal, said high pass filtering being complementary to said low pass filtering, combining said filtered first processed image and said filtered second processed image to provide an image signal, determining the spatial location of edges of said artifacts, and selectively switching from said improved processed image signal to a signal based on said first processed image signal at the spatial locations of artifacts.
processing said plurality of measurements to provide a first processed image representing a desired parameter of said object, processing said plurality of measurements to provide a second processed image signal having greater signal-to-noise ratio than said first processed signal and introducing artifacts, low pass filtering said first processed image signal to reduce its noise, high pass filtering said second processed image signal, said high pass filtering being complementary to said low pass filtering, combining said filtered first processed image and said filtered second processed image to provide an image signal, determining the spatial location of edges of said artifacts, and selectively switching from said improved processed image signal to a signal based on said first processed image signal at the spatial locations of artifacts.
11. The method as defined by claim 10 wherein said step of determining the spatial location of extraneous artifact edges include determining the components of the spatial gradient signal vector of the difference between said first processed image signal and said second processed image signal.
12. The method as defined by claim 10 wherein said first processed image signal is derived from a first weighted sum of said measurements and said second processed image signal is derived from a second weighted sum of said measurements.
13. The method as defined by claim 10 wherein said imaging system comprises an X-ray system and said measurements are at different X-ray energies.
14. The method as defined by claim 10 wherein said imaging system comprises an X-ray system and said measurements are at different times.
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| US06/468,656 US4499493A (en) | 1983-02-22 | 1983-02-22 | Multiple measurement noise reducing system using artifact edge identification and selective signal processing |
| US468,656 | 1983-02-22 |
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| US4541106A (en) * | 1984-02-22 | 1985-09-10 | General Electric Company | Dual energy rapid switching imaging system |
| US4729100A (en) * | 1984-08-28 | 1988-03-01 | Kabushiki Kaisha Toshiba | CT System which convolutes projection data with a frequency varying filter function |
| GB2170373B (en) * | 1984-12-28 | 1989-03-15 | Canon Kk | Image processing apparatus |
| US4678996A (en) * | 1985-05-07 | 1987-07-07 | Picker International, Inc. | Magnetic resonance imaging method |
| GB2181330B (en) * | 1985-09-26 | 1990-05-09 | Toshiba Kk | X-ray inspection apparatus |
| US4827528A (en) * | 1985-11-15 | 1989-05-02 | Stanford University | Error-minimizing noise-reduction system |
| US4792900A (en) * | 1986-11-26 | 1988-12-20 | Picker International, Inc. | Adaptive filter for dual energy radiographic imaging |
| US4761819A (en) * | 1987-02-27 | 1988-08-02 | Picker International, Inc. | Adaptive noise reduction filter for reconstructed images |
| JP2536094B2 (en) * | 1988-10-20 | 1996-09-18 | 富士ゼロックス株式会社 | Color image processing device |
| US4918543A (en) * | 1989-01-24 | 1990-04-17 | Eastman Kodak Company | Apparatus for thresholding an image signal |
| EP0411911B1 (en) * | 1989-08-02 | 1996-03-27 | Canon Kabushiki Kaisha | Image processing apparatus |
| JP2993014B2 (en) * | 1989-08-30 | 1999-12-20 | 富士ゼロックス株式会社 | Image quality control method for image processing device |
| JPH03185574A (en) * | 1989-12-15 | 1991-08-13 | Fuji Xerox Co Ltd | Multivalued image filtering processor |
| US5347590A (en) * | 1991-06-10 | 1994-09-13 | General Electric Company | Spatial filter for an image processing system |
| US5273040A (en) * | 1991-11-14 | 1993-12-28 | Picker International, Inc. | Measurement of vetricle volumes with cardiac MRI |
| KR950003035B1 (en) * | 1992-04-17 | 1995-03-29 | 주식회사 금성사 | Apparatus and method for emphasizing image transition portion |
| US5738096A (en) * | 1993-07-20 | 1998-04-14 | Biosense, Inc. | Cardiac electromechanics |
| US5391199A (en) * | 1993-07-20 | 1995-02-21 | Biosense, Inc. | Apparatus and method for treating cardiac arrhythmias |
| JP3372611B2 (en) * | 1993-10-18 | 2003-02-04 | キヤノン株式会社 | Video transmission system, video processing device, and video processing method |
| US5795298A (en) * | 1995-03-28 | 1998-08-18 | Sonometrics Corporation | System for sharing electrocardiogram electrodes and transducers |
| US5830144A (en) * | 1995-03-28 | 1998-11-03 | Vesely; Ivan | Tracking data sheath |
| US5868673A (en) * | 1995-03-28 | 1999-02-09 | Sonometrics Corporation | System for carrying out surgery, biopsy and ablation of a tumor or other physical anomaly |
| US5797849A (en) * | 1995-03-28 | 1998-08-25 | Sonometrics Corporation | Method for carrying out a medical procedure using a three-dimensional tracking and imaging system |
| US5817022A (en) * | 1995-03-28 | 1998-10-06 | Sonometrics Corporation | System for displaying a 2-D ultrasound image within a 3-D viewing environment |
| US6246898B1 (en) | 1995-03-28 | 2001-06-12 | Sonometrics Corporation | Method for carrying out a medical procedure using a three-dimensional tracking and imaging system |
| US5718241A (en) * | 1995-06-07 | 1998-02-17 | Biosense, Inc. | Apparatus and method for treating cardiac arrhythmias with no discrete target |
| US5954665A (en) * | 1995-06-07 | 1999-09-21 | Biosense, Inc. | Cardiac ablation catheter using correlation measure |
| JPH09261481A (en) * | 1996-03-22 | 1997-10-03 | Toshiba Corp | Image forming device |
| US6125213A (en) * | 1997-02-17 | 2000-09-26 | Canon Kabushiki Kaisha | Image processing method, an image processing apparatus, and a storage medium readable by a computer |
| US6019725A (en) * | 1997-03-07 | 2000-02-01 | Sonometrics Corporation | Three-dimensional tracking and imaging system |
| US6490474B1 (en) | 1997-08-01 | 2002-12-03 | Cardiac Pathways Corporation | System and method for electrode localization using ultrasound |
| US6950689B1 (en) | 1998-08-03 | 2005-09-27 | Boston Scientific Scimed, Inc. | Dynamically alterable three-dimensional graphical model of a body region |
| US6917697B2 (en) * | 2001-05-08 | 2005-07-12 | Ge Medical Systems Global Technology Company, Llc | Method and apparatus to automatically determine tissue cancellation parameters in X-ray dual energy imaging |
| US20050261571A1 (en) * | 2004-05-21 | 2005-11-24 | Willis Nathaniel P | 3-D ultrasound navigation during radio-frequency ablation |
| US7590303B2 (en) * | 2005-09-29 | 2009-09-15 | Samsung Electronics Co., Ltd. | Image enhancement method using local illumination correction |
| JP5106978B2 (en) * | 2007-10-15 | 2012-12-26 | ジーイー・メディカル・システムズ・グローバル・テクノロジー・カンパニー・エルエルシー | X-ray CT system |
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| US4445226A (en) * | 1981-05-05 | 1984-04-24 | The Board Of Trustees Of The Leland Stanford Junior University | Multiple-energy X-ray subtraction imaging system |
| NL8105223A (en) * | 1981-11-18 | 1983-06-16 | Philips Nv | DEVICE FOR DIFFERENCE IMAGE DETERMINATION. |
| US4463375A (en) * | 1982-09-07 | 1984-07-31 | The Board Of Trustees Of The Leland Standford Junior University | Multiple-measurement noise-reducing system |
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- 1984-02-21 EP EP84301118A patent/EP0117154A3/en not_active Withdrawn
- 1984-02-21 IL IL71012A patent/IL71012A/en unknown
- 1984-02-22 JP JP59032254A patent/JPS59214433A/en active Pending
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| AU558490B2 (en) | 1987-01-29 |
| AU2473084A (en) | 1984-08-30 |
| IL71012A0 (en) | 1984-05-31 |
| EP0117154A2 (en) | 1984-08-29 |
| JPS59214433A (en) | 1984-12-04 |
| IL71012A (en) | 1988-11-15 |
| US4499493A (en) | 1985-02-12 |
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