Matched filter for x-ray hybrid subtraction

• US 4,542,459 A
• Filed: 11/26/1982
• Issued: 09/17/1985
• Est. Priority Date: 11/26/1982
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Riederer, Stephen J.
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): Woo, Louis
• Application Number:
  US06/444,953
• Time in Patent Office: 1,026 Days
• Field of Search: 364/414, 250/363 S, 378/99, 378/5, 378/901, 378/11, 378/12, 358/111
• US Class Current: 600/431
• CPC Class Codes: A61B 6/405 Source units specially adapted to modify characteristics of the beam during the data acquisition process A61B6/4021, A61B6/4035 take precedence
• CPC Class Codes: A61B 6/481 involving the use of contrast agents
• CPC Class Codes: A61B 6/504 for diagnosis of blood vessels, e.g. by angiography
• CPC Class Codes: H04N 5/3205 using subtraction imaging techniques
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

Low and high energy x-ray exposures are made before and after an injected x-ray contrast medium arrives at a blood vessel of interest. In one mode, low and high energy mask images are made and these are subtracted from subsequent low and high energy images, respectively, to yield temporal difference images. The projected intensities of the contrast medium with respect to time constitute matched filter coefficients by which the difference images are mulitplied. The matched filtered images are summed, multiplied by weighting factors and subtracted from each other to yield a final hybrid image. In an alternative mode, successive pairs of low and high energy images are subtracted to yield energy difference images. The difference images are subjected to matched filtering and summed and the results subtracted to produce a final hybrid image. The matched filter coefficients are selected so the dc component in the image signal is equal to zero so everything that is constant in the initial series of images cancels out by subtraction and only contrast medium signal remains.

Claims

1. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images, and including means operative to produce data representative of the respective images, the method including the following steps:

initializing a sequence of pairs of low and high x-ray energy exposures of the blood vessel during the pre-contrast period and continuing the exposures at least into the post-contrast and optionally into the after post-contrast periods to thereby provide data representative of the respective images resulting from the exposures, the data representative of an image in a pair resulting from one pre-contrast exposure at said low x-ray energy being designated the low energy mask image data and the data representative of an image resulting from one pre-contrast exposure in said pair at said high x-ray energy being designated the high energy mask image data,

after the low and high energy mask image data are acquired perform temporal subtraction constituting subtracting the low energy mask image data from the data for each of the ensuing low energy images and send the resulting series of low energy temporal difference images data to storage as they are produced and alternately subtracting the high energy mask image data from the data for each of the ensuing high energy images and send the resulting series of high energy temporal difference images data to storage as they are produced, said temporal subtraction causing data representative of structure that remains constant throughout the sequence of images to be cancelled and data representative of said contrast medium and data representative of structure that changes during said sequence remain,

access from storage the low energy temporal difference images data in succession and the high energy temporal difference images data in succession and multiply said successive low energy temporal difference images data by matched filter coefficients, respectively, and multiply said successive high energy temporal images data by said matched filter coefficients, respectively,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h), of the x-ray contrast medium at times (t) and registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast temporal difference images and any after-post-contrast temporal difference images are selected so that the sum of all of the coefficients equals zero,

multiply said low energy temporal difference images data by their respective matched filter coefficients and sum the results and multiply said high energy temporal difference images data by said coefficients, respectively, to thereby produce one set of data representative of a matched filtered low energy temporal difference image and another set of data representative of a matched filtered high energy temporal difference image,

multiply said one low energy temporal difference image data set by a constant (k_L) and said other high energy temporal image data set by a constant (k_H), said constants being so chosen that when said sets of multiplied image data are subtracted data representative of motion of a specific material are substantially cancelled, and

after the preceding multiplications, subtracting the resulting sets of data to yield a set of data representative of the image of the contrast medium in said blood vessel.

2. The method as in claim 1 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time over the period during which contrast medium is typically present in said vessel in one or more representative human bodies into which contrast medium has been injected for reaching the vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the low energy temporal difference images data and the high energy temporal difference images data representing images acquired at a corresponding time in said body being examined.

3. The method as in claim 1 wherein said coefficients are determined by displaying in sequence the series of temporal difference image data that has been stored and selecting a corresponding zone in the sucessive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images,

determining the intensities (h) at said zones in each of the post-contrast temporal difference images and converting said intensities (h) to match filter coefficients that are respectively proportional to intensities (h) at successive times (t) at which the temporal images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed low energy temporal difference image data and said multiplication of the accessed high energy temporal difference image data.

4. The method as in claim 3 wherein the intensities (h) at said zones are determined in each of the post-contrast temporal difference images, intensities (h) of zero are assumed for the pre-contrast and after-post-contrast temporal difference images, if any, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

5. The method as in any one of claims 1, 2, 3, or 4 wherein said coefficients applied to the respective low energy temporal difference images data and the respective high energy temporal difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the low energy and high energy temporal difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all of the coefficients equals zero to effect cancellation of body structure that remains constant in successive images.

6. The method as in claim 1 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of low energy temporal difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images, and also identifying any image in the sequence of displayed post-contrast difference images which exhibits artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast temporal difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the low energy temporal images data and said multiplication of the accessed high energy temporal difference images data but setting equal to zero the coefficients for multiplying the low energy temporal difference images that have been identified as containing artifacts and setting to zero the corresponding high energy temporal difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

7. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images and including means operative to produce data representative of the images, the method including the following steps:

initiating a sequence of pairs of low and high x-ray energy exposures of the blood vessel which sequence will extend through said pre-contrast period, at least into said post-contrast period and optionally into said after-post-contrast period to produce data representative of the image acquired for each exposure,

beginning with the first pair of low and high energy images data, weight these data so that when they are subtracted data representative of soft tissue will cancel out and data representative of bone and contrast medium will remain, then subtract these high and low energy images data in a pair and put the resulting difference image data in storage, and repeat this process of weighting the data for ensuing pairs of high and low energy images, subtracting these data and storing the resulting difference images for the entire exposure sequence so there will be in storage a series of energy difference images,

access from storage the series of energy difference image data in succession and multiply these data, respectively, by matched filter coefficients,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h) of the x-ray contrast medium at times (t) and registered in time with the post-contrast low energy images so that a selected one of the coefficients is applied to the corresponding post-contrast low energy image containing maximum contract medium, and the coefficients applied to the low energy pre-contrast and after-post-contrast images, if any, are selected so that the sum of all of the coefficients equals zero to thereby produce the equivalent of having performed temporal subtraction when the matched filtering step is performed, and

when said energy subtracted image data have been multiplied by their respective coefficients, sum the image data resulting from each multiplication to yield data representative of a single hybrid subtracted and matched filtered image that exhibits the contrast medium in the blood vessel.

8. The method as in claim 7 wherein said coefficients are determined by measuring the projected intensity of the contrast medium in a zone in said vessel versus time during the period contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected for reaching the vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the energy difference images data representing images acquired at a corresponding time in said body being examined.

9. The method as in claim 8 wherein the projected intensities (h) in said zone are determined in each of the post-contrast energy difference images, intensity values (h) of zero are assumed for the pre-contrast and any after-post-contrast energy difference images, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient value at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

10. The method as in claim 7 wherein said coefficients are determined by displaying in sequence the series of energy difference image data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images,

determining the projected intensity (h) in said zone in each of the post-contrast energy difference images and converting the intensities to match filter coefficients that are respectively porportional to (h) at successive times (t) at which the images at the different x-ray energies were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed energy difference images data.

11. The method as in any one of claims 7, 8, 9 or 10 wherein said coefficients applied to the respective energy difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the energy difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

12. The method as in claim 7 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of energy difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images, and also identifying any image in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast energy difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the energy difference images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the energy temporal difference images data but setting equal to zero the coefficients for multiplying the energy difference images that have been identified as containing artifacts and setting to zero the corresponding high energy difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

13. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in a vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images, and including means operative to produce data representative of the respective images, the method including the following steps:

initiating a sequence of low and high x-ray energy exposures of the blood vessel during the pre-contrast period and continuing the exposures through the post-contrast period and optionally into the after-post-contrast period to thereby provide data representative of the low energy images and high energy images resulting from the exposures with low and high energy x-rays, respectively,

integrating the data for a first predetermined number of low energy images in the sequence and storing the result of the integration in a first memory device as the low energy mask image, and also integrating the data for a first same predetermined number of high energy images in the sequence and storing the result of this integration in a second memory device as the high energy mask image,

integrating the data for every successive predetermined number of low energy images in the sequence in a third memory device and integrating the data for every successive predetermined number of high energy images in sequence in a fourth memory device, and every time an integration is completed in said third memory device subtract the low energy mask image data in said first memory device from the image data in said third memory device and send the resulting difference image to storage as a low energy temporal difference image, and every time an integration is completed in the fourth memory device subtract the high energy mask image data in said second memory device from the image data in the fourth memory device and send the resulting difference image to storage as a high energy temporal difference image, to thereby have a sequence of alternate low and high energy temporal difference images in storage in which body structures that remain, constant throughout the sequence are cancelled and in which the data representative of the contrast medium and body structures that move during acquiring the sequence of images remains,

access from storage the low energy temporal difference images data in succession and the high energy temporal difference images data in succession and multiply the successive low energy temporal difference images data by matched filter coefficients, respectively, and multiply the successive high energy temporal images data by said matched filter coefficients, respectively,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h) of the x-ray contrast medium at times (t) and registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast and after-post-contrast temporal difference images, if any, are selected so that the sum of all of the coefficients equals zero.

multiply said low energy temporal difference images data by their respective matched filter coefficients and sum the results and multiply said high energy temporal difference images data by said coefficients and sum the results, to thereby produce one set of data representative of a matched filtered low energy temporal difference image and another set of data representative of a matched filtered high energy temporal difference image,

multiply said one low energy temporal difference image data set by a constant (k_L) and said other high energy temporal image data set by a constant (k_H), said constants being so chosen that when said sets of multiplied image data are subtracted data representative of motion of a specific material in the body is cancelled, and

after the preceding multiplications, subtracting the resulting sets of data to yield a set of data representative of the image of the contrast medium in said blood vessel.

14. The method as in claim 13 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time over the period during which contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected for reaching the vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the low energy temporal images data and the high energy temporal difference images data representing images acquired at a corresponding time.

15. The method as in claim 13 wherein said coefficients are determined by displaying in sequence the series of temporal difference images data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images,

determining the intensities (h) at said zones in each of the post-contrast temporal difference images and converting said intensities (h) to match filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed low energy temporal difference image data and said multiplication of the accessed high energy temporal difference image data.

16. The method as in claim 13 wherein the intensities (h) at said zones are determined in each of the post-contrast temporal difference images, intensity values (h) of zero are assumed for the pre-contrast and after-post-contrast temporal difference images, if any, the average intensity (h) of the entire set of measured or assumed intensities is determined, and the matched filter coefficient at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

17. The method as in any one of claims 13, 14, 15 or 16 wherein said coefficients applied to the respective low energy temporal difference images data and the respective high energy temporal difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the low energy and high energy temporal difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all of the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

18. The method as in claim 13 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of low energy temporal difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images, and also identifying any images in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast temporal difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the low energy temporal images data and said multiplication of the accessed high energy temporal difference images data but setting equal to zero the coefficients for multiplying the low energy temporal difference images that have been identified as containing artifacts and setting to zero the corresponding high energy temporal difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

19. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to product x-ray images and means operative to produce data representative of the images, the method including the following steps:

initiating a sequence of pairs of low and high x-ray energy exposures of the blood vessel which sequence will extend through a pre-contrast period, at least into the post-contrast period and optionally into said after-post-contrast period to produce data representative of the image acquired for each exposure,

alternately integrate the data for a predetermined number of the successive low energy images and integrate the date for the same number of successive alternate high energy images and each time a pair of low and high energy integrated image data are completed weight the integrated low and high energy image data and then subtract the integrated low and high energy data to yield the data representing an energy difference image and send the difference image to storage and repeat the process of integrating successive series of low and high energy images and of weighting, of subtracting and of storing for the entire exposure sequence so as to have in storage a series of energy subtracted image data in which data representative of soft tissue is substantially cancelled out and data representative of bone and x-ray contrast medium remain,

access from storage the series of energy difference image data in succession and multiply these data, respectively, by matched filter coefficients,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h), of the x-ray contrast medium at times (t) and registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast and after post-contrast temporal difference images, if any, are selected so that the sum of all of the coefficients equals zero to thereby produce the equivalent of having performed temporal subtraction when the matched filtering step is performed, and

multiply said energy difference image data by their respective coefficients and sum the image data resulting from each multiplication to yield the data representative of a single hybrid subtracted and matched filtered image that exhibits substantially only the contrast medium in the blood vessel.

20. The method as in claim 19 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time over the period during which contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected for reaching the vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the energy difference images data representing images acquired at a corresponding time in said body being examined.

21. The method as in claim 19 wherein said coefficients are determined by displaying in sequence the series of energy difference image data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images,

determining the intensities (h) at said zones in each of the post-contrast energy difference images and converting said intensities (h) to match filter coefficients that are proportional to (h) at successive times (t) at which the energy difference images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed energy difference image data.

22. The method as in claim 21 wherein the intensities (h) at said zones are determined in each of the post-contrast energy difference images, intensities (h) of zero are assumed for the pre-contrast and after-post-contrast energy difference images, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

23. The method as in any of claims 19, 20, 21 or 22 wherein said coefficients applied to the respective energy difference images data acquired during times when the contrast medium was present in the vessel are postitive coefficients and the coefficients applied to the energy difference images acquired during the pre-contrast period and post-contrast period, if any, are negative coefficients such that the sum of all the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

24. The method as in claim 19 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of energy difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images, and also identifying any image in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast energy difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the energy difference images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the accessed energy difference images data but setting equal to zero the coefficients for multiplying the energy difference images that have been identified as containing artifacts and setting to zero the corresponding energy difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

25. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images, and including means operative to produce data representative of the respective images, the method including the following steps:

initiating a sequence of pairs of low and high x-ray energy exposures of said blood vessel during the pre-contrast period and continuing the exposures into the post-contrast and optionally into the after-post-contrast periods,

as each low and high energy image is acquired store the data sets representative of the images for subsequent sequential access from storage,

use one or an integration of a predetermined number of data sets representative of pre-contrast low energy images as a low energy mask image, and use one or an integration of the same predetermined number of pre-contrast high energy images, respectively, as a high energy mask image,

subtract the low energy mask image data set from each subsequent one or integration of low energy images data sets, respectively, and alternately subtract the high energy mask image data set from each subsequent one or integration of high energy data sets, respectively, for the entire exposure sequence to thereby yield an alternating series of low and high temporal difference images in which data representing structures that remain constant through the sequence of images are cancelled and letting data representative of said contrast medium and representative of structures that change during acquisition of the series of images remain,

multiply the successive low energy temporal difference images data by matched filter coefficients, respectively, and multiply the successive high energy temporal images data by matched filter coefficients, respectively,

said matched filter coefficients by which said images are multiplied being proportional to the projected intensity, (h) of the x-ray contrast medium at times (t) and substantially registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast and after-post-contrast temporal difference images, if any, are selected so that the sum of all of the coefficients equals zero,

multiply said low energy temporal difference images data by the respective matched filter coefficients and sum the results and multiply said high energy temporal difference images data by said coefficients and sum the results, to thereby produce one set of data representative of a matched filtered low energy temporal difference image and another set of data representative of a matched filtered high energy temporal difference image,

multiply said one low energy temporal difference image data set by a constant (k_L) and said other high energy temporal image data set by a constant (k_H), said constants being so chosen that when said sets of multiplied image data are subtracted data representative of motion of a specific material in the body are cancelled, and

after the preceding multiplications, subtracting the resulting sets of data to yield a set of data representative of the image of the contrast medium in said blood vessel.

26. The method as in claim 25 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time over the interval during which contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected for reaching the vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the low energy temporal difference images data and the high energy temporal difference images data representing images acquired at a corresponding time.

27. The method as in claim 25 wherein said coefficients are determined by displaying in sequence the series of temporal difference images data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images,

determining the intensities (h) at said zones in each of the post-contrast temporal difference images and converting said intensities (h) to match filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed low energy temporal difference image data and said multiplication of the accessed high energy temporal difference image data.

28. The method as in claim 27 wherein the intensities (h) at said zones are determined in each of the post-contrast temporal difference images, intensity values (h) of zero are assumed for the pre-contrast and after-post-contrast temporal difference images, if any, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient value at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

29. The method as in any one of claims 25, 26, 27 or 28 wherein said coefficients applied to the respective low energy temporal difference images data and the respective high energy temporal difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the low energy and high energy temporal difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all of the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

30. The method as in claim 25 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of low energy temporal difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images, and also identifying any in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast temporal difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the low energy temporal images data and said multiplication of the accessed high energy temporal difference images data but setting equal to zero the coefficients for multiplying the low energy temporal difference images that have been identified as containing artifacts and setting to zero the corresponding high energy temporal difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

31. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images and including means operative to produce data representative of the images, the method including the following steps:

initiating a sequence of low an high x-ray energy exposures of the blood vessel which sequence will extend through a pre-contrast period, into the post-contrast period and optionally into an after-post-contrast period to produce data sets representative of the images acquired for each exposure, and put the sequence of low and high energy image data sets in storage as they are acquired,

access from storage and take pairs of low and high energy image data where each pair includes one of a low energy image data set or an integration of a predetermined number of successive low energy image data sets and each pair also includes one of a corresponding high energy image data set or a corresponding integration of the same predetermined number of successive high energy image data sets, respectively, and weight these data in each pair so that when the low energy data and high energy data in a pair are subtracted, energy subtracted image data will result in which data representative of soft tissue will substantially cancel out and data representative of bone and contrast medium will remain,

repeat the steps of taking pairs of low and high energy image data, of weighting the data and of subtracting the pairs of data for the entire exposure sequence to produce a sequence of energy subtracted images,

multiply these data by respective matched filter coefficients,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h) of the x-ray contrast medium at times (t) and registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast temporal difference images and after-post-contrast temporal difference images are selected so that the sum of all of the coefficients equals zero to thereby produce the equivalent of having performed temporal subtraction when the matched filtering step is performed, and

multiply said energy difference images data by their respective coefficients and sum the image data resulting from each multiplication to yield the data representative of a single hybrid subtracted and matched filtered image that exhibits substantially only the contrast medium in the blood vessel.

32. The method as in claim 31 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time over the period during which contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected, for reaching a vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the energy difference images data representing images acquired at a corresponding time.

33. The method as in claim 31 wherein said coefficients are determined by displaying in sequence the series of energy difference image data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images,

determining the intensities (h) at said zones in each of the post-contrast energy difference images and converting said intensities (h) to match filter coefficients that are respectively proportional to (h) at successive times (t) at which the energy images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed energy difference images data.

34. The method as in claim 33 wherein the intensities (h) at said zones are determined in each of the post-contrast energy difference images, intensities (h) of zero are assumed for the pre-contrast and after-post-contrast energy difference images, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient value at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

35. The method as in any one of claims 32, 33 or 34 wherein said coefficients applied to the respective energy difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the energy difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

36. The method as in claim 31 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of energy difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed energy difference images, and also identifying any image in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast energy difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the energy difference images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the energy difference images data but setting equal to zero the coefficients for multiplying the energy difference images that have been identified as containing artifacts and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

37. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images, the method including the following steps:

initiating a sequence of low and high x-ray energy exposures of the blood vessel during the pre-contrast period and continuing the exposures through the post-contrast and optionally into the after-post-contrast periods to thereby provide data representative of the images resulting from the exposures, the data representative of an image resulting from one pre-contrast exposure at said low x-ray energy being designated the low energy mask image data and the data resulting from a pre-contrast exposure at said high x-ray energy being designated the high energy mask image data,

after the low and high energy mask image data are acquired subtract the low energy mask image data from the data for each of the ensuing low energy images and send the resulting series of low energy temporal difference image data to storage as they are produced and alternately subtract the high energy mask image data from the data for each of the ensuing high energy images and send the resulting series of high energy temporal difference image data to storage as they are produced, said subtraction causing body structure that remain constant throughout the sequence of images to be cancelled and letting data representative of said contrast medium and body structure that changes remain,

access from storage successive pairs of low energy and high energy image data and weight the data comprising each pair and then subtract the data for one image in the pair from the other to yield a series of energy subtracted image data sets wherein substantially only data representative of motion of a specific structure in the body are cancelled,

multiply the energy subtracted images data by matched filter coefficients,

said matched filter coefficients by which said images data are multiplied being proportional to the projected intensity, (h) of the x-ray contrast medium at times (t) and registered in time with the post-contrast temporal difference images so that a selected one of the coefficients is applied to the corresponding post-contrast temporal difference image containing maximum contrast medium, and the coefficients applied to the pre-contrast temporal difference images and after-post-contrast temporal difference images are selected so that the sum of all of the coefficients equals zero to thereby produce the equivalent of having performed temporal subtraction when the matched filtering step is performed, and

multiply said energy difference image data by their respective coefficients and sum the image data resulting from each multiplication to yield the data representative of a single hybrid subtracted and matched filtered image that exhibits only the contrast medium in the blood vessel.

38. The method as in claim 37 wherein said coefficients are determined by measuring the projected intensity of the contrast medium at a zone in said vessel versus time during the time in which contrast medium is typically present in the vessel of one or more representative human bodies into which contrast medium has been injected for reaching a vessel corresponding to the vessel of interest in said body being examined, then using coefficients that are proportional to the intensity at any time to multiply the low energy temporal images data and the high energy temporal difference images data representing images acquired at a corresponding time in said body being examined.

39. The method as in claim 37 wherein said coefficients are determined by displaying in sequence the series of temporal difference image data that has been stored and selecting a corresponding zone in the successive post-contrast images obtained while said contrast medium was flowing in said vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images,

determining the intensities (h) at said zones in each of the post-contrast temporal difference images and converting said intensities (h) to match filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired, and

storing said coefficients and accessing them in sequence for said multiplication of the accessed low energy temporal difference image data and said multiplication of the accessed high energy temporal difference image data.

40. The method as in claim 39 wherein the intensities (h) at said zones are determined in each of the post-contrast temporal difference images, intensities (h) of zero are assumed for the pre-contrast and after-post-contrast temporal difference images, the average intensity (h) of the entire set of measured or assumed intensities (h) is determined, and the matched filter coefficient value at a time (t) is set proportional to the difference between the intensity (h) measured or assumed at that time (t) and the average intensity (h).

41. The method as in any one of claims 37, 38, 39 or 40 wherein said coefficients applied to the respective low energy temporal difference images data and the respective high energy temporal difference images data acquired during times when the contrast medium was present in the vessel are positive coefficients and the coefficients applied to the low energy and high energy temporal difference images acquired during the pre-contrast period and post-contrast period are negative coefficients such that the sum of all the coefficients equals zero to effect cancellation of any body structure that remains constant in successive images.

42. The method as in claim 37 wherein:

said matched filter coefficients are determined by displaying on a television monitor in sequence the series of low energy temporal difference image data that have been stored and selecting a corresponding zone in successive post-contrast images obtained when said contrast medium was flowing in the vessel which zone is representative of the projected contrast medium intensity in the respective displayed temporal difference images, and also identifying any image in the sequence of displayed post-contrast difference images which exhibit artifacts, such as artifacts due to body motion during an x-ray exposure, of such significance as to justify discarding these images,

determining the intensities (h) at said zones in the post-contrast temporal difference images and converting said intensities (h) to matched filter coefficients that are respectively proportional to (h) at successive times (t) at which the temporal images were acquired,

storing said coefficients and accessing them in sequence for said multiplication of the low energy temporal images data and said multiplication of the accessed high energy temporal difference images data but setting equal to zero the coefficients for multiplying the low energy temporal difference images that have been identified as containing artifacts and setting to zero the corresponding high energy temporal difference images, and then assigning negative values to some of the coefficients so that all of the coefficients add up to zero.

43. A method of imaging a blood vessel in a body where the period before a bolus of x-ray contrast medium arrives in the vessel is designated the pre-contrast period, the period during which contrast medium is flowing through the vessel is designated the post-contrast period and the period following the latter when the medium has left the vessel is designated the after-post-contrast period, and where an x-ray source, when energized, projects a beam through said body to produce x-ray images, and including means operative to produce data representative of the respective images, the method including the following steps:

initiating a sequence of closely successive pairs of low and high x-ray energy exposures of the blood vessel during the pre-contrast period and continuing the exposures through the post-contrast and after-post-contrast periods to thereby provide data representative of the images resulting from the exposures,

multiply the data representative of each low energy image in a pair by a weighting factor (k₁) and multiply the data representative of each high energy image in the same pair by a weighting factor (k₂), and perform the multiplications in the order in which the images are acquired, said weighting factors being chosen so that when the weighted data for the images in each pair are subtracted the data representative of soft tissue will be cancelled and the data representative of bone and the x-ray contrast medium will remain,

subtract the weighted data for one of the images in each pair from the weighted data for the other to thereby yield a series of energy subtracted images data,

input the series of energy subtracted images data simultaneously to first and second recursive filter circuits which each have different time constants (K and K'"'"') and each of which has a dc response equal to 1 so that when the results of recursive filtering in the one circuit are subtracted from the results in the other the dc components of the image data will cancel to thereby achieve the equivalent of temporal image subtraction which is characterized by canceling data that is representative of body structure that is constant in the sequence of images and letting the data representative of the contrast medium remain,

finally subtract the results of recursive filtering in one circuit from the results in the other to yield a single difference image data set for an image that can be displayed.