Subtraction fluoroscopy method and apparatus

• US 4,393,402 A
• Filed: 06/08/1981
• Issued: 07/12/1983
• Est. Priority Date: 06/08/1981
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: DallaPiazza, Dennis G., Keyes, Gary S., Georges, Jean-Pierre J.
• Primary Examiner(s): Orsino, Jr., Joseph A.
• Application Number:
  US06/271,314
• Time in Patent Office: 764 Days
• Field of Search: 358/111, 358/105, 358/135, 358/136, 250/416 TV
• US Class Current: 378/98.11
• CPC Class Codes: H04N 5/3205 using subtraction imaging techniques

Abstract

Image frames produced consecutively with x-ray beams having different spectral bands or average energy levels are converted to analog video signals and then to digital data. The digital data for an image at one energy is stored in a memory and the ensuing data for the next image is subtracted from the stored data in an alternate or cyclic fashion. The resulting difference data is converted to analog video signals and displayed on a television monitor at standard frame rates. The same system can be used to store a digitized data mask frame and the digital data for ensuing frames can be subtracted from the mask. In some embodiments a buffer is used to allow removal of data from memory without having the data from a preceding frame overwritten by ensuing frames. Other embodiments use more than one memory and, in some cases, buffers to allow manipulating the data so snapshot, integrated and continuous or real-time subtraction images can be displayed individually on a single monitor or jointly on additional monitors.

Claims

1. A method of producing visible images by integrating difference images that are obtained by subtracting images acquired in pairs that result from exposing a subject to alternate low and high energy x-ray beams including the steps of:

projecting an x-ray beam having one energy and an x-ray beam having another energy through a subject in quick succession to produce a sequential pair of x-ray images,

converting the x-ray images in sequence to television frames comprised of lines of analog video signals,

converting said analog video signals to digital pixel signals each representing a picture element in an image frame,

storing the digital pixel signals for a frame at one energy in one digital memory and transferring the pixel signals out of said one memory in phase with corresponding digital pixel signals for the succeeding current frame at the other energy while simultaneously storing the pixel signals for the current frame in another memory and concurrently combining the pixel signals for the stored and current frames to yield difference digital pixel signals for a frame representative of the difference between the consecutive x-ray images,

next transferring the digital pixel signals for the frame at said other energy out of the second memory in phase with corresponding digital pixel signals for the current frame at the one energy while simultaneously storing the signals for the last-mentioned current frame at the one energy in the one memory and concurrently combining the pixel signals for the stored and current frames to yield difference digital pixel signals for a frame representative of the difference between the consecutive low and high energy x-ray images,

feeding the difference digital pixel signals for the first subtracted image in a series to be integrated to a third digital memory as the difference image signals are produced,

transferring the digital pixel signals out of said third memory for being combined with corresponding difference digital signals for the next frame and feeding back the combined signals to the locations in the third memory out of which corresponding difference digital pixel signals were transferred, and

then converting the integrated digital pixel signals in the third memory to analog video signals for displaying the integrated difference image.

2. A method of producing visible images representative of the difference between a pair or a succession of pairs of x-ray images and for displaying the difference images in the continuous imaging mode and optionally in one or the other of the serial and integration modes, comprising the steps of:

projecting an x-ray beam having one energy and an x-ray beam having another energy through a subject in quick succession to produce a sequential pair of x-ray images,

converting the x-ray images in sequence to television frames comprised of lines of analog video signals,

converting said analog video signals to digital pixel signals each representing a picture element in an image frame,

for the continuous imaging mode repeatedly storing the digital pixel signals for a frame at one energy in a first digital memory and following completion of said storage transferring a first line and succeeding lines of stored pixel signals to a buffer and transferring the pixel signals for said lines successively out of said buffer in phase with corresponding pixel signals for the succeeding current image frame at the other energy and concurrently feeding the pixel signals for the other energy image into said memory in place of the signals for the preceding frame and continuously combining the digital pixel signals for the preceding frame as they are transferred out of the buffer in phase with corresponding digital pixel signals for the current frame to yield difference digital pixel signals for a frame representative of the difference between the consecutive x-ray images in each pair,

using a look-up table to adjust the amplification and offset of the difference digital pixel signals representative of the continuous mode difference images thus produced to the bit range of a first digital-to-analog converter,

then using said first digital-to-analog converter to convert said successively produced difference digital pixel signals to analog video signals, and

using said analog video signals to control a first television monitor to display the successive difference images, and

for imaging in said serial mode, storing any selected one of the difference digital signals for a frame in a second memory for a selected interval, using a second look-up table to adjust the amplification and offset of the selected and stored difference digital pixel signals to the bit range of a second digital-to-analog converter, then using said second digital-to-analog converter to convert said selected difference digital pixel signals for the frame to convert said signals to analog video signals, and using said analog video signals to control a second television monitor to display the selected image continuously for the duration of said interval or until other difference digital signals for a frame are selected and replace the signals previously stored in said second memory, and

for imaging in said integration mode alternatively to said serial mode, feeding said difference digital pixel signals for a predetermined number of image frames to be integrated to said second digital memory as the signals are produced, and when said number are integrated in said memory using said second look-up table to alter the amplification and offset of the difference digital pixel signals representative of the integrated difference image frame to the available bit range of said second digital-to-analog converter, then using said second digital-to-analog converter to convert the integrated image frame digital pixel signals to analog video signals for controlling said second television monitor to display the image.

3. Apparatus for producing visible images representative of the difference between x-ray images comprising:

an x-ray source and means for controlling said source to project x-ray beams having different energies consecutively through a subject,

means including video camera means for converting the images produced by the beams to lines of analog video signals composing the frames corresponding to the successive different energy images, respectively,

analog-to-digital converter means for converting the analog video signals for the different energy frames in succession to lines of digital pixel signals corresponding to the picture elements in the respective images,

processor means including a digital signal output, a plurality of digital signal inputs and means for subtracting digital signals,

bus means for coupling the digital pixel signals for the current image frame directly to an input of said processor means,

first and second digital memories each having sufficient capacity to store at least the digital signals representative of a single image frame, said memories having input and output means,

first and second buffers for coupling the output means of the respective memories to inputs of said processor means,

a wrap around bus for feedback of the digital signals for difference images from the output of said processor means to the input means of the memories,

control means for controlling said apparatus to operate in a selected mode including a continuous difference imaging mode, a serial difference imaging mode and an integrated difference imaging mode,

for said continuous difference imaging mode said control means causing the lines of digital pixel signals for a preceding image at one energy to be written into one memory and to transfer the first line of signals to its associated buffer during the retrace time of said video camera means and then to transfer following lines of pixel signals in sequence to said buffer so they are input to said processor means in phase with corresponding digital pixel signals resulting from the current image frame at the other energy on said bus means, for said processor means to subtract the pixel signals for the different energy images and provide on its output means lines of digital difference pixel signals,

digital-to-analog converter means and means for coupling said difference signals from said processor to said converter, said converter being operative to convert said digital difference signals to analog video signals, and

television means responsive to the last-named analog video signals by displaying visible images representative of the difference between the x-ray images at the different energies, said images being displayed at the rate at which pairs of different energy x-ray images are produced, and

for said integrated imaging mode said control means causing said difference image signals from said processor to be fed back to the other of said memories and for the first line of said digital difference signals to the buffer associated with said other memory during said retrace time,

said difference signals produced by said processor by adding the pixel signals for the different energy frames being combined with the signals stored in said other memory and fed back from said processor to said other memory for a predetermined number of frames to effect said integration and then said pixel signals from said other memory being coupled to said digital-to-analog converter to effect display of the integrated difference image.

4. The apparatus set forth in claim 3 including:

another digital-to-analog converter means and means coupling the output means of said processor to said other digital-to-analog converter and it being operative to convert digital pixel signals to analog video signals,

said control means being operative to cause the digital pixel signals for a selected one of said serial or integrated difference images to be input to said other digital-to-analog converter,

another television means responsive to analog signals from said other converter by displaying visible images corresponding to the serial or integrated image selected.

5. Apparatus for producing visible images representative of the difference between x-ray images comprising:

an x-ray source and means for controlling said source to project x-ray beams having different energies consecutively through a subject,

means including video camera means for converting the images produced by the beams to lines of analog video signals composing the frames corresponding to the successive different energy frames, respectively,

analog-to-digital converter means for converting the analog video signals for the different energy frames in succession to lines of digital pixel signals corresponding to the picture elements in the respective images,

processor means including a digital signal output, a plurality of digital signal inputs and means for subtracting digital signals,

bus means for coupling the digital pixel signals for the current image frame directly to an input of said processor means,

first and second digital memories each having sufficient capacity to store at least the digital signals representative of a single image frame, said memories having input and output means,

first and second buffers for coupling the output means of the respective memories to inputs of said processor means,

a wrap around bus for feedback of the digital signals for difference images from the output of said processor means to the input means of the memories,

control means for controlling said apparatus to operate in a selected mode including a continuous difference imaging mode, a serial difference imaging mode and an integrated difference imaging mode,

for said continuous difference imaging mode said control means causing the lines of digital pixel signals for a preceding image at one energy to be written into one memory and to transfer the first line of signals to its associated buffer during the retrace time of said video camera means and then to transfer following lines of pixel signals in sequence to said buffer so they are input to said processor means in phase with corresponding digital pixel signals resulting from the current image frame at the other energy on said bus means, for said processor means to subtract the pixel signals for the different energy images and provide on its output means lines of digital difference pixel signals,

digital-to-analog converter means and means for coupling said difference signals from said processor to said converter, said converter being operative to convert said digital difference signals to analog video signals, and

television means responsive to the last-named analog video signals by displaying visible images representative of the difference between x-ray images at the different energies, said images being displayed at the rate at which pairs of different energy x-ray images are produced,

for said integrated imaging mode said control means causing said difference image signals from said processor to be fed back to the other of said memories and for the first line of said digital difference signals to the buffer associated with said other memory during said retrace time,

said difference signals produced by said processor by adding the pixel signals for the different energy frames being combined with the signals stored in said other memory and fed back from said processor to said other memory for a predetermined number of frames to effect said integration and then said pixel signals from said other memory being coupled to said digital-to-analog converter to effect display of the integrated difference image, and including look-up table means having input means coupled to the output means of the processor and output means coupled to said digital-to-analog converter, said look-up table means being operative to adjust the difference digital pixel signals from the processor to fill the dynamic range of the converter and to correct for negative values in the difference image signals.

6. Apparatus for producing visible images representative of the difference between x-ray images comprising:

an x-ray source and means for controlling said source to project x-ray beams having different energies consecutively through a subject,

means including video camera means for converting the images produced by the beams to lines of analog video signals composing the frames corresponding to the successive different energy images, respectively,

analog-to-digital converter means for converting the analog video signals for the different energy frames in succession to lines of digital pixel signals corresponding to the picture elements in the respective images,

processor means including a digital signal output means, a plurality of digital signal inputs and means for subtracting digital signals,

bus means for coupling the digital pixel signals for the current image frame directly to an input of said processor means,

first, second and third digital memories each having the capacity to store at least the digital signals representative of a single image frame, said memories having input and output means, the respective output means being coupled to the inputs of the processor,

a wrap around bus for feedback of digital difference image signals from the output means of the processor to the input means of the first memory,

control means operative to cause the lines of digital pixel signals for an image at the higher of the energies to be cyclically written into one of the memories and to be read out in phase with the digital pixel signals on said bus means for an ensuing image at the lower of the energies while said signals for the lower energy image are also being written into the second memory, and to cause the digital pixel signals for the next ensuing higher energy image to be written into said first memory again while said signals for the preceding lower energy image in said second memory are read out in phase with the signals for the said next ensuing higher energy image on said bus means, the in-phase pairs of signals comprised of signals read out from a first or second memory and signals supplied on said bus means being subtracted in said processor means to provide digital difference signals to the output means of the processor representative of the difference between images corresponding with a successive pair of different energy x-ray images,

first digital-to-analog converter means having input and output means and means for coupling said difference signals from the output means of the processor to the input means of the converter, said converter means being operative to convert said digital difference image signals to analog video difference signals, and

television means responsive to said analog difference signals by displaying visible images representative of the difference between the x-ray images at the different energies at the rate of which pairs of different energy images are produced,

said control means being operable to effect display of a series of images spaced apart in time by causing said digital difference signals for a difference image frame to be transmitted by way of said wrap around bus to said input means of the third digital memory for storage therein for a predetermined interval,

another digital-to-analog converter means having input and output means and means for coupling said digital difference image signals from said third memory means to the input of said other converter means, said converter means being operative to convert said signals to analog video difference signals,

another television means responsive to said last-named analog signals by displaying a visible image representative of the difference between the x-ray images at the different energies for whose signals were stored in said third memory, said image being displayable until the difference image signals corresponding to another pair of x-ray images at the different energies is stored in said third memory for being displayed.

7. The apparatus set forth in claim 6 wherein said control means is operable to effect display integrated difference images by causing the digital difference signals for the first in a succession of frames to be coupled from the output means of said processor to the input means of said third memory for storage therein, said control means being further operable to cause said processor means to combine the digital difference signals for additional frames cyclically during a predetermined interval with corresponding digital difference signals accumulated in said third memory and to feed back said combined signals from the output means of said processor to the input means of said third memory to thereby enable display on said other display means of an integrated difference image at the end of said interval.

8. The apparatus set forth in any of claims 6 or 7 wherein the respective means for coupling the output means of said processor means to the input means of a digital-to-analog converter includes look-up table means for adjusting the digital pixel signals to fill the dynamic range of the converter.