Scanned x-ray selective imaging system

• US 4,686,695 A
• Filed: 11/17/1980
• Issued: 08/11/1987
• Est. Priority Date: 02/05/1979
• Status: Expired due to Term

• Current Assignee: CooperSurgical Acquisition Corp. (The Cooper Cos., Inc.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Macovski, Albert
• Primary Examiner(s): Church, Craig E.
• Application Number:
  US06/207,351
• Time in Patent Office: 2,458 Days
• Field of Search: 378/5, 378/19, 378/146, 378/99, 378/100, 378/111
• US Class Current: 378/146
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4035 the source being combined with a filter or grating
• 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 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/4291 the detector being combined with a grid or grating
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: G01N 23/043 using fluoroscopic examination, with visual observation or video transmission of fluoroscopic images
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating
• CPC Class Codes: G06T 2211/408 Dual energy
• CPC Class Codes: G06T 2211/412 Dynamic
• CPC Class Codes: H04N 5/3205 using subtraction imaging techniques
• CPC Class Codes: H05G 1/60 Circuit arrangements for obtaining a series of X-ray photographs or for X-ray cinematography

Abstract

An x-ray beam is scanned through a sequence of subsections of a volume. At each position the x-ray transmission is measured at two energies. The resultant transmission signals are processed to produce a signal representing the projected amount of a specific material in the volume. The two energies are chosen so that the mass attenuation coefficients of bone and soft tissue are comparable to each other.

Claims

1. In a method for producing a low-scatter two-dimensional projection image of a specific material within a volume of the body the steps of:

forming an x-ray beam from the x-rays emitted from an x-ray source which irradiates a subsection of the volume and a corresponding subsection of the two-dimensional projection image;

collimating the x-ray beam emerging from the volume;

measuring the x-ray transmission through each subsection of the volume at two energy spectra using an integrating detector which receives transmitted x-rays substantially only from the extent of the collimated x-ray beam whereby most scattered radiation is eliminated;

synchronously scanning the x-ray beam and integrating detector with respect to the volume over the entire two-dimensional projection image;

processing the measurements at the two energy spectra to produce a processed two-dimensional projection signal representing the projected amount of the specific material in the volume; and

displaying the processed projection signal to provide a two-dimensional projection image of the specific material in the volume.

2. The method as in claim 1 wherein the step of measuring the x-ray transmission at two energy spectra includes the step of varying the energy of the scanning x-ray beam at each subsection.

3. The method as in claim 1 wherein the step of measuring the x-ray transmission at two energy spectra includes the step of detecting the transmitted x-rays using an energy-sensitive detector.

4. The method as in claim 1 where the material being imaged is iodine and the step of measuring the x-ray transmission of the volume at two energy spectra includes the step of measuring the x-ray transmission at a first energy at which the mass attenuation coefficients of bone and soft tissue are substantially equal and the step of measuring the x-ray transmission at a second energy at which the mass attenuation coefficients of bone and soft tissue are substantially equal and the mass attenuation coefficient of iodine is substantially different than that of the first measurement.

5. The method as in claim 1 including the step of measuring the x-ray transmission of each subsection of the body at a third energy spectra and the step of processing this measurement along with those of the two energy spectra to remove the effects of bone.

6. The method as in claim 5 where two of the energy spectra are above the iodine K edge energy and the third energy spectra is below the iodine K edge energy.

7. In a method for providing low-scatter multiple energy two-dimensional x-ray transmission measurements of a volume the steps of:

collimating the emitted beam from the x-ray source into a planar fan beam;

scanning the fan beam through the volume in a direction normal to the plane of the fan beam;

collimating the fan beam emerging from the volume;

synchronously scanning a detector array which substantially intercepts only the collimated planar fan beam emerging from the volume whereby most of the scattered radiation is eliminated; and

measuring the x-ray transmission at each position of the scanning planar beam at two energy spectra using the detector array.

8. In a method for providing low-scatter two-dimensional projection images of a specific material in regions of the body containing moving structures the steps of:

collimating the emitted beam from an x-ray source into a planar fan beam which spans a subsection of the body;

scanning the fan beam through the volume in a direction normal to the plane of the fan beam at a speed such that the time spent at each subsection involves substantially no motion of the moving structures;

collimating the fan beam emerging from the volume;

synchronously scanning a detector array which substantially intercepts only the extent of the collimated planar fan beam emerging from the volume whereby most scattered radiation is eliminated;

measuring the x-ray transmission at each position of the scanning beam at two energy spectra;

processing the measurements to provide a processed two-dimensional projection signal representing the projected amount of the specific material in the volume; and

displaying the processed two-dimensional projection signal to provide a two-dimensional image of the specific material in the volume.

9. In a method for providing isolated two-dimensional projection images of bone and soft tissue within a volume the steps of:

collimating the emitted beam from an x-ray source into a planar fan beam;

scanning the fan beam through the volume in a direction substantially normal to the plane of the fan beam;

collimating the fan beam emerging from the volume;

synchronously scanning a detector array which substantially intercepts only the extent of the collimated planar fan beam emerging from the volume whereby most scattered radiation is eliminated;

measuring the x-ray transmission, using the detector array, at two energy spectra where the relative mass attenuation coefficient of bone and soft tissue are substantially different at each spectra;

processing the measurements to provide two-dimensional projection signals representing the projected amounts of bone and soft tissue; and

displaying one of the processed projection signals.

10. Apparatus for providing a two-dimensional projection image of a specific material within a volume of the body comprising:

an x-ray tube source producing x-rays which are collimated into an x-ray beam which is projected through a subsection of the volume onto a subsection of the two-dimensional image;

collimation means for receiving and collimating the x-ray beam emerging from the volume,

means for sequentially scanning the collimated x-ray beam with respect to the volume through each subsection of the volume and the two-dimensional image;

means for measuring the transmission of the x-ray beam through the volume at two energy spectra using an integrating detector which intercepts substantially only the extent of the x-ray beam whereby most scatter is eliminated;

means for processing the transmission measurements to produce a processed projection signal representing the projected amount of the specific material in the volume; and

means for displaying the processed projection signal to produce a two-dimensional projection image of the specific material.

11. Apparatus as recited in claim 10 wherein the means for measuring the transmission of the x-ray beam through the volume at two energy spectra includes means for sequentially changing the energy spectrum of the x-ray tube source.

12. Apparatus as recited in claim 11 wherein the means for sequentially changing the energy spectrum of the x-ray tube source includes changing the anode to cathode voltage of the x-ray tube.

13. Apparatus as recited in claim 12 wherein the means for changing the anode to cathode voltage of the x-ray tube includes the application of a sinusoidally varying voltage component between the anode and the cathode of the x-ray tube.

14. Apparatus as recited in claim 12 wherein the x-ray tube has a control grid and the means for changing the anode to cathode voltage of the x-ray tube includes applying a time varying voltage between anode and cathode and pulsing the control grid at times corresponding to different anode to cathode voltages.

15. Apparatus as recited in claim 11 wherein the means for sequentially changing the energy of the x-ray tube source includes means for sequentially inserting x-ray filter material in front of the x-ray tube source.

16. Apparatus as recited in claim 10 where the integrating detector is energy sensitive and the means for measuring the transmission of the x-ray beam through the volume at two energy spectra includes means for providing separate detector outputs at the two energy spectra.

17. Apparatus as recited in claim 16 wherein the energy sensitive detector comprises two sections including a first section receiving the x-ray beam after it leaves the volume and a second section receiving the x-ray beam after it passes through the first section and including means for measuring the absorbed energy in each section.

18. Apparatus as recited in claims 10, 11, or 16 wherein the x-ray beam is a pencil beam, the subsection of the volume is the projection of the pencil beam and the scanning means includes means for moving the pencil beam through a two-dimensional raster scan.

19. Apparatus as recited in claim 18 including a scanning aperture moving synchronously with the scanned pencil beam and positioned between the volume and the means for measuring the transmission of the x-ray beam whereby scattered x-rays are further prevented from being detected.

20. Apparatus as recited in claims 10, 11, or 16 wherein the x-ray beam is an array of pencil beams, the subsection of the volume is the sum of the projections of the array of pencil beams and the scanning means includes means for moving the array of pencil beams through individual raster scans which combine to scan the entire volume.

21. Apparatus as recited in claim 20 including a multiple scanning aperture moving synchronously with the array of pencil beams and positioned between the volume and the means for measuring the transmission of the x-ray beam whereby scattered x-rays are further prevented from being detected.

22. Apparatus as recited in claim 20 where the integrating detector includes an array of detectors each detecting one of the array of pencil beams.

23. Apparatus as recited in claims 10,11,12,13,14,15,16 or 17 where the x-ray beam is a sheet beam, the subsection of the volume is a thin planar section and the scanning means includes means for translating the sheet beam in a direction substantially normal to the plane of the beam.

24. Apparatus as recited in claim 23 where the integrating detector is a linear detector array positioned to detect the transmitted sheet beam and produce an array of measurements representing the transmission of the sheet beam through the volume at two energy spectra.

25. Apparatus as recited in claim 24 including a sheet beam collimator positioned between the linear detector array and the volume which allows passage of the transmitted sheet beam to the linear detector array and further prevents scattered radiation from reaching the detector array.

26. Apparatus as recited in claim 23 including a slit collimator between the x-ray source and the volume for producing the sheet beam and where the scanning means includes means for moving the slit collimator with respect to the x-ray source in a direction normal to the slit.

27. Apparatus as recited in claim 26 where the scanning means further includes means for sequentially oscillating the slit collimator in a direction normal to the slit whereby a sequence of projection images are provided for dynamic studies.

28. Apparatus as recited in claims 10,11,12,13,14,15,16 or 17 wherein the x-ray beam is a plurality of sheet beams and where the integrating detector is a plurality of linear detector arrays with each detector array detecting the transmitted radiation from each sheet beam.

29. Apparatus as recited in claim 28 including a plurality of sheet beam collimators positioned between the linear detector array and the volume which allows passage of each of the plurality of sheet beams and further prevents scattered radiation from reaching each of the linear detector arrays.

30. Apparatus as recited in claims 10, 11, or 16 further comprising:

a second x-ray source producing a second x-ray beam which is projected through a subsection of the volume of the body at a second angle different than that of the first x-ray source;

means for sequentially scanning the second x-ray beam through each subsection of the volume;

means for measuring the transmission of the second x-ray beam through the volume at the same two energy spectra as that of the first x-ray beam;

means for processing the transmission measurements to produce a second processed projection signal representing the projected amount of the specific material in the volume at the second angle; and

means for displaying the second processed projection signal.

31. Apparatus as recited in claims 10, 11, or 16 where the volume of the body contains bone and soft tissue, the specific material is an iodinated contrast agent and the two energy spectra used for measuring the transmission through the body are in regions such that the mass attenuation coefficients of bone and soft tissue are substantially equal to each other at each energy spectrum and the mass attenuation coefficients of iodine are substantially different at each energy spectrum whereby the iodine information can be separated with two measurements.

32. Apparatus as recited in claims 10, 11, 12, 13, 14, 15, 16 or 17 including means for measuring the transmission of the x-ray beam through the volume at a third energy spectrum whereby the specific material can be separated from two types of tissue within the volume of the body.

33. Apparatus as recited in claim 32 where the volume of the body contains bone and soft tissue, the specific material is an iodinated contrast material and the third energy spectrum has a mean energy below the K edge of iodine.

34. Apparatus as recited in claim 10 wherein the time required to scan through each subsection of the volume is sufficiently small that moving structures in the volume of the body are essentially stationary.

35. Apparatus as recited in claim 10 including means for subtracting portions of the two-dimensional processed projection signal and windowing the resultant signal prior to the display whereby vessel images may be separated from background structures.

36. Apparatus as in claims 10, 11 or 16 wherein the means for processing the transmission measurements includes means for combining nonlinear functions of the logarithms of the measurements whereby the beam hardening of each measurement is corrected.

37. Apparatus as recited in claims 10,11,12,13,14,15,16 or 17 wherein the specific materials are bone and soft tissue and the two energy spectra are chosen such that the relative values of the mass attenuation coefficients of bone and soft tissue are substantially different in each of the two energy spectra.

38. Apparatus for providing a projection image of a specific material within a volume of the body containing bone and soft tissue comprising:

an x-ray source producing an x-ray beam which is projected through the volume;

means for measuring the transmission of the x-ray beam through the volume at a first energy spectra where the mass attenuation coefficients of bone and soft tissue are substantially equal;

means for measuring the transmission of the x-ray beam through the volume at a second energy spectra where the mass attenuation coefficients of bone and soft tissue are substantially equal and the mass attenuation coefficient of the specific material is substantially different than its value at the first energy spectra; and

means for processing the measurements to provide a projection image of the specific material.

39. Apparatus as recited in claim 38 wherein the means for measuring the transmission of the x-ray beam through the volume at the two energy spectra includes means for sequentially changing the energy spectrum of the x-ray beam and detecting the transmitted x-ray beam.

40. Apparatus as recited in claim 38 wherein the means for measuring the transmission of the x-ray beam through the volume at the two energy spectra includes an energy sensitive detector providing individual measurements at each energy spectra.

41. In a method for providing a projection image of a specific material within a volume of the body containing bone and soft tissue the steps of:

measuring the x-ray transmission of the volume at a first energy spectra where the mass attenuation coefficients of bone and soft tissue are substantially equal;

measuring the x-ray transmission of the volume at a second energy spectra where the mass attenuation coefficients of bone and soft tissue are substantially equal and the mass attenuation coefficient of the specific material is substantially different than its value at the first energy spectra; and

processing the measurements to produce a projection image of the specific material in the volume.