Four-dimensional helical tomographic scanner

• US 7,042,975 B2
• Filed: 10/25/2002
• Issued: 05/09/2006
• Est. Priority Date: 10/25/2002
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Heuscher, Dominic J.
• Primary Examiner(s): Glick, Edward J.
• Assistant Examiner(s): KEANEY, ELIZABETH MARIE
• Application Number:
  US10/280,734
• Publication Number:
  US 20040081270A1
• Time in Patent Office: 1,292 Days
• Field of Search: 378/144, 378/143, 378/8, 378/15, 378/4, 378/901
• US Class Current: 378/8
• CPC Class Codes: A61B 6/027 characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4021 involving movement of the focal spot
• CPC Class Codes: A61B 6/4085 Cone-beams
• CPC Class Codes: A61B 6/4488 Means for cooling A61B6/045 takes precedence
• CPC Class Codes: A61B 6/507 for determination of haemodynamic parameters, e.g. perfusion CT
• CPC Class Codes: A61B 6/5288 involving retrospective matching to a physiological signal
• CPC Class Codes: A61B 6/541 involving acquisition triggered by a physiological signal
• CPC Class Codes: G06T 11/008 Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
• CPC Class Codes: G06T 2211/412 Dynamic
• CPC Class Codes: H01J 35/30 by deflection of the cathode ray

Abstract

A computed tomography imaging scanner (10) acquires helical cone beam projection data for a volume of interest (46) using at least two source trajectory helices. A reconstruction processor (62) reconstructs the projection data for each helix to generate a corresponding time skewed image representation. A voxel time processor (66) computes an acquisition time for each voxel in each time skewed image representation. A voxel interpolator (68) computes an interpolated voxel value for each voxel based on values of the voxel in the time skewed image representations and corresponding voxel acquisition times. In an electronic embodiment, the computed tomography scanner (10) includes an x-ray source (12) with an axially oriented cylindrical anode (92), an electron source (96₁, 96₂) irradiating the cylindrical anode (92) to produce an x-ray beam (120, 122, 124, 126), and an electron beam deflector (98, 100) that deflects the electron beam along the anode (92) to axially sweep the x-ray beam.

Claims

1. A helical cone beam computed tomography imaging apparatus comprising:

means for acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices that temporally overlap, each source trajectory helix being triggered based on detection of a selected cardiac phase, the selected triggering cardiac phase being different for each helix;

means for reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest, the time skewed volume image representations temporally overlapping due to the temporal overlap of the source trajectory helices;

means for computing a voxel acquisition time for each voxel for each time skewed volume image representation; and

means for computing an interpolated voxel value for each voxel based on values of the voxel in the plurality of image representations and corresponding voxel acquisition times.

2. The imaging apparatus as set forth in claim 1, wherein the volume of interest undergoes a cyclical temporal variation, and each source trajectory helix spans the volume of interest over a time interval less than one cycle period of the cyclical temporal variation of the volume of interest.

3. The imaging apparatus as set forth in claim 1, wherein the computing of a voxel acquisition time for each voxel of each time skewed volume image representation includes:

computing the voxel acquisition time as a time average of the contiguous acquisition time interval corresponding to the voxel.

4. The imaging apparatus as set forth in claim 1, wherein the computing of an interpolated voxel value includes:

for each voxel, computing a time-dependent voxel value based on values of the voxel in the plurality of time skewed volume image representations and corresponding voxel acquisition times.

5. A helical cone beam computed tomography imaging method comprising:

acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices;

reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest, each voxel being reconstructed based on projection data acquired over a single contiguous acquisition time interval of the corresponding source trajectory helix;

for each time skewed volume image representation, computing a voxel acquisition time for each voxel by;

identifying a PI line associated with the voxel;

determining a PI line time interval corresponding to the PI line; and

computing the voxel acquisition time as a statistical characteristic time value of the PI line time interval; and

for each voxel, computing an interpolated voxel value based on values of the voxel in the plurality of image representations and corresponding voxel acquisition times.

6. The imaging method as set forth in claim 5, wherein time intervals between voxel acquisition times for at least some voxels are less than a time interval over which a helix is acquired.

7. The imaging method as set forth in claim 5, wherein the acquiring of helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices includes:

for each helix, acquiring generally non-overlapping projection views during adjacent helical turns.

8. The imaging method as set forth in claim 5, wherein at least some of the plurality of source trajectory helices span less than the entire volume of interest.

9. The imaging method as set forth in claim 5, wherein the acquiring of helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices includes:

rotating a radiation source about the volume of interest; and

simultaneously with the rotating, cyclically relatively axially moving the volume of interest and the radiation source.

10. The imaging method as set forth in claim 9, wherein the acquiring of helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices includes:

during the simultaneous rotating and relative axial moving, acquiring projection data using a plurality of axially spaced radiation cone beam source positions.

11. The imaging method as se forth in claim 5, wherein the volume of interest includes a cyclically temporally varying organ an the computing of an interpolated voxel value includes:

interpolating voxels of the time skewed volume image representations that have voxel acquisition times corresponding to a selected state of the cyclically temporally varying organ.

12. A helical cone beam computed tomography imaging method comprising:

rotating a cone beam radiation source about a volume of interest;

simultaneously with the rotating, axially sweeping an electron beam parallel to an axis of radiation source rotation across an axially elongated anode of the radiation source, the electron beam defining an x-ray cone beam generation position on the anode, the rotating and the axial sweeping cooperating to generate the source trajectory helices about the volume of interest;

reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest; and

for each time skewed volume image representation, computing a voxel acquisition time for each voxel.

13. The imaging method as set forth in claim 12, wherein the acquiring of helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices further includes:

fast re-tracing the electron beam between source trajectory helices.

14. The imaging method as set forth in claim 12, wherein the axial sweeping includes simultaneously axially sweeping at least two x-ray cone beam generation positions across the axially elongated anode.

15. The imaging method as set forth in claim 12, wherein the volume of interest is a cardiac region and the acquiring of helical cone beam computed tomography projection data for the volume of interest using a plurality of source trajectory helices includes:

triggering each source trajectory helix based on detection of a selected cardiac phase.

16. The imaging method as set forth in claim 12, further comprising:

keeping the volume of interest stationary during the rotating of the cone beam radiation source and the sweeping of the electron beam across the axially elongated anode of the radiation source.

17. A cardiac helical cone beam computed tomography imaging method comprising:

acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality, of source trajectory helices, each source trajectory being triggered based on detection of a selected cardiac phase, the selected triggering cardiac phase being different for each helix;

reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest;

for each time skewed volume image representation, computing a voxel acquisition time for each voxel; and

for each voxel, computing an interpolated voxel value based on values of the voxel in the plurality of image representations and corresponding voxel acquisition times.

18. A cardiac helical cone beam computed tomography imaging method comprising:

acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices, each source trajectory being triggered based on detection of a selected cardiac phase, at least two source trajectory helices being triggered within a single cardiac cycle;

reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest;

for each time skewed volume image representation, computing a voxel acquisition time for each voxel; and

for each voxel, computing an interpolated voxel value based on values of the voxel in the plurality of image representations and corresponding voxel acquisition times.

19. An apparatus for performing helical cone beam computed tomography imaging, the apparatus comprising:

a means for acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices, each source trajectory helix being triggered based on detection of a selected cardiac phase, at least two source trajectory helices being triggered within a single cardiac cycle;

a means for triggering the acquiring of conebeam projection data starting at points in a physiological cycle which vary among the trajectory helices;

a means for reconstructing the acquired helical cone beam computed tomography projection data for each helix to generate a corresponding time skewed volume image representation of the volume of interest;

a means for computing a voxel acquisition time for each voxel of each time skewed image representation; and

.

a means for computing an interpolated voxel value for each voxel based on values of the voxel in the plurality of time skewed image representations and corresponding voxel acquisition times.

20. The apparatus as set forth in claim 19, wherein the means for acquiring helical cone beam computed tomography projection data includes:

a rotating gantry;

an x-ray source arranged on the rotating gantry, the x-ray source rotating with the rotating gantry and producing an x-ray cone beam that passes through the volume of interest;

a radiation detector arranged to detect x-rays produced by the x-ray cone beam source after passing through the volume of interest;

a support structure that supports an imaging subject, at least a portion of which imaging subject defines the volume of interest; and

a means for relatively axially moving the support structure and the x-ray cone beam, the axial moving cooperating with rotating of the gantry to produce the source trajectory helices.

21. The apparatus as set forth in claim 19, wherein the means for computing an interpolated voxel value for each voxel includes:

computing a time-dependent voxel value based on the values of the voxel in the plurality of time skewed volume image representations and corresponding voxel acquisition times.

22. An apparatus for performing helical cone beam computed tomography imaging, the apparatus comprising:

a means for triggering the acquiring of conebeam projections data for a volume of interest starting at points in a physiological cycle which vary among a plurality of trajectory helices;

a means for acquiring helical cone beam computed tomography projection data responsive to the triggering, the acquiring means including;

(i) a rotating gantry, (ii) an x-ray source arranged on the rotating gantry including an axially extended anode and an electron source that axially sweeps an electron beam along the anode to produce an axially sweeping x-ray cone beam in coordination with the triggering means, the axial sweeping cooperating with rotating of the gantry to produce the source trajectory helices, (iii) a radiation detector arranged to detect x-rays produced by the x-ray source after passing through the volume of interest, and (iv) a support structure that supports an imaging subject, at least a portion of which imaging subject defines the volume of interest;

a means for reconstructing the acquired helical cone beam computed tomography projection data for the helixes to generate a corresponding time skewed image representations of the volume of interest;

a means for computing voxel acquisition times for the voxels of the time skewed image representations; and

a means for computing interpolated voxel values for selected voxels based on values of the corresponding voxel the time skewed image representations and corresponding voxel acquisition times.

23. The apparatus as set forth in claim 22, further including:

a beam-switching means for switching the sweeping electron beam between a plurality of axially spaced positions on the anode to produce a plurality of axially spaced sweeping x-ray cone beams.

24. The apparatus as set forth in claim 22, wherein the volume of interest includes at least a portion of the heart, and the means for acquiring helical cone beam computed tomography projection data for a volume of interest using a plurality of source trajectory helices includes:

an electrocardiograph that triggers the source trajectory helices.

25. The apparatus as set forth in claim 24, wherein the means for computing an interpolated voxel value includes:

selecting voxel values from the time skewed volume image representations whose corresponding voxel acquisition times correspond to an occurrence of one of a selected cardiac phase and a selected state of cardiac motion; and

combining the selected voxel values to generate an image representation of the selected cardiac phase or selected state of cardiac motion.

26. An apparatus for performing high-speed computed tomography imaging, the apparatus comprising:

a rotating gantry;

an x-ray source disposed on the rotating gantry and rotating therewith, the x-ray source including an axially oriented cylindrical anode, an electron source irradiating the cylindrical anode to produce an x-ray beam traversing a volume of interest, and an electron beam deflector that axially deflects the electron beam along the cylindrical anode to axially sweep the x-ray beam, a period of the axial sweep of the x-ray beam along the cylindrical anode being coordinated to a period of rotation of the rotating gantry to produce a helical trajectory of the x-ray beam about the volume of interest;

a radiation detector arranged to measure the x-ray beam after passing through the volume of interest; and

a reconstruction processor that reconstructs the acquired projection data to produce a time skewed image representation corresponding to the helical trajectory.

27. The apparatus as set forth in claim 26, wherein the electron beam deflector switches the electron beam between at least two axially spaced positions on the anode, the at least two axially spaced positions selected to define at least two helical trajectories each spanning a portion of the volume of interest and arranged to cooperatively define a helical trajectory spanning the volume of interest.

28. The apparatus as set forth in claim 26, wherein the electron beam deflector switches the electron beam between at least two axially spaced positions on the anode, the at least two axially spaced positions selected to define at least two interlaced helical trajectories.

29. In a conebeam helical computed tomography imaging system including a rotating gantry and a means for controlling sweeping of an x-ray tube electron beam in accordance with rotation of the gantry, an x-ray tube comprising:

a cylindrical anode whose cylindrical axis is axially oriented with respect to a rotation axis of the rotating gantry;

an electron source that produces an electron beam generally directed toward the cylindrical anode, which electron beam interacts with the cylindrical anode to produce a cone beam of x-rays; and

an electron beam deflector that sweeps the electron beam axially across the cylindrical anode;

wherein a ratio of a sweep speed of the electron beam to a rotation rate of the rotating gantry being selected to generate a selected helical trajectory of the cone beam about a region of interest.