Virtual contouring for transmission scanning in spect and pet studies

• US 6,388,244 B1
• Filed: 03/20/2000
• Issued: 05/14/2002
• Est. Priority Date: 03/20/2000
• Status: Expired due to Fees

• Current Assignee: Marconi Medical Systems, Inc. (Koninklijke Philips N.V.)
• Original Assignee: Philips Medical Systems (Cleveland) Incorporated (Koninklijke Philips N.V.)
• Inventors: Gagnon, Daniel
• Primary Examiner(s): LE, QUE TAN
• Application Number:
  US09/531,840
• Time in Patent Office: 785 Days
• Field of Search: 250/208.1, 250/363.02, 250/363.03, 250/363.04, 250/363.05, 250/234, 250/235, 382/131, 382/132, 128/665
• US Class Current: 250/208.1
• CPC Class Codes: A61B 6/037 Emission tomography
• CPC Class Codes: A61B 6/4258 for detecting non x-ray radiation, e.g. gamma radiation A61B6/037 takes precedence
• CPC Class Codes: G01T 1/1615 using both transmission and emission sources simultaneously SPECT imaging G01T1/1642; PET imaging G01T1/2985; detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects G01V5/20
• CPC Class Codes: G01T 1/1648 Ancillary equipment for scintillation cameras, e.g. reference markers, devices for removing motion artifacts, calibration devices adapted for flow studies G01T1/1647
• CPC Class Codes: G01T 1/2985 In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis); using external radiation sources A61B6/02

Abstract

A nuclear gamma camera employs a virtual contouring technique in order to maximize the portion of transmission radiation fan beams (32a, 32b) which pass through a subject (12). A plurality of radiation detector heads (20a-20c) having radiation receiving faces and a plurality of radiation sources (30a, 30b) are mounted to a gantry (16). An orbit memory (42) stores clearance offset orbit (45) around the subject and a subject support (10). A tangent calculator (46) calculates virtual lines (48a, 48b) between the radiation sources (30a, 30b) and the corresponding radiation detector heads (20a, 20b). The virtual lines (48a, 48b) correspond to edge rays of the transmission radiation fans (32a, 32b). A shift calculator (50) calculates and sends shift commands to a motor orbit controller (52) which controls rotational and translational drives attached to the detector heads (20a-20c). The detector heads are translated such that the virtual lines (48a, 48b) remain tangent to a predefined contour of the subject throughout rotation of the detector heads about the subject receiving aperture (18). The detected transmission radiation (32a, 32b) is reconstructed (64t) into an attenuation volumetric image representation and used to correct (68) detected emission radiation data. The corrected emission data is then reconstructed (64e) into a volumetric image representation. The virtual contouring minimizes lost rays (40) of transmission radiation and facilitates an artifact-free attenuation volumetric image representation.

Claims

1. A nuclear medicine gamma camera for diagnostic imaging, said gamma camera comprising:

a rotating gantry which defines a subject receiving aperture;

a plurality of radiation detector heads movably attached to the rotating gantry, said detector heads rotating about the subject receiving aperture with rotation of the rotating gantry about an axis of rotation;

at least one radiation source mounted to the rotating gantry for rotation therewith, such that a divergent beam of transmission radiation from the at least one radiation source is directed toward and received by a corresponding detector head positioned across the subject receiving aperture from the radiation source;

a rotational drive which rotates the plurality of detector heads around the subject receiving aperture;

a plurality of translational drives which translate independently the plurality of detector heads (i) laterally in directions tangential to the subject receiving aperture and (ii) radially in directions orthogonal to the axis of rotation;

an orbit memory which stores a predefined orbit which clears a subject disposed in the subject receiving aperture;

a tangent calculator which calculates the position of a virtual line between the at least one radiation source and an edge of a radiation receiving face of the corresponding detector head which receives transmission radiation from the at least one radiation source;

a shift calculator which calculates lateral and radial shifts for the plurality of detector heads such that the detector head positions are dynamically adjusted in order to maintain the virtual line tangent to an outer boundary of the subject throughout rotation of the gantry around the subject receiving aperture; and

a motor orbit controller which controls the plurality of translational drives and the rotational drive in accordance with the orbit from the orbit memory and shift inputs from the shift calculator.

2. The nuclear medicine gamma camera according to claim 1, said gamma camera further comprising:

a contouring device which determines outer boundaries of the subject disposed in the subject receiving aperture, the determined outer boundaries of the subject being stored in the orbit memory.

3. The nuclear medicine gamma camera according to claim 2, wherein the outer boundaries of the subject are determined prior to running an imaging operation.

4. The nuclear medicine gamma camera according to claim 1, wherein:

the plurality of radiation detector heads includes a first detector head and a second detector head arranged on the rotating gantry on opposite sides of the subject receiving aperture such that radiation receiving faces of the first and second detector heads face one another; and

,

the at least one radiation source includes;

a first radiation source mounted to the first detector head such that transmission radiation from the first radiation source is directed toward and received by the second detector head; and

,

a second radiation source mounted to the second detector head such that transmission radiation from the second radiation source is directed toward and received by the first detector head.

5. The nuclear medicine gamma camera according to claim 4, wherein the first and second radiation sources include:

a radioactive point source contained within a shielded cylinder, said radioactive point source generating a plurality of transmission radiation fan beams.

6. The nuclear medicine gamma camera according to claim 5, wherein:

the virtual line calculated by the tangent calculator corresponds to end rays of the transmission radiation fan beams.

7. The nuclear medicine gamma camera according to claim 6, wherein:

the lateral shifts calculated by the shift calculator maximize the portion of the transmission radiation fan beams which pass through the subject disposed in the subject receiving aperture.

8. A method of diagnostic imaging using a nuclear medicine gamma camera, the method comprising:

(a) placing a subject in a subject receiving aperture;

(b) injecting the subject with a radiopharmaceutical;

(c) positioning a plurality of radiation sources and corresponding radiation detector heads about the subject receiving aperture such that the radiation sources are across the subject receiving aperture from their corresponding radiation detector heads;

(d) obtaining a contour of the subject disposed in the subject receiving aperture;

(e) detecting radiation emitted by the injected radiopharmaceutical using the plurality of radiation detector heads;

(f) calculating the position of virtual lines extending from each radiation source to an edge of a radiation receiving face disposed on each corresponding radiation detector head;

(g) shifting the detector heads laterally such that the virtual lines are tangent to the contour of the subject;

(h) transmitting radiation from the radiation sources toward the corresponding radiation detector heads positioned across the subject receiving aperture;

(i) detecting radiation transmitted by the radiation sources using one of the plurality of radiation detectors; and

(j) reconstructing the detected transmission and emission radiation into a volumetric image representation.

9. The method according to claim 8, wherein step (e) includes:

rotating the radiation sources and corresponding radiation detector heads about the subject receiving aperture.

10. The method according to claim 9, wherein step (i) includes:

rotating the detector heads and radiation sources about the subject receiving aperture; and

dynamically adjusting the positions of the detector heads with radiation sources attached thereto in order to maintain the virtual lines tangent to the contour of the subject throughout rotation about the subject receiving aperture.

11. The method according to claim 10, wherein dynamically adjusting the detector heads includes translating the detector heads laterally in directions tangential to the subject receiving aperture.

12. The method according to claim 11, wherein step (j) includes:

reconstructing the detected transmission radiation into an attenuation volume image representation;

correcting emission radiation data using the attenuation volume image representation; and

reconstructing the corrected emission radiation data into an emission volume image representation.

13. The method according to claim 12, wherein the correcting step includes:

calculating attenuation factors from the attenuation volume image representation, said attenuation factors corresponding to each ray along which emission data is received.

14. A nuclear camera system comprising:

a rotating gantry which defines a subject receiving aperture;

a plurality of real radiation detector heads movably attached to the rotating gantry, said real detector heads rotating about the subject receiving aperture with rotation of the rotating gantry about an axis of rotation;

a plurality of radiation sources mounted to the plurality of real detector heads for rotation with the rotating gantry, such that transmission radiation from the radiation sources is directed toward and received by the corresponding real detector heads positioned across the subject receiving aperture from the plurality of radiation sources;

a plurality of virtual detector heads, said virtual detector heads imposing shift restrictions on the real detectors heads during rotation about the subject receiving aperture;

a rotational drive which rotates the real detector heads around the subject receiving aperture;

a plurality of translational drives which translate independently the plurality of real detector heads at least one of laterally and radially with respect to the subject receiving aperture;

an orbit memory which stores a predefined contour of a subject disposed in the subject receiving aperture;

a shift calculator which calculates shifts in the real detector heads according to the predefined contour of the subject and the shift restrictions imposed by the virtual detector heads; and

a motor orbit controller which controls the translational and rotational drives in response to commands from the shift calculator.

15. The nuclear camera system according to claim 14, said nuclear camera system further comprising:

a contouring device which determines outer boundaries of the subject disposed in the subject receiving aperture, the outer boundaries of the subject being stored in the orbit memory.

16. The nuclear camera system according to claim 15, wherein the plurality of radiation sources include:

a radioactive point source contained within a shielded cylinder, said radioactive point source generating a plurality of transmission radiation fan beams.

17. The nuclear camera system according to claim 16, wherein the virtual detector heads are located in positions corresponding to virtual lines which extend from the plurality of radiation sources to the corresponding real detector heads.

18. The nuclear camera system according to claim 17, wherein:

the virtual lines are calculated by a tangent calculator, said virtual lines corresponding to end rays of the transmission radiation fan beams.

19. The nuclear camera system according to claim 18, wherein:

the shift calculator calculates lateral shifts in order to maximize the portion of the transmission radiation fan beams which pass through the contour of the subject disposed in the subject receiving aperture.

20. A method of controlling a nuclear camera which includes a rotating gantry on which at least first and second detector heads are mounted, the first detector head carrying an offset transmission radiation source that projects a fan beam of transmission radiation to the second detector head, the fan beam extending between edge rays, a rotating drive which rotates the rotating gantry continuously or in steps, a radial drive which moves the detector heads in a radially inward direction toward a center of rotation of the rotating gantry and a radially outward direction away from the center of rotation, and a lateral drive which moves the detector heads with a component of motion orthogonal to the radially inward and outward directions, the method comprising:

positioning a subject on a subject support with a region of interest at the center of rotation;

calculating a clearance offset orbit around and displaced from the subject and the subject support;

calculating a subject orbit around the region of interest;

injecting the subject with a radiopharmaceutical;

controlling the rotating drive and the radial drive such that the detector heads are maintained tangent to the clearance offset orbit as the detector heads are rotated around the subject; and

controlling the lateral drive such that one of the fan beam edge rays is maintained tangent to the subject orbit as the detector heads rotate.

21. The method according to claim 20, wherein the subject orbit is coincident with a circumference of the subject.