Combined PET/MRT unit and method for simultaneously recording pet images and MR images

• US 20070055127A1
• Filed: 08/23/2006
• Published: 03/08/2007
• Est. Priority Date: 08/24/2005
• Status: Active Grant

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Ladebeck, Ralf, Renz, Wolfgang
• Granted Patent: US 8,073,525 B2
• Time in Patent Office: Days
• US Class Current: 600/407
• CPC Class Codes: A61B 6/037 Emission tomography
• CPC Class Codes: G01R 33/481 MR combined with positron emission tomography [PET] or single photon emission computed tomography [SPECT]
• CPC Class Codes: G01T 1/1603 with a combination of at least two different types of detector see provisionally also G01T1/16
• 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 combined PET/MRT unit is disclosed that includes a PET detector which is reduced by comparison with the prior art, and that consists, for example, of a PET detector with a polygonal arrangement of the detector elements or with a PET detector ring. The PET detector is reduced in an axial direction by comparison with the detectors of the prior art, as a result of which the costs for producing the expensive PET detectors are lowered. The reduction of the PET detector is possible because the MR measurement usually lasts longer than the PET measurement, and so a reduced PET detector can be used for the temporally sequential recording of a number of PET tomograms by mechanical displacement of the PET detector. Since the MR measurement lasts substantially longer, this mechanical displacement does not lead to a lengthening of the measuring time. The invention also relates to methods for simultaneously recording MR and PET tomograms in which the PET/MRT units according to the invention are used.

Claims

1. A combined positron emission tomography/magnetic resonance tomography unit, comprising:

a magnetic resonance tomography including at least one basic field magnet, a system of gradient coils, and a high-frequency system, including an MR antenna, to generate HF excitation pulses and to detect the emitted resonance signals, a measurement object being movable into the MR tomography in an axial direction;

a PET detector including at least two detector elements to detect the gamma radiation emitted from the measurement object, the detector elements being arranged about the measurement object on a circular periphery and including at least a size such that the gamma radiation formed on the line between the detector elements in the measurement object and emitted in the direction of the detector elements is detected; and

at least one unit computer, including control software to process the resonance signals detected by the MR antenna, and the gamma radiation detected by the PET detector, to store the MRT data and the PET data and for displaying the MR images and the PET images, the PET detector being displaceable in an axial direction and including, in the axial direction, a lesser extent than the MR antenna, selected such that the PET detector must be displaced in an axial direction in order to detect the same number of at least one of layers and cross-sectional surfaces of the measurement object as the MR antenna.

2. A combined PET/MRT unit as claimed in claim 1, wherein the extent of the PET detector in an axial direction is such that the measured data for the PET images from at most 5 layers of the measurement object are aquireable without displacing the PET detector.

3. The combined PET/MRT unit as claimed in claim 1, wherein the PET detector includes at least one of:

a PET detector that includes two separate large-area detector plates, arranged parallel to one another on opposite sides of the measurement object and rotatable in a transaxial direction about the measurement object for the purpose of complete data acquisition;

a PET detector that includes a number of large-area detector plates that surround the measurement object completely in a polygonal arrangement, the number of the detector plates being at least one of even, and comprising at least 4 plates, and odd;

a PET detector that includes a detector ring that surrounds the measurement object and is completely occupied with small PET detector elements; and

a PET detector that includes a detector ring that is partially occupied with small detector elements whose number and distribution on the detector ring are selected such that the acquisition of all the measured data that are required for producing the PET images of at least one layer of the measurement object is possible with or without rotation of the detector ring.

4. The combined PET/MRT unit as claimed in claim 3, wherein a number of the PET detectors are stacked directly one after another in an axial direction to form a resulting, the extent of the resulting PET detector being less in an axial direction than the extent of the MR antenna.

5. The combined PET/MRT unit as claimed in claim 1, wherein the MR antenna is arranged inside the PET detector and is separated therefrom for the purpose of mutual decoupling of interference by a PET transparent and MR compatible HF shield.

6. The combined PET/MRT unit as claimed in claim 1, wherein the MR antenna is installed to be movable in an axial direction, and wherein the MR antenna and the PET detector include at least one of a common drive unit and separate drive units, enabling the independent movement of the MR antenna and the PET detector in an axial direction.

7. The combined PET/MRT unit as claimed in claim 1, wherein the drive unit of the PET detector is at least one of arranged inside the magnet and includes at least one of a fluid hydraulics and a compressed air hydraulics, and arranged outside the magnet, the transmission of the drive being performed with the aid of at least one of Bowden cables, push rods and toothed belts.

8. The combined PET/MRT unit as claimed in claim 1, wherein the PET detector is permanently connected to a couch of the patient, and wherein the drive unit of the PET detector includes the drive unit of the patient couch such that the PET detector is displaceable in an axial direction together with the patient couch.

9. The combined PET/MRT unit as claimed in claim 1, wherein the drive unit of the MR antenna includes the drive unit of the couch if the patient such that the MR antenna is displaceable in an axial direction together with the patient couch.

10. The combined PET/MRT unit as claimed in claim 1, wherein, in at least one of a transaxial direction and an axial direction, the detector elements of the PET detector have a length that is in the range from 0.5 to 10 cm.

11. The combined PET/MRT unit as claimed in claim 1, wherein the PET detector includes a photodiode array and an upstream array made from a detector material that is sensitive to gamma radiation and is selected from the group consisting of lutetium oxyorthosilicate (LSO), cerium doped LSO, cerium doped lutetium yttrium aluminum perovskite, bismuth germanium oxide (BGO), sodium iodide (NaI) and thallium doped NaI.

12. The combined PET/MRT unit as claimed in claim 11, wherein the photodiode array is an APD photodiode array.

13. A combined PET/MRT imaging method for simultaneously recording at least one MRT tomogram and at least one PET tomogram, the method comprising:

introducing a measurement object into a combined PET/MRT unit;

recording the MR tomograms by carrying out MR tomography; and

recording the PET tomograms by carrying out PE tomography, wherein the combined PET/MRT imaging method is carried out in a combined PET/MRT unit as claimed in claim 1.

14. The method as claimed in claim 13, wherein a plurality of PET images are recorded sequentially by mechanically displacing the PET detector in an axial direction and, if appropriate, rotating the PET detector in a peripheral direction about the measurement object, and wherein the MR images are recorded while maintaining the position of the MR antenna, the position of a couch of the patient and the position of the measurement object.

15. The method as claimed in claim 13, wherein the at least one PET image is recorded in conjunction with parallel mechanical displacement of a couch of the patient and of the PET detector, permanently connected to the patient couch, in an axial direction and, if appropriate, rotation of the PET detector in a peripheral direction about the measurement object, and a number of MR images are sequentially recorded while maintaining the position of the MR antenna, the measuring range for the MR images then being greater in an axial direction than the extent of the MR antenna in an axial direction.

16. The method as claimed in claim 13, wherein a plurality of MR images are recorded sequentially by mechanically displacing the MR antenna in an axial direction, and the at least one PET image is recorded while maintaining the position of the PET detector and, if appropriate, while rotating the PET detector in a peripheral direction about the measurement object, and while maintaining the position of a couch of the patient and of the measurement object.

17. The method as claimed in claim 13, wherein the PET detector and the MR antenna are moved simultaneously and independently of one another.

18. The method as claimed in claim 13, wherein recording of the at least one MR image comprises:

positioning the region of interest of the measurement object in the basic magnet;

carrying out a pulse sequence in the presence of a homogeneous magnetic field that comprises irradiating HF excitation pulses, emitted by the MR antenna of the HF system, switching gradient fields for the purpose of slice selection and spatial coding with the aid of gradient coils, and detecting the emitted resonance signals with a receiving antenna of the HF system;

relaying to the unit computer the MR resonance signals registered and processed by the HF system; and

producing the at least one MR tomogram and displaying the at least one MR tomogram with the aid of a unit computer.

19. The method as claimed in claim 13, wherein recording of the at least one PET image comprises:

positioning the region of interest of the measurement object in the PET detector that surrounds the measurement object;

introducing a radiopharmacon into the measurement object by at least one of injection and inhalation;

detecting with the PET detector the photons emitted by the measurement object as a consequence of the positron decay; and

reconstructing the at least one PET tomogram with the aid of the detected PET signals in the unit computer.

20. A combined PET/MRT unit as claimed in claim 1, wherein the extent of the PET detector in an axial direction is such that the measured data for the PET images from exactly one layer of the measurement object is aquireable without displacing the PET detector.

21. The combined PET/MRT unit as claimed in claim 2, wherein the PET detector includes at least one of:

a PET detector that includes two separate large-area detector plates, arranged parallel to one another on opposite sides of the measurement object and rotatable in a transaxial direction about the measurement object for the purpose of complete data acquisition;

a PET detector that includes a number of large-area detector plates that surround the measurement object completely in a polygonal arrangement, the number of the detector plates being at least one of even, and comprising at least 4 plates, and odd;

a PET detector that includes a detector ring that surrounds the measurement object and is completely occupied with small PET detector elements; and

a PET detector that includes a detector ring that is partially occupied with small detector elements whose number and distribution on the detector ring are selected such that the acquisition of all the measured data that are required for producing the PET images of at least one layer of the measurement object is possible with or without rotation of the detector ring.

22. The combined PET/MRT unit as claimed in claim 21, wherein a number of the PET detectors are stacked directly one after another in an axial direction to form a resulting, the extent of the resulting PET detector being less in an axial direction than the extent of the MR antenna.

23. The method as claimed in claim 18, wherein recording of the at least one PET image comprises:

positioning the region of interest of the measurement object in the PET detector that surrounds the measurement object;

introducing a radiopharmacon into the measurement object by at least one of injection and inhalation;

detecting with the PET detector the photons emitted by the measurement object as a consequence of the positron decay; and

reconstructing the at least one PET tomogram with the aid of the detected PET signals in the unit computer.