Integrated Pet-Mri Scanner

• US 20080214927A1
• Filed: 04/28/2006
• Published: 09/04/2008
• Est. Priority Date: 04/29/2005
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Cherry, Simon, Catana, Ciprian, Pichler, Bernd J.M.
• Granted Patent: US 7,835,782 B2
• Time in Patent Office: Days
• US Class Current: 600/411
• CPC Class Codes: G01R 33/481 MR combined with positron emission tomography [PET] or single photon emission computed tomography [SPECT]

Abstract

One embodiment of the present invention provides an integrated PET-MRI scanner. This integrated scanner includes a main magnet that generates a magnetic field, wherein images of the subject is generated in a central region of the magnetic field. It also includes a PET scanner which is enclosed by the main magnet. The PET scanner further comprises: (1) at least one ring of scintillators, which is situated in the central region of the magnetic field and, (2) one or more photodetectors, which are coupled to the ring of scintillators, so that the one or more photodetectors are outside the central region of the magnetic field. The integrated scanner also includes radio-frequency (RF) coils which are enclosed by the PET scanner. By keeping the photodetectors and associated circuitry outside the central region of the magnetic field, the integrated scanner reduces the electromagnetic interference (EMI) between the PET scanner and the MRI scanner.

Claims

1. An integrated positron emission tomography (PET)-magnetic resonance imaging (MRI) scanner, comprising:

a main magnet that generates a magnetic field during an MRI process for a subject, wherein the image is generated in a central region of the magnetic field;

a PET scanner that detects annihilation photons produced by positron decays within a subject during a PET imaging process, wherein the PET scanner is enclosed by the main magnet, wherein the PET scanner further comprises;

at least one ring of scintillators that detect positron-annihilation photons and output light photons in response to the detected positron-annihilation photons, wherein the ring of scintillators is situated in the central region of the magnetic field; and

one or more photodetectors that convert the light photons output by the ring of scintillators into electrical signals, wherein the one or more photodetectors are coupled to the ring of scintillators, so that the one or more photodetectors are located outside of the central region of the magnetic field; and

a set of radio-frequency (RF) coils that transmit signals to and receive signals from the subject during the MRI process, wherein the set of RF coils are enclosed by the PET scanner;

wherein keeping the photodetectors and associated circuitry outside of the central region of the magnetic field reduces the electromagnetic interference (EMI) between the PET scanner and the MRI scanner.

2. The integrated PET-MRI scanner of claim 1, wherein the one or more photodetectors are coupled to the ring of scintillators through optical fibers, wherein one end of the optical fibers is attached to the outputs of the scintillators, while the other end of the optical fibers is attached to the inputs of the one or more photodetectors, wherein the optical fibers transfer the photons outputted by the ring of scintillators to the one or more photodetectors, wherein using the optical fibers facilitates keeping the photodetectors outside of the central region of the magnetic field.

3. The integrated PET-MRI scanner of claim 2, wherein the optical fibers are a fraction of the size of the main magnet, which limits light transmission loss.

4. The integrated PET-MRI scanner of claim 2, wherein the optical fibers include at least one cladding layer which reduces light transmission loss.

5. The integrated PET-MRI scanner of claim 2, wherein the optical fibers include more than one cladding layer which reduces light transmission loss.

6. The integrated PET-MRI scanner of claim 2, wherein the spaces between the optical fibers are filled with reflective material which reduces light transmission loss and decreases optical crosstalk between the optical fibers.

7. The integrated PET-MRI scanner of claim 2, wherein the optical fibers are bent sharply near the ring of scintillators in order to fit the optical fibers inside the main magnetic of the MRI.

8. The integrated PET-MRI scanner of claim 2, wherein the optical fibers can have:

circular cross-section;

rectangular cross-section;

or

hexagonal cross-section.

9. The integrated PET-MRI scanner of claim 1, wherein the at least one ring of scintillators includes multiple rings of scintillators to facilitate multi-slice PET scanning.

10. The integrated PET-MRI scanner of claim 1, wherein the circuitry associated with the photodetectors includes amplifiers for amplifying the electrical signals generated by the photodetectors.

11. The integrated PET-MRI scanner of claim 10, wherein the amplifiers are charge-sensitive preamplifiers (CSPs).

12. The integrated PET-MRI scanner of claim 1, wherein the scintillators can comprise:

lutetium oxyorthosilicate (LSO) crystals;

bismuth germinate (BGO) crystals;

gadolinium oxyorthosilicate (GSO) crystals,

LYSO (a mixture of LSO and yttrium oxyorthosilicate) crystals; and

mixed lutetium silicates (MLS) crystals.

13. The integrated PET-MRI scanner of claim 1, wherein the one or more photodetectors can comprise:

avalanche photodetectors (APDs); and

position-sensitive photodetectors (PSPDs), which include position-sensitive avalanche photodiodes (PSAPDs).

14. The integrated PET-MRI scanner of claim 13, wherein each PSAPD is used to readout a block or an array of scintillators in the ring of scintillators.

15. The integrated PET-MRI scanner of claim 14, wherein the PSAPD produces a position map for the block or the array of scintillators which indicates the light intensity distribution across of the block or the array of scintillators.

16. The integrated PET-MRI scanner of claim 13, wherein an array of the APDs is used to readout a block or an array of scintillators in the ring of scintillators.

17. The integrated PET-MRI scanner of claim 1, wherein the photodetectors and associated circuitry of the PET scanner are contained within a magnetic field produced by the main magnet of the MRI.

18. The integrated PET-MRI scanner of claim 1, further comprising a shield configured to shield the photodetectors and associated circuitry of the PET scanner from the RF signals generated by the RF coils of the MRI.

19. The integrated PET-MRI scanner of claim 1, wherein the MRI can be:

a low-field MRI;

or

a high-field MRI.

20. A method for simultaneously imaging a subject using a positron emission tomography (PET) scanner and a magnetic resonance imaging (MRI) device, the method comprising:

receiving a subject;

placing the subject inside an integrated PET-MRI scanner, wherein the integrated PET-MRI scanner comprises;

an MRI scanner, wherein the MRI scanner further comprises;

a main magnet that generates a magnetic field during an MRI imaging process for the subject; and

a set of radio-frequency (RF) coils that transmit signals to and receive signals from the subject during the MRI imaging, wherein the set of RF coils is situated in a central region of the magnetic field inside the main magnet;

a PET scanner that detects annihilation photons produced by positron decays within the subject during a PET imaging process, wherein the PET scanner is placed inside of the main magnet, wherein the PET scanner further comprises;

at least one ring of scintillators that detect positron-annihilation photons and output light photons in response to the detected positron-annihilation photons, wherein the ring of scintillators is situated in the central region of the magnetic field; and

one or more photodetectors that convert the light photons output by the ring of scintillators into electrical signals, wherein the one or more photodetectors are coupled to the ring of scintillators, so that the one or more photodetectors are located outside of the central region of the magnetic field;

wherein the PET scanner encloses the RF coils; and

wherein the subject is inside the RF coils; and

imaging the subject using the PET scanner and the MRI scanner simultaneously, wherein keeping the photodetectors and associated circuitry outside of the central region of the magnetic field reduces the electromagnetic interference (EMI) between the PET scanner and the MRI scanner.

21. The method of claim 20, wherein the at least one ring of scintillators includes multiple rings of scintillators for multi-slice PET scanning.

22. The method of claim 20, wherein coupling the one or more photodetectors to the ring of scintillators involves:

receiving a set of optical fibers;

attaching one end of the set of optical fibers to the output end of the scintillators; and

attaching the other end of the set of optical fibers to the inputs of the one or more photodetectors;

wherein using the optical fibers facilitates keeping the photodetectors outside of the central region of the magnetic field.

23. The method of claim 22, wherein coupling the one or more photodetectors to the ring of scintillators using the optical fibers further involves bending the optical fibers sharply near the ring of scintillators in order to fit the optical fibers inside the magnetic of the MRI scanner.

24. The method of claim 23, wherein bending the optical fibers involves:

heating the optical fibers to a predetermined temperature;

bending the optical fibers at the predetermined temperature; and

cooling the bent optical fibers slowly back to ambient temperature.

25. The method of claim 22, wherein prior to attaching the set of optical fibers to the output end of the scintillators, the method further comprises mechanically polishing the output end of the scintillators.

26-34. -34. (canceled)