Randoms correction using artificial trigger pulses in a gamma camera system

• US 6,198,104 B1
• Filed: 10/23/1998
• Issued: 03/06/2001
• Est. Priority Date: 10/23/1998
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Adam Laboratories Inc.
• Inventors: Geagan, Michael J., Scharf, Thomas E., Petrillo, Michael J., Wellnitz, Donald R.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US09/178,036
• Time in Patent Office: 865 Days
• Field of Search: 250/363.03, 250/363.04
• US Class Current: 250/363.04
• 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 1/1647 Processing of scintigraphic data not related to a particular imaging system G01T1/2992
• CPC Class Codes: G01T 1/172 with coincidence circuit arrangements G01T1/178 takes precedence ; combination of detectors, see G01T1/1603, G01T1/30, G01T1/361

Abstract

A technique for correcting for random coincidences in a gamma camera system is provided. The system includes a pair of scintillation detectors coupled to a processing system and is configured to detect radiation coincidences. Each detector generates trigger pulses in response to scintillation events to generate a plurality of event-based trigger pulses. Each detector includes a pulse generator, which generates a plurality of artificial trigger pulses. When an artificial trigger pulse in one detector occurs in coincidence with an event-based trigger pulse in the other detector, data is registered by the corresponding detectors, and the artificial trigger pulse is associated with a predetermined energy level. The data processing system examines the data to identify singles events that were registered as a result of artificial trigger pulses and prevents such singles events from contributing to the coincidence images. Instead, such singles events are used to generate a singles image for each detector. The singles images from the detectors are then used to create a randoms image, which is used to correct the coincidence images for random coincidences.

Claims

1. A method of obtaining a measure of random coincidences in an imaging system including a radiation detector, the method comprising:

using the radiation detector to acquire coincidence data of an object to be imaged;

generating a plurality of artificial trigger signals; and

using the plurality of artificial trigger signals to acquire a measure of random coincidences associated with the coincidence data.

2. A method according to claim 1, wherein generating the plurality of artificial trigger signals comprises injecting a plurality of artificial trigger pulses into a stream of real trigger pulses, wherein only the real trigger pulses are based on radiation induced events.

3. A method according to claim 2, wherein generating the plurality of artificial trigger pulses comprises generating the plurality of artificial trigger pulses at a selected rate, the method further comprising adjusting the selected rate based on a current singles rate associated with the detector.

4. A method according to claim 2, wherein generating the plurality of artificial trigger pulses comprises selecting a pulse width for the plurality of artificial trigger pulses based on a current singles rate associated with the detector.

5. A method according to claim 2, wherein using the plurality of artificial trigger pulses to acquire a measure of random coincidences comprises:

using the plurality of artificial trigger pulses to acquire a singles image; and

using the singles image to determine the measure of random coincidences.

6. A method of using a gamma camera system to generate an image of an object corrected for random coincidences, the method comprising:

generating a plurality of event-based trigger pulses in response to scintillation events associated with the object;

generating a plurality of artificial trigger pulses;

acquiring coincidence data of the object based on the event-based trigger pulses;

acquiring randoms data representing random coincidences based on the artificial trigger pulses;

using the randoms data to correct the coincidence data; and

generating the image of the object based on the corrected coincidence data.

7. A method according to claim 6, wherein generating the plurality of artificial trigger pulses comprises generating the plurality of artificial trigger pulses at a selected rate based on a current measured singles rate.

8. A method according to claim 6, wherein generating the plurality of artificial trigger pulses comprises selecting a pulse width for the plurality of artificial trigger pulses based on a current measured singles rate.

9. A method according to claim 6, wherein acquiring randoms data based on the artificial trigger pulses comprises:

using the plurality of artificial trigger pulses to acquire a singles image associated with the object; and

using the singles image to acquire the measure of random coincidences.

10. A method according to claim 6, wherein the gamma camera system includes a pair of gamma radiation detectors, and wherein generating the plurality of event-based trigger pulses comprises independently generating a plurality of event-based trigger pulses for each of the detectors;

and wherein generating the plurality of artificial trigger pulses comprises independently generating the plurality of artificial trigger pulses for each of the detectors.

11. A method according to claim 10, further comprising:

combining the artificial trigger pulses with the event-based trigger pulses to produce a single pulse stream for each of the detectors; and

generating a coincidence trigger in response to each of a plurality of coincidental pairs of trigger pulses, each coincidental pair of trigger pulses including one trigger pulse from the single pulse stream of each of the pair of detectors.

12. A method according to claim 11, further comprising associating a predetermined energy level with each coincidental pair of trigger pulses that is based on an artificial trigger pulse.

13. A method of correcting for random coincidences in a medical imaging system, the medical imaging system including a pair of detectors, each of the detectors for detecting scintillation events associated with an object to be imaged, the method comprising:

using each of the detectors to generate a trigger pulse in response to each scintillation event detected by said detector to produce a plurality of event-based trigger pulses;

using each of the detectors to generate a plurality of artificial trigger pulses at a selected rate; and

combining the artificial trigger pulses with the event-based trigger pulses to produce a pulse stream for each of the detectors;

generating a coincidence trigger in response to each of a plurality of coincidental pairs of trigger pulses, each coincidental pair of trigger pulses including one trigger pulse from the pulse stream of each of the detectors, the coincidental pairs of trigger pulses representing true coincidences, event-based random coincidences, and artificial random coincidences, each artificial random coincidence representing a singles event associated with one of the artificial trigger pulses;

causing each of the detectors to register an event in response to each coincidence trigger;

identifying the ones of the coincidence triggers which correspond to artificial random coincidences;

for each identified coincidence trigger which corresponds to an artificial random coincidence, updating a singles image for one of the detectors based on a registered singles event associated with said identified artificial random coincidence, to generate a singles image for each of the detectors;

generating a randoms image based on the singles images for the detectors;

forming a coincidence image of the object; and

using the randoms image to correct the coincidence image for random coincidences.

14. A method according to claim 13, further comprising adjusting the rate at which the artificial trigger pulses are generated for one of the detectors based on a current singles rate of said one of the detectors.

15. A method according to claim 13, further comprising selecting a pulse width for the artificial trigger pulses based on a current singles rate of one of the detectors.

16. A method according to claim 13, wherein said identifying comprises:

for each coincidence trigger that corresponds to an artificial random coincidence, associating a predetermined energy level with a singles event corresponding to said coincidence trigger; and

distinguishing singles events associated with artificial coincidences from singles events associated with true coincidences or event-based random coincidences based on energy levels associated with each of said singles events.

17. A gamma camera imaging system comprising:

means for generating a plurality of event-based trigger signals in response to scintillation events associated with the object;

means for generating a plurality of artificial trigger signals;

means for acquiring coincidence data of the object based on the event-based trigger signals;

means for acquiring randoms data representing random coincidences based on the artificial trigger signals;

means for using the randoms data to correct the coincidence data; and

means for generating the image of the object based on the corrected coincidence data.

18. A gamma camera system according to claim 17, wherein the means for generating the plurality of artificial trigger pulses comprises means for generating the plurality of artificial trigger pulses at a selected rate, the gamma camera system further comprising further comprising means for selecting the rate based on a current measured singles rate.

19. A gamma camera system according to claim 17, wherein the means for generating the plurality of artificial trigger pulses comprises means for generating the plurality of artificial trigger pulses with a selected pulse width, the gamma camera system further comprising further comprising means for selecting the pulse width based on a current measured singles rate.

20. A gamma camera system according to claim 17, wherein the means for acquiring randoms data based on the artificial trigger pulses comprises:

means for using the plurality of artificial trigger pulses to acquire a singles image associated with the object; and

means for using the singles image to acquire the measure of random coincidences.

21. A gamma camera system according to claim 17, further comprising a pair of gamma radiation detectors, wherein the means for generating the plurality of event-based trigger pulses comprises means for independently generating a plurality of event-based trigger pulses for each of the detectors, and wherein the means for generating the plurality of artificial trigger pulses comprises means for independently generating the plurality of artificial trigger pulses for each of the detectors.

22. A gamma camera system according to claim 21, further comprising:

means for combining the artificial trigger pulses with the event-based trigger pulses to produce a single pulse stream for each of the detectors; and

means for generating a coincidence trigger in response to each of a plurality of coincidental pairs of trigger pulses, each coincidental pair of trigger pulses including one trigger pulse from the single pulse stream of each of the pair of detectors.

23. A gamma camera system according to claim 21, further comprising means for identifying a plurality of singles events that are registered in response to the artificial trigger pulses by associating a predetermined energy level with each of said singles events.

24. A nuclear medicine imaging system comprising:

a plurality of scintillation detectors, each of the scintillation detectors configured to generate a plurality of event-based trigger pulses in response to scintillation events and a plurality of artificial trigger pulses and configured to combine the event based trigger pulses and the artificial trigger pulses into a combined trigger signal;

a coincidence detection circuit coupled to receive the combined trigger signal from each of the detectors and configured to cause each of the detectors to register an event in response to coincidences between the combined trigger signals of the dectors; and

a processing system coupled to the detectors and configured to acquire randoms data representing random coincidences based on the artificial trigger pulses, to acquire coincidence data of the object, to correct the coincidence data based on the randoms data, and to form images of the object based on the corrected coincidence data.

25. A nuclear medicine imaging system according to claim 24, wherein each of the detectors comprises:

a trigger circuit for generating the plurality of event-based trigger pulses; and

a programmable pulse generator for generating the plurality of artificial trigger pulses at a programmed rate, wherein the programmed rate is based on a current measured singles rate.

26. A nuclear medicine imaging system according to claim 24, wherein each of the detectors comprises:

a trigger circuit for generating the plurality of event-based trigger pulses; and

a programmable pulse generator for generating the plurality of artificial trigger pulses using a programmed pulse width, wherein the programmed pulse width is based on a current measured singles rate.

27. A nuclear medicine imaging system according to claim 24, further comprising a logic circuit for combining the event based trigger pulses and the artificial trigger pulses into the combined trigger signal.

28. A nuclear medicine imaging system according to claim 24, wherein each detector is further configured to associate a predetermined energy level with each said event that results from one of the artificial trigger signals.

29. A nuclear medicine imaging system according to claim 24, wherein the processing system is further configured to acquire the randoms data based on the artificial trigger pulses by using coincidences detected based on the artificial trigger pulses to acquire a singles image for each of the detectors, and further by using the singles image from each detector to generate the randoms data.

30. A gamma camera based medical imaging system comprising:

plurality of scintillation detectors, each of the detectors including;

a trigger circuit configured to generate event-based trigger pulses in response to scintillation events; and

a pulse generator configured to generate artificial trigger pulses;

a coincidence detection circuit coupled to receive, from each of the detectors, a combined pulse stream including event-based trigger pulses and artificial trigger pulses, the coincidence detection circuit outputting a coincidence trigger signal in response to coincidences between the combined pulse stream from each of detector;

wherein each of the detectors is configured to;

register an event in response to receiving the coincidence trigger signal; and

tag each registered event that is based on one of the artificial trigger pulses to produce a plurality of tagged events; and

a processing system coupled to receive data representing the events registered by each of the detectors, wherein the processing system is configured to;

distinguish the tagged events from events that have not been tagged;

generate a singles image for each of the detectors based on the data representing the tagged events;

generate a randoms image based on the singles image from each of the detectors;

generate a coincidence image based on the data representing events that have not been tagged; and

correct the coincidence image based on the randoms image.

31. A gamma camera based medical imaging system according to claim 30, wherein each of the detectors is further configured to tag each registered event that is based on one of the artificial trigger pulses by associating a predetermined energy level with each said event.

32. A method of obtaining a measure of random coincidences in an imaging system including a plurality of radiation detectors, the method comprising:

using the radiation detectors to acquire singles data associated with an object simultaneously with using the radiation detectors to acquire coincidence data associated with the object, by generating a plurality of artificial trigger signals to acquire the singles data; and

using the singles data to acquire a measure of random coincidences associated with the coincidence data.

33. A method according to claim 32, wherein generating the plurality of artificial trigger signals comprises combining a plurality of artificial trigger pulses with a plurality of event-based trigger pulses.