Correction for spatial variations of deadtime of a monolithic scintillator based detector in a medical imaging system

• US 6,403,960 B1
• Filed: 04/29/1999
• Issued: 06/11/2002
• Est. Priority Date: 04/29/1999
• 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: Shao, Lingxiong, Wellnitz, Donald R., Petrillo, Michael J.
• Primary Examiner(s): Epps, Georgia
• Assistant Examiner(s): HANIG, RICHARD E
• Application Number:
  US09/302,161
• Time in Patent Office: 1,139 Days
• Field of Search: 250/370.11, 250/370.06, 250/363.02, 250/363.03, 250/363.04, 250/363.07, 250/363.09, 250/370.09, 250/390.11, 250/369, 250/391
• US Class Current: 250/363.09
• CPC Class Codes: G01T 1/171 Compensation of dead-time counting losses see provisionally also G01T1/17

Abstract

A nuclear medicine imaging system includes the capability to correct for the deadtime, including the capability to correct for spatial variations in deadtime across the imaging surface of a detector. The imaging system includes one or more radiation detectors, each using a large, monolithic scintillation crystal. Each detector has deadtime associated with it. A given detector is used to acquire an energy profile of a patient based on emission radiation. The detector includes a number of timing channels. The energy profile is used to select a zone influence map indicating the extent of spatial overlap in response between the various timing channels. Emission data of the patient is then acquired during an emission scan. During acquisition of the emission data, a rate meter assigned to each timing channel samples the number of counts associated with each timing channel to acquire deadtime data. A unique deadtime function is provided for each unique zone represented in the zone influence map, including each region of overlap. The deadtime data acquired from the rate meters are then applied to the deadtime functions to correct the emission data for deadtime on a pixel-by-pixel basis. An image is generated based on the deadtime-corrected data.

Claims

1. A method of operation in an imaging system, the imaging system having a radiation detector including a monolithic scintillator, the radiation detector having deadtime associated therewith, the method comprising:

generating data of an object in response to radiation detected by the detector, including collection of deadtime data associated with the detector while generating said data of the object;

correcting said data of the object for said collected deadtime data, including correcting said, data of the object for spatial variations in said collected deadtime data across an imaging area of the monolithic scintillator; and

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

2. A method as recited in claim 1, wherein the image includes a plurality of fundamental image elements, and wherein said correcting comprises correcting the data of the object in accordance with said collected deadtime data independently for each of the fundamental image elements.

3. A method as recited in claim 1, wherein said correcting of said data of the object comprises applying the collected deadtime data to a plurality of deadtime functions, each of the deadtime functions corresponding to a unique subset of an imaging area of the detector, and each of the fundamental image elements being associated with one of the subsets.

4. A method as recited in claim 3, wherein each of the deadtime functions is a function of a sampling of events detected for a corresponding one of the subsets.

5. A method. as recited in claim 1, wherein said correcting of said data of the object in accordance with said collected deadtime data comprises:

acquiring an energy profile of the object; and

using also the energy profile in said correcting of said data of the object in accordance with the collected deadtime data.

6. A method of operation in an imaging system, the method comprising:

generating image data of an object in response to events detected by a detector of the imaging system;

applying collected deadtime data to a plurality of deadtime functions while generating the image data, each of the deadtime functions corresponding to a different subset of an imaging area of the detector; and

correcting the image data based on the result of said application of said collected deadtime data to said plurality of deadtime functions.

7. A method as recited in claim 6, wherein the image data represents a plurality of fundamental image elements, and wherein said correcting of the image data comprises correcting the image data independently for each of the fundamental image elements using the result of said application of said collected deadtime data.

8. A method as recited in claim 6, wherein each of the deadtime functions is a function of a sampling of the events detected at a corresponding subset of the imaging area of the detector.

9. A method as recited in claim 6, wherein said correcting of the image data comprises:

acquiring an energy profile of the object; and

using also the energy profile in said correcting of the image data in accordance with the collected deadtime data.

10. A method as recited in claim 9, wherein said detector comprises a block detector.

11. A method of operation in an imaging system, the method comprising:

generating image data of an object in response to event-based triggers;

collecting and applying deadtime data based on a sampling of the event-based triggers while generating the image data; and

using the applied deadtime data to correct the image data of the object.

12. A method as recited in claim 11, the image data representing a plurality of fundamental image elements, further comprising using the applied deadtime data to correct the image data of the object independently for each of the fundamental image elements.

13. A method as recited in claim 11, wherein said applying of deadtime data comprises applying the deadtime data to a plurality of deadtime functions, each of the deadtime functions corresponding to a different subset of an imaging area of a detector of the imaging system, each of the fundamental image elements corresponding to one of the subsets of an imaging surface of the detector.

14. A method of operation in an imaging system, the method comprising:

detecting events using a plurality of subsets of an imaging area of a detector of the imaging system;

generating image data of an object in response to the detected events, the image data representing a plurality of fundamental image elements;

collecting and applying deadtime data based on the detected events and a plurality of deadtime functions while generating the image data, each of the deadtime functions corresponding to a different one of the subsets; and

using the applied deadtime data to correct the image data independently for each of the fundamental image elements.

15. A method as recited in claim 14, wherein each of the deadtime functions is a function of a sampling of the events detected at a corresponding subset of the imaging area of the detector.

16. A method as recited in claim 14, wherein the detector has a plurality of overlapping timing zones, wherein the plurality of deadtime functions comprise a deadtime function for each region of overlap of two or more of said overlapping timing zones.

17. A method as recited in claim 16, wherein the detector comprises a monolithic scintillator, such that the plurality of timing zones comprise a plurality of timing zones of said monolithic scintillator.

18. A method as recited in claim 16, wherein said collecting and applying of the deadtime data comprises:

generating a plurality of sample pulses to sample the events detected in each of the timing zones; and

collecting and applying the deadtime data for each of the fundamental image elements based on the sampled events and the deadtime functions.

19. A method as recited in claim 16, wherein said collecting and applying of the deadtime data based on the detected events and a plurality of deadtime functions comprises using an energy-dependent zone influence map in said collecting and application of the deadtime data, wherein the zone influence map indicates said regions of overlap.

20. A method as recited in claim 19, wherein said using an energy dependent zone influence map in said collecting and application of the deadtime data comprises determining the zone influence map indicating said regions of overlap by:

acquiring an energy profile of the object; and

using the energy profile and characteristics of the detector to select the zone influence map.

21. A method as recited in claim 20, wherein the detector comprises a plurality of block detectors.

22. A method as recited in claim 20, wherein said using of the energy profile and characteristics of the detector to select the zone influence map comprises selecting one of a plurality of zone influence maps based on the energy profile.

23. A method of operation in a medical imaging system, the medical imaging system including a detector, the detector having a plurality of zones with at least one overlap region, each overlap region representing a region of the detector in which a detected event may affect more than one of the zones, the method comprising:

generating image data of an object in response to a plurality of events detected by the detector, the image data representing a plurality of fundamental image elements;

collecting and applying deadtime data based on the detected events and a plurality of deadtime functions while generating the image data, the plurality of deadtime functions including a deadtime function for each overlap region; and

correcting each of the fundamental image elements based on a portion of the applied deadtime data, each of said portion of the applied deadtime data resulting from one of the deadtime functions associated with a subset of said fundamental image elements.

24. A method as recited in claim 23, wherein each of the plurality of zones is a timing zone.

25. A method as recited in claim 23, wherein said collecting and applying of the deadtime data comprises:

sampling the radiation-induced event triggers; and

collecting and applying the deadtime data for each of the pixels based on the sampling and the deadtime functions.

26. A method as recited in claim 23, further comprising determining a zone influence map specifying the plurality of zones and the plurality of overlap regions, wherein said generating the zone influence map comprises:

acquiring an energy profile of the object; and

using the energy profile and characteristics of the detector to determine the zone influence map.

27. A method as recited in claim 26, wherein said determining the zone influence map comprises selecting one of a plurality of selectable zone influence maps based on the energy profile of the object.

28. A method as recited in claim 24, wherein the detector comprises a monolithic scintillator, the plurality of zones comprising a plurality of zones of the monolithic scintillator.

29. A method of operation in a medical imaging system, the method comprising:

generating a zone influence map, the zone influence map specifying a plurality of timing zones of a detector of the imaging system, including specifying a plurality of overlap regions, each the overlap regions representing a region of the detector in which a detected event may affect more than one of the timing zones;

generating image data of an object in response to a plurality of events detected by the detector, the image data representing a plurality of pixels;

collecting and applying deadtime data based on the detected events, the zone influence map, and a plurality of deadtime functions, the plurality of deadtime functions including a separate deadtime function for each of the overlap regions while generating the image data; and

correcting each of the pixels based on a subset of the results of said collecting and application of the deadtime data, each of said subsets of the results of said collecting and application of the deadtime data resulting from one of the deadtime functions associated with a subset of said pixels.

30. A method as recited in claim 29, wherein the deadtime function for each overlap region is based on a number of sampled counts for each of the zones associated with said overlap region.

31. A method as recited in claim 29, wherein said collecting and applying of the deadtime data comprises collecting a sampling of the events for each of the zones, wherein each of the deadtime functions represents a function of one or more of said samplings.

32. A method as recited in claim 29, wherein said generating the zone influence map comprises:

simulating operation of the detector; and

identifying said overlap regions based on said simulation.

33. A method as recited in claim 32, further comprising:

acquiring an energy profile of the object; and

selecting the zone influence map from among a plurality of zone influence maps based on the energy profile.

34. A method as recited in claim 29, wherein the detector comprises a monolithic scintillator, the plurality of zones comprising a plurality of zones of the monolithic scintillator.

35. A method of operation in a nuclear medicine imaging system, the method comprising:

selecting a zone influence map, the zone influence map specifying a plurality of zones of a detector of the imaging system, including specifying a plurality of overlap regions, each the overlap regions representing a region of the detector in which a radiation-induced event may affect more than one of the zones;

generating image data of an object in response to a plurality of radiation-induced event triggers of the detector, the image data including a plurality of pixels;

collecting and applying deadtime data for each of the pixels based on the radiation-induced event triggers and a plurality of deadtime functions while generating the image data, the plurality of deadtime functions including a deadtime function for each of the overlap regions, wherein the deadtime function for each overlap region is based on a number of counts measured for each of the zones associated with said overlap region; and

correcting each pixel based on a subset of the results of the collected and applied deadtime data, each of said subsets of the results of the collected and applied deadtime data resulting from one of the deadtime functions associated with said pixel.

36. A method as recited in claim 35, wherein said collecting and applying of the deadtime data comprises:

generating a plurality of sample pulses; and

collecting and applying the deadtime data for each of the pixels based on the plurality of sample pulses, the radiation-induced event triggers, and the deadtime functions while generating the sample pulses, wherein each of said measured counts represents a coincidence between one of the radiation-induced event triggers and one of the sample pulses.

37. A method as recited in claim 35, wherein said selecting the zone influence map comprises:

using the detector to acquire an energy profile of the object to be imaged; and

selecting the zone influence map based on the energy profile.

38. A method as recited in claim 35, wherein the detector comprises a monolithic scintillator, the plurality of zones comprising a plurality of zones of the monolithic scintillator.

39. A method of operation in a nuclear medicine imaging system, the method comprising:

acquiring an energy profile of an object to be imaged;

using the energy profile to select a zone influence map from a plurality of selectable zone influence maps, the zone influence map specifying a plurality of zones of a detector of the imaging system, including specifying a plurality of overlap regions, each the overlap regions representing a region of the detector in which a scintillation event may affect more than one of the zones;

generating image data of the object in response to scintillation event based triggers of the detector, the image data representing a plurality of pixels;

collecting and applying deadtime data based on the scintillation event based triggers of the detector, the zone influence map, and a plurality of deadtime functions, the plurality of deadtime functions including a different deadtime function for each of the overlap regions while generating the image data, wherein the deadtime function for each overlap region is based on a number of sampled counts for each of the zones associated with said overlap region, said number of sampled counts representing a number of coincidences between the scintillation event based triggers of the detector and a plurality of sample pulses;

correcting the image data on a pixel-by-pixel basis using the results of the collected and applied deadtime data to generate deadtime-corrected image data, including correcting each pixel based on a subset of the results of the collected and applied deadtime data, each of said subsets of the results of the collected and applied deadtime data resulting from one of the deadtime functions associated with said pixel; and

generating an image of the object based on the deadtime-corrected image data.

40. A method as recited in claim 39, wherein the zone influence map is a function of physical characteristics of the detector.

41. A method as recited in claim 40, wherein the detector comprises a, the plurality of zones comprising a plurality of zones of the monolithic scintillator.

42. A method of operation in a nuclear medicine imaging system, the method comprising:

providing a plurality of zone influence maps, each zone influence map based on physical characteristics of a monolithic scintillation detector of the imaging system, each zone influence map corresponding to a particular energy level and specifying a plurality of timing zones of the detector, including specifying a plurality of overlap regions for said energy level, each the overlap regions representing a region of the detector in which a scintillation event may affect more than one of the timing zones;

using the detector to acquire an energy profile of an object to be imaged based on radiation emitted from the object;

using the energy profile to select one of the zone influence maps;

generating emission data of the object in response to scintillation event based triggers of the detector, the emission data representing a plurality of pixels;

collecting and applying deadtime data based on the emission data, the selected zone influence map, and a plurality of deadtime functions, the plurality of deadtime functions including a different deadtime function for each of the overlap regions specified by the selected zone influence map while generating the emission data of the object, wherein the deadtime function for each overlap region is based on a number of counts measured for each of the zones associated with said overlap region, said counts representing coincidences between scintillation event based triggers of the detector and a plurality of sample pulses;

correcting the emission data on a pixel-by-pixel basis using the results of said collection and application of the deadtime data to generate deadtime-corrected emission data, including correcting each pixel based on a subset of the results of said collection and application of deadtime data, each of said subsets of the deadtime data resulting from one of the deadtime functions associated with said pixel; and

generating an image of the object based on the deadtime-corrected emission data.

43. A nuclear medicine imaging system comprising:

a radiation detector to generate data of an object in response to detected radiation, the radiation detector including a monolithic scintillator, the radiation detector having deadtime associated therewith;

means for collecting deadtime data for said deadtime associated with said detector while generating said data of the object;

means for correcting the data of the object in accordance with said collected deadtime data, including means for correcting for spatial variations in said collected deadtime data with respect to an imaging area of the monolithic scintillator; and

means for generating images of the object based on the corrected data of the object.

44. A nuclear medicine imaging system as recited in clam 43, wherein the imaging area of the monolithic scintillator corresponds to a plurality of pixels of an image, and wherein said means for correcting the data of the object based on the collected deadtime data comprises means for correcting the image data based on the collected deadtime data separately for each of the pixels.

45. A nuclear medicine imaging system as recited in claim 44, wherein said means for collecting and applying deadtime data comprises means for applying the collected deadtime data to a plurality of deadtime functions, each of the deadtime functions corresponding to a different subset of an imaging area of the detector, each of the pixels corresponding to one of the subsets of the imaging surface of the detector.

46. A nuclear medicine imaging system as recited in claim 44, wherein each of the deadtime functions is a function of a sampling of the events detected at a corresponding subset of the imaging area of the detector.

47. A nuclear medicine imaging system comprising:

a radiation detector for detecting radiation-induced events;

means for generating image data of an object in response to the radiation-induced events;

means for collecting and applying deadtime data based on a sampling of the event-based triggers while generating the image data; and

means for using the collected and applied deadtime data to correct the image data.

48. A nuclear medicine imaging system as recited in claim 47, the image data representing a plurality of fundamental image elements, further comprising means for using the collected and applied deadtime data to correct the image data independently for each of the fundamental image elements.

49. A nuclear medicine imaging system as recited in claim 48, wherein said means for collecting and applying deadtime data comprises means for applying the collected deadtime data based on a plurality of deadtime functions, each of the deadtime functions corresponding to a different subset of an imaging area of the detector, each of the fundamental image elements corresponding to one of the subsets of the imaging surface of the detector.

50. A medical imaging system comprising:

a plurality of radiation detectors, each of the detectors having an imaging area comprising a plurality of zones to detect events at each of the zones, each of the detectors employed to generate event data of an object in response to the detected events, each of the detectors further employed to generate a sampling of the detected events for each of the zones;

a processing system coupled to each of the detectors, the processing system configured to generate image data based on the event data, the image data representing a plurality of fundamental image elements, the processing system further employed to collect and apply deadtime data based on said samplings and a plurality of deadtime functions while generating the image data, the processing system further employed to use the results of said collection and application of deadtime data to correct the image data independently for each of the fundamental image elements.

51. A medical imaging system as recited in claim 50, wherein the plurality of zone overlap at a plurality of overlap regions, and wherein the plurality of deadtime functions comprises a deadtime function for each of the overlap regions.

52. A medical imaging system as recited in claim 51, wherein the detector comprises a monolithic scintillator, the plurality of zones comprising a plurality of zones of the monolithic scintillator.

53. A nuclear medicine imaging system comprising:

a gantry;

a plurality of radiation detectors supported by the gantry so as to be rotatable about an object to be imaged, each of the detectors having an imaging area comprising a plurality of timing zones to detect events at each of the zones, wherein the plurality of timing zones overlap in at least one overlap region for a given energy-level, each of the detectors employed to generate event data of the object in response to the detected events, each of the detectors further employed to acquire a sampling of the detected events; and

a processing system coupled to each of the detectors to generate image data based on the event data, the processing system further employed to collect and apply deadtime data based on a plurality of deadtime functions and said samplings of the detected events while generating said image data, and wherein the plurality of deadtime functions includes a deadtime function for each of the at least one overlap regions, the processing system further configured to use the results of the collected and applied deadtime data to correct the image data.

54. A nuclear medicine imaging system as recited in claim 53, wherein the processing system is further configured to use the corrected image data to generate a tomographic image of the object.

55. A nuclear medicine imaging system as recited in claim 53, wherein the image data comprises a plurality of pixels, and wherein the processing system is configured to correct the image data by applying to each pixel the result of applying the collected deadtime data to one of the deadtime functions which corresponds to the pixel.

56. A nuclear medicine imaging system as recited in claim 55, wherein said one of the deadtime functions which corresponds to said pixel is a function of the samplings of the detected events for all of the timing zones to which said pixel corresponds, as specified by said at least one overlap region.

57. A nuclear medicine imaging system as recited in claim 55, wherein the detector comprises a monolithic scintillator, the plurality of zones comprising a plurality of zones of the monolithic scintillator.