System and method for calibrating and tuning a gamma camera

• US 20040036026A1
• Filed: 08/21/2002
• Published: 02/26/2004
• Est. Priority Date: 08/21/2002
• Status: Active Grant

• Current Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Original Assignee: Siemens Medical Solutions USA Incorporated (Siemens AG)
• Inventors: Engdahl, John C., Caruba, James F.
• Granted Patent: US 6,835,935 B2
• Time in Patent Office: Days
• US Class Current: 250/363.09
• CPC Class Codes: A61B 6/4258 for detecting non x-ray radiation, e.g. gamma radiation A61B6/037 takes precedence
• CPC Class Codes: G01T 1/1642 using a scintillation crystal and position sensing photodetector arrays, e.g. ANGER cameras
• 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

Abstract

A gamma camera having a system for performing a quality control procedure with minimal to no intervention from a user of the camera. In one aspect, the gamma camera includes a relatively weak radioactive source positioned at a fixed or known location relative to the gamma camera scintillation crystal and positioned so that the entrance window side of the crystal is facing the source, wherein the photons emitted from the source have an energy that is below the energy of photons used for diagnostic imaging. The response of the gamma camera photo-multiplier tubes to the absorption events caused by the radioactive source when the camera is idle can be compared to a baseline response to determine whether one or more of the PMTs need to be adjusted.

Claims

1. A gamma camera, comprising:

a scintillation crystal having an entrance window side;

a radioactive source positioned at a fixed or known location relative to the crystal and positioned so that the entrance window side is facing the source, wherein the photons emitted from the source have an energy that is below the energy of photons used for diagnostic imaging; and

a photo-multiplier tube (PMT) for detecting scintillation photons emitted from the scintillation crystal.

2. The gamma camera of claim 1, wherein the photons emitted from the source have a sufficiently low photon energy such that regulatory agencies do not require licensing or inventory control of the source.

3. The gamma camera of claim 1, wherein the source comprises Americium-241.

4. The gamma camera of claim 1, wherein the source consists essentially of Americium-241.

5. The gamma camera of claim 1, wherein the source is attached to a component of the gamma camera.

6. The gamma camera of claim 1, wherein the source is attached to the crystal.

7. The gamma camera of claim 1, further comprising a plurality of the radioactive sources.

8. In a gamma camera having a photo-multiplier tube, a scintillation crystal, and a source of radioactivity, wherein the photons emitted from the source have an energy that is below the energy of photons used for diagnostic imaging, a method for tuning the gamma camera comprising:

monitoring an output of the PMT for a period of time when the camera is idle;

for each absorption event caused by the source of radioactivity during the period of time, recording the amplitude of an output pulse produced by the PMT at said output in response to the absorption event;

calculating a mean pulse amplitude based on the recorded amplitudes; and

comparing said calculated mean pulse amplitude to a baseline value.

9. The method of claim 8, wherein the recorded amplitudes have a distribution and the method further comprises calculating a variance of the amplitude distribution.

10. The method of claim 8, further comprising comparing said calculated variance to a baseline variance.

11. The method of claim 10, wherein, prior to the step of monitoring the output of the PMT, the method includes the step of determining whether the gamma camera is idle.

12. The method of claim 8, wherein the photons emitted from the source have a sufficiently low photon energy such that regulatory agencies do not require licensing or inventory control of the source.

13. The method of claim 8, wherein the source comprises Americium-241.

14. The method of claim 8, wherein the source consists essentially of Americium-241.

15. In a gamma camera having a plurality of photo-multiplier tubes (PMTs), a scintillation crystal, and a plurality of radioactivity sources, wherein the photons emitted from the sources have an energy that is below the energy of photons used for diagnostic imaging, a method for tuning the gamma camera comprising:

determining whether the gamma camera is idle; and

performing the following acts after determining that the gamma camera is idle;

(A) detecting an absorption event caused by one of the plurality of sources;

(B) determining the source that caused the event;

(C) for each PMT affected by the event, measuring the amplitude of an output pulse produced by the PMT in response to the event, recording a value corresponding to the measured amplitude, and associating the value with the determined source and the PMT; and

(D) repeating steps (A)-(C) at least a pre-determined number of times or for at least a pre-determined amount of time.

16. The method of claim 15, wherein after performing step (D), the method further comprises:

selecting one of the plurality of PMTs;

selecting one of the plurality of souces;

reading the set of recorded values that are associated with the selected source and the selected PMT;

calculating the mean of said values;

comparing the calculated mean to a baseline mean.

17. The method of claim 16, wherein the set of recorded values that are associated with the selected source and the selected PMT have a distribution and the method further comprises calculating a variance of the distribution.

18. The method of claim 17, further comprising comparing said calculated variance to a baseline variance.

19. The method of claim 15, wherein the photons emitted from the source have a sufficiently low photon energy such that regulatory agencies do not require licensing or inventory control of the source.

20. The method of claim 15, wherein the source comprises Americium-241.

21. The method of claim 15, wherein the source consists essentially of Americium-241.