Nuclear imaging using three-dimensional gamma particle interaction detection

• US 20050023474A1
• Filed: 06/23/2004
• Published: 02/03/2005
• Est. Priority Date: 06/17/1999
• Status: Active Grant

• Current Assignee: Siemens Medical Systems, Inc. (Siemens AG)
• Original Assignee: Siemens Medical Systems, Inc. (Siemens AG)
• Inventors: Engdahl, John C., Persyk, Dennis E.
• Granted Patent: US 7,397,038 B2
• Time in Patent Office: Days
• US Class Current: 250/370.100
• 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

An improved method of, and apparatus for, nuclear imaging takes advantage of the ability to determine the depth of gamma ray/electron interaction within a semiconducting gamma ray detector to determine the (most highly probable) location of the first gamma ray/electron interaction within the detector. Lines of interaction constructed between opposing detector arrays, extending between the location of the first gamma ray/electron interaction in each detector associated with the coincident detection of gamma radiation, permits a positron-emitting object of interest to be imaged according to protocols known in the art, but with better spatial resolution than previously believed to have been known.

Claims

1-6. -6. (Cancelled).

7. A method of positron emission tomographic nuclear medical imaging, comprising the steps of:

detecting a plurality of gamma interactions in a first gamma ray detector, wherein said plurality of gamma interactions corresponds to a single coincidence event;

for each of said plurality of detected gamma interactions, determining the depth of interaction in said gamma ray detector and the amount of energy deposited in said gamma ray detector;

determining which one of said plurality of detected gamma interactions in said gamma ray detector occurred first, by

1) selecting an arbitrary one of said plurality of detected gamma interactions as a tentative first interaction;

2) selecting a remaining one of said plurality of detected gamma interactions as a tentative second interaction;

3) calculating a hypothetical Compton scatter angle between said tentative first and second interactions based on the determined amount of energy deposited thereby in said gamma ray detector;

4) comparing said hypothetical Compton scatter angle with an actual Compton scatter angle as obtained from said determined depth of interaction of said tentative first and second interactions;

5) determining whether said tentative first and second interactions are actual first and second interactions based on the result of said comparison;

6) if the determination of step

     5) is negative and additional remaining detected gamma interactions exist, repeating steps

     2) through

     5) for a different remaining one of said plurality of detected gamma interactions;

7) if the determination of step

     5) is negative and no additional remaining detected gamma interactions exist, repeating steps

     1) through

     6) for a different arbitrary one of said plurality of detected gamma interactions; and

generating a line of interaction between a determined actual first interaction in said first gamma ray detector and a similarly determined actual first interaction in a second gamma ray detector, to thereby determine the location of said coincidence event.

8. The method of claim 7, wherein said gamma ray detectors comprise arrays of individual, three-dimensional semiconductor elements, and wherein the step of determining the depth of interaction comprises identifying the semiconductor element in which a gamma interaction occurs and calculating the distances from said interaction to respective electrode surfaces of the respective semiconductor element in which the interaction has occurred.

9. The method of claim 8, wherein said distances are calculated based on the amount of time between the time at which charge pulses attributable to the flow of electrons are first detected at an anode on one of said electrode surfaces and the time at which charge pulses attributable to the flow of holes are first detected at a cathode on the other of said electrode surfaces.

10. Apparatus for positron emission tomographic nuclear medical imaging, comprising:

a pair of three-dimensional gamma ray detectors that detect a coincident gamma event as a plurality of gamma interactions in each detector, each of said detectors being capable of determining the depth of interaction and the amount of energy deposited by a gamma interaction therein; and

a data processor capable of determining, for each coincident gamma event, which one of said plurality of detected gamma interactions in each of said gamma ray detectors occurred first, by performing the following functions;

1) selecting an arbitrary one of said plurality of detected gamma interactions as a tentative first interaction;

2) selecting a remaining one of said plurality of detected gamma interactions as a tentative second interaction;

3) calculating a hypothetical Compton scatter angle between said tentative first and second interactions based on the determined amount of energy deposited thereby in said gamma ray detector;

4) comparing said hypothetical Compton scatter angle with an actual Compton scatter angle as obtained from said determined depth of interaction of said tentative first and second interactions;

5) determining whether said tentative first and second interactions are actual first and second interactions based on the result of said comparison;

6) if the determination of step

     5) is negative and additional remaining detected gamma interactions exist, repeating steps

     2) through

     5) for a different remaining one of said plurality of detected gamma interactions;

7) if the determination of step

     5) is negative and no additional remaining detected gamma interactions exist, repeating steps

     1) through

     6) for a different arbitrary one of said plurality of detected gamma interactions; and

generating a line of interaction between a determined actual first interaction in one of said pair of gamma ray detectors with a determined actual first interaction in the other of said pair of gamma ray detectors, to thereby determine the location of said coincidence event.

11. The apparatus of claim 10, wherein each of said gamma ray detectors comprise arrays of individual, three-dimensional semiconductor elements extending in first and second orthogonal directions, and the location of a gamma interaction in a third direction orthogonal to each of said first and second directions is determined.

12. The apparatus of claim 10, wherein each of said gamma ray detectors comprise multiple pluralities of essentially planar gamma ray detector elements extending in first and second orthogonal directions, said multiple pluralities of planar gamma ray detector elements being stacked substantially parallel to each other in a third direction orthogonal to each of said first and second directions.

13. A method of positron emission tomographic nuclear medical imaging, comprising the steps of:

detecting a plurality of gamma interactions in a first gamma ray detector, wherein said plurality of gamma interactions corresponds to a single coincidence event;

for each of said plurality of detected gamma interactions, determining the depth of interaction in said gamma ray detector and the amount of energy deposited in said gamma ray detector;

determining which one of said plurality of detected gamma interactions in said gamma ray detector occurred first, by performing an iterative process of comparing hypothetical Compton scatter angles between arbitrarily chosen first and second gamma interactions obtained from deposited energy values, with actual Compton scatter angles obtained from determined depths of interaction, until an actual first occurring gamma interaction has been identified; and

generating a line of interaction between a determined actual first interaction in said first gamma ray detector and a similarly determined actual first interaction in a second gamma ray detector, to thereby determine the location of said coincidence event.