Apparatus and method for scanning a structure, and collimator therefor

1. An apparatus for scanning a structure to detect differences in density between different parts of the structure, the apparatus comprising:

a source of radiation;

a plurality of first detectors arranged to detect radiation emitted by said source along a plurality of respective first paths; and

a plurality of second detectors arranged to detect radiation emitted by said source along a plurality of respective second paths;

wherein each said first and second paths is substantially aligned with a respective radius of a circle centred on the source;

wherein an angular separation between at least two neighbouring first paths is S;

wherein the first and second detectors and the source are arranged for rotation in a fixed relationship with respect to each other, about an axis of rotation located between the source and the detectors, wherein said axis of rotation is substantially orthogonal to said circle;

wherein there are 2N+1 detectors;

wherein said first paths are located on a first side of a plane containing the source and said axis of rotation and the positions D L of the first detectors are given by D L =nS, where n=0, 1, 2, . . . N; and

wherein said second paths are located on a second side of said plane and the positions DR of the second detectors are given by D R =(n+f)S, where n=0, 1, 2, . . . N−1 and where 0<f<1.

2. The apparatus according to claim 1 , wherein f is substantially equal to 0.5.

3. The apparatus according to claim 1 , wherein said first and second detectors are arranged for rotation by 360 degrees about said axis of rotation.

4. The apparatus according to claim 1 , wherein said first and second paths are defined, at least in part, by respective collimator channels.

5. The apparatus according to claim 1 , wherein said first and second paths are defined, at least in part, by respective detection surfaces of said detectors.

6. The apparatus according to claim 1 , further comprising at least one collimator block, comprising: a plurality of first collimator channels, wherein said first paths are defined at least in part by respective first collimator channels; and/or a plurality of second collimator channels wherein said second paths are defined at least in part by respective second collimator channels.

7. The apparatus according to claim 1 , wherein said source is a gamma radiation source.

8. The apparatus according to claim 1 , wherein at least one said first or second detector comprises a scintillating material for emitting light in response to incident radiation.

9. A collimator arrangement for an apparatus for scanning a structure to detect differences in density between different parts of the structure, the collimator arrangement comprising:

a plurality of first collimator channels defining, at least in part, a plurality of respective first radiation paths; and

a plurality of second collimator channels defining, at least in part, a plurality of respective second radiation paths;

wherein each said first and second radiation path is substantially aligned with a respective radius of a circle;

wherein an angular separation between neighbouring first paths is S;

wherein there are 2N+1 collimator channels;

wherein said first paths are located on a first side of a plane containing the source and said axis of rotation and the positions D L of the first collimator channels are given by D L =nS, where n=0, 1, 2, . . . N; and

wherein said second paths are located on a second side of said plane and the positions D R of the second collimator channels are given by D R =(n+f) S, where n=0, 1, 2, . . . N−1 and where 0<f<1.

10. The collimator arrangement according to claim 9 , wherein f is substantially equal to 0.5.

11. The collimator arrangement according to claim 9 , wherein said first and second collimator channels are provided in a single block of collimating material.

12. A method for scanning a structure to detect differences in density between different parts of the structure, comprising:

providing at least one source of radiation;

providing a plurality of first detectors arranged to detect radiation emitted by said source along a plurality of respective first paths; and

providing a plurality of second detectors arranged to detect radiation emitted by said source along a plurality of respective second paths;

wherein each said first and second path is substantially aligned with a respective radius of a circle having the source at its origin;

wherein an angular separation between at least two neighbouring first paths is S;

the method further comprising:

rotating said first and second detectors and said source in a fixed relationship to each other about an axis of rotation located between said detectors and the source, wherein said axis of rotation is substantially orthogonal to said circle;

wherein there are 2N+1 detectors;

wherein said first paths are located on a first side of a plane containing the source and said axis of rotation and the positions D L of the first detectors are given by D L =nS, where n=0, 1, 2, . . . N; and

wherein said second paths are located on a second side of said plane and the positions D R of the second detectors are given by D R =(n+f) S, where n=0, 1, 2, . . . N−1 and where 0<f<1.

13. The method according to claim 12 , wherein f is substantially equal to 0.5.

14. The method according to claim 12 , further comprising:

rotating said first and second detectors and said source in a fixed relationship to each other by at least 360 degrees about said axis of rotation.

15. The apparatus according to claim 2 , wherein said first and second detectors are arranged for rotation by 360 degrees about said axis of rotation.

16. The collimator arrangement according to claim 10 , wherein said first and second collimator channels are provided in a single block of collimating material.

17. The method for detecting radiation according to claim 13 , further comprising: rotating said first and second detectors and said source in a fixed relationship to each other by at least 360 degrees about said axis of rotation.