Rotating hoop chopper wheel for x-ray imagers

1. An x-ray imaging apparatus comprising:

a holdable housing;

an x-ray source mounted within the housing and configured to output a fan beam of x-rays, wherein the x-ray source is a transmission-type x-ray tube configured to output the fan beam of x-rays through an exit window of the x-ray source and centered in an x-ray extraction direction forming an angle greater than 0 degrees with respect to a longitudinal axis of the transmission-type x-ray tube; and

a hoop chopper wheel rotatably mounted within the housing and comprising an x-ray attenuating material configured to block x-rays of the fan beam, the hoop chopper wheel defining a set of beam apertures of which each aperture is configured to pass therethrough a corresponding angular portion of x-rays from the fan beam, so that rotation of the hoop chopper wheel causes scanning of the corresponding angular portion of x-rays.

2. The apparatus of claim 1 , wherein the x-ray extraction direction is defined by an orientation of a collimator.

3. The apparatus of claim 1 , wherein the x-ray extraction direction forms an angle in a range of about 10 degrees to about 60 degrees with respect to the longitudinal axis.

4. The apparatus of claim 3 , wherein the angle is in a range of about 20 degrees to about 50 degrees.

5. The apparatus of claim 4 , wherein the angle is in a range of about 25 degrees to about 35 degrees.

6. The apparatus of claim 1 , wherein a minimum distance between an outer surface of the hoop chopper wheel and a front of the housing is less than about 50 mm.

7. The apparatus of claim 6 , wherein the minimum distance is less than about 30 mm.

8. The apparatus of claim 7 , wherein the minimum distance is less than about 10 mm.

9. The apparatus of claim 8 , wherein the minimum distance is less than about 5 mm.

10. The apparatus of claim 8 , wherein the minimum distance is between about 10 mm and about 1 mm.

11. The apparatus of claim 1 , further including a set of x-ray detectors configured to detect incident x-rays scattered by, or transmitted through, a target object that receives x-rays of the corresponding angular portion of x-rays from the fan beam, wherein at least one x-ray detector of the set of x-ray detectors comprises:

a scintillator volume having an entrance surface and an exit surface, the entrance surface configured to receive the incident x-rays, the scintillator volume configured to emit scintillation light responsive to the incident x-rays, and the exit surface configured to pass a portion of the incident x-rays that traverse a thickness of the scintillator volume between the entrance surface and the exit surface;

at least one first photodetector configured to output a first signal responsive to scintillation light received through the entrance surface of the scintillator volume;

a plurality of exit surface light guides optically coupled to the exit surface of the scintillator volume; and

at least one second photodetector optically coupled to an end of the plurality of exit surface light guides and configured to output a second signal responsive to scintillation light received through the exit surface of the scintillator volume.

12. The apparatus of claim 11 , further including a light cavity configured to direct the scintillation light received through the entrance surface to the at least one first photodetector.

13. The apparatus of claim 11 , further comprising a plurality of entrance surface light guides optically coupled to the entrance surface of the scintillator volume, wherein the at least one first photodetector is optically coupled to an end of the first plurality of light guides.

14. The apparatus of claim 11 , further comprising a spectrum analyzer configured to receive the first and second signals and to determine a characteristic of an energy spectrum of the incident x-rays based on the first and second signals.

15. The apparatus of claim 11 , further comprising an image generator configured to generate an image based on the detected x-rays.

16. The apparatus of claim 1 , wherein a focal spot of the x-ray source is substantially centered on a rotational axis of the hoop chopper wheel.

17. The apparatus of claim 1 , wherein a focal spot of the x-ray source has a substantial forward radial offset from a rotational axis of the hoop chopper wheel, the substantial forward radial offset configured to decrease a distance from the focal spot to a beam aperture of the set of apertures that is irradiated.

18. The apparatus of claim 1 , wherein a focal spot of the x-ray source has a substantial reverse radial offset from a rotational axis of the hoop chopper wheel, the substantial reverse radial offset configured to increase a distance from the focal spot to a beam aperture of the set of apertures that is irradiated.

19. An x-ray imaging apparatus comprising:

a housing;

a transmission-type x-ray tube mounted within the housing and configured to output a fan beam of x-rays, through an exit window of the transmission-type x-ray tube, centered in an x-ray extraction direction forming an angle greater than 0 degrees with respect to an longitudinal axis of the transmission-type x-ray tube; and

a hoop chopper wheel rotatably mounted within the housing and comprising an x-ray attenuating material configured to block x-rays of the fan beam, the hoop chopper wheel defining a set of beam apertures of which each aperture is configured to pass therethrough a corresponding angular portion of x-rays from the fan beam, so that rotation of the hoop chopper wheel causes scanning of the corresponding angular portion of x-rays.

20. The apparatus of claim 19 , wherein the x-ray extraction direction forms an angle in a range of about 10 degrees to about 60 degrees with respect to the longitudinal axis.

21. The apparatus of claim 20 , wherein the angle is in a range of about 20 degrees to about 50 degrees.

22. The apparatus of claim 21 , wherein the angle is in a range of about 25 degrees to about 35 degrees.

23. The apparatus of claim 19 , wherein a minimum distance between an outer surface of the hoop chopper wheel and a front of the housing is less than about 50 mm.

24. The apparatus of claim 23 , wherein the minimum distance is less than about 30 mm.

25. The apparatus of claim 24 , wherein the minimum distance is less than about 10 mm from a front of the housing.

26. The apparatus of claim 25 , wherein the minimum distance is less than about 5 mm from a front of the housing.

27. The apparatus of claim 26 , wherein the minimum distance is between about 10 mm and about 1 mm.