Patent Number: 
Section: claims

1. An apparatus for characterizing an emission from a field of view and an x-ray transmissivity of the field of view, the apparatus comprising:an x-ray source located adjacent to the field of view, the x-ray source providing x-rays;a source mask located between the x-ray source and the field of view, the source mask having a source aperture through which the x-rays pass, the x-rays having a path direction through the field of view;an emission detector located adjacent to the field of view, the emission detector detecting the emission from the field of view; andan x-ray detector located between the emission detector and the field of view so as to receive the x-ray beam after the x-ray beam passes through the field of view,wherein the emission detector is shielded from the x-rays, the emission detector providing an emission signal correlated with the emissions from the field of view,the x-ray detector providing an x-ray detector signal correlated with the x-ray transmissivity of the field of view for the path direction,the apparatus further comprising an x-ray shield having a plurality of shield apertures therethrough,the shield apertures being positioned so as to allow emission from the field of view to reach the emission detector, the x-ray shield preventing x-rays from reaching the emission detector. 2. The apparatus of claim 1, further comprising an actuator operable to move the source aperture relative to the x-ray source, so as to provide a change in the path direction through the field of view,the x-ray detector moving in response to the change in the path direction so that the x-ray detector continues to receive the x-rays,the emission detector remaining shielded from the x-rays as the path direction is changed. 3. The apparatus of claim 2, wherein the x-ray detector is mounted on an x-ray shield, the x-ray detector and x-ray shield moving together in response to the change in the path direction. 4. The apparatus of claim 1, wherein the emission detector is a gamma detector, the emission being gamma emission from the field of view. 5. The apparatus of claim 4, wherein the apparatus provides a gamma emission image of the field of view using a first signal from the emission detector,the apparatus further providing an x-ray transmission image of the field of view using a second signal from the x-ray detector. 6. An apparatus for characterizing an emission from a field of view and an x-ray transmissivity of the field of view, the apparatus comprising:an x-ray source located adjacent to the field of view, the x-ray source providing x-rays;a source mask located between the x-ray source and the field of view, the source mask having a source aperture through which the x-rays pass, the x-rays having a path direction through the field of view;an emission detector located adjacent to the field of view, the emission detector detecting the emission from the field of view; andan x-ray detector located between the emission detector and the field of view so as to receive the x-ray beam after the x-ray beam passes through the field of view,wherein the emission detector is shielded from the x-rays, the emission detector providing an emission signal correlated with the emissions from the field of view,the x-ray detector providing an x-ray detector signal correlated with the x-ray transmissivity of the field of view for the path direction,wherein the x-ray source is pulsed between an on state and an off state, so as to provide x-ray pulses having a pulse duration, the pulses separated by a pulse interval during which the x-ray source is in the off state, the x-ray source having a duty cycle equal to the pulse duration divided by the pulse interval,the duty cycle being selected so that emission data and x-ray data are collected over a substantially concurrent time period,wherein the pulse duration is between approximately 0.01 milliseconds and approximately 200 milliseconds,the pulse interval being at least 10 times longer than the pulse length. 7. The apparatus of claim 6the pulse interval being at least 100 times longer than the pulse length. 8. The apparatus of claim 1, wherein the source mask includes a plurality of source apertures, providing x-rays having a plurality of path directions through the field of view,the apparatus further including an actuator operable to move the source mask relative to the x-ray source, so as to modify the plurality of path directions through the field of view. 9. The apparatus of claim 8, the apparatus further comprising a plurality of x-ray detectors positioned to detect at least part of the x-rays having the plurality of path directions. 10. The apparatus of claim 8, further comprising a plurality of x-ray sources arranged substantially in a first arc, and wherein the plurality of source apertures are arranged substantially in a second arc. 11. An apparatus for characterizing a field of view, the apparatus comprising:an x-ray source;a source mask located between the x-ray source and the field of view, the source mask having a source aperture;a detector, located adjacent the field of view;a detector shield located between the field of view and the detector, the detector shield having a detector aperture; andan actuator, operable to move the source mask and the detector shield relative to the x-ray source, so as to adjust a path direction of an x-ray beam passing through the source aperture, the field of view, and the detector aperture,wherein the source aperture and detector aperture are sized so that the x-ray beam is substantially non-divergent through the field of view. 12. The apparatus of claim 11, wherein the apparatus comprises a plurality of x-ray sources,the source mask has a plurality of source apertures,the detector shield has a plurality of detector apertures,the actuator being operable to move the source mask and the detector shield relative to the plurality of x-ray sources, so as to adjust path directions of a plurality of substantially non-divergent x-ray beams through the field of view. 13. The apparatus of claim 12, wherein:the plurality of x-ray sources is arranged substantially in a first arc,the plurality of source apertures is arranged substantially in a second arc, andthe plurality of detector apertures is arranged in a third arc. 14. The apparatus of claim 12, wherein movements of the x-ray source, the source aperture, and detector aperture are coordinated so that the x-ray beam is continuously capable of being received by the detector. 15. The apparatus of claim 11, wherein the detector is part of an arcuate detector assembly. 16. The apparatus of claim 11, wherein the x-ray source is pulsed between an on state and an off state, so as to provide x-ray pulses having a pulse duration, the pulses separated by a pulse interval during which the x-ray source is in the off state, the x-ray source having a duty cycle,wherein the apparatus provides an x-ray image of the field of view using the detector signal obtained when the x-ray source is in the on state,the apparatus further providing an emission image of the field of view using the detector signal obtained when the x-ray source is in the off state,the duty cycle being selectable so that emission data and x-ray data are collected over a substantially concurrent time period. 17. The apparatus of claim 16, wherein the emission image is an image of gamma emission from the field of view. 18. The apparatus of claim 16, wherein the pulse duration is between approximately 0.01 milliseconds and approximately 200 milliseconds. 19. The apparatus of claim 16, wherein the pulse duration is between approximately 0.5 milliseconds and 20 milliseconds. 20. The apparatus of claim 16, wherein the pulse interval is at least 10 times longer than the pulse length. 21. An apparatus for providing an emission image and an x-ray image of a field of view, the apparatus comprising:an x-ray source, pulsed between an on state and an off state, so as to provide x-ray pulses having a pulse duration, the pulses separated by a pulse interval during which the x-ray source is in the off state, the x-ray source having a duty cycle;an emission detector, providing an emission detector signal in response to emissions from the field of view;an x-ray detector, providing an x-ray detector signal in response to x-rays passing through the field of view and incident on the x-ray detector; andelectronic circuitry operable to:form an x-ray image of the field of view from the x-ray detector signal, andform an emission image of the field of view from the emission detector signal, the emission image being an image of the emissions from the field of view,the duty cycle being selectable so that emission data and x-ray data are collected over a substantially concurrent time period,the pulse duration being between approximately 0.01 milliseconds and approximately 200 milliseconds, andthe pulse interval being at least 10 times longer than the pulse length. 22. The apparatus of claim 21, wherein the emission detector and x-ray detector are both provided by the same detector assembly, the detector assembly providing a detector signal,the x-ray detector signal being the detector signal when the x-ray source is in the on state,the emission detector signal being the detector signal when the x-ray source is in the off state. 23. The apparatus of claim 21, wherein the pulse interval is over one hundred times greater than the pulse length. 24. The apparatus of claim 21, wherein the emission is gamma emission.