Patent Number: 
Section: claims

1. An X-ray imaging apparatus for determining a surface profile of an object under inspection and positioned at a distance from said apparatus, comprising:an X-ray source for producing a scanning beam of X-rays directed toward said object;a detector assembly adapted to provide a signal representative of an intensity of X-rays backscattered from said object; andprocessing circuitry adapted to determine a time difference between when the X-ray source is switched on and when the backscattered X-rays arrive at the detector assembly and adapted to output data representative of the surface profile of the object under inspection, wherein said processing circuitry comprises a comparator capacitor adapted to be charged by a current source when said X-ray source is turned on, a switch that disconnects said comparator capacitor from the current source when a voltage of the comparator capacitor equals or exceeds a reference voltage, an analog to digital converter to generate a digital value representative of said voltage, and circuitry to determine said time difference from said digital value. 2. The X-ray imaging apparatus of claim 1 wherein a minimum distance between the apparatus and the object under inspection is 100 mm. 3. The X-ray imaging apparatus of claim 1 wherein a maximum distance between the apparatus and the object under inspection is 5 m. 4. The X-ray imaging apparatus of claim 1 wherein the X-ray source is pulsed such that a duration of the X-ray source being on is in the range of 1 μs to 100 μs and a duration of the X-ray source being off is in the range of 1 μs to 100 μs. 5. The X-ray imaging apparatus of claim 1 wherein a duration of the X-ray beam on time and off time is each less than 1 ns. 6. The X-ray imaging apparatus of claim 1 wherein the X-ray imaging apparatus is mounted on a vehicle which is adapted to be driven past the object under inspection. 7. The X-ray imaging apparatus of claim 1 wherein the X-ray imaging apparatus is mounted on a vehicle that is adapted to be driven to an inspection site and kept stationary while the object under inspection passes the vehicle. 8. A portal gantry having a top side, left side, and right side, comprising the X-ray imaging apparatus of claim 1. 9. The portal gantry of claim 8 wherein the X-ray imaging apparatus is integrated into at least two of the top side, left side, or right side. 10. An X-ray imaging apparatus for determining the presence and location of a threat beneath an exterior surface of an object under inspection, comprising:an X-ray source for producing a scanning pencil beam of X-rays directed toward said object;a detector assembly adapted to provide a first signal representative of an intensity of the X-rays backscattered from said exterior surface of the object under inspection and a second signal representative of an intensity of the X-rays backscattered from said threat beneath the exterior surface of the object under inspection; andprocessing circuitry adapted to determine a first time difference between when the X-ray source is switched on and when the X-rays backscattered from the exterior surface of the object under inspection arrive at the detector assembly and a second time difference between when the X-ray source is switched on and when the X-rays backscattered from the threat beneath the exterior surface of the object under inspection arrive at the detector assembly and adapted to output data representative of a surface profile of the object under inspection based upon at least one of said first time difference or second time difference, wherein said processing circuitry comprises a comparator capacitor adapted to be charged by a current source when said X-ray source is turned on, a switch that disconnects said comparator capacitor from the current source when a voltage of the comparator capacitor equals or exceeds a reference voltage, an analog to digital converter to generate a digital value representative of said voltage, and circuitry to determine said first or second time difference from said digital value. 11. The X-ray imaging apparatus of claim 10 wherein a minimum distance between the apparatus and the object under inspection is 100 mm. 12. The X-ray imaging apparatus of claim 10 wherein a maximum distance between the apparatus and the object under inspection is 5 m. 13. The X-ray imaging apparatus of claim 10 wherein the X-ray source is pulsed such that a duration of the X-ray source being on is in the range of 1 μs to 100 μs and a duration of the X-ray source being off is in the range of 1 μs to 100 μs. 14. The X-ray imaging apparatus of claim 10 wherein a duration of the X-ray beam on time and off time is each less than 1 ns. 15. The X-ray imaging apparatus of claim 10 wherein the X-ray imaging apparatus is mounted on a vehicle which is adapted to be driven past the object under inspection. 16. The X-ray imaging apparatus of claim 10 wherein the X-ray imaging apparatus is mounted on a vehicle that is adapted to be driven to an inspection site and kept stationary while the object under inspection passes the vehicle. 17. A method for determining a surface profile of an object under inspection, said method comprising the steps of:positioning an object under inspection at a distance from an X-ray imaging apparatus, wherein said X-ray imaging apparatus comprises an X-ray source and a detector array;operating said X-ray source to produce a scanning pencil beam of X-rays directed toward said object;detecting a signal representative of an intensity of the X-rays backscattered from said object, using said detector array;determining a time difference between when the X-ray source is switched on and when the backscattered signal is detected using processing circuitry, wherein said processing circuitry comprises a comparator capacitor adapted to be charged by a current source when said X-ray source is turned on, a switch that disconnects said comparator capacitor from the current source when a voltage of the comparator capacitor equals or exceeds a reference voltage, an analog to digital converter to generate a digital value representative of said voltage, and circuitry to determine said time difference from said digital value; andoutputting data representative of the surface profile of the object under inspection. 18. The method of claim 17 wherein the object under inspection is positioned no closer than 100 mm and no farther than 5 m from the X-ray imaging apparatus. 19. The method of claim 17 wherein the X-ray source is kept on for no less than 1 μs and no more than 100 μs and is kept off for no less than 1 μs and no more than 100 μs. 20. The method of claim 17 wherein the X-ray source is kept on for less than 1 ns and kept off for less than 1 ns.