Spectral Discrimination Using Wavelength-Shifting Fiber-Coupled Scintillation Detectors

Abstract

The present specification provides a detector for an X-ray imaging system. The detector includes at least one high resolution layer having high resolution wavelength-shifting optical fibers, each fiber occupying a distinct region of the detector, at least one low resolution layer with low resolution regions, and a single segmented multi-channel photo-multiplier tube for coupling signals obtained from the high resolution fibers and the low resolution regions.

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         21 . An under-vehicle backscatter imaging system comprising:
 an X-ray source configured to direct X-rays upward toward an underside of a vehicle;   a detector positioned adjacent to the X-ray source and configured to detect X-rays backscattered from the underside of the vehicle, wherein the detector comprises:
 a first scintillation layer adapted to receive the X-rays backscattered from the underside of the vehicle and generate light; 
 a first plurality of wavelength-shifting optical fibers optically coupled to the first scintillation layer; and 
 a first photodetector coupled to the first plurality of wavelength-shifting optical fibers configured to receive and direct the light generated from the first scintillation layer and directed through the first plurality of wavelength-shifting optical fibers. 
   
     
     
         22 . The under-vehicle backscatter imaging system of  claim 21 , wherein the detector is adapted to be placed on a ground surface. 
     
     
         23 . The under-vehicle backscatter imaging system of  claim 21 , wherein the X-ray source and the detector do not extend more than six inches above the ground surface. 
     
     
         24 . The under-vehicle backscatter imaging system of  claim 21 , wherein the detector is adapted to be placed on a mobile chassis. 
     
     
         25 . The under-vehicle backscatter imaging system of  claim 21 , wherein the detector further comprises:
 a second scintillation layer positioned below and parallel to the first plurality of wavelength-shifting optical fibers; and   a second plurality of wavelength-shifting optical fibers optically coupled to the second scintillation layer and configured to receive and direct the light generated from the second scintillation layer to the first photodetector or a second photodetector.   
     
     
         26 . The under-vehicle backscatter imaging system of  claim 25 , wherein the detector further comprises a filter positioned between the first scintillation layer and the second scintillation layer. 
     
     
         27 . The under-vehicle backscatter imaging system of  claim 25 , wherein the detector further comprises a filter positioned between the first scintillation layer and the second scintillation layer and wherein the filter is adapted to shift an energy level of X-rays backscattered from the underside of the vehicle by 20 kV to 30 kV. 
     
     
         28 . The under-vehicle backscatter imaging system of  claim 25 , wherein fibers of the first plurality of wavelength-shifting optical fibers and fibers of the second plurality of wavelength-shifting optical fibers each have a first edge and wherein the detector further comprises a rigid strip connected to the first edge of the fibers of the first plurality of wavelength-shifting optical fibers and of the fibers of the second plurality of wavelength-shifting optical fibers and adapted to provide mechanical support to each fiber of the first plurality of wavelength-shifting fibers and second plurality of wavelength-shifting fibers. 
     
     
         29 . The under-vehicle backscatter imaging system of  claim 25 , wherein at least one of the first photodetector or second photodetector is multi-channel photomultiplier tube. 
     
     
         30 . The under-vehicle backscatter imaging system of  claim 29 , wherein the multi-channel photomultiplier tube comprises 8 to 16 channels. 
     
     
         31 . The under-vehicle backscatter imaging system of  claim 25 , wherein at least one of the first photodetector or second photodetector is a silicon photomultiplier. 
     
     
         32 . The under-vehicle backscatter imaging system of  claim 21 , wherein each fiber in the first plurality of wavelength-shifting optical fibers is positioned adjacent each other without a space in between each fiber of the first plurality of wavelength-shifting fibers. 
     
     
         33 . The under-vehicle backscatter imaging system of  claim 21 , wherein a diameter of each fiber of the first plurality of wavelength shifting fibers is less than 200 micrometers. 
     
     
         34 . An under-vehicle backscatter imaging system comprising:
 an X-ray source configured to direct X-rays upward toward an underside of a vehicle;   a detector positioned adjacent to the X-ray source and configured to detect X-rays backscattered from the underside of the vehicle, wherein the detector is adapted to be placed on a ground surface, wherein the detector does not extend more than six inches above the ground, and wherein the detector comprises:
 a first scintillation layer adapted to receive the X-rays backscattered from the underside of the vehicle and generate light; 
 a first plurality of wavelength-shifting optical fibers optically coupled to the first scintillation layer; and 
 a first photodetector coupled to the first plurality of wavelength-shifting optical fibers configured to receive and direct the light generated from the first scintillation layer and directed through the first plurality of wavelength-shifting optical fibers. 
   
     
     
         35 . The under-vehicle backscatter imaging system of  claim 34 , wherein the detector further comprises:
 a second scintillation layer positioned below and parallel to the first plurality of wavelength-shifting optical fibers; and   a second plurality of wavelength-shifting optical fibers optically coupled to the second scintillation layer and configured to receive and direct the light generated from the second scintillation layer to the first photodetector or a second photodetector.   
     
     
         36 . The under-vehicle backscatter imaging system of  claim 35 , wherein the detector further comprises a filter positioned between the first scintillation layer and the second scintillation layer. 
     
     
         37 . The under-vehicle backscatter imaging system of  claim 35 , wherein the detector further comprises a filter positioned between the first scintillation layer and the second scintillation layer and wherein the filter is adapted to shift an energy level of X-rays backscattered from the underside of the vehicle by 20 kV to 30 kV. 
     
     
         38 . The under-vehicle backscatter imaging system of  claim 35 , wherein fibers of the first plurality of wavelength-shifting optical fibers and fibers of the second plurality of wavelength-shifting optical fibers each have a first edge and wherein the detector further comprises a rigid strip connected to the first edge of the fibers of the first plurality of wavelength-shifting optical fibers and of the fibers of the second plurality of wavelength-shifting optical fibers and adapted to provide mechanical support to each fiber of the first plurality of wavelength-shifting fibers and second plurality of wavelength-shifting fibers. 
     
     
         39 . The under-vehicle backscatter imaging system of  claim 35 , wherein at least one of the first photodetector or second photodetector is at least one of a multi-channel photomultiplier tube or a silicon photomultiplier. 
     
     
         40 . The under-vehicle backscatter imaging system of  claim 34 , wherein each fiber in the first plurality of wavelength-shifting optical fibers is positioned adjacent each other without a space in between each fiber of the first plurality of wavelength-shifting fibers. 
     
     
         41 . The under-vehicle backscatter imaging system of  claim 35 , wherein a diameter of each fiber of the first plurality of wavelength shifting fibers and the second plurality of wavelength shifting fibers is less than 200 micrometers.