Split energy level radiation detection

Abstract

An energy discriminating apparatus and method is disclosed for use in connection with digital radiography and fluoroscopy. In use of the detection system and method an x-ray source is actuated to direct x-rays through a patient's body, the x-rays including both higher and lower energy radiation. A first detector element, including a plurality of segments, is positioned opposite the source to receive and respond predominantly to x-rays in a lower energy range, the remaining x-rays, being generally of higher energy, passing through the first detector element. A second detector element, also including a plurality of segments, each segment including a phosphor coating layer and a sensor, is positioned to receive and respond to the higher energy radiation passing through the first element. The sensors are coupled respectively to each detector element segment for substantially simultaneously sensing the response and spatial location, relative to the detector elements, of radiation to which each detector element respectively responds. A filter element is interposed between the first and second detectors to enhance discrimination in the energy response of the respective detector elements. Particular preferred detector phosphor materials are identified. The sensors produce separately and simultaneously information representing patterns of relatively lower and higher energy emergent from the patient's body. Digital data processing and conversion equipment responds to the sensors to produce digital information representing each of said images, which can be digitally processed to enhance image characteristics.

I claim:  
     
       1. An  In an imaging system, an energy discriminating radiation detector comprising: 
       (a) a first element comprising a first material of a kind which is preferentially responsive to penetrative radiation of a first energy range;  
       (b) a second element comprising a second material different in kind from said first material and of a kind which is preferentially responsive to penetrative radiation of a second energy range extending higher than said first energy range and which is positioned to receive radiation which has penetrated through a portion of said first element; and  
       (c) a filter of penetrative radiation interposed between said first and second elements; and  
       ( d )  means coupled to said elements for producing an image of a portion of an object from radiation emerging from the object and incident on the first and second elements.    
     
     
       2. The detector of  claim 1 , wherein said filter contains copper. 
     
     
       3. The detector of  claim 1 , wherein said filter comprises brass. 
     
     
       4. The detector of  claim 2  or  3 , wherein said filter is selected to have a thickness of from about 0.2 mm to about 1.0 mm. 
     
     
       5. The detector of  claim 1 ,  An energy discriminating radiation detector comprising: 
       ( a )  a first element comprising a first material of a kind which is preferentially responsive to penetrative radiation of a first energy range;    
       ( b )  a second element comprising a second material different in kind from said first material and of a kind which is preferentially responsive to penetrative radiation of a second energy range extending higher than said first energy range and which is positioned to receive radiation which has penetrated through a portion of said first element; and    
       ( c )  a filter of penetrative radiation interposed between said first and second elements;   
       wherein each said element comprises:  
       (a)  a phosphor layer, and  
       (b)  a photodiode optically coupled to the phosphor.  
     
     
       6. A split energy radiation detector comprising: 
       (a) a first energy responsive element comprising a layer of phosphor material including one of yttrium oxysulfide and zinc cadmium sulfide; and  
       (b) a second energy responsive element positioned to receive energy penetrating through said first element, said second element including a second phosphor layer comprising one of gadolinium oxysulfide and cadmium tungstate.  
     
     
       7. The detector of  claim 6  further comprising: 
       a copper containing filter element interposed between said first and second elements.  
     
     
       8. The detector of  claim 6 , wherein: 
       (a) said first phosphor layer has a coating weight of about 20 to 100 mg/cm 2 , and  
       (b) said second phosphor layer has a coating weight of about 50 mg/cm 2  to 1000 mg/cm 2 .  
     
     
       9. A digital radiography system comprising: 
       (a) an x-ray source for directing x-rays along a path;  
       (b) a split energy radiation detector spaced from the source to receive x-rays from said source, said detector comprising:  
       (i) a first element comprising a first material of a kind which is preferentially responsive to radiation of a first energy range and being located in said path;  
       (ii) a first sensor for sensing radiation response of said first element;  
       (iii) a second element at least partially positioned to receive source radiation passing through said first element, said second element comprising a second material of a kind which is preferentially responsive to radiation of a second energy level extending higher than said first range;  
       (iv) a second sensor for sensing radiation response of said second element; and  
       (c) interpretive circuitry coupled to said sensors for at least partially digitizing information from said sensors and producing from said digitized information a representation of at least a portion of internal body structure of a subject when interposed in said path.  
     
     
       10. The system of claim  9   14 , wherein said first material includes one of yttrium oxysulfide and zinc cadmium sulfide. 
     
     
       11. The system of claim  9   14 , wherein said second material includes one of gadolinium oxysulfide and calcium tungstate. 
     
     
       12. The system of claim  9   14 , further comprising: an x-ray filter layer between said first and second elements. 
     
     
       13. The system of  claim 12 , wherein said filter layer contains copper. 
     
     
       14. The system of  claim 9 ,  A digital radiography system comprising: 
       ( a )  an x - ray source for directing x - rays along a path;    
       ( b )  a split energy radiation detector spaced from the source to receive x - rays from said source, said detector comprising:    
       ( i )  a first element comprising a first material of a kind which is preferentially responsive to radiation of a first energy range and being located in said path;    
       ( ii )  a first sensor for sensing radiation response of said first element;    
       ( iii )  a second element at least partially positioned to receive source radiation passing through said first element, said second element comprising a second material of a kind which is preferentially responsive to radiation of a second energy level extending higher than said first range;    
       ( iv )  a second sensor for sensing radiation response of said second element; and    
       ( c )  interpretive circuitry coupled to said sensors for at least partially digitizing information from said sensors and producing from said digitized information a representation of at least a portion of internal body structure of a subject when interposed in said path;   
       wherein said sensors each comprise a photodiode. 
     
     
       15. The system of  claim 9 ,  A digital radiography system comprising: 
       ( a )  an x - ray source for directing x - rays along a path;    
       ( b )  a split energy radiation detector spaced from the source to receive x - rays from said source, said detector comprising:    
       ( i )  a first element comprising a first material of a kind which is preferentially responsive to radiation of a first energy range and being located in said path;    
       ( ii )  a first sensor for sensing radiation response of said first element;    
       ( iii )  a second element at least partially positioned to receive source radiation passing through said first element, said second element comprising a second material of a kind which is preferentially responsive to radiation of a second energy range extending higher than said first range;    
       ( iv )  a second sensor for sensing radiation response of said second element; and    
       ( c )  interpretive circuitry coupled to said sensors for at least partially digitizing information from said sensors and producing from said digitized information a representation of at least a portion of internal body structure of a subject when interposed in said path;    
       
         wherein said sensors each comprise a photodiode; and 
       
       wherein said x-ray source is capable of simultaneously producing x-rays in both said energy ranges. 
     
     
       16. The system of claim  9   14 , wherein each of said elements is substantially planar, one said element being substantially behind the other with respect to the source. 
     
     
       17. An imaging method comprising the steps of: 
       (a) directing x-rays through a subject to be imaged, said x-rays including both higher and lower energy radiation;  
       (b) separately detecting higher and lower energy x-radiation emergent from the subject by passing said radiation successively through scintillators comprising respectively different kinds of materials each preferentially responsive to radiation of a different one of said lower and higher energy ranges, including sensing responses of said scintillators;  
       (c) at least partially digitizing information derived in said detecting step;  
       (d) processing said digitized information; and  
       (e) utilizing said processed digital information to produce a representation of internal structure of the subject.  
     
     
       18. The method of  claim 17 , wherein said digital processing step includes a step of subtracting information obtained in said lower energy sensing step from information obtained in said higher energy sensing step. 
     
     
       19. The method of  claim 17 , wherein said sensing step comprises producing information in response to radiation incident on a plurality of separate detector elements, said information including spatial location representation of said incident radiation with respect to a said sensing element. 
     
     
       20. An  In an imaging system, an energy discriminating radiation detecting method utilizing first and second detector elements, a first of said elements being preferentially responsive to radiation of a first energy range, a second of said elements being preferentially responsive to energy  radiation of a second energy range extending higher than said first energy range, said method comprising the steps of; : 
       (a) directing radiation extending over both said first and second energy ranges through a subject;  
       (b) positioning said first element to receive incident radiation emergent from the subject for response thereto;  
       (c) positioning said second element to receive radiation from the source passing through said first element, and  
       (d) filtering radiation transmitted through said first element prior to the arrival of said energy incident upon said second element; and  
       ( e )  producing an image of a portion of the subject from the radiation emerging from the subject and incident on the first and second elements.    
     
     
       21. A radiographic system comprising: 
       (a) an x-ray source;  
       (b) a radiation detector positioned to receive x-rays from the source;  
       (c) a phototimer comprising:  
       (i) an energy discriminating detector located to receive x-rays from the source and to produce signals indicating x-ray energy received in each of two energy ranges, and  
       (ii) circuitry coupled between the discriminating detector and the source for controlling the source as a function of the x-rays detected in said two energy ranges.  
     
     
       22. A radiation imaging system comprising: 
       (a) a source of penetrative radiation;  
       (b) a dual energy detector assembly comprising two side-by-side columns of individual detector elements, one column being staggered with respect to the other by a distance equal to less than the dimension of a single detector element taken along the direction of its column, and additional detector elements positioned behind said columns, relative to said source;  
       (c) mounting structure for maintaining said source and said detector assembly sufficiently spaced to provide a subject examining space and for maintaining said detector aligned continuously in said penetrative radiation when produced by said source;  
       (d) power means for actuating said source to direct penetrative radiation through the subject examination space and incident onto the detector assembly;  
       (e) means coupled to said detector elements for producing an image of a portion of a subject, when located in the subject space, from radiation emergent from said subject.  
     
     
       23. The system of  claim 22 , wherein said staggered columns of detector elements are offset with respect to one another by a distance equal approximately one-half the height of a single detector element taken in a direction along its column. 
     
     
       24. An energy discriminating radiation detector comprising: 
       (a) a first component comprising a first material of a first kind which is preferentially responsive to penetrative radiation of a first energy range;  
       (b) a second component comprising a second material different in kind from said first material and of a kind which is preferentially responsive to penetrative radiation of a second energy range extending higher than said first energy range, said second component being positioned to receive radiation which has penetrated through a portion of said first component, and  
       (c) means coupled to said first and second components to produce electrical signals representing radiation when incident respectively on said first and second components.  
     
     
       25. The detector of  claim 24 , wherein: said filter comprises  further comprising a filtering material having an atomic number in the range of 24-58. 
     
     
       26. The detector of  claim 24 , wherein: 
       said first component comprises a phosphor layer comprising an element having an atomic number lying in the range of 39-57.  
     
     
       27. The detector of  claim 24 , wherein said second component comprises: 
       a phosphor layer comprising an element having an atomic number lying within the range of 56-83.  
     
     
       28. The detector of  claim 24 , wherein one of said first and second components comprises: 
       a phosphor layer proximate and aligned with a layer of light sensitive film.  
     
     
       29. The detector of claim  24   1 , wherein one of said first and second componentselements comprises: 
       a phosphor layer; and  
         wherein said means for producing an image comprises a photoconductive plate, said phosphor layer being  proximate and aligned with a portion of said photoconductive plate.  
     
     
       30. The detector of claim  24   1 , wherein one of said first and second componentselements comprises: 
       a phosphor layer; and  
         wherein said means for producing an image comprises a thermoluminescent plate, said phosphor layer being  proximate and aligned with a portion of said thermoluminescent plate.  
     
     
       31. The detector of  claim 24 , further comprising: 
       a filter of said penetrative radiation interposed between said first and second components.  
     
     
       32. The detector of  claim 31 , wherein: 
       said filter comprises material having an atomic number in the range of 24-58, and a thickness in the range of about 0.2 mm to 1.0 mm.  
     
     
       33. the detector of  claim 24 , wherein said second material comprises material having a primary radiation absorber having a higher atomic number than that of said first material. 
     
     
       34. The detector of  claim 24 , wherein: 
       (a) said first material comprises one of yttrium oxysulfite  oxysulfide, zinc cadmium sulfide, barium sulfate, barium cadmium sulfate, lanthium oxysulide  lanthanum oxysulfide and barium fluorochloride,  
       (b) said second material comprises one of gadolinium oxysulfide, cadmium tungstate, calcium tungstate and barium lead sulfate.  
     
     
       35. The detector of  claim 24 , wherein: 
       (a) said first material comprises a first layer of phosphor material having a coating weight of about 20 to 100 mg/cm 2 , and  
       (b) said second material comprises a second phosphor layer having a coating weight of about 50 mg/cm 2  to 1000 mg/cm 2 .  
     
     
       36. The detector of  claim 24 , wherein: 
       (a) said first component comprises a portion of a first scintillator material, and  
       (b) said second component comprises a portion of a second scintillator material.  
     
     
       37. The detector of  claim 24 , further comprising: 
       a portion of penetrative radiation filtering material interposed between said first and second components and being capable of absorbing substantially all radiation incident on said filter element lying within said first energy range, while not absorbing substantially all such radiation of said second energy range.  
     
     
       38. A method for detecting area distribution of differing energy levels of penetrative radiation, said method comprising: 
       (a) detecting preferentially lower energy radiation by passing it through a first detector element including a scintillator and a plurality of segments;  
       (b) detecting higher energy radiation by transmitting radiation emergent from said first detector incident onto a second detector element including a scintillator and a plurality of segments;  
       (c) filtering penetrative radiation emergent from said first detector before said second detecting step, and  
       (d) producing information in said first and second detecting steps spatially locating radiation over an area with respect to at least one of said detector elements.  
     
     
       39. An energy discriminating radiation detector comprising: 
       (a) a first component comprising a first phosphor material including a primary radiation absorber having an atomic number lying the range of 39-57;  
       (b) a second component comprising a second phosphor material aligned with said first phosphor material to receive radiation when said radiation has penetrated through a portion of said first component, said second phosphor material including a primary radiation absorber having an atomic number lying within the range of 56-83, and  
       (c) means coupled to said first and second components for producing electrical signals representing radiation when incident on said detector.  
     
     
       40. An energy discriminating radiation detector comprising: 
       (a) a first component comprising a first material of a first kind which is preferentially responsive to penetrative radiation of a first energy range;  
       (b) a second component comprising a second material different in kind from said first material and of a kind which is responsive to penetrative radiation of a second energy range extending higher than said first energy range, said second component being aligned with said first component to receive radiation when said radiation has penetrated through a portion of said first component, and  
       (c) means coupled to said first and second components to produce electrical signals representing penetrative radiation when incident on said detector.  
     
     
       41. A radiation imaging system comprising: 
       (a) a source for propagating penetrative radiation along a path from a focal spot;  
       (b) a detector assembly spaced from said source and interposed in said path, said detector assembly comprising:  
       (i) a front array of individual detector elements, each front array element including a penetrative radiation sensitive receiving face having a discrete geometry, said front array element faces being located at substantially a distance F 1  from said focal spot;  
       (ii) a rear array of individual detector elements, each said rear array element including a penetrative radiation sensitive receiving face having a discrete geometry, wherein each element of said rear array is substantially aligned behind a corresponding element of said front array, with respect to said focal spot, and in which each rear array element has a receiving face which has a larger area then the receiving face of its corresponding aligned front array element, said rear array receiving faces being located at substantially a distance F 2  from said focal spot, and  
       (c) circuitry coupled to said detector arrays for producing a representation of radiation when incident on said detector elements.  
     
     
       42. The system of  claim 41 , wherein: 
       (a) said receiving faces of said detector elements of said front and rear arrays have similar geometry, and  
       (b) a dimension D 1  of one of said front array elements is related to a corresponding dimension D 2  of one of said rear array elements by the following relation:  
       
         
           D 2 /D 1 =F 2 /F 1 .