Method and apparatus for correcting the offset induced by field effect transistor photo-conductive effects in a solid state X-ray detector

Abstract

A method and apparatus for correcting the offset induced by Field Effect Transistor (FET) photo-conductive effects in solid state x-ray detectors includes dedicating rows at the beginning and end of an x-ray detector scan. The dedicated rows may be used to measure the “signal” induced by the photo-conductivity of FET switches in solid state x-ray detectors. Since the signal induced by FET photo-conductivity decays over time, the measurements taken at the beginning and end of a detector scan may be used to predict by interpolation the amount of signal contributed by photo-conductive induced offset for each row of the detector scan on a column by column basis.

What is claimed is:  
     
         1 . A method for generating a medical diagnostic image acquired by a detector in a medical diagnostic imaging system comprising: 
 exposing a detector to an energy source to form an exposed detector section including an exposed patient subsection;    measuring at least first and second data sets generated by the detector, one of said first and second data sets being representative of at least a portion of said exposed detector section outside said exposed patient subsection and one of said first and second data sets being representative of at least a portion of said exposed patient image; and    generating a medical diagnostic image based on said exposed patient subsection and a relation between said first and second data sets.    
     
     
         2 . The method of  claim 1  wherein said step of exposing a detector to an energy source comprises exposing said detector to x-ray energy.  
     
     
         3 . The method of  claim 1  wherein said first and second data sets comprise an exposure data set and a correction data set.  
     
     
         4 . The method of  claim 3  wherein said step of measuring at least first and second data sets comprises measuring said at least a portion of said exposed detector section outside said exposed patient image for said correction data set and measuring said at least a portion of said exposed patient image for said exposure data set.  
     
     
         5 . The method of  claim 3  wherein said step of generating said medical diagnostic image comprises subtracting a value from said correction data set from a corresponding value in said exposure data set.  
     
     
         6 . The method of  claim 1  wherein said step of generating said medical diagnostic image comprises subtracting a value from said first data set from a corresponding value in said second data set.  
     
     
         7 . The method of  claim 1  wherein said step of generating a medical diagnostic image comprises activating pixels in a digital display according to said measurements in said first and second data sets.  
     
     
         8 . The method of  claim 3  wherein said correction data set includes a measure of Field Effect Transistor photo-conductive effects.  
     
     
         9 . The method of  claim 1  wherein said step of measuring at least first and second data sets comprises said first data set being representative of at least a portion of said exposed detector section outside said exposed patient image and said second data set being representative of at least a portion of said exposed patient image.  
     
     
         10 . The method of  claim 9  further comprising measuring at least a third data set being representative of at least a second portion of said exposed detector section outside said exposed patient image.  
     
     
         11 . A detector subsystem for acquiring an image comprising: 
 a panel being exposed to energy representative of an object and energy outside of said object, said panel formed of an array of cells detecting discrete amounts of energy; and    a scanner for reading data sets, each of which is representative of an amount of energy stored by a cell; said scanner reading at least first and second data sets before and after said panel being exposed to said energy; one of said at least first and second data sets read from at least a portion of said object and one of said at least first and second data sets read from at least a portion of said outside of said object; said scanner producing a detector output based on a relation between the first and second data sets.    
     
     
         12 . The subsystem of  claim 11  wherein said array of cells comprises: 
 an array of photodiodes storing charge representative of said discrete amounts of energy; and  
 an array of Field Effect Transistors switchably interconnecting said photodiodes and said scanner.  
 
     
     
         13 . The subsystem of  claim 11  wherein said first and second data sets comprise an exposure data set and a correction data set.  
     
     
         14 . The subsystem of  claim 13  wherein said correction data set includes Field Effect Transistor photo-conductive effects.  
     
     
         15 . The subsystem of  claim 13  wherein said scanner reads said first data set from at least a portion of said panel with said object for said exposure data set and said scanner reads said second data set from at least a portion of said panel outside said object for said calibration data set.  
     
     
         16 . A medical diagnostic imaging system, comprising: 
 a detector for detecting an energy pattern emanating from a patient; said detector having an array of discrete collecting elements storing charge representative of an amount of detected energy both from said patient and outside said patient;    an image acquisition module scanning a charge stored on said collecting elements; and    said image acquisition module scanning said collecting elements during a first pass to obtain data representative of the intrinsic energy characteristic from an unexposed detector and during a second pass to obtain both exposure data representative of an energy pattern from said patient and correction data representative of an energy pattern of said detector from outside said patient;    
     
     
         17 . The system of  claim 16  further comprising: 
 an image adjustment module correcting said exposure data using said correction data to minimize the effect of said energy characteristic of said detector.  
 
     
     
         18 . The system of  claim 16  wherein said detector further comprises: 
 an array of Field Effect Transistors switchably interconnecting said collecting elements and said image acquisition module.  
 
     
     
         19 . The system of  claim 18  wherein said energy characteristic of said detector includes Field Effect Transistor photo-conductive effects.  
     
     
         20 . The system of  claim 16  wherein said collecting elements comprise photodiodes.  
     
     
         21 . The system of  claim 16  wherein said energy pattern is an x-ray energy pattern.