Self-Adaptive Tuning of Gamma Camera

Abstract

An improved system and method for tuning individual sensors (e.g., photomultiplier tubes) of a multi-sensor imaging system such as, e.g., a gamma camera having an array of photo-multiplier tubes is provided that produces a uniform response over the entire system. Individual sensors of a multi-sensor imaging system are tuned based explicitly or implicitly on gain characteristics of individual sensors of the multi-sensor imaging system so as to produce a uniform response over the system.

1 . A method for tuning a nuclear imaging system having a plurality of nuclear radiation sensors, comprising: 
 a) exposing the sensors to nuclear radiation of known energy and location of origin;    b) using individual sensor responses to said nuclear radiation, determining sensor gain changes required to adjust the system sensors toward a previously determined tuned state;    c) using the sensor gain changes determined in step b), determining sensor gain control values required to produce desired gain changes;    d) modifying the sensor gain control values in accordance with the sensor gain control values determined in step c); and    e) repeating steps a) through d) until the previously determined tuned state is achieved.    
   
   
       2 . The method of  claim 1 , wherein sensor gain response characteristics for each of the sensors in the imaging system have been stored previously in a predefined data structure and wherein said determining sensor gain changes in step b) is effected by referencing said predefined data structure.  
   
   
       3 . The method of  claim 2 , wherein said sensors comprise photomultiplier tubes, said gain control values comprise DAC values, and said sensor gain response characteristics include at least one of mathematically represented gain-versus-voltage curves and mathematically represented gain-versus-control-dynode-DAC curves.  
   
   
       4 . The method of  claim 3 , wherein for a given desired change dg in voltage-related gain or dynode DAC-related gain, i) desired gain change factor is determined as gf=1+dg; ii) current relative gain G at current DAC value D is determined as G=D_G(D), where D_G is a calibrated DAC-to-Gain response function; and iii) a new gain G′ and a new DAC D′ are determined as G′=gf·G and D′=G_D(G′), respectively, where G_D is the inverse of D_G.  
   
   
       5 . The method of  claim 3 , wherein for a given desired change dg in dynode DAC-related gain, change in dynode DAC ΔDAC is determined as ΔDAC=β·dg, where β=[(1/G)·∂G/∂DAC] −1 .  
   
   
       6 . The method of  claim 1 , wherein said sensor gain changes determined in step b) are modified in subsequent iterations of said steps based on an excessive gain factor Xgf=(ΔG/G) Observed /(ΔG/G) Predicted ,  
     wherein (ΔG/G) Predicted  is determined from a generic gain response curve.  
   
   
       7 . The method of  claim 6 , wherein (ΔG/G) Observed  is determined based on changes in peak location Z i  as (ΔG/G) Observed =(Z i −Z i−1 )/Z i−1 .  
   
   
       8 . The method of  claim 6 , wherein (ΔG/G) Observed  is determined based on changes in observed peak locations (E) in an E sum  spectra, such that (ΔG/G) Observed  is determined as C −1  # (ΔE/E) Observed , where ΔG/G and ΔE/E are column vectors, C −1  is an inverse contribution matrix, and # indicates matrix multiplication.  
   
   
       9 . The method of  claim 6 , wherein said sensors comprise photomultiplier tubes, said gain control values comprise DAC values, and updated DAC values DAC i+1  are determined as DAC i +ΔDAC i , where ΔDAC i =β i ·dg and β i  has been empirically determined from a previous iteration β i ≈ΔDAC i /(ΔG/G) iObserved .  
   
   
       10 . The method of  claim 9 , wherein (ΔG/G) Observed  is determined based on changes in peak location Z i  as (ΔG/G) Observed =(Z i −Z i−1 )/Z i−1 .  
   
   
       11 . The method of  claim 9 , wherein (ΔG/G) Observed  is determined based on changes in observed peak locations (E) in an E sum  spectra, such that (ΔG/G) Observed  is determined as C −1  #(ΔE/E) Observed , where ΔG/G and ΔE/E are column vectors, C −1  is an inverse contribution matrix, and # indicates matrix multiplication.  
   
   
       12 . A method for tuning a nuclear imaging system having a plurality of nuclear radiation sensors, comprising: 
 a) exposing the sensors to nuclear radiation of known energy and location of origin;    b) using individual sensor responses to said nuclear radiation, determining sensor gain changes required to adjust the system sensors toward a previously determined tuned state;    c) using the sensor gain changes determined in step b), determining sensor gain control values required to produce desired gain changes based on individual response curves for each of said sensors;    d) modifying the sensor gain control values in accordance with the sensor gain control values determined in step c); and    e) repeating steps a) through d) until the previously determined tuned state is achieved.    
   
   
       13 . A method for tuning a nuclear imaging system having a plurality of nuclear radiation sensors, comprising: 
 a) exposing the sensors to nuclear radiation of known energy and location of origin;    b) using individual sensor responses to said nuclear radiation, determining sensor gain changes required to adjust the system sensors toward a previously determined tuned state;    c) using the sensor gain changes determined in step b), determining sensor gain control values required to produce desired gain changes based on a generic response curve for all of said sensors;    d) modifying the sensor gain control values in accordance with the sensor gain control values determined in step c); and    e) repeating steps a) through d) until the previously determined tuned state is achieved.