Patent ID: 6858850
Filing Date: 2005-02-22
Classification: A61B,G01T

Abstract:
1. A method for calibrating PET detector PMT gains in a detector unit, the method comprising the steps of: (a) conducting a calibration procedure; (b) determining whether a number of photons absorbed by a corresponding crystal exceeds a count threshold; (c) if the threshold is not exceeded, repeating steps (a) and (b); and, (d) if the threshold is not exceeded, ending the calibration procedure wherein the detector unit includes at least one detector block, where a block includes a two dimensional crystal array including crystal arranged adjacent an imaging area and a PMT array including a two dimensional array of a PMTs arranged adjacent the crystal array opposite the imaging area, a target energy level being associated with the known average energy of a photon, the method further comprising the steps of: providing a calibration photon source adjacent the at least one block during a calibration period and, for each unit crystal: (i) obtaining a calibration energy spectrum where the calibration spectrum indicates the number detected photons at each of several possible energy levels; and (ii) mathematically combining the calibration spectrum and a crystal specific gain factor to generate a shifted spectrum for the crystal; combining the shifted spectrums for all unit crystals to generate a unit spectrum; identifying a peak unit energy level for the unit spectrum where the peak unit energy level is the energy level at which the greatest number of photons was detected; comparing the peak unit energy level and the target energy level; and based on the difference between the peak unit energy level and the target energy level, adjusting the PMT gains for the units PMTs.