Method for rapid localization of a scintillation event in a gamma camera using a maximum likelihood estimator

In a process for localizing a scintillation event in a gamma camera having a plurality of photomultipliers forming a camera surface, each photomultiplier generating an output signal in response to said scintillation event, said process including the steps of generating a plurality of comparative signal sets from output signals of said photomultipliers corresponding to respective scintillation events of known locations, spaced from one another at a pixel distance, forming a location-dependent probability function based on a comparison of outputs of said photomultipliers for a scintillation event of unknown location with said comparative signal sets, said probability function having a maximum, and defining the location of said scintillation event of unknown location as the location corresponding to said maximum of said location-dependent probability function, the improvement comprising:

• dividing said camera surface into a plurality of overlapping partial camera surfaces;
• identifying a point within each partial camera surface at which said location-dependent probability function has a maximum within that partial camera surface;
• identifying one of said partial camera surfaces in which said location probability function has a largest value;
• dividing said partial camera surface in which said location-dependent probability function has a largest value into overlapping further partial camera surfaces and identifying a further partial camera surface in which said location-dependent probability function has a largest value;
• successively dividing said further partial camera surface in which said location-dependent probability function has a largest value into a plurality of further, increasingly smaller, overlapping partial camera surfaces and successsively identifying one of said further partial camera surfaces in which said location-dependent probability function has a largest value until a further partial surface is reached having a size equal to said pixel distance;
• and
• defining the location of said scintillation event of unknown location as being within said further partial camera surface having said size equal to said pixel distance.