Scintillation cameras are used in many fields of study. In the medical field they are used to obtain images of internal organs in-situ and in real-time. For a gamma type scintillation camera, the subject is injected with one of a number of radioactive isotopes common to one skilled in the art. The specific isotope used is selected according to its different physical properties, including how much radiation it will emit. For an x-ray type scintillation camera, the x-rays are radiated from a source located outside of the body of the subject, with the subject positioned between the x-ray source and the scintillation camera.
The scintillation camera creates an image of the subject by detecting the HEP's emitted. The detector may incorporate a scintillating material that produces VLP's when a HEP is absorbed.
It is beneficial to maximize imaging rate, spatial resolution, and ease of manufacture, and to minimize noise and cost of manufacture. Unfortunately, in traditional scintillation camera designs, these goals compete against each other. Those designs which increase imaging rate, for example, tend to decrease spatial resolution, and those designs which increase spatial resolution tend to decrease imaging rate.
One complication to achieving the goal of a high imaging rate is the fact that only a single scintillation event can be recorded within a single scintillation crystal during a single data collection interval. This is because the VLP's generated by the scintillation event propagate throughout the scintillation crystal such that information relating to a single HEP strike, and that relating to multiple HEP strikes, would be confounded. Since HEP's impinge within the scintillator crystal at an asynchronous rate that increases proportionally with an increase in the strength of the radiation source presenting the HEP's, the data collection interval must be extremely short so as not to include more than one strike.
As the data collection interval is decreased to reduce the probability of multiple strikes within the interval, the rate at which the processing circuitry must handle the data increases. A point is reached at which the processing circuitry becomes the rate determining step, and no further decrease in data collection interval is possible because the processing circuitry is not able to keep up with the amount of data received from the VLP detector, or the speed at which the data is being sent, and the scintillation camera will thus be too slow for applications where a higher rate is required.
Another problem with the traditional scintillation camera designs is the high level of spurious noise received from the PMT's in the VLP detector. PMT's in a traditional design are subject to dark current pulse. This means that sometimes, even when there is no VLP input at the photocathodes to trigger an electron shower and resultant electrical signal, a current pulse will be generated and sent out from the PMT. This dark current pulse results in a low signal to noise ratio, and further decreases the number of detectable scintillation events.
There is a need, therefore, for a scintillation camera that has a fast imaging rate, fine spatial resolution, and a high signal to noise ratio, yet is easy and inexpensive to manufacture.