Radiant energy – Invisible radiant energy responsive electric signalling – Semiconductor system
Reexamination Certificate
2000-11-24
2002-10-01
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Semiconductor system
C250S370010, C250S370090
Reexamination Certificate
active
06459086
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention deals with the radiation detection arts. It finds particular application in conjunction with electronics used in nuclear cameras and will be described with particular reference thereto. However, it is to be appreciated that it is not limited to the aforementioned application.
Heretofore, nuclear imaging has employed a source of radioactivity to image the anatomy of a subject. Typically, a radiopharmaceutical is injected into the patient. This radiopharmaceutical contains atoms that decay at a predictable rate. Each time an atom decays, it releases a &ggr;-ray. These &ggr;-rays are detected, and from information such as their detected position and energy, a representation of the interior of the subject is reconstructed.
Typically, a nuclear camera has one, two, or three detector heads. Each head has a large scintillator sheet, such as doped sodium iodide, which converts incident radiation photons into scintillations, i.e. flashes of light. An array of photomultiplier tubes is disposed in back of the scintillator to monitor for light flashes. The output of the photomultiplier tubes and associated circuitry indicates the coordinates of each scintillation on the sodium iodide crystal and its energy. Unfortunately, there are numerous non-uniformities and inaccuracies when using a large scintillator crystal and an array of photomultiplier tubes.
This type of detector is only capable of processing one nuclear event at a time. &Ggr;-rays incident upon the detector temporally too close together are typically ignored. The reset time is determined in part by the afterglow of the crystals, and to a lesser extent, the processing time of the electronics.
Rather than using a single, large scintillator and photomultiplier tubes, others have proposed using an array of small scintillators, each associated with a photodiode or other photoelectrical device which senses a scintillation in each individual scintillation crystal. Other types of individual solid-state detectors have also been suggested.
Previously, the most common means of processing data from solid state detectors has been to detect the peak voltage of an analog pulse which results from integrating the released charge and shaping the resulting waveform. Typically, such a peak detection system will use a non-linear analog circuit which follows an input voltage only as long as it is monotonically increasing. Such a peak detecting circuit is usually followed by a high resolution (12 bits) analog to digital converter (ADC) to provide digital data suitable for reconstruction. The ADC is commanded to begin conversion at some point following the beginning of the pulse, providing enough time for the analog peak detector to have operated. Subsequent to the ADC conversion time, the peak detector must be reset before it is ready to accept another pulse. The sum of the time to peak (~1 &mgr;sec), the ADC conversion time (~1-5 &mgr;sec), and the reset time (~500 ns including analog voltage settling time) creates a “dead time” in which the system cannot respond to a new pulse.
Further, these analog systems are not trivially constructed. That is, they are not made using easily attainable parts. The amplifiers required to provide quick action in controlling the non-liner elements and provide high accuracy at these speed typically use high power supply currents. High accuracy ADCs are expensive, slow, and relatively power consumptive.
The present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a nuclear imaging apparatus is given. An array of solid state detectors emits current spikes in response to incumbent &ggr;-irradiation. The current spike is spread into a Gaussian pulse, and an amplitude is detected of the pulse. A reconstruction processor reconstructs an image from the energy and location of the current spikes.
According to another aspect of the present invention, a method of nuclear imaging is given. Radiation events are detected with an array of solid state detectors, generating current spikes in response to the radiation. The spikes are spread into pulses. A peak amplitude is detected of each of the pulses. An image is reconstructed from peak amplitude information representing event energies, and address information, representing event location.
According to a more limited aspect of the present invention, a timeout feature resets detector circuitry to avoid system lockup.
One of the advantages of the present invention is that it decreases the effective event processing time of the system.
Another advantage is that it provides a detector much smaller than present detectors.
Another advantage is that it creates very little dead time when the detector cannot process new data.
Another advantage is that it requires very low supply voltages and currents to operate.
Another advantage is that count rates are improved.
Yet another advantage of the present invention is that it provides a detector that is more easy to maintain than present detectors.
Still further benefits and advantages of the present invention will become apparent to those skilled in the art upon a reading and understanding of the preferred embodiments.
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Griesmer Jerome J.
Kline Barry D.
Fay Sharpe Fagan Minnich & McKee LLP
Hannaher Constantine
Israel Andrew
Koninklijke Philips Electronics , N.V.
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