Fault-tolerant detector for gamma ray imaging
First Claim
Patent Images
1. A nuclear imaging apparatus comprising:
- a radiation detector including a plurality of rows of tiles of detector elements, each of the detector elements generating an output pulse in response to each detected radiation event;
a rotor which rotates the radiation detector;
an analyzer which compares the response of each detector element with preselected response criteria when the radiation detector is subjected to a calibration radiation source;
read out electronics which suppresses output pulses from detector elements whose response fails to meet the preselected response criteria;
a plurality of summing circuits, each summing circuit being connected with one of the plurality of rows of tiles of detector elements to generate a sum of the output pulses therefrom during a sampling period;
a correction circuit which adjusts the sums with correction factors, each row having a preselected one of the correction factors after the output pulses from detector elements whose response fails to meet the preselected response criteria are suppressed; and
a reconstruction processor that reconstructs an image representation from the adjusted sums and rotational position of the radiation detector corresponding to each sampling period.
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Abstract
A nuclear imaging apparatus includes a radiation detector comprising an array (18) of solid state detector elements (22) responsive to incident gamma radiation by emitting a current spike. A pixel correction processor (44) detects defective detector elements in the array and a flood correction circuit (66) corrects detected radiation events (70) based on sensitivity differences between a plurality of groupings of detector elements in the array. A reconstruction processor (76) reconstructs an image representation from the corrected radiation events (74).
93 Citations
18 Claims
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1. A nuclear imaging apparatus comprising:
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a radiation detector including a plurality of rows of tiles of detector elements, each of the detector elements generating an output pulse in response to each detected radiation event;
a rotor which rotates the radiation detector;
an analyzer which compares the response of each detector element with preselected response criteria when the radiation detector is subjected to a calibration radiation source;
read out electronics which suppresses output pulses from detector elements whose response fails to meet the preselected response criteria;
a plurality of summing circuits, each summing circuit being connected with one of the plurality of rows of tiles of detector elements to generate a sum of the output pulses therefrom during a sampling period;
a correction circuit which adjusts the sums with correction factors, each row having a preselected one of the correction factors after the output pulses from detector elements whose response fails to meet the preselected response criteria are suppressed; and
a reconstruction processor that reconstructs an image representation from the adjusted sums and rotational position of the radiation detector corresponding to each sampling period. - View Dependent Claims (2)
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3. A nuclear imaging apparatus comprising:
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a radiation detector comprising an array of solid state detector elements arranged in a plurality of rows of tiles of detector elements, the detectors elements responsive to incident gamma radiation by emitting output pulses;
a pixel correction processor which detects defective detector elements in the array;
means for comparing a spectral response of each detector element with preselected spectral response criteria when the radiation detector is subjected to a calibration radiation source;
read out electronics which suppresses output pulses from defective detector elements whose spectral response fails to meet the preselected response criteria;
a plurality of summing circuits, each summing circuit being connected with one of the plurality of rows of tiles of detector elements to generate a sum of the output pulses therefrom during a sampling period;
a flood correction circuit which corrects detected radiation events based on sensitivity by adjusting the sums with correction factors, each row having a preselected one of the correction factors after the output pulses from defective detector elements are suppressed; and
a reconstruction processor which reconstructs an image representation from the corrected radiation events. - View Dependent Claims (4, 5, 6, 7, 8)
a pulse height analyzer for generating an energy spectrum for each pixel;
an a pixel offset correction circuit for normalizing the detector elements with respect to a baseline voltage when no gamma radiation is incident on the radiation detector; and
a gain correction circuit for normalizing the detector elements with respect to pulse height of the current spikes when gamma radiation is incident on the radiation detector.
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6. The apparatus of claim 3, wherein:
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the pixel correction processor utilizes gamma radiation events received from a known radiation source, the gamma radiation events collected within a wide energy range relative to a collected photopeak; and
the flood correction circuit utilizes gamma radiation events received from the known radiation source, the gamma radiation events collected within a narrow energy range relative to the collected photopeak.
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7. The apparatus of claim 6, wherein the flood correction circuit utilizes gamma radiation events collected within an energy window which is 10% of the collected photopeak and which is centered about the photopeak.
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8. The apparatus of claim 3, wherein the radiation detector comprises an array of semiconductor crystals selected from cadmium-zinc-telluride crystals and cadmium-telluride crystals.
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9. A method of diagnostic imaging of a subject comprising:
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exposing a solid state radiation detector array to a known radiation source, the radiation detector comprising a two-dimensional array of detector elements generating a detectable signal responsive to incident gamma radiation, and each detector element comprising a distinct channel;
detecting radiation events at each detector element;
identifying defective and nondefective detector elements and electronically disabling defective detector elements whose response to radiation is outside of preselected specifications;
introducing a radioactive isotope into a subject located in an imaging region;
spinning the radiation detector array according to a preselected spin orbit;
rotating the radiation detector array about a longitudinal axis of the subject;
during said spinning and rotating, detecting radiation events indicative of nuclear decay to generate a plurality of planar projections of an examination region;
weighting the detected radiation events for each row of a plurality of detector elements with weighting factors to generate corrected data after the defective detector elements are disabled;
reconstructing the corrected data into an image representation of the subject in the imaging region. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16)
calculating detector element correction values which normalize a spectrum of each nondefective detector element; and
defining an energy window based on the energy resolution of the normalized spectra, the energy window for screening radiation events according to energy;
calculating a the weighting factors for each row of a the plurality of detector elements, the weighting factor scaling each row to a nominal value when the detector is exposed to the known radiation source.
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11. The method of claim 10, wherein calculating detector element correction values includes:
calculating an offset value and a gain correction factor for each detector element.
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12. The method of claim 10, wherein the energy window is defined as 10% of a collected photopeak, centered about the photopeak.
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13. The method of claim 9, wherein identifying defective detector elements includes:
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determining whether the number of radiation events detected by each detector element exceeds a preselected threshold value;
recording as defective each detector element for which the preselected threshold value is not exceeded;
generating an energy spectrum for each detector element for which the preselected threshold value is exceeded;
analyzing the generated energy spectra for a preselected degree of energy resolution; and
recording as defective each detector element which lacks the preselected degree of energy resolution.
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14. The method of claim 9, wherein the array of detectors elements is a multi-channel cadmium-zinc-telluride detector array.
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15. The method of claim 9, wherein the array of detectors elements further comprises:
radiation-absorbing collimator plates disposed parallel to one another for collimating the gamma radiation incident on the radiation detector array.
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16. The method of claim 9, wherein spinning includes:
rotating the radiation detector array about an axis extending through a center point of the radiation detector array.
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17. A method of calibrating a nuclear imaging device comprising:
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exposing a solid state radiation detector to a known radiation source, the radiation detector having a two-dimensional array of detector elements generating a detectable signal responsive to incident gamma radiation, and each detector element defining a distinct channel;
detecting radiation events at each detector element;
defining an energy window based on energy resolution of normalized spectra, the energy window for screening radiation events according to energy;
identifying defective and nondefective detector elements;
calculating detector element correction values which normalize a spectrum of each nondefective detector element; and
calculating a weighting factor for each of a plurality of detector element rows, after the spectra of each nondefective detector element is normalized, the weighting factor scaling each row to a nominal value when the radiation detector is exposed to a the known radiation source. - View Dependent Claims (18)
identifying one or more rows having a the weighting factor which is outside a preselected range of values; and
rearranging the tile detector element subarrays such that the weighting factor of each of the identified one or more rows falls within said preselected range of values.
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Specification