Gamma camera correction system and method for using the same

Claim 1

In a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction; and a storage means responsive to events, each of whose total energy lies within an energy window functionally related to the coordinates of the event, for storing a distorted representation of the image of the radiation field, the improvement comprising: sequentially applying to the distorted representation of the image two sets of independent, spatially dependent, correction factors whereby the sequence of application independently corrects different types of distortions in the distorted image.

Claim 13

A method for calibrating a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction; said method comprising: (a) flooding the head with a uniform radiation field using a perforated plate interposed between the field and the head; (b) calculating the coordinates of certain interactions with the head; (c) recording interactions in a storage medium for producing a map representative of the image of the field as seen through the plate; (d) calculating dislocation correction factors for the map where such correction factors are determined in accordance with the deviation from linearity of the response of the photodetectors to stimuli which interact with the head; (e) calculating energy window correction factors for the map where such correction factors are determined in accordance with deviations from a peak value of the total energy of each event; (f) removing the perforated plate; (g) flooding the head with a uniform radiation field; (h) recording interactions in a storage medium only if the total energy of an interaction lies within an energy window determined by the energy window correction factors associated with the calculated coordinates of the event for producing a map representative of the image of the uniform radiation field after the perforated plate has been removed; (i) applying the dislocation correction factors to the map representative of the image of the uniform radiation field after the perforated plate has been removed for producing a relocated map whose contents have been corrected for dislocations due to non-linearity in the response of the photodetectors; (j) calculating sensitivity correction factors by calculating, for a given picture element of the relocated map, the ratio of the average number of events per picture element to the actual number of events in a given picture element; and (k) storing a representation of the radiation field by applying the three correction factors so obtained.

Claim 14

A method for calibrating a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction; said method comprising: (a) flooding the head with a uniform radiation field using a perforated plate interposed between the field and the head; (b) calculating the coordinates of certain interactions with the head; (c) recording interactions in a storage medium for producing a map representative of the image of the field as seen through the plate; (d) calculating dislocation correction factors for the map where such correction factors are determined in accordance with the deviation from linearity of the response of the photodetectors to stimuli which interact with the head; (e) calculating energy window correction factors for the map where such correction factors are determined in accordance with deviations from a peak value of the total energy of each event; (f) removing the perforated plate; (g) flooding the head with a uniform radiation field; (h) recording interactions in a storage medium only if the total energy of an interaction lies within an energy window determined by the energy window correction factors associated with the calculated coordinates of the event for producing a map representative of the image of the uniform radiation field after the perforated plate has been removed; (i) applying the dislocation correction factors to the map representative of the image of the uniform radiation field after the perforated plate has been removed for producing a relocated map whose contents have been corrected for dislocations due to non-linearity in the response of the photodetectors; (j) calculating sensitivity correction factors by calculating, for a given picture element of the relocated map, the ratio of the average number of events per picture element to the actual number of events in a given picture element; and (k) storing a representation of the radiation field by applying the three correction factors so obtained.

Claim 18

A method for using a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction which define the distorted coordinates of the interaction; said method comprising the steps of: (a) converting the distorted coordinates into relocated coordinates by applying to the distorted coordinates corrections that correct for non-linearities of the components of the device and for variations in energy resulting from inhomogeniety of the optical system; and (b) converting the relocated coordinates into undistorted coordinates by applying to the relocated coordinates a sensitivity correction that corrects for the non-uniform stopping power of the head.

Claim 19

A method for using a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction which define the distorted coordinates of the interaction; said method comprising the steps of: (a) converting the distorted coordinates into relocated coordinates by applying to the distorted coordinates corrections that correct for non-linearities of the components of the device and for variations in energy resulting from inhomogeniety of the optical system; and (b) converting the relocated coordinates into undistorted coordinates by applying to the relocated coordinates a sensitivity correction that corrects for the non-uniform stopping power of the head.

Claim 24

A method for using a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction which define the distorted coordinates of the interaction; said method comprising the steps of: system; (d) means for storing spatially dependent energy window correction factors based on a relocated coordinate system; (e) means for storing spatially dependent sensitivity correction factors based on a relocated coordinate system; (f) means for converting the calculated coordinates of an interaction into relocated coordinates by applying to the calculated coordinates the dislocation correction factor evaluated at the calculated coordinates; (g) means for producing a validating signal validating an interaction if the total energy thereof satisfies the energy window correction factor evaluated at the relocated coordinates of the interaction; and (h) means for converting the relocated coordinates of a validated interaction into undistorted coordinates by applying to the relocated coordinates the sensitivity correction factor evaluated at the relocated coordinates of the validated interaction.

Claim 25

A method for using a nuclear imaging device having a head that includes a plurality of photodetectors for producing output signals in response to radiation stimuli which are emitted by a radiation field and interact with the device; and coordinate computation circuitry responsive to said signals for producing a pair of calculated coordinate signals for each interaction which define the distorted coordinates of the interaction; said method comprising the steps of: system; (d) means for storing spatially dependent energy window correction factors based on a relocated coordinate system; (e) means for storing spatially dependent sensitivity correction factors based on a relocated coordinate system; (f) means for converting the calculated coordinates of an interaction into relocated coordinates by applying to the calculated coordinates the dislocation correction factor evaluated at the calculated coordinates; (g) means for producing a validating signal validating an interaction if the total energy thereof satisfies the energy window correction factor evaluated at the relocated coordinates of the interaction; and (h) means for converting the relocated coordinates of a validated interaction into undistorted coordinates by applying to the relocated coordinates the sensitivity correction factor evaluated at the relocated coordinates of the validated interaction.