Scintillation camera with improved linearity

Claim 2

In combination: a scintillation camera comprising a single crystal scintillator, a plurality of photomultiplier tubes spaced from said scintillator with overlapping fields of view thereof, circuit means coupled to said photomultiplier tubes for producing coordinate electrical signals representing spatial coordinates of interaction of a gamma ray with said scintillator, and display means for displaying said electrical signals in the form of a spatially positioned dot of light, said camera having an inherent characteristic non-linear spatial response such that a displayed map of a uniform spatial distribution of gamma rays interacting with said scintillator comprises a non-uniform spatial distribution of dots having a characteristic denser clustering of dots in regions of said map corresponding to locations of central areas of central ones of said photomultiplier tubes, said denser clustering being explained at least in part by the observed phenomenon that a gamma ray interaction at a particular location in said scintillator near the spatial position of a central axis of a particular one of said central photomultiplier tubes produces coordinate electrical signals representing an apparent location nearer said central axis of said particular photomultiplier tube; and signal correction circuitry coupled to the aforesaid circuit means and operative to produce corrected coordinate electrical signals representing more accurately said spatial coordinates of interaction comprising a plurality of correction signal generators, each being associated with one of said central ones of said photomultiplier tubes and operating in response to a gamma ray interaction in a portion of said scintillator near said associated photomultiplier tube to produce correction signals; and circuit means for combining said correction signals and said coordinate electrical signals to produce said corrected coordinate electrical signals.

Claim 3

An improved Anger-type scintillation camera comprising: a scintillator; nineteen photomultiplier tubes and preamplifiers therefor, said tubes viewing said scintillator and outputs from said prEamplifiers being signals having amplitudes which vary inversely with the distance between the coordinate position of a particular tube and the coordinate position of an interaction of a gamma ray quantum with said scintillator; computing circuitry coupled to said preamplifiers to produce an uncorrected set of signals, +x, -x, +y, -y, representing spatial coordinates of interaction of a gamma ray quantum with said scintillator; a first pair of difference circuits receiving said uncorrected set of signals and producing a pair of uncorrected coordinate signals, x,y; seven second pairs of difference circuits, each pair associated with one of a central seven of said photomultiplier tubes and having as differential inputs said pair of uncorrected coordinate signals, x,y and a pair of reference signals representing coordinates of said associated photomultiplier tube, each pair also having as a gain control input a version of said output from said preamplifier for said associated photomultiplier tube and producing a set of coordinate correction signals +xc, -xc, +yc, -yc for gamma ray interactions near said associated photomultiplier tube; summing circuits for individually adding said coordinate correction signals +xc, -xc, +yc, -yc to respective ones of said uncorrected set of signals, +x, -x, +y, -y, to produce a corrected set of signals +x'', -x'', +y'', -y'', said corrected set of signals more accurately representing spatial coordinates of a gamma ray quantum with said scintillator.

Claim 4

An improved Anger-type scintillation camera comprising: a scintillator; nineteen photomultiplier tubes and preamplifiers therefor, said tubes viewing said scintillator and outputs from said prEamplifiers being signals having amplitudes which vary inversely with the distance between the coordinate position of a particular tube and the coordinate position of an interaction of a gamma ray quantum with said scintillator; computing circuitry coupled to said preamplifiers to produce an uncorrected set of signals, +x, -x, +y, -y, representing spatial coordinates of interaction of a gamma ray quantum with said scintillator; a first pair of difference circuits receiving said uncorrected set of signals and producing a pair of uncorrected coordinate signals, x,y; seven second pairs of difference circuits, each pair associated with one of a central seven of said photomultiplier tubes and having as differential inputs said pair of uncorrected coordinate signals, x,y and a pair of reference signals representing coordinates of said associated photomultiplier tube, each pair also having as a gain control input a version of said output from said preamplifier for said associated photomultiplier tube and producing a set of coordinate correction signals +xc, -xc, +yc, -yc for gamma ray interactions near said associated photomultiplier tube; summing circuits for individually adding said coordinate correction signals +xc, -xc, +yc, -yc to respective ones of said uncorrected set of signals, +x, -x, +y, -y, to produce a corrected set of signals +x'', -x'', +y'', -y'', said corrected set of signals more accurately representing spatial coordinates of a gamma ray quantum with said scintillator.

Claim 5

In combination: an Anger-type scintillation camera comprising a scintillator, a plurality of photomultiplier tubes viewing said scintillator, circuit means coupled to said photomultiplier tubes for producing coordinate electrical signals representing spatial coordinates of interaction of a gamma ray with said scintillator, and display means for displaying said electrical signals in the form of a spatially positioned dot of light, said camera having an inherent characteristic non-linear spatial response such that a displayed map of a uniform spatial distribution of gamma rays interacting with said scintillator comprises a non-uniform spatial distribution of dots having a characteristic denser clustering of dots in regions of said map corresponding to locations of central areas of central ones of said photomultiplier tubes, said denser clustering being explained at least in part by the observed phenomenon that a gamma ray interaction at a particular location in said scintillator near the spatial position of a central axis of a particular one of said central photomultiplier tubes produces coordinate electrical signals representing an apparent location nearer said central axis of said particular photomultiplier tube; and signal correction circuitry operative to produce corrected coordinate electrical signals representing more accurately said spatial coordinates of interaction comprising a plurality of correction signal generators, each being associated with one of said central ones of said photomultiplier tubes and operating in response to a gamma ray interaction in a portion of said scintillator near said associated photomultiplier tube to produce correction signals, and each employing a. a pair of difference circuits, each having inputs of a version of one of said pair of electrical signals and a fixed reference voltage of a magnitude corresponding to a respective coordinate of said axis of said associated photomultiplier tube and producing an output generally representing the difference therebetween; and b. a function generator having its output coupled to a gain control lead of each of said difference circuits to vary the gain of said circuits inversely with the magnitude of the distance between the coordinate location of said axis of said associated photomultiplier tube and the coordinate location of a gamma ray interaction with said scintillator; And circuit means for combining said correction signals and said coordinate electrical signals to produce said corrected coordinate electrical signals.

Claim 6

In combination: an Anger-type scintillation camera comprising a scintillator, a plurality of photomultiplier tubes viewing said scintillator, circuit means coupled to said photomultiplier tubes for producing coordinate electrical signals representing spatial coordinates of interaction of a gamma ray with said scintillator, and display means for displaying said electrical signals in the form of a spatially positioned dot of light, said camera having an inherent characteristic non-linear spatial response such that a displayed map of a uniform spatial distribution of gamma rays interacting with said scintillator comprises a non-uniform spatial distribution of dots having a characteristic denser clustering of dots in regions of said map corresponding to locations of central areas of central ones of said photomultiplier tubes, said denser clustering being explained at least in part by the observed phenomenon that a gamma ray interaction at a particular location in said scintillator near the spatial position of a central axis of a particular one of said central photomultiplier tubes produces coordinate electrical signals representing an apparent location nearer said central axis of said particular photomultiplier tube; and signal correction circuitry operative to produce corrected coordinate electrical signals representing more accurately said spatial coordinates of interaction comprising a plurality of correction signal generators, each being associated with one of said central ones of said photomultiplier tubes and operating in response to a gamma ray interaction in a portion of said scintillator near said associated photomultiplier tube to produce correction signals, and each employing a. a pair of difference circuits, each having inputs of a version of one of said pair of electrical signals and a fixed reference voltage of a magnitude corresponding to a respective coordinate of said axis of said associated photomultiplier tube and producing an output generally representing the difference therebetween; and b. a function generator having its output coupled to a gain control lead of each of said difference circuits to vary the gain of said circuits inversely with the magnitude of the distance between the coordinate location of said axis of said associated photomultiplier tube and the coordinate location of a gamma ray interaction with said scintillator; And circuit means for combining said correction signals and said coordinate electrical signals to produce said corrected coordinate electrical signals.

Claim 7

The combination as claimed in claim 3, wherein said function generator comprises circuit means deriving a gain control signal directly from an output signal from said associated photomultiplier tube.

Claim 8

The combination as claimed in claim 3, wherein said function generator comprises circuit means deriving a gain control signal from said fixed reference voltages and said pair of electrical signals.

Claim 9

In a scintillation camera having a single crystal scintillator, a plurality of photomultiplier tubes spaced from said scintillator with overlapping fields of view thereof, circuit means coupled to said photomultiplier tubes for producing coordinate electrical signals representing X and Y coordinates of interaction of a gamma ray with said scintillator in a rectilinear coordinate system, and display means for displaying said electrical signals in the form of a spatially positioned dot of light, the improvement comprising signal correction circuitry connected to said circuit means and operative to produce corrected coordinate electrical signals representing more accurately said spatial coordinates of interaction comprising a plurality of correction signal generators, each being associated with selected ones of said photomultiplier tubes and each operating in response to a gamma ray interaction in a portion of said scintillator near said associated photomultiplier tube to produce correction signals; and circuit means for combining said correction signals and said coordinate electrical signals to produce said corrected coordinate electrical signals.

Claim 10

In a scintillation camera having a single crystal scintillator, a plurality of photomultiplier tubes spaced from said scintillator with overlapping fields of view thereof, circuit means coupled to said photomultiplier tubes for producing coordinate electrical signals representing X and Y coordinates of interaction of a gamma ray with said scintillator in a rectilinear coordinate system, and display means for displaying said electrical signals in the form of a spatially positioned dot of light, the improvement comprising signal correction circuitry connected to said circuit means and operative to produce corrected coordinate electrical signals representing more accurately said spatial coordinates of interaction comprising a plurality of correction signal generators, each being associated with selected ones of said photomultiplier tubes and each operating in response to a gamma ray interaction in a portion of said scintillator near said associated photomultiplier tube to produce correction signals; and circuit means for combining said correction signals and said coordinate electrical signals to produce said corrected coordinate electrical signals.

Claim 11

In the scintillation camera of claim 6 the further improvement wherein said correction signal generators employ function generator means in conjunction with each interiorally located photomultiplier tube to produce the aforesaid correction signals in a strength that varies inversely with the magnitude of the distance between the coordinate location of the axis of an associated photomultiplier tube and the coordinate location of a gamma ray interaction with said scintillator and wherein threshold circuit means is associated with said function generator means to selectively prevent the generation of correction signals to those coordinate electrical signals having an amplitude strength less than a predetermined threshold setting.