US 5,841,140 A · Gamma camera for pet and spect studies

Abstract

A gamma camera is modified to perform PET studies as well as SPECT studies by utilization of the camera's SPECT electronics to likewise generate triggering pulse signals for photons indicative of a positron annihilation event which are corrected, on a bundled basis, for position, linearity and uniformity by the same digital processors used by the camera for SPECT studies. In addition the triggering pulse signals generate analog timing signals passed through a coarse coincidence circuit to establish matched pairs of timing signals which are digitally time stamped and processed along with the bundled set of pulse signals that the timing signals originated from. The timing signals in turn are corrected from a mapped detector head look up table on the basis of the corrected position of the triggering pulse signal and the time lag between each matched timing signal pair passed through a fine coincidence window processor thus insuring that the line of response passing through the corrected, precisely established positions of scintillations that produced the triggering pulse signals occurred within a time period clearly indicative of a positron annihilation event. By counting only true LORs images having high resolution can be constructed even though the camera's detecting heads cover a limited solid angle of event detections. The timing correction table is generated from an improved calibration technique which factors out those inherent time delays, including signal noise and jitter, which are specific to that gamma camera.

Claims32

Dependent claims

In a gamma camera having two detector heads between which a patient is positioned for SPECT studies;

each detector head spanning a discrete area vis-a-vis a plurality of PMTs behind a scintillation crystal, each PMT generating a pulse signal in response to a scintillation;
an event detector circuit detecting when any given PMT pulse signal becomes a triggering pulse signal indicative of a scintillation radiation event and quantifying the energy of said triggering pulse signal;
centroid calculator means for grouping with a PMT triggering pulse signal a plurality of pulse signals from PMTs adjacent that PMT which generated said triggering pulse signal and digital signal processors for determining by weighting the signals within each bundle the corrected intensity and pixel position of each scintillation event, the improvement comprising:
a) timing signal means for generating from each triggering pulse signal a trigger timing signal;
b) coincident means for determining when any given triggering timing signal from one head occurs within a set coarse time from any triggering timing signal from the opposite detector head and grouping any two triggering timing signals originating from opposite detector heads and occurring within said coarse time into matched pairs;
c) time stamping means for marking each triggering timing signal in a matched pair with a time stamp signal indicative of the difference in time between the triggering signals in each matched pair;
and
d) timing signal digital signal processor means for correcting said difference in time between said time stamp signals as a function of the corrected position of said scintillation events in turn established for each triggering pulse signal in each matched pair by said camera's digital signal processors whereby each matched pair establishes a LOR for tomographic imaging when the gamma camera is used for PET studies.

5 more elements

A gamma camera for conducting PET studies comprising:

a) first and second detector heads between which a patient with an ingested or injected radioactive isotope is positioned, each detector head having a plurality of PMT's arranged in a two dimensional array behind a scintillation crystal, each PMT generating PMT electrical analog pulse signals in response to patient emitted gamma radiation producing scintillations in said crystal;
b) detecting means for each PMT to determine when the intensity of any given pulse signal generated by its PMT, a triggering pulse signal, is indicative of a scintillation event caused by a positron annihilation;
c) constant fraction discrimination means for each PMT receiving said PMT signals and generating electrical triggering pulse signals corresponding to said PMT triggering pulse signals;
d) coincident window means sequentially receiving triggering timing signals from all the PMTs on both heads and sequentially determining for the earliest triggering timing signal generated by either detector head if a second triggering timing signal from the opposite detector head occurred within a coarse time period to establish a matched coincident pair of triggering timing signals while discarding said earliest triggering timing signal if said second in time triggering timing signal from the opposite detector head did not occur within said coarse time period;
e) time stamping means for receiving each matched pair of triggering timing signals indicative of a positron annihilation event from said coincident window means and generating a digitized time stamp signal for each PMT triggering timing signal in each matched pair indicative of the time difference between said triggering timing signals of each matched pair;
f) means for grouping a fixed plurality of PMT pulse signals from PMTs adjacent any PMT generating a triggering pulse signal along with said triggering pulse signal into a bundle of signals and digitizing said bundled group of PMT pulse signals;
g) means for assigning to each group of PMT pulse signals its corresponding time stamp signal generated by said time stamping means;
h) digital signal processing means for determining from a weighted average of each grouping corrected i) x,y spatial coordinates and, ii) an energy intensity, "z" indicative of a positron annihilation scintillation event and matching each bundled group of signals from one head with a bundled group from the opposite head by their time stamp signals to establish a coincident pair whereby the response time of said camera is improved by virtue of processing through said digital signal processing means only matched triggering signals indicative of a positron annihilation event while discarding random events.

5 more elements

A method for generating imaging data to perform a PET study in a gamma camera, said gamma camera having first and second detector heads between which a patient with an injected or ingested radioisotope is placed, each detector head having a plurality of PMTs generating PMT pulse signals situated behind a scintillation crystal, said method comprising the steps of:

continuously detecting for each PMT in each detector head triggering pulse signals indicative of photon induced scintillations resulting from positron annihilations;
generating a triggering timing signal for each triggering pulse signal indicative of the time at which said photon induced said scintillation;
continuously comparing the first in time triggering timing signal generated from either detector head with the first in time triggering timing signal generated from the opposite detector head to determine if the two signals occurred within a coarse given time of another to establish a matched pair and to discard the earliest triggering timing signal if a matched triggering timing signal from the opposite detector head did not occur within said coarse time period;
time stamping each triggering timing signal of each matched pair with a digitized time stamp, the difference between the two signals in any matched pair indicative of the time lag therebetween;
grouping a plurality of pulse signals generated by PMTs adjacent to and along that PMT which developed said triggering pulse signal during the time triggering pulse signal developed its triggering pulse signal and integrating each pulse signal in said grouping to develop digitized pulse signals indicative of the intensity and position of each PMT in each grouping;
assigning a time stamp correlated to that grouping of pulse signals containing the triggering pulse signal which generated the triggering timing signal;
weighting each digitized signal in each grouping to arrive at a corrected pixel position and intensity signal having assigned thereto a time stamp signal correcting said time stamp signal by a time factor stored in a look up table for the corrected position of said triggering pulse signal;
rejecting any matched pair of corrected signals if the difference between the corrected time signals of a matched pair exceeds a fine time period shorter than said coarse period and utilizing the corrected position signals for each matched pair within fine time period or a valid LOR resulting from a coincident photon pair.

5 more elements

Dependencies are inferred from the claim text.

Gamma camera for pet and spect studies

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Gamma camera for pet and spect studies

Life of this patent

Abstract

Claims32