Trigger methods in nuclear medical imaging
Disclosed herein are a system, method, and computer-readable storage medium for determining a time pickoff for both digital and analog photomultiplier circuits. Rather than basing time pickoff on the leading edge of a photomultiplier signal crossing a threshold or the first signal from a digital photomultiplier, a method for more accurate time calculations is disclosed. The system searches for peak values associated with the signal using differentiation, peak hold searching, and Gaussian distributions. Based on these calculations and comparisons, a more accurate time pickoff is determined.
1. A nuclear imaging apparatus comprising:
an array of radiation sensors; and
analog circuitry which performs a method comprising:
receiving a current pulse;
branching the current pulse into at least two pulses, to yield a first pulse and a second pulse;
in a first path associated with the first pulse:
delaying the first pulse; and
shaping the first pulse, to yield a shaped current pulse;
in a second path associated with the second pulse:
subjecting the second pulse to a low-pass filter, to yield a filtered current pulse;
differentiating the filtered current pulse, to yield a first derivative signal; and
applying peak hold detection to the first derivative signal, to yield a slew-rate voltage selecting a percentage of the slew-rate voltage as a trigger level; and
comparing the shaped current pulse to the trigger level.
2. The nuclear imaging apparatus of claim 1 , wherein the radiation sensor is at least one of a photomultiplier tube and a passive quenching silicon-photomultiplier.
3. The nuclear imaging apparatus of claim 1 , wherein the analog circuitry comprises additional circuitry which results in the method further comprising recording a time associated with the current pulse based on the comparing of the shaped current pulse to the trigger level.
4. The nuclear imaging apparatus of claim 1 , wherein the slew-rate voltage is associated with a peak-value of the current pulse.
5. The nuclear imaging apparatus of claim 1 , wherein comparing the shaped current pulse to the trigger level comprises use of a comparator circuit.
6. The nuclear imaging apparatus of claim 5 , wherein the shaped current pulse is applied to one of an inverting input of the comparator circuit and a non-inverting input of the comparator circuit.
7. A system of photoelectron triggering comprising:
a processor; and
a computer-readable storage medium having instructions stored which, when executed by the processor, cause the processor to perform a method comprising:
receiving a current pulse;
branching the current pulse into at least two pulses, to yield a first pulse and a second pulse;
in a first path associated with the first pulse:
delaying the first pulse; and
shaping the first pulse, to yield a shaped current pulse;
in a second path associated with the second pulse:
subjecting the second pulse to a low-pass filter, to yield a filtered current pulse;
differentiating the filtered current pulse, to yield a first derivative signal; and
applying peak hold detection to the first derivative signal, to yield a slew-rate voltage selecting a percentage of the slew-rate voltage as a trigger level; and
comparing the shaped current pulse to the trigger level.
8. The system of claim 7 , wherein the radiation sensor is at least one of a photomultiplier tube and a passive quenching silicon-photomultiplier.
9. The system of claim 7 , wherein the computer-readable medium has additional instructions stored which result in the method further comprising recording a time associated with the current pulse based on the comparing of the shaped current pulse to the trigger level.
10. The system of claim 7 , wherein the slew-rate voltage is associated with a peak-value of the current pulse.
11. The system of claim 7 , wherein comparing the shaped current pulse to the trigger level comprises use of a comparator circuit.
12. The system of claim 11 , wherein the shaped current pulse is applied to one of an inverting input of the comparator circuit and a non-inverting input of the comparator circuit.