US 5,384,699 A · Preventive maintenance system for the photomultiplier detector blocks of pet scanners

Abstract

A system including a method and apparatus for preventive maintenance of PET scanner photomultiplier detector blocks is disclosed. The quantitive comparisons used in the method of the present invention to provide an indication in the form of a display or printout advising the user that the photomultiplier block is stable, intermittently unstable, or drifting unstable, and also advising of the expected date of failure of a photomultiplier block in the PET scanner. The system alerts the user to replace the defective photomultiplier block prior to catastrophic failure in a scheduled preventative maintenance program, thus eliminating expensive and unscheduled downtime of the PET scanner due to photomultiplier failure. The apparatus for carrying out the method of the present invention preferably resides in the host computer controlling a PET scanner. It includes a memory adapted for storing a record of a number of iterative adjustments that are necessary to calibrate the gain of a photomultiplier detector block i at a time t.sub.0, a time t.sub.1 and a time T, where T>t.sub.1 >t.sub.0, which is designated as Histo(i,j(t)). The apparatus also includes a processor configured by a software program or a combination of programmed RAM and ROM devices to perform a number of calculations and operations on these values, and also includes a counter for analyzing each photomultiplier detector block i=1 through I of a PET scanner.

Claims27

Dependent claims

A computer implemented method for the preventive maintenance of photomultiplier detector blocks of a PET scanner, to determine if a detector block is intermittently unstable, the method comprising the steps of:

(a) calibrating a photomultiplier detector block i of a PET scanner by iteratively adjusting a gain by which photomultipliers in said photomultiplier detector block i amplify a detected signal, and storing a record of a number of iterative adjustments that are necessary at time t.sub.0 to calibrate the photomultiplier detector block i, wherein said record is designated as Histo(i),j(t));
(b) repeating step (a) for a time t.sub.1 and for a time T, where T>t.sub.1 >t.sub.0 ;
(c) computing an average of the number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said average through said time T is stored as av(i);
(d) computing a standard deviation of the number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said standard deviation through said time T is stored as sd(i);
(e) determining whether said photomultiplier detector block i is an intermittent unstable block with a peak at said time T, by computing at said time T if:
Histo(i,j(T))>av(i)+2sd(i),
wherein if it is determined that said detector block is an intermittent unstable block with a peak at said time T, said method further comprising:
(1) storing said number of iterative adjustments required for said detector block i at said time T as npeak(i,jp)=T, wherein jp denotes the number of intermittent peaks detected for said photomultiplier detector block i from time t=t.sub.0 through t=T;
(2) calculating a minimum time designated mintp, between peaks of said intermittent unstable block from said times t.sub.0 to said time T;
and
(3) providing an output signal to advise that photomultiplier detector block i is an intermittently unstable block and should be changed or serviced prior to a time=T+mintp when a new peak is likely to occur.

8 more elements

A computer implemented method for the preventative maintenance of photomultiplier detector blocks of a PET scanner, to determine if a photomultiplier detector block is a drifting unstable block, the method comprising the steps of:

(a) calibrating a photomultiplier detector block i of a PET scanner by iteratively adjusting a gain by which photomultipliers in said photomultiplier detector block i amplify a detected signal, and storing a record of a number of iterative adjustments that are necessary at a time t.sub.0 to calibrate the gain of a photomultiplier detector block i, wherein said record is designated as Histo(i,j(t));
(b) repeating step (a) for a time t.sub.1 and for a time T, where T>t.sub.1 >t.sub.0 ;
(c) computing an average of the number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said average through said time T is stored as av(i);
(d) computing a standard deviation of the number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said standard deviation through said time T is stored as sd(i);
and
(e) determining whether said detector block i is a drifting unstable block at said time T if:
Histo(i,J(T))>Histo(i,j(T-1))>Histo(i,j(T-2))>av(i);
wherein if said detector block is a drifting unstable block at said time T, said method further comprises:
(e1) determining whether the photomultiplier detector block i is at its calibration range limit and should be replaced or serviced by computing if said number of iterative adjustments required to calibrate said photomultiplier detector block at said time T is greater than or equal to a predetermined number designating the photomultiplier detector block limit of calibration range;
and
wherein if it is determined that said photomultiplier detector block i is at its calibration range limit, said method further comprises:
(e2) providing an output signal advising that photomultiplier detector block i is a drifting unstable block at time T, and to change or service said block i as soon as possible to avoid photomultiplier block failure, since said block i has reached the limit of its calibration range.

9 more elements

A computer implemented method for the preventive maintenance of photomultiplier detector blocks of a PET scanner, the method comprising the steps of:

(a) calibrating a photomultiplier detector block i of a PET scanner by iteratively adjusting a gain by which photomultipliers in said photomultiplier detector block i amplify a detected signal, and storing a record of a number of iterative adjustments that are necessary at a time t.sub.0 to calibrate the gain of a photomultiplier detector block i wherein said record is designated as Histo(i,j(t));
(b) repeating step (a) for a time t.sub.1 and for a time T, where T>t.sub.1 >t.sub.0 ;
(c) computing an average number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said average through said time T is stored as av(i);
(d) computing a standard deviation of the number of iterative adjustments necessary to calibrate said detector block for said time t.sub.0 through said time T, wherein said standard deviation through said time T is stored as sd(i);
(e) determining whether said photomultiplier detector block i is an intermittent unstable block with a peak at said time T, by computing at said time T if:
Histo(i,j(T))>av(i)+2sd(i);
(f) determining whether said photomultiplier detector block i is a drifting unstable block at said time T if:
Histo(i,J(T))>Histo(i,j(T-1))>Histo(i,j(T-2))>av(i);
and
(g) determining that said photomultiplier block i is a stable detector block if said detector block i is not an intermittent unstable detector block as defined in step (e), and said detector block i is not a drifting unstable detector block as defined in step (f);
wherein if it is determined that said detector block is an intermittent unstable block with a peak at said time T, said method further comprising:
(g1) storing said number of iterative adjustments J required for said detector block i at said time T as npeak(i,jp)=T, wherein jp denotes the number of intermittent peaks detected for said photomultiplier detector block i from time t=t.sub.0 through t=T;
(g2) calculating an average time designated avtp, and a minimum time designated mintp, between peaks of said intermittently unstable block from said time t.sub.0 to said time T;
and
(g3) providing an output signal to advise that photomultiplier detector block i is an intermittent unstable block and should be changed or serviced prior to a time=T+mintp when a new peak is likely to occur;
wherein if it is determined that said detector block is a drifting unstable block at said time T, said method further comprises:
(1) determining whether the photomultiplier detector block i is at its calibration range limit and should be replaced or serviced by computing if said number of iterative adjustments required to calibrate said photomultiplier detector block at said time T is greater than or equal to a predetermined number designating the photomultiplier detector block limit of calibration range;
and
wherein if it is determined that said drifting unstable photomultiplier detector block i is at its calibration range limit, said method further comprises:
(2) providing an output signal advising that photomultiplier detector block i is a drifting unstable block at time T, and to change or service said blocks i as soon as possible to avoid photomultiplier block failure, since it has reached the limit of its calibration range;
wherein if it is determined that said detector block is a drifting unstable block at time T and said number of iterations is less than said predetermined number designating the photomultiplier detector block limit of calibration range, said method further comprising:
(h) predicting a time of failure of detector block i, designated tf(i), when said detector block i will reach said predetermined calibration range limit of iterative adjustments designated Histo(i,j(tf(i))) by satisfying the equation:
tf(i)=[-B+{BB-4A(C-Z)}exp0.5]/2A
wherein
A=0.5[Histo(i,j(T-2))-2 Histo(i,j(T-1))+Histo(i,J(T))],
B=-0.5[3 Histo(i,j(T-2))-4 Histo(i,j(T-1))+Histo(i,J(T))],
C=Histo(i,j(T-2)), and
Z=said predetermined number designating the detector block i calibration range limit of iterative adjustments;
and
(i) providing an output signal advising that photomultiplier detector block i is a drifting unstable block i at time T, that it is likely to reach the limit of its calibration range at a time=T-2 (tfi) and that it should be replaced or serviced prior to reaching its calibration range limit;
and
wherein if it is determined that said detector block i is a stable detector block at said time T, said method further comprising:
(i1) determining if said detector block i has reached its calibration range limit and should be replaced or serviced by computing if said Hist(i,J(T)) is greater than or equal to a predetermined number designating the photomultiplier detector block limit of calibration range, and
(j) providing an output signal advising that at said time T said photomultiplier detector block i is a stable detector block;
and
wherein if it is determined that said detector block i has reached its calibration range limit, said method further comprises:
(j1) providing an output signal advising that said detector block i has reached its calibration range limit and should be replaced or serviced as soon as possible to avoid photomultiplier detector block failure;
wherein if it is determined that said detector block i is a stable detector block and has not reached its calibration range limit at said time T, said method further comprises:
(k) determining if said detector block i is a stable detector block with a high degree of stability, a medium degree of stability, or a marginal degree of stability at said time T, wherein:
(k1) if the value of av(i) is less than a first predetermined value, then said detector block i has a high degree of stability;
(k2) if the value of av(i) is greater than or equal to said first predetermined value and less than a second predetermined value, then said detector block i has a medium degree of stability;
and
(k3) if the value of av(i) is greater than or equal to said second predetermined value, then said detector block has a marginal degree of stability;
and
said method further comprising:
(1) providing an output signal advising that said photomultiplier detector block i has said av(i), said sd(i) and said degree of stability as determined in step (k).

43 more elements

A computer based apparatus for the preventive maintenance of photomultiplier detector blocks of a PET scanner, the apparatus comprising:

means for calibrating photomultiplier detector blocks i=1 through i=I of a PET scanner, including means for iteratively adjusting a gain by which photomultipliers in said photomultiplier detector block i amplify a detected signal, said apparatus further comprising,
(a) memory for storing:
(a1) a record of a number of iterative adjustments that are necessary to calibrate the gain of a photomultiplier detector block i at a time t.sub.0, a time t.sub.1 and a time T, where T>t.sub.1 >t.sub.0, said record is designated as Histo(i,j(t));
(a2) an average value of the number of iterative adjustments necessary to calibrate said detector block i, designated av(i), and a standard deviation value of the number of iterative adjustments necessary to calibrate said detector block i, designated as sd(i);
(b) processing means to:
(b1) compute the average number of iterative adjustments necessary to calibrate said detector block i for said time t.sub.0 through said time T, and storing said average value through said time T in said memory;
(b2) compute the standard deviation of the number of iterative adjustments necessary to calibrate said detector block i for said time t.sub.0 through said time T, and store said standard deviation value through said time T in said memory;
(b3) compute at said time T if:
Histo(i,j(T))>av(i)+2sd(i) to determine that said detector block i is an intermittent unstable block;
(b4) compute at said time T if:
Histo(i,J(T))>Histo(i,j(T-1))>Histo(i,j(T-2))>av(i) to determine that said detector block i is a drifting unstable block;
(b5) determine that said photomultiplier block i is a stable detector block, if said detector block i is not an intermittent unstable detector block and is not a drifting unstable detector block, and to generate an output signal advising that at said time T said photomultiplier detector block i is a stable detector block;
and
(b6) compute if said number of iterative adjustments required to calibrate said photomultiplier detector block i at said time T is greater than or equal to a predetermined number designating the photomultiplier detector block limit of calibration range, to determine that the photomultiplier detector block i is at its calibration range limit and should be replaced or serviced;
and to generate an output signal for advising that said detector block i has reached its calibration range limit and should be replaced or serviced as soon as possible to avoid photomultiplier detector block failure.

12 more elements

Dependencies are inferred from the claim text.

Preventive maintenance system for the photomultiplier detector blocks of pet scanners

Life of this patent

Preventive maintenance system for the photomultiplier detector blocks of pet scanners

Life of this patent

Abstract

Claims27