Gamma radiation detector with enhanced signal treatment

• US 4,889,991 A
• Filed: 09/23/1988
• Issued: 12/26/1989
• Est. Priority Date: 09/23/1988
• Status: Expired due to Term

• Current Assignee: Neoprobe Corporation Columbus
• Original Assignee: Neoprobe Corporation
• Inventors: Thurston, Marlin O., Ramsey, Raymond C.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US07/248,816
• Time in Patent Office: 459 Days
• Field of Search: 128/659, 128/654, 250/370.07, 250/370.01, 250/336.1
• US Class Current: 250/336.1
• CPC Class Codes: A61B 6/4258 for detecting non x-ray radiation, e.g. gamma radiation A61B6/037 takes precedence
• CPC Class Codes: G01T 1/161 Applications in the field of nuclear medicine, e.g. in vivo counting apparatus for radiation diagnosis A61B6/00

Abstract

A hand-held gamma radiation probe is employed to locate radiation concentrations in animal tissue in conjunction with a control function providing an enhanced audio output particularly suited for cuing the user as to source position. The probe is positioned at a location on the animal body representing background radiation and a squelch low count rate is developed therefrom. The squelch low count rate is multiplied by a range factor to develop a squelch high count rate and frequencies are developed from a look-up frequency table from lowest to highest in correspondence with the developed high and low squelch count rates. Slew rate limiting of the count rates is provided by development of a squelch delta value representing the difference between the squelch high and low count rates divided by a time element. Selection of frequencies for audio output from the frequency table is limited by the value of the squelch delta value. A weighting of received radiation counts is carried out continuously to develop count rate values used by the system.

Claims

1. A system for detecting and locating sources of gamma radiation within a region of interest, comprising:

a probe movable from position to position within said region of interest including;

a housing having a forward portion extending to a radiation window positionable in the vicinity of a said source;

detector means within said housing for deriving induced charges in response to gamma ray interaction therewith and providing corresponding output signals;

transmission means for transmitting said output signals; and

signal treatment means including;

energy level network means for validating said output signals and deriving count signals in response thereto;

control means responsive to said count signals for entering them into a continuously fed queue from earliest to latest received representing a given period of continuous sampling time, said control means effecting a select weighting of predetermined time defined increments of count signals within said queue and generating from said weighted count signals a stabilized count rate value; and

perceptible indicator means for providing a perceptible output corresponding with said stabilized count rate value.

2. The system of claim 1 in which said queue receives said count signals to an extent representing a one-half second count time interval of twenty-five entries from said earliest to said latest.

3. The system of claim 2 in which the earliest increment of ten said entries is weighted by unity, the next latest increment of five entries is weighted by a factor of two, the next latest increment of five entries is weighted by a factor of four and the increment representing the five latest entries is weighted by a factor of eight.

4. The system of claim 3 in which said control means is responsive to sum said weighted twenty-five entries and multiply said sum by five eighths to derive said stabilized count rate value.

5. The system of claim 1 which:

said perceptible indicator means provide an audible output in response to a drive signal of select frequency; and

said control means includes memory means for retaining a sequence of frequency values representing a predetermined range of frequency signals from lowest to highest, and is responsive to said stabilized count rate value for accessing said memory means frequency values to generate said drive signal in correspondence therewith.

6. A system for detecting and locating gamma radiation source concentrations at specific tissue regions of an animal body further having a predetermined body region selectable as emanating gamma radiation at background levels, comprising:

a probe movable from position to position along said tissue region and to said predetermined body region, including;

a housing having a forward portion extending to a radiation window positionable in the vicinity of said tissue regions and said predetermined body region;

detector means within said housing for deriving induced charges in response to gamma ray interaction therewith and providing corresponding output signals; and

transmission means for transmitting said output signals; and

signal treatment means including;

energy level network means for validating said output signals and deriving count signals in response thereto;

squelch mode activation means actuable for deriving a squelch range calibration sequence;

audible indicator means for providing an audible output in response to input signals;

memory means for retaining count rate data;

control means responsive to said count signals derived when said probe is located at said predetermined body region for deriving a basic background count rate, responsive to said basic background count rate to derive a squelch low count rate, responsive to derive the product of said squelch low count rate and a predetermined range for deriving a squelch high count rate, responsive to retain said squelch low count rate and said squelch high count rate in said memory means, responsive subsequently to said count signals for deriving count rate signals, and for deriving said audible indicator input signals at predetermined frequencies corresponding therewith when said count rate signals exhibit a value intermediate said memory retained squelch low count rate and said squelch high count rate.

7. The system of claim 6 in which said signal treatment means control means is responsive to derive a squelch difference value as the difference between said squelch low count rate and said squelch high count rate, responsive to divide said squelch difference value by a predetermined rate limit time value to derive a squelch delta value, responsive to retain said squelch delta value in said memory means, and responsive to limit change of said audible indicator input signals to correspond with changes of said count rate signals of value at least equivalent to said memory means retained squelch delta value.

8. The system of claim 7 in which:

said memory means includes a table of frequency deriving values representing lowest to highest said predetermined frequencies;

said control means is responsive to current said count rate signals and previous said count rate signals to derive the difference therebetween as a rate delta value and responsive to effect access of a said memory means frequency deriving value in controlled correspondence to said current rate signals when the absolute value of said rate delta value equals or exceeds said squelch delta value.

9. The system of claim 8 in which said signal treatment means control means includes a system clock having a clock output of predetermined clock frequency, said memory means retained frequency deriving values are a sequence of values of system clock cycles, and said control means is responsive to select said frequency deriving values to provide interrupt signals as said input signals to said audible indicator means.

10. The system of claim 6 in which said signal treatment means control means is responsive to said squelch high count rate to derive a high rate limit of predetermined count rate value greater than said squelch high count rate, and is responsive to limit the value of said count rate signals to said high rate limit, so as to enhance response performance of said system.

11. The system of claim 6 in which said signal treatment means control means is responsive to said squelch low count rate to derive a low rate limit of predetermined count rate value less than said squelch low count rate, and is responsive to limit the minimum value of said count rate signals to said low rate limit, so as to enhance the response performance of said system.

12. The system of claim 6 in which:

said signal treatment means control means is responsive to said squelch high count rate to derive a high rate limit of predetermined count rate value greater than said squelch high count rate, and is responsive to limit the value of said count rate signals to said high rate limit, so as to enhance response performance of said system; and

said signal treatment means control means is responsive to said squelch low count rate to derive a low rate limit of predetermined count rate value less than said squelch low count rate, and is responsive to limit the minimum value of said count rate signals to said low rate limit, so as to enhance the response performances of said system.

13. The system of claim 6 in which said signal treatment means control means is responsive to derive said squelch low count rate as said basic background count rate combined with a reference deviation of said basic background count rate.

14. The system of claim 13 in which said reference deviation of said basic background count rate is twice the square root of said basic background count rate.

15. The system of claim 6 in which:

said signal treatment means includes count mode activation means actuable for deriving a count rate mode when said probe is moved along said tissue regions; and

said control means is responsive to said actuation of said squelch mode activation means and, subsequently, to said count mode activation means actuation to effect response to said count signals when said probe is located at said predetermined body region.

16. The system of claim 6 in which said control means is responsive to said count signals derived when said probe is located at said tissue regions for entering them into a continuously fed queue from earliest to latest received representing a given increment of continuous sampling time, said control means effecting a select weight of predetermined, time defined increments of count signals within said queue and generating said count rate signals from said weighted count signals as stabilized count rate values.

17. The system of claim 16 in which said queue receives said count signals to an extent representing a one-half second count time interval of twenty-five entries from said earliest to said latest.

18. The system of claim 17 in which the earliest increment of ten said entries is weighted by unity, the next latest increment of five entries is weighted by a factor of two, the next latest increment of five entries is weighted by a factor of four and the increment representing the five latest entries is weighted by a factor of eight.

19. The system of claim 18 in which said control means is responsive to sum and weighted twenty-five entries and multiply said sum by five eighths to derive said stabilized count rate value.

20. The method for generating audible cuing signals locating gamma radiation concentrations within tissue of an animal body, said body having a region selectable as emanating gamma radiation at background levels comprising the steps of:

providing a hand manipular probe movable about said tissue and generating output signals in response to gamma radiation impinging thereon;

positioning said probe at said body region and evaluating said output signals for a predetermined interval to derive a squelch low background count rate;

deriving a squelch high count rate by multiplying said squelch low background count rate by a select range factor;

deriving a squelch difference value as the difference between squelch low background count rate and said squelch high count rate;

deriving a squelch delta value by dividing said squelch difference value by a predetermined time value;

providing a memory retained table of frequency deriving values from lowest to highest;

providing an audible sound generator actuable to produce a cuing sound output at frequencies of value selected from said table of frequency values;

positioning said probe at select locations of said tissue of said animal body and determining previous and next count rates from resulting said output signals;

accessing said table of frequency deriving values in correspondence with said previous count rate as a proportion of said squelch difference to provide a first said frequency deriving value;

actuating said sound generator in correspondence with said first frequency deriving value;

determining a rate delta value as the difference between said previous and next count rates;

comparing said rate delta value with said squelch delta value and accessing said table of frequency values in correspondence with a frequency value representing the sum of said previous count rate and said squelch delta value as a proportion of said squelch difference when said rate delta value equals or exceeds said squelch delta value to determine a second said frequency deriving value;

accessing said table of frequency deriving values for said second frequency deriving value; and

actuating said sound generator in correspondence with said second frequency deriving value.

21. The method of claim 20 wherein said sound generator is actuated in correspondence with said first frequency when said rate delta value is less than said squelch delta value.

22. The method of claim 20 in which said squelch low background count rate is derived as the count rate of said output signals summed with the value of a reference deviation thereof.

23. The method of claim 20 in which said previous and next count rates are determined by selectively weighting predetermined time defined increments of said output signals.

24. The method of claim 20 in which said range factor is selected as about 1.5.