Scanning system and method for locating sources of radiation emission

• US 6,272,373 B1
• Filed: 10/23/1998
• Issued: 08/07/2001
• Est. Priority Date: 10/23/1998
• Status: Expired due to Term

• Current Assignee: Devicor Medical Products Incorporated (Danaher Corporation)
• Original Assignee: Neoprobe Corporation
• Inventors: Bouton, Chad E.
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): MANTIS MERCADER, ELENI M
• Application Number:
  US09/177,714
• Time in Patent Office: 1,019 Days
• Field of Search: 600/407, 600/436, 250/370.06, 250/370.08, 250/370.09
• US Class Current: 600/436
• 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 scanning system for a hand-held probe employs a 50 ms scanning interval in conjunction with circular memory. Combinations of segment bins from the circular memory are acquired following each short scanning interval. A threshold is computed for each combination initially based upon a threshold factor which is statistically significant and has a value of three. Audible cueing is developed if any three of six of these combinations of segment bin scan counts exceeds a correspondingly computed threshold value. Thereafter, the threshold factor is diminished to a value of one and the same thresholding tests are carried out to maintain audible cueing. Running count rates are computed as the average of the entire circular buffer memory divided by its corresponding total collection time. This computation is provided on a one half second updated basis.

Claims

1. A system for detecting and locating sources of radiation at a region of interest evidencing background radiation, comprising:

a probe moveable within said region of interest to provide a scan pulsed output corresponding with said sources and positionable to evaluate said background radiation and derive a background pulsed output corresponding therewith;

an audible indicator responsive to an audio input for providing an audibly perceptive output;

a signal treatment network responsive to validate said scan pulsed output and said background pulsed output to provide respective scan count signal and background count signals;

a background switch actuable to provide a background activation signal;

a control circuit including temporary memory, responsive to said background activation signal and to said background count signals to derive a background count value, BCV, responsive to compile said scan count signals for a sequence of scan intervals to derive a scan interval count value with respect to each scan interval and locate said scan interval count values in said sequence in said temporary memory as memory segment counts, responsive for each said scan interval to access an initial select number of said memory segment counts in predetermined sequential memory segment count combinations, each said combination having a combined count period, T, responsive to said background value, BCV, to a first threshold factor, f1, and said combined count period, T, to compute a first count rate threshold value for each said count combination in correspondence with the expression;

$\frac{\left(\mathrm{BCV}*T\right)+\left(\mathrm{f1}<br><br>\sqrt{\mathrm{BCV}*T}\right)}{T},$

responsive to generate said audio input when a predetermined number of said sequential memory segment count combinations represent a count rate greater than the corresponding said first count rate threshold value, responsive for a next said scan interval when said audio output has been generated to access a next select number of said memory segment counts in predetermined sequential memory segment count combinations, each said combination having a combined count period, T, responsive to said background value, BCV, to a second threshold factor, f2, less than said first threshold factor, f1, and said combined count period to compute a second count rate threshold value for each said count combination in correspondence with the expression;

$\frac{\left(\mathrm{BCV}*T\right)+\left(\mathrm{f2}<br><br>\sqrt{\mathrm{BCV}*T}\right)}{T},$

responsive to generate said audio input when a predetermined number of said sequential memory segment count combinations represent a count rate greater than the corresponding said second count rate threshold value.

2. The system of claim 1 in which said control circuit is responsive to terminate said generated audio input when less than said predetermined number of said sequential memory segment count combinations represent a count rate greater than the corresponding said second count rate threshold value.

3. The system of claim 1 in which said temporary memory is a circular buffer memory having at least a six memory segment capacity;

and

said predetermined memory segment count combinations comprise;

(a) a first memory segment count corresponding with the most current one of said sequence of scan intervals, (b) said first memory segment count in combination with the next previous thereto second memory segment count, (c) said first memory segment count in combination with said second memory second count and the next previous thereto third memory segment count, (d) said first memory segment count in combination with said second memory segment count, said third memory segment count and the next previous thereto fourth memory segment count, (e) said first memory segment count in combination with said second memory segment count, said third memory segment count, said fourth memory segment count and the next previous thereto fifth memory segment count, and (f) said first memory segment count in combination with said second memory segment count, said third memory segment count, said fourth memory segment count, said fifth memory segment count and the next previous thereto sixth memory segment count.

4. The system of claim 1 in which each said scan interval has a duration of about 50 milliseconds.

5. The system of claim 1 in which said initial select number of said memory segment counts is six.

6. The system of claim 1 in which said next select number of said memory segment counts is six.

7. The system of claim 1 in which:

said temporary memory is a circular buffer memory having a predetermined count display number of memory segments each retaining a said scan interval count value;

including a visually perceptible readout responsive to a rate signal to display a count rate readout; and

said control circuit is responsive at the timeout of successive update intervals to access said predetermined count display number of memory segments and derive said rate signal in correspondence with the combination of each said scan interval count value then retained by said circular buffer memory.

8. The system of claim 7 in which:

said circular buffer memory is a first in-last out buffer memory wherein each said memory segment represents a scan interval of 50 milliseconds; and

said predetermined number of memory segments is 15.

9. The system of claim 8 wherein said update interval is 500 milliseconds.

10. The system of claim 1 in which said first threshold factor, f1, is three.

11. The system of claim 1 in which said second threshold factor, f2, is one.

12. The system of claim 1 in which said expression deriving said first count rate threshold value is modified by a ceiling function altering said value to a next higher integer value when said first count rate threshold value is a non-integer value.

13. The system of claim 1 in which said expression deriving said second count rate value is modified by a ceiling function altering said value to a next higher integer value when said second count rate threshold is a non-integer value.

14. A method for detecting and locating sources of radiation at a region of interest evidencing background radiation, comprising:

(a) providing a probe movable within said region of interest;

(b) positioning said probe at said region of interest for a background interval to derive a background pulsed output;

(c) scanning said probe within said region of interest to derive a scanned pulsed output;

(d) providing an audible indicator responsive to an audio input for providing an audibly perceptive output;

(e) providing a signal treatment network responsive to validate said scan pulsed output and said background pulsed output to provide respective scan count signals and background count signals;

(f) providing a control circuit including a circular memory having a predetermined number of memory bins from first to last;

(g) deriving a background count value (BCV), from said background pulsed output;

(h) compiling said scan output signals for a sequence of scan intervals to derive a scan interval count value with respect to each scan interval;

(i) locating each said scan interval count value as a memory segment count in said sequence in sequential said memory bins;

(j) for each compiled said scan interval, accessing a first predetermined number of combinations of said memory bins which include said first bin and the corresponding count period, T, represented by each of said combinations, and computing a first count rate threshold value for each said combination in correspondence with the expression;

$\frac{\left(\mathrm{BCV}*T\right)+\left(\mathrm{f1}<br><br>\sqrt{\mathrm{BCV}*T}\right)}{T},$

where f1 is a first threshold factor;

(k) deriving said audio input when a predetermined first number of said combinations represent a count rate greater than the said first count rate threshold value corresponding therewith;

(l) for the compiled next scan interval following said compiled scan interval of step (j), when said audio input has been derived in step (k), accessing a second predetermined number of combinations of said memory bins and the corresponding count period, T, represented by each of said combinations, and computing a second count rate threshold value for each said combination in correspondence with the expression;

$\frac{\left(\mathrm{BCV}*T\right)+\left(\mathrm{f2}<br><br>\sqrt{\mathrm{BCV}*T}\right)}{T},$

where f2 is a second threshold factor less than said first threshold factor; and

(m) deriving said audio input when a predetermined second number of said combination derived in step (l) represent a count rate greater than the said second count rate threshold value corresponding therewith.

15. The method of claim 14 including the step:

(n) terminating said derived audio input when less than said predetermined second number of said combinations derived in step (h) represent a count rate greater than said second count rate threshold value corresponding therewith.

16. The method of claim 14 in which:

said step (j) includes the step of modifying the said first count rate threshold value to a next higher integer value when said first count rate threshold value is a non-integer value.

17. The method of claim 14 in which:

said step (l) includes the step of modifying the said second count rate threshold value to a next higher integer value when said second count rate threshold value is a non-integer value.

18. The method of claim 14 in which said first threshold factor, f1, is three.

19. The method of claim 14 in which said second threshold factor, f2, is one.

20. A system for detecting and locating sources of radiation at a region of interest within an environment evidencing background radiation, comprising:

a probe movable within said region of interest to provide a scan pulsed output corresponding with radiation from said sources and positionable to evaluate said background radiation and derive a background pulsed output corresponding therewith;

an audible indicator responsive to an audio input for providing an audibly perceptive output;

a signal treatment network responsive to validate said scan pulsed output and said background pulsed output to provide respective scan count signal and background count signals;

a background switch actuable to provide a background activation signal;

a control circuit including temporary memory, responsive to said background activation signal and to said background count signals to derive a background value, responsive to compile said scan count signals for a sequence of scan intervals to derive a scan interval count value with respect to each of said scan intervals and locate said scan interval count value in said sequence in said temporary memory as memory segment counts, responsive for each said scan interval to access a select number of said memory segment counts in predetermined memory segment count combinations to derive a corresponding select number of scanned count rate values, responsive to said background value, to a first statistically significant threshold factor and each scan interval represented by said memory segment count combinations to derive a first count rate threshold value for each of said combinations responsive to generate said audio input when a predetermined number of corresponding said combinations represent a count rate greater than a corresponding said first count rate threshold value, then responsive for a next said scan interval when said audio output has been generated, to access a select number of said memory segment counts in predetermined memory segment count combinations to derive a corresponding select number of scanned count rate values, responsive to said background value, to a second statistically significant threshold factor less than said first threshold factor and each scan interval represented by said memory count combinations to derive a second count rate threshold value for each said combination, responsive to generate said audio output when a predetermined number of corresponding said combinations represent a count rate greater than said second count rate threshold value.

21. The system of claim 20 in which said temporary memory is a circular buffer memory having at least a six memory segment capacity;

and

said predetermined memory segment Count combinations comprise;

(a) a first memory segment count corresponding with the most current one of said sequence of scan intervals, (b) said first memory segment count in combination with the next previous thereto second memory segment count, (c) said first memory segment count in combination with said second memory second count and the next previous thereto third memory segment count, (d) said first memory segment count in combination with said second memory segment count, said third memory segment count and the next previous thereto fourth memory segment count, (e) said first memory segment count in combination with said second memory segment count, said third memory segment count, said fourth memory segment count and the next previous thereto fifth memory segment count, and (f) said first memory segment count in combination with said second memory segment count, said third memory segment count, said fourth memory segment count, said fifth memory segment count and the next previous thereto sixth memory segment count.

22. The system of claim 20 in which said control circuit select number of memory segment counts is six and said predetermined number of scanned count rate values is three.

23. The system of claim 20 in which said control circuit is responsive for said next scan interval to access said select number of said memory segment counts wherein said select number is six.

24. The system of claim 23 in which said control circuit is responsive to terminate said audio input when fewer than three of said scanned count rate values are greater than said second threshold count rate value.

25. The system of claim 24 in which said control circuit is responsive to generate said audio output when three of said corresponding select number of scanned count rate values represent count rates greater than said second threshold count rate value.

26. The system of claim 20 in which:

said temporary memory is a circular buffer memory having a predetermined count display number of memory segments each for retaining a said scan interval count value;

including a visually perceptible readout responsive to a rate signal to display a count rate readout; and

said control circuit is responsive at the timeout of successive update intervals to access said predetermined count display number of memory segments and derive said rate signal in correspondence with the combination of each said scan interval count value then retained by said circular buffer memory.

27. The system of claim 26 in which:

said circular buffer memory is a first in-last out buffer memory wherein each said memory segment represents a scan interval of 50 milliseconds; and

said predetermined count display number of memory segments is 15.

28. The system of claim 27 wherein said update interval is 500 milliseconds.

29. The system of claim 20 in which:

said first statistically significant threshold factor is three; and

said second statistically significant threshold factor is one.

30. The system of claim 20 in which said signal treatment network comprises:

an energy window network including a lower threshold operational amplifier having a lower threshold reference value and responsive to said scan and background pulse outputs to validate the minimum energy values thereof; and

a pulse width discriminator for validating only those scan and background pulse outputs having pulse widths below a pulse width value representing noise.

31. The system of claim 30 in which said pulse width discriminator is responsive to validate said pulse widths of said pulse outputs in correspondence with said lower threshold reference value.