Method and apparatus for separating the different components of evoked response and spontaneous activity brain signals as well as of signals measured from the heart

• US 5,655,534 A
• Filed: 06/08/1995
• Issued: 08/12/1997
• Est. Priority Date: 11/30/1992
• Status: Expired due to Term

• Current Assignee: Nexstim OY
• Original Assignee: Risto Ilmoniemi
• Inventors: Ilmoniemi, Risto
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US08/446,657
• Time in Patent Office: 796 Days
• Field of Search: 128/653.1, 128/696, 128/731, 128/901, 364/413.05
• US Class Current: 600/408
• CPC Class Codes: A61B 5/245 specially adapted for magnetoencephalographic [MEG] signals

Abstract

The present invention is related to a method and an apparatus for separating the different components of evoked responses and spontaneous activity of the brain, as well as signals measured from the heart, from each other. The apparatus according to the invention presents the measured signals in graphic form and the user selects from the signals such a time instant, time interval or frequency band, which plausibly can be related to a given source component. The apparatus forms a signal vector from the temporal or frequency signals thus selected, projects the unprocessed signal onto the signal vector thus formed, and subtracts the projection from the unprocessed signals, whereby the projected vector and the set of signals remaining after the subtraction step provide the separation of the unprocessed signals into the selected component and such a part which is clean of contribution of the selected component.

Claims

1. A method for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the head, said measured signal being obtained from a plurality of measurement channels, said method comprising:

(a) selecting a time instant at which the measured signal is representative of activity of a given source component,

(b) forming a template vector from the measured signal at the selected time instant,

(c) projecting the input measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the input measured signal is separated from the measured signal, and

(d) subtracting at least part of said projection component from the measured signal.

2. A method according to claim 1, wherein step (a) further comprises selecting a time interval during which the measured signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of the measured signal at the selected time instant and changes in the measured signal over the selected time interval.

3. A method according to claim 1, wherein step (a) further comprises selecting a frequency at which the measured signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of the measured signal at the selected time instant and frequency components of the measured signal at the selected frequency.

4. A method according to claim 1, wherein step (a) further comprises selecting a frequency band over which the input measured signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of the measured signal at the selected time instant and frequency components of the measured signal over the selected frequency band.

5. A method according to claim 1, comprising displaying graphically the measured electrical signal and selecting the time instant on the basis of the graphic display.

6. A method according to claim 1, wherein step (a) comprises using an algorithm programmed into a computer to select said time instant.

7. A method according to claim 1, wherein step (d) comprises subtracting the entire projection component from the measured signal.

8. A method according to claim 1, wherein step (d) comprises subtracting the projection component multiplied by a factor smaller than one from the measured signal, said factor being a monotonically increasing function of signal-to-noise ratio prevalent during the determination of the selected template vector.

9. A method according to claim 8, wherein the factor is a function of time or frequency.

10. A method according to claim 1, further comprising:

(e) selecting a second time instant at which the measured signal is representative of activity of a given source component,

(f) forming a template vector from the measured signal at the time instant selected in step (e),

(g) projecting the measured signal onto a unit vector parallel to the template vector formed in step (f), whereby for each channel of the measured signal a time varying projection component of the measured signal is separated from the measured signal, and

(h) subtracting at least a part of the projection component formed in step (g) from the measured signal.

11. A method for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said method comprising:

(a) selecting a time interval during which the measured signal is representative of activity of a given source component,

(b) forming a template vector from changes in the measured signal over the selected time interval,

(c) projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

(d) subtracting said projection component from the measured signal.

12. A method according to claim 11, wherein step (a) further comprises selecting a frequency at which the signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of changes in the measured signal over the selected time interval and frequency components of the measured signal at the selected frequency.

13. A method according to claim 11, wherein step (a) further comprises selecting a frequency band for which the measured signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of changes in the measured signal over the selected time interval and frequency components of the measured signal over the selected frequency band.

14. A method according to claim 11, comprising displaying graphically the measured electrical signal and selecting the time interval on the basis of the graphic display.

15. A method according to claim 11, wherein step (a) comprises using an algorithm programmed into a computer to select said time interval.

16. A method according to claim 11, wherein step (d) comprises subtracting the entire projection component from the measured signal.

17. A method according to claim 11, wherein step (d) comprises subtracting the projection component multiplied by a factor smaller than one from the measured signal, said factor being a monotonically increasing function of signal-to-noise ratio prevalent during the determination of the selected template vector.

18. A method according to claim 17, wherein the factor is a function of time or frequency.

19. A method according to claim 11, further comprising:

(e) selecting a second time interval for which the measured signal is representative of activity of a given source component,

(f) forming a template vector from changes in the measured signal over the time interval selected in step (e),

(g) projecting the measured signal onto a unit vector parallel to the template vector formed in step (f), whereby for each channel of the measured signal a time varying projection component of the measured signal is separated from the measured signal, and

(h) subtracting at least a part of the projection component formed in step (g) from the measured signal.

20. A method for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said method comprising:

(a) selecting a frequency at which the measured signal is representative of activity of a given source component,

(b) forming a template vector from frequency components of the measured signal at the selected frequency,

(c) projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

(d) subtracting said projection component from the measured signal.

21. A method according to claim 20, wherein step (a) further comprises selecting a frequency band over which the measured signal is representative of activity of a given source component and step (b) comprises forming the template vector from a combination of frequency components of the measured signal at the selected frequency and frequency components of the measured signal over the selected frequency band.

22. A method according to claim 20, wherein step (d) comprises subtracting the entire projection component from the measured signal.

23. A method according to claim 20, wherein step (d) comprises subtracting the projection component multiplied by a factor smaller than one from the input multi-channel signal, said factor being a monotonically increasing function of signal-to-noise ratio prevalent during the determination of the selected template vector.

24. A method according to claim 20, wherein the factor is a function of time or frequency.

25. A method according to claim 20, further comprising:

(e) selecting a second frequency at which the input measured signal is representative of activity of a given source component,

(f) forming a template vector from frequency components of the measured signal at the frequency selected in step (e),

(g) projecting the measured signal onto a unit vector parallel to the template vector formed in step (f), whereby for each channel of the measured signal a time varying projection component of the input multi-channel signal is separated from the measured signal, and

(h) subtracting at least a part of the projection component formed in step (g) from the measured signal.

26. A method for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said method comprising:

(a) selecting a frequency band over which the measured signal is representative of activity of a given source component,

(b) forming a template vector from frequency components of the measured signal over the selected frequency band,

(c) projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

(d) subtracting said projection component from the measured signal.

27. A method according to claim 26, comprising displaying graphically the measured electrical signal and selecting the frequency band on the basis of the graphic display.

28. A method according to claim 26, wherein step (a) comprises using an algorithm programmed into a computer to select said frequency band.

29. A method according to claim 26, wherein step (d) comprises subtracting the entire projection component from the measured signal.

30. A method according to claim 26, wherein step (d) comprises subtracting the projection component multiplied by a factor smaller than one from the measured signal, said factor being a monotonically increasing function of signal-to-noise ratio prevalent during the determination of the selected template vector.

31. A method according to claim 30, wherein the factor is a function of time or frequency.

32. A method according to claim 26, further comprising:

(e) selecting a second frequency band over which the measured signal is representative of activity of a given source component,

(f) forming a template vector from frequency components of the measured signal over the frequency band selected in step (e),

(g) projecting the measured signal onto a unit vector parallel to the template vector formed in step (f), whereby for each channel of the measured signal a time varying projection component of the measured signal is separated from the measured signal, and

(h) subtracting at least a part of the projection component formed in step (g) from the measured signal.

33. Apparatus for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said apparatus comprising:

a means for selecting a time instant at which the measured signal is representative of activity of a given source component,

a means for forming a template vector from the measured signal at the selected time instant,

a means for projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

a means for subtracting at least part of said projection component from the measured signal.

34. Apparatus according to claim 33, comprising a display means for providing a graphic time-varying display of the projection component and of components of a remainder vector returned by subtraction of the projection component from the measured signal.

35. Apparatus for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said apparatus comprising:

a means for selecting a time interval during which the measured signal is representative of activity of a given source component,

a means for forming a template vector from changes in the measured signal over the selected time interval,

a means for projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

a means for subtracting said projection component from the measured signal.

36. Apparatus according to claim 35, comprising a display means for providing a graphic time-varying display of the projection component and of components of a remainder vector returned by subtraction of the projection component from the measured signal.

37. Apparatus for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said apparatus comprising:

source component being coupled into a signal component by a sensitivity function, said apparatus comprising;

a means for selecting a frequency at which the measured signal is representative of activity of a given source component,

a means for forming a template vector from frequency components of the measured signal at the selected frequency,

a means for projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the measured signal, and

a means for subtracting said projection component from the measured signal.

38. Apparatus according to claim 37, comprising a display means for providing a graphic time-varying display of the projection component and of components of a remainder vector returned by subtraction of the projection component from the measured signal.

39. Apparatus for separating the different components of a measured signal, said different components including evoked electric and magnetic responses, spontaneous activity of the brain and signals measured from the heart, said measured signal being obtained from a plurality of measurement channels, said apparatus comprising:

a means for selecting a frequency band over which the measured signal is representative of activity of a given source component,

a means for forming a template vector from frequency components of the measured signal over the selected frequency band,

a means for projecting the measured signal onto a unit vector parallel to the template vector, whereby for each channel of the measured signal a time-varying projection component of the measured signal is separated from the input multi-channel signal, and

a means for subtracting said projection component from the measured signal.

40. Apparatus according to claim 39, comprising a display means for providing a graphic time-varying display of the projection component and of components of a remainder vector returned by subtraction of the projection component from the measured signal.