Determining a position of objects in a predetermined coordinate system

• US 6,876,196 B1
• Filed: 09/22/2003
• Issued: 04/05/2005
• Est. Priority Date: 03/19/2001
• Status: Active Grant

• Current Assignee: Megin Oy
• Original Assignee: Elekta Neuromag Oy
• Inventors: Taulu, Samu, Parkkonen, Lauri, Kajola, Matti
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US10/665,543
• Time in Patent Office: 561 Days
• Field of Search: 702150-153, 324/207.12, 324/207.17, 324/207.22, 324/207.23, 324/232, 324/247, 324/207.26, 600/424, 600/409, 600/407, 600/595
• US Class Current: 324/247
• CPC Class Codes: A61B 5/1113 Local tracking of patients, e.g. in a hospital or private home
• CPC Class Codes: A61B 5/246 using evoked responses
• CPC Class Codes: G01B 7/004 for measuring coordinates of points
• CPC Class Codes: G01S 5/0247 Determining attitude

Abstract

The invention relates to a method and device by means of which the location and position of an object may be determined in relation to another object by electromagnetic signals. In the arrangement in accordance with the invention there are two objects to the one of which there are attached signal sources, i.e. transmitters that generate electromagnetic signals, and the other object contains one or more receivers for measuring the transmitter signals. Usually the object containing transmitters is the one whose location or position is of interest and which is the object of the measurement. For example, in MEG measurements the object associated with the transmitters is the head of a human being on whose surface the transmitters are placed. By means of the arrangement in accordance with the invention is possible to find out the location and position of the head, in which case the location of the signals generated by the brain may be found out and utilized when examining the brain activity. The transmitters are also used to measure the signals emanating from the brain.

Claims

1. A method for determining the location and/or orientation of an object in a predetermined coordinate system, in which method in the object there is arranged a set of signal sources in a known manner in relation to the co-ordinate system of the object, the method comprising:

transmitting a predetermined signal from the signal sources,

receiving the signal transmitted from the signal sources with a receiver which comprises signal receivers,

computing the location and/or orientation of the object based on received amplitudes of the signals,

determining the amplitudes of the received signals, said amplitudes being independent of each other, by computationally taking into account the correlation between the transmitted signals, said transmitted signals being transmitted simultaneously and having arbitrary waveforms,

determining each signal source separately from the independent amplitudes, and

computing the location and/or orientation of the object at the time interval being examined based on the independent amplitude distributions associated with the signal sources by adjusting numerical amplitudes of the signal sources to the received amplitudes measured using the receiver, said adjusting the numerical amplitudes performed by setting the geometrical free parameters of the signal sources and/or of the receiver to values by which the difference between the calculated and measured amplitude distributions is at its smallest.

2. The method according to claim 1, wherein

computing the location and/or orientation of the signal sources in the co-ordinate system of both the object and the receiver from values set to free parameters, and

computing the location and/or orientation of the object in relation to the receiver by using known locations of the signal sources.

3. The method according to claim 2, wherein in order to determine an individual signal source:

generating the product of a signal to be estimated for each signal specifically and of a signal received by the receiver,

integrating the products over a predetermined time T in order to obtain a preliminary result for the measured amplitudes sent by the signal sources, and

generating the product of the preliminary result and of the correction coefficient, in which the correction coefficient is a quantity describing the correlation between the signals sent from different signal sources, in order to obtain the amplitude of the received signal for each signal specifically.

4. The method according to claim 3, wherein the products are accentuated by a window function w.

5. The method according to claim 4, wherein using signal forms of known sources of interference as the estimated signal.

6. The method according to claim 2, wherein

generating the product of the signal to be estimated, of the correlation efficient and of the received signal, in which the correction coefficient is a quantity describing the correlation between the signals sent from different signal sources, and

integrating the products over a predetermined time T in order to obtain a measuring result for the measured amplitudes of the signals sent by the signal sources.

7. The method according to claim 2, wherein

generating the signal product of the signal to be estimated and a chosen coefficient,

generating the product of the received signal product and of the received signal,

generating the products of the obtained signal product and of the received signal,

integrating the products over a predetermined time T in order to obtain a preliminary result for the measured amplitudes of the signals sent by the signal sources, and

generating the product of the preliminary result and of a correction coefficient, in which the correction coefficient is a quantity describing the correlation between the signals sent from different signal sources and the effect of the chosen coefficient, in order to obtain the amplitude of the received signal for each signal specifically.

8. The method according to claim 1, further comprising

sending a signal in a sine form from the signal sources, and

using in the computation as the estimated signal a signal of almost the same form as the sent signal.

9. The method according to claim 8, wherein using in the computation a second signal being at the same frequency with the sent signal that has a difference in phase in relation to the estimated signal.

10. The method according to claim 1, further comprising

receiving useful signal by means of the receiver, and

filtering the sent signals from the useful signal by the signal source.

11. The method according to claim 1, further comprising

estimating signals that correspond to the signals of the signal sources attached to a moving object in a predetermined manner for estimating the motion of the object.

12. The method according to claim 1, wherein the determination of the location and/or orientation of the object is repeated in order to determine the relative location of the object by repeating temporally overlapping measuring periods.

13. The method according to claim 1, further comprising

generating a feedback from the obtained amplitudes to the signal sources, and

controlling the transmission power of the signal sources by means of the feedback.

14. The method according to claim 1, further comprising

subtracting the signals computed at the received signals, and

specifying a measuring result by means of a remaining signal.

15. The method according to claim 1, further comprising

estimating at least one signal that differ from the signals of the signal sources or from those of the known sources of interference, and

specifying the location result based on the obtained measuring result.