Method and apparatus for dose computation of magnetic stimulation

• US 20030073899A1
• Filed: 10/15/2002
• Published: 04/17/2003
• Est. Priority Date: 10/17/2001
• Status: Active Grant

• Current Assignee: Nexstim OY
• Original Assignee: Nexstim OY
• Inventors: Karhu, Jari, Ruohonen, Jarmo
• Granted Patent: US 6,849,040 B2
• Time in Patent Office: Days
• US Class Current: 600/417
• CPC Class Codes: A61N 2/02 using magnetic fields produced by coils, including single turn loops or electromagnets A61N2/12 takes precedence

Abstract

The invention relates to a method for determining the effect of magnetic stimulation on human brain. According to the method, the stimulation dose is determined in different parts of the brain by summing cumulatively the electric field strength generated by the individual stimulus pulses. According to the invention, the position and alignment of a magnetic stimulation coil (1) is determined separately for each applied stimulus pulse in three dimensions relative to the head (5), the number, repetition rate and intensity generated by the magnetic stimulation coil (1) are measured separately for each pulse, the coordinate data of the brain are determined substantially unambiguously in the same coordinate system with the magnetic stimulation coil (1) on the basis of information obtained from other kind of measurement, such as a tomographic scan or, e.g., a statistic database collected from a large number of patients, and the cumulative dose of electromagnetic radiation imposed on said desired point in the brain is determined on the basis of the location data available from the brain and the measurement data computed for the cumulative effect of the electromagnetic field evoked by said magnetic stimulation coil (1).

Claims

1. A method for determining the effect of magnetic stimulation on human brain, the method comprising the step of

determining the stimulation dose in different parts of the brain by summing cumulatively the electric field strength generated by the individual stimulus pulses,

characterized in that

the position and alignment of a magnetic stimulation coil (1) is determined separately for each applied stimulus pulse in three dimensions relative to the head (5),

the number, repetition rate and intensity of the pulses generated by the magnetic stimulation coil (1) are measured separately for each pulse,

the coordinate data of the brain are determined substantially unambiguously in the same coordinate system with the magnetic stimulation coil (1) on the basis of information obtained from other kind of measurement, such as a tomographic scan or, e.g., a statistic database collected from a large number of patients, and

the cumulative dose of electromagnetic radiation imposed on said desired point in the brain is determined on the basis of the location data available from the brain and the measurement data computed for the cumulative effect of the electromagnetic field evoked by said magnetic stimulation coil (1).

2. The method of claim 1, characterized in that the computed dose is graphically visualized to the system operator.

3. The method of any one of claims 1-2, characterized in that the value of the computed dose is used in the assessment of the therapeutic effect of the treatment administered by means of the magnetic stimulation.

4. The method of any one of claims 1-3, characterized in that the effective dose is determined from the value of the computed dose by weighting the measurement value of the applied dose using weighting coefficients representing known physiological effects.

5. The method of any one of claims 1-4, characterized in that the cumulative dose or the effective dose is used in the monitoring of the patient safety of the method.

6. The method of any one of claims 1-5, characterized in that the cumulative dose or the effective dose is used in the comparison of physiological effects evoked by magnetic stimulation in different test persons or patient groups.

7. The method of any one of claims 1-5, characterized in that the brain anatomy is recorded by magnetic resonance imaging.

8. The method of any one of claims 1-6, characterized in that the dose is visualized on anatomic pictures.

9. The method of any one of claims 1-7, characterized in that the dose determined in a realtime fashion is used for realtime monitoring.

10. The method of any one of claims 1-8, characterized in that the dose is monitored in a realtime fashion and the stimulation being applied is terminated if a preset stimulus dose limit value is exceeded on any or a preset region of the brain.

11. The method of any one of foregoing claims, characterized in that

the location of said coil (1) is determined separately for each applied stimulus pulse, and

the results of the dose computation are displayed coded in colors and tones on the brain pictures obtained by magnetic imaging techniques.

13. The apparatus of claim 11, characterized in that said location device (2) operates using infrared light.

14. The apparatus of any one of claims 11-12, characterized in that said location device (2) is adapted to locate the position and alignment of both said coil (1) and the head (5).

15. The apparatus of any one of claims 11-13, characterized in that a maximum limit is defined for the value of the applied dose, whereby the apparatus will inform the system operator immediately when the limit value is exceeded.

16. The apparatus of any one of claims 11-14, characterized in that in lieu of the computer (3) therein is used any other kind of computing device.

17. The apparatus of any one of claims 11-15, characterized in that the apparatus includes means for weighting the doses of the stimulus pulse trains by their repetition rate in order to compute the effective dose thereby.

18. The apparatus of any one of foregoing claims, characterized in that the apparatus includes robotic means for controlling said coil (1) such that the cumulative dose or effective dose defined by the system operator will be automatically administered correctly on the predetermined brain region.

19. The apparatus of any one of foregoing claims, characterized in that the apparatus includes mechanical means for determining the position of both the head (5) and said coil (1).

12. An apparatus suited for stimulation of living tissue such as human brain, the apparatus comprising

a magnetic stimulator (8) with a coil (1), and

a computer (3) with a display device (4),

characterized in that the apparatus includes

a location device (2, 7) for locating the position and alignment of the coil (1) relative to the head (5), and

a measurement unit (2) capable of measuring the intensity of stimulation in relative units between the individual pulses and then issuing to the computer (3) information on the instant of stimulus pulse application, whereby the apparatus is capable of computing from the position and alignment of the coil (1) the magnitude of electromagnetic field or the electric current generated thereby in the different parts of the brain and subsequently performing dose computation after the administration of the stimulus pulses by way of summing the magnitudes of the electric field or current separately at desired points in the brain.