US-12616402-B2 - Unshielded pulsed pump magnetometers for biomagnetic measurements

Abstract

The pulsed pump magnetometer (PPM) is a new type of magnetometer with much higher dynamic range, linearity, and sensitivity than all other types of magnetometers. These features allow more faithful subtracting and cancelling sources of magnetic noise, enabling high quality biomagnetic measurements. Using an array of PPM sensors enables high quality measurements of biomagnetic signals even in magnetically noisy, real-world conditions like medical offices. Arrays of PPM sensors improve upon pulsed magnetic gradiometers in providing higher sensitivity per sensor and superior noise rejection through noise decorrelation and covariance modeling. Arrays of PPM sensors enable localization and imaging of biomagnetic sources.

Inventors

• Elizabeth L. Foley
• Thomas W. Kornack
• Lucia A. Rathbun
• David H Newby
• Nancy G. Ford

Assignees

• TWINLEAF LLC

Dates

Publication Date

20260505

Application Date

20240410

Claims (20)

1. 1 . A system for measuring biomagnetic signals of a biological subject in an unshielded measurement environment, comprising: a pulsed pump magnetometer (PPM) configured to be arranged at a desired location over the biological subject; at least one processor configured to: operate the PPM to detect a biomagnetic signal from the biological subject over a period of time; and process the detected biomagnetic signal to generate a result indicative of a characteristic or condition associated with the biological subject; wherein the PPM comprises: at least one atomic vapor cell; at least one pulsed pump laser and at least one probe laser which is pulsed or operated continuously; and a magnetic field coil configured to generate a pulsed magnetic field that has a component parallel to a pump axis of one of the at least one pulsed pump laser, the magnetic field coil being configured to be turned off faster than a Larmor precession period of a gas in one of the at least one atomic vapor cell.
2. 2 . The system of claim 1 , wherein one or more of the PPM are arranged as an array in a device configured to fit on or near a head of the subject, the array is configured to detect neuromagnetic signals from the subject over the period of time.
3. 3 . The system of claim 2 , wherein each of the one or more of the PPM measures a total magnetic field in a background magnetic field of greater magnitude than a brain-generated field, the PPM measurement being dominated by a projection of the brain-generated field onto the background magnetic field.
4. 4 . The system of claim 2 , wherein the head and/or a background magnetic field is configured to be reoriented relative to the array to measure different components of neuromagnetic fields generated by a brain.
5. 5 . The system of claim 2 , wherein the array is arranged as a set of paired PPMs, as two-point gradiometers, or as a set of multiple independent PPMs operated independently and the set of multiple independent PPMs being subject to post-processing as higher order multiple gradiometers.
6. 6 . The system of claim 1 , wherein one or more of the PPM are arranged as an array in a vest or apparatus configured to be worn or placed over a part of a torso of the subject, the array is configured to measure gastric magnetic fields at corresponding locations of an organ inside the torso of the subject over the period of time.
7. 7 . The system of claim 1 , wherein one or more of the PPM are arranged as an array in a vest or apparatus configured to be worn or placed over a part of a torso of the subject, the array is configured to measure neuromagnetic fields associated with sensory activities at corresponding locations of a cervical spinal cord and spinal nerve of the subject over the period of time.
8. 8 . The system of claim 1 , wherein one or more of the PPM are arranged as an array in a vest or apparatus configured to be worn or placed over a part of an arm, leg or muscle of interest of the subject, the array is configured to measure magnetic fields associated with sensory activities at corresponding locations of muscles of the subject over the period of time.
9. 9 . The system of claim 1 , further comprising: an injection device for administering magnetic nanoparticles into a region of interest of the subject; a magnetic field generator configured to apply a magnetic field to the region of interest to magnetize the magnetic nanoparticles; wherein one or more of the PPM are arranged as an array configured to detect magnetization decay signals of the magnetic nanoparticles at corresponding locations after the magnetic field is off.
10. 10 . The system of claim 1 , wherein the PPM comprises a controller configured to convert detected light signals from the PPM to total magnetic field measurements, and wherein the PPM is configured to operate in a range of background magnetic field strengths from less than 1 μT to more than 100 μT.
11. 11 . A method of measuring biomagnetic signals of a biological subject in an unshielded measurement environment using a pulsed pump magnetometer (PPM), comprising: arranging one or more of the PPM at a desired location over a biological subject; operating the one or more of the PPM to detect a biomagnetic signal from the biological subject over a period of time; processing the detected biomagnetic signal to generate a result indicative of a characteristic or condition associated with the biological subject; wherein each of the one or more of the PPM comprises: at least one atomic vapor cell; at least one pulsed pump laser and at least one probe laser which is pulsed or operated continuously; and a magnetic field coil configured to generate a pulsed magnetic field that has a component parallel to a pump axis of one of the at least one pulsed pump laser, the magnetic field coil being configured to be turned off faster than a Larmor precession period of a gas in one of the at least one atomic vapor cell.
12. 12 . The method of claim 11 , further comprising: arranging the one or more of the PPM as an array in a device configured to fit on or near a head of the subject, and configuring the array to detect neuromagnetic signals at corresponding locations of a brain of the subject over the period of time.
13. 13 . The method of claim 12 , wherein each of the one or more of the PPM measures a total magnetic field in a background magnetic field of greater magnitude than a brain-generated field, the PPM measurement being dominated by a projection of the brain-generated field onto the background magnetic field.
14. 14 . The method of claim 12 , further comprising reorienting the head and/or a background magnetic field relative to the array to measure different components of neuromagnetic fields generated by the brain.
15. 15 . The method of claim 12 , further comprising arranging the array as a set of paired PPMs as two-point gradiometers, or as a set of multiple independent PPMs operated independently and the set of multiple independent PPMs being subject to post-processing as higher order multiple gradiometers.
16. 16 . The method of claim 12 , wherein the magnetic field coil is configured to aid pumping in the one or more of the PPM to maximize the biomagnetic signal.
17. 17 . The method of claim 11 , further comprising: arranging the one or more of the PPM as an array in a vest or apparatus configured to be worn or placed over a torso of the subject, and configuring the array to measure gastric magnetic fields at corresponding locations of an organ inside the torso of the subject over the period of time.
18. 18 . The method of claim 11 , further comprising: arranging the one or more of the PPM as an array in a vest or apparatus configured to be worn or placed over a torso of the subject, and configuring the array to measure neuromagnetic magnetic fields associated with sensory activities at corresponding locations of a cervical spinal cord and spinal nerve of the subject over the period of time.
19. 19 . The method of claim 11 , further comprising: arranging the one or more of the PPM as an array in a vest or apparatus configured to be worn or placed over a part of an arm, leg or muscle of interest of the subject, and configuring the array to measure magnetic fields associated with sensory activities at corresponding locations of muscles of the subject over the period of time.
20. 20 . The method of claim 11 , further comprising: injecting magnetic nanoparticles into a region of interest of the subject; applying a magnetic field to the region of interest to magnetize the magnetic nanoparticles; arranging the one or more of the PPM as an array configured to detect magnetization decay signals of the magnetic nanoparticles at corresponding locations after the magnetic field is off.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation of U.S. Non-provisional patent application Ser. No. 18/389,433 filed on Nov. 14, 2023, which claims the benefit of U.S. Provisional Patent Application No. 63/425,453 filed on Nov. 15, 2022, and U.S. Provisional Patent Application No. 63/425,446 filed on Nov. 15, 2022. The contents of U.S. Non-provisional patent application Ser. No. 18/389,433, U.S. Provisional Patent Application No. 63/425,453 and U.S. Provisional Patent Application No. 63/425,446 are hereby incorporated by reference. TECHNICAL FIELD The present disclosure generally relates to magnetic field and magnetic field gradient measurements, and more particularly to magnetic field measurements of biological sources. BACKGROUND Biomagnetic measurements are magnetic measurements of biological activity, including but not limited to the heart (magnetocardiography), brain (magnetoencephalography), nerves and muscles (magnetomyography), and digestion (magnetogastrography). Various types of magnetometer have been used to perform biomagnetic measurements, such as superconducting quantum interference device (SQUID) sensors, and zero field/SERF optically pumped magnetometers (OPM). High quality measurements are obtained only with extensive magnetic shielding and/or magnetic environment conditioning. Measurements are significantly degraded by magnetic noise when magnetometers are operated without shielding. Typical magnetic noise is a combination of geomagnetic sources such as the dynamics of the ionosphere and the solar wind and human sources such a power lines, electronics, and movement of magnetic objects. Pulsed pump gradiometers have been demonstrated to reject magnetic noise by subtracting the magnetic field measurement at two points. SUMMARY The pulsed pump magnetometer (PPM) is a new type of magnetometer with much higher dynamic range, linearity, and sensitivity than all other types of magnetometers. These features allow it to more faithfully subtract and cancel sources of magnetic noise, enabling high quality biomagnetic measurements. Using an array of PPM sensors enables high quality measurements of biomagnetic signals even in magnetically noisy, real-world conditions like medical offices. Arrays of PPM sensors improve upon pulsed magnetic gradiometers in providing higher sensitivity per sensor and superior noise rejection through noise decorrelation and covariance modeling. Arrays of PPM sensors enable localization and imaging of biomagnetic sources. An embodiment of the present disclosure provides a system for measuring biomagnetic signals a biological subject in an unshielded environment, including: a pulsed pump magnetometer (PPM) arranged at a desired location over the biological subject; a controller configured to operate the PPM to detect a biomagnetic signal from the biological subject over a period of time; and a processor configured to process the detected biomagnetic signal to generate a result indicative a characteristic or condition associated with of the biological subject; wherein the PPM measures the projection of the biomagnetic signal on the background magnetic field in the unshielded measurement environment; wherein the PPM includes at least one atomic vapor cell with at least one pulsed pump laser and at least one probe laser which is pulsed or operated continuously and a control unit configured to convert the detected light signals from the probe to total magnetic field measurements and the PPM is configured to operate in the range of background magnetic fields from less than 1 μT to more than 100 μT. An embodiment of the present disclosure provides a method of measuring biomagnetic signals in an unshielded environment using a pulsed pump magnetometer (PPM), including: arranging one or more PPM at a desired location over a biological subject; operating the one or more PPM to detect a biomagnetic signal from the biological subject over a period of time; processing the detected biomagnetic signal to generate a result indicative a characteristic or condition associated with of the biological subject; wherein the PPM measures the projection of the biomagnetic signal on the background magnetic field in the unshielded measurement environment; wherein each PPM includes at least one atomic vapor cell with at least one pulsed pump laser and at least one probe laser which is pulsed or operated continuously and a control unit configured to convert the detected light signals from the probe to total magnetic field measurements and the PPM is configured to operate in the range of background magnetic fields from less than 1 μT to more than 100 μT. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the measurement of biomagnetic signals using sensors in an unshielded environment according to one embodiment. FIG. 2 shows an unshielded array of sensors for magnetocardiography (MCG) arranged over the heart according to one embodiment. FIG. 3 shows an unshielded array of se