Patent Application
20210290143
The present application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2020-051880, filed on Mar. 23, 2020, Japanese Patent Application No. 2020-051881, filed on Mar. 23, 2020, and Japanese Patent Application No. 2020-189868, filed on Nov. 13, 2020, the contents of which are incorporated herein by reference in their entirety.
The present invention relates to a bioelectric current estimation method, a bioelectric current estimation apparatus, a biomagnetic measurement apparatus, and a biomagnetic measurement system.
As a method of examining the functions of the spinal cord, peripheral nerves, and muscles, there is known a method of measuring the magnetic field generated from a living body based on activities of these portions. For example, in a biomagnetic measurement apparatus that measures the magnetic field generated from the neck or the back of a subject under examination, the leading ends of the respective sensors in a sensor array are disposed along the curved shape of the measurement portion. Then, an X-ray image is captured from the side of the subject to acquire the positional relationship between the sensor array and the nerve (see Patent Document 1).
In another biomagnetic measurement apparatus, an ultrasound probe of an ultrasonic diagnostic apparatus is disposed in a shield room in which the biomagnetic measurement apparatus is disposed. Then, a sensor array, which is for measuring the magnetic field generated from the heart of the subject by using an ultrasonic tomography image of the heart, is disposed at an appropriate measurement position of the subject to measure the biomagnetic field (see Patent Document 2).
In yet another biomagnetic measurement apparatus, by making it possible to change the relative position between the detection target portion of a subject supported on a supporting part and a biomagnetic measuring unit, it is possible to dispose a radiation detecting unit between the supporting part and the biomagnetic measuring unit. Accordingly, it is possible to acquire the position information of the detection target portion by the radiation detecting unit while the subject is in the same posture as the posture at the time when the biomagnetic field is measured (see Patent Document 3).
In another example, by placing the lower leg in a synthetic plastic boot-shaped water bath containing hot water, and applying an ultrasound probe to the outer wall of the water bath, it is possible to acquire the cross-sectional image of the lower leg while preventing a change in the shape of the lower leg that would be caused by the pressing force of the ultrasound probe. For example, the ultrasound probe is applied to the outer wall of the water tank corresponding to a position directly marked on the body surface of the subject (see Non-patent Document 1).
Patent Document 1: Japanese Patent No. 4834076
Patent Document 2: Japanese Patent No. 3094988
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2019-98156
Non-patent Document 1: Seiichi Hisamoto, Masatoshi Higuchi, “Study of an ultrasonic echo method for observing extremity cross sections using a water bath”, Journal of the Society of Biomechanisms, vol. 34, no. 1(2010)
According to one aspect of the present invention, there is provided a bioelectric current estimation method including acquiring position information of a nerve in a measurement target region of a subject for which magnetic data is measured with a magnetic sensor, the position information of the nerve being acquired based on a nerve image included in a morphological image of the measurement target region; acquiring a positional relationship between a position of the nerve and a position of the magnetic sensor, based on the acquired position information of the nerve and position information of the magnetic sensor when the magnetic sensor is positioned to face the measurement target region; and estimating a neural activity current, which is generated in association with neural activity of the subject, based on the acquired positional relationship and the magnetic data of the measurement target region measured by the magnetic sensor.
In a biomagnetic measurement system such as a magnetospinography system of the conventional technology, for example, the nerve function is evaluated by estimating the electrical current distribution in the body by using an estimation technique such as spatial filtering from magnetic field data obtained by the sensor array. The magnetic field data signal changes rapidly depending on the distance between the magnetic field source and the sensor, and, therefore, it is necessary to acquire the position information of the nerve beforehand and apply the acquired position information to the estimation technique such as the spatial filtering method.
For example, when attempting to estimate the neural activity current of the spinal cord, the spinal cord is located in the spinal canal within the spine, so it is possible to acquire the positional relationship between the spinal cord and the sensor array, from the spinal canal appearing in the X-ray image. However, when attempting to estimate the activity of a nerve, such as a peripheral nerve, for which the positional relationship between the bone and the nerve is not uniquely determined, it is difficult to acquire the positional relationship between the nerve and the sensor array from an X-ray image, and it is difficult to accurately estimate the neural activity current.
A problem to be addressed by an embodiment of the present invention is to acquire the positional relationship between a sensor for measuring a biomagnetic field and a nerve by using a nerve image included in an image of the measurement target region, and to estimate the neural activity current generated in association with the neural activity of a subject under examination.
Further, an ultrasound measurement apparatus of the conventional technology can acquire ultrasound images including images of nerves. However, there is no established technique for accurately detecting the position of a subject on which an ultrasound probe is being applied. Thus, in the conventional technology, for example, the position at which the ultrasound probe is to be applied on the body surface of the subject, has been directly marked. Furthermore, when pressing the ultrasound probe against the body surface of the subject, the position of the nerve in the ultrasound image may be displaced relative to the position of the nerve at the time of acquiring the biomagnetic field.
Another problem to be addressed by an embodiment of the present invention is to estimate the current distribution from the biomagnetic field data by using an ultrasound image to enable the identification of the positional relationship between the position of the nerve and the position of the magnetic sensor at the time of magnetic field measurement.
Hereinafter, embodiments will be described with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals and overlapping descriptions may be omitted.
For example, the magnetic field measuring unit 10 is included in a biomagnetic measurement apparatus installed in a magnetic shield room (not illustrated), and the bioelectric current estimation apparatus 30 is included in a computer such as a Personal Computer (PC) or a server installed outside the magnetic shield room. The bioelectric current estimation apparatus 30 may be implemented by a bioelectric current estimation program executed by a central processing unit (CPU) installed in a computer.
The magnetic field measuring unit 10 includes a magnetic sensor 12 and a cover member 16 covering the leading end of the magnetic sensor 12.
The magnetic sensor 12 includes a plurality of sensor units 14 arranged in an array to measure the magnetic field of a subject P under examination. The cover member 16 is disposed at a position to cover the leading ends of the sensor units 14 and has a curved cross-sectional shape. Here, the plane of the diagram corresponds to the cross-sectional plane, and the depth direction of the diagram corresponds to a vertical direction. A plurality of the sensor units 14 are disposed so that the leading end positions facing the subject P are disposed along the curved shape of the cover member 16.
For example, the sensor unit 14 includes a superconducting quantum interference device (SQUID). That is, the magnetic sensor 12 is a SQUID sensor array. Hereinafter, a plurality of the sensor units 14 are also referred to as the sensor array 14. The magnetic field measuring unit 10 measures a magnetic field induced in a nerve of the measurement target of the subject P measured by electrical stimulation by a nerve stimulating apparatus (not illustrated). The magnetic field measuring unit 10 outputs the measured magnetic field to the bioelectric current estimation apparatus 30 as magnetic field data.
For example, the ultrasonic measuring unit 20 is an ultrasonic examination apparatus including an ultrasound probe 22 and may be located either inside or outside the magnetic shield room. An ultrasound image examination apparatus uses an image examination technique in which ultrasound is applied to a subject and the echoes from the subject are visualized, and, therefore, a nerve image indicating a nerve that cannot be obtained by X-ray photography can be directly visually confirmed. The ultrasonic measuring unit 20 outputs a morphological image of the subcutaneous tissue obtained by measuring the measurement target region (region to be measured), to the bioelectric current estimation apparatus 30. For example, when the ultrasound image of the subcutaneous tissue of the forearm is measured by the ultrasonic measuring unit 20, the morphological information output to the bioelectric current estimation apparatus 30 includes a nerve image of the forearm.
Here, the measurement target region is the region of the subject P that faces the sensor array 14, and is a region A for acquiring the magnetic field data represented by the XY coordinates on the left side of
The ultrasonic measuring unit 20 outputs ultrasonic waves from the ultrasound probe 22 toward the measurement target region of the subject P and receives echoes from the subject P, thereby acquiring an image (morphological information) of the subcutaneous tissue (muscle, nerve, bone, etc.) of the measurement target region of the subject P.
When the ultrasonic measuring unit 20 is installed in the magnetic shield room, and the magnetic field data of the subject P in the magnetic shield room is measured by the magnetic field measuring unit 10, an ultrasound image of the measurement target region of the subject P is captured by the ultrasonic measuring unit 20. On the other hand, when the ultrasonic measuring unit 20 is installed outside the magnetic shield room, for example, the ultrasound image of the measurement target region of the subject P is captured by the ultrasonic measuring unit 20 at a timing different from the timing of measuring the magnetic field data of the subject P by the magnetic field measuring unit 10.
In the present embodiment, the nerve for which the magnetic field is to be measured, is a peripheral nerve. For example, when the neural activity current generated in association with the neural activity is acquired by measuring the magnetic field data of the peripheral nerve of the forearm of the subject P, the magnetic field data is measured by the magnetic field measuring unit 10 while the cubital fossa portion of the forearm is in contact with the cover member 16. The ultrasound probe 22 is applied to (positioned to face) the cubital fossa of the forearm to acquire an ultrasound image of the subcutaneous tissue of the cubital fossa.
The biomagnetic measurement system 100 may include a magnetic resonance tomography apparatus instead of the ultrasonic measuring unit 20. In this case, the position information acquiring unit 32 receives a Magnetic Resonance (MR) image from the magnetic resonance tomography apparatus as a morphological image of a measurement target region including a nerve image, instead of an ultrasound image, and acquires the position information of the nerve.
In the bioelectric current estimation apparatus 30, the position information acquiring unit 32 receives the morphological image of the measurement target region including the nerve image from the ultrasonic measuring unit 20 and the probe position information representing the XY position of the ultrasound probe 22 when each morphological image is acquired. The probe position information includes time information. The position information acquiring unit 32 acquires the position information of the nerve (for example, the XY position and the Z position at a plurality of points on the travel path of the nerve) based on the morphological image and the probe position information. The position information acquiring unit 32 may receive a morphological image in which the probe position information is added to the morphological image acquired by the ultrasonic measuring unit 20, instead of receiving the probe position information.
The positional relationship acquiring unit 34 acquires the positional relationship between the position of the nerve and the position of each of the sensor units 14 based on the position information of the nerve acquired by the position information acquiring unit 32 and the position information of each of the sensor units 14 of the magnetic sensor 12. For example, the positional relationship acquiring unit 34 acquires the positional relationship between a plurality of points on the nerve and each of the sensor units 14 based on the position (XY position and Z position) of the plurality of points on the nerve on three-dimensional coordinates and the position (XY position and Z position) of each of the sensor units 14 on three-dimensional coordinates.
The position information of each of the sensor units 14 of the magnetic sensor 12 is acquired in advance by using design data, etc., of the magnetic field measuring unit 10. The Z position of the nerve and the Z position of each of the sensor units 14 indicate the Z coordinate value assuming that the Z position of a reference point, which is the most protruding point on the surface of the cover member 16, is set to “0”, and indicate the distance with a sign from the reference point.
The current estimating unit 36 performs arithmetic processing (computational processing) to identify the estimated current of the neural activity at a specified measurement point in the measurement target region by using an estimation algorithm such as a spatial filtering method based on the positional relationship between a plurality of points of the nerve and each of the sensor units 14 acquired by the positional relationship acquiring unit 34. The current estimating unit 36 outputs current information representing the estimated neural activity current.
The specified measurement point in the measurement target region may be a point on the nerve or a plurality of points included in a predetermined range within the measurement target region. The estimated neural activity current is displayed on a display screen of a data processing apparatus including the bioelectric current estimation apparatus 30, as a current waveform indicative of the variation over time (timewise variation), for example, as illustrated in
First, in step S10, when the ultrasound probe 22 is applied to (positioned to face) the skin of the measurement target region of the subject P and is moved along the travel direction of the nerve, the ultrasonic measuring unit 20 generates an ultrasound image (morphological image) of the measurement target region including the nerve.
At this time, probe position information indicating the trajectory where the ultrasound probe 22 has moved is recorded together with the ultrasound image. The probe position information may be extracted, for example, from an image captured by a camera from above the ultrasound probe 22 in a region that includes the measurement target region, and may be synchronized with the ultrasound image based on the time information.
Next, in step S12, the position information acquiring unit 32 acquires a Z position and an XY position at each of a plurality of points of the nerve based on the ultrasound image. The method of acquiring the Z position of the nerve will be described with reference to
Next, in step S14, the magnetic field measuring unit 10 measures the neuromagnetic field of the measurement target region of the subject P. Next, in step S16, the positional relationship acquiring unit 34 acquires continuous position information (distance information), for example, by n-order function approximation, based on the position information of the nerve and the sensor array 14 acquired discretely in the measurement target region. For example, the positional relationship acquiring unit 34 acquires the positional relationship between a plurality of positions of the nerve and the positions of each of the sensor units 14 based on the position Z and the XY position of the nerve acquired by the position information acquiring unit 32 and the position information of each of the sensor units 14 of the magnetic sensor 12 acquired in advance.
Next, in step S18, the current estimating unit 36 estimates the neural activity current at a specified measurement point using, for example, a spatial filtering method based on the positional relationship between a plurality of positions of the nerve and the positions of each of the sensor units 14 acquired by the positional relationship acquiring unit 34. The estimated neural activity current is displayed, for example, as a current waveform or current intensity map, on a display screen of a data processing apparatus including the bioelectric current estimation apparatus 30.
The ultrasound image illustrated in
In each ultrasound image, the distance (depth) from the skin surface to the nerve can be measured by using a distance measurement function by specifying two positions in the ultrasound image.
With respect to the position of the nerve in the ultrasound image, the positional relationship with the blood vessel and the positional relationship with the skin are clear for each measurement target region (e.g., forearm). Furthermore, the cross-sectional shape of the nerve in the ultrasound image is unique for each measurement target region. Therefore, the distance (depth) from the skin surface to the nerve may be obtained by image analysis of the ultrasound image to determine the position of the skin surface and the position of the nerve. In this case, a mechanical learning method, such as deep learning, may be used.
It is also clear where the ultrasound probe 22 is applied to in the measurement target region while the ultrasound probe 22 is acquiring the ultrasound image. As described with reference to
Note that
The small circles dispersed in a staggered manner indicate the XY positions of the sensor units 14 of the magnetic field measuring unit 10. A plurality of double circles indicate the XY positions of the nerve and are acquired by the position information acquiring unit 32. The positions of the double circles are also the positions where the ultrasound images have been acquired by the ultrasound probe 22.
In the measurement target region A, a plurality of markers MC are disposed on the outside of the left and right of the region where the sensor units 14 are disposed. The marker MC is a coil photographed together with the subject P to associate the morphological image, such as an X-ray image, with the measurement position of the magnetic field data measured by the magnetic sensor 12, and a predetermined current is applied to the coil.
The positional relationship between the marker MC and each of the sensor units 14 is acquired in advance. Therefore, by identifying the positions of the markers MC by the magnetic sensor 12, it is possible to detect that each of the sensor units 14 is positioned at a small circle in the drawing. The dashed-dotted line extending laterally from the left image to the right graph in
The graph on the right side of
When the biomagnetic field is measured by the magnetic field measuring unit 10, the anterior side (the palm side) of the elbow portion of the subject P is brought in contact with the cover member 16. Thus, in the right graph, the distance between the Z position of a curve obtained by connecting the circles and the Z position of the nerve indicates the distance from the surface of the skin to the nerve. A value obtained by adding the distance from the surface of the skin to the nerve and the distance from the surface of the cover member 16 to the leading end of the sensor unit 14, represents the distance from the leading end of the sensor unit 14 to the nerve.
The surface of the cover member 16 and the plane connecting the leading ends of the sensor units 14 have a curved cross-section, and, therefore, the Z position of the nerve is corrected according to the difference between the Z position of the nerve and the Z position of the leading end of the sensor unit 14, rather than using the “0” position of the Z coordinate as a reference. In this case, correction of the Z position of the nerve may be performed in consideration of the gap between the surface of the cover member 16 and the leading end of the sensor unit 14 and the thickness of the cover member 16.
The current estimating unit 36 estimates the neural activity current at a specified measurement point (in the example of
XY position of each of the sensor units 14 illustrated on the left side of
The current waveform of the solid line on the right side of
The timewise variation of the current intensity illustrated in
Further, in terms of neurophysiology, the peak intensity of the current waveform is almost constant or decreases as the position is closer to the proximal side that is far from the position where the electrical stimulation is applied. However, the peak intensity of the current waveform of the dashed line becomes smaller as the position is closer to the distal side, and, therefore, the current intensity is not estimated correctly. This is because, when estimating the current intensity assuming that the Z position of the nerve is constant, an error occurs with respect to the depth of the actual nerve, and this error appears as an error when executing an arithmetic process to estimate the current intensity from the magnetic field data.
On the other hand, the peak intensity of the current waveform of the solid line estimated based on the Z position of the actual nerve does not appreciably change, and it can be determined that the current intensity is correctly estimated by an arithmetic process using an estimation algorithm such as the spatial filtering method.
Note that also when a plurality of points for estimating the current intensity are provided in the measurement target region A, and the direction of the current or the intensity distribution of the current flowing in the nerve and around the nerve is estimated, the current intensity can be correctly estimated, similar to the case described with reference to
The CPU 301 controls the overall operation of the bioelectric current estimation apparatus 30. The CPU 301 implements the function of the position information acquiring unit 32, the positional relationship acquiring unit 34, and the current estimating unit 36 by executing a bioelectric current estimation program stored in the ROM 303 or the auxiliary storage device 304. The CPU 301 may control the operation of the biomagnetic measurement system 100, such as the magnetic field measuring unit 10 and the ultrasonic measuring unit 20.
The RAM 302 is used as a work area of the CPU 301 and stores a bioelectric current estimation program and various parameters such as the Z position and the XY position. The ROM 303 stores a bioelectric current estimation program.
The auxiliary storage device 304 is a storage device such as a Solid State Drive (SSD) or a Hard Disk Drive (HDD). For example, the auxiliary storage device 304 stores a control program, such as an operating system (OS) for controlling the operation of the bioelectric current estimation apparatus 30, an ultrasound image, morphological image data, various parameters, and the like.
The input output interface 305 is coupled to a mouse, keyboard, or the like. The input output interface 305 may include a communication interface for communicating with other devices. The display device 306 displays windows for displaying the current waveforms illustrated in
Thus, in the present embodiment, the position of the nerve relative to the sensor array 14 can be accurately acquired by using an image (an ultrasound image or a Magnetic Resonance (MR) image) that includes a nerve image in which the nerve is directly captured, as compared to indirectly acquiring the position of the nerve from an X-ray image. For example, by using the actual XY position and Z position of the nerve acquired by using an ultrasound image or an MR image, the positional relationship with the XY position and the Z position of each of the sensor units 14 can be accurately acquired. Because the position of the nerve can be accurately obtained, for example, by an arithmetic process using a spatial filtering method, the intensity of the current flowing through the nerve can be correctly estimated, and the accuracy of estimating the current intensity can be improved.
When acquiring the position Z of the nerve, by correcting the Z position of the nerve according to the shape of the surface of the cover member 16 and the plane obtained by connecting the leading ends of the sensor units 14, the positional relationship between the XY position and the Z position of the nerve and the XY position and the Z position of each of the sensor units 14 can be accurately acquired. Thus, the intensity of the current flowing through the nerve can be estimated even more correctly, and the accuracy in estimating the current intensity can be further improved.
The magnetic measurement apparatus 210 includes a sensor array 211 including a plurality of superconducting quantum interference devices (SQUID) and a signal processing apparatus 212. The magnetic measurement apparatus 210 is coupled to the data processing apparatus 50, and the operation thereof is controlled by the data processing apparatus 50. The data processing apparatus 50 includes a computer, such as a server or a Personal Computer (PC), which can execute various kinds of data processes by executing programs.
The sensor array 211 is housed within a protruding part 21 protruding from the Dewar 220. For example, the top surface of the protruding part 21 has a curved cross-sectional shape. The magnetic detecting units at the leading ends of the respective magnetic sensors (SQUID sensors) of the sensor array 211, are positioned facing and along the curved-shape inner surface of the protruding part 21. The protruding part 21 is an example of a sensor housing unit in which magnetic sensors of the sensor array 211 are housed.
A guide rail 70 disposed along the protruding direction of the protruding part 21 is fixed on the protruding part 21. The guide rail 70 is an example of a guide member. A movable plate 60 is slidably mounted to the guide rail 70 in the protruding direction of the protruding part 21 (the right lower direction in the figure, the orthogonal direction of the cross-section). For example, the movable plate 60 has a curved shape corresponding to the curved shape of the top surface of the protruding part 21 and is movable on the guide rail 70 to slide along the top surface of the protruding part 21. The movable plate 60 is an example of a plate member, and the upper surface of the protruding part 21 is an example of an opposing surface facing the magnetic sensor.
For example, the movable plate 60 is a resin plate, for example, made of polyethylene terephthalate, and uses a plate material that is transparent to visible light and passes a magnetic field. It is preferable that the movable plate 60 is colorless and transparent. Preferably, the material of the movable plate 60 is a non-magnetic material and has an acoustic impedance that is close to that of the human body. The movable plate 60 may be made of polycarbonate other than polyethylene terephthalate. The movable plate 60 is set to have a thickness (e.g., approximately 1 mm to 5 mm, preferably approximately 1 mm to 2 mm) so as not to deflect when the ultrasound probe is pressed against the movable plate 60. The movable plate 60 may be thicker at the peripheral portions (on the sides corresponding to the guide rail 70) that requires more strength compared to the central portion.
Mounting the guide rail 70 to the protruding part 21 facilitates the construction of a mechanism for moving the movable plate 60, as compared to a mechanism for moving the movable plate 60 together with a chair or bed. Therefore, the guide rail can be easily mounted to the magnetic measurement apparatus 210 which is already in operation, and the magnetic measurement apparatus 210 can be converted into an apparatus which can acquire ultrasound images with minimal cost.
The nerve stimulation apparatus 230 applies electrical stimulation to the subject via an electrode attached to the body surface of the subject to induce the neural activity of the subject. The nerve stimulation apparatus 230 is coupled to the data processing apparatus 50 and the operation thereof is controlled by the data processing apparatus 50. In
The ultrasonic measurement apparatus 40 acquires an ultrasound image of the measurement target region before the magnetic measurement apparatus 210 measures the biomagnetic field of the subject. As will be described with reference to
The Dewar 220, which includes the protruding part 21, and the ultrasonic measurement apparatus 40 are disposed within a magnetic shield room 200 that shields the magnetism. The magnetic shield room 200 has an interior space, for example, which is approximately 2.5 m wide and 2.5 m high, and approximately 3 m long, and has a door 2210 for conveying objects such as the Dewar 220 and for the entry of people.
Within the magnetic shield room 200, a chair 80 may be disposed near the protruding part 21 for seating the subject. In the present embodiment, the subject sitting on the chair 80 places his or her forearm on the upper surface of the movable plate 60 so that the anterior side (palm side) of the elbow portion contacts the movable plate 60 and the elbow portion faces the upper surface of the protruding part 21 via the movable plate 60. At this time, the movable plate 60 is drawn toward the Dewar 220.
The ceiling of the magnetic shield room 200 is provided with a camera 300 above the movable plate 60. The camera 300 may be a video camera capable of capturing videos or a digital still camera capable of capturing still images. When the ultrasound image of a subject is acquired by the ultrasonic measurement apparatus 40, the camera 300 captures the measurement target portion (forearm) of the subject placed on the movable plate 60 drawn out along the guide rail 70, and an ultrasound probe (not illustrated) visible through the movable plate 60.
The camera 300 is coupled to the data processing apparatus 50. An image acquired by the camera 300 can be transferred to the data processing apparatus 50 and can be displayed on the display device 50a. Further, if the camera 300 is a digital still camera, a release operation of the camera 300 may be performed by an operator operating the ultrasound probe. Accordingly, with the digital still camera, it is possible to acquire an image at any timing intended by the operator (i.e., the timing at which an appropriate ultrasound image is acquired).
While the movable plate 60 is retracted toward the Dewar 220, the subject sits in the chair (
Then, while the anterior side (the palm side) of the elbow portion is in contact with the movable plate 60, the movable plate 60 is moved while sliding on the guide rail 70 and is pulled away to the side opposite the Dewar 220. In this manner, the movable plate 60 can be separated from the top surface of the protruding part 21. The movable plate 60 is moved against a stopper 72 attached to the leading end of the guide rail 70. For example, the movable plate 60 is fixed to the stopper 72 by a locking mechanism, such as a latch (not illustrated), with the leading end of the movable plate 60 positioned against the stopper 72.
The movable plate 60 merely moves while the arm is placed thereon, and, therefore, the contact state of the anterior side (palm side) of the elbow portion with respect to the movable plate 60 when the movable plate 60 is fixed to the stopper 72, is the same as that when the movable plate 60 is retracted toward the Dewar 220. That is, the contact state of the anterior side (the palm side) of the elbow portion with the movable plate 60 is the same as the state when the biomagnetic field is measured by the magnetic measurement apparatus 210. With the movable plate 60 fixed to the stopper 72, the ultrasound probe of the ultrasonic measurement apparatus 40 is applied to the back side (lower side) of the movable plate 60, and an ultrasound image is acquired at a plurality of points of the measurement target portion of the subject via the movable plate 60.
At this time, a pressing force caused by the leading end of the ultrasound probe is applied to the back surface of the movable plate 60, but the movable plate 60 is not flexed because the movable plate 60 is stiff, so the contact state of the anterior side (palm side) of the elbow portion to the movable plate 60 is not changed. Therefore, an ultrasound image can be acquired by maintaining the shape of the measurement target portion of the subject to be the same as that when a biomagnetic field is measured by the magnetic measurement apparatus 210.
Here, the measurement target portion of the subject being the same shape, means that position of the nerve of the measurement target portion is the same at the time of acquiring the ultrasound image and at the time of measuring the biomagnetic field. The position of the nerve in the measurement target portion includes the position in the plane direction facing the movable plate 60 and the position in the depth direction from the movable plate 60. Hereinafter, the position in the plane facing the movable plate 60 is also referred to as the XY position, and the depth from the movable plate 60 (skin) is also referred to as the Z position.
Because the movable plate 60 is transparent, the operator of the ultrasound probe can recognize the position of the ultrasound probe without peering into the back side of the movable plate 60. Because the movable plate 60 is transparent, the position of the ultrasound probe can be captured by the camera 300 mounted on the ceiling of the magnetic shield room 200 while the movable plate 60 is drawn out, and the image captured by the camera 300 can be recognized.
The movable plate 60 and the stopper 72 are unlocked with respect to each other, after the ultrasound image has been acquired and position information indicating the position of the nerve in the measurement target region of the subject has been acquired. The acquisition of the position information of the nerve is described in
Then, while the anterior side (palm side) of the elbow portion is in contact with the movable plate 60, the movable plate 60 is retracted toward the Dewar 220 along the guide rail 70, to return to the state illustrated on the left side of
In this state, electrical stimulation is applied to the subject from the nerve stimulation apparatus 230 (
The data processing apparatus 50 estimates the neural activity current based on the position information of the nerve obtained from the ultrasound image and the image captured by the camera 300, the position information of the magnetic sensor, and the biomagnetic field data measured by the magnetic measurement apparatus 210. The data processing apparatus 50 displays a current waveform, etc., representing the estimated current, on the display device 50a. The process of estimating the neural activity current by the data processing apparatus 50 will be described with reference to
In
When the movable plate 60 is mounted to the Dewar 220 in a manner as to be movable in the vertical direction, ultrasonic imaging and measurement of the biomagnetic field may be performed while the subject is standing, without providing a chair in the magnetic shield room 200. A chair which moves vertically in conjunction with the vertical movement of the movable plate 60 may be disposed within the magnetic shield room 200. In this case, the movable plate 60 may be mounted together with the chair on a moving mechanism that moves vertically, and may be moved together with the chair. Then, ultrasonic imaging and measurement of the biomagnetic field are performed while the subject is seated in a the chair.
Further, in
As illustrated in
At the time of acquiring an ultrasound image, the camera 300 captures the movable plate 60 and the surrounding area thereof to acquire an image of a measurement target portion (e.g., the forearm) of the subject P, the movable plate 60, and the ultrasound probe visible through the movable plate 60. The camera 300 outputs the acquired image as probe position information indicating the position of the ultrasound probe to the data processing apparatus 50. The camera 300 may be installed on the floor of the magnetic shield room 200 as illustrated in
The nerve stimulation apparatus 230 receives application timing information indicative of the application timing of the electrical stimulation from the data processing apparatus 50 and generates the electrical stimulation. The magnetic measurement apparatus 210 measures the magnetic field induced in the nerve in the measurement target portion of the subject P in response to the electrical stimulation from the nerve stimulation apparatus 230. The magnetic measurement apparatus 210 outputs the measured magnetic field as magnetic field data to the data processing apparatus 50.
The data processing apparatus 50 includes a position information acquiring unit 52, a positional relationship acquiring unit 54, and a current estimating unit 56. For example, the position information acquiring unit 52, the positional relationship acquiring unit 54, and the current estimating unit 56 function as a biomagnetic current estimation apparatus for estimating the neural activity current based on magnetic field data, etc., measured by the magnetic measurement apparatus 210. The position information acquiring unit 52, the positional relationship acquiring unit 54, and the current estimating unit 56 may be implemented by a biomagnetic current estimation program executed by a Central Processing Unit (CPU) installed in the data processing apparatus 50.
The position information acquiring unit 52 receives a morphological image (ultrasound image) of a measurement target region including a nerve image received from the ultrasonic measurement apparatus 40 and probe position information including an image representing the XY position of the ultrasound probe 42 captured by the camera 300 when the morphological image is acquired. The probe position information includes time information. The position information acquiring unit 52 acquires the position information of the nerve (for example, the XY position and the Z position at a plurality of points on the travel path of the nerve) based on the morphological image and the probe position information.
Note that as illustrated in
The positional relationship acquiring unit 54 calculates the positional relationship information representing the positional relationship between the position of the nerve and the position of each magnetic sensor based on the position information of the nerve acquired by the position information acquiring unit 52 and the position information of each magnetic sensor of the sensor array 211. For example, the positional relationship acquiring unit 54 calculates the positional relationship information between a plurality of points on the nerve and each magnetic sensor based on the position (XY position and Z position) of a plurality of points on the nerve on the three-dimensional coordinates and the position (XY position and Z position) of each magnetic sensor on the three-dimensional coordinates.
The position information of each magnetic sensor is acquired in advance using design data or the like of the magnetic measurement apparatus 210. For example, the Z position of the nerve and the Z position of each of the sensor units 14 indicate a Z coordinate value assuming that the Z position of a reference point, which is the most protruding point among the leading ends of the magnetic sensors facing the inner surface of the curved shape of the protruding part 21, is set to “0”, and indicate the distance with a sign from the reference point.
The current estimating unit 56 estimates the neural activity current at a specified measurement point in the measurement target region using an estimation algorithm such as a spatial filtering method based on the positional relationship information between a plurality of points on the nerve and each magnetic sensor acquired by the positional relationship acquiring unit 54. The current estimating unit 56 outputs current information (current distribution) representing the estimated neural activity current.
The measurement point specified in the measurement target region may be a point of the nerve or a plurality of points included in a predetermined range within the measurement target region. The estimated neural activity current is displayed on the display device 50a of the data processing apparatus 50 as a current waveform indicative of timewise variation, for example, as illustrated in
Before starting the operation of
In this state, at step S10, the ultrasound probe 42 is applied to the inner surface of the movable plate 60 and an ultrasound image of the measurement target portion of the subject P is acquired through the movable plate 60. The camera 300 captures an image indicating the positional relationship between the ultrasound probe 42 and the movable plate 60 at the time when the ultrasound image is acquired.
The ultrasound image is acquired in step
S10 by controlling the ultrasonic measurement apparatus 40 by the data processing apparatus 50. The position information of the ultrasound probe 42 is acquired in step S10 by controlling the camera 300 by the data processing apparatus 50. The data processing apparatus 50 associates the position information of the ultrasound probe 42 with the ultrasound image, based on the time information output from the camera 300 together with the image and the time information included in the ultrasound image data.
If the marker coil 62 is mounted on the movable plate 60 and a magnetic sensor is mounted in the ultrasound probe 42, instead of the photographing by the camera 300, the magnetic sensor of the ultrasound probe 42 detects the magnetic field generated by the marker coil 62 mounted on the movable plate 60. The acquisition of position information of the ultrasound probe 42 in step S10 is performed based on the magnetic field detected by the magnetic sensor of the ultrasound probe 42. The data processing apparatus 50 associates the position information of the ultrasound probe 42 with respect to the movable plate 60 with the ultrasound image, based on the time information included in the ultrasound image data output from the ultrasonic measurement apparatus 40.
Next, in step S12, the position information acquiring unit 52 acquires the Z position and the XY position of a plurality of points of the nerve, respectively. The method of acquiring the Z position of the nerve will be described with reference to
The Z position and the XY position are the position information of a plurality of points specified at the time of acquisition of the ultrasound image.
After step S12, the movable plate 60 on which the measurement target portion is mounted is returned onto the protruding part 21. Step S12 may be performed after the movable plate 60 is returned onto the protruding part 21 or may be performed while the movable plate 60 is being returned onto the protruding part 21. Step S12 may be performed after step S14 and before performing step S16.
Next, in step S14, the magnetic measurement apparatus 210 measures the neuromagnetic field of the measurement target portion of the subject P. Next, in step S16, the positional relationship acquiring unit 54 acquires continuous position information (distance information), for example, by n-order function approximation, based on the position information of the nerve and the sensor array 211 acquired discretely in the measurement target region. For example, the positional relationship acquiring unit 54 receives the Z position and the XY position of the nerve acquired by the position information acquiring unit 52 and the position information of each magnetic sensor of the sensor array 211 previously acquired. Then, the positional relationship acquiring unit 54 acquires positional relationship information representing the positional relationship between a plurality of positions of the nerve and the position of each magnetic sensor of the sensor array 211 based on the received Z position and the XY position and the position information of each magnetic sensor.
Next, in step S18, the current estimating unit 56 estimates the neural activity current at the specified measurement point using, for example, a spatial filtering method based on the positional relationship information between a plurality of positions of the nerve and the positions of each magnetic sensor acquired by the positional relationship acquiring unit 54. The estimated neural activity current is displayed on the display device 50a of the data processing apparatus 50, for example, as a current waveform or a current intensity map.
The ultrasound image illustrated in each of
For example, in an ultrasound image, the distance (depth) from the surface of the skin to the nerve can be measured by a distance measuring function of the ultrasonic measurement apparatus 40 by specifying two positions in the ultrasound image. With respect to the position of the nerve in an ultrasound image, the positional relationship with a blood vessel and the positional relationship with the skin are clear for each measurement target region (e.g., forearm). Furthermore, the cross-sectional shape of the nerve in an ultrasound image is unique for each measurement target region.
However, when the ultrasound probe 42 is pressed against the skin to acquire an ultrasound image, the distance of the nerve from the skin surface varies depending on the extent of the pressing force or the like on the skin. Also, when the ultrasound probe 42 is pressed against the skin, the position of the nerve and the positional relationship the nerve and the blood vessel change. However, by applying the ultrasound probe 42 to the skin surface through the movable plate 60, the distance from the skin surface to the nerve, the position of the nerve, and the positional relationship between the nerve and the blood vessel can be made the same as when measuring the biomagnetic field. Therefore, for example, by performing image analysis of ultrasound images to obtain the position of the skin surface and the position of the nerve, the distance (depth) from the surface of the skin to the nerve can be obtained. In this case, a machine learning method, such as deep learning, may be used.
While the ultrasound image is being acquired by the ultrasound probe 42, the position where the ultrasound probe 42 is being applied in the measurement target region can be determined by analyzing an image acquired by the camera 300 with the data processing apparatus 50. That is, by the image acquired by the camera 300, probe position information (the XY position of the ultrasound probe 42) can be acquired.
Further, in the upper center of the ultrasound image, there is displayed a key mark indicating the center position of the ultrasound probe 42. Therefore, based on the probe position information and the ultrasound image, the data processing apparatus 50 can acquire the XY position of the nerve in the measurement target region.
The small circles dispersed in a staggered manner indicate the XY positions of each of the magnetic sensors of the sensor array 211. A plurality of double circles indicate the XY positions of the nerve and are acquired by the position information acquiring unit 52. The positions of the double circles are included in the positions where the ultrasound images have been acquired by the ultrasound probe 42.
In the measurement target region A, a plurality of markers MC are disposed on the outside of the left and right of the region where the sensor array 211 is disposed. The marker MC is a coil photographed together with the subject P to associate the morphological image, such as an X-ray image, with the measurement position of the magnetic field data measured by the sensor array 211, and a predetermined current is applied to the coil.
The positional relationship between the marker MC and the sensor array 211 is acquired in advance. Therefore, by identifying the positions of the markers MC by each of the magnetic sensors, it is possible to detect that each of the magnetic sensors is positioned at a small circle in the drawing. The dashed-dotted line extending laterally from the left image to the right graph in
The graph on the right side of
The Z position of the nerve obtained from the ultrasound image acquired through the movable plate 60 is the same as the Z position of the nerve when measuring the biomagnetic field. Therefore, by acquiring the ultrasound image through the movable plate 60, the relationship between the Z position of the nerve illustrated on the right side of
The movable plate 60 and the plane connecting the leading ends of the magnetic sensors have a curved cross-section, and, therefore, the Z position of the nerve is calculated by using the Z position of the leading end of the magnetic sensor as the reference, rather than using the “0” position of the Z coordinate as a reference. The current estimating unit 56 estimates the neural activity current at a specified measurement point (in the example of
The current waveform of the solid line on the right side of
The timewise variation of the current intensity illustrated in
Further, in terms of neurophysiology, the peak intensity of the current waveform is almost constant or decreases as the position is closer to the proximal side that is far from the position where the electrical stimulation is applied. However, the peak intensity of the current waveform of the dashed line becomes smaller as the position is closer to the distal side, and, therefore, the current intensity is not estimated correctly. This is because, when estimating the current intensity assuming that the Z position of the nerve is constant, an error occurs with respect to the depth of the actual nerve, and this error appears as an error when estimating the current intensity from the magnetic field data.
On the other hand, the peak intensity of the current waveform of the solid line estimated based on the Z position of the actual nerve does not appreciably change, and it can be determined that the current intensity is correctly estimated. As described with reference to
Therefore, the current estimating unit 56 can estimate the correct current intensity based on the correct Z position of the nerve and obtain the current waveform represented by the solid line.
Note that also when a plurality of points for estimating the current intensity are provided in the measurement target region A, and the direction of the current or the intensity distribution of the current flowing in the nerve and around the nerve is estimated, the current intensity can be correctly estimated, similar to the case described with reference to
Thus, in the present embodiment, the use of a transparent movable plate 60 allows, for example, an operator of the ultrasound probe 42 to recognize the position of the ultrasound probe 42 without peering into the back side of the movable plate 60. Further, the camera 300 located on the ceiling or floor of the magnetic shield room 200 allows the ultrasound probe 42 to be photographed through the movable plate 60. Then, from the image obtained by photographing, the XY position of the ultrasound probe 42 with respect to the movable plate 60 when the ultrasound image is acquired can be detected.
Accordingly, it is possible to detect the Z position and XY position of the nerve when measuring the biomagnetic field, based on the ultrasound image and the image acquired by the camera 300. The relationship between the position of the movable plate 60 when measuring a biomagnetic field and the position of each magnetic sensor of the sensor array 211 has been acquired in advance. Therefore, the positional relationship between the position of the nerve (the Z position and the XY position) and the position of each magnetic sensor (the Z position and the XY position) can be detected, and the current distribution of the measurement target portion can be estimated from the biomagnetic field data based on the positional relationship. That is, an ultrasound image including a nerve image can be used to estimate the electrical current distribution in an living body from biomagnetic field data of peripheral nerves.
The movable plate 60 is separably disposed on the protruding part 21, so that an ultrasound image of the measurement target portion can be acquired by maintaining the measurement target portion in the same state as that when measuring the biomagnetic field. Accordingly, the position information acquiring unit 52 can detect the same position of the nerve as that when measuring the biomagnetic field even when the target measurement portion is moved to a position different from that when measuring the biomagnetic field. Therefore, the positional relationship acquiring unit 54 can accurately detect the positional relationship between the position of the nerve and the position of each magnetic sensor, and estimate the current distribution in a living body with less error from the biomagnetic field data of the peripheral nerve.
Mounting the guide rail 70 to the protruding part 21 facilitates the construction of a mechanism for moving the movable plate 60, as compared to a mechanism for moving the movable plate 60 together with a chair or bed. Therefore, the guide rail can be easily mounted to the magnetic measurement apparatus 210 which is already in operation, and the magnetic measurement apparatus 210 can be converted into an apparatus which can acquire ultrasound images with minimal cost.
On the bed 90, a subject (not illustrated) lies down, for example, in a supine position with his or her head at the lower left side of
However, in the present embodiment, in the movable plate 60, both sides in the width direction of the curved cross-sectional shape (the portions mounted to the guide rail 70 of
An ultrasound image of the knee portion is acquired by the ultrasonic measurement apparatus 40 with the bed 90 moved to the opposite side of the
Dewar 220 and the movable plate 60 moved to the outside of the protruding part 21. At this time, similar to the above-described embodiment, an image indicating the positional relationship between the ultrasound probe and the movable plate 60 is captured by the camera 300. Thereafter, the bed 90 is moved toward the Dewar 220 until the movable plate 60 is positioned on the protruding part 21 (on the sensor array 211), and the biomagnetic field in the knee portion is measured by the magnetic measurement apparatus 210.
The function of the biomagnetic measurement system 102 is similar to that of
As described above, in the present embodiment, the same effect as in the above-described embodiment can be achieved. Further, in the present embodiment, a mechanism for moving the movable plate 60 with the bed 90 is provided, and therefore, it is possible to further accurately acquire the relationship between the position of the nerve in the knee portion of the subject and the position of the sensor array 211 using ultrasound images, as compared to the case where the movable plate 60 is not used. This allows a more accurate estimation of the neural activity current of the knee portion based on the measurement of the biomagnetic field generated by the nerve of the knee portion, compared to the case where the movable plate 60 is not used.
In
A movable plate 60A illustrated in
The movable plate 60A includes a sensor facing region 61A positioned at the center of the movable plate 60A, which has a different configuration from that of the sensor facing region of the movable plate 60 illustrated in
The sensor facing region 61A is the region in which the ultrasound probe 42 of the ultrasonic measurement apparatus 40 (
The sensor facing region 61A of the movable plate 60A is formed of a material or is formed to have a shape that facilitates the acquisition of an ultrasound image with the ultrasound probe 42. For example, the thickness of the sensor facing region 61A of the movable plate 60A is preferably less than the thickness of the region of the movable plate 60A surrounding the sensor facing region 61A. Examples of the materials and thicknesses of the sensor facing region 61A are indicated in
Note that the material and the thickness of the region of the movable plate 60A surrounding the sensor facing region 61A may different from that of the sensor facing region 61A, provided that the material of the surrounding region has a rigidity that does not deform with respect to the weight of the measurement target portion of the subject P mounted on the movable plate 60A. In this case, the material of the region surrounding the sensor facing region 61A in the movable plate 60A is preferably transparent to visible light.
12 MHz and 22 MHz indicate the frequency of the ultrasound probe 42. In the ultrasound probe 42, as the frequency decreases, the resolution will be reduced, but it will be easier to reach deep portions in the body. Ultrasound images are acquired by placing the measurement target portion that is the upper limb or the lower limb on the movable plate 60A and applying the ultrasound probe 42 to the measurement target portion from the lower side of the movable plate 60A through the sensor facing region 61A in a state where the movable plate 60A is pulled out.
In
By the evaluation indicated in
Note that the movable plate 60A is not limited to the structure described above, as long as an ultrasound image of the measurement target portion of the subject P mounted on the movable plate 60A can be acquired. For example, a slit or hole may be provided in the sensor facing region 61A of the movable plate 60A at predetermined intervals. Furthermore, when the area of the measurement target portion is small, an opening may be provided in the sensor facing region 61A in accordance with the measurement target portion.
Further, when the area of the measurement target portion is small and the strength of the sensor facing region 61A is not required, the sensor facing region 61A may be formed of a material having an acoustic impedance close to the acoustic impedance of the human body (e.g., a gel material), rather than a solid material such as a resin.
As described in
As described above, in the present embodiment, the same effect as in the above-described embodiment can be obtained. In the present embodiment, an ultrasound image of a measurement target portion having good image quality (visibility) can be acquired while maintaining the strength (stiffness) of the movable plate 60A. Accordingly, based on the ultrasound image and the image acquired by the camera 300 illustrated in
The CPU 501 controls the overall operation of the data processing apparatus 50. The CPU 501 implements the functions of the position information acquiring unit 52, the positional relationship acquiring unit 54, and the current estimating unit 56 by executing a bioelectric current estimation program stored in the ROM 503 or the auxiliary storage device 504. The CPU 501 may control the operation of the biomagnetic measurement system 2100, such as the magnetic measurement apparatus 210 and the ultrasonic measurement apparatus 40.
The RAM 502 is used as a work area of the CPU 501 and stores the bioelectric current estimation program and various parameters such as the Z position and the XY position. The ROM 503 stores a bioelectric current estimation program.
The auxiliary storage device 504 is a storage device such as a Solid State Drive (SSD) or a Hard Disk Drive (HDD). For example, the auxiliary storage device 504 stores a control program such as an operating system (OS) for controlling the operation of the data processing apparatus 50, an ultrasound image, morphological image data, various parameters, and the like.
The input output interface 505 is connected to a mouse, keyboard, or the like. The input output interface 505 may include a communication interface for communicating with other devices. The display device 50a displays windows and operation windows for displaying the current waveform illustrated in
According to one embodiment of the present invention, the positional relationship between a sensor for measuring the biomagnetic field and a nerve can be acquired by using a nerve image included in an image of a measurement target region to estimate the neural activity current generated in association with the neural activity of a subject.
According to another embodiment of the present invention, the positional relationship between the position of a nerve and the position of a magnetic sensor at the time of measuring a magnetic field can be identified by using an ultrasound image, so that the current distribution can be estimated from the biomagnetic field data.
The bioelectric current estimation method, the bioelectric current estimation apparatus, the biomagnetic measurement apparatus, and the biomagnetic measurement system are not limited to the specific embodiments described in the detailed description, and variations and modifications may be made without departing from the spirit and scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-051880 | Mar 2020 | JP | national |
| 2020-051881 | Mar 2020 | JP | national |
| 2020-189868 | Nov 2020 | JP | national |
