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Claims  |
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What is claimed is:
1. Apparatus for making magnetic measurements of the human body,
comprising:
biomagnetometer means including a magnetic sensing coil for measuring
magnetic fields arising form a selected portion of the body; and
means for recording in real time the location of the selected portion of
the body from which the magnetic fields emanate, said means for recording
including electromagnetic means for sensing the location of the selected
portion of the body using an electromagnetic signal, said electromagnetic
means including a transmitter and a receiver of electromagnetic signals.
2. The apparatus of claim 1, wherein said biomagnetometer means includes a
superconducting quantum interference device to measure the magnetic fields
produced by the body.
3. The apparatus of claim 1, wherein the selected portion of the body is
the head.
4. The apparatus of claim 1, wherein said electromagnetic means includes
sending means for transmitting an electromagnetic signal through the air,
and receiving means for receiving the transmitted electromagnetic signal,
one of said sending means and said receiving means being mounted on the
selected portion of the body and the other being mounted separated from
the body.
5. The apparatus of claim 1, wherein said electromagnetic means includes at
least two receiving units mounted on the selected portion of the body.
6. The apparatus of claim 1, wherein said electromagnetic means includes at
least one receiving unit mounted on the selected portion of the body, said
receiving unit having an antenna which receives electromagnetic signals in
three axes.
7. The apparatus of claim 1, wherein said electromagnetic means includes
sending means for transmitting an electromagnetic signal through the air,
mounted on the body.
8. The apparatus of claim 1, wherein said electromagnetic means includes
sending means for transmitting an electromagnetic signal through the air,
mounted on said biomagnetometer means.
9. The apparatus of claim 1, wherein said electromagnetic means includes
sending means for transmitting an electromagnetic signal through the air,
mounted separately from the body and from said biomagnetometer means.
10. The apparatus of claim 1, wherein said electromagnetic means includes
at least one receiving unit mounted on the selected portion of the body by
an elastic band.
11. The apparatus of claim 1, further including a magnetically shielded
room enclosing said biomagnetometer and the body being measured.
12. The apparatus of claim 1, wherein said electromagnetic means is
constructed to have substantially no residual magnetism when not
operating.
13. A process for obtaining biomagnetic data from the human body and
correlating that data to the structure of the body, comprising the steps
of:
supplying apparatus according to claim 1;
operating said means for recording intermittently to record the location of
the selected portion of the body;
taking data from said biomagnetometer means when said means for recording
is not operating, thereby avoiding magnetic interference of the
biomagnetic data from said means for recording; and
recording the biomagnetic data with the information on the location of the
selected portion of the body, whereby the biomagnetic data is correlated
with the position of the body.
14. A process for obtaining biomagnetic data from the human body and
correlating that data to the structure of the body, comprising the steps
of:
supplying apparatus according to claim 1;
operating said means for recording conitnuously to record the location of
the selected portion of the body, said means for recording operating at a
frequency greater than about 10 KHz;
taking data from said biomagnetometer means and filtering out signals
having a frequency greater than about 10 KHz, thereby avoiding magnetic
interference of the biomagnetic data from said means for recording; and
recording the biomagnetic data with the information on the location of the
selected portion of the body, whereby the biomagnetic data is correlated
with the position of the body.
15. Apparatus for making magnetic measurements of the human body,
comprising:
a biomagnetometer including a sensor for measuring magnetic fields arising
from a selected portion of the body;
an elecromagnetic transmitter adjacent the body being measured, said
transmitter having substantially no residual magnetism when no electric
current is flowing therethrough;
at least one electromagnetic receiver mounted on the selected part of the
body, said electromagnetic receiver having substantially no residual
magnetism when no electric current is flowing therethrough;
an electromagnetic wand receiver that may be touched to points on the
selected portion of the body to indicate the location of such points
relative to said electromagnetic transmitter; and
computer means for controlling and recording the locations of said
receivers and said wand receiver, for taking data from said
biomagnetometer, and for controlling said transmitter.
16. The apparatus of claim 15, wherein said receivers are mounted to the
body by means of an elastic band.
17. The apparatus of claim 15, wherein said transmitter includes three
orthogonal antennas, said antennas having no ferromagnetic cores therein.
18. The apparatus of claim 15, wherein said receivers include three
orthogonal antennas, said antennas having no ferromagnetic cores therein.
19. The apparatus of claim 15, wherein said transmitter is potted in a
nonmagnetic potting compound.
20. The apparatus of claim 15, wherein said receivers are potted in a
nonmagnetic potting compound.
21. A process for obtaining biomagnetic data from the human body and
correlating that data to the structure of the body, comprising the steps
of:
supplying apparatus according to claim 15;
operating said transmitter and said receivers and said wand receiver
intermittently to record the location of the selected portion of the body;
taking data from said biomagnetometer when said transmitter, said
receivers, and said wand receiver are not operating, thereby avoiding
magnetic interference of the biomagnetic data from said transmitter, said
receivers, and said wand receiver; and
recording in said computer means the biomagnetic data with the information
on the location of the selected portion of the body, whereby the
biomagnetic data may be correlated with the location of the body.
22. The process of claim 21, wherein said step of operating includes the
steps of:
touching the wand receiver to selected reference points on the selected
portion of the body with said transmitter on, to record the locations of
said reference points with respect to said transmitter;
operating the transmitter and said receivers to record the positions of
said receivers with respect to said transmitter, thereby also correlating
the positions of the reference points with respect to said receivers,
whereby the locations of the reference points may be correlated with
biomagnetic data taken from the selected portion of the body.
23. The processes of claim 21, wherein the selected portion of the body is
the head, and the reference points are the left and right perauricular
points and the nasion.
24. A process for obtaining biomagnetic data from the human body and
correlating that data to the structure of the body, comprising the steps
of:
supplying apparatus according to claim 15;
operating said transmitter and said receivers and said wand receiver
continuously at a frequency greater than about 10 KHz to record the
location of the selected portion of the body;
taking data continuously from said biomagnetometer and filtering signals
from said data having a frequency greater than about 10 KHz; and
recording in said computer means the biomagnetic data with the information
on the location of the selected portion of the body, whereby the
biomagnetic data may be correlated with the location of the body. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to medical diagnostic instruments, specifically such
instruments for making measurements of magnetic fields in the human body,
and, more specifically, to instruments wherein the location of the portion
of the body being measured may be correlated directly with the biomagnetic
measurements.
The human body produces various kinds of energy that may be used to monitor
the status and health of the body. Perhaps the best known of these types
of energy is heat. Most healthy persons have a body temperature of about
98.6.degree. F. A measured body temperature that is significantly higher
usually indicates the presence of an infection of other deviation from
normal good health. A simple medical instrument, the clinical thermometer,
has long been available to measure body temperature.
Over 100 years ago, medical researchers learned that the body also produces
electrical signals. Doctors today can recognize certain patterns of
electrical signals that are indicative of good health, and other patterns
that indicate disease or abnormality. The best known types of electrical
signals are those from the heart and from the brain, and instruments have
been developed that measure such signals. The electrocardiograph measures
electrical signals associated with the operation of the heart, and the
electroencephalograph measures the electrical signals associated with the
brain. Such instruments have now become relatively common, and most
hospitals have facilities wherein the electrical signals from the bodies
of patients can be measured to determine certain types of possible disease
or abnormality.
More recently, medical researchers have discovered that the body produces
magnetic fields of a type completely different than the other types of
energy emitted from the body. The research on correlating magnetic fields
with various states of health, disease and abnormality is underway, but
sufficient information is available to demonstrate that certain emitted
magnetic fields are associated with conditions such as epilepsy and
Alzheimer's disease. Present medical studies are investigating the nature
of the normal and abnormal magnetic fields of the brain, and seeking to
correlate those fields with the precise location in the brain from which
they emanate. If it were known that a particular abnormality, such as
Alzheimer's disease, were associated with an abnormal magnetic field
produced at a particular location in the brain, then it might be possible
to detect the abnormality at an early stage, while it was treatable, and
then apply other medical knowledge to treat that precise portion of the
brain. Magnetic studies of the brain therefore offer the potential for
understanding and treating some of the most crippling diseases and
conditions known.
The biomagnetometer is an instrument that has been developed for measuring
magnetic fields produced by the body, particularly the brain. The
biomagnetometer is a larger, more complex instrument than the medical
instruments mentioned earlier, primarily because the magnetic fields
produced by the body are very small and difficult to measure. Typically,
the strength of the magnetic field produced by the brain is about
0.00000001 Gauss. By comparison, the strength of the earth's magnetic
field is about 0.5 Gauss, or over a million times larger than the strength
of the magnetic field of the brain. Most electrical equipment also
produces magnetic fields, in many cases much larger than that of the
earth. It is apparent that, unless special precautions are taken, it is
not possible to make magnetic measurements of the human body because the
external influences such as the earth's magnetism and nearby apparatus can
completely mask the magnetic fields from the body.
The biomagnetometer is a medical instrument that includes a very sensitive
detector of magnetic signals. The currently most widely used detector is a
Superconducting QUantum Interference Device or SQUID, which is
sufficiently sensitive to detect magnetic signals produced by the brain.
(See, for example, U.S. Pat. Nos. 4,386,361 and 4,403,189, whose
disclosures are incorporated by reference, for descriptions of two types
of SQUIDs.) This detector and its associated equipment require special
operating conditions such as a cryogenic dewar, and cannot be placed into
the body or attached directly to the surface of the body.
The present biomagnetometer therefore provides a table upon which the
patient lies, and a structure which places the SQUID in proximity with the
head of the patient, as about 8 inches away. Special electronics is
provided to filter out external effects such as the earth's magnetic field
and the magnetic fields of nearby electrical instruments. (For a
description of such a device, see U.S. Pat. Nos. 3,980,076 and 4,079,730,
whose disclosures are herein incorporated by reference.) The patient and
detector can also be placed into a magnetically quiet enclosure that
shields the patient and the detector from the external magnetic fields.
(For a description of such an enclosure, see U.S. Pat. No. 3,557,777,
whose disclosure is herein incorporated by reference.) With these special
precautions, medical researchers and doctors can now make accurate,
reliable measurements of the magnetic fields produced by the brain, and
are studying the relationship of these fields with diseases and
abnormalities.
As discussed above, it is particularly important to be able to correlate
the measured biomagnetic field with the exact location in the brain from
which the field emanates. It is well established that certain physically
identifiable locations in the brain are responsible for specific types of
activities and functions. It is therefore important to correlate the
measured biomagnetic field with the particular location in the brain which
produces the field. Such a correlation is important to understanding the
mechanism by which disease and disorder arise, and also to the treatment
of the problem.
At the present time, there is no automatic, reliable, and accurate method
for correlating the measured biomagnetic field with the precise location
from which it emanates, within the head of the patient. The person whose
biomagnetic fields are being measured may be asked to keep his head
motionless during the course of the measurements, and his head position
determined by physical measurements, photographs, or X-rays before or
after the magnetic measurements. While this approach may have value in a
few situations, in others it is nearly useless. The person may be asked to
keep his head stationary to within 1 millimeter or so for several hours.
For example, if the disease under study is epilepsy, many consecutive
hours of observation may be required before an attack occurs. Movements of
the person's head during the taking of data can invalidate any attempted
correlation of the data with head position. That some data is invalid may
be hard to detect, since the head movement may be brief and the patient
may return his head to nearly the same initial location.
Alternatively, the person's head may be constrained to a relatively fixed
position with a restraint system such as a frame and straps, and then
photographed, X-rayed or physically measured at the beginning and end of
the biomagnetic measurement session. This approach is likely to be
uncomfortable for the patient, and may result in spurious signals that
interfere with the biomagnetic measurements of interest. Even if the
patient can keep his head stationary, the accuracy of correlation of the
head position and the biomagnetic signal is not sufficiently great for
some applications.
There is therefore a need for an apparatus and method for measuring
biomagnetic fields and correlating those fields with the position of the
patient's body, in a more exact manner than has been heretofore achieved.
Preferably, such an approach would operate automatically to record head
position in real time, so that the measured biomagnetic field could be
correlated with the body position at the moment of measurement. Further,
the measurement approach must not produce magnetic fields that are so
large as to interfere with the principal function of the instrument, the
measurement of very weak biomagnetic fields. This last requirement is
particularly demanding, as most measurement devices having any electrical
current flow produce magnetic fields of a magnitude that can interfere
with the biomagnetic measurements. The present invention fulfills the need
for such a biomagnetic measuring system, and further provides related
advantages.
SUMMARY OF THE INVENTION
The present invention is embodied in an apparatus and process for making
biomagnetic measurements of the human body, wherein the location of the
portion of the body from which measurements are taken is determined and
recorded with the biomagnetic data itself. The biomagnetic data is thus
correlated with the exact location of it source within the body, even when
the patient moves during the course of a measurement session. The body
location data is used to construct an internal coordinate system of the
portion from which biomagnetic data is taken, so that the exact interior
source of the data is determined. The body location measurement system is
noncontacting in the sense that the movement of the patient is not
restrained, and is comfortable for the patient to use during a protracted
session.
In accordance with the invention, apparatus for making magnetic
measurements of the human body comprises biomagnetometer means including a
sensor for measuring magnetic fields arising from a selected portion of
the body; and means for recording in real time the location of the
selected portion of the body from which biomagnetic fields are measured,
said means for recording including electromagnetic means for sensing the
location of the selected portion of the body using an electromagnetic
signal. A related process for obtaining biomagnetic data from the human
body and correlating that data to the structure of the body comprises the
steps of supplying apparatus as just described, operating said means for
recording to record the location of the selected portion of the body;
taking data from said biomagnetometer means; and recording the biomagnetic
data with the information on the location of the selected portion of the
body, whereby the biomagnetic data is correlated with the location of the
body.
The biomagnetometer means is preferably a unit having a superconducting
quantum interference device (SQUID) operating at cryogenic temperature for
making sensitive measurements of the magnetic fields produced by the human
brain, although the magnetic fields produced by other parts of the body
can also be studied. The patient rests with his head and body on a table
in the apparatus, with at least one and possible two dewars containing
SQUIDs movably positioned about 12 inches or so from his head. Magnetic
fields produced by the brain are picked up by magnetic sensing coils,
detected by the SQUIDs, and recorded in a computer, after the necessary
filtration, amplification, and signal processing of the magnetic field
signal. The SQUIDs are movable relative to the body of the person so that
a map of the origins of the magnetic fields may be prepared.
The biomagnetic measurements may be accomplished in a shielded or
unshielded environment, but the shielded environment is preferred. The
magnetic fields of the brain are typically less than 1/10,000,000 as great
as the earth's magnetic field and the magnetic fields of laboratory and
medical apparatus normally found near to such a biomagnetometer apparatus.
The effects of these external fields can overwhelm those of the brain and
make their measurement impossible, when the fields due to the brain are to
be measured by an external instrument, unless measures are taken to
nullify their influence. Electronic signal processing can be used to
enhance the magnetic field signal of the brain relative to the
environmental magnetic fields. Alternatively, the patient and SQUID sensor
can be placed into a magnetically quiet enclosure which shields the
patient and sensor from the external effects.
The exact location of the head of the person is measured and recorded in a
rapid, automatic fashion substantially simultaneously with the recording
of the biomagnetic data, so that the location of the head, and the
interior regions of the brain, can be determined from the location
information obtained just before and just after each bit of biomagnetic
data. The location of the head is preferably measured using an
electromagnetic locating signal transmitted between the body of the person
and the apparatus. This locating signal is electromagnetic in nature, but
is to be clearly distinguished from the magnetic field generated by the
body itself and measured by the biomagnetometer. The locating signal is
generated by a transmitter and received by a receiver which are provided
as part of the apparatus. In one embodiment of such an apparatus, one of a
transmitter or receiver is mounted on the head of the person, and the
other is mounted stationary on the apparatus. In another embodiment, the
transmitter is mounted separately from the head and apparatus, and
receivers are mounted on both the head and the apparatus. Normally, the
receiver is mounted on the head and the transmitter on the apparatus, and
for ease of description the following discussion will follow that
convention.
In this preferred approach, the transmitter includes three coils orthogonal
to each other, through which a current is passed to generate a magnetic
loading signal. The signal is received by the receiver, which also
includes three coils orthogonal to each other, and converts the received
signal to an electrical current. The resulting information permits the
determination of the position and relative orientation of the receiver to
the transmitter in six axes. Most preferably multiple receivers, as three
receivers, are used to reduce measurement errors inherent in the system,
obtain redundant data, and account for shape variations and body
flexibility during measurements. The general approach for obtaining
location and orientation data is known for use in certain other
applications such as aircraft landing systems, see, for example, U.S. Pat.
No. 3,868,565, whose disclosure is herein incorporated by reference.
However, the apparatus used in other applications cannot be used for
measurements of the location of the body in conjunction with biomagnetic
measurements, because the magnetic fields produced by conventional
electromagnetic locating devices overwhelm the biomagnetic signals and
because of specific problems associated with measurements of a portion of
the body itself.
In one embodiment, the locating device is operated intermittently with the
taking of biomagnetic data. That is, the biomagnetic data is taken for a
period of time, and then data taking is discontinued. The electromagnetic
location recording means is activated for a period sufficiently long to
obtain the necessary locating signal information, and then turned off.
Taking of biomagnetic data then resumes. The positioning signal
information can be obtained in about 1/10 second or less, and therefore
the interruption to the biomagnetic data is hardly perceivable. Yet in
that short interruption, suffficient locating data is obtained so that the
location of the source of the data relative to the sensor is determined
with an accuracy of about 1-3 millimeters.
In another embodiment, the locating device is operated continuously, even
while biomagnetic data is taken. In this continuous operation embodiment,
the transmitter of the locating device is operated at a frequency much
greater than the frequencies of the magnetic signals of interest, so that
any transmitter signal picked up by the biomagnetometer may be readily
filtered from the biomagnetic signal.
The transmitters and receivers previously available were not suitable for
use in the location recording means, as they exhibited a residual
magnetism after being turned off during the taking of biomagnetic data.
The residual magnetism is sufficiently great to interfere with the
measurements of the biomagnetic fields. The design of the transmitters and
receivers was therefore selected to reduce the residual magnetism to an
acceptably low level. Specifically, a sufficient reduction in residual
magnetism can be accomplished by removing the ferromagnetic cores used in
the standard commercial antenna loops, and by using a potting compound for
the transmitter and receivers that has no residual magnetism. The
elimination of the ferromagnetic cores reduces the power and range of the
electromagnetic location recording system, but such capabilities are not
needed in the present system, wherein the separation of the transmitter
and receivers is never more than about 12-24 inches.
The mounting of the transmitter on the apparatus poses no problem, but the
mounting of the receivers on the body does. The ultimate locating
information required is not simply the location of the receivers with
respect to the transmitter, but instead is the location of the interior
portions of the head, specifically the portions of the brain, with respect
to the transmitter. An approach for determining the location of the brain
with respect to the receivers is therefore required. That is, the problem
posed by the need to correlate biomagnetic measurements with their source
is more complex than that of an aircraft landing system, one prior
application of electromagnetic positioning systems, in that the relative
location of interior objects is required. The comparable requirement for a
landing system would be that not just the location of the airplane, but
the location of each passenger therein, was required by the landing
system.
The present invention further provides for mounting the receivers to the
head in a comfortable and acceptable manner, and then electromagnetically
measuring the locations of identifiable features of the head with respect | | |
