DARPA's AMBIIENT program

DARPA's program entitled "Atomic Magnetometer for Biological Imaging In Earth’s Native Terrain" (AMBIENT)

Taking Animal Magnetism to the Extreme

DARPA News, 2017-05-17

Facebook post: https://www.facebook.com/photo?fbid=10155334317827150&set=a.67177297149

Notes and excerpts from the news release follow.

A human (the human body) emits magnetic fields of 10 picoTesla (10-11 Tesla) to 10 femtoTesla (10-14 Tesla).

Planet Earth's "average magnetic field is 50 millionths of a Tesla (10-6 Tesla)".

"This means that Earth’s magnetic field is a million to a billion times stronger than the 10 picoTesla (10-11 Tesla) to 10 femtoTesla (10-14 Tesla) magnetic fields emanating from human bodies."

Our planet is compared to an "elephant in the room" which has  "preventing biomagnetic field sensing from extending beyond its current limitations."

Traditionally, the problem has been addressed using the gradiometric technique. A gradiometer consisting of two magnetometers is used. One is placed close to the human, thereby measuring both the human magnetic field and the Earth's magnetic field. Another is placed further away, thereby measuring only the Earth's magnetic field. By subtracting the value of the Earth's magnetic field, we can determine that of the human.

Demonstration of a heart measurement using a magnetic field sensor developed by the AMBIIENT program of DARPA

https://www.youtube.com/watch?v=Zmd_SWNvmP8&

[t=435s] "Magnetocardiography or MCG is the detection and imaging of magnetic signals from the heart. Cellular currents that initiate the periodic muscle contractions of the heart generate volume currents, which produce magnetic fields near the surface of the chest. These signals are stronger than the brain activity due to the highly synchronous activity needed to keep the heart beating." 

"While MCG exists today, it's too expensive and it's unavailable to patient's bedsides. Developing such a technology could be truly game-changing and it would greatly improve medical intervention for heart disease."

https://www.youtube.com/watch?v=Zmd_SWNvmP8&t=501s

"Before performing the demo I'd like to briefly describe the signal we're going to see. 

[Figure "AMBIIENT DEMO"] The left image shows a previously recorded signal with the AMBIIENT sensor. 

🔹The y-axis is the gradient magnetic field in picotesla per centimeter and the x-axis is time.

🔹The plot shows 10 seconds of averaging from a heartbeat. 

🔹The first bump is known as the P wave which is the depolarization and contraction of the atriums.

🔹This is followed by the QRS wave which is the rapid electrical impulse and depolarization of the ventricles 

🔹Finally, the T wave is the ventricular repolarization.

Now that we know what to expect, let's get to the demo.

Now, we have a live feed of the magnetometer. (...)

What we're displaying on the top is the field coming off of this signal. And you can see it's really noisy. It's because we're in a room, there are fans, there are 60 hertz everywhere. And this has to operate in a hospital setting in the future. So this is a good step. 

The bottom signal here is the actual spectral density and we could see our 60 hertz and our 180 Hertz. 

If we swipe, we can get to the premise of AMBIIENT which is using a gradiometer. And the bottom plot down is better. 

And now we're showing the gradient field which is orders of magnitude lower noise floor. 

And if we swipe again, we have a live feed here of that gradient signal in green." 

The volunteer approaches the sensor.

"Eventually, we'll see his heartbeat live in a non-contact method. So there is that heartbeat that we can see. And if we swipe again we'll see a time average of this clearly showing that we can see all of these different various elements in a non-contact way. Which will be incredibly useful for burn victims or even for severni patients. 

So this is a completely new modality and we braved it and showed it live on stage! So, today we've demoed the underlying technology from the AMBIIENT program and we're all incredibly excited and I hope you are too. We're looking to commercialize this sensor into arrays for both MEG and MCG and hope this can be brought out, really across the world, in different hospital settings."

Demonstration

Demonstration of a sensor from the DARPA AMBIIENT program for the measurement of magnetic fields in the ambient environment, without interference from the Earth's magnetic field or other sources.

"An atom-based magnetometer known as an optically-pumped magnetometer".

This in an OPM measuring the Larmor frequency of atoms to determine the magnetic field strength (Free-Induction-Decay regime).

A gradiometer setting is used: A gradiometer consists of a system of two magnetometers in close proximity, one near the subject or object to be measured and one further away, providing a setting that allows to subtract the background magnetic field.

Excerpt: https://youtu.be/Zmd_SWNvmP8?t=368

"We measured an auditorially-evoked signal (shown). This is the first ever auditorily-evoked signal measured outside of a shielded room and it's a key first step towards mobile MEG."

"We're going to demonstrate a heart measurement which is an equally potential important spin-off of the AMBIIENT technology".

"I'd like to briefly describe the signal we're going to see. The left image shows a previously recorded signal with the AMBIIENT sensor. The y-axis is the gradient magnetic field in picotesla per centimeter and the x-axis is the time. The plot shows 10 seconds of averaging from a heartbeat. The first bump is known as the P wave which is the depolarization and contraction of the atriums. This is followed by the QRS wave which is the rapid electrical impulse and depolarization of the ventricles. Finally, the T wave is the ventricular repolarization."

"What we're displaying on the top is the field coming off of this signal. And you can see it's really noisy, it's because we're in a room, there are fans, there is 60 Hertz everywhere. And this has to operate in a hospital setting in the future, so this is a good step."

🔹 "Now we're showing the gradient field which is orders of magnitude lower noise floor". 

🔹 "We have a live feed here of that gradient signal in green".

🔹 And Tom "will walk up to the sensor and eventually we'll see his heartbeat live in a non-contact method. So there is that heartbeat." 

🔹"A time average of this is clearly showing."

🔹"We can see all of these different various elements in a non-contact way which will be incredibly useful for burn victims or even for several patients." 

"So this is a completely new modality and we braved it and showed it live on stage. So today we've demoed the underlying technology from the AMBIIENT program and we're all incredibly excited and I hope you are too. We're looking to commercialize this sensor into arrays for both MEG and MCG and hope this can be brought out really across the world in different hospital settings."

Journal article: Portable Magnetometry for Detection of Biomagnetism in Ambient Environments

(Freely available: https://arxiv.org/abs/2001.03534)

Figure 1

Technical presentation

"Portable Magnetometry for Detection of Biomagnetism in Ambient Environments"* AMBIIENT program by DARPA

Description of an Evoked-Potential Response (EPR) MEG conducted with a developed optically-pumped magnetometer. This OPM measures the Larmor frequency of atoms to determine the magnetic field strength (Free-Induction-Decay regime).

Technical presentation by Mark E. Limes*

https://youtu.be/nboSFFK_h5Y

Selected excerpts:

https://youtu.be/nboSFFK_h5Y?feature=shared&t=532

"This particular test is a measurement of your auditory cortex neurons firing to a conscious observation of a little beep".

"We set up our gradiometer next to a subject's auditory cortex, a little above the ear" (Figure). "Then we send in a randomized 1 kilohertz audio beep, that randomly occurs every 1.5 to 2.5 seconds, into the opposite ear, with a special earphone that has a long non-magnetic tube that goes into the ear. Then, we record data for about 10 to 20 minutes, which apparently is typical for this type of experiment, to build up some statistics."

Presentation of the chart of the image: "So we've labeled some peaks for people in the neuroscience community and 100 N, for example, stands for negative 100 milliseconds magnetic peak, which is a big signature of the auditory response."

"So here's our proof-of-principle demonstration of a portable rubidium 87 gradiometer to make signals. This is, as far as we're aware of, the first time a first-order gradiometer has been used in an unshielded demonstration."

"Something outside the scope of AMBIIENT that is being actively pursued is making the scalar sensor a vector sensor by applying some rotating fields". 

Image is figure from publication below

*https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.14.011002

Demonstration of brain wave measurement using a magnetic field sensor developed by the AMBIIENT program of DARPA

Researchers of the AMBIIENT program, funded by DARPA, created, a few years ago, a magnetic field sensor that can be used in ambient conditions.

In the featured demonstration, the sensor is used for brain wave detection, and specifically for magnetoencephalography (MEG).

https://www.youtube.com/watch?v=nboSFFK_h5Y&t=533s

Researcher M. Limes mentions (t=553s): "For a proof-of-principle MEG demonstration, we do an Audio-Evoked Field (AEF) detection." 

It is noted that the above refers to the measurement of magnetic fields produced (evoked) by the brain in response to auditory stimuli. In this case, an ear-piece that generates a beep is mounted onto the ear of a subject.

The earliest brain responses, consisting of the firing of auditory cortex neurons, occur around 30-50 milliseconds after the stimulus. A prominent response named the N100m component, occurs at 100 ms after the stimulus and consists of a negative-directed (N) deflection in the magnetic field.

The researcher continues as follows.

"This particular test is a measurement of your auditory cortex neurons firing to a conscious observation of a little beep".

"We set up our gradiometer next to a subject's auditory cortex, a little above the ear" (Figure). "Then we send in a randomized 1 kilohertz audio beep, that randomly occurs every 1.5 to 2.5 seconds, into the opposite ear, with a special earphone that has a long non-magnetic tube that goes into the ear. Then, we record data for about 10 to 20 minutes, which apparently is typical for this type of experiment, to build up some statistics."

Presentation of the chart of the image: "So we've labeled some peaks for people in the neuroscience community. And N100m, for example, stands for negative 100 milliseconds magnetic peak, which is a big signature of the auditory response."

We can appreciate that further to the N100m signal obtained, there exist positive deflections at 40ms and 150 ms, which have been labeled accordingly as P40m and P150m.

The researcher concludes as follows (selected excerpts).

"So here's our proof-of-principle demonstration of a portable rubidium 87 gradiometer to make signals. This is, as far as we're aware of, the first time a first-order gradiometer has been used in an unshielded demonstration."

"Something outside the scope of AMBIIENT that is being actively pursued is making the scalar sensor a vector sensor by applying some rotating fields". 

The chart is included in a figure from the following publication:

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.14.011002

https://arxiv.org/pdf/2001.03534 (Figure 2)