David Cohen

Associate Professor in Radiology, Harvard Medical School
Associate Neuroscientist, Massachusetts General Hospital
Visiting Scientist, Massachusetts Institute of Technology
(Previously Group Leader, Francis Bitter Magnet Lab, MIT)



  • Ph.D.  (Experimental Nuclear Physics), University of California, Berkeley, US, 1955
  • B.S.    (Liberal Arts), University of Manitoba, Winnipeg, Canada, 1948


My Research

I have had two research careers. First, prior to 1965, I was an accelerator physicist at the Argonne Lab, specializing in strong magnetic fields, and using heavy nuclear shielding.  But I had begun to think about very weak magnetic fields, and that the human body must be a rich source of such fields.  For example, the same currents from the heart which produce the ECG should also produce a weak magnetic field over the chest.  Also, the same currents from the brain which produce the EEG should produce a weak field over the head.  And there should be new information in these fields. To pursue this new work, I switched careers. In 1965 I joined the faculty of the U. of Illinois. My idea was to try to measure these weak fields inside a magnetically-shielded room, to keep out the much larger external fields; similar to the idea of nuclear shielding.  I soon built such a room.

However, a bit earlier, the first measurement of the body’s magnetic field had been made elsewhere.  This was of the heart, but using a magnetic gradiometer -- two large coils -- to reduce the background (the first magnetocardiogram or MCG); but they used no shielding, and the signal was barely seen above background noise. Then later, in my shielded room, I also measured the heart, but using a somewhat better detector; I obtained a much clearer MCG signal, and was able to plot a vector picture of what was happening. Also, I measured the much weaker field of the human brain; this was the first magnetoencepahalogram (MEG). But the signals were not yet as clear as conventional ECGs and EEGs, because the room still allowed some background leakage, and the detector was itself noisy.

Then, in 1969, I moved to MIT, where I built a really good shielded room.  Fortunately, an extremely sensitive magnetic detector, called a SQUID, had just been invented (virtually no noise), and the inventor brought his SQUID to my lab.  We used this detector inside the new room, to again look at the heart.  This combination of SQUID and good room now allowed the MCG to be as clear as the conventional ECG , and aroused the interest of the medical and research community.  Science journal called this event the birth of biomagnetism.  I soon measured the first clear signal of dc from the heart, the first clear signal from skeletal muscle, and, more dramatically, the first clear MEG over the head. These were followed by the first measurements over the lung (due to contaminating magnetic particles), and the first evoked MEG . Now, various research groups began to repeat and confirm these measurements, and biomagnetism was growing.

Of all the organs, the heart (the  dcMCG) at first interested me the most, because of diagnostic possibilities.  Then I became interested in the magnetic measurements over the lung, as a way of seeing magnetic dust in the lung, especially asbestos.  Eventually, I returned to the MEG, and our group studied the physics of MEG vs. EEG. Should these be competing or should they be complementary technologies?  We concluded, in a lively controversy, that they were complementary.  Now, some years later, both MEG and EEG are often used, along with MRI and fMRI, in multi-modal imaging of the brain. I still maintain my interest in how to best use the MEG, and after joining the MEG group at Mass. General Hospital, I spend my time in mentoring the new MEG users, and in measuring dc fields from the body.


Special Awards

  • Isbister Scholarship, 1947, for high average at the University of Manitoba
  • Established Investigatorship of the American Heart Association, 1969-1974; five-year salary for beginning work on Biomagnetism, at MIT
  • MIT (McGovern Institute) award for MEG development [Photo]