David Cohen (physicist)
Encyclopedia
David Cohen is known mostly for his pioneering work in the area of Biomagnetism
(magnetic fields produced by the body), where he made many of the first measurements.
Cohen was born of immigrant parents in Winnipeg, Canada; he was raised here and earned an arts degree at the University of Manitoba
. Then, in the USA, he attended graduate school at the University of California, Berkeley
, where he gained a PhD in experimental nuclear physics. Working in this area, and using large magnets, he became interested in the other extreme; this was the measurement of very weak magnetic fields, which for example might be produced by the weak natural currents in the human body. In 1963 he proposed a method using a magnetically-shielded room to keep out external magnetic disturbances, as in radiation shielding in nuclear experiments. At that time others reported the first biomagnetic measurement, where the MCG (magnetocardiogram, the magnetic field due to heart currents) was measured; this was done without shielding, hence showed much external interference. Cohen then built a modest shielded room, and with somewhat clearer signals verified the heart’s magnetic field. He also made the first measurement of the MEG (magnetoencephalogram, the magnetic field of the brain) . However, all these early biomagnetic measurements were generally too noisy, both because of the use of insensitive detectors, and incomplete magnetic shielding.
To get clearer results, in 1969 Cohen built an elaborate shielded room at MIT, but still needed a more sensitive detector. James Zimmerman had just developed an extremely sensitive detector called the SQUID
(Superconducting Quantum Interference Device). Cohen and Zimmerman set up this detector in the new room, to look at the body’s heart signal, the MCG. For the first time the signals were now clear, and their resulting report, called the magna carta of biomagnetism, ushered in a new era in biomagnetism, attracting other researchers. Cohen then measured the first clear MEG, and signals from other organs. As interest rapidly grew, other laboratories also produced new recordings. Today, most biomagnetic measurements are of the human brain (MEG); these are made in a shielded room, using a helmet over the head containing hundreds of SQUID
s. There are perhaps 120 such MEG systems in existence, worldwide.
Cohen continuously worked in biomagnetism, authored many publications, mostly concerning the MEG, and has been called "the father of the MEG". He remains active, is on the faculty at the Harvard Medical School
, and is a mentor in the MEG group at MIT's Martinos Imaging Center, located at the Massachusetts General Hospital.
Biomagnetism
Biomagnetism is the phenomenon of magnetic fields produced by living organisms; it is a subset of bioelectromagnetism. The study of the biological effects of magnetic fields is magnetobiology...
(magnetic fields produced by the body), where he made many of the first measurements.
Cohen was born of immigrant parents in Winnipeg, Canada; he was raised here and earned an arts degree at the University of Manitoba
University of Manitoba
The University of Manitoba , in Winnipeg, Manitoba, Canada, is the largest university in the province of Manitoba. It is Manitoba's most comprehensive and only research-intensive post-secondary educational institution. It was founded in 1877, making it Western Canada’s first university. It placed...
. Then, in the USA, he attended graduate school at the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...
, where he gained a PhD in experimental nuclear physics. Working in this area, and using large magnets, he became interested in the other extreme; this was the measurement of very weak magnetic fields, which for example might be produced by the weak natural currents in the human body. In 1963 he proposed a method using a magnetically-shielded room to keep out external magnetic disturbances, as in radiation shielding in nuclear experiments. At that time others reported the first biomagnetic measurement, where the MCG (magnetocardiogram, the magnetic field due to heart currents) was measured; this was done without shielding, hence showed much external interference. Cohen then built a modest shielded room, and with somewhat clearer signals verified the heart’s magnetic field. He also made the first measurement of the MEG (magnetoencephalogram, the magnetic field of the brain) . However, all these early biomagnetic measurements were generally too noisy, both because of the use of insensitive detectors, and incomplete magnetic shielding.
To get clearer results, in 1969 Cohen built an elaborate shielded room at MIT, but still needed a more sensitive detector. James Zimmerman had just developed an extremely sensitive detector called the SQUID
SQUID
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions....
(Superconducting Quantum Interference Device). Cohen and Zimmerman set up this detector in the new room, to look at the body’s heart signal, the MCG. For the first time the signals were now clear, and their resulting report, called the magna carta of biomagnetism, ushered in a new era in biomagnetism, attracting other researchers. Cohen then measured the first clear MEG, and signals from other organs. As interest rapidly grew, other laboratories also produced new recordings. Today, most biomagnetic measurements are of the human brain (MEG); these are made in a shielded room, using a helmet over the head containing hundreds of SQUID
SQUID
A SQUID is a very sensitive magnetometer used to measure extremely weak magnetic fields, based on superconducting loops containing Josephson junctions....
s. There are perhaps 120 such MEG systems in existence, worldwide.
Cohen continuously worked in biomagnetism, authored many publications, mostly concerning the MEG, and has been called "the father of the MEG". He remains active, is on the faculty at the Harvard Medical School
Harvard Medical School
Harvard Medical School is the graduate medical school of Harvard University. It is located in the Longwood Medical Area of the Mission Hill neighborhood of Boston, Massachusetts....
, and is a mentor in the MEG group at MIT's Martinos Imaging Center, located at the Massachusetts General Hospital.
External links
- http://www.nmr.mgh.harvard.edu/martinos/people/showPerson.php?people_id=33
- http://www.Biomag2004.net
See also
- James Edward ZimmermanJames Edward ZimmermanJames Edward Zimmerman was born in Lantry, South Dakota. He was a coinventor of the radio-frequency superconducting quantum interference device and he is credited with coining the term.- Career :...
- MagnetocardiographyMagnetocardiographyMagnetocardiography is a technique to measure the magnetic fields produced by electrical activity in the heart using extremely sensitive devices such as the Superconducting Quantum Interference Device...
- MagnetoencephalographyMagnetoencephalographyMagnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
- Hosaka-Cohen TransformationHosaka-Cohen TransformationHosaka-Cohen Transformation is a mathematical method of converting a particular two-dimensional scalar magnetic field map to a particular two-dimensional vector map...