NMR Imaging of Action Currents
In graduate school, I kept detailed notes about my research. My PhD advisor, John Wikswo, insisted on it, and he provided me with sturdy, high-quality notebooks that are still in good shape today. I encourage my students to keep a notebook, but most prefer to record “virtual” notes on their computer, which is too newfangled for my taste.
My Vanderbilt Notebook 11 covers January 28 to April 25, 1985 (I was 24 years old). On page 69, in an entry dated April 3, I taped in a list of abstracts from the Sixth Annual Conference of the IEEE Engineering in Medicine and Biology Society, held September 15–17, 1984 in Los Angeles. A preview of the abstracts were published in the IEEE Transactions on Biomedical Engineering (Volume 31, Page 569, August, 1984). I marked one as particularly important:
NMR Imaging of Action Currents
J. H. Nagel
The magnetic field that is generated by action currents is used as a gradient field in NMR imaging. Thus, the bioelectric sources turn out to be accessible inside the human body while using only externally fitted induction coils. Two- or three-dimensional pictures of the body’s state of excitation can be displayed.
That’s all I had: a three sentence abstract by an author with no contact information. I didn’t even know his first name. Along the margin I wrote (in blue ink):
I can’t find J H Nagel in Science Citation Index, except for 3 references to this abstract and 2 others at the same meeting (p. 575, 577 of same Journal [issue]). His address is not given in IEEE 1984 Author index. Goal: find out who he is and write him for a reprint.
How quaint; I wanted to send him a little postcard requesting reprints of any articles he had published on this topic (no pdfs back then, nor email attachments). I added in black ink:
3–25–88 checked biological abstracts 1984-March 1, 1988. None
Finally, in red ink was the mysterious note
See ROTH21 p. 1
In Notebook 21 (April 11, 1988 to December 1, 1989) I found a schedule of talks at the Sixth Annual Conference. I wrote “No Nagel in Session 14!” Apparently he didn’t attend the meeting.
Why tell you this story? Over the years I’ve wondered about using magnetic resonance imaging to detect action currents. I’ve published about it:
Wijesinghe, R. and B. J. Roth, 2009, Detection of peripheral nerve and skeletal muscle action currents using magnetic resonance imaging. Ann. Biomed. Eng., 37:2402–2406.
Jay, W. I., R. S. Wijesinghe, B. D. Dolasinski and B. J. Roth, 2012,Is it possible to detect dendrite currents using presently available magnetic resonance imaging techniques? Med. & Biol. Eng. & Comput., 50:651–657.
Xu, D. and B. J. Roth, 2017,The magnetic field produced by the heart and its influence on MRI. Mathematical Problems in Engineering, 2017:3035479.
Much recent research has focused on using MRI to image neural activity directly, rather than through changes in blood flow (Bandettini et al. 2005). Two methods have been proposed to do this. In one, the biomagnetic field produced by neural activity (Chap. 8) acts as the contrast agent, perturbing the magnetic resonance signal. Images with and without the biomagnetic field present provide information about the distribution of neural action currents. In an alternative method, the Lorentz force (Eq. 8.2) acting on the action currents in the presence of a magnetic field causes the nerve to move slightly. If a magnetic field gradient is also present, the nerve may move into a region having a different Larmor frequency. Again, images taken with and without the action currents present provide information about neural activity. Unfortunately, both the biomagnetic field and the displacement caused by the Lorentz force are tiny, and neither of these methods has yet proved useful for neural imaging. However, if these methods could be developed, they would provide information about brain activity similar to that from themagnetoencephalogram, but without requiring the solution of an ill-posed inverse problem that makes the MEG so difficult to interpret.
Apparently all this activity began with my reading of Nagel’s abstract in 1985. Yet, I was never able to identify or contact him. Recent research indicates that the magnetic fields in the brain are tiny, and they produce effects that are barely measurable with modern technology. Could Nagel really have detected action currents with nuclear magnetic resonance three decades ago? I doubt it. But there is one thing I would like to know: who is J. H. Nagel? If you can answer this question, please tell me. I’ve been waiting 35 years!
Originally published at http://hobbieroth.blogspot.com.