As part of a project to design the electronics for a portable, low-cost cancer detector, I had to understand NMR (nuclear magnetic resonance), a measurement technique that excites and measures the spin precessions of atomic nuclei. I also relied on the expertise of Hakho Lee, PhD, and David Issadore, PhD, two researchers at Massachusetts General Hospital’s Center for Systems Biology. Lee had been using magnetic-relaxation switching to explore ways to reduce the size and bulk of an NMR machine to the point at which it could be carried into the field to perform medical diagnostics.
Lee had refined an NMR-based technique for detecting tuberculosis-specific proteins, using a fist-sized permanent magnet and a rack full of electronics. My task was to squeeze that rack into a book-sized unit. The electronics box needed to create a string of RF pulses of precisely controlled frequency in the range of 20 to 30 MHz, and the phase between the first and subsequent pulses also had to change by a precisely controlled amount.
This article begins with a brief review of the principles of NMR (nuclear magnetic resonance) imaging. It then continues with a detailed description of the signal-processing challenge, the hardware uses to solve them, and the software which both makes use of the hardware and manages it, as well as the signal analysis.
This is not a "here's what we would do if we wanted to" conceptual article; it is a real, hands-on, "how we did it and why" article. To read the article, click here.
Jim MacArthur is the chief engineer at Harvard University’s Electronic Instrument Design Laboratory. He has a bachelor’s degree in electrical engineering from the Massachusetts Institute of Technology (Cambridge, MA).