2008 Woodie Awards
New MRI Technology for Better Diagnoses
Professor Susan Kohler; Chemistry Department
Issue date: 11/1/07 Section: Sci/Tech
Many of you are probably familiar with Magnetic Resonance Imaging (MRI). It is an imaging technique that has developed over the last twenty years to become one of the premiere diagnostic imaging modalities. It can provide amazingly detailed images of the soft tissue in your body, and is used routinely to detect and diagnose problems ranging from head trauma to sports injuries to cancer. What you may not know about MRI is that a lot of the development of MRI has taken place right here in the Schenectady area at the research headquarters of General Electric and Intermagnetics General (now part of Philips). An interesting exhibit on MRI has just opened at the Schenectady Museum, just a few blocks from campus.
MRI is based on a technique called Nuclear Magnetic Resonance (NMR) that has been used by chemists since the 1960s as a spectroscopic technique to identify and characterize chemical compounds. The basic idea behind this technique is simple: You place a sample in a magnet, shine radiofrequency "light" at it, and see which frequencies of this light are absorbed ("resonate" with) the nuclei. In other words, certain Nuclei when placed in a Magnetic field will Resonate (absorb) radiofrequency light. This is useful for chemists, since the frequencies that are absorbed depend on the chemical environment of the nuclei. By looking at a spectrum of the frequencies absorbed, we can identify the molecules in our samples. Usually we look at the resonance of hydrogen or carbon nuclei. Only one percent of the naturally occurring carbon is 13C (most is 12C) and NMR is not a very sensitive technique, so it can take a lot of signal averaging to get a good carbon spectrum.
MRI takes NMR a step further by adding magnetic field gradients that cause the magnetic field to vary in space. Since the magnetic field now varies in space and the resonance frequencies depend on how strong the magnetic field is, we can get spatial information that can be used to mathematically generate an image. Almost all of the MRI images are based on the 1H nuclei in our bodies, which are predominantly in the water and fat. Most of the soft tissue in our bodies is water and/or fat, so MRI is a great technique for imaging our soft tissue. There are some techniques that combine MRI and NMR spectroscopy so that we can get both spatial images and local chemical information, but traditionally these techniques take a long time (because NMR is not very sensitive) and usually only detect a few chemical compounds containing hydrogen.
MRI is based on a technique called Nuclear Magnetic Resonance (NMR) that has been used by chemists since the 1960s as a spectroscopic technique to identify and characterize chemical compounds. The basic idea behind this technique is simple: You place a sample in a magnet, shine radiofrequency "light" at it, and see which frequencies of this light are absorbed ("resonate" with) the nuclei. In other words, certain Nuclei when placed in a Magnetic field will Resonate (absorb) radiofrequency light. This is useful for chemists, since the frequencies that are absorbed depend on the chemical environment of the nuclei. By looking at a spectrum of the frequencies absorbed, we can identify the molecules in our samples. Usually we look at the resonance of hydrogen or carbon nuclei. Only one percent of the naturally occurring carbon is 13C (most is 12C) and NMR is not a very sensitive technique, so it can take a lot of signal averaging to get a good carbon spectrum.
MRI takes NMR a step further by adding magnetic field gradients that cause the magnetic field to vary in space. Since the magnetic field now varies in space and the resonance frequencies depend on how strong the magnetic field is, we can get spatial information that can be used to mathematically generate an image. Almost all of the MRI images are based on the 1H nuclei in our bodies, which are predominantly in the water and fat. Most of the soft tissue in our bodies is water and/or fat, so MRI is a great technique for imaging our soft tissue. There are some techniques that combine MRI and NMR spectroscopy so that we can get both spatial images and local chemical information, but traditionally these techniques take a long time (because NMR is not very sensitive) and usually only detect a few chemical compounds containing hydrogen.