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Detecting Chemicals Through Bone

Posted by Unknown on from the full-of-poison dept.

MTorrice writes "To understand the brain and its chemical complexities, researchers would like to peer inside the skull and measure neurotransmitters levels as the brain at work. Unfortunately, research methods to measure levels of chemicals in the brain require drilling holes in the skull, and noninvasive imaging techniques, such as MRI, can't detect specific molecules. Now, as a first step toward a new imaging tool, chemists report they can detect molecules hidden behind 3- to 8-mm-thick bone."

7 of 23 comments (clear)

  1. Drill, baby, drill by Travis+Mansbridge · · Score: 5, Funny

    Trepanning always gets a bad rap.

  2. Question by excelsior_gr · · Score: 3, Interesting

    Isn't MRI practically NMR? NMR is used for chemical analysis. Then how come MRI machines can't be programmed to do the same?

  3. It's NUCLEAR magnetic resonance by localroger · · Score: 3, Interesting

    NMR only reports the presence of (certain isotopes of) nuclei. With most biochemicals of interest being made almost entirely of the same four atoms (carbon, hydrogen, oxygen, and nitrogen) there's nothing to tell the MRI which particular large molecule the atoms are part of.

    --
    Brackets contain world's first nanosig, highly magnified:[.]
    1. Re:It's NUCLEAR magnetic resonance by Anonymous Coward · · Score: 3, Informative

      NMR only reports the presence of (certain isotopes of) nuclei. With most biochemicals of interest being made almost entirely of the same four atoms (carbon, hydrogen, oxygen, and nitrogen) there's nothing to tell the MRI which particular large molecule the atoms are part of.

      Are you sure you know what you're talking about?

      NMR spectroscopy perhaps the most powerful analytic technique in modern organic chemistry -- it works on molecules as simple as hydrocarbons and as complex as proteins. Information is extracted from the fact that the resonant frequency of a hydrogen atom changes slightly depending on the nearby atoms. This has to do with the shielding of the nuclei by electrons. It's really amazing what it can do -- you can detect not only the different functional groups, but also their relative numbers and positions in the molecule.

      The relatively small "alphabet" of biomolecules is certainly no barrier to NMR spectroscopy.

      The answer to the GP's question, by the way, is that NMR spectroscopy requires a pure substance. If you tried to do NMR spectroscopy on someone's head, you would probably just get the overlapping spectra of every molecule in the head. Not too helpful.

    2. Re:It's NUCLEAR magnetic resonance by venicebeach · · Score: 4, Interesting

      The summary is overly dismissive of existing techniques.

      In addition to MR spectroscopy, chemical activity in the brain can be measured with techniques like PET and SPECT.

      All of these techniques have their advantages and disadvantages, and its certainly always great to have new options.

  4. Spectroscopy with MRI by DrLudicrous · · Score: 3, Informative

    Disclaimer: I am a physicist who works in MRI. MRI can be used to measure concentrations of certain biochemicals. MRI is sensitive enough to different proton-containing species that the frequency difference between fat and water causes image artifacts that can pose great difficulty. Not all biomolecules are sufficiently concentrated in the brain, or have a spectrum that is unique enough to be measured in vivo. A good example of a brain chemical that can be measured is N-acetyl aspartate (NAA), which has a proton peak at around 2 ppm that doesn't overlap with much else. Magnetic resonance spectroscopy is very difficult, and is most easily accomplished on research scanners operating at 3 tesla or higher. The reason for this is that rather than letting all hydrogen nuclei contribute to one signal that is then spatially located, one must parse what kinds of nuclei (i.e. what their chemical shift is) within each voxel. This not only imposes technical difficulties, but reduces the signal to noise ratio, potentially requiring more signal averaging in order to see sufficient signal above the noise floor.

  5. MR Spectroscopy by Qwerpafw · · Score: 2

    The article summary is incorrect. MR Spectroscopy (MRS) is used today to measure molecules inside the brain. Resolution is not great for 3D MRS in clinical applications (due to the tradeoff between SNR and resolution, acquisition times are slow), but it's more than high enough to distinguish between different regions of the brain. And it's very common to perform single-voxel imaging and only get the spectroscopy for a given piece of tissue - for example, where a tumor is located.

    MRS easily detects metabolites and ratios, like choline, NAA, as well as things like lipids, and alcohols. It requires expensive scanners, but it works and is used routinely in brain imaging today. The article mentions something that does not work clinically, and is being demonstrated in a lab with a piece of meat. The technology in the article is not a "first step" to understanding molecules in the brain, because we already have that technology today with MRS.