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Massively Parallel X-Ray Holography

Posted by Soulskill on from the thank-you-for-not-inventing-a-witty-acronym dept.

Roland Piquepaille writes "An international group of scientists has produced some of the sharpest x-ray holograms of microscopic objects ever made. According to one of them, they improved the efficiency of holography by a factor of 2,500. In order to achieve these spectacular results, they put a uniformly redundant array next to the object to image. And they found that this parallel approach multiplied 'the efficiency of X-ray Fourier transform holography by more than three orders of magnitude, approaching that of a perfect lens.' Besides these impressive achievements, it's worth noting that this technology has been inspired by the pinhole camera, a technique used by ancient Greeks. 'By knowing the precise layout of a pinhole array, including the different sizes of the different pinholes, a computer can recover a bright, high-resolution image numerically.'"

11 of 41 comments (clear)

  1. Lack of Disclaimer by Graff · · Score: 4, Funny

    The hologram of the Spiroplasma bacterium was made in precisely the same way, with much brighter x-ray beams and a much shorter pulse of light. So bright was the flash of light that the sample was vaporized

    I guess this means they can't use the disclaimer: "No bacteria were harmed in the making of this hologram."

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    Sapere aude!
  2. Re:One important note by Iamthecheese · · Score: 4, Insightful

    *cough*tissue sample*cough*

    --
    If video games influenced behavior the Pac Man generation would be eating pills and running away from their problems.
  3. "Computer processing improved the resolution" ? by gardyloo · · Score: 4, Interesting

    I'm a bit skeptical. Whatever information one can get is present in the original diffraction pattern. "Processing" *probably* means interpolation, or convolution with the known regular array. One can only keep the same information already present, or lose information in this way. They probably mean that the pattern was smoothed so as to look nicer to the eye (which is certainly valid), but I doubt they increased resolution in any way.

    1. Re:"Computer processing improved the resolution" ? by gardyloo · · Score: 4, Informative

      The arxiv paper (referenced elsewhere in these posts) mentions that the obtainable information drops rapidly at 75nm. Their phase-recovery algorithm, combined with the snr inherent in the system, conspire to do this. It's really not a function of the computer post-processing (which can't, after all, improve the image resolution). The caption on one of the figures in the linked article is simply a little misleading; however, the entire article is quite good. Science reporting ftw!

    2. Re:"Computer processing improved the resolution" ? by Raven737 · · Score: 4, Informative

      i'm no expert, but i think by 'processing' they mean the fourier transform that is needed to get a 'usable' image from the hologram.
      So, no interpolation, but a kind of signal processing, sort of like what your cell phone/wifi does to make sense a jumble of transmissions.
      Check out:
      http://www-group.slac.stanford.edu/ais/publicDocs/presentation71.pdf

    3. Re:"Computer processing improved the resolution" ? by FilipeMaia · · Score: 5, Interesting

      By post processing they mean the phasing algorithm. The imaging method is divided in two parts. First they recover a low resolution image of the object that was imaged by looking directly at the hologram and deconvoluting with the known pinholes (in this case a Uniformly redundant array (URA), which assures that the deconvolution is well behaved). This step cannot achieve a resolution higher than the size of the pinholes in the URA. In a second step the entire image is phased, meaning that an algorithm is aplied to it that tries to mimick a lense. This increases the resolution obtained to the maximum possible, that is to the limit of the numerical aperture.

    4. Re:"Computer processing improved the resolution" ? by Graff · · Score: 4, Informative

      Whatever information one can get is present in the original diffraction pattern. "Processing" *probably* means interpolation, or convolution with the known regular array. One can only keep the same information already present, or lose information in this way. They probably mean that the pattern was smoothed so as to look nicer to the eye (which is certainly valid), but I doubt they increased resolution in any way.

      It's not that the computer processing improved the resolution, it's that the computer processing is a necessary part of the process which improves the resolution.

      This article talks about taking normal x-ray radiation and using that to make a hologram. Holograms are usually made from laser illumination because a laser beam is coherent light, light in which the waves are all in phase (in step) with each other. It is difficult to make an x-ray laser but there is another way to get coherent light and that is through the use of pinholes.

      The major problem of pinholes is that the smaller they are the less light is let through so the dimmer the image. However a large pinhole produces a very inaccurate (low resolution) image. One answer is to use a lot of small pinholes in the place of a few large pinholes. This is a great solution which produces sharp, bright images but now there is an additional problem, each pinhole makes a separate image and all these pinholes cause multiple overlapping images, offset a tiny bit from each other. This is where the computer works. Since the original pinhole pattern is known (you created it) you can feed that pattern into the computer and it can use that pattern to "slide" all the overlapping images so they exactly fit on each other. This makes a single, bright, sharp image.

      The computer is not increasing the resolution of the detector, that's fixed. What it is doing is working as part of a process to produce better images.

      --
      Sapere aude!
    5. Re:"Computer processing improved the resolution" ? by Graff · · Score: 4, Informative

      Actually, after going back to the article and re-reading it I find that they are using pinholes to produce coherent reference light but they are only using two of them to do this, not a pattern of many of them. In the method described in the article the pattern is instead off to one side of the object to be imaged. It appears that they are using the pattern to deconvolute the final image. Since the pattern is known you can use a deconvolution function based on that pattern to re-create the original pattern in the image. This has the side effect of correcting the image of the object you wish to view, increasing the resolution of the image.

      In essence they are using the pattern to calibrate their instrument in order to improve the imaging.

      --
      Sapere aude!
  4. A related .pdf on arxiv here: by gardyloo · · Score: 5, Informative

    http://arxiv.org/PS_cache/arxiv/pdf/0801/0801.4969v3.pdf

  5. Re:One important note by Pope+Raymond+Lama · · Score: 4, Informative

    It can't be used on living organisms as it causes instant cancer and death. Sorry, Bob.

    Actually, from TFA:
     

    So bright was the flash of light that the sample [bacteria] was vaporized, but not before both the scattered object beam and the reference beams from the URA had been recorded.

    Indeed, as one can see, the part of "instant death" is quite accurate.

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    -><- no .sig is good sig.
  6. "2500 times more efficient" can mean... by jeffb+(2.718) · · Score: 3, Interesting

    2500 times better signal/noise, or (I think) 50 times better resolution, or 2500 times shorter exposures, or 2500 times less radiation intensity.

    Conventional X-ray and CT imaging are vastly different from X-ray holography, but this research might well end up contributing to those modalities as well. Everyone would be very happy to get useful resolution with vastly lowered exposures.