Faster Laser-Based X-Ray Imaging

The high-performance laser in LMU’s Laboratory for Extreme Photonics, paved the way for the tomographic reconstruction of the three-dimensional fine structure of a bone sample within a few minutes. (Source: T. Naeser)

Researchers from Ludwig-Maxi­milians-Univer­sität LMU, the Max Planck Institute of Quantum Optics MPQ and the Tech­nical Uni­versity of Munich TUM have taken a major step towards the clinical appli­cation of a new laser-based source of X-rays. They recently demonstrated that the instrument enables the tomo­graphic recon­struction of the three-dimen­sional fine structure of a bone sample within a few minutes. Up to now, laser-based measure­ments of this sort took several hours. The break­through was made possible by the further development of Atlas, the high-performance laser in  the Laboratory for Extreme Photonics on the Research Campus in Garching. Reconstruction of the sample from the imaging data was also faci­litated by the use of specially designed computer programs.

The X-rays used for medical imaging or to inspect the contents of passengers’ baggage at airports are produced by X-ray tubes. Research scientists prefer to use what is known as synchro­tron radiation as an X-ray source. Synchro­tron radiation is many times brighter and thus allows one to carry out far more detailed structural analyses. However, sources of synchro­tron radiation are rela­tively thin on the ground, as its gene­ration requires the acce­leration of electrons to ultra-rela­tivistic velocity. To harness the advantages of synchro­tron radiation for general use in medicine the physicists have been exploring the application of high-perfor­mance lasers to the production of X-rays. In their set-up, hydrogen atoms are irra­diated with extremely intense pulses of laser light. The highly energetic optical fields strip the electrons from the atoms and part of the ionized plasma electrons are acce­lerated. Simul­taneously, these electrons oscillate in the plasma fields, which causes them to emit the desired synchro­tron radiation, i.e. high-intensity X-rays. Moreover, this whole process takes place over a path-length of less than 15 mm. So laser-based X-ray sources have a far smaller footprint, and are much less expen­sive to build, than conven­tional synchrotrons, but produce X-radiation of compa­rable quality.

In the early trials carried out at the Max Planck Institute in 2015, the research team was able to derive the three-dimen­sional structure of an insect from two-dimen­sional projection images taken from different angles. For the latest experi­ments, Stefan Karsch and his colleagues have boosted the pulse rate, photon yield and photon energies, and this time they chose to image a sample of human bone. Thanks to an improved proces­sing algorithm, developed by Franz Pfeiffer and his group at the TUM, the team needed to collect signi­ficantly less data than before. Accordingly, the complete tomogram could be obtained within less than three minutes.

The project was conceived and initiated in the Munich-Centre for Advanced Photonics and is under­going further deve­lopment at the Center for Advanced Laser Appli­cations (CALA) in Garching. The laser systems available at CALA are expected to signi­ficantly enhance the efficiency of the source and the quality of the radia­tion generated, thus making this new form of tomo­graphy available for clinical appli­cations for the first time. (Source: MPQ)

Reference: A. Döpp et al.: Quick x-ray microtomography using a laser-driven betatron source, Optica 5, 199 (2018); DOI: 10.1364/OPTICA.5.000199

Link: Laboratory for Extreme Photonics (LEX Photonics), Ludwig-Maximilians-Universität LMU, Garching, Germany


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