Researchers identify noise threshold blocking X-ray imaging of proteins
Scientists have determined that background interference must stay below 60% of the signal strength for X-ray imaging to successfully map protein structures at room temperature. The finding sets a practical requirement for facilities operating billion-dollar laser instruments, helping operators decide when experiments are worth running versus when equipment needs upgrades.
Originaltitel: Coherent X-ray Diffraction Imaging of Single Particles: Background Impact on 3D Reconstruction
<p>Coherent diffractive imaging with X-ray free-electron lasers could enable structural studies of macromolecules at room temperature. This type of experiment could provide a means to study structural dynamics on the femtosecond time scale. However, the diffraction from a single protein is weak compared to the incoherent scattering from background sources, which negatively affects the reconstruction analysis. In this work, we evaluated the effects of the presence of background on the analysis pipeline. Background measurements from the European X-ray free-electron laser were combined with simulated diffraction patterns, and treated by a standard reconstruction procedure including orientation recovery with the expand, maximize and compress algorithm and 3D phase retrieval. Background scattering did have an adverse effect on the estimated resolution of the reconstructed density maps. Still, the reconstructions generally worked when the signal-to-background ratio was 0.6 or better, at the momentum transfer shell of the highest reconstructed resolution. The results also suggest that the signal-to-background requirement increases at higher resolution. This study gives an indication of what is possible at current setups at X-ray free-electron lasers, with regards to expected background strength and establishes a target for experimental optimization of the background.</p>