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The Physics and Image Processing of Cryo-ElectronTomography and the Estimation of Resolution using the Programs MOTIONCOR2 1.0.2 and CTFFIND 4.1.8
Umeå University, Faculty of Science and Technology, Department of Physics.
2019 (English)Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
Abstract [en]

We present a brief overview of the physics of cryo-electron tomography (cryo-ET) and the Image Processing related to this field. This serves as an introduction for readers unfamiliar with cryo-ET and as a background to the second part of the report, which concerns the programs CTFFIND and MOTIONCOR2. We correct tiltseries for sample motion with two different settings with MOTIONCOR2: with (only) Global Motion Correction and with Global+Local Motion Correction (5x5 patches). Then, using CTFFIND, we estimate the resolution in the tiltseries for the data sets without Motion Correction, with (only) Global Motion Correction, and with Global+Local Motion Correction, and make an assessment of the reliability of CTFFIND as a program for estimating the resolution. A total of 410 images were analyzed (10 tiltseries of 41 images each). When considering mean resolutions, we find CTFFIND to be useful and reliable, particularly when differences in means are of interest (e.g. differences between angles or defoci). However, due to e.g. the sensitivity of CTFFIND with respect to input parameters, we conjecture that CTFFIND is less reliable when individual images are analyzed, particularly when absolute resolutions are of interest. Provided that CTFFIND is accurate enough for a statistical analysis with respect to resolution, which we believe it is, the average increase in resolution when (only) Global Motion Correction is used for tiltseries from -60° to 60° with defocus -3 μm is around 0.9 Å (246 images analyzed). For defocus -5 μm, the equivalent average increase in resolution is around 1.1 Å (164 images analyzed). Results indicate that resolution is roughly linearly proportional to the magnitude of the tiltangle. The average difference in resolution between data sets with (only) Global Motion Correction and Global+Local Motion Correction for both defocus -3 μm and -5 μm is 0.0 Å, for two significant figures. This suggests that the sample motion is predominantly Global. For defocus -3 μm and -5 μm, there is a confidence level of 95% that if only Global Motion Correction is applied to a large set of tiltseries, a majority of the images will have a resolution that is higher than the images in the same set to which Motion Correction has not been applied (when corresponding images are compared). In an equivalent statistical analysis, we can not claim that either “(only) Global Motion Correction” or “Global+Local Motion Correction” is superior.

Place, publisher, year, edition, pages
2019.
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Other Physics Topics
Identifiers
URN: urn:nbn:se:umu:diva-165518OAI: oai:DiVA.org:umu-165518DiVA, id: diva2:1372957
Subject / course
Fysik D - examensarbete II
Available from: 2019-11-28 Created: 2019-11-25 Last updated: 2019-11-28Bibliographically approved

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CiteExportLink to record
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Citation style
  • apa
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  • de-DE
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  • Other locale
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