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Unsupervised learning approaches to characterizing heterogeneous samples using X-ray single-particle imaging

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journal contribution
posted on 17.05.2022, 05:16 authored by Y Zhuang, S Awel, A Barty, R Bean, J Bielecki, M Bergemann, BJ Daurer, T Ekeberg, AD Estillore, H Fangohr, K Giewekemeyer, MS Hunter, M Karnevskiy, RA Kirian, H Kirkwood, Y Kim, J Koliyadu, H Lange, R Letrun, J Lübke, A Mall, T Michelat, AJ Morgan, N Roth, AK Samanta, T Sato, Z Shen, M Sikorski, F Schulz, JCH Spence, P Vagovic, T Wollweber, L Worbs, PL Xavier, O Yefanov, FRNC Maia, DA Horke, J Küpper, ND Loh, Adrian MancusoAdrian Mancuso, HN Chapmanc, K Ayyera
One of the outstanding analytical problems in X-ray single-particle imaging (SPI) is the classification of structural heterogeneity, which is especially difficult given the low signal-to-noise ratios of individual patterns and the fact that even identical objects can yield patterns that vary greatly when orientation is taken into consideration. Proposed here are two methods which explicitly account for this orientation-induced variation and can robustly determine the structural landscape of a sample ensemble. The first, termed common-line principal component analysis (PCA), provides a rough classification which is essentially parameter free and can be run automatically on any SPI dataset. The second method, utilizing variation auto-encoders (VAEs), can generate 3D structures of the objects at any point in the structural landscape. Both these methods are implemented in combination with the noise-tolerant expand-maximize-compress (EMC) algorithm and its utility is demonstrated by applying it to an experimental dataset from gold nanoparticles with only a few thousand photons per pattern. Both discrete structural classes and continuous deformations are recovered. These developments diverge from previous approaches of extracting reproducible subsets of patterns from a dataset and open up the possibility of moving beyond the study of homogeneous sample sets to addressing open questions on topics such as nanocrystal growth and dynamics, as well as phase transitions which have not been externally triggered.

History

Publication Date

01/03/2022

Journal

IUCrJ

Volume

9

Issue

2

Pagination

(p. 204-214)

Publisher

International Union of Crystallography (IUCr)

ISSN

2052-2525

Rights Statement

Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).