Maximum likelihood methods in DIALS

Authors: James Parkhurst (Diamond Light Source) , Graeme Winter (Diamond Light Source) , David Waterman (CCP4) , Richard Gildea (Diamond Light Source) , Luis Fuentes-montero (Diamond Light Source) , Garib Murshudov (Laboratory of Molecular Biology, Cambridge) , Gwyndaf Evans (Diamond Light Source)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: Twenty-Fourth Congress and General Assembly of the International Union of Crystallography
Peer Reviewed: No

State: Published (Approved)
Published: August 2017

Abstract: In macromolecular crystallography, integration programs - such as DIALS (Waterman et al. 2013) - are used to estimate the intensities of Bragg reflections recorded on a series of X-ray diffraction images. The reflection intensities are estimated using the following procedure. A model for the shape of the reflection profile is estimated from a set of strong reflections. This model is then applied to each reflection in order to estimate the size and shape of the reflection on the detector surface and to label each pixel as either foreground or background. The intensity of each reflection is then estimated (in the case of summation integration) by summing the total counts minus the estimated background counts in the foreground region. Since the background level under the reflection peak cannot be measured directly, it is estimated from the surrounding background pixels assuming a given model.

Journal Keywords: Integration; maximum likelihood; modelling

Subject Areas: Technique Development

Technical Areas: Data acquisition , Detectors

Discipline Tags:

Technical Tags: