BRUKER MICRO-CT ACADEMY

A warm message to all microCT enthusiasts

In these uncertain times, we are doing our best to help anybody and will continue to support our customers, also remotely. Therefore do not hesitate to contact microCT applications team if you have any questions when analyzing your data.

Stay healthy!

All about flat-fields: The why, when and how of flat-field corrections

The foremost subject of this newsletter is on what most of you will think of as a routine task in the everyday scan set-up: flat-fields corrections! If you don’t think of them as a routine task right now, hopefully you will after reading this newsletter and the Method Note 129 Flat Field Corrections.

Flat-field corrections are background corrections that are a necessity for good quality and reproducible scans. This software solution ensures that the background of any scan is always represented in the same grayscale level and normalizes the pixel response variation of the x-ray detector (or camera). This correction also makes sure that certain artefacts correlated with the detector response, either a CCD or CMOS (also Flat Panel), such as ring artefacts, are minimized. Furthermore, because the flat-field correction is correlated to the detector response, any change in scan parameters that affects the detector requires a flat field update. This means that when changing voltage, current, power, filter, exposure time and resolution (binning mode) the flat-fields should be updated before scanning. It is also recommended to update them each day, even if the scan parameters stay the same throughout a study for all the samples, preferably before any scanning starts. If this is not done then the possibility exists that an out-of-date flat-field will be used and certain artefacts will become prominent, such as rings or intensity differences between scans. This could happen for example when loading previously taken flatfields from a configuration file.

Figure 1. a detector image without the flat-field correction, showing intensity variation due to the x-ray cone beam and the honey comb shaped pattern of the fiber optic bundles in the SKYSCAN1276.

Figure 2. shows the uniform background of the detector image after updating the flat-field correction in the SKYSCAN 1276.

Image of the Month

This microCT-scanned fiber sample was collected from a small piece of cotton fabric found in a burial belonging to a 20–30 years old woman in northern Finland. The fabric was preserved on a belt’s silver ring. During the late 14th and early 15th centuries cotton was a rare import product from Asia.

This fiber was scanned with a SKYSCAN 2214 with voxel size 0.7um.
Courtesy of Mikko Finnilä (faculty of medicine) and Sana Lipkin (archeology) of the University of Oulu, Finland.

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