Selected Scan Image Acquisition and Reconstruction Parameters

ParameterSet ValueParameter Description
Scan image acquisitionEnergy source (voltage, current)100 kV, 100 µASource voltage and current are adjusted for each sample depending on its material. High absorbing materials, such as glass and aluminum, need high energy.
X-ray filterAl 0.5 mm + Cu 0.038 mmFilter placed between the X-ray source and the sample reduces the polychromaticity of the source (filtering out X-ray energies outside the target); strong filters are needed for high absorbing materials.
Pixel setting and resolution2k (1632 × 1092) pixel setting with a length of 15 µmPixel length can be adjusted by increasing the pixel setting (1k, 2k, and 4k), moving the sample, or both. Smaller pixel lengths generate images of higher resolution.
Exposure time2575 msExposure time is affected by camera position, source voltage and current, and selected filter. Higher exposure times are generally needed for higher absorbing materials; however, the detector may deteriorate faster under long high-power scans.
Rotation step0.3° up to 180°A projection image is generated at each rotation step. Generally, smaller rotation steps produce higher quality projections.
Frame averaging7 framesMultiple projections are averaged at each rotation step to reduce background noise.
Vertical random movement100 µmThe sample is moved up and down between projections at random distances within 100 µm to reduce ring artefacts (described below).
Image reconstructionBeam hardening45%Beam hardening artefacts cause the edge of an object of the same material to be brighter than the center. A procedure of postcorrection during reconstruction minimizes these artefacts. Postcorrection values are held constant between scans if the material and scan settings are identical.
Gaussian smoothing1Postcorrection smoothing can reduce background noises and is held constant between scans if the material and scan settings are identical.
Ring artifact correction2–4Ring artefacts, commonly caused by dust or miscalibrated detector elements (19), appear as concentric circles in a reconstructed slice. Their effect is reduced by applying a reduction value between 0 (not corrected) and 20 (heavily corrected).
Misalignment compensationVariableMisalignment compensation values are visually assessed for the best alignment within a reconstructed slice.
Reconstructed cross-sectional images550The number of cross-sectional images is kept constant at 550; these images encompass the top of the aluminum cap (plastic button removed) and the bottom of the vial flange.