Selected Scan Image Acquisition and Reconstruction Parameters
| Parameter | Set Value | Parameter Description | |
|---|---|---|---|
| Scan image acquisition | Energy source (voltage, current) | 100 kV, 100 µA | Source 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 filter | Al 0.5 mm + Cu 0.038 mm | Filter 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 resolution | 2k (1632 × 1092) pixel setting with a length of 15 µm | Pixel 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 time | 2575 ms | Exposure 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 step | 0.3° up to 180° | A projection image is generated at each rotation step. Generally, smaller rotation steps produce higher quality projections. | |
| Frame averaging | 7 frames | Multiple projections are averaged at each rotation step to reduce background noise. | |
| Vertical random movement | 100 µm | The sample is moved up and down between projections at random distances within 100 µm to reduce ring artefacts (described below). | |
| Image reconstruction | Beam hardening | 45% | 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 smoothing | 1 | Postcorrection smoothing can reduce background noises and is held constant between scans if the material and scan settings are identical. | |
| Ring artifact correction | 2–4 | Ring 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 compensation | Variable | Misalignment compensation values are visually assessed for the best alignment within a reconstructed slice. | |
| Reconstructed cross-sectional images | 550 | The 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. |