Abstract: Micro-CT imaging of objects at very high magnification runs into the
problem of small geometric movements of the x-ray emission spot relative to the
object, thermally induced or otherwise, causing magnified shifts in the
projection images during scanning. This produces movement artefacts in the
reconstructed images. Here a technique is described to correct such movements
by adding a short reference scan at the end of a high magnification scan, with
a very large rotation step. Where geometry changes during a scan are slow, such
movements can be considered minimal during this very short "post-scan".
Registration of the post-scan images with corresponding images in the main scan
allow X/Y pixel shifts in the projection images associated with the geometry
movement to be calculated, and corrected during reconstruction. This post-scan
correction method was applied here to scans of three small objects, all with a
voxel size less than one micron, in a desktop micro-CT and a nano-CT scanner.
The method substantially reduced movement artefacts from the reconstructed
images, improving image quality and resolution. Where the geometry movement
results largely from thermal movement of the x-ray micro-focus emission spot,
the post-scan method allows the reconstruction of the spatio-temporal
trajectory of this spot movement.
