X-ray Computed Tomography
Principles of Operation
X-ray source step-by-step rotation sample array detector X-ray source step-by-step rotation + shift sample line detector X-ray source < 360° sample detector

360°

360°

ROI high magnification

ROI low magnification

tube control

CNC object stage

data acquistion

tube control

CNC object stage

data acquistion

computed tomography / volume reconstruction

computed tomography / volume reconstruction

Cone beam CT:
Generating three-dimensional images using microfocus CT starts with the acquisition of a series of two dimensional X-ray images while progressively rotating the sample step by step through a full 360° rotation at increments of less than 1° per step. These projections contain information on the position and density of absorbing object features within the sample. This accumulation of data is then used for the numerical reconstruction of the volumetric data.

Fan beam CT:
For each slice, a set of X-ray line profiles is acquired while progressively rotating the sample step by step through a full 360° rotation at increments of less than 1° per step. The line profiles contain information on the position and density of absorbing object features within the sample slice and are the input for the numerical reconstruction of the tomographic slice image. By vertically shifting the sample through the fan beam and repeating the procedure a set of slices is compiled to obtain a representation of the volume.
Voxel l

W h a t d e t e r m i n e s t h e v ox e l re s o l u t i o n ?
In order to reproduce an accurate reconstruction of the volumetric data, the entire sample depth / diameter should remain within the field of view and cone / fan of radiation so that the full diameter is completely displayed in each projection or line profile captured in the acquisition process. Hence, the magnification is limited by sample diameter d and detector width D to M = D/d. For a detector pixel size