Computed Tomography

tomo (ancient Greek): cut (noun)
graphein (ancient Greek): write (verb)

The principle of industrial computed tomography (short: CT) is very similar to medical CT. In both cases you can view the inside of an object without actually opening it.

Typical tasks are
- detection of shapes and structures
- determination of dimensions and location
- detection of defects
- control of completeness and function

The key components of a CT system are just a few:
The rays of the X-ray source radiograph the test object, that usually rotates on a turntable. Finally they are detected by a detector. The distances between these components can be changed using a manipulator. The entire arrangement is encased in a protective lead shielding, so that the system operators are not exposed to radiation.
For each angular position of the turntable, the detector elements record the radiation intensity. These data are calculated into 3D data and visualised by a computer.



Various CT Methods:

Fan Beam Tomography (2D CT)
The radiation source casts its rays in a fan shape through the object to a linear detector.

Advantage:
high detail resolution
very little scattered radiation
fast generation of a single slice image

Disadvantage:
long scanning times for volume scans

This method is used for defect checks and dimensional measurement, particularly for thick-walled objects.

Cone Beam Tomography (3D CT)
The X-ray source casts its rays in a cone shape through the object to a flat-panel detector.

Advantage:
short measuring times

Disadvantage:
scattered radiation, especially in thick-walled objects

This method is used for:
- visualization of internal structures
- defect checks (e.g. porosity)
- dimensional measurement

Helix CT
The rotating test object is simultaneously moved lengthwise.

Advantage:
investigation of long objects improved level of detail

Disadvantage:
longer measuring times than with 3D CT

Region of Interest CT (ROI CT)
This special technology makes it possible to scan objects that are wider than the beam cone.

Advantage:
inspection of large objects
high level of details in partial areas

Disadvantage:
only partial areas are inspected

This method is used for:
inspection of connection technology (welding seams, rivets, adhesive joints), e.g. in automotive engineering

Transverse CT
In this case, the X-ray source and the detector move in opposite directions, while the object is fixed.

Advantage:
examination of objects with very large dimensions

Disadvantage:
With increasing distance from the focal point, the image sharpness continuously decreases.

Is used for: objects that cannot be rotated.