MicroCT Specimen Requirements

WHAT MATERIALS CAN BE IMAGED?

Low atomic number and density materials such as organic and biological materials, polymers, and many ceramics can be imaged. As the density and the atomic number increases, the x-ray absorption also increases. For such specimens, a small cross section is required to assure adequate transmission. As a rule of thumb plastics, and organic materials with a effective transmission thickness of 2-5 centimeters, ceramics of 1-2 cm, low density metals of 2-5 mm.  See examples here for previously processed specimens.

WHAT SIZE SPECIMEN CAN FIT IN THE MACHINE?

Specimens must fit in a volume of about 6.5 cm height by 6.5 cm diameter. For optimum performance the cross sections to be evaluation should be less than the field of view (see below). If this is not possible the specimen may still be imaged but there may be some restrictions on the shape of the component.

WHAT RESOLUTION CAN BE ACHIEVED?

Nominally, strong contrast images can be resolved down to 1 micron. If the contrast between features is not strong then the resolution is of the order of few microns (2-5 microns). Geometric features need to be few times larger than the resolution limit in order to be clearly observable. Note that when a very high resolution is sought there there may be a limit on the diameter of the specimen as the camera comes very close to the specimen.

WHAT IS THE MAXIMUM FIELD OF VIEW?

There are 3 camera settings:

  • Coarse 1000 x 500 pixels - (rapid test - few minutes)
  • Medium 2000 x 1000 pixels - (medium duration test - 0.5-2 hours)
  • Fine 4000 x 2000 pixels - (several hours 2-10 hours)

The first and second numbers denote the diameter and the height of the field of view. The camera settings and the desired resolution determine the size of the field of view. For example at medium camera settings (2K x 1K) and 5 micron resolution a volume of 10 mm diameter and 5 millimeter height can be imaged. Large volumes can be scanned at the same resolution and camera setting either by

  • wide scan: can double the diameter of the space that can be imaged (and doubles the scanning time/price)
  • oversize scan: can image sequentially and "stitch" together multiple views along the height of the specimen (the specimen is raised or lowered with respect to the camera). The scanning time (and price) is proportional to the number of views

In some cases the same sample an be scanned at different camera settings but at the same resolution. Fine camera pixels will give a larger field of view at the expense of scanning time.