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The University of Southampton
µ-VIS: Multidisciplinary, Multiscale, Microtomographic Volume Imaging

Frequently asked questions (FAQ) and answers

I am not a University of Southampton researcher. Can I still access the facility?

Yes! The centre provides both academic and industrial consultancy services. We are working hard to provide accessible and top-quality X-Ray imaging services to a wide range of users. This includes external academic researchers and the industry.

Find out more here.

How much does a CT scan cost?

Beam-time is costed by session rather than "per scan" basis. Prices vary depending on the nature of the project; i.e. internal/external academic or industrial project. Representative figures are listed here and can be used for guidance. However, as each project presents unique technical challenges. Most of the times, especially when specimen type or geometry is nonstandard, we will perform trials/sanity checks in close consultation with users before funds are committed.

Please contact us with specific queries and we will be pleased to provide a quote.

How long does it take to acquire an scan?

Scanning times vary significantly. In principle it depends on the geometrical characteristics of the specimen, its material (electron density) and the system/hardware arrangement that needs to be used. Your scientific aim and objectives can also influence the scanning time. For example, one might need to limit scanning duration to "capture" time-critical processes for 4D-CT (e.g. S.D. Keyes et al.; scan duration 7 min per volume) in the expense of contrast or noise. Equally, when high resolution and low noise conditions are required for the analysis one might choose to increase scanning time (e.g. SM Yusuf et al.; scan duration 20 h per volume).

In general, scan duration can increase rapidly if resolution below 2-3 µm is sought, and/or underlying contrast is low (i.e. distinguishing subtle density changes in materials of similar atomic makeup). The following set of rules should be kept in mind:

Shorter scanning times can be achieved when

  • the specimen is not very dense (e.g. polymeric materials)
  • the features of interest within the specimen exhibit good density contrast against the surrounding matrix (e.g. air pores in organic matrix)
  • the features of interest are fairly large in proportion to the overall size of the specimen (e.g. Smarties in candy tube)

Longer scanning times should be expected when

  • the specimen is dense (e.g. rock, fossils, metals)
  • the features of interest within the specimen exhibit poor density contrast against the surrounding matrix (e.g. soft tissue embeded in parafin wax)
  • the features of interest are small in proportion to the overall size of the specimen (e.g. grains of sand in a 30 mm diameter core)
  • low noise conditions are required

To get a more accurate scan-time estimate, please contact us to discuss your sample and imaging requirements.

Are there sample preparation and mounting requirements?

The sample should be mechanically stable and stationary, both inside and out, for the duration of the scan. Scan durations vary from a few minutes to many hours (see above). For most solid/rigid objects this is not an issue: samples containing liquid, visco-elastic, loose-packed powder or living material may require packing, physical support, cooling etc.

If the sample is to be kept within a container during scanning (e.g. to maintain moisture levels), it is best to minimise the density, thickness and external dimensions of the container. Simple polymer tubes/vials are ideal (e.g. see here). A conforming polymer wrap (cling film) can be ideal in self-supporting objects.

Samples MUST NOT shed any material (e.g. liquids or powder) into the CT equipment. If there is any risk, then some form of containment must be used.

What's the voxel resolution your scanners can achieve?

The range of equipment available in the centre allows a continuous voxel (3D pixel) size range that spans from hundreds of micrometres to hundreds of nanometres. However what's achievable in each case largely depends on the specimen.

A useful rule of thumb to find out the smallest voxel size achievable for a cuboid specimen scanned using a "default" imaging protocol is to measure its larger dimension (in mm) and divide that by 2000. The result will be the voxel-size (in mm) of a scan using a 2000 x 2000 pixels detector with the entire specimen fitting tightly in the field of view. 

However other, non-standard, acquisition techniques can push the envelope further.

If you are unsure as to what is possible with your specimens please get in contact with us to discuss your sample and imaging requirements.

What's the biggest/heaviest specimen you can scan?

The largest field of view can be achieved by our custom walk-in scanning room (Custom 450/225 kVp Hutch) is approximately 1x1x1.2 m and can support specimens up to 100 kg.

 

Do you accept all type of specimens?

We would scan most type of specimens our equipment can scan provided they are no safety and/or ethical issues associated with them. We always reserve the right to refuse scanning any specimen we think that might endanger the safety of personnel or equipment.

How can I submit a scan request and what do you need to know about my project?

If you are an internal or external academic user or Part III/MSc student wishing to submit a scan request please fill the appropriate "scan request" form located under the Access menu. All we need to know is described in the form. 

If you are an industrial customer please contact us directly

What kind of images are generated during CT data acquisition?

A set of 2-D images (usually called angular projections or radiographs) is captured at different angular positions as the sample is rotated during the scan. These projection images contain information about the attenuated X-ray beam, which passes through the sample.

Grey-scale values of pixels and their variation in angular projection images represent changes in the attenuation coefficient and therefore local density of the sample.

What kind of 3-D datasets are reconstructed from the set of 2-D radiographs?

An acquired set of 2-D angular projections is reconstructed into a 3-D rectangular grid composed of cuboidal building blocks known as voxels, which grey-scale values correspond to the linear attenuation coefficients of the sample material in these elementary volumes.

This 3-D volumetric map of linear attenuation coefficients can also be reconstructed as a stack of 2-D cross-sectional slices. CT reconstruction can be used for visualisation and quantification work, e.g. detection, extraction and measurement of features of interest. Volumetric datasets can also be converted into high-fidelity finite element meshes and CAD models.

What kind of data should I expect to find in my CT data folder?

A typical CT data folder contains [a] the raw projection data underlying the CT scan and [b] the raw reconstructed volume data (i.e. the "3D volume" file).

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