Scanners
SIB Labs has two devices for X-ray tomography: Nikon XTH 225 and Bruker Skyscan 1172. Skyscan is suitable for small samples with size of few cm and without metallic components. Nikon is capable of scanning samples from an ant to a basketball, and metallic samples too.
Samples can be scanned with circular scan or helical scan in Nikon XTH, and with circular scan in Skyscan 1172. Best resolution for few millimeter size samples is 2-3 micrometers.
Voltage of the X-ray tube of Nikon XTH can be between 20 and 225 kV, and power as much as 225 W. Reflection target can be changed to W, Mo, Cu or Ag.
Voltage of the X-ray tube of Skyscan 1172 can be between 20 and 100 kV, and power even 10 W.
X-ray detector in Nikon XTH is a 43 x 43 cm Varex panel with 2880 x 2880 pixels. Frame rate can be 15 fps. Standard filters vary from 0.1 mm to 1.0 mm to 2.5 mm Sn, Ag, Al and Cu.
X-ray detector in Skyscan 1172 is a scintillator and CCD camera. Field of view is 34 x 18 mm with even 4000 x 2624 pixels. Field of view can be doubled to 68 x 18 mm. Standard filters are 0.5 mm Al, and Al+Cu which is equivalent to about 2 mm of Al.
Samples in Nikon XTH can have weight as much as 15 kg. Smallest samples can be less than a millimeter, and largest even over 30 cm in diameter. A sample can be as long as 65 cm but movements are limited in that case.
Optimal samples for Skyscan 1172 are less than 3 cm in diameter and less than 5 cm in height.
A sample can be, for example, a piece of a plant or wood, plastic, metal or an item of mixture of these. An insect, a seed, a tablet or a tooth are common samples, as well as foodstuff, geological samples, a welded seam or a 3D printed object.
Smaller the sample better the resolution. For few millimeter size samples 2-3 micrometer resolution is achievable. On the other hand the resolution of a basketball is about half of a millimeter.
Materials can be pressed or stretched with maximum strength of 220 N with precision of 1 N. Travelling length is 6 mm.
Clear height is 13-22 mm, and inner diameter 20 mm.
Small samples can be cooled 50°C below ambient temperature, normally to -25°C, with precision of 0.5 degrees.
Clear height is 14 mm, and inner diameter 20 mm.
Operation
Sample must be fixed securely. The sample must not move or vaporize harmful contaminants into the chamber. Thawing or drying of the sample can cause artefacts, as well as fluid flows. A fan inside the chamber may cause air flows and detach light parts from the sample during the scan.
Scanning speed depends on many things, including resolution, sample size and material, and image optimization. Short imaging time comes true for easily penetrable, light and small samples. A dense and large sample with thick X-ray filter requires long imaging time. Additionally, image optimization settings can readily multiply the imaging time.
At SIB Labs projection images are from cone beam scans. Skyscan NRecon calculates slices with a Feldkamp algorithm from 16 bit tiff images. Slices can be saved to 16 bit tiff, 8 bit bmp, 8 bit jpg, or DICOM image file format. Nikon CTPro3D can save reconstructed volume also to Volume Graphics format.
In the course of reconstruction one can use beam hardening, scatter reduction, smoothing, or some image processing filters.
In Skyscan NRecon reconstruction volume can be demarcated with rectangles, squares, ellipses or circles. In addition, a scale can be added. In Nikon CTPro3D reconstruction volume is demarcated with a right-angled parallelogram.
Skyscan CT-Analyser accepts binary images and 8 bit bmp images. During the transform 16 bit to 8 bit image one can narrow down gray scale in order to optimize the range of 256 gray levels.
One can measure angles, lengths, areas, and save coordinates. The area and volume for analysis can be demarcated with rectangles, squares, ellipses or circles, or with a manually drawn polygons.
In analysis of binary images white pixels are calculated in different ways. Analysis results are practical only if one is very thorough in binarisation and demarcating phases of the analysis volume.
In Volume Graphics Studio Max we have analysis modules for coordinate measurements, porosity / inclusion, fiber composite materials, and foam / powder analysis.
Series of slices can be easily studied with Skyscan DataViewer. DataViewer allows to reorient, resize, and resave data, narrow grayscale, and measure the density and distance between pixels.
Images can be manipulated with common image processing softwares. One can, for example, make false-colour images, use filtering, extract features, or recognize patterns.
Original slices are allways reconstructed in a particular direction. However, slices can be studied and resaved in the direction one desires.
Here are slices of 'jauhopukki' (Tenebrio molitor). The original pixel size of slice images is 5 micrometers.
Videos can be made from slice images, binary images, or 3D-images. One can change the transparency and colour of different volume regions, if these volumes are unconnected in earlier phases of analysis procedures.
Here are Tenebrio molitor, and a larva inside a seed of a pine.
Matters worth noting
Sample must be fixed securely. The sample must not move or vaporize harmful contaminants into the chamber. Thawing or drying of the sample can cause artefacts, as well as fluid flows. A fan inside the chamber may cause air flows and detach light parts from the sample during the scan.
A common service
- planning of optimal scan, reconstruction, and analysis
- one X-ray tomographic scan
- projection images and slice images
- one analysis of standard shape region of interest (ROI) or volume of interest (VOI)
Handling the sample
- How to store the sample? What is the ambient humidity and temperature?
- Is cutting or reshaping the sample possible?
- Are any preparations needed before the scan?
- How the sample can be fixed (tape, glue or clamping)? Is the surface fragile?
- Note that the sample must not thaw or dry, or vaporize harmful contaminants into the chamber.
- Surface contamination? Safe handling? Operational safety bulletin?
- How to handle and dispose the sample after the scan?
The idea of the scan
- What is the sample, and what is the size of it? How many samples there is?
- What is the purpose of the scan? Do one scan the whole sample or only some part of it?
- Is there a standard procedure for scanning or analysis?
- What is the scale of the features? Do you want a certain pixel size in the images?
- Do you need density measurements? What is the range of attenuation (or density) inside the sample?
- Do you need analysis in 2D or 3D?
- How to define the region of interest (ROI), or the volume of interest (VOI)?
- What parameters one needs to calculate?
- Do you need filtered slice images or 3D-stl file?
- Are false-colour images needed? How about 3D-images (stl) or videos in colours?
Use of images and results
- Can we (the University) utilize the images or results in teaching, or research, or publishing, or public marketing?
- Is there confidential documents or information?
- How to handle the documents and material a client may deliver?
- What is the content of the report? On paper or digitally?
- What files a client wants or needs? Storage media or digital delivery?
- What is the desired schedule?
