3D Printed IQIs for X-ray Examination

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These days, when colour images are taken of museum objects it is generally good practice to include a colour calibration chart, like a ColorChecker. This allows the captured images to be colour calibrated and then compared, with reasonable confidence, with other images captured within the same organisation or with image captured using different imaging systems by other individuals or organisations. But his is often not the case when X-ray images are taken of museum objects.

Calibration targets or Image quality Indicators (IQIs), are available[1] for X-radiography and are in fact used in some fields, but they may not be appropriate for all type of cultural heritage X-radiography. In some institutions specialists often construct their own custom IQIs to help ensure the quality of their images. This works well within an institution but is generally less appropriate when comparing images generated by different institutions.

As it is becoming easier and more common to share and compare large complex technical images between different cultural heritage institutions the need for use of consistent IQIs is becoming more important. This is also becoming an increasingly important issue when it comes to comparing X-ray images produced from analogue film and images created using new digital X-ray systems.

One possible option for producing consistent, but custom designed, IQIs, tailor made for the examination of specific groups of cultural heritage materials might be the use of new 3D-printers. This pilot study was put together to begin to explore this possibility.

3D Printed Samples

The following samples where sourced and or prepared by Carinna Parrama.

No. Printer Name Material Process Resolution Colour
1 Envision Tec Photo-cure Acylic Direct Light Projecting 25 - 50 Microns Dark Red
2 Dimension ABS Extrusion 250 Microns Black
3 SLS: EOS P385 Glass Filled Nylon Selective Laser Sintering 150 Microns Light Grey
4 Object Eden 250 Photo-cure Poly-Jet Printer 16 - 32 Microns White
5 Z-Corp Plaster of Paris Powder based system with a binder using Ink Jet technologies 100 Micorns at 460DPI Bright White

National Gallery Examination

Set-up Images

Data Processing

Image preparation

  • Each X-ray plate was scanned at 600 DPI and saved as a 1-band 16-bit tif image.
  • All additional images processing was carried out using the Nip2 software.
  • The resultant X-ray images where balanced, as required, to calibrate for slightly uneven exposure of the plates, principally some appeared slightly brighter along the side edges, see image below.
    • The images for the examinations at 50KV, 40KV and 30KV required this process.

Profile extraction

  • Using Nip2, and arrow was marked across the central length of each image of each sample wedge, see image.
Process_Wedges_Prep = class
  Menuaction (_ "Process Wedges Prep") (_ "IQIs") {
    action x = class 
      _result {
        _vislevel = 3; 
        _w = 10;
        _area = extract_arrow 0 0 _w x;
        _sa = scale _area; 
        im = image_set_type Image_type.B_W _sa;				
        pt = Mark_relative im 0.1 0.5;
        _a' = resize Interpolate_bilinear 1 (1 / _w) _area;
        _a'' = _a', pt.left < (im.width/2)
             = fliplr _a';
        _ofs = 250 - pt.left, pt.left < (im.width/2)
             = 250 - (im.width - pt.left);
        _nw = 1500;
        _bg = Image (image_new _nw 1 1 _a''.format _a''.coding _a''.type 0 0 0);
	_result = insert_noexpand _ofs 0 _a'' _bg;

Graphs of IQI profiles for given X-ray Exposures

Images of IQI X-ray examinations for given Exposures