N.De Clerck & A.Postnov: “X-ray microtomography in biomedical research”

Questions for the students
For some questions several choices are correct

1. Why do we use polychromatic X-rays for micro-CT?

• a. They penetrate better than monochromatic X-rays
• b. They are easy to generate in a table-top system
• c. They provide better contrast
• d. They allow to study objects with variable dimensions

2. Why filtering of polychromatic X-rays may become necessary?

• a. To reduce beam-hardening
• b. To reduce radiation dose when in vivo studies are performed
• c. To prevent detector damage
• d. To increase resolution

3. Why is back-projection algorithm so popular for reconstruction?

• a. It provides the best accuracy of reconstruction
• b. It is fast and robust
• c. It is suitable for modern processors
• d. It allows us to compensate for acquisition errors

4. Is it possible to compensate all the differences in CCD pixels response?

• a. No, because we cannot measure them
• b. The question is not valid because there is not much difference
• c. Flat field correction does this perfectly
• d. Flat field correction improves the situation only partially

5. Why do we need to use fibre glass optics in a X-ray CCD detector?

• a. It allows to change field of view
• b. It protects CCD from radiation damage
• c. It allows to count each photon separately
• d. It is necessary as a substrate for a scintillator

6. What made micro-CT appear in the late 1990’s.

• a. Advances in X-ray sources
• b. Advances in computer calculation speed
• c. Progress in X-ray detectors
• d. Demand from the scientific society (this means that it was possible earlier but that there was no need for such an instrument)

7. Why is micro-CT not frequently used to visualize tumors in soft tissues or to visualize inner organs of laboratory animals (in contrast to medical CT)

• a. Inner organs and tumors do not absorb enough X-rays of the energies that are used for imaging
• b. Density resolution of micro-CT is less than of medical CT
• c. Spatial resolution of micro-CT is not enough
• d. X-ray detectors for micro-CT systems are not sensitive to the energies that are absorbed in the mentioned tissues

8. What are the unique advantages of micro-CT (and medical CT) that are not available in other complementary techniques (like MRI, PET, SPECT etc.)?

• a. Short and variable acquisition time
• b. 3D imaging
• c. Possibility to investigate dense materials (bones, metals)
• d. Isotropic resolution
• e. Safe for living animals/patients
• f. Almost no limits for theoretical spatial resolution

9. Is it possible to define true bone parameters with micro-CT?

• a. Yes, that is what we do
• b. No, bone parameters are always wrong and serve for illustration only
• c. No, bone parameters are not correct but can be compared if the same reconstruction and threshold parameters are applied to all datasets
• d. No, bone parameters are very sensitive to instabilities in scanner performance

10. Indicate correct statements for in vivo scanning

• a. Compromise should be made between exposure time and density resolution
• b. All motion artefacts can be compensated
• c. Spatial resolution for small animal studies can be higher than for humans
• d. Anaesthesia is always required

The correct answers can be seen HERE (password needed!)