Module 2 - PPT – Data Acquisition Methods

Flashcards covering patient orientation, positioning, centering/landmarking, localizers, scan methods, pitch, MDCT detector configurations, and related CT data acquisition concepts.

Q1. What two factors define how a patient is set up for CT?

Orientation (head first or feet first) and position (prone or supine).

Q2. Why is correct orientation selection important?

Because it ensures images are displayed correctly; incorrect orientation can mislabel anatomy.

Q3. What is centering in CT?

Bringing the table height to the patient’s midcoronal plane and aligning to the midsagittal plane.

Q4. What is zeroing (landmarking)?

Setting the reference point or starting location for the scan.

Q5. What are localizer scans?

Low-dose radiographs (scout/topogram/scanogram) used to plan the scan.

Q6. How many localizers are usually taken?

At least two (AP and lateral).

Q7. What are the main functions of a localizer?

To determine anatomy coverage, set display field of view, and ensure correct tube current calculation.

Q8. Why is accurate centering important before localizer scans?

Because it affects scan planning and automatic tube current calculation.

Q9. What is the main advantage of axial scanning?

Slightly higher image quality.

Q10. What are disadvantages of axial scanning?

Longer scan times and higher risk of motion artifacts; limited post-processing flexibility.

Q11. Why is helical scanning most common?

It provides faster scans, less motion artifact, and more post-processing options.

Q12. What is dynamic scanning used for?

Special protocols (like perfusion), imaging the same region repeatedly to observe function over time.

Q13. Define pitch in helical CT.

Table movement per rotation divided by beam width.

Q14. What happens if pitch is high?

Faster scan, lower dose, but lower resolution.

Q15. What happens if pitch is low?

Slower scan, higher dose, better resolution.

Q16. What does MDCT detector configuration determine?

The z-coverage and the minimum slice thickness available during reconstruction.

Q17. Why is detector configuration important?

It influences scan speed, radiation dose, and resolution.

Q18. What other names are used for a CT localizer scan?

Scout, topogram, or scanogram.

Q19. Why are localizer scans considered low dose?

Because they are radiographic projections designed only for planning, not diagnostic imaging.

Q20. Which CT method is more prone to motion artifacts, axial or helical?

Axial, because it takes longer to acquire images.

Q21. Which CT method is more flexible for post-processing, axial or helical?

Helical, due to continuous data acquisition.

Q22. In which situation might axial still be preferred over helical?

When slightly higher image quality is needed and motion artifacts are less of a concern.

Q23. How is dynamic scanning similar to time-lapse photography?

The same region is imaged repeatedly over time to observe function (e.g., contrast flow, perfusion).

Q24. What is the formula for pitch in MDCT?

Pitch = Table movement per rotation ÷ Beam width.

Q25. Why does increasing pitch reduce image quality?

Because the data is more spread out, leading to lower resolution and potential artifacts.

Q26. Why does lowering pitch increase patient dose?

Because the table moves more slowly, concentrating the X-ray exposure over the same anatomy.

Q27. How does detector configuration affect z-axis coverage?

More detector rows = greater z-axis coverage per rotation.

Q28. How does MDCT enable thinner slice reconstructions?

By using multiple detector rows that allow the reconstruction of smaller slice thicknesses.

Q29. Why is slice thickness important in reconstruction?

Thinner slices = higher spatial resolution and more accurate 3D reformats, but with increased noise.