QA & QC In CT

Question 1

Excessive radiation dose from CT brain leads to?

Answer 1

Hair loss, memory loss, depression, dizziness.

Question 2

Why is conventional radiography inferior to CT?

Answer 2

You can see small density differences of 5% whereas CT combines multidirectional projections & digital filtering coupled with high sensitivity detectors to differentiate densities of 0.5%

Question 3

A Brain CT is the equivalent to how many chest x-rays?

Answer 3

100

Question 4

List 5 ways to manage radiation dose in CT.

Answer 4

• Justification
• Optimisation
• Monitoring of local DRL’s & compare with national DRL’s
• Assessment of status of CT scanner on installation.
• Ongoing monitoring of scanner ensuring consistency of Image Quality & Safety.

Question 5

The procedure of verifying that a system is operating optimally is..?

Answer 5

Quality Assurance

Question 6

The procedure of verifying that CT is operating with specifications is..?

Answer 6

Quality Control

Question 7

List 3 essential phantoms.

Answer 7

• Water phantom
• Slice thickness phantom
• MTF phantom/ High Contrast Phantom

Question 8

What does MTF stand for?

Answer 8

Modulation transfer function.

Question 9

List the 8 checks of the constancy test.

Answer 9

• Correct phantom inserted.
• Phantom position correct.
• Position of lightmarker.
• Real slice thickness.
• Homogeneity
• Noise
• MTF
• Table positioning

Question 10

What phantom is used in the noise test?

Answer 10

Water phantom.

Question 11

How do you carry out the noise test?

Answer 11

Water phantom measured twice without moving phantom. 2 images subtracted to generate noise image.

Question 12

What is the need for table feed accuracy? (3)

Answer 12

• Required for accurate and repeatable positioning.
• Essential for helical pitch.
• Essential for interventional procedures (CT biopsy)