In Service CT

Question 1

Dose in a helical CT study

Answer 1

1/pitch

Question 2

What will happen to mAs, patient dose, SNR, and temporal resolution if the rotation time of the CT x-ray tube from 1s to 0.5s without changing mA or kVp

Answer 2

Cutting the rotation time in half will decrease mAs (same mA, but half the rotation time) and patient dose to 50%.

Signal-to-noise ratio (SNR) will decrease to 70% (square root relationship).

It will double temporal resolution.

Question 3

In pregnant women undergoing a CT, the radiation dose to the fetus is primarily derived from which of the following types of radiation?

Answer 3

Internal scatter

Question 4

which strategy has the MOST effect in reducing pediatric dose?

Answer 4

Using tube current modulation

The use of tube current modulation allows the CT scanner to vary the tube current based on the patient
thickness, scanning at lower tube current while scanning thinner part of the anatomy and higher tube
current while scanning thick part of the anatomy and still maintaining consistent image quality.

Question 5

Lower than normal tube current in a CTA results in:

Answer 5

increased noise