Computed Tomography 2

Question 1

What does a CT scanner consist of

Answer 1

Gantry = houses the x-ray tube, detectors and generator

X-ray tube which rotates 360 degrees in the axial plane around the patient’s body

Filter = which improve the efficiency of the x-ray beam

Collimators = reduce patient dose and improve image quality

Detectors = arranged in rows rotating in a continuous arch directly opposite the x-ray tube

Question 2

What features do CT x-ray tubes have to help them dissipate heat quickly?

Answer 2

• High-speed rotors which provide good heat dissipation
• Direct oil cooling of the anode
• Scanners are designed to use focal spot cooling algorithms

Question 3

Where are the collimators in a CT scanner located?

Answer 3

Ct scanners have collimators in two positions.
There are pre patient collimators that collimate the x-ray beam at the x-ray tube

There are pre detectors that collimate the x-ray beam after it passes through the patient.

Question 4

What is the purpose of collimators in CT

Answer 4

• Collimators reduce the radiation dose by limiting the volume of tissue irradiates.
• They also improve the image contrast by limiting scatter and reducing noise
• The pre detector collimators provide a contrast beam width on the detectors.

Question 5

What is the purpose of detectors in CT ?

Answer 5

Detectors convert x-ray photons into electrical signals called analog data which is then converted to digital information for computer reconstruction.

Question 6

What are the ideal properties of a CT detector?

Answer 6

• They should have a high dynamic range to allow the detector to respond to a wide range of X-ray intensities.
• The detector should be highly efficient so it can capture, absorb and convert x-ray photons to electrical signals
• The detector should be robust, stable, and have a fast response.
• The detector should produce little after glow to maintain image quality