CT

Question 1

How does a CT tube work?

Answer 1

Tube and film rotate around a fulcrum which defines the plane which will be sharp in the image

Question 2

By changing the fulcrum level what is selected?

Answer 2

The anatomical plane needed for the examination

Question 3

What is the tomographic angle?

Answer 3

The angle between the CR positions at the the begining and end of exposure

Question 4

What does the tomographic angle control?

Answer 4

The thickness of the “cut”

Question 5

What does a small angle produce?

Answer 5

Thick cut

Question 6

What does a large angle produce?

Answer 6

Thin cut

Question 7

What direction do the tube and bucky move in CT?

Answer 7

Lengthwise or multi-directionally and the patient remains stationary

Question 8

What does CT produce?

Answer 8

Cross-sectional images of the body with the aid of computerized image reconstruction

Question 9

What are the advantages of CT?

Answer 9

Resolves radiography limitations
- Eliminates anatomic superimposition
- Improved soft tissue contrast
- Higher resolution
- Multiple projection data

Question 10

What is the biggest disadvantage of CT?

Answer 10

Patient dose is much larger than general radiography

Question 11

Why is the contrast better in CT?

Answer 11

Collimation is kept very tiny, which reduces scatter

Question 12

What are the steps of CT imaging?

Answer 12

• X-ray beam is passed at a cross section through a patient’s body.
• The beam is finely collimated which reduces scatter and gives better contrast resolution
• The collimated beam passes through the body, the body tissue absorbs the beam
• The remnant beam exits the body and strikes the detectors.
• The detectors are quantitative and distinguish differences in tissue contrast
• Detector converts photons to an analog signal via a scintillator and photodiode
• The ADC converts it to digital signal
• Digital data is sent to CPU for reconstruction

Question 13

What is the data acquisition system?

Answer 13

System that converts xrays to light by a scintillator and photodiode

Question 14

How are the images reconstructed?

Answer 14

Each set of projection data are created by measuing the linear attenuation coefficient of the tissues that the beam travels through

Question 15

How does the filtered back projection method work in reconstruction

Answer 15

• Projection profiles are obtained
• Logarithm of data is obtained
• Logarithmic values are multiplied by digital filter or convolution filter to generate filtered profiles
• Filter profiles are now back projected (smeared)
• Filtered projections are summed and the negative and positive components are therefore canceled providing an image free of blurring that looks like the original object

Question 16

What are the types of CT scnanners?

Answer 16

Conventional
High-Speed (Cardiovascular)
Spiral/Helical
Mobile
CT Fluoroscopy
Dual Source/Dual Energy

Question 17

What are Advanced CT Techniques?

Answer 17

Multiplanar Reconstruction (MPR)
CT Angiography
PET/CT
CT Endoscopy

Question 18

What is MPR?

Answer 18

Allows axial images to be converted into another plan of anatomy, like sagittal or coronal

Question 19

What is CT angiography?

Answer 19

A test that combies the technology of conventional CT with the tradition of angiogrpahy to created a detailed image of blood vessels in the body

Question 20

What is PET/CT?

Answer 20

A dual purpose image device that combines PET scanning and CT to creased an single, overlapped or fused image of metabolic activity of the body with its anatomical structures

Question 21

What are some historical milestones of CT?

Answer 21

Roentgen Nobel Prize (1901)
Hounsfield & Cormack Nobel Prize (1979)
First whole-body CT Scanner (1975)