CT Scan

Principle

 

Irradiate a slice of tissue from multiple angles

 

Measure the output from different sides

 

Tissues have different densities

- with denser tissue fewer x-rays reach the detectors

 

Hounsfield scale

 

Bone    2000

ST        40

Water   0

Fat       -100

Air       -1000

 

Settings

 

Grey scale

- eye can only see 11 different shades

 

Adjust settings to bone or soft tissue

 

Osteoblastoma Soft Tissue CTOsteoblastoma Bone Window

 

Multislice

 

Multiple detectors at any one time

- increase amount of data acquired in a single slice

- increased speed

- reduces artefact

 

Slice thickness

 

Decreased slice thickness

- increased info

- increased radiation

 

Reconstruction

 

Axial 

Sagittal

Coronal

 

Axial Spine CTSagittal CTCoronal CT

 

3D

 

3D CT Reconstruction3D CT Hip

 

Radiation dose

 

CXR                 1

Pelvis               35

CT Chest          400

CT Abdo/pelvis  500