2166-Handout

College on Medical Physics. Digital Imaging Science and Technology to Enhance Healthcare in the Developing Countries

Slavik Tabakov

13 September - 1 October, 2010

King's College London United Kingdom

Basic Principles of CT scanners and image reconstruction

Planar x-ray Sinogram

Rot

ate

arou

nd

obje

ct

Reconstructed image

2 types of images :

- invisible digital image “latent”

(in computer memory)

- visible image in the display (on the computer monitor)

Helical / spiral modeStep and shoot / sequential mode

Recon position

Measured data

Interpolated data

Travel = 10 mm/rotBeam = 10 mmPitch = 1

Travel = 20 mm/rotBeam = 10 mmPitch = 2

Single slice Multi slice

Parallel banksof detectors

Single row of detectors

1024 projections 128 projections

-1000 HU

4000+ HU

WWWL

0 HU WW

-1000 HU

4000+ HU

WL

WL WW

WL + WW/2

WL - WW/2

CT number = 1000 . ( tissue - water)/ water

CT number = 1000 . ( tissue - water)/ water