CT+成像原理介绍 PPT课件.ppt

CT 成像原理介紹
Computed Tomography
CT Basics
Principle of Spiral CT
Scan Parameter & Image Quality
Optimizing Injection Protocols
Clinical Applications
X-Ray Discovery
X-ray was discovered by a German scientist Roentgen 100 years ago.
This made people for the first time be able to
view the anatomy structure of
human body without operation
But it's superimposed
And we couldn't view soft tissue
My name is Godfrey Hounsfield
I work for the Central Research
Labs. of EMI, Ltd in England
I developed the the first clinically
useful CT scanner in 1971
History puted Tomography
Early 1970s
1963 - Alan Cormack developed a mathematical method of reconstructing images from x-ray projections
For the first time we could view:
CT Broke the Barrier
- Tomographic or “Slice” anatomy- Density difference
But it's time consuming
And resolution needs to be improved
Concept of X-ray Attenuation
An X-ray beam passing through
the body is attenuated (loses its
energy) by :
Absorption
Scattering
Incident X-ray
Transmitted ray
SCATTERED X-RAYS
BODY
TISSUE
Absorption by the tissue is proportional to the density
Less
dense
tissue
More
dense
tissue
MORE ATTENUATION
LESS ATTENUATION
How does CT Work?
Recon. & postpro.
Data acquisition
X-ray generation
X-ray goes through
collimator therefore
rate only an axial
layer of the object, called
"slice"
How does CT Work?
Patient is placed in the center of the measurement field
X-ray is passed through the patient’s slice from many direction along a 360° path
The transmitted beams are captured by the detectors which digitizes these signals
These digitized signals called raw data are sent to puter which create the CT image
How does CT Work?
The object slice is divided into small volume elements called voxels.
Each voxel is assigned a value which is dependent on the average amount of attenuation
How is CT Image generated?