Lecture 8

Question 1

What is a tomagraphic image?

Answer 1

Slice of an image
512x512 pixels
4096 shades of gray
Typical Slice thickness(1-10 mm)
Each voxel represents mu value

Question 2

Goal of computed tomography?

Answer 2

To find the value of each voxel of the slice
Collect rays at all positions and angles

Question 3

How is computer tomography done?

Answer 3

Rotate the detector around the person

Question 4

Calculate the mu’s

Answer 4

Fixed voxel size =t
I1= I0e^-ut
I2=I1e^-u2t*Ioe^(-u1t)
In=Ioe-unt

Question 5

Tomography geometries

Answer 5

Parallel Geomoetry, Fan geometry and cone geometry

Question 6

Parallel Geometry

Answer 6

all the lines go straight through the patient, and there are deteectors lined up parallel to each other

Question 7

Fan geometry

Answer 7

All the rays come from one source, and are more evenly distributed over the body

Question 8

Cone geometry

Answer 8

Like fan but 3D

Question 9

Transmission

Answer 9

How many of the mu values were transmitted to the detectors

Question 10

What is a sinogram?

Answer 10

2D matrix of data of a tomographic slice BEFORE reconstruction

Question 11

Rays

Answer 11

Data across the detectors

Question 12

Views

Answer 12

The angle of a ray

Question 13

Data Reconstruction

Answer 13

Sinogram shows already computed values for each view

Question 14

Define position of array with?

Answer 14

It is defined by radius(ray) and theta the projection angle

Question 15

What is the radon transform?

Answer 15

ln(Ii/Io)=sum of mu values