Imaging Technologies 1

Question 1

Which imaging technologies are ionising?

Answer 1

X-ray, CT scanning & PET scanning

Question 2

What are pixels?

Answer 2

Elements on a grid.

Question 3

What is meant by image resolution?

Answer 3

The number of pixels along each axis of the grid/matrix.

Question 4

What is meant by intensity/grey scale?

Answer 4

This is a number assigned to each pixel.

Question 5

What is meant by intensity/grey scale resolution?

Answer 5

The range of possible intensity/grey scale values a pixel can take.

Question 6

What is spatial resolution?

Answer 6

It is a measure of the smallest discernible detail that can be seen in an image.

Question 7

What is aspect ratio?

Answer 7

The ratio of an image width to image height.

= W / H

In medical imaging this is usually equal to 1.

Question 8

What is dynamic range?

Answer 8

The range of intensity/grey scale values used to display an image (as not all values may be utilised).

Question 9

What is the difference W eternal low spatial resolution and low intensity resolution?

Answer 9

Low spacial resolution = small structures will not be resolvable.

Low intensity resolution = small structures visible but differentiation between similar looking structures will not be possible.

Question 10

What is meant by an “n-bit image”?

What would an 8-bit image mean?

Answer 10

It means 2^n different intensity/grey scale values.

This means 8-bit = 2^8 = 256 possible intensities.

Question 11

What are pixels referred to when imaging is 3D?

Answer 11

Voxels.

Question 12

What is the name of the file type that medical images are usually stored as? Give the acronym and its full title.

Why is this image file type used?

Answer 12

DICOM = Digital Imaging & Communications in medicine.

It is a non-compressed file type.

Question 13

What is the wavelength of X-rays?

Answer 13

10^-8 —> 10^-10 (lambda).

Question 14

How are x-rays generated?

Answer 14

An external PD produces a voltage across X2 electrons in a vacuum. This accelerates a beam of electrons across the gap which strike the anode and create X-ray radiation as photons in the process.

Question 15

What is the anode made of in x-ray production and why?

Answer 15

Tungsten metal as it has a high melting point, and 99% of the K.E. given off in X-ray production is thermal. Only 1% is as X-rays.

Question 16

How is the system cooled?

Answer 16

It spins and is also cooled with water/oil.

Question 17

What are the X2 types of radiation produced?

How is each produced?

Answer 17

1) Braking radiation
= electrons slows by the electric field of the anode.

2) Characteristic radiation
= incoming electrons knock out inner electron of the anode and x-ray photons are given off as an electron in an outer shell drops down into the space from the knocked out electron.

Question 18

Which law is involved in the attenuation of x-rays?

What is the law?

Answer 18

Lambert-Beer law

I = I(o) x e^(-μx)

I = final intensity
I(o) = initial intensity
μ = linear attenuation coefficient 
X = material thickness

Question 19

What are the X5 densities?

Answer 19

• air
• fat
• soft tissue/water
• bone
• metal

Question 20

What is a limitation of x-rays?

Answer 20

All structures are superimposed therefore depth is hard to establish.

Question 21

What is CT?

Answer 21

It is 180 degrees of x-rays using a fan shaped beam.