Basic Radiation Science/Principle of Digital Imaging

Question 1

Define voxel

Answer 1

Volume Element

A voxel is a unit of graphic information that defines a point in three-dimensional space.

Since a CT section has a finite thickness, each pixel actually represents a small volume element, or voxel

Question 2

Define Pixel

Answer 2

the smallest discrete two-dimensional unit of a digital image

Question 3

What is the structure of any atom

Answer 3

Atoms are made up of protons and neutron located within the nucleus, with electrons in orbitals surrounding the nucleus.

Question 4

The number of protons in the nucleus

Answer 4

Atomic number

Question 5

The total number of nucleons (neutrons + protons) in the nucleus

Answer 5

Atomic mass number

Question 6

Any nucleus which contains same number of protons as the given nucleus but has a different mass number

Answer 6

Isotope

Question 7

An atom with an unstable nucleus, characterised by excess energy available which undergoes radioactive decay and creates: gamma rays, alpha or beta particles

Answer 7

Radioisotope

Question 8

o A radiation which removes an electron from the outer shell of an atom

Answer 8

Ionising radiation

Question 9

Non-ionising radiation

Answer 9

Electromagnetic radiation which does not cause the breakage of atoms- can be waves or particles

Question 10

Negative effects of ionising radiation

Answer 10

Produces highly reactive ions which can cause damage to DNA etc.

Question 11

Negative effects of non-ionising radiation

Answer 11

Can agitate body tissues as they produce heat, but not long term biological effects

Question 12

How does: Increases in wavelength = decreases in frequency Effects energy

Answer 12

decreases energy

Question 13

——— are extremely high energy, they are used in radiotherapy. They can cause severe ionisation and can pass through the body.

Answer 13

Gamma Rays

Question 14

——– uses sound waves, and produces heat in the body but no radiation

Answer 14

Ultrasound

Question 15

How is EMR refracted

Answer 15

High energy electromagnetic radiations are not refracted.

Question 16

What does the transmission of radiations depends on (tissue)

Answer 16

Different materials transmit different amount of radiations- depends on the density and type of tissue. The higher the atomic number, the higher the absorption of x-rays.

Question 17

The higher the atomic number, the ——- the absorption of x-rays.

Answer 17

Higher

Question 18

Define attenuation

Answer 18

Attenuation is the reduction of the intensity of an electromagnetic beam as it traverses matter. It can be due to photoelectric absorption, Compton scattering and pair production

Question 19

Define luminescence

Answer 19

Fluorescence and phosphorescence ( electron transitions within the material being irradiated cause the emission of photons that have less energy than the incident photons).

Question 20

What is Newton’s Law on the conservation of energy

Answer 20

Energy can neither be created nor destroyed but can be changed from one form to another. The amount of energy in system is constant.

Question 21

What is Newton’s Law on Conservation of Momentum

Answer 21

The total linear or rotational momentum in a given system is constant (when we consider collision of two bodies)

Question 22

What are Newton’s 3 laws of motion

Answer 22

1. A body will be at rest or will travel with a constant velocity unless acted upon by a net external force 2. The rate of change of momentum of a body is proportional to the applied force 3. The action has equal and opposite reaction

Question 23

What is the purpose of image processing?

Answer 23

This influences the image appearance, and is affected by the amount of collimation, and whether the field was centred correctly (by anatomical location or not)- If the object in the centre of the film it will appear correct in orientation (no elongation etc).

Question 24

Describe ‘DDR’ image receptors

Answer 24

• DDR is cassetteless.
• The x-rays are recorded by a digital image capture device which records the x-ray image.
• There are two types, flat panel detectors and solid-state detectors.
• The x-rays are converted into a charge which forms an analogue signal which is then converted into a digital signal, giving a number for each pixel representing its level of exposure.
• The thin film transistors reflect pixels of an image.
• The crystals are ionised by the photons which forms a pre-electron current.
• The lighter the pixel, the less current present, the more grey the colour.

Question 25

Describe the 'computed' image receptors

Answer 25

Computed radiography employs the process of photon stimulated luminescence. A phosphor coated imaging plate is exposed to x-rays. The energy is stored in the phosphor layer. This is then scanned by a laser. This stimulates the phosphor layer, which then emits light of a brightness related to the original exposure.

Question 26

Describe the 'Film-Screen' Image receptors

Answer 26

Film-screen fluoresces in the presence of x-rays, it emits visible light whose brightness depends on the level of exposure. Photographic film is placed in contact with the screen to produce an image.

Question 27

Describe the 'Film' image receptors

Answer 27

Film involves the direct exposure of photographic film to x-radiation, this is then chemically processed and becomes permanently darkened to a degree which depends on the level of exposure.

Question 28

Give 2 generic EMR properties

Answer 28

* Travel in straight lines (Rectilinear Propagation) * Travel at the speed of light (3x10⁸ms^-1) in a vacuum * Carry energy and momentum * Unaffected by electrical or magnetic fields * Travel explained by 'Wave' or **'Quantum' Theory**

Question 29

What controls the penetrating power of the x-ray beam (_Quality_)

Answer 29

KvP

Question 30

What controls the _quantity_ of x-rays

Answer 30

mAs

Question 31

'if you increase the KVp by 15% and halve the mAs the image will seemingly appear to have received a ‘similar’ exposure.' what is this an example of

Answer 31

Rule of constant intensity

Question 32

An image can be defined as a two-dimensional function *f_{(x, y)}* What are x and y?

Answer 32

x and y are spatial (plane) coordinates

Question 33

What constitutes BETTER SPATIAL RESOLUTION

Answer 33

More pixels = finer detail seen

Question 34

Define Bit Depth

Answer 34

The number of grey shades avaliable for image display

Question 35

If 2ⁿ is the number of grey shades. What is the usual clinical number?

Answer 35

2^10/12 most common for clinical use

Question 36

* cassette with a plate, where the image is formed on the cassette * Takes longer time * One reader but in theory can have multiple rooms imaging, so more cost-effective * Quality of image not as good Which aquisition system is being described?

Answer 36

Computed

Question 37

* Almost instantaneous * Better quality * Only get the information you irradiated * Only the exposed pixels contribute to image database Which aquisition system is being described here?

Answer 37

Direct/Indirect

Question 38

In order to examine a specific body part, the radiographer normally selects it via the programme on the generator console. ‘---------’ exposure factors are automatically selected.

Answer 38

**‘Recommended’ exposure factors are automatically selected**.

Question 39

What should the histogram 'signature' tell you about the image

Answer 39

The histogram 'signature' should tell you how the **exposure** of the image will appear to the eye

Question 40

If this were the histogram for the image, would it be under or over exposed?

Answer 40

The image on the right will be underexposed, as the pixels are at the white end of the spectrum

Question 41

What does "white to the right" refer to on a histogram

Answer 41

Histogram is pushed to the RIGHT if under-exposed

Question 42

What is the purpose of gamma for image optimisation

Answer 42

Gamma controls the **contrast** (via a look-up-table (LUT) curve in Radiography practice) LUT is always automatically directly proportional, but can be edited

Question 43

What is this line?

Answer 43

look-up-table (LUT) curve Controls the contrast of the image LUT is always automatically directly proportional, but can be edited

Question 44

What is windowing of an image

Answer 44

The input range is reduced to only include the 'useful' data, and the output range remains unchanged

Question 45

What is wrong with the top image, and why?

Answer 45

as exposure factors weren’t correct, lots of the image was lacking ‘full blackness’. The left cursor of the histogram was moved to the right, to the edge of the active pixels.

Question 46

How can contrast be corrected?

Answer 46

A LUT curve is applied to create the optimal image. An infinite array of LUT's could be applied to suit the potential desires of every clinical situation

Question 47

Purpose of inverting an image

Answer 47

Once optimised, the image can also be inverted by flipping the LUT. This allows detection of fractures etc which weren’t previously spotted.

Question 48

Why Originally was x-ray film tinted blue.

Answer 48

Colour makes it easier to see pathologies on images, as we see in colour better than monochrome:

Question 49

Why aren't all iimages in colour if we can see pathologies better with colour?

Answer 49

An RGB colour file is 3 times bigger than monochrome * requires 3 times more image storage space * takes 3 times longer to transmit over a network * visual benefits cannot be justified

Question 50

**Low Pass** filters create what effects

Answer 50

**Low Pass** filters create relatively gentle **smoothing** effects e.g. * 'Blur' * 'Blur More' The ‘Gaussian’ low pass filter is very fierce.

Question 51

Purpose of high pass filters

Answer 51

**High Pass** filters **sharpen** the edges e.g. * ‘Laplacian’ or ‘Laplacian-like’ * ‘Sobel Gradient’

Question 52

How are smoothing masks achieved

Answer 52

Blue ‘Smoothing’ Mask The smoothing is achieved by attenuating **high** **spatial frequency** details and therefore **reducing ‘noise’.**

Question 53

What does the Gaussian mask do

Answer 53

The Gaussian mask utilises a ‘bell shaped’ distribution and is typically applied using masks up to 25 x 25 in size but is often circular. The blurring (smoothing) effect is very strong, even at low settings!

Question 54

What is the golden rule for smoothing and sharpening an image

Answer 54

**Golden Rule – ‘Smooth then Sharpen’** If you ‘sharpen’ before ‘smoothing’ you will also ‘sharpen the noise’ and the image will look speckled

Question 55

Diagnostic Images are created and stored in DICOM: what does that stand for

Answer 55

**_D**_igital _**I**_maging and _**Co**_mmunications in _**M_**edicine

Question 56

Images may be converted into other formats in order to reduce their file size e.g. TIFF or JPEG The greater the compression the......?

Answer 56

1. the smaller the image file size 2. the less storage space required 3. the faster it will transmit across a network 4. the lesser the image quality

Question 57

DICOM file contains?

Answer 57

both a _header_ *_and_* _the image data_ * _Header_: Stores patient information, the type of scan, image dimensions, etc.. * _Image Data_: Image Matrix as an array of binary numbers. Can be multiple slices that form a 3D representation

Question 58

What is PACS data storage

Answer 58

Linked to radiology information system. Images are stored in a server off-site and after a predetermined number of years may be jpged to store for a longer time.