X Ray

Question 1

What is the basic principle behind how an Xray produces an image?

Answer 1

Different structures stop Xrays at different degrees depending on the structure and atomic number. This relates to the attenuation.

Question 2

what type of radiation is X rays?

Answer 2

electromagnetic radiation that is ionising and penetrating

Question 3

What are the different effects of the ionising radiation from X ray?

Answer 3

1. direct action

2. indirect action

Question 4

what is direct action of the Xray ionising radiation?

Answer 4

The Xrays hit inside the actual cells and break one or both of the sugar-phosphate DNA backbone or base pairs of DNA

Question 5

What is indirect action of Xrays?

Answer 5

the radiation acts on water and forms free radicals. These are highly reactive and damage cells

Question 6

what effect of X ray radiation is most common?

Answer 6

indirect. As Xray radiation is penetrating so rarely hits directly inside of the cells

Question 7

what is Xray radiation dosage measured in?

Answer 7

milliseverts (mSv)

Question 8

what does the Xray radiation dosage depend on?

Answer 8

the energy of the imaging method

the sensitivity of the organ

Question 9

what is the typical annual background radiation?

Answer 9

2.2mSv

Question 10

what is the radiation dosage of a chest xray?

Answer 10

0.02mSv

Question 11

what is the radiation dosage of a CT pelvis?

Answer 11

7mSv

Question 12

what is the imaging chain of an X ray?

Answer 12

X ray tube | Detector | Processor | Film

Question 13

where in the imaging chain does the patient go?

Answer 13

between the X ray tube and the detector

Question 14

what is the role of the Xray tube?

Answer 14

together with a generator produces X rays.

Question 15

what are types of detectors for linear 2D XRays?

Answer 15

1. Film hardcopy
2. Computer Phosphor plate
3. Digital radiology

Question 16

what is the film hardcopy detector for linear Xray?

Answer 16

A film processor is used with a tank of chemicals

Allows for high spatial resolution but digital is more commonly used now

Question 17

what is the computer phosphor plate detector for linear xray?

Answer 17

A laser scanner or CR reader is used. It’s electronically processed without chemicals but a phosphor plate is still needed.

Question 18

what is digit radiology detector for xray?

Answer 18

A flat panel detector is used and a digital system automatically produces the image

Question 19

what is the analogue image type?

Answer 19

The characteristics of the object are represented by brightness of colour. No digital representation is provided

Question 20

what is the digital image type?

Answer 20

Image information is stored as digital numbers. This is processed to provide an image. Can also store and copy.

Question 21

what values are involved in formatting a digital image?

Answer 21

N bits= provides the bit depth

Format= x by y by N per pixel

Question 22

what are advantages of digital image?

Answer 22

ability to store and retrieve
able to analyse
can be processed
can provide an interactive display during procedures

Question 23

what is involved in assessing performance of the system?

Answer 23

Efficiency
Spatial resolution
Contrast Resolution
Dynamic range

Question 24

what is efficiency?

Answer 24

How much output signal you get for a given radiation dose
A high efficiency means more input energy is turned into the actual image.
Also referred to as speed as assesses safety.

Question 25

what is spatial resolution?

Answer 25

ability to see images close together

Question 26

what is dynamic range?

Answer 26

the range between the lowest and highest signal. Tells you how well the system copes with high values compared to low values. the bigger the dynamic range the better

Question 27

what is exponential attenuation?

Answer 27

the thicker the material being imaged the more attenuation there will be. The intensity curve never goes to zero so regardless of how thick the tissue is some x rays will always pass through

Question 28

what causes high attenuation?

Answer 28

high atomic number: the more electrons the more x rays won't pass through high density Xray basically gives an attenuation map

Question 29

how do you measure spatial resolution?

Answer 29

number of lines per mm high resolution: 20 lines per mm standard: 8 lines per mm

Question 30

what is contrast resolution?

Answer 30

ability to see objects of low contrast described by the smallest size of the object visible as the stated contrast level threshold.

Question 31

what is the relationship between contrast resolution, noise and signal?

Answer 31

The signal has to be large enough to see above noise. Image noise affects how we see low contrast objects

Question 32

what is object contrast?

Answer 32

difference in signal/contrast due to the object

Question 33

what is image contrast?

Answer 33

difference between image characteristic between two locations on the image

Question 34

what is image noise?

Answer 34

random variations in signal

Question 35

what are disadvantages of planar Xray?

Answer 35

shadow imaging: reduced contrast in the image due to overlapping structures hard to get 3D localisation Poor geometric accuracy

Question 36

why does Xray give poor geometric accuracy?

Answer 36

The Xrays come from a joint focal point and then fan out around the object. As the detector object distances increases there is more magnification due to this fanning out from the focal point

Question 37

what is fluoroscopy with X ray?

Answer 37

allows real time x ray imaging.A catheter is fed inside of an artery and a dye injected. The dye is dense allowing you to see flow inside the vessel.

Question 38

why is Xray tomography different to normal Xray?

Answer 38

in tomography the image corresponds to a cut transaxial cross section which allows you to see areas seperated instead of overlapping allowing for better contrast.

Question 39

how does tomography work?

Answer 39

The detectors are on a mobile gantry which moves upto 4 times a second. This produces data which is used to form an image. Just like X rays measures attenuation.

Question 40

what numbers are used in tomography?

Answer 40

CT numbers. This is the density of the tissue in reference to the density of water Density of tissue above water: positive number density of tissue below water: negative number

Question 41

what is helical scanning for tomography?

Answer 41

A larger bank of detectors so more coverage is achieved per rotation. This is much faster.

Question 42

why is hybrid scanning with PET:CT good?

Answer 42

PET provides functional information and CT provides the anatomical location