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Images of anatomy > X Ray > Flashcards

X Ray Flashcards

1
Q

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

A

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

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2
Q

what type of radiation is X rays?

A

electromagnetic radiation that is ionising and penetrating

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3
Q

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

A
  1. direct action

2. indirect action

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4
Q

what is direct action of the Xray ionising radiation?

A

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

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5
Q

What is indirect action of Xrays?

A

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

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6
Q

what effect of X ray radiation is most common?

A

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

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7
Q

what is Xray radiation dosage measured in?

A

milliseverts (mSv)

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8
Q

what does the Xray radiation dosage depend on?

A

the energy of the imaging method

the sensitivity of the organ

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9
Q

what is the typical annual background radiation?

A

2.2mSv

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10
Q

what is the radiation dosage of a chest xray?

A

0.02mSv

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11
Q

what is the radiation dosage of a CT pelvis?

A

7mSv

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12
Q

what is the imaging chain of an X ray?

A

X ray tube | Detector | Processor | Film

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13
Q

where in the imaging chain does the patient go?

A

between the X ray tube and the detector

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14
Q

what is the role of the Xray tube?

A

together with a generator produces X rays.

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15
Q

what are types of detectors for linear 2D XRays?

A
  1. Film hardcopy
  2. Computer Phosphor plate
  3. Digital radiology
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16
Q

what is the film hardcopy detector for linear Xray?

A

A film processor is used with a tank of chemicals

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

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17
Q

what is the computer phosphor plate detector for linear xray?

A

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

18
Q

what is digit radiology detector for xray?

A

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

19
Q

what is the analogue image type?

A

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

20
Q

what is the digital image type?

A

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

21
Q

what values are involved in formatting a digital image?

A

N bits= provides the bit depth

Format= x by y by N per pixel

22
Q

what are advantages of digital image?

A

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

23
Q

what is involved in assessing performance of the system?

A

Efficiency
Spatial resolution
Contrast Resolution
Dynamic range

24
Q

what is efficiency?

A

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.

25
Q

what is spatial resolution?

A

ability to see images close together

26
Q

what is dynamic range?

A

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

27
Q

what is exponential attenuation?

A

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

28
Q

what causes high attenuation?

A

high atomic number: the more electrons the more x rays won’t pass through
high density

Xray basically gives an attenuation map

29
Q

how do you measure spatial resolution?

A

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

30
Q

what is contrast resolution?

A

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

31
Q

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

A

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

32
Q

what is object contrast?

A

difference in signal/contrast due to the object

33
Q

what is image contrast?

A

difference between image characteristic between two locations on the image

34
Q

what is image noise?

A

random variations in signal

35
Q

what are disadvantages of planar Xray?

A

shadow imaging: reduced contrast in the image due to overlapping structures

hard to get 3D localisation

Poor geometric accuracy

36
Q

why does Xray give poor geometric accuracy?

A

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

37
Q

what is fluoroscopy with X ray?

A

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.

38
Q

why is Xray tomography different to normal Xray?

A

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.

39
Q

how does tomography work?

A

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.

40
Q

what numbers are used in tomography?

A

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

41
Q

what is helical scanning for tomography?

A

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

42
Q

why is hybrid scanning with PET:CT good?

A

PET provides functional information and CT provides the anatomical location

Images of anatomy (3 decks)

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