X-Rays Flashcards
1
Q
what are the three essential components for the x-ray?
A
- source of x-ray (uniform distribution)
- object (attenuation by object)
- image receptor (spatial distribution of x-rays on image receptor)
2
Q
what led to the discovery of x-rays?
A
Wilhem Roentgen noticed a barium screen fluorescing while generating cathode rays
3
Q
what are the features of X-ray tube?
A
- mobile (enables x-rays production at different angles and positions)
- uniform (to provide image contrast)
- collimated (adjustment of size)
4
Q
which factors in uniform distribution of x-rays control the image appearance?
A
controls image appearance by
- x-ray energy (kVp)
- amount of x-rays (mAs)
- penetration -> contrast
- image density -> blackening
5
Q
what does the x-ray interaction with matter (attenuation) result in?
A
- alters properties of incident beam
- attenuation (absorption and scatter)
- magnification and distortion of objects
6
Q
what are the features of an image receptor?
A
- converts x-rays into image - influences image appearance
- consists of film and film-screen - chemical reaction
- computed radiography - scanning laser
- direct-digital radiography - computing
7
Q
what are the two types of DDR?
A
- solid state detectors
2. flat panel detectors
8
Q
name four factors on the basis of which image is evaluated and interpreted?
A
- centring and collimation
- exposure factors
- processing
- artefacts
9
Q
name the SEVEN essential components in x-ray?
A
- tube
- collimator
- light beam diaphragm
- generator
- casette
- bucky
- couch
LGBT CCC
10
Q
what are the characteristics of x-rays?
A
- penetrate matter
- interact with matter
- cause certain material to fluorescence
- cause certain materials to produce electric charge
11
Q
how are x-rays produced?
A
produced by a side deceleration of electrons in target
12
Q
what is the protective role of tube housing?
A
provides
- physical protection
- radiation protection
- electrical protection
- filled with oil for
a. heat dissipation (excess)
b. electrical insulation
13
Q
what are the features of cathode?
A
- source of electrons - negatively charged to focus the electrons towards anode and stop spatial spreading
it consists of - filament (wire filament for small and large focal spot)
- focusing cup - surrounds the cathode which consists of the two wire filaments
14
Q
why is tungsten used as filament?
A
- good thermionic emitter (emission of electrons from heat source)
- high melting point - 3140 degree C
- high atomic number (Z=74, higher attraction property)
- can be manufactured into thin wires
15
Q
what causes the heating in thermionic emission and how much current is supplied?
A
- electric current causes heating
2. above 4As electrons are boiled off
16
Q
what are the features of anode?
A
- Positively charged to attract electrons
- Target made of tungsten for same reasons as for filament (in cathode)
- Rhenium added to tungsten to prevent cracking of anode target at high temperatures and usage
- Set into an anode disk of molybdenum with stem
- Set at an angle to direct x-ray photon beam down towards patient. Usual angle is 5º - 15º
17
Q
what are the three functions of anode?
A
- support target material
- electrical conductor
- thermal conductor
18
Q
what are the two types of anode?
A
- stationary - consists of an anode fixed in position with the electron beam constantly streaming onto one small area
- rotating - consists of a disc with thin tungsten around the circumference that rotates. Due tot he rotation it overcomes heating by having different areas exposed to the electron stream over time
19
Q
X-rays are electromagnetic waves?
A. True
B. Fasle
A
True
20
Q
what is an X-ray tube and what does it consists of?
A
- The X-ray tube is a vacuum tube that converts electrical input power into X-rays, it’s composed by a glass envelope with a cathode (filaments) and an anode (target) inside
- It consists of collimator, light beam diaphragm, filtration and ionisation chamber. They are movable (x,y,z).
21
Q
in which year did Rongten discovery x-ray accidentally?
A
1895
22
Q
how are x rays formed?
A
- electrons produced at the filament of X-ray tube
- accelerated towards the anode target of tube and collide with target atoms
- electrons then lose energy and decelerate, then energy released in the form of x-rays
23
Q
what are three ways electrons might collide with target atom?
A
- interaction b/w them and outer electrons in the atom = no x-rays, heat
- interaction b/w them and the nuclei of the atom - x-rays + heat (Bremsstahlung)
- interaction b/w them and individual electron in the inner orbits = X-rays + heat (characteristic)
24
Q
why is x-ray production an inefficient process?
A
95-99% of energy produced in x-rays is heat and the rest 5-1% is x-rays
25
what are the two famous ways of x-ray production?
1. bremstrahlung
| 2. characteristic
26
what is bremstrahlung radiation?
energetic electrons from the filament interact with the nuclei of target atoms and are slowed down thus giving off energy in the form of x-rays. It is also called braking radiation.
27
what is characteristic radiation?
energetic electrons remove electrons from the inner orbital and the vacancies created are filled by electrons from outer orbitals, giving off energy in the form of x-rays
28
what is atomic number and melting point of tungsten?
atomic number - 74
| melting point - 3370 degree C
29
why is tungsten used an ideal target material or anode in X-ray tubes?
1. high atomic number has higher attractive property
| 2. high melting point will prevent the excess heart production damage
30
name an alloy used with tungsten
rhenium
31
which atoms are used in mammography as anodes?
1. molybdenum - atomic number 42
| 2. rhodium - atomic number 45
32
what are the features of stationary anode?
1. used in low output tubes
| 2. 99.5% of electron energy is converted to heat
33
what are the features of rotating anode?
1. typically glass envelope insert
2. increase heat dissipation
3. increase anode load
34
what is anode pitting/ cracking?
It is line formed by the hitting of electrons on the rotating anode from prolonged use
35
what is anode angle?
it is a spectrum of angle with varying intensity to create effective x-rays via small focus
36
what is anode heel effect?
refers to the lower field intensity towards the anode in comparison to the cathode due to lower x-ray emissions from the target material at angles perpendicular to the electron beam
37
what does a large focus and small focus result in terms of images obtained?
1. large focus - blurred image
| 2. small focus - sharp image
38
why dual filaments are used? and state three usual combinations
```
dual filaments offer two effective spot sizes
the common combinations are
1. 0.6mm and 1.2mm
2. 0.3mm and 1.2mm
3. 0.4mm and 0.8mm
```
39
what is an ideal x-ray source?
point source
40
what is the efficiency of x-ray process?
1. 99.5% of electron energy is converted into heat
2. only a small % of x-rays produced exit the window
3. the useful x-ray beams are usually attenuated within the patient
41
why do we need filtration?
adding filtration enriches beam with high energy photons by absorbing and eliminating lower energy x-rays referred to as beam hardening
42
what will higher average energy result in?
1. greater penetration
| 2. reduced skin-dose
43
which filtration is used for normal diagnostic work?
~2.5mm aluminium
44
what does the ionisation chamber consist of? and why is it used?
1. gas filled ionisation chamber
| 2. a proportion of incident photons cause ionisation which is collected at charged anode of chamber
45
what does the ionisation chamber measure?
measures the dose area product (DAP) in cGy.cm2 (grey centimetres squared)
46
what are three essential criteria for the required voltage in x-ray generators?
1. volts
2. potential
3. current
1. 100,000+ volts
2. constant potential
3. DC - direct current
47
what are two essential criteria for the main sockets in x-ray generators?
1. power from electric supply - 240 volts
| 2. AC - alternating current, oscillating 50Hz
48
what are the features of voltage generators?
1. high voltage transformer - step up transformer, converts 240 Vs to 100,00Vs
2. voltage rectifier - converts oscillating voltage to constant voltage
49
what is exposure time and its role in diagnossis?
1. the length of time, the current is allowed to flow to anode to facilitate x-ray production
2. should be as short as possible to minimise blur from patient
3. reduced time - increase current (mA)
50
what happens to the attenuation as x-ray energy increases?
reduced attenuation and increased penetration
51
what does the following result in?
1. high kVp
2. low kVp
1. high kVp - high penetration + less absorption/scattering + low contrast = grey
2. low kVp - low penetration + high absorption + high contrast = more b&w
52
what are the EMR properties?
1. travel in target line - rectilinear propagation
2. travel at the speed of light in a vacuum
3. carry energy and momentum
4. unaffected by electrical or magnetic field
5. travel explained by wave or quantum theory
53
what are the four exposure controlling factors?
1. kVp - controls the penetrating power of x-ray beam (quality) and thus, the attenuation
2. mA - controls the quantity of x-rays regulating the patient dose
3. time - linked with mA to create mAs, the time of exposure for the current flow to anode to generate x-rays
4. distance - usual praise dictates 100 or 180cm FRD (focus to receptor distance)
54
what is the rule of constant intensity?
if you increase the kVp (voltage) by 15% and 1/2 (half) the mAs (current), the image will appear to have received similar exposure
55
Define image with respect to digital radiography
can be defined as two-dimensional function f(x,y)
56
what is f (x,y), x and y?
1. x and y are spatial (plane) coordinates
| 2. f (x,y) is the amplitude at any pair of coordinates, also called the intensity or grey level of image at that point
57
Define pixels and its impact on spatial resolution?
1. the finite number of elements with particular location and value is called pixels
2. more pixels = finer detail seen/ better spatial resolution
58
Define bit depth and how does it determine the grey shades
- the number of grey shades available for image display
- number of grey shades available for an image is 2 to the power n, where n is the number of bits available for each pixel
59
what are two types of acquisition system in radiography?
1. computed radiography
| 2. digital radiography - direct and indirect
60
what type of cassettes are used in computed radiography?
cassettes that have phosphor screen
61
explain the computed radiography procedure?
1. x rays hit the cassettes to form a latent image on the phosphor layer
2. the cassette is then moved to a reader with laser shone on it
3. this releases the stored photons and signals are collected
4. the signals are then digitised to be displayed on the screen
62
outline indirect digital radiography proceudre
1. x-ray photons hit the scintillator layer (caesium iodide:CsI)
2. which then releases photons
3. these photons then hit an active matrix array that digitises the signals
63
what does the active matrix consist of?
formed of amorphous silicon and consists of
1. photodiode
2. storage capacitor
3. thin-film transistor (TFT)
64
outline the steps involved in direct digital radiography
1. x ray photons act directly on the semi-conductor
2. the +ve charge is attracted to the storage capacitor that stores the latent image
3. it is then read out by the thin film transistor (TFT) pixel by pixel
65
why is histogram used in post-processing of images?
histogram analysis of a grey scale image reject very high and low values that contain no clinical information
66
why is gamma used in post-processing of images?
it controls the contrast via an LUT (look up table) curve
| LUT is used to map a set of input values to a set of output values
67
how is histogram setting changes if the image is
1. underexposed
2. overexposed
1. underexposed (white) - pushed to the right
| 2. overexposed (dark) - pushed to the left
68
what are the key techniques used in image optimisation and how and why?
1. windowing - input range is reduced to include only useful data
2. contrast correction - LUT curve is applied to create the optimal image
69
which dye was used in traditional film imaging?
blue dye
70
why is RGB colour not used in radiology?
1. RGB colour file is x3 times bigger than monochrome
2. requires x3 more image storage space
3. x3 longer to transmit over a network
71
why is pseudo colour used in nuclear medicine and PET and give an example?
1. pseudo colour is used to code the pixels
| 2. e.g. - areas of higher uptake red, medium yellow, cold spots are blue etc
72
when is low and high pass filter used? and give 2 examples of each?
1. low pass filters are used to create relatively gentle smoothing effects e.g. blur and blur more - gaussian low pass
2. high pass filters are used to sharpen the edges e.g. laplacian or laplacian like and sober gradient
73
how is smoothing achieved in blur mask?
by attenuating (reducing) high spatial frequency and therefore, reducing the noise
74
what is the impact of strong mask on the smoothing effect?
stronger the mask (bigger matrix), the greater the amount of noise that will be removed from the image resulting in smooth image
75
what is the gaussian smoothing filter?
1. it is smoothing mask filter that uses masks unto 25 x25 in size and if often circular
2. it utilises bell shaped distribution
3. the blurring (smoothing) effect is very strong even at low settings
76
what is difference between gaussian smoothing, laplacian sharpening filter and sober gradient filter?
gaussian smoothing filter
1. blurs/smooths the image
2. all values are +1 so no change to centre value
laplacian sharpening filter
1. sharpens the image
2. centre value is +ve and surrounding values are -ve
sobel gradient filter
1. creates semi-3D effect for images
2. -ve on one side, +ve on the other and neutral (1) value in centre
77
how are diagnostic images created and stored?
they are created and stored in DICOM and PACS
78
what is DICOM?
Digital Imaging and Communications in Medicine
79
why are the formats available for the storage of DICOM? give some examples
they are converted to reduce there file size e.g. TIFF or JPEG
80
why greater compressed file formats are preferred?
greater the compression -
1. smaller the image file size
2. less storage space required
3. faster it will transmit across network
4. lesser the image quality (disadvantage)
81
what does a DICOM file consists of and what are they?
1. consist of a both header and image data
2. header - stores patient information, type of scan, image dimensions etc
3. image data - image matrix as an array of binary numbers
82
what is PACS?
1. Picture Archiving and Communication System (PACS).
2. It is a form of image storage.
3. it collects images from various imaging modalities like CT, MRI, x-ray and sends it the work station, external clinic, radiologists office
83
# Define the following
1. Atomic (Z)
2. Atomic mass number (A)
3. Isotope
4. Radionucleotide or radioisoptope
1. Atomic (Z) - the no. of protons in the nucleus
2. Atomic mass number (A) - the no. of nucleons (protons+neutrons) in nucleus
3. Isotope - nucleus with same number of protons but different mass number
4. Radionucleotide or radioisoptope - any isotope which is radioactive
84
what are the two types of radiation used in diagnostic modaltiies?
1. ionising - x-rays
| 2. non- ionising - sound waves
85
why can we see only see the visible light if the electromagnetic radiation spectrum consists of a wide range of radiation types?
because humans are only sensitive to a small selection of these radiations
86
how are the following properties altered after interaction EMR with matter?
1. Reflection
2. Refarction
3. Transmission
4. Attenuation
5. Luminescence
1. Reflection - EMRs are reflected back by the matter but higher energy ones are not capable of reflection back (e.g. x-rays and gamma rays)
2. Refarction - high energy EMRs are not refracted
3. Transmission - different material transmit different amount of radiations
4. Attenuation - it is the reduction of intensity of EM beam as it traverses though the matter
5. Luminescence - Fluorescence and phosphorescence produced due to the excitation of a photon
87
name three phenomenon contributing to attenuation?
1. photoelectric absorption
2. compton scattering
3. pair production
88
what causes the luminescence of EMR while interacting with matter?
electron transitions within the material being irradiated cause the emission of photons that have less energy than the incident photons
89
Define acceleration and deceleration
acceleration - Change in velocity per minute
deceleration - if accelerating force is in opposite direction of moving body then it will cause loss of velocity resulting in deceleration; reduction in speed or rate
90
what is energy? Define PE and KE
1. Energy is the capacity to do work
2. PE is the energy that is possessed by the body at rest
3. KE is the energy that the body possesses by the virtue of its motion
91
what determines the quality and quantity of x-rays?
1. the amount of current (mAs)
| 2. potential difference (kVp)
92
What is the potential difference and its measuring unit ?
1. it is the driving force which moves electrons along a conductor and has an effect on KE
2. measured in kVp
93
what is electric current and its measuring unit?
1. the amount of current which determines the amount of thermionic emission, it is flow of electrons in a material
2. measured in milliamperes (mA) or mAs
94
why is molybdenum used in cathode as focusing cup?
1. high melting point
| 2. poor thermionic emitter so electrons aren't released to interfere with electron beam from filament
95
explain why anode heel effect is required in x-ray production?
An x-ray beam gets attenuated on the way out by the target material itself causing a decrease in intensity gradually from the cathode to anode direction as there is more of the target material to travel through
96
what are the changes made to ensure sharp image is obtained with small focal size?
1. the cathode side should be placed over the area of greatest density as this is the side with the most penetrating beam
2. Decreasing the anode angle gives a smaller effective focal spot size, which is useful in imaging, but a larger anode heel effect
3. This results in a less uniform and more attenuated beam ; smaller angle = smaller focal spot size but larger anode heel effect
97
what are the factors controlling the anode heel effect?
1. anode angle
2. target to film distance
3. field size
4. positioning
98
what is an x-ray spectrum?
- it a graph showing the bremsstrahlung and characteristic radiation
- the peaks of specific photo-energy represents the characteristic radiation of an specific target material
- the rest of the graph is bremsstrahlung representing a range of photon energy
99
name five ways to alter an x-ray spectrum
1. kVP - increase
2. mAs - increase
3. filtering - to reduce low energy photons
4. waveform of current - more rectified (uniform) current
5. atomic number of target - increase
