Physics Flashcards
1
Q
What is electromagnetic radiation?
A
Wave of energy that does not require a media to travel in (like in vacuum)
Velocity is fixed at 3 x 10^8
2
Q
What is the formula for velocity in relation to frequency and wavelength?
A
Velocity = frequency x wavelength
3
Q
How is energy calculated in relation to frequency?
A
Energy = frequency x h, where h is a constant
4
Q
List the forms of electromagnetic radiation in order of increasing frequency/energy.
A
- Radiowaves
- Microwaves
- Infrared
- Visible light
- UV
- X-ray/gamma ray
5
Q
What type of radiation is used for MRI?
A
Radiowaves, which are NON ionizing radiation
6
Q
What is ionizing radiation?
A
The ability to remove electrons from an atom
7
Q
When does ionizing radiation occur?
A
Occurs as the frequency increases and the wave gets more energetic
8
Q
What is the effect of a missing electron in an atom?
A
Creates an imbalance in the atom, which is now considered ‘ionized’
9
Q
What types of radiation cause ionization?
A
- X-rays
- Gamma rays
- Alpha particles
- Beta particles
10
Q
What are alpha particles composed of?
A
2 protons and 2 neutrons, with a net charge of 2+
11
Q
What is the penetrating ability of alpha particles?
A
Cannot travel far, or penetrate deep
12
Q
What are beta particles?
A
Electrons which are emitted from the nucleus (not the orbit)
13
Q
How do beta particles compare to alpha particles in terms of speed and distance?
A
Faster and lighter than alpha particles, travel farther
14
Q
What are soft X-rays characterized by?
A
Long wavelength, low frequency/energy
15
Q
What are hard X-rays characterized by?
A
Short wavelength, high frequency/energy
16
Q
How are X-rays produced?
A
Emitted by electrons originating from interaction between fast moving electrons and atoms
17
Q
What is the role of tungsten in X-ray production?
A
High melting point and high atomic number make it a good thermionic emitter
18
Q
What is thermionic emission?
A
Boiling off of electrons due to extreme temperature
19
Q
What is the space charge in an X-ray tube?
A
Escaped electrons form a cloud close to the filament
20
Q
What limits the emission of electrons in an X-ray tube?
A
Space charge limits emission of electrons
21
Q
What happens when electrons hit the anode?
A
Lose kinetic energy via excitation, ionization, and radiative loss (bremsstrahlung)
22
Q
What percentage of energy is converted to X-ray during electron interaction with the anode?
A
1% converted to X-ray, the rest is lost as heat
23
Q
What is the focal spot in an X-ray tube?
A
Where electrons land on the anode
24
Q
What is the effect of a smaller anode on spatial resolution?
A
Better spatial resolution but heat limitations
25
What does the term 'heel effect' refer to?
Variation/spectrum in beam intensity, strongest beam closest to cathode
26
What is the minimum filtration required for X-ray operating over 70 kVp?
2.5 mm aluminum
27
What does kVp stand for?
Peak kilovoltage
28
How does increasing kVp affect X-ray production?
* Increases maximum X-ray energy
* Increases average X-ray energy
* Increases total number of X-rays produced
29
What is the relationship between kVp and beam intensity?
Beam intensity increases as square of kVp
30
What is the relationship between mass attenuation and density?
Mass attenuation is not affected by density of material
31
What determines the half value layer (HVL)?
Amount of material required to attenuate X-ray to half original output
32
What is the effect of filtration on X-ray quality and quantity?
* Increased filtration -> decrease quantity
* Increased filtration -> increase quality
33
What is the primary source of occupational exposure in X-ray?
Compton scatter
34
What is differential absorption?
Difference between X-rays that are absorbed or pass right through
35
What is the photoelectric effect?
X-ray strikes inner shell electron and removes it from orbit, completely absorbed
36
How does atomic number affect photoelectric interactions?
Probability of photoelectric interaction is directly proportional to atomic number cubed (Z^3)
37
What is Beer's Law?
Linear relationship of X-ray and attenuating substance
38
What factors affect entrance skin dose (ESD)?
* Tube current (mA)
* Time of exposure (s)
* Peak kilovoltage (kVp)
39
What is quantum mottle?
Noisy image due to not enough X-rays reaching film/detector
40
What interaction does scatter primarily arise from?
Mostly Compton interactions
41
What happens to penetration with an increase in kVp?
More penetration (decreased attenuation)
## Footnote
Higher kVp allows more x-rays to pass through the body, reducing the amount of radiation that is absorbed.
42
What is the effect of increasing the number of photons hitting the imaging receptor?
More signal to noise
## Footnote
Increasing the number of photons improves the overall quality of the image by reducing noise.
43
What is quantum mottle?
Noisy image due to not enough x-rays reaching film/detector
## Footnote
It is the most important source of random noise in radiographic imaging.
44
How can quantum mottle be reduced?
By increasing x-ray (mAs) or using more efficient detection
## Footnote
Increasing the mAs results in more photons, which helps improve image quality.
45
What type of interactions primarily cause scatter?
Compton interactions
## Footnote
Compton scattering is a critical factor in determining the quality of radiographic images.
46
What factors determine the amount of scatter?
* kVp
* Thickness of the body part
* Field of view (FOV)
## Footnote
Higher kVp increases scatter, thicker body parts have more interactions, and smaller FOV decreases scatter.
47
What is the role of collimation in imaging?
Decreases noise (scatter)
## Footnote
While collimation reduces scatter, it may also lower the signal to noise ratio, necessitating increased mAs.
48
What is the purpose of a grid in radiography?
Improves contrast by reducing scatter
## Footnote
Using a grid involves a tradeoff of increased dose/mA.
49
What is grid cutoff?
Risk of using grid that blocks too many photons
## Footnote
Can lead to quantum mottle and a noisy image if the grid is misaligned.
50
What technique can reduce scatter by separating the patient from the receptor?
Air gap technique
## Footnote
This technique helps in minimizing scatter radiation affecting the image quality.
51
What does radiographic density refer to?
How dark the film is
## Footnote
Increased exposure leads to darker films, resulting in higher radiographic density.
52
How does increasing mA and kVp affect quantum mottle?
Decreases quantum mottle, but increased kVp also increases Compton scatter
## Footnote
The balance between mA and kVp is essential for optimal image quality.
53
What is the inverse square law?
Energy twice as far from source is ¼ the intensity
## Footnote
As distance increases, the energy is spread over a larger area, resulting in more noise.
54
How does noise change with distance between the tube and detector?
Noise increases as distance increases
## Footnote
Greater distances can lead to reduced image clarity.
55
What is the contrast to noise ratio (CNR)?
How visibility of finding is affected
## Footnote
CNR is a critical factor in image interpretation.
56
How can CNR be improved under normal circumstances?
By increasing mA
## Footnote
This method enhances visibility without altering contrast.
57
What is spatial resolution?
How close two lines can be to one another and still visibly resolved
## Footnote
High spatial resolution is crucial for detailed imaging.
58
What is unsharpness in imaging?
Loss of spatial resolution
## Footnote
It can occur due to various factors including motion and system limitations.
59
What is geometric unsharpness?
Blur caused by the focal spot size and distances
## Footnote
Smaller focal spots reduce blur but can increase exposure time.
60
What does magnification affect in imaging?
More magnification leads to more blur
## Footnote
Magnification is calculated by the ratio of source to image distance (SID) to source to object distance (SOD).
61
What is pixel density?
More pixels per unit area, better spatial resolution
## Footnote
Higher pixel density improves the clarity and detail of digital images.
62
What is the modulation transfer function (MTF)?
Information recorded/information available
## Footnote
MTF indicates the accuracy of the imaging system in reproducing detail.
63
What does detective quantum efficiency (DQE) measure?
Efficiency of detector to convert x-ray energy into image
## Footnote
DQE helps predict the dose required for optimal imaging.
64
How does DQE relate to spatial resolution and noise?
DQE is directly proportional to MTF and inversely proportional to SNR
## Footnote
This relationship highlights the trade-offs in imaging efficiency.
65
What factors affect contrast in imaging?
* Linear attenuation coefficient
* Energy (kVp)
* Density
* Atomic number
## Footnote
Adjusting these factors can significantly improve image contrast.
66
Order of increasing frequency/energy
Radiowaves, microwaves, infrared, visible light, UV, Xray/gamma ray
## Footnote
This order represents the electromagnetic spectrum from lowest to highest energy.
67
What are alpha particles composed of?
2 protons and 2 neutrons
## Footnote
Alpha particles have a net charge of 2+.
68
What is the penetration ability of alpha particles?
Cannot travel far, or penetrate deep
## Footnote
Alpha particles are relatively heavy and positively charged, limiting their range.
69
What are beta particles?
Electrons which are emitted from the nucleus
## Footnote
Unlike alpha particles, beta particles are lighter and can travel farther.
70
What are X-rays emitted by?
Electrons
## Footnote
X-rays originate from the interaction between fast moving electrons and atoms.
71
Where do gamma rays originate from?
Nucleus of atom
## Footnote
Gamma rays are emitted as excess energy when an atom decays.
72
What is the function of a focusing cup in X-ray tubes?
Help electron beam strike the target in acceptable size and reduce spatial spreading
## Footnote
The focusing cup has a negative charge around the filament.
73
What does the tube/envelope in an X-ray machine maintain?
A vacuum
## Footnote
This allows the speed and amount of electrons to be controlled independently.
74
What is bremsstrahlung?
Radiation released due to diversion of bombarding electron interacting with entire atom
## Footnote
It is proportional to the energy of incoming charged particles and atomic number Z.
75
What materials can shield beta emitters to minimize bremsstrahlung production?
Low Z materials like plastic
## Footnote
Using lead would increase bremsstrahlung production.
76
What are Auger electrons?
Ejected outer shell electron after energy imparted to it from filling inner shell vacancy
## Footnote
This process occurs with lighter elements like tissues.
77
What is characteristic radiation dependent on?
Binding energy of shell
## Footnote
The energy released is equal to the difference in binding energies between outer and inner shells.
78
What do characteristic X-rays carry?
Exact and discrete energies
## Footnote
They are depicted as sharp peaks over the bremsstrahlung continuum.
79
Which elements exhibit characteristic radiation?
Heavier elements like tungsten
## Footnote
Characteristic radiation occurs when outer shell electrons fill inner shell vacancies.
80
What does mA impact in x-ray production?
Quantity of x-rays produced, not quality.
81
What does mAs influence in x-ray production?
Exposure time impacts quantity, not quality.
82
How does kVp affect x-ray production?
Affects quality and quantity of x-rays.
83
Where is the cathode side positioned in relation to denser tissue?
To denser/thicker tissue, unless it is pediatric thigh.
84
What is the purpose of a filter in x-ray production?
Blocks soft x-rays that don’t help imaging but add dose.
85
How does the atomic number (Z) of the target material affect x-ray production?
Higher Z increases bremsstrahlung x-rays produced and affects characteristic x-ray energy shell levels.
86
What happens to maximum x-ray energy as kVp increases?
Maximum x-ray energy will increase to match kVp.
87
What is the relationship between kVp and average x-ray energy?
Average x-ray energy is ⅓ to ½ of maximum energy.
88
What is the effect of dropping kVp below the threshold for k shell electrons?
Lose characteristic peaks.
89
What does mAs represent in x-ray production?
The number of electrons per amount of time.
90
What happens to the quantity of x-rays as mAs increases?
Quantity of x-rays increases.
91
How does changing kVp affect mA to maintain x-ray density?
If kVp x 1.15 then mA/2 maintains same x-ray density; if kVp x 0.85 then mA x 2 maintains same density.
92
What is the half value layer (HVL)?
Amount of material required to attenuate x-ray to half original output.
93
What factors determine HVL?
* Beam filtration
* Anode material
* kVp
* Wide beam
94
Which factors change the x-ray spectrum?
* Tube current
* Tube potential
* Voltage generator
* Atomic number
* Filtration
95
What is collimation in x-ray production?
Restricting size and shape of x-ray beam.
96
What is the outcome of classical (coherent/elastic) interactions?
X-ray strikes orbital electron and bounces off, no ionization or contribution to image.
97
What happens in a Compton scatter interaction?
X-ray strikes outer shell electron, removes it, and atom is ionized.
98
What is a major source of occupational exposure in x-ray?
Compton scatter.
99
What type of interactions contribute to image contrast?
Photoelectric interactions.
100
What is the probability of a photoelectric interaction dependent on?
* Photon energy
* Atomic number of the absorber
101
How does the photoelectric effect relate to dose and contrast?
More PE, more dose; more PE, more contrast.
102
What happens to the photoelectric effect as kVp increases?
More kVp, less PE.
103
What is the effect of binding energy on the probability of photoelectric interactions?
Increased probability when binding energy and incident photon energy are similar.
104
Fill in the blank: The probability of photoelectric interaction is inversely proportional to _______.
incident photon energy cubed (1/E^3).
105
Fill in the blank: Probability of photoelectric interaction is directly proportional to _______.
atomic number cubed (Z^3).
106
What are the two interactions that deposit energy in the patient and attenuate the beam?
Photoelectric effect (PE) and Compton scattering
## Footnote
PE contributes to image quality while Compton scattering degrades it.
107
What happens to transmission when photoelectric effect (PE) increases?
Transmission decreases
## Footnote
Increased PE leads to greater absorption and attenuation.
108
What factors increase photoelectric effect (PE) and attenuation?
* Higher atomic number
* Increased tissue density
* X-ray beam energy (kVp) closer to K edge
109
At what energy level (keV) are the probabilities of photoelectric effect (PE) and Compton scattering equal?
30 keV
110
What is the trend in the probability of photoelectric effect (PE) and Compton scattering with varying energy levels?
* Increased probability of PE at lower keV
* Increased relative probability of Compton at higher keV
111
What is the mass attenuation coefficient?
Rate of energy loss by X-ray beam as it travels through a material
## Footnote
It is not affected by the density of the material.
112
What does the linear attenuation coefficient represent?
The probability of a material to attenuate X-ray beam over a set distance
## Footnote
It is affected by the density of the material.
113
What factors determine the entrance skin dose (ESD)?
* Tube current (mA): proportional
* Time of exposure (s): proportional
* Peak kilovoltage (kVp): square
* Distance
114
What is quantum mottle?
Noisy image due to not enough X-rays reaching the film/detector
## Footnote
It is the most important source of random noise.
115
How can quantum mottle be reduced?
* Increase X-ray (mAs)
* Use more efficient detection
116
What factors determine scatter in X-ray imaging?
* kVp: higher kVp results in more Compton scatter
* Thickness: thicker body part has more scatter interactions
* Field of view: smaller FOV decreases Compton scatter
117
What does collimation do to noise?
Decreases noise (scatter)
## Footnote
This results in lower signal to noise, requiring an increase in mAs to compensate.
118
What is grid cutoff?
Block too many photons leading to quantum mottle/noisy image
## Footnote
Can occur when the grid is incorrectly aligned (upside down, wrong distance, off center).
119
What does the inverse square law state about energy at double the distance?
It is ¼ the intensity
## Footnote
The energy is spread out across four times the area, leading to more noise.
120
How does noise change with distance between the tube and detector?
Noise increases as distance increases
121
What happens if you quadruple the energy/mA?
The mottle is cut in half
122
What is the effect of automatic exposure control (AEC) on noise?
Noise is fixed
123
How can contrast-to-noise ratio (CNR) be improved using AEC?
By decreasing kVp which improves contrast
124
What is the effect of a smaller focal spot?
Less blur
## Footnote
Smaller spots are used in mammography to compensate for blur related to magnification and in extremity exams to maximize spatial resolution.
125
What does a larger focal spot minimize?
Motion artifact
## Footnote
It allows for more mA and less exposure time, thus decreasing blur.
126
How can contrast be improved?
By decreasing energy (kVp), increasing density, or increasing atomic number
127
What does detective quantum efficiency (DQE) measure?
Efficiency of detector to convert x-ray energy into image
128
What is the relationship between DQE and spatial resolution?
Low DQE indicates high dose and high spatial resolution; high DQE indicates low dose and low spatial resolution
129
What is DQE directly proportional to?
MTF (Modulation Transfer Function)
130
What is DQE inversely proportional to?
SNR (Signal-to-Noise Ratio)
131
How does pixel density affect spatial resolution?
More pixels per unit area lead to better spatial resolution
132
What is pixel pitch?
Measurement from center of one pixel to the next
133
What are major determinants of spatial resolution in digital images?
Pixel size and pixel pitch
134
What is the result of increased pixel density and decreased pixel pitch?
Better spatial resolution
135
What is the relationship between matrix size and spatial resolution?
Large matrix leads to small pixels, resulting in better spatial resolution
136
How does magnification affect blur?
More magnification leads to more blur
137
How is magnification calculated?
By SID/SOD (Source to Image Distance / Source to Object Distance)
138
What is brightness gain?
Brightness gain is the combined effects of flux gain and minification gain
## Footnote
Brightness gain is crucial for understanding how image quality is affected in radiography.
139
What is flux gain?
Flux gain is the increase in magnitude of light from output phosphor relative to input, accomplished with higher voltage, increasing brightness
## Footnote
Flux gain plays a key role in enhancing image brightness.
140
What is minification gain?
Minification gain is the concentration of electrons from a large photocathode to a small output phosphor, increasing electron and thus energy per unit area, increasing brightness
## Footnote
Minification gain contributes to the overall brightness gain.
141
How does the age of the tube affect brightness gain?
The ability of the intensifier to increase brightness deteriorates with age, requiring more dose to produce the same level of output brightness
## Footnote
Aging tubes may lead to decreased image quality and increased radiation exposure.
142
What effect do both electronic and geometric magnification have on dose?
Both electronic and geometric magnification increase dose
## Footnote
Understanding the relationship between magnification and dose is vital for patient safety.
143
What is geometric magnification?
Geometric magnification involves moving an object closer to the focal spot to improve spatial resolution, but it increases blur
## Footnote
Geometric magnification is a trade-off between resolution and image clarity.
144
How is geometric magnification compensated?
To compensate for increased blur from geometric magnification, the focal spot is decreased in size
## Footnote
Adjusting the focal spot size is a common technique in radiographic imaging.
145
What does the R/F ratio describe?
The R/F ratio describes the relationship between intrinsic receptor resolution and focal spot size
## Footnote
The R/F ratio is an important parameter in evaluating image quality.
146
What happens if the R/F ratio is greater than 0.5?
If R/F is greater than 0.5, then magnification will increase sharpness
## Footnote
Higher R/F ratios are often desired in imaging for better resolution.
147
What is the typical R/F ratio in general radiography?
In general radiography, R/F is less than 0.5, so magnification decreases resolution
## Footnote
This highlights the limitations of magnification in general radiographic practices.
148
What is the typical R/F ratio in mammography?
In mammography, R/F is greater than 0.5, so magnification increases resolution
## Footnote
Mammography benefits from higher R/F ratios to enhance image clarity and detail.
149
what is the radiation dose change with each magnification (general radiology)
increases dose by 1.4- 2.0x
150
best position of II and X-ray tube
xray tube far from patient, II close to patient
151
what does increasing distance of patient to xray tube and decreasing distance to II do?
decrease dose, scatter, and blur/magnification (which improves image sharpness)
152
What is brightness gain compared to?
Minification gain
## Footnote
Brightness gain refers to the increase in brightness perceived when viewing through an optical system.
153
What happens to brightness with a larger field of view?
More minification (less magnification) = more brightness
## Footnote
A larger field of view generally allows for a wider perspective but at the cost of less magnification.
154
What happens to brightness with a smaller field of view?
Less minification (more magnification) = less brightness
## Footnote
A smaller field of view can provide greater detail through magnification but results in reduced overall brightness.
155
True or False: A larger field of view increases magnification.
False
## Footnote
A larger field of view decreases magnification.
156
As magnification increases and brightness decreases, what does ABC do
increases exposure to maintain brightness
157
How does collimation reduces KAP
Decrease beam area, but compared to electronic magnification, no increase in beam dose
158
What does electronic magnification increase?
Air kerma and skin dose
## Footnote
Electronic magnification enhances the radiation dose received by the skin and the air kerma, which is the kinetic energy released per unit mass in air.
159
What does electronic magnification not increase?
Kerma area product (KAP)
## Footnote
KAP is a measure of the total amount of radiation delivered to a specific area and remains unchanged with electronic magnification.
160
How to lower dose
1) Move patient away from source, closer to image intensifier/detector
2) increase collimation (small field of view)
3) avoid magnification
161
What is air kerma limit
87 mGy per min or 10 R/min
(High level control is double)
162
Which artifacts are unique to II system compared to FPD
Pincushion, s distortion, vignetting, glare, and saturation artifacts
163
What does binning do
Increases signal to noise ratio (SNR), but decreases spatial resolution
Binning only applies to FPD
164
Pulsed fluoro
What happens to dose
Pulses of higher mA instead of continuous mA
If frame rate is below 30 from/sec, overall dose is reduced (though each individual pulse will have more mA)
165
8 factors affecting spatial resolution
FOV (smaller is better), focal spot size, image receptor limitations (FPD detector element and II television), motion factors, dynamic range, pixel binning (decrease spatial resolution but improve SNR), frame averaging, pulsed fluoro (better for spatial resolution)
166
Grids are not used in what situations
Peds and extremities (less tissue)
167
What is the relationship of dose to distance and time
Inverse square law dictates relationship between dose and distance
Direct relationship between dose and exposure time
168
When using carbon dioxide instead of iodinated contrast you should
Never use above diaphragm
Never use in pts getting nitrous oxide
Place pt in trendelenberg
169
DSA is performed at what kVp
70, to maximize iodine k edge of 33
170
What does filtration do to average energy, penetration power, contrast, and half value layer
Filters out low energy xrays, increasing average energy (higher energy beam aka increased penetrating power) and half value layer
Decreases contrast
171
What caused a film to be over or underexposed?
Too much mA (and kVp) causes overexposed (too dark)
Too little mA causes underexposed (too bright/mottled)
172
How does increased exposure time affect dose, mottle, and blur
What if AEC is present and exposure time is increased
Increases dose and motion blur, decreases mottle/noise
If there is AEC and the exposure is increased, dose is maintained, which also does not decrease mottle/noise, but motion blur still increases
173
What will show intrinsic high contrast
Different thickness, density and atomic number
174
What will cause increased contrast
Low kVp
High density (barium)
High atomic number (iodine)
Decrease scatter (grid or air gap)
Decrease filtration
NOT AFFECTED BY MAS
175
Indirect digital detector uses what
What is an issue with indirect type
Cesium iodide scintillator
Lateral light dispersion which decreases spatial resolution
This is not an issue with direct using photoconductor amorphous selenium
176
What is the fill factor of direct digital radiography
Nearly 100% (compared to indirect)
This is more efficient and means higher DQE
177
What is radionuclide purity of 99Tc testing for? When? How? What order and what is the limit?
Mo concentration/breakthrough at the time of ADMINISTRATION (not elution).
Must assay Mo first with dose calibrator and lead shield
0.15 microCi of Mo per 1 milliCi Tc
178
How does free Tc look
Uptake in stomach, salivary gland, lingual, thyroid
