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Terms in this set (160)
Energy is measured in
Power is measured in
Joules/second (rate energy is measured in)
How much E does an electron accelerated through one 1 Volt gain?
Roughly how many eV does an outer shell electron need to be ejected
A few eV
Roughly how many eV does an inner shell electron need to be ejected
keV or 10s of keV
Roughly how much eV does a nuclear transition take
Atomic number of O? k shell binding?
8; 0.5 keV
Atomic number of Ca? k shell binding?
20; 4 keV
Atomic number of I? k shell binding?
Atomic number of Ba? k shell binding?
56; 36 keV
Atomic number of Pb? k shell binding?
82; 88 keV
Electron density is proportional to?
Electromagnetized radiation is quantified in what?
What is Electromagnetized radiation proportional to?
Name 3 types of ionizing radiation?
UV, x-rays and gamma rays
What type of targets are used in x-ray tubes?
Where are the targets embedded?
What is the electron source in the x-ray tube?
When a voltage is applied how does current flow?
From filament to anode
x rays are formed when they interact with which part of the tungsten atom?
Which types of x rays are formed by electron deceleration in the electric fields of nuclei?
Characteristic electrons are formed when energetic electrons eject what?
k shell electrons
What type of x rays make up the majority of the spectra
What is the relation of the average energy to maximum energy for most spectra?
the average energy is usually half the max
What is the average kV for a belly x ray
What is the average kV for an extremity x ray
what is the average kV for a chest x ray?
Are tube currents higher in radiography/ct or fluoro?
radiography/ct! (usually 100s of mA) versus a few mA in fluoro
Which has the longest exposure time? Chest, abdomen, CT or flouro?
Exposure times are a few ms (chest), 50 ms (abdomen), 500 ms (CT) and "minutes" in fluoro.
How do you calculate mAs?
product of tube current (mA) and exposure time (ms)
T/F Increasing the mAs increases the average photon energy
False. Changing the mAs doesn't affect the average photon energy
T/F Chest x ray uses 80 kV/20mAs
False. Chest x ray is 120 kV/1 mAs and Abd x ray uses 80 kV/20 mAs
T/F Coherent scatter transfers no energy to atomic electrons
T/F Coherent scatter makes up the majority of all x ray interactions
False. (less than 5%)
Photoelectric interactions absorb or deflect x rays?
Absorb. (all x rays absorbed by k shell electrons and energy deposited locally)
At what Z values are photoelectric effects important? At what energies?
T/F. To maximize photoelectric interactions photon energy should be just below the k edge energy
False. Should be just above the k edge
Where does a k edge filter transmit photons?
Just below the k edge energy (e.g. < 20 kev for Mo filter)
What type of interactions are compton scatter the result of?
x rays with outer shell electrons
What is the result of compton scatter?
lower energy scatter photons
What parameter of image quality do scatter photons degrade?
What is compton scatter proportional t?
Electron density (which is proportional to physical density)
T/F Both photoelectric and compton interactions increase with increasing photon energy
False, both decrease with increasing photon energy
In tissue at what kV are compton and photoelectric equal?
At what energies does PE dominate? Compton?
PE dominates at lower E; Compton dominates at higher E
What value describes the exponential attenuation of x rays?
Attenuation coeffecient u cm-1
When u is 0.1 cm-1 what percent are attenuated in 1 cm?
T/F About 1/3rd of x ray energy is absorbed by the patient and 2/3rd scattered ?
False. 1/3 is absorbed and 2/3 are scattered
What percentage of x ray energy is transmitted?
less than 1 %
How much tissue attenuates 50% of x rays?
How does Z number of a substance relate to the amount needed to attenuate 50% of x rays
Inversely proportional (Al has Z of 13 and needs 3mm to attenuate 50% and Cu has Z of 29 and needs 0.3mm to attenuate 50%)
What does air kerma measure?
x ray radiation intensity
What unit is air kerma measured in?
What is the Entrance Kair for the lateral skull
About how much is incident on the image receptor for most x rays
What factors make the intensity lower at the image receptor?
Patient attenuation, grid losses and the inverse square law
T/F Entrance Air Kerma is 10 times greater for x ray than IR
False. 1000 times greater in IR (a few Gy)
Beam quality refers to what?
Penetrating power (related to beam energy)
Quality is measured by the amount of Al to reduce an x ray beam by what percentage of its initial value?
T/F Quality can be increased by increasing the tube voltage
T/F Quality can be increased by decreasing the fiitration
False. Passing x rays through filters knocks out lower E photons, increasing the average energy
Beam hardening does what?
increases the energy
What are filters used in radiology made out of?
Al and Cu
How do you get more x rays (quanitity)?
increase the mAs (not kV)
How do you increase penetration?
kV or increased filtration (then mAs is adjusted)
With AEC do more penetrating beams have higher or lower radiation into the patient?
What is the Kair for a chest x ray?
What is the Kair for a lateral lumbar spine x ray?
What is the Kair rate (per min) for flouro?
How do you calculate Kerma-Area Product?
Entrance Kair (mGy) times beam area (cm2)
What unit is absorbed dose measured in ?
mGy (energy absorbed divided by mass)
How does Kair differ from dose?
Dose depends on absorber characteristics
Are skin doses greater in radiography or Ir
IR (>500 mGy) versus (<10 mGy in radiography)
Eye lens dose in radiography?
Eye lens doses can be ~ 1 mGy in radiography
Eye lens dose in IR?
< 500 mGy in IR.
Average Glandular Doses in mammography ?
2 mGy/view, or 4 mGy for a screening exam.
Embryo doses in radiography? CT?
~ 1 mGy in radiography and ~ 30 mGy in CT.
What is Equivalent dose?
The absorbed dose (mGy) times a radiation weighting factor (wr).
What unit is equivalent dose in?
t/f Alpha particle and neutrons kill more cells than x ray at the same radiation dose in Gy
What is the Wr in radiology?
In radiology Organ absorbed dose (mGy) is the same as
Equivalent dose (msV)
t/f Equivalent dose and organ absorbed dose are the same in NM
Name 3 out of 5 of the most radiosensitive organs
RBM, breast, lung, colon and stomach
Very low dose exams are defined as
effective dose <0.1 mSv
Moderate exams are defined as
effective dose 1 to 10 mSv
How much radiation dose the average american from Ubiquitous Radiation?
How much radiation dose the average american from radon?
T/F scatter increases with decreasing thickness?
Scatter increases with increasing thickness
T/F scatter decreases with increasing Beam area?
Scatter decreases with decreasing beam area
T/F Lesion contrast is not affected by scatter
False. Lesion contrast improves with reduced scatter
At what thickness does scatter need to be reduced?
Increasing the x ray tube voltage results in increased or decreased scatter?
Anti Scatter grids are seldom or often used in radiography? flouro?
Often used in both
What materials are used in High attenuating strips?
Pb or W
Are the high attenuating strips aligned with or against the primary beam?
What is the grid ratio?
ratio of Height to gap
What is the typical grid ratio?
Why do we not see the grid lesion during exposures?
What percentage of primary photons do grids transmit?
What percent of scattered photons do they transmit?
90% (check this)
What will Increasing the grid ration do to the transmission rate?
decrease rate of transmission of primary and scatter
What is the Bucky factor?
ratio of incident ratio ON grid/transmitted THROUGH grid
When are grids not used?
bedside, thin body parts or extremities
what are the grains used in the emulsions for Film made of?
Film processor passed an exposed film through a?
Developer, fixer, and washer/drier.
What happens to exposed grains?
reduced to clumps of silver in the developer
What happens to non-exposed grains?
removed by the fixer
What do the large number of silver specs located on exposed regions of film do?
Absorb incident light
What does a Characteristic curve in film imaging plot?
Film blackening (density) as a function of radiation exposure
Where is the image contrast very low on the characteristic curve?
"to and shoulder region"
T/F The linear part of the characteristic curve has high image contrast (density ~ 1.5).
Steeper slopes of the linear part of the characteristic curve have higher or lower image contrast?
Screens (scintillators) absorb x rays and generate
What screen film Kair is required to produce the right film density (1.5)?
What is Latitude?
Latitude is the difference between the highest and lowest Kair values that can be used with film.
Dynamic range of what?
Highest and lowest Kair values that can be used with fiim
Who uses wider latitudes in screen film, chest or mammo?
chest (mammo uses narrow latitudes)
In digital imaging in what form are light produced by the scintillators captured in?
CsI is used in what?
image intensifiers and in flat panel detectors (indirect)
Direct Flat panels detectors are used in?
What photoconductor is used in direct flat panel detectors?
Detector thickness increases, decreases or has no effect on dose?
Thicker detectors capture more of the incident x-rays and thereby help reduce patient doses.
T/F thinner detectors produce blurrier images
False. Thinner detectors minimize the spread of light, and generally produce sharper images.
Do PSP or photoconductors have better resolution?
T/F Scintillators result in the highest dose
False. Scintillators generally absorb most x-rays, and result in the lowest patient doses.
Do digital detectors or screen film have the wider dynamic range?
Digital. Digital detectors have a wider dynamic range (10,000:1) than screen-film (40:1).
What is the matrix size for a CXR?
2k x 2.5k
How many bits code for each pixel in a cxr?
10 bits (2 Byte)
How much storage space does a cxr require? CT?
A chest x-ray requires 10 MB to store, and a CT image requires 0.5 MB.
What do SMPTE patterns check?
Number of Megapixels
How may Megapixels do diag worskstations generally have?
Why is Unsharp Mask enhancement useful in ICU chest films?
The difference in xray transmission by a lesion relative to background tissue is the definition of what?
What is the effect of photon ENERGIES have on contrast?
Low energies improve contrast
What affect does scatter have on contrast?
Increased scatter decreases contrast
T/F Increasing the level reduces contrast
False. Increasing Level reduces image brightness, and increasing Window (width) reduces contrast.
How is mottle affected by the Kair?
Decreased mottle with increased number of photons(kair)
Increasing the number of photons to 10,000 results in a random fluctuation of about
Do radiographs or fluoro frames have more mottle?
Radiographs use X 100 more radiation than fluoroscopy frames, and have 10 times less mottle.
What ratio determines lesion visibility?
HOW DOES mAs Affect CNR?
Increased mAs results in decreased noise leading to improved CNR
How does kV affect CNR?
Increasing contrast (result of decreasing kV) results in improved CNR.
Full width half max (mm) measures ______
the width of the image of a line (line spread function)
Line pair phantoms can be used to measure _______
Low spatial frequencies affect ______
High spatial frequencies provide _______
What factors affect resolution?
Focal spot, image size and motion during imaging
Large focal spots result in _____
reduced image sharpness (decreased resolution
T/F decreased magnification results in increased focal blur
False. Increased magnification increases focal blur
In scintillators what parameter determines the amount of blur?
How do you calculate pixel size?
image dimension divided by number of pixels
How does the size of the pixel affect blur?
larger the pixel, the blurrier the iamge
T/F Chest x rays have large pixels 5mm
False, small pixels 0.175
How man pixels are per mm in cxr? what is the best achievable resolution?
6; 3 line pairs per mm
What happens when objects contain frequencies greater than the nyquist frequency?
aliasing occurs (high frequencies are poorly seen)
Does KV influence CNR? Spatial resoultion?
Does mA influence CNR? Spatial resolution?
What is a scientific way of representing resolution performance?
Modulation transfer function
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