Shared Flashcard Set

Details

Radiology I Lectures 1-5
X-ray properties, films, development, digital
85
Veterinary Medicine
Professional
10/30/2011

Additional Veterinary Medicine Flashcards

 


 

Cards

Term
What types of imaging does radiology include?
Definition
-CT
-diagnostic and interventional radiology
-nuclear medicine
-ultrasound
-MRI
-radiation therapy
Term
What is an x-ray?
Definition
high energy electromagnetic radiation
Term
Who discovered x-rays, and when?
Definition
Wilhelm Conrad Rontgen in 1895
Term
What was Rontgen working on when he discovered x-rays?
Definition
cathode ray tube
Term
What was Rontgen's first image?
Definition
his wife's hand where he could see her bones and rings
Term
What award did Rontgen win?
Definition
Nobel Prize for Physics in 1901
Term
Who did the first clinical radiograph, and of what?
Definition
-Dr Frost = fractured forearm
-Dr Cox = gunshot wound
Term
What society was founded in 1900?
Definition
American Roentgen Ray Society (ARRS)
Term
Who produces the first animal radiographs?
Definition
Josef Eder in 1896 (dead small animals)
Term
What veterinary organization was founded in 1962?
Definition
American College of Veterinary Radiology (ACVR)
Term
What is ionizing radiation?
Definition
-has the ability to eject an electron from its orbit
-has high frequency and short wavelength
Term
What is the relationship between wavelength, frequency, and energy?
Definition
increased wavelength = decreased frequency = decreased energy
Term
How are x-rays produced?
Definition
electrons are accelerated from the negative cathode to the positive anode
Term
How are electrons accelerated from cathode to anode?
Definition
there's a high voltage differental between the two (kVp)
Term
What are the adjustable components of the x-ray machine that determine radiograph quality?
Definition
kVp
mAs
Term
What is mA?
Definition
-milliamperes
-the number of electrons liberated from the cathode
Term
What is the souce of electrons?
Definition
cathode
Term
What does the size of the cathode determine?
Definition
-size of electron beam
-size of target on the anode (focal spot)

therefore, the size of the origin of the x-ray beam
Term
What is the souce of x-ray product as the accelerated electrons from the cathode filament interact with the atoms of the metallic target?
Definition
anode
Term
What is the anode composed of?
Definition
tungsten (high atomic number and melting point)
Term
What determines the speed/energy of the electrons?
Definition
kVp
Term
What is the anode angle?
Definition
-reduces temperature by spread x-rays out but keeps focal spot small
Term
What are the advantages of a rotating anode?
Definition
-When a high tube current is used (more than 100 mA), it can spread the heat over a larger surface area
-anode angle can be decreased for the same number of electrons, therefore the image quality is better
Term
What type of anode is seen in portable x-ray machines?
Definition
stationary anode
Term
What is the heel effect?
Definition
non-uniform x-rays due to the anode angle because some of the x-rays were absorbed by the anode (target)
Term
How does one compensate for the heel effect?
Definition
placing thicken portion of the patient towards the cathode
Term
What are the two types of x-rays produced in an x-ray tube?
Definition
-general (braking or bremsstrahlung) radiation
-characteristic (collisional) radiation
Term
What is collisional radiation?
Definition
-an electron is ejected from its orbit
-an electron from a higher shell drops down into lower shell
-energy produced
Term
What is bremsstrahlung radiation?
Definition
-predominant type of x-rays produced in a tube
-electron passes through an atom, slows down and curves due to positive nucleus
-slowing down gives off energy (x-ray and heat)
Term
How much of the energy emitted from bremsstrahlung is heat vs x-rays?
Definition
99% heat, 1% x-ray
Term
X-rays have a wide spectrum of energy. What happens to low energy x-rays?
Definition
-not useful for diagnostics
-aluminum filter in x-ray tube remove them
Term
What is the mean energy of x-rays?
Definition
the quality of x-rays
Term
What is the relationship between kVp and x-ray energy?
Definition
the mean energy of the x-rays is 1/3 the max kVp (max electron energy)
Term
What determines the quantity of electrons?
Definition
mAs
Term
What is the main reason for filtration of x-rays?
Definition
protection
Term
What are the two main reasons for collimation in diagnostic radiology?
Definition
-radioprotection (restricts beam so the amt of primary and scatter radiation is reduced)
-image quality (reduced scatter = better contrast)
Term
When is attenuation?
Definition
process by which x-ray beam energy is reduced as it passes through a tissue
Term
Attenuation of the x-rays depends on four things. Name them.
Definition
-x-ray energy (kVp)
-tissue thickness
-density
-atomic number of object being radiographed
Term
What is the photoelectric effect?
Definition
-responsible for contrast (good!)
-happens when an inner shell electron gets bumped out, resulting in a photoelectron, a positive ion, and a little x-ray energy that is absorbed quicky
-explains why better contrast is achieved with low kVp
Term
What is the probability of the photoelectric effect?
Definition
k x Z^3 / E^3
Z = atomic number of object
E = power of x-ray energy
Term
When does the photoelectric effect occur most often?
Definition
low E and high Z
Term
What is the Compton effect?
Definition
-results in deviation of incoming x-rays from its initial path with a loss of energy (BAD!)
-x-ray encounters outer shell electron and bumps it out, scattering an emitted x-ray
Term
Why is high kVp bad?
Definition
more scatter radiation from the Compton effect and less contrast
Term
What is film density?
Definition
-the degree of film blackness
-directly related to how many x-ray have reached the film (gone through patient)
Term
What determines film density?
Definition
mAs, and to a lesser extent kVp
Term
What is FFD?
Definition
-focal-film distance
-the distance of the x-ray tube to the film
Term
What is the relationship of FFD to film density?
Definition
decreased FFD = increase film density
Term
What is the inverse square law?
Definition
-the x-ray beam intensity changes as a function of the square of the distance
-if FFD is doubled, the intensity decreases by 4 (1/4)
Term
What is the relationship between mAs and kVp when making a diagnostic image?
Definition
as one goes up, the other must go down, as to keep the film density at the correct level
Term
How does mAs affect radiographic density?
Definition
mAs and film density have a direct relationship (doubling mAs = double film density)
Term
How does kVp affect radiographic density?
Definition
-in the 40-100 kVp range, you need to +/- 10% of kVp to make the radiograph twice/half the original film density
-in the 100 kVp range, make that 15%
Term
What is image contrast?
Definition
-the difference in opacity between two region on the radiograph
-we don't want TOO much contrast, we need shades of gray
Term
What is latitude?
Definition
-the number of shades of gray in an image
-we want this!
Term
What determines contrast?
Definition
-energy of x-rays (kVp)
-difference in density and Z between two regions
Term
What happens to contrast as the kVp goes up?
Definition
-contrast decreases
-latitude (shade of gray) increases
Term
What kVp setting is preferred for thoracic radiographs and why?
Definition
-high kVp
-increases latitude
-need extra energy to get through thickness
Term
what kVp setting is preferred for bone radiography and why?
Definition
-low kVp
-maximizes contrast to get good bone detail
Term
What affects film density?
Definition
mAs (sorta kVp)
Term
What affects film contrast?
Definition
kVp
Term
What is film speed?
Definition
-determined by size of film crystals
-has inverse relationship to image quality
Term
Describe the intensifying screens in the film cassette.
Definition
-improves efficiency of the x-ray system (amplifier)
-faster screens provide less detail
-emit a certain wavelength of light, so must match the film
Term
Describe the emulsion, crystal size, exposure requirements, and film quality in fast screen/fast film.
Definition
-thick emulsion
-large crystal
-requires less exposure
-grainier image
Term
What is the most common source of degraded image quality?
Definition
patient movement
Term
What are some common technical errors affecting film quality?
Definition
-increased or decreased film density
-loss of film contrast
-localized areas of increases/decreased film density
-blurred images
-grad artifacts
Term
What would cause increased film density error?
Definition
-too high kVp or mAs
-decreased FFD
-overestimating thickness
-use of grid technique without a grid
Term
What would cause decreased film density error?
Definition
-too low kVp or mAs
-increased FFD
-underestimating thickness
-loading two films in a cassette
-use of slower film
Term
What would cause loss of film contrast error?
Definition
-darkroom lead
-back scatter
-out of date film
Term
What would cause localized areas of increased film density error?
Definition
-scratch on film
-static
Term
What would cause localized areas of decreased film density error?
Definition
-foreign material on film
-bent film
Term
What would cause a blurred image error?
Definition
-patient motion
-cassette or table motion
Term
What would cause grid artifacts?
Definition
-grid inverted
Term
What is a technique chart?
Definition
-based on the measured thickness, we can increase of decrease kVp (with relatively same mAs)
-used to standardize how to make radiographs and to ensure that the image quality is good
Term
What are the pros and cons to computer radiography (CR)?
Definition
pros: no need to modify existing machinery, cassettes can be used for more than one machine

cons: needs a film reader (maintenance), 30-60 second read time
Term
What is computer radiography (CR)?
Definition
-image plate contains image
-plate reader has laser that reads latent image
-analog signal converted to digital signal
-plate erased so it can be reused
Term
What is direct digital radiography (DDR)?
Definition
captures x-rays as they exit patient without using plate reader
-two types: CCD, and flat panel (direct and indirect conversion)
Term
What is the direct flat panel DDR?
Definition
-directly attached to a computer
-thin film transistor array directly reads out image
Term
What is the indirect flat panel DDR?
Definition
-scintillator converts x-rays to visible light
-diode turns light to electric signal to get image readout
Term
What are the pros and cons to direct flat panel DDR?
Definition
pros: 4 second reading, better resolution

cons: expensive, directly attached to computer
Term
What is CCD?
Definition
-scintillator releases light, lens makes it smaller, goes through CCD detector, then get image readout
Term
What are the pros and cons to CCD?
Definition
pros: less expensive than flat panel

cons: attached to table, some light photons lost during optical reduction therefore less resolution
Term
How many megapixels are medical grade monitors?
Definition
2-5 MP
Term
What is DICOM?
Definition
Digital Imaging and Communication in Medicine
Term
What type of imaging stands up to legal scrutiny and why?
Definition
-DICOM
-images cannot be altered
-header contains patient info
-image file has a unique ID#
Term
Where are digital images stored?
Definition
PACS (picture archiving and communication system)
Term
What is teleradiology?
Definition
-transmission of image from one doctor to another for interpretation
-use DICOM
Supporting users have an ad free experience!