Lecture 1: Intro/X-ray Production/Image Formation/QUIZ 1 (Winter) Flashcards
Radiology is used as a clinical tool for 4 main things:
1) detect presence or absence of disease
2) specific disease recognition and/or localization
3) progression of disease
4) evaluation of therapeutic success of failure
4 types of diagnostic imaging
1) MRI
2) Nuclear medicine (i.e. PET scans)
3) Radiography (i.e. CT, fluoroscopy)
4) Ultrasound (i.e. echocardiography)
who discovered x-rays?
Roentgen
who discovered radioactivity?
Becquerel
radiation
the transfer of energy as particles or electromagnetic (EM) waves. Radiation differs in its wavelength, frequency, and energy
energy and wavelength are (directly/inversely) proportional?
inversely
ionizing radiation
radiation with sufficient energy to cause the atom or molecule that it reacts with to lose an electron; an essential characteristic of high energy radiations when interacting with matter.
The energy of electromagnetic radiation is inversely proportional to:
wavelength
light travels at the same SPEED, but at different ENERGIES because of the varying frequencies and wavelengths of light
:)
How are x-rays produced? Where does this occur?
through the conversion of energy within particulate radiation (electrons) to electromagnetic energy (x-rays). Occurs inside the x-ray tube when high speed electrons collide with the metal anode
Which end of x-ray tube is positive? negative?
positive: anode
negative: cathode
What causes electrons to be drawn across the negative and positive ends of the x-ray tube?
high voltage
what metal comprises the cathode filament?
tungsten
fx of focusing cup
negatively charged and focuses the electron cloud from the cathode toward the anode
the cathode of an x-ray tube has (low/high) voltage and (low/high) resistance
low voltage, high resistance
what metal comprises the anode (target)?
tungsten, rhenium
The (cathode/anode) determines the NUMBER of electrons?
cathode
The (cathode/anode) determines the ENERGY of electrons?
anode
The anode has (low/high) voltage and (low/high) resistance
high voltage, low resistance
kVp
- the energy potential applied from cathode to anode
- kilovoltage peak applied across the tube
- refers to the maximum energy of xrays
- determines how many of the x-rays make it through the patient
mA:
- (milliamperes) controls the resistance of the circuit through the tungsten filament
- refers to the NUMBER of electrons boiled off the tubngsten tube/number of x-rays produced
keV:
the duration of a photon/EM wave
s-time
- the duration of a radiographic exposure
- combined with mA, determines # of x-rays that will be produced during a given exposure
Which of the following is true of electromagnetic radiation?
a: has properties of a wave
b: has properties of a particle
c: travels at the same velocity regardless of wavelength or frequency
d: has a charge
a,b,c
Bremsstrahlung
the process by which an x-ray is emitted by an e- during loss of kinetic energy
In the diagnostic energy range typically used, the primary interaction of x-rays w/ matter is:
compton scatter
ALARA stands for:
As Low As Reasonably Achievable
Penumbra
a blurred area around the image of an object that results from use of a large focal spot, or decreased FOD
quantum mottle
- relates to the # of photons that are incident on the detector and cause film blackening
- mottle caused by the statistical fluctuation of the number of photons absorbed by the intensifying screens to form the light image on the film
summation
the perceived increase in opacity observed when two objects are superimposed upon one another, but not necessarily in the same plane
border effacement
the inability to distinguish margins of objects that are of the same opacity and in contact w/ one another
the 5 radiographic opacities are:
gas, fat, soft tissue, mineral, metal
3 settings we have control over when taking a radiograph
time (sec), mA, and kVp
What happens if kVp is set too low?
rad will be a shadow of an image b/c x-rays don’t make it through the patient
fx of filtration
removes the low energy x-rays that we don’t need (won’t be diagnostic, and may cause harm)
fx of collimation
reduces scatter, protects patients, and focuses on an area of interest when taking a rad
clicker Q: X-rays are produced in an x-ray tube by:
interactions of electrons with metal
photoelectric effect vs. compton scatter
Both involve the ejection of an electron when light strikes a metal.
Photoelectric effect:
- photon is absorbed and does NOT contribute to image formation, electron is released
- Usually occurs at lower energies
Compton scatter:
- photon is scattered at some angle and contributes to image formation, and the electron is released with another direction
- Usually occurs at higher energies
- degrades image
increased kVp –> likelihood of Compton scatter
increases
increased kVp –> likelihood of photoelectric effect (PE)
decreases
increased atomic number –> likelihood of PE
increases
thickness/density of object –> compton scatter
increases
attenuation
reduction in intensity of the primary beam as it travels through an object/patient (i.e. via absorption, scatter)
latitude
- the ability of a film to record differences in density
- maximum difference in radiographic density of anatomical structures that can be evaluated on a given radiograph
- inversely related to contrast with many shades of gray
- obtained with HIGH kVp and LOW mAS
- used for abdomen and thoracic evaluation
contrast
- the state of being strikingly different from something else, typically in juxtaposition or close association
- difference in the photo density (optical whiteness/blackness) b/w 2 adjacent anatomic structures
- short gray scale
- obtained with LOW kVp and HIGH mAS
- used for musculoskeletal evaluation
clicker Q: when creating a radiograph of the thorax, your settings should aim to:
decrease the inherent contrast in the image, and use a higher kVp
increasing kVp –> contrast
decreases
more scatter will be produced with increases in:
kVp, field size (collimation), and patient thickness
2 methods to reduce scatter after x-ray prod.
grids, air gap
What are grids?
- series of radioopaque material (lead) alternated with strips of radiolucent material
- fx: transmits only those x-rays on a straight line from the source to the image receptor
- placed b/w the patient and the film to remove scatter prod. by the interaction of the primary beam with the patient
grid ratio
height of strips/space between the strips (standard ratio = 8:1, 10:1)
purpose of the image recording system
to form a visual display and permanent record for future comparison
what do intensifying screens do?
convert x-ray energy into visible light which then exposes the film. Film by itself is an inefficient detector of x-rays
4 main components of the intensifying screen and their functions?
1) protective coating: prevents damage
2) phosphor: active layer that emits light
3) reflective layer: reflects light photons toward film
4) base: support layer
screen speed
relative number that identifies the efficiency of conversion of x-ray radiation into light
3 factors that determine screen speed
1) phosphor type
2) crystal size
3) secondary factors (dye, reflective layer)
faster screen speed –> detail of image
decreases
advantages of intensifying screens
- decrease x-ray dose to the patient, exposure times
- increase image contrast
disadvantages of intensifying screens
- decrease detail
- artifacts
Computed Radiography (CR)
- uses cassettes w/ image plate
- phosphorescence records and stores latent image
- read by laser
Direct Digital Radiography (DR)
- x-rays converted to electronic signal
- immediate display
What is DICOM?
(Digital Imaging and Communications in Medicine)
- standard for handling, storing, printing, and transmitting info for medical imaging.
- safe, legal storage of medical record document
what is PACS?
(Picture archive and communication system)
-storage of DICOM images in a complex database
