Diagnostic Imaging Flashcards
Wavelength
Distance between peaks or crests of one wave to another (measured in horizontal length)
List 12 Properties of X-rays
- Highly penetrating invisible rays that form electromagnetic radiation
- Electrically neutral, not affected by electric or magnetic fields
- Produce a wide variety of energies and wavelengths
- Release small amounts of heat as they pass through matter
- Travel in straight lines
- Travel at the speed of light in a vacuum
- Ionize matter
- Cause fluorescence of specific crystals
- Not focused by lens
- Affects photographic film
- Create chemical and biological changes in matter due to ionization and excitation
- Produce secondary and scatter radiation
Direct Current (DC) vs Alternating Current (AC)
DC: electrons flow in one direction
AC: electrons flow in 2 directions
How many volts are needed to produce x-rays?
65,000-100,000
Define transformer
mechanism used in an electrical circuit to increase or decrease voltage
List what the control panel displays
On-off switches
Milliamperage
Time
Kilovoltage
Define Ampere
number of electrons per second
-increase in amperage increase the number of electrons that work
Define volt
Force that moves electrons
Kilovoltage peak (kVp)
peak voltage of an alternating current
What does kVp determine?
-Speed at which electrons are propelled from the cathode
-Penetrating power of the x-ray beam (known as quality)
What 2 things does the lead glass vacuum housing contain?
2 electrodes: cathode and anode
What controls the cathode (negative) electrode?
milliamperage (mA) settings
Function of the tungsten filament
emits electrons when heated
-When mA is applied to the filament, electron cloud forms around it
Function of the molybdenum cup
Focuses direction of electrons towards the anode
What controls the anode (positive) electrode?
kVp settings
What is the tungsten target?
spot where electrons hit to produce x-rays
What is the focal spot and what originates from it?
Small area on target on the anode where the electrons are directed
x-rays originate from this spot
What is the function of the copper stem?
Dissipates excessive heat
X-ray production results in the generation of ______ and ______
1% x-ray
99% heat
What is the tube head?
Protective metal covering that contains the x-ray tube, high/low-voltage transformers, and insulating oil
What is the position-indicating device (PID) collimator?
What is its function?
Attaches to the tube head and directs x-ray beams to the object and film
Helps reduce exposure
Describe the steps of an x-ray
-Electrons are generated at the cathode by the filament
-Voltage is passed between the cathode and anode
-The electrons pass from the cathode side of the tube to the anode side of the tube at
great speeds and collide with the target on the anode
-X-ray are produced with the majority being guided downward for medical purposes (primary
beam) but some x-rays do go in all directions (scatter radiation)
What creates scatter radiation?
Created because the primary beams interact with an object
Define exposure
quantity of ionization in the air
-measurement is taken at the skin surface before radiation penetrates tissues
Define absorbed dose
amount of radiation absorbed by object
-amount absorbed will vary depending on material
Define dose equivalent
absorbed dose adjusted to biological damage potential of the radiation
List 3 Absolutes of Radiation Safety
- Don’t place any part of the human body in the primary x-ray beam at any time, whether it’s
covered by protective clothing or not. - Pregnant women should stay away from the radiation area.
- Don’t allow anyone under the age of 18 in the radiation area.
Which organ should ALWAYS be shielded when taking an x-ray?
Thyroid
What are intensifying screens?
What is the function?
Screens that are plastic sheets coated with fluorescent material (phosphors)
-Helps decrease the amount of radiation needed to produce a diagnostic image
-Helps increase the contrast of the image
What is a dosimeter?
film badge that measures exposure to radiation
Define the ALARA concept.
As Low As Reasonably Achievable
-Exposure should be kept to a minimum by increasing distance, increasing shielding, and decreasing time
Describe the 3 ways to reduce radiation exposure.
-Time: Make sure the image taken the first time is the correct image with the correct
exposure and correct positioning.
-Distance: Stay as far away from the primary beam and patient as possible.
-Shielding: Wear proper personal protective equipment.
Define radiolucency
Dark areas
Produced by less dense structures that permit passage of x-rays
Define radiopaque
Light areas
Produced by denser structures as radiation has been absorbed by those structures
Define Focal Film Distance (FFD). What can it create?
Distance between x-ray tube and film
-When set appropriately, it will create a sharper image
Difference between FFD for conventional machine and small portable machine
Conventional machine: 40 inches
Portable machine: 26 inches
Define intensity. What affects it?
Total energy contained in the beam
-Affected by mA, kVp, distance, and exposure time
How do you increase beam intensity?
Increase mA, kVp, and time
Decreae the distance
How do you decrease beam intensity?
Decrease mA, kVp, and time
Increase the distance
Define half-value layer and its function.
Thickness of aluminum filters reduces the intensity of the beam by half
-filters remove less penetrating, longer wavelengths
Define inverse square law.
Intensity of radiation is inversely proportional to the square distance from the source of radiation
Define density and list what it’s proportional to.
Darkness
-Proportional to amperes, kVp, and time
Define milliampere-seconds (mAs)
product of mA and time that represents the blackening of the image or the density
To maintain similar density:
-Time is ___; milliamperage must be ___
-Time is ___; milliamperage must be ___
-Increased, decreased
-Decreased, increased
Define contrast
difference between lighter and darker shades of grays on a radiograph
Increased kVp results in ___ shades of gray (___ contrast)
many
low
Decreased kVp results in more ____ areas (___ contrast)
black and white
high
Define kilovoltage
Refers to the energy of the electrons when they reach the anode
Soft tissue requires ___ kVp and ___ mA
Higher
Lower
Extremities require ___ kVp and ___ mA
Lower
Higher
What does the developer do in image processing?
Converts sensitized silver halide crystals into black metallic silver
List the 6 components of developer.
-Developing agents (usually phenidone and hydroquinone)
-Activator (sodium bicarbonate)
-Restrainer (potassium bromide)
-Preservative (sodium and potassium sulfite)
-Hardener (potassium aluminum sulfate or aluminum chloride)
-Solvent (water)
Define latent image
image formed by x-rays on the film but not visible yet
Reducing agent function
reduces exposed silver halide crystals into black metallic silver
(ex. hydroquinone, elon)
Alkalizer function
Softens film emulsion and speeds up action
(ex. sodium carbonate)
Restrainer function
inhibits development of unexposed silver halide crystals (ex. potassium bromide)
Preservative function
preservative that prevents oxidation (ex. sodium sulfite)
Fixing agent function
Clears unexposed silver halide crystals (ex. sodium thiosulfate)
Hardener function
Shrinks and hardens emulsion (ex. potassium alum)
Acidifier function
Keeps medium acidic and stops additional development
(ex. acetic acid)
Preservative function
Prevents oxidation
(ex. sodium sulfite)
What does the fixer do in image processing?
-Removes uncharged silver halide crystals from the emulsion layer on the film
-Stops the developing process
List the 5 components of fixing.
-Fixing agent (sodium or ammonium thiosulfate)
-Acidifier (acetic or sulfuric acid)
-Preservative (sodium sulfite)
-Hardener (potassium aluminum sulfate or aluminum chloride)
-Solvent (water)
What causes overlap in images?
What fixes it?
-Inappropriate horizontal angulation
-Direct beams through contacts
What causes forshortening in images? What fixes it?
-Too much vertical angulation
-Decrease angulation
What causes elongation? What fixes it?
-Too little vertical angulation
-Increase vertical angulation
What causes a mark across the film? What fixes it?
-Bent film
-Store film properly
What causes a circular white border? What fixes it?
-Cone cut
-PID should cover entire surface of film
What causes herringbone or waffle pattern? What fixes it?
-Placement of film
-Place the film with smooth, white side next to tooth and bumpy side away
What causes heavy lines on radiograph?
Grid out of proper focal distance
Grid out of alignment
Grid upside down
Damaged grid
What causes inconsistent film density?
Bucky not centered under primary beam
Cassette not locked into bucky correctly
What causes a lack of detail?
X-ray beam not directed at the film
Increased object-film distance
Patient movement
What causes lack of contrast?
-kVp too high
-out of date film
What causes the film to be too light?
-kVp too low
-mA too low
What causes the film to be too dark?
-kVp too high
-mA too high
What causes the film to be too dark in image processing?
too much development time or temperature too high
What causes the film to be too light in image processing?
not enough development time, temperature too low, or exhausted developing solution
What causes darker areas on film in image processing?
developing solution touches film before processing procedure
What causes lighter areas on film in image processing?
fixer solution touches the film before processing procedure
How do you fix a film that is too dark?
Lower kVp
Lower mAs
How do you fix a film that is too light?
-Increase kVp
-Increase mAs
How do you fix a film that has a lack of contrast?
Decrease kVp
How do you fix a film that has a lack of detail?
Decrease object-film distance
Define contrast medium. What is its function?
-Substance administered to patient that is either more radiopaque or more radiolucent than the surrounding tissue
-Allows assessment of position, size, shape, and internal architecture of organ that was not apparent on original radiograph
List negative contrast media and what studies it is used for?
-Air, oxygen, carbon dioxide, and nitrous oxide
-Used in bladder, GI tract, and joint studies
-Useful for showing location, size, and wall thickness of organ and marked wall thickening/large luminal filling defects (masses, foreign bodies)
List positive contrast media and what studies it is used for?
-Barium and Iodine
-Useful for detecting small defects in the wall of the organ
Do NOT use _____ _____ in myelography or respiratory studies
Soluble ionic agents
Define ultrasound
imaging procedure that uses sound waves inaudible to the human ear
How does an ultrasound work?
Sounds echo off corresponding site which produces images that are mapped by black(fluid) and grey (tissue)
List the uses of ultrasounds
Pregnancy
Detect ingested foreign bodies
Cardiac function
Organ enlargement
Tumor or mass
Quality of blood flow through the arteries
Define linear transducers
-Wide and create a rectangle picture that has a wider near field than a sector transducer
-Used for large animal scans
Define sector transducers
-Creates a pie-shaped picture and are good for looking in between ribs to image the heart
-Good for cardiac scans and abdominal scans
Anechoic
-black
-waves have travelled completely through them
Hypoechoic
Dark grey compared to other tissues
Hyperechoic
Lighter gray or whiter compared to other tissues
Define A (Amplitude) Mode and its clinical uses
-Displays returning echoes as peaks that designate their intensity
-Used for ophthalmology evaluations and measurement of subcutaneous fat in production
animals
Define B (Brightness) Mode
-Most commonly used
-Returning echoes are displayed as bright dots on the monitor with varying degrees of
brightness corresponding to the intensity of the returning signal
Describe M (Motion) Mode and its clinical uses
-B mode in motion
-Primarily used in echocardiography
What is doppler mode primarily used for?
Evaluating blood flow
Define Computed Tomography (CT) and its Clinical Applications
-Creates cross-sectional images of body parts and displays images on the monitor
-Better visualization of the brain, soft tissue, and muscle
-Ability to perform direct imaging of the discs and vertebrae of the spinal cord
Define Magnetic Resonance Imaging (MRI)
Powerful magnetic field which generates detailed anatomic images
Define mirror artifact
Seen when there is a highly reflective surface in the path of the primary beam
Define impedance
Resistance to propagation of ultrasound waves through tissues
When does distal acoustic shadowing occur?
When sound is totally reflected or scattered so no sound penetrates deep to the reflector which results in anechoic area on ultrasound images
