Test 1 Flashcards
Who discovered x-rays?
Wilhelm Conrad Roentgen
What was the date (month, day, year) x-rays were discovered?
November 8, 1895
3 types of IRs?
Film Computed radiography (CR) Digital radiography (DR)
Invisible and undeveloped image
Latent image
Latent image that’s made visible
Manifest image
What is the point of the glass envelope of an x-ray tube?
It’s pyrex to resist heat and air is removed so gas molecules won’t interfere with x-ray production
What is the wire filament made of?
Tungsten
What is the melting point of this metal?
3370 C
Heating of the filament emits electrodes
Thermionic emission
What is the target made of?
Tungsten
What charge does the target have?
Positive
What charge does the cathode have?
Negative
Is the filament located on the anode or cathode side of an x-ray tube?
Cathode side
What percentage of electrons are converted to x-rays?
1%
If I increase wavelength, what happens to frequency?
The frequency decreases
If I increase frequency, what happens to energy?
Energy increases
With respect to a sine wave, the distance between a given point on one wave cycle and the corresponding point on the next successive wave cycle
Wavelength
Number of times per second a crest passes a given point
Frequency
The distance between the crest and valley
Amplitude
What is the speed of light?
186000 miles/second = 3x10^8 m/sec
X-rays are emitted from a point and spread out in all directions
Divergent
If I am 2 meters from an x-ray source and move to 4 meters away, how much exactly does radiation intensity change?
It’s reduced by 4
Allows variation of radiation light field size
Collimator
What are the two most common distances an x-ray tube is set from an image receptor (IR)?
40 cm and 72 cm
Define what mAs is:
Quantity or quality?
Does it control contrast or density (degree of darkening)?
Quantity, controls density
Define what mAs is:
Quantity or quality?
Does it control contrast or density (degree of darkening)?
Quality, controls contrast
What is fluoroscopy?
Produces dynamic/moving images
Function to terminate the exposure when a desired quantity of radiation is given
Automatic exposure controls (AEC’s)
If I want a constant mAs, and increase my mA while decreasing my time(s), what benefit do I gain?
The patient has less time to move so there’s less blur
What is SID?
Distance between the x-ray tube and image receptor, source to image distance
What is OID?
Object to image distance, the distance between the object and the image receptor
What is the function of a screen?
Reduces the exposure required to produce an image
Concerning screen, what does a slow screen do?
A slow screen gives a more detailed image but requires more exposure
Concerning screen, what does a fast screen do?
They require less exposure and are better for large body parts but are less detailed
What body parts use a slow screen?
Extremities
Computer hardware and software used to manage digital images in healthcare, provides archives for storage of images from all digital images in healthcare, connects images to patient database information, facilitates printing and transfer of images and displays images and information at work stations
Picture Archiving and Communication System (PACS)
4 elements of radiographic density
Density
Contrast
Detail
Distortion
The overall blackness of an image
Density
The difference in orbital density between adjacent structures
Contrast
The sharpness of the image
Detail
Variation in size or shape of the image compared to the object it represents
Distortion
Does a smaller focal spot size have better or worse detail?
Better
Used to measure how much radiation is in the air, how much radiation the tube is leaking through the tube housing and how much radiation is transmitted outside the x-ray room in a hallway
Radiation exposure
What are the units for radiation exposure?
Roentgen (R or r)
How radiation dose is prescribed in radiation therapy or energy absorbed per mass of medium
Absorbed dose
What are the units of radiation exposure?
Radiation absorbed dose (rad), 1 Gray = 100 rads
How various radiation types are related to each other in terms of their equivalence of biological effects
Dose equivalent
What are the units for dose equivalent?
Sv or rem
Weighting factors - approximate measurements of the relative biologic effectiveness of a particular radiation compared with a reference radiation (250 keV x-rays)
Quality factor
4 laws of Bergonie and Tribondeau (states that cell sensitivity to radiation exposure depends on 4 cell characteristics)
Age: younger cells are more sensitive than older ones
Differentiation: non-specialized cells are more sensitive than highly complex ones
Mitotic rate: cells that divide and multiply more rapidly are more sensitive than those that replicate slowly
Metabolic rate: cells that use energy rapidly are more sensitive than those with a slower metabolism
Describes biologic radiation effects that are predictable; their intensity is dose dependent. These effects occur only after a certain threshold amount of exposure has been received
Non-stochastic
Describes biologic radiation effects that are random and unpredictable. Their likelihood is dose dependent but not their severity. There is no threshold amount of exposure necessary to produce these effects
Stochastic
Whole body radiation dose that’s lethal to 50% of the population in 30 days; for humans its 3Gy
LD 50/30
3 cardinal principles of lowering radiation dose and exposure
Time: amount of exposure received is directly proportional to the time spent in a radiation field
Distance: an increase in distance results in an increase of exposure by the square of the distance (inverse square law)
Shielding: using a lead wall as a primary barrier
What does ALARA stand for?
As Low As Reasonable Achievable
A healthcare insurance plan in which insurance companies reimburse patients for the costs of their healthcare within the limits of the policy and the patient is responsible for any costs not covered
Fee-for-service program
