Radiology Physics & Safety Flashcards
(55 cards)
Radiology physics
- X-rays are part of the electromagnetic spectrum, which also includes radio waves, microwaves, infrared, visible light, UV, and gamma rays
- The difference between these rays is the amount of energy, frequency and wavelength
Wavelength
Defined as the distance between two similar points on two successive waves
Frequency
Can be defined as the number of waves that pass a given point per unit time
- The sorter the wavelength, the higher the frequency
- X-rays have very short frequency and high energy
X-ray production
- Fast moving electrons are released from x-ray tube
- The tube contains a heated tungsten filament and a cathode
- The electrons slam into a metal object (the anode)
- 99% of the electrons produce thermal energy in this process, only 1% actually produce x-rays
Energy difference and transfer
- The energy difference going from cathode to anode is measured in kilivolts (kV)
- When the electrons strike the target, the energy is transfered in the form of kinetic energy (KE=1/2mv^2) where m = mass and v = velocity
Image formation
Factors controlled by operator:
- mA, which idicates number of electrons that reach the anode (high mA = dark film, low mA = light film)
- kV, which indicates the penetrating power of the electrons
- Distance from x-ray tube
“Soft x-rays”
- Lower voltage = decreased speed of electrons
- Lower speed electrons = longer wavelength x-rays
- Decreased penetrating power
Produced by decreased kVp, have long wavelength, low frequency, low penetration and are more dangerous to the patient
“Hard x-rays”
- Increased voltage = increased speed of electrons
- High speed electrons = shorter wavelength x-rays
- Increased penetrating power
Produced by increased kVp, have shorter wavelength, higher frequency, increased penetration and are less dangerous to the patient
Intensifying screens
Intensifying screens, which are within the film cassette, convert the energy of the x-ray beam into visible light
After the image is intensified, a fluorescent image is produced and recorded on photosensitive film
Roentgen
International unit of quantity of radiation exposure
Ionization of air by radiation
Radiation absorbed dose (rad)
Unit of absorbed dose by the patient
1 RAD = 100 ERGS of energy per gram of tissue
Roentgen equivalent man (rem)
Unit of biological exposure in man
Equivalence between roentgen, rad and rem
1 roentgen = 1 rad = 1 rem
Curie (Ci)
Unit to measure radioactivity
Lethal dose
The dose of radiation that will result in death within 30 days in 50% of people
300 rad in a human
Radiation effects of gonads
10 rads = delayed menstruation/decreased spermatozoa
200 rads = temporary sterility
500 rads = permanent sterility
Fetal dose of radiation
10 rads
- Spontaneous abortion rate increases by 0.1%
- Congenital abnormalities increase by 1%
- Malignant disease increases
Leakage radiation
All radiation from within the x-ray tube housing except the useful beam
Scatter radiation
Radiation that, during the passage through matter, has deviated in a direction beyond the image plane
Radiation protection ALARA concept
“As low as reasonably achievable”
- A principle to protect occupational exposure to radiation
- Three basic principles: time, distance and shielding
Time, distance, shielding
- Radiation directly proportional to time exposed to radiation
- Reduced radiation by keeping greater distance
- Shielding your body from radiation via protective equiptment
Structural barriers
- Walls and doors
- Control-booth barrier
Control booth barriers
Must be at least 7 feet tall from floor and be permanently secured
Primary protective barrier
A wall that lies directly perpendicular to un-deflected line of travel of x-ray beams and its purpose is to prevent direct or un-scattered radiation from reaching the public
