Test 1: Radiology/ Laser Safety (Andy's Cards) Flashcards
Who/when discovered X-ray therapy and how?
- Wilhelm Roentgen (1895)
- While experimenting with currents in a glass tube noticed that a fluorescent screen in the lab began to glow.
- Placed objects between the screen and the tube –> called “x” ray = something unknown
What are the four types of radiation?
- Electromagnetic = from motion of atoms (combined with electricity and magnetism)
- Mechanical = travel through substances
- Nuclear (neutron) = unstable atom nuclei
- Cosmic (beta) = electrons only; travels at almost speed of light (ex: sunlight)
What is non-ionizing radiation?
- Radiation that cannot knock electrons off atoms and doesn’t break molecular bonds
- Only harmful from heat energy (ex: radiowaves or microwaves)
What is ionizing radiation?
- These types of radiation knock off electrons
- When electrons are knocked off atoms, they create ions
- Ion electrical charge causes intracellular chemical changes (cell apoptosis, cancer, defects)
- Risk can be additive (can add up)
What are the negative effects of ionizing radiation?
- Break DNA chains = cell apoptosis
- Mutate DNA chain = cancer
- Mutated sperm or egg cell = birth defects
What are the similarities of x-rays to visible light rays?
What is the difference?
Similar:
- Both are electromagnetic energy
- Carried by particles called photons
Difference in energy levels (wavelengths)
X-rays have _______ wavelengths and _________ energy.
Radio waves have _______ wavelengths and ________ energy.
- X-rays have shorter wavelengths and higher energy.
- Radio waves have longer wavelengths and lower energy.
How is light emitted?
- Caused by the movement of electrons in an atom
1. Moving particles excite atoms (when heated)
2. Electron “jumps” to a higher energy level (orbit)
3. To fall back to the original orbit, it must release energy (photon or light)
How do smaller atoms affect the amount of photons released?
- Electron orbitals are by low jumps in energy
- Less likely to absorb X-ray photons
- This will show up as a greyish (darker) color on the X-ray image
Ex: soft tissue
How do larger atoms affect the amount of photons released?
- Greater energy difference between orbitals d/t orbits being further apart
- More likely to absorb photons
- This will show up as a whiter or brighter color on the X-ray image
ex: bones
What makes up an electrode pair of an X-ray machine?
- Cathode
- Anode
What is a cathode?
- A filament (in the center) shape that is heated up as machine charges.
- The heat filament current causes electrons to fly off of filament
- Negative charged side of the x-ray tube
What is an anode?
- A positively charged metal disc of tungsten that will attract electrons across the tube from the cathode
Components of the x-ray machine
- Thick shield surrounds the entire machine
- The window in the shield allows a narrow beam of photons to escape
- A camera is on the opposite side of the tube that records the patterns of the X-ray photons
What does the camera of the x-ray machine do?
- Produces a chemical reaction on the film
- Ambient light can darken or lighten
- Intensity changes to photon beam (over/under exposure) alter appearance
What do we use medical x-rays for?
Diagnostics
Radiography
- bone fractures, tube placement, foreign objects
Mammography
Computed Tomography (CT)
- 3D image generated when x-ray combines with computer processing
Fluoroscopy
- real-time image (with/without contrast), uses high levels of radiation
Can x-rays be used therapeutically?
- YES, as radiation therapy
- At higher doses, radiation can damage the cancer cell’s DNA
What is the most common side effect of radiation therapy throughout the body systems?
Fatigue
Be familiar with this chart:
Annual allowable radiation dose:
- Whole body in 1 year
- Extremities
- Eye lens
- Pregnancy
- Whole body in 1 year = 5,000 mrem
- Extremities = 50,000 mrem
- Eye lens = 15,000 mrem
- Pregnancy (after 2nd/3rd) Trimester = 500 mrem
What is a Rem? How are radiation doses generally presented?
- Radiation dose times a weighting factors
- Nearly equivalent to Rad
- radiation doses generally measured in mrem’s (1/1000 of a rem)
What is known as the direct sources of radiation?
- Primary X-ray beam
- Leaking from other sites within the equipment
Amount of Rem exposure from the following sources:
CXR
Coronary angiogram
Angioplasty
CT
- CXR: 5-10 mrem
- Coronary angiogram: 1,500 mrem
- Angioplasty: 5,700 mrem
- CT: 5,000 mrem
What are indirect sources of radiation?
- Scattered radiation
- This is radiation that reflect off tables, patients, and other surfaces
What are three factors that affect scatter radiation?
- Collimation (width of the beam; wider collimation has more radiation scatter)
- Object thickness (thicker patients will result in more radiation scatter)
- Air Gap (distance between patient and cassette; the greater the distance, the more radiation scatter)
*Clarified by Dr. Kane
How much rem will generally cause transient erythema?
- 200,000 mrem
What is ALARA?
- As Low As Reasonably Achievable
- Radiation protection
What are the 3 things to reduce radiation?
- Limit time spent near beam entry
- Distance
- direct source: double distance from beam = 1/4 (75% drop) the exposure rate
- indirect source: scatter = > 6 ft from patient - Shielding
- lead aprons, portable shields, thyroid, lead glasses
How do fat and water appear on a T1 weighted image?
Fat appears bright
Water appears dark
How do fat and water appear on a T2 weighted image?
Fat is darker
Water is lighter
What does L.A.S.E.R. stand for?
- Light Amplification by Stimulated Emission of Radiation
