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 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)
Can x-rays be used theraputically?
- 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?
Fatigue
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 Rem?
- Radiation dose times a weighting factors
- Nearly equivalent to Rad
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 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 the exposure rate
- indirect source: scatter = > 6 ft from patient - Shielding
- lead aprons, portable shields, thyroid, lead glasses
How do you wear the dosimeters?
Two badges:
1. Outside the apron on the collar
2. Inside the apron on the waist
What are the 3 “Don’t” to dosimeters?
- Don’t mix up
- Don’t share dosimeter with others
- Don’t leave in the car on the dashboard/seat
The principles of MRI are based on interactions between what two things?
- Based on the interaction between the static magnetic field and individual atom nuclei.
The magnetic field of the MRI is used to orient the nuclei of _______ molecules to north-south poles.
- Hydrogen
How does the MRI create an image?
- Radio wave pulses change the orientation of specific atoms, which radiates energy to create an image.
How is contrast generated?
- Contrast is generated by time til tissue relaxation when the radio frequency is turned off.
- When the radio frequency is turned off, protons realign with the magnetic field releasing electromagnetic energy.
What factors affect the contrast generated?
- Various densities of hydrogen nuclei in tissues
- Different chemical and physical properties of the tissues
What are the two contrast images for MRI?
- T1 contrast/ view
- T2 contrast/ view
Describe a T1 contrast/view.
- Relaxation of the magnetic vector
- Radio frequency is off and not trying to move the orientation of the atom
- Provides a good grey-white matter contrast
- Good for viewing anatomy
How do fat and water appear on a T1 weighted image?
Fat appears bright
Water appears dark
Describe a T2 contrast/view.
- Axial spin relaxes
- Radio frequency turned on
- Great for identifying tissue edema
- Good for viewing pathology
How do fat and water appear on a T2 weighted image?
Fat is darker
Water is lighter
What is the most common contrast material used for MRI?
- Gadolinium
How does Gadolinium enhance the equality of MRI images?
- Gadolinium dye alters the magnetic properties of nearby water molecules, enhancing the quality of MRI images.
What are the side effects of Gadolinium?
How is it cleared from the body and how quickly?
- Mild side effects: itching, rash, abnormal skin sensation
- Cleared with normal GFR in 24 hours.
Is the magnetic field always on?
YES
Risks in MRI?
- Projectile risk
- Radiofrequency energy causes tissue/device heating
- Electromagnetic interference causes artifacts such as the interpretation of ECG
- Acoustic noise up to 125 dB == wear hearing protectors (CRNA and patient)
What are the AANA Standards of Care for MRI?
- EKG, pulse ox, BP, capnography q 15 minutes when providing anesthetics
- Airway (cannula, mask, ETT vs. LMA)
- Suction
- Spontaneous ventilation vs. ventilator
- Minimize movement (versed comes in handy)
- Complications (ex. airway access)
- MRI-compatible infusion pumps…. vs long, long, IV tubing
- Laryngoscope handles, blades…induction may occur in a separate room
Things to know about patient positioning for MRI?
- Head and neck scans will result in an inaccessible airway.
- Abdominal scans will have the patient’s arms over their head. This can lead to brachial plexus injuries.
What objects could be in the patient that can be effected or affect the MRI scan?
- Pacemakers
- AICDs
- Implanted insulin pumps
- New generations of these devices are MRI-compatible
What objects are considered MRI-compatible?
- Heart valves safe
- Endovascular and biliary stents are usually embedded after eight weeks
- Coronary stents OK immediately
- Vascular ports and IVC filters are safe
- Any Orthopedic implants…titanium, safe; screws are made of lead and securely in bone.
What happens if you move too quickly toward an MRI field (ie: running into the MRI room)?
- Rapid movement toward the field (> 1m/sec) will result in dizziness, HA, light flashes, nausea
- Move calmly in the MRI room.
What does L.A.S.E.R. stand for?
- Light Amplification by Stimulated Emission of Radiation
What is ordinary light vs laser light?
- Ordinary light contains many wavelengths that spread out in many directs
- Laser has a specific wavelength with a focused narrow beam and high intensity
The unexcited state electrons orbit the nucleus at the _________ energy.
- lowest
In the unexcited state, electrons occupy orbits _________ to the nucleus.
- closest
How is radiation produced?
- As the electrons absorb energy, they become excited and move to a higher orbit
- Upon return from an excited state to ground state, they spontaneously emit photons of energy (electromagnetic radiation)
Properties of Laser Radiation?
- Monochromatic: All photons in the laser beam are the same wavelength
- Coherence: Travel of photons is synchronized in time and space (no random movement)
- Collimation: Laser beam photons are parallel (allow the beam to focus on a small area)
What gives a type of laser its name?
- The Lasing Medium
What are the 3 lasing mediums?
- Argon
- Carbon dioxide
- Nd:YAG
What should be known about Argon lasers?
- Used in dermatology
- Modest tissue penetration (0.05-2 mm)
What should be known about CO₂ lasers?
- Used in vocal cords, oropharynx
- Scatter is minimal
- Surrounding tissue damage is negligible and absorbed by water/disperse little heat
What should be known about Nd:YAG lasers?
- Most powerful laser
- Used for tumor debulking (prostate, bladder tumors)
- Deeper tissue penetration (2-6 mm)
What are the 5 hazards of laser?
What are the two hazards CRNAs are most concerned with for lasers?
- Atmospheric contamination (most concern)
- Airway fire (most concern)
- Perforation of a vessel or structure
- Embolism
- Inappropriate energy transfer
What is a Laser Plume?
- Fine particulates produced d/t vaporization of tissue
- Laser Plume can result in HA, nausea after inhalation
- Laser Plumes could cause interstitial pneumonia, bronchiolitis, emphysema
- Laser Plumes could be carcinogenic
What makes up the fire triad?
- Ignition source (aka Laser)
- Fuel (drapes, ET Tube, nasal cannula)
- Oxidizer (oxygen)
What are the two major sources for OR fires?
- ESU (Electrosurgical units aka “Bovie”)
- Laser
What are some scenarios for endotracheal fire discussed in the lecture?
- Surgeon is lasering airway through the ETT and burns through PVC tube…
- Surgeon is completing tonsillectomy in a pediatric patient with an uncuffed tube…
- Surgeon uses bovie to “cut” through trachea for a tracheotomy…
How to prevent Airway fire?
- Laser-resistant ETTs
- Low-inspired (21% if possible) O2
- Wet pledgets around the ETT
- Methylene blue in the ETT cuff (visual)
- Use scissors to cut into trachea instead of bouvie
- Remove ETT during laser procedure and reinsert ETT prn sats
Anesthesia Plan for the patient undergoing Laser therapy.
- Preoperative evaluation of airway (stridor, flow volume loops, CT, fiberoptic eval)
- Mutual planning with surgeon) Intermittent apneic oxygenation, jet ventilation)
- Total IV anesthesia (Propofol, remifentanil, Xylocaine spray)
Anesthesia plan to prevent airway fire:
- Methylene blue in cuff
- Saline gauze protection of airway/face
- Short, repeated pulses of laser instead of long continuous mode
- Keep O2 < 30%, avoid nitrous
- Communicate and monitor video camera for signs of airway fire
