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MRI, Laser Safety Flashcards

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1
Q

What does LASER stand for?

A

Light
Amplification by
Stimulated
Emission of
Radiation

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2
Q

How are lasers classified, labeled?

A

Potential to cause biological damage
Class 1 = safest
Class 4 = most dangerous

wavelength, output power, tissue exposure time

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3
Q

Which lasers are most frequently used in vet med?

A

Class 3B/4

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4
Q

What body oversees safety guidelines of lasers?

A

American National Standard’s Institute Z136.3

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5
Q

What is the primary hazard of lasers?

A

Accidental exposure to laser emissions

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6
Q

In what ways can someone experience laser exposure?

A
  1. directly from laser beam or beam reflection (polished surfaces, metal instruments, etc)
    –Reflected laser beams unaltered, same energy as direct beam
  2. Backscattering
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7
Q

Backscattering

A

energy partially reflects on impact with tissue
 Energy less than direct or reflected beam
 Still potential to cause damage
 Nd:YAG, argon lasers produce significant backscatter

Greatest risk to eyes, skin

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8
Q

Eye damage from laser

A

Extremely sensitive to laser radiation; permanent damage from direct, diffuse, reflected beams
* Brief/partial exposures: instantly damage cornea, lens or retina

Extent of ocular damage determined by laser irritants, exposure duration, beam size

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9
Q

What is challenging about identifying eye injury from laser?

A

Infrared radiation = invisible -> possible for damage to occur w/o knowing
* Eye cannot detect invisible beam, cannot respond with blink or aversion
* One or both eyes
* Temporary or permanent

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10
Q

What is the OSHA requirement for laser use?

A

eye protection for personnel and presence of lasers that may result in injury

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11
Q

Eye Protection with Laser Use

A

Selection based on particular type of laser and use, rated for specified wavelength range, optical density (ability to decrease beam power)
* Optical density unique to each laser

Wavelength, optical density imprinted directly on glasses

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12
Q

Good Ocular Safety Practices for Laser Use

A
  • Never look directly at laser even with eye protection
  • Protect eye protection: scratched, cracked, discolored or loose lenses may allow injury

-OD recommendations should match or be greater than manufacturer recommendations

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13
Q

CO2 Laser OD

A

6+ - greatest
(wavelength 10,600nm)

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14
Q

Nd:YAG laser OD

A

6 - second most
(wavelength 1064nm)

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15
Q

Ho:YAG laser OD

A

4+ - least
(wavelength 2100)

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16
Q

Diode Laser OD

A

5+ - third
wavelength 810, 980nm

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16
Q

Diode Laser OD

A

5+

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17
Q

KTP laser OD

A

6+ most
532nm

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18
Q

Argon Laser OD

A

6+
wavelength 488, 514

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19
Q

Which two lasers produce most backscatter?

A

Argon, Nd:YAG

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20
Q

patient eye protection

A
  • Protect eyes from direct or scattered laser beam: close eyelids, protect with drapes
  • Pet protection goggles: variety of sizes suitable for use with lasers classified OD 6 plus, wavelength 800 to 1100nm
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21
Q

Laser-related skin damage

A

 Severity depends on total energy deposited, penetration depth of laser beam
 Mild erythema to severe burn
 Effective protection = drapes for patients
 Skin protection not usually necessary for personnel bc energy density decreases rapidly beyond focal point

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22
Q

Are lasers a fire hazard?

A

Direct or reflected beam of high emission class 3b or 4 laser: ignite combustible materials, fire risk

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23
Q

Lasers, Fire Hazard Near Airway

A

Lasers frequently used for sx near oral cavity, close to airway in SA, LA – intubation necessary to ensure proper ventilatory support

PVC, red rubber, silicone = combustible
 Intense heat of laser burns: burns through ETT in seconds = fire when contacts oxygen inside ETT

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24
Q

Options for Minimizing Combustion Risk with ETT

A
  1. Metal, copper-shielded, or insulated ETTs
  2. Self-adhesive non-reflective copper or aluminum tape around ETT
  3. Thick layer of saline soaked sponges around ETT
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25
Q

Aluminum or Copper Tape Around ETT

A

As safe or safer than commercially available stainless steel or insulated ETT for use with CO2, Nd:YAG lasers

ETT increases external diameter, potentially makes surface irritating to delicate tracheal tissue

Tape can become loose from wrapped tube during use

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26
Q

Thick layer of saline soaked sponges around ETT

A

Sponges must remain moist throughout procedure to dissipate heat from any inadvertent exposure from laser beam

Count sponges before, after placement - ensure all removed from area of the airway

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27
Q

ETT Cuff Protection

A

leakage of high oxygen concentration, anesthetic gases into oral cavity, around head of patient = FIRE

 Protecting pilot balloon with saline soaked gauze sponges or using saline instead of air to fill cuff can help dissipate heat, maintain patency of cuff

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28
Q

Face Mask Considerations with LASER

A

Fit tightly around face, head
 Use lowest flow rates possible
 Physical barrier to prevent oxygen enriched gases from coming into contact with laser beam to reduce risk

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29
Q

Other Strategies to Mitigate Fire Risk

A

TIVA, reducing oxygen concentrations, alternative intubation strategy (NTT, tracheostomy)

To further reduce risk, flammable prep solutions, drying agents, oil based lubricants or ointments or flammable plastics should be avoided whenever lasers are used

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30
Q

Smoke Safety with Laser Use

A

produce plume of smoke, may contain bacterial/viral particles as small as 0.1-0.3 microns +/- toxic gases (carcinogens)

Air evacuation systems used to remove laser generated smoke, reduce pollution of the workspace

Laser rated filter surgical masks available for added protection
 Standard surgical masks: inadequate protection during laser procedures
 Patients who are intubated, connected to AM not at risk for inhaling laser smoke
 Precautions for non-intubated patients to prevent inhalation exposure

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31
Q

Consequences of Inhaled Smoke

A

Bronchospasm from bronchial irritation
alveolar edema
interstitial pneumonia
diffuse pulmonary atelectasis

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32
Q

Ionizing Radiation

A

Injury at cellular level by transferring high levels of energy into atoms and molecules - DNA RNA, other cellular proteins

Transferred energy = damage to cellular bonds, creates free radicals/ions

If cellular damage exceeds body’s ability to repair cells resulting changes in structure, behavior of damaged cells, potential for AEs

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33
Q

Which cells are most sensitive to effects of ionizing radiation?

A

Rapidly dividing cells: skin, BM, SI, reproductive cells

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34
Q

Which cells are most resistant to effects of ionizing radiation?

A

Nerve and muscle cells

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35
Q

What is chronic radiation exposure associated with?

A

increased incidence of cataracts, SCC, leukemia, premature aging

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36
Q

ALARA

A

As low as reasonably achievable

Increasing distance from source shielding minimizing number of images, length of time of procedure

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37
Q

Primary source of exposure to ionizing radiation?

A

XR that bounce off, scatter from objects in primary beams

Patient = major source of scatter radiation

Amount of potential exposure directly related to proximity of personnel to source of ionizing radiation, decreases rapidly with increased distance from source
 If cannot leave room, at least >3’ away, PPE

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38
Q

What is true of lead-lined PPE?

A

not designed to provide protection from direct beam exposure

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39
Q

What is true of radiation exposure?

A

CUMULATIVE

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40
Q

How is the radiation of CT/RT vs XR?

A

Risk of potential radiation exposure increase with CT RT due to higher levels of radiation involved in these procedures

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41
Q

Radio-opaque stripe on ETT

A

visibility in XR, artifact on CT
 May interfere with diagnostic value of images and head and neck

Consider using ETT without stripe

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42
Q

Why use contrast agents?

A

Improve visibility of tissue during XR, CT

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43
Q

What is barium primarily used for?

A

Orally for GI studies

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44
Q

Risks Assoc with barium use?

A

Aspiration of barium = serious health effects, pneumonia to acute death

Prevention of barium aspiration = one of anesthesia’s most important roles during, after GI studies

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45
Q

Mitigation of risk assoc with barium use?

A

Appropriately sized ETT, inflated cuff, thorough inspection in back of the mouth prior to extubation

46
Q

Iodine Based Contrast Agents

A

Routes: PO, IV, intraluminal, subarachnoid

47
Q

Reactions to Iodine-Based Contrast Agents

A

AEs infrequent, depend on site of administration and type of contrast media used

Reactions related to osmolality, molecular size, complexity of agent being used

Minor physiologic alterations to bronchospasm, renal insufficiency, life threatening anaphylaxis

48
Q

Contrast-Induced Nephropathy

A

poorly understood, increasingly reported in diabetic people with pre-existing renal insufficiency given contrast agents

Dehydrated dogs show reduction in RBF, GFR following parenteral administration of hypertonic contrast media

Evaluate renal, hydration status; correct hypotension prior to administration of contrast

49
Q

Myelography

A

contrast study of subarachnoid space using radiography +/- CT

Consists of injection of water soluble, non ionic contrast medium in LS or cerebellomedullary cistern

Invasive, noxious procedure - requires adequate anesthesia

Patient movement= spinal cord damage, non diagnostic study

50
Q

Extravasation of contrast agents

A

LOCAL TISSUE DAMAGE
Mild swelling, erythema to ulceration and tissue necrosis

Some radiographic studies require rapid injection of contrast agent by hand or via rapid injector pump FR 0.5-5mL/s, lrg vol if perivascular

51
Q

Tx extravasation of contrast agents

A
  • Early recognition of catheter failure, place fresh catheter that preferably >20g
    -Cold compress to site
    -Infiltrate area with saline to dilute contrast agent
    -Symptomatic Therapy PRN
52
Q

MRI

A

Powerful static magnetic field; several weaker, rapidly changing, gradient magnetic fields; high frequency electromagnetic radio frequency waves

53
Q

MRI Classification

A

basic shape (open or closed), way magnetic field generated (permanent magnet material or currents in superconducting coils)

54
Q

Measurement of MRI Strength

A

T = Tesla
3.0T > 1.5T

55
Q

Permanent magnets

A

low field strengths, <1.0T with open configuration

56
Q

Superconducting magnets

A

high field strengths, closed cylindrical shapes, clinically functional strengths at 1.0, 1.5, 3.0T

57
Q

Magnetic Field

A

ALWAYS ON

extends outside wall of magnet in all directions

Magnetic field weakest at outside edge of room, increases in strength as it approaches the scanner

58
Q

What is the 5 gauss line?

A

designates perimeter of MRI safety zone

Inside: restricted to MRI safety trained personnel, screened patients and MRI designated safe slash conditional devices

Strength markedly increases beyond this point, increased risk of projectile accidents, medical device malfunction

59
Q

What is true about ferromagnetic objects and proximity to the magnet?

A

Closer ferromagnetic object to magnet, stronger the attraction

Potential to become projectile

Large objects propelled faster more difficult to remove should they become attached

60
Q

Where is the magnetic field the strongest?

A

Bore of magnet

61
Q

What is the most significant hazard to personnel, patients in magnetic field environment?

A

Projectile/missile effect

62
Q

Implant Devices

A

Implanted, non-spherical metallic objects will torque rotate as they attempt to align with magnetic field

Induced rotation = tissue damage, tear vital structures

Microchips, intravascular coil/stents, vascular clamps: imaged safely 6wks following placement once adequate scarring (degree of fibrosis, granulation tissue) has occurred

63
Q

Effects of exposure to MRI?

A

No substantial or harmful biologic effects reported in patients or MRI technologists following short term exposures of static magnetic fields up to 9.4 T

no current studies regarding prolonged chronic exposure

64
Q

How are medical devices tested/labeled for MRI compatibility?

A

ASTM International classifications

MRI Safe
MRI Conditional
MRI Unsafe

65
Q

MRI Safe

A

items made from materials considered safe and MRI environment
* Glass plastic silicone

Devices that have been tested, considered safe for patient or individuals working in MRI environments

66
Q

MRI Conditional

A

depending on specific MRI environment objects may or may not be safe for patient or personnel

STEEL

67
Q

MRI Unsafe

A

Magnetic or metallic items known to pose human hazards in all MRI environments
* 2 subcategories depending on type, degree of risk default magnetic field used to categorize devices as 1.5 Tesla

68
Q

Paramagnetic materials

A

Weakly attracted to magnetic fields

69
Q

Diamagnetic materials

A

Weakly repelled by magnetic field

70
Q

Ferromagnetism

A

Extreme form of paramagnetism - super attracted to magnet

71
Q

Metals Attracted to MRI - DO NOT ENTER MAGNET

A

 Iron
 Iron Oxide
 Iron-containing alloys
 Nickel
 Cobalt

72
Q

Materials Safe for Magnet

A

 Aluminum
 Brass
 Plastic
 Titanium
 Copper
 Beryllium
 Silver
 Gold
 Bronze
 Zinc

73
Q

What determines rotational or translational (attractive) motion of artifact?

A

o Configuration of field, shape/mass/position of object

74
Q

Gradient Magnetic Fields

A

AKA time varying magnetic fields

Created by weaker magnets located within primary magnet
 Switched on, off many times per second  variations in magnetic fields  formation of image slices
 Induces electrical currents: conscious human patients reported nerve stimulation, tingling

“clanging” noises during MRI

75
Q

Gradient Magnetic Field Noise

A

Level of acoustic noise depends on scan sequence called magnet strength

Noise levels: 103-115dB for 1.5T, 126-131bB for 3.0T

76
Q

Noise levels for 1.5T

A

103-115dB

77
Q

Noise Levels for 3.0T

A

126-131dB

78
Q

What are the limits for noise levels and who regulates them?

A

FDA, International Electrotechnical Commission: permissible sound levels <99dB with hearing protection in place

OSHA, UK Department of Health: max noise exposure of 85db over 8hrs

79
Q

Noise Reduction Capability with ear plugs?

A

 Disposable/reusable ear plugs with noise reduction rating (NRR) 30-33dB

80
Q

Noise Reduction Capability with close fitting headphones?

A

NRR ratings of 20-30dB

81
Q

Additional protection provided by ear plugs + head phones?

A

5-10dB additional protection

82
Q

Data on veterinary patient noise exposure?

A

Isoflurane anesthesia: protective effect on noise induced hearing loss and mice

Hearing protection commercially available for dogs and cats, MRI safe

83
Q

Radiofrequency

A

pulsed into tissue, eliciting release of energy or resonance signal - allows image construction

Majority of RF energy transformed into heat within patient tissues, can elevate body temperature

Especially large dogs, long scan times

84
Q

RF, magnet strength

A

Stronger the magnet, more RF energy required (3.0T>1.5T)

85
Q

Specific Absorption Rate of RF

A

measured throughout scan to prevent systemic thermal overload

Strictly limited based on guidelines by FDA, limited by MR scanner software
 SAR calculated based on weight of patient

86
Q

Majority of MRI related imaging injury reports in humans

A

related to RF burns from electrical currents induced in conductive materials

Cables placed against patients bare skin or looped to remove slack -> create strong voltage -> tissue burning

Cables should be straight (not looped, run parallel to bore of magnet, insulated from areas of non haired skin

87
Q

RF Coil

A

RF transmitter/receiver used to transfer energy into the tissue, capture energy released from tissue

Body, surface coil

88
Q

Body Coil

A

Part of Scanner

89
Q

Surface Coil

A

Placed over or wrapped around body part being scanned

90
Q

Effects of RF noise?

A

cause artifacts, interferes with acquisition of images

MRI suites shielded from external sources of RF by copper sheeting inwalls, building a metal Faraday cage around scanner

Electrical devices produce RF signals, must be kept outside of five gauss line unless internally shielded, tested MRI safe or conditional

91
Q

Transdermal Patches

A

contain aluminum or other metal substances that can cause skin burns if exposed to RF field

Second degree burns reported in humans DT transdermal patches, FDA warning

Remove before put in magnet

92
Q

How is heat generated by MRI normally dissipated?

A

Superconducting high field strength magnets generate large amount of energy, heat - must be encased in super cooled liquefied gas (usually liquid helium)

93
Q

BLEVE

A

Boiling liquid expanding vapor explosion

94
Q

What is another name for BLEVE?

A

QUENCH

95
Q

What happens with BLEVE?

A
  • If system malfunctions and temp of He rises, can have generation/accumulation of enormous pressures -> EXPLOSION (of He vapor)
  • Magnetic field lost
96
Q

Normal Safety Mechanisms in Event of BLEVE

A

Rooms equipped with large vent pipes for evacuation of He vapor if occurs

97
Q

What triggers BLEVE?

A

Rare spontaneously

Manually triggered in the event of a fire in the magnet room or emergent termination of magnetic field

98
Q

What happens if vent pipe system fails to contain He vapor?

A

a cloud of vapor will enter MRI

Vapor still very cold, can cause frostbite, asphyxiation due to displacement of oxygen in the room

IMMEDIATE EVACUATION

Magnet could have high voltage electrical charge, should not be touched -> patient should not be moved until room returns to normal

Magnetic field takes time to dissipate, do not rush into room

99
Q

What type of oxygen tank is safe for use in MRI?

A

Aluminum

100
Q

Where position non-MRI compatible machine?

A

Non MRI compatible machines must be positioned outside the 5 gauss line
* Secure to wall or floor to prevent movement toward magnet

101
Q

Receiver coils

A

plug into connections located in the MRI table

Protect from organic fluids or leakage from IV line -> short circuit, expensive to replace

102
Q

Pilot Tube of ETT

A

small amount of metal - causes artifact on images if in scan field

103
Q

Ventilators in MRI

A

improve patient management and image quality by providing ventilatory support, consistent plan of anesthesia, and control of respiratory motion

Patients with pre-existing respiratory depression

Patients with suspected elevated ICP - require careful control of PaCO2

104
Q

Patient Monitoring

A

not be assumed that monitor safe for use with 1.5T will be safe with 3.0T

105
Q

ECG Effects in MRI

A

Gradient magnetic fields, radiofrequencies can interfere
* Can be unreadable during many sequences
Newer MRI safe monitoring systems: filters to help eliminate interference

106
Q

ECG Artifacts

A

Appearance of T wave or ST segment of complex may appear due to superimposed voltages generated by aortic blood flow in a magnetic field

107
Q

Carbon Graphite ECG Electrodes

A

patches work best with direct skin contact so shaving required

108
Q

Gadolinium Based Contrast Agents

A

Enhance visibility of tissues for MRI studies

109
Q

How Gadolinium Contrast Agents Made

A

Paramagnetic metal highly toxic in natural state, blocks physiological pathways that rely on calcium
 When chelated with large organic molecules to form stable complex, safe
 Improved water solubility
 Excreted predominantly unchanged the kidneys

110
Q

What are most common SE of gadolinium based contrast admin?

A

bradycardia tachycardia hypotension hypertension

Mild to severe anaphylactoid reactions in dogs

111
Q

Which patient population is more likely to have an adverse reaction?

A

Dogs with hx atopy

112
Q

Humans and administration of gadolinium based contrast agent

A

administration has been linked to life threatening skin disorder: nephrogenic systemic fibrosis or nephrogenic fibrosing dermatopathy

Severe renal failure, insufficiency with GFR <15mL/min

113
Q

What metal is most commonly assoc with being safe under some circumstances?

A

Steel

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