Physics review Flashcards
TRUE or FALSE: Gadolinium crosses the placenta, enters the amniotic fluid and is ingested by the fetus. The text suggest avoiding gadolinium in pregnant patients.
True
TRUE or FALSE: There have been no known long-term adverse biological effects associated with extended exposure to the magnetic fields in MR imaging. However, several reversible effects can be observed.
True
What is the rotational force in the MRI environment?
moving or twisting
What is the translational force in the MRI environment?
violent attraction
What is the missile force in the MRI environment?
metal object becomes airborn
In the MRI environment, the translational force increases how?
close to isocenter
In the MRI environment, the translational force decreases how?
away from isocenter
What is the direction of the static fields of closed bore superconducting magnet?
Bo is horizontal
What is the direction of the static fields of vertical magnets for open permanent magnet:
Bo is vertical
Where can/do MRI technologists reference the safety of an implanted device?
- Dr. Frank Shellock’s reference manual
- Institute for Magnetic Resonance, Safety and Education and Research
- the manufacturer of the device
- www.mrisafety.com
Concerning foreign bodies in the eyes … what is more accurate?
computed tomography
Concerning foreign bodies in the eyes … what is adequate for screening?
radiography
The FDA limits of Bo for babies is what?
4T
The FDA limits of Bo for patients 1 month+ is what?
8T
Concerning SAR, what is the FDA limit for heating?
1-degree Celcius in the core
What are the units of SAR?
watts per kilogram (W/kg)
What is important when monitoring SAR?
the patient’s weight
What does SAR stand for?
specific absorption rate
What concerns for MRI patients apply to pregnant patients?
No known biological effects to fetus but prefer to delay until after 1st trimester
What concerns for MRI patients apply to pregnant employees?
Can enter the scan room but should leave before RF and gradient fields are employed. Make informed decisions.
What concerns for MRI patients apply to patients in medical emergency?
remove from Zone 4 before start CPR
What is the FDA limit of magnetic field strengths for babies up to 1 month old?
4T
What is the FDA limit of magnetic field strengths for those older than 1 month?
8T
Which of the following does the text state as reported accidents and near misses in MRI? Choose all that apply …
- burns
- device failures
- contrast reactions
- death
- ferromagnetic metal objects flying
How should unconscious, comatose, sedated or hearing-impaired patients be monitored while in MRI? Choose all that apply …
- verbally
- visually
- with pulse oximetry
What does nagnetophosphenes mean?
Patient may report seeing flashes of light or “seeing stars”
What does Bo mean?
main/static magnetic field
What does hemodynamic effect mean?
reversible amplitude of the T-wave
What does quench mean?
helium escapes
What does cryogens mean?
cools superconducting
What does fringe field mean?
Magnetic field outside the bore. Not confined to ceilings, floors, or walls. Shielded to 5G.
What is MRI Facility Zone 1?
free to general public
What is MRI Facility Zone 2?
waiting or dressing room
What is MRI Facility Zone 3?
b/t Zone 2 and the scanner
What is MRI Facility Zone 4?
scan room
Which magnetic field spatially encode data, altering the MF in a linear fashion?
gradients
Who should be screened for MRI safety?
Screen every patient every time and verify with metal detector
In 2001, a 6-year old patient was killed in a MRI scanner.
Which of the following are correct concerning this tragedy? Choose all correct.
- caused by a ferromagnetic oxygen tank
- lead to the publication of a White Paper called “ACR Guidance Document for Safe MR Practices”
- published in 2002
- intended to provide guidelines for the development and implementation of safety policies and procedures
- has been reviewed and updated periodically since publication
What was the text’s example of a missile effect?
terminal velocity of a paperclip can reach 40mph
The green box with MR inside safety label means what?
Item poses no known hazards in all MRI environments
The yellow triangle with MR inside safety label means what?
Item poses no known hazards in a specified MRI environment with specified conditions of use
The red circle with a line thru MR safety label means what?
Item is known to pose hazards in all MRI environments
TRUE or FALSE: An implant that is safe for 3 T is automatically deemed safe at 1.5 T.
False
What is the most likely side effect of RF fields?
heating of tissue, antennae effects, thermal injuries
What is the most likely side effect of gradients?
peripheral nerve stimulation, magnetophosphenes, noise
What is the most likely side effect of static field?
associated with devices, implants, and projectiles
What is the best device to use when monitoring a patient’s status in MRI?
Pulse ox
Which of the following describe T1 Recovery? Choose all correct …
- spin lattice relaxation
* caused by the nuclei giving up their energy to the surrounding environment or lattice
Which of the following describe the purpose of gradients in MRI? Choose all correct …
- After the main magnetic field in a linear fashion
* Spatially encode data
Which way does the main magnetic field run in superconducting magnets?
Along the bore of the magnet (horizontal)
Identify the two factors that determine which hydrogen nuclei align parallel and which align anti-parallel with the main magnetic field.
- The strength of the external magnetic field
* The thermal energy level of the nuclei
What are the guidelines for pregnant employees?
Pregnant employees may enter the scan room, but should leave before scanning begins.
What would you do in the event of a CODE BLUE in MRI? (Select all that apply)
- Begin CPR
- Activate the Code Blue response process (push the Code Blue button)
- Get the patient out of the scanner and into Zone III; locking the scan room door and monitoring it when other Code Team members arrive
What are the two results of resonance? Choose all correct …
- The NMV moves out of alignment and away from BO
* The magnetic moments of hydrogen nuclei move into phase with each other
What must be done prior to anyone entering the scan room? Select the best answer …
The completed screening sheet must be signed by a level II staff member and the patient must be scanned with the metal detector
What is another term for T2 Decay?
Spin-spin relaxation
What does SAR stand for?
Specific Absorption Rate
Which of the following best describe spin-lattice relaxation? Choose all correct …
- T1 Recovery
* Nuclei give up energy to the surrounding environment, resulting in longitudinal recovery.
What makes a nucleus an MR active nucleus? Choose all correct …
- Odd mass numbers
* Nuclei with a net spin or angular momentum
We always scan pregnant patients with contrast.
False
We ONLY scan pregnant patients after discussing it with a radiologist (who will determine risk vs. benefit) and having the patient sign a release form. It is recommended to avoidgiving contrast to pregnant women.
What effect does the magneto-hemodynamic effect have? Is this a permanent effect? Choose all correct …
- Increase in the amplitude of the “T” wave on EKG gating.
* Reversible effect– EKG tracing returns to normal when the patient is removed from the static magnetic field.
What is the T2 relaxation time of tissue?
Hint: Think about which axis T2 relaxation is occurring in (longitudinal vs. transverse) and whether T2 relaxation indicates recovery vs. decay.
The time it takes 63% of the transverse magnetization to decay in the tissue.
<strong>T2 relaxation</strong> results in <strong>decay</strong> or loss of coherent <strong>transverse</strong> magnetization. It is an exponential process and the T2 relaxation time of a tissue is its time constant of decay, or the time it takes 63% of the transverse magnetization to be lost. See pages 16-17 in the text.
What does the Larmor Equation calculate?
The precessional frequency
Where do we look up the safety of an implanted device? Check all that apply …
- www.MRISafety.comLinks to an external site.
- Shellock’s reference manual
- The manufacturer’s website
What is the terminal velocity of a paperclip at 1.5T?
40 mph
The gyromagnetic ratio expresses the relationship between the angular momentum and the magnetic moment of each MR active nucleus.
True
The “warm zone” in MRI is the scan room itself.
False
The “warm zone” in MRI is Zone III, or the controlled area just outside of the scan room, which usually includes the patient holding and control room area.
Identify which of the following describe a “fringe field.” Choose all correct …
- The stray magnetic field outside the bore of the magnet.
- Active or passive shielding is used to reduce the size of the fringe field.
- The fringe field is not confined by walls, floors, or ceilings.
What does the net magnetization vector (NMV) represent?
The relative balance of spin-up to spin-down nuclei
What are the three types of motion present in an atom? Choose all correct …
- Electrons spinning on their own axis.
- Electrons orbiting the nucleus.
- The nucleus itself spinning about its own axis.
Which way does the main magnetic field run in permanent magnets?
Vertically
For resonance of hydrogen to occur, RF at exactly the Larmor frequency of hydrogen must be applied.
True
What is the gyromagnetic ratio of hydrogen?
42.57 MHz/T
Select the three components of the magnetic field from those listed below.
- Static Magnetic Field
- Radiofrequency Fields
- Time Varying Magnetic Fields
What happens to the alignment of hydrogen protons when placed in an external magnetic field? Check all that apply …
- The magnetic moments of the nuclei align with or against the main magnetic field.
- Slightly more nuclei line up with the main magnetic field than against it.
