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Chapter 9, Chapter 10, Field Lines and Gradient Coils, Magnetic Properties of Matter & Types of Magnets, Cryogens

Terms in this set (247)

Identify the requirements of an MRI scanner to ensure homogenous, powerful magnetic field and a system that can both transmit and receive pulses of electromagnetic radiation.
a. . Powerful magnet to create magnetic fields over a 40-50 cm spherical volume. b. . A shim system to improve the homogeneity of the magnetic field.
c. . A gradient system to create linear slopes in field strength in any direction.
d. . An RF transmission system to generate and transmit pulses of electromagnetic radiation.
e. . A set of RF receiver coils to detect signal from the patient.
f. . A computer system to allow input of parameters and displaying images.
g. . A computer subsystem capable of coordinating the application of RF pulses and gradients and reconstructing the acquired data into images and storing them.
Use the diagram below to identify key parts of the MRI scanner.
A. . Shim Coil
B. . Main magnet
C. . Active shielding D. . Quench
E. . Gradient amplifier F. . RF transmitter
G. . RF amplifer
Attraction to an external magnetic field (B0):
Diamagnetic
Paramagnetic
Ferromagnetic
Weak
Weak
Large
Magnetic Susceptibility:
Diamagnetic
Paramagnetic
Ferromagnetic
Small
Small Positive
Large Positive
Electrons:
Diamagnetic
Paramagnetic
Ferromagnetic
Evenly Paired
Unpaired
Unpaired
What happens when exposed to the B0:
Diamagnetic
Paramagnetic
Ferromagnetic
Magnetic fields cancel out

Slight increase in magnetic field

High attraction to the static magnetic field
What happens when removed from the B0:
Diamagnetic
Paramagnetic
Ferromagnetic
Doesn't retain any magnetism

Electrons path loses alignment, no magnetism once removed

Retain magnetic moments
List examples
Diamagnetic
Paramagnetic
Ferromagnetic
Hydrogen, and helium

Calcium, Oxygen, and many metals, aluminum, titanium, and platinum

Iron, nickel, cobalt, gadolinium
Gadolinium contrast is highly ferromagnetic? (T/F)
False
Closed system
encloses the body front, back, and sides. Generates the main magnetic field using toroidal superconducting solenoid electromagnets
Open System
Open on the sides and only encloses patient above and below. To generate a magnetic field the scanners, use a large permanent magnet to allow for a 1.2 T superconducting MRI system.
Extremity System
About the size of a washing machine. The field is typically generated by a permanent magnet and is restricted to below 1T.
Identify the six (6) main requirements required for high-quality anatomical imaging.
a. . the field strength (flux density) must be high typically between 1 and 8 T
b. . Fringe field having a strength of (5 G) must not extend outside of safety zones III and IV
c. . Field must be spatially homogenous to a very high degree.
d. . Homogeneity must extend over a large spherical imaging volume (40 cm) to accommodate the required anatomical FOVs.
e. . Field must be temporally stable. This means that the flux density must not vary over time.
f. . Weight and bulk of the magnet must be kept at a level that does not pose any problems with installation in a normal imaging department.
Permanent Magnets-
Large disks of ferromagnetic allow such as boron, iron, nickel, and cobalt. The magnetic field is created by the inherent ferromagnetism of the alloy, namely the combined forces of unpaired electrons in the atoms of the metal that create a macroscopic magnetic field.
Resistive Magnets -
Employ copper-wound solenoids that operate just below normal room temperature. The principal advantage of this type of system is that the field strength can be adjusted, and the magnet switched off safely after use.
Superconducting Magnets -
The same way as a resistive magnet; however, the windings of the solenoid are spun from a type of metal alloy that is superconductive [5] (typically niobium/titanium).
In the Right hand grip rule, the thumb indicates:
a. The magnetic field direction
b. The current direction
c. The number of windings in the solenoid
d. None are correct.
b. The current direction
This type of magnet uses cryogens to reduce resistance.
a. Permanent magnets
b. Resistive magnets
c. Superconducting magnets
d. Paramagnetic magnets
b. Resistive magnets
The difference between Resistive and Superconducting magnets is that the resistive magnets use cryogens to reduce resistance.
T/F
False
Identify the physical construction of a cryostat
a. . Outer structure consists of a hollow cylindrical steel tank b. . Area inside of the chamber is termed the warm bore.
c. . Quench pipe
d. . Refrigeration
Identify the properties of cryogen.
a. . Extremely low temperature
b. . Readily available c. . Be able to shield heat transfer
Briefly explain why solenoid coils of the MRI scanner are broken into segments vs all one unit.
A single cylindrical solenoid of a suitable length for an MRI scanner is not capable of creating a large enough homogenous imaging volume to achieve the required FOV. Splitting into evenly spaced solenoids ensure that homogenous imaging volume if large enough to cover the requisite 40 cm sphere
Solenoid windings are made of:
a. Niobium
b. Titanium
c. Copper
d. Gold
e. A-C
f. B-D
e. A-C
Briefly discuss the steps for ramping up the magnet.
When the parallel winding with a heating coil is heated, the terminals of the solenoid are connected to an external power supply to power up the magnet When the required field strength is achieved, the heater is turned off, and the persistent switch becomes superconductive. This creates a closed loop of superconductive wire and effectively bypasses the external power supply because the flowing electrons show a preference for the non resistive circuit.
Identify the measurement and symbol used for magnetic field strength.
Amperes(A) per meter
and is given the symbol H
Identify the measurement and symbol used for flux density.
Tesla and is given the B symbol
As the field strength increases, the signal to noise ration increases. T/F
T
As the field strength increases, chemical shift increases. T/F
F
How should the receive bandwidth be adjusted to decrease chemical shift artifact?
Increase bandwidth
As the field strength increases, the energy deposition in the patient's body decreases. T/F
F
Passive
• Reroutes the fringe field away from the outside environment and back towards the scanner

• Causes lines of flux to pass though steel cladding in preference to air

• Disadvantages-iron cladding can weigh over 20 tons, very expensive, proximity of ferromagnetic metal can adversely affect the homogeneity of the scanner that is intended to shield

• Replaced by active shielding in most clinical scanners and some ultra-high-field research systems
Active
• 2 larger diameter solenoids positioned at each end of the bobbin-known as bucking coils (oppose the effect of the main magnet windings)
• Function is to actively shield the local environment by constraining the 5G footprint of the fringe field within a short distance from the scanner
• Bucking coils carry a current flowing in the opposite direction to the main magnet windings, reversing the flux
• We should be more cautious about projectile safety because active shielding causes a very steep static field gradient
What happens if a current-carrying conductor is placed perpendicular to an external magnetic field?
The Lorentz force acts on the moving charges in the wire and causes physical defection of the conductor
What is the purpose of the Shim System?
Ensure homogeneity of the magnetic field within the imaging volume
Identify the unit of measurement for magnetic field homogeneity.
ppm over the 40cm (diameter) spherical imaging volume
Describe the following:
Passive Shimming
o Uses shims to adjust for large changes in magnetic homogeneity
o Inner circumference of the warm bore of the cryostat is lined with long plastic trays that fit along the full length of the bore- designed to accommodate the small ferromagnetic shims
o Used to balance out any inhomogeneity present in the bare field by manipulating the lines of flux
Describe the following:
Active Shimming
o Uses electromagnets of ferromagnetic shims and is used in addition to passive shims
o Resistive shimming coils-positioned close to the gradient coils, the shim can be manipulated at any time by adjusting the current flowing through the windings o Active shimming is usually performed by additional superconducting solenoids inside the cryostat
o Advantage is there is no electrical power required
Describe the following:
Gradient offset (dynamic shimming)
o It is possible to apply a current to the gradient coils that offsets any minor inhomogeneity in the main magnetic field
o By introducing a large patient into the bore, the homogeneity can be changed by up to 9pom by diameter repulsion-dynamic shimming can help correct this
o The primary purpose of the gradient system is to create linear slopes along the main magnetic field
Identify the imaging plane that will be a result from the active gradient. :
a. Z-gradient
b. X-gradient
c. Y-gradient
a. Z-gradient
Elements of the gradient coil are supplied by three separate power sources called ___.
a. Gradient amplifiers
b. Gradient dampeners
c. Gradient coils
d. Gradient residual
a. Gradient amplifiers
Degradation of image quality can occur if the gradient fields are allowed to extend into the main magnet solenoids. This is the result of:
a. Rapid currents
b. Ghosting
c. Riptides
d. Eddy currents
d. Eddy currents
All of the following are true about gradient coils, except:
a. When activated, the gradient coils change the main magnetic field in a linear slope.
b. The polarity of a gradient may be changed by reversing the current flow in the gradient coil elements.
c. Adding current in the same direction of the windings of the main magnet solenoid simulates the increasing of windings in the coil thus increasing the magnetic strength.
d. Adding current to the coil makes the field strength throughout the bore of the MRI scanner the same.
d. Adding current to the coil makes the field strength throughout the bore of the MRI scanner the same.
When a gradient amplifier is applied, the Larmor frequencies of magnetic moments vary depending on where they lie on the linear slope. (T/F)
T
identify the measurement unit for Gradient Amplitude.
mT/m or G/cm
Identify the measurement unit for Gradient Rise Time.
microseconds
Identify the measurement unit for Gradient Slew Rate.
T/m/s
Identify the safety considerations for Gradient power duty cycle.
a. In terms of MRI hardware, rapid gradient switching can cause overheating of the gradient coils
b. Some implanted devices may be adversely affected, and manufacturers place conditions of scanning related to gradient slew rate
c. The physiological limitation to gradient slew relates to the fact that a time-changing magnetic field causes an induced voltage in a nearby conductor. This includes a patient's nervous system.
What technical factors determine the geometry of the MRI image due to the gradient amplitude?
a. . Slice thickness
b. . Phase resolution c. . FOV
Pulse sequences that require rapid gradient switching tend to cause the highest levels of acoustic noise. (T/F)
T
A gradient that has a positive lobe equal to the negative lobe is known as a _______ gradient.
a. Balanced
b. Sloped
c. Unbalanced
d. None are correct.
a. Balanced
The gradient system determines the scan time, slice location, spatial encoding and indirectly the image contrast. (T/F)
T
The ______________ of a gradient is determined by the amount of current passing through the coil.
amplitude
The ____________ of a gradient is determined by the direction of the current flowing through the coil.
polarity
The amplitude of a gradient determines the ___________ ______________.
spatial resolution
The _____________ determines how fast data can be acquired.
slew
What is the purpose of the transmitted RF system?
To target a volume slice of tissue within the region to be examined and increase the energy level of a proportion of the hydrogen nuclei within that slice.
What is the gyromagnetic ratio of Hydrogen at 1 T?
42.58 MHz/T
Identify the material used and the name of the protective shielding used to prevent RF frequencies from entering or leaving the MRI suite.
The protective shielding is the Faraday Cage. Copper was the original material of choice. Aluminum panels are now favored.
Define transmit bandwidth.
The transmitted RE is an electromagnetic wave, which contains a narrow range of frequencies centered around the Larmer frequency of the magnetic moments of hydrogen nuclei at the external field strength of the system, The narrow range of frequencies is the transmit bandwidth.
Identify the roles of the RF Transmit System:
Waveform generator:
Generates a sinc pulse
Identify the roles of the RF Transmit System:
Frequency Synthesizer:
Ensures that the frequencies in the pulse are centered around the Larmor frequency of the magnetic moments of the spins.
Identify the roles of the RF Transmit System:
RF Amplifier:
Provides enough energy to couple with the nuclei in the region of interest.
Describe the purpose of an RF Transmitter coil.
Generates radio waves at the desired frequency, which are transmitted into the anatomical area.
RF homogeneity improves as coil sizes increase. The trade-off is that the filling factor can be compromised. This affects the SNR and image quality. To improve filling factor, what considerations should be used when using an RF transmit coil?
a. . Positioned close to patient
b. . Enclose the entire region of interest
c. . Must be evenly spaced
What technical factor determines when the RF receive system should receive the signal?
Time TE
Amplification, filtering, and digitization of analog signals are done inside the receiver coil assembly or body of the MRI scanner. T/F
T
Compare and Contrast Surface RF receive coils and Volume RF receive coils.
Surface coils are not typically used as RF transmitters because of their poor RF homogeneity. They are described as receive-only coils.

Volume coils they offer a comparatively homogenous RF field over a large imaging volume unlike surface coils.

Volume coils are typically as transmit coils like surface coils are.
Choose all that apply] Identify the true statements about receiver coils.
a. Receiver coils are a critical part of image optimization. The selection of the appropriate receiver coil for the area under examination is very important
b. Large coils provide large coverage but a relatively poor SNR. This is because the anatomical area may not fill the entire sensitive area of the coil. The filling factor is low.
c. Small coils provide small coverage but relatively good SNR. This is because the sensitive volume of the coil will be filled with tissue. The filling factor is high. However, aliasing is more likely
d. Phased array coils of the linear and volume type are the best option, as they combine the benefits of using small coils with those of using large ones
a. Receiver coils are a critical part of image optimization. The selection of the appropriate receiver coil for the area under examination is very important
b. Large coils provide large coverage but a relatively poor SNR. This is because the anatomical area may not fill the entire sensitive area of the coil. The filling factor is low.
c. Small coils provide small coverage but relatively good SNR. This is because the sensitive volume of the coil will be filled with tissue. The filling factor is high. However, aliasing is more likely
d. Phased array coils of the linear and volume type are the best option, as they combine the benefits of using small coils with those of using large ones
Where in the MRI scanner is the magnetic homogeneity the greatest?
True isocenter of the imaging volume
What is the role of the Pulse Generator Module (PGM) in the MRI process?
The PGM is an independent computer that is responsible for sending instructions relating to the timing, amplitude, and shape of the transmitted RF pulses and the timing and duration of the sampling window. It also is connected to the gradient amplifiers and generates pulses to determine the shape and duration of the gradients used during the scan.
What is the format used for storing patient images in a PACS system?
DICOM
SAR is measured in __________ units
W/kg
What is the purpose of the ACR guidance document on MRI safety?
· Non-MRI personnel include patients, visitors, or facility staff who have not undergone formal safety training (within the last 12 months) as designated by the MRI safety director.

· Level 1 personnel include office staff and patient aides who have passed minimal safety education to ensure their own safety as they work within Zone III.

· Level 2 personnel include MRI technologists, radiologists, and nursing staff who have been extensively trained in MRI safety, including issues relating to thermal loading, burns, and neuromuscular excitation from rapidly changing gradients.
List three of the five field conditions that define the MR environment, according to the reading:
a. static magnetic field strength
b. spatial gradient
c. time rate of change of the magnetic field (dB/dt)
List the possible safety issues that should be taken into consideration when testing for MR conditional?
Testing for items that may be placed in the MR environment should address magnetically induced displacement force and torque, and RF heating.
An implanted device has been deemed MR Conditionally safe for a 3T MRI system. You are scanning on a 1.5 T MRI system. The patient is safe to scan. (T/F)
F
What are the five main factors that are considered to have an impact on patient safety?
· Psychological effects
· The spatially varying static magnetic field
· Electromagnetic (radiofrequency) fields
· Time-varying gradient magnetic fields
· Cryogens
Claustrophobia has caused many people to not be able to hold still, terminate the exam, or have otherwise undiagnostic images. What have you learned while in clinical to mitigate the patient's struggles with claustrophobia?
I have learned proper communication between tech and patient is vital. I have learned if you talk a patient thought the entire exam it will reduce their nerves and help them make it through.
What four implications for patient safety are caused by the Static Field?
· Transient biological effects
· Projectile hazards
· Torque on implanted devices
· Foreign bodies in the static field
What might a person feel that has quickly moved through the flux lines of a high static magnetic field?
Vertigo, causing dizziness, nausea, nystagmus (involuntary eye movement), and postural instability.
What mechanism may be at play for a person experiencing transient biologic effects?
The main magnetic field B0
What is the mechanism that causes phosphenes and metallic taste to occur?
Faraday's law of electromagnetic induction to consider. This phenomenon causes the induction of an electrical current through a conductor that is moved through an external magnetic field.
What is responsible for maintaining the 5 G threshold as close to the magnet as possible?
Active shielding by the bucking coils is used to maintain the 5G
The force required to accelerate a ferromagnetic item toward isocenter of the magnet is inversely proportional to the product of the field strength and the spatial static-field gradient.
T/F
Why is active shielding so important when thinking about ferromagnetic objects coming into the MRI suite?
Static field gradient extends to such a distance that large ferromagnetic items are attracted from up to several meters away.
According to the reading, when should a Quench be performed?
Necessity if there is an immediate danger to life or limb.
What might happen to the image should a bobby pin or other ferrous object be inside the magnet during scanning?
This is likely to degrade image quality due to phase mipmapping artifacts
According to the Learning Tip: What is needed to prevent incidents from occurring?
Protective zoning of the MRI suite, a locked physical barrier between any public areas and the magnet room, and the training of all hospital staff on the dangers of MRI.
Items that are short and wide are more apt to experience a rotational and torque force?
T/F
F
Which static magnetic field force results in the projectile missile effect?
The gradient field
[Choose all that apply] Of the following objects, identify those that are MOST likely to experience torque.
o Abdominal Aortic Aneurysm clip
o Pacemaker
o Braces
o Brain aneurysm clip
o Heart stents
o Knee replacement
o Abdominal Aortic Aneurysm clip
o Pacemaker
o Brain aneurysm clip
o Heart stents
After answering the previous question, what should be done when any implant or device is in question for MRI safety?
The implant must be researched if it is MRI safe and what magnet it can go into (1.5T or 3T)
A patient states they had metal removed from their eye by a doctor and they have had a MRI before.
Is it safe to scan the patient without further research?Justify your answer.
No, the patient is not safe. Many times, patients will lie to be able to obtain the exam in a timely fashion. Orbit imaging using Xray should be ordered to rule out possible foreign bodies.
According to the ACR guidance on MRI safety, what is the recommendations to clear a patient for foreign bodies in the eye?
Orbit imaging using Xray should be ordered to rule out possible foreign bodies.
The energy contained in a photon of electromagnetic radiation is directly proportional to the frequency and wavelength T/F
F
Inversely proportional to its wavelength.
[Choose all that apply] Identify the principle safety hazards associated with RF.
o Adverse effects on implant function
o Antenna effect
o Hearing damage
o Missile effect
o Patient heating/burns
o Torque
o Rotation
o Adverse effects on implant function
o Antenna effect
o Patient heating/burns
What is the dosimetric unit for SAR?
(W/kg)
Discuss how whole-body SAR is calculated?
The amount of energy required for all the pulses in a pulse sequence is summed, divided by the TR, and then divided by the mass of the patient to calculate the whole-body SAR.
The Lens of the eye and the germ cells of the male reproductive system are the most sensitive to heat from the RF pulse. T/F
T
2nd level controlled operating mode is for research-only and is not used in the clinical setting. T/F
T
List the five (5) conditions that may adversely affect the ability of the patient to dissipate heat properly.
a. Age
b. Body habitus
c. Fever
d. Medications that alter thermoregulatory responses.
e. Inability to communicate.
Lower-field strength scanner

Response
Trade-off
Center-frequency decreases, RF transmitted is reduced

Reduction in SNR if all other factors remain equal. This may require a higher NSA, and this at least doubles the examination time.
Remove/Reduce pre-saturation pulses
Response
Trade-off
Remove any additional RF pulses that are being used to saturate signal in structures inside or outside the FOV.

An increase in phase mismapping artifact that the saturation pulses were intended to reduce
Increase the TR
Response
Trade-off
Reduces the number of RF excitations per unit time.

Weighting changed, less T1W
Decrease the # of slices
Response
Trade-off
Reduces the # of RF pulses per repetition and unit time

Reduced coverage of the anatomical area unless extra acquisitions are used, and this increases the scan time.
Use a different receiver coil
Response
Trade-off
Quadrature vs linear = more efficient

No trade-off if an appropriate coil is selected at the outset.
Avoid TSE/FSE or reducing the ETL/TF in pulse sequences
Response
Trade-off
--------

Energy deposition increases with the square of the flip angle. 180° RF pulses deploy four times more energy than 90° RF pulses.
Reduce the flip angle of the RF rephasing pulses
Response
Trade-off
Reduces the RF deposition

A slight reduction in image quality but is unlikely to render the images nondiagnostic.
How does patient positioning contribute to the patient heating?
If the hands are in contact with the sides of the legs, or if the heels are resting against each other, there may be a small surface area of skin in contact. This creates a "biological circuit" through which induced current may flow. Because skin contact may only be over a few square centimeters, the amount of induced current is concentrated in this small area, and intense heating may result.
The greatest energy where heat may occur can be found:
a. Antinode
b. Node
c. Anywhere along the pacing wire
d. None are correct
a. Antinode
1.0 T
RF frequency
Full wavelength
Most significant heating
42.58 MHz
720 mm
360 mm
1.5 T
RF frequency
Full wavelength
Most significant heating
63.87 MHz
480 mm
240 mm
3.0 T
RF frequency
Full wavelength
Most significant heating
127.74 MHz
240 mm
120 mm
All pacemakers are MRI unsafe? T/F
F
Identify the risks to the patient for time varying gradient magnetic field
o Antennae effect
o Hearing damage
o Missile effect
o Patient heating or burning
o Peripheral nerve stimulation (PNS)
o Hearing damage
o Peripheral nerve stimulation (PNS)
Finish the sentence. Current safety guidelines state that in NORMAL operating mode, the gradient system should operate at a level that does not exceed ____ % of the mean threshold for peripheral nerve stimulation and should never exceed 100 %.
a. 10
b. 50
c. 80
d. 90
c. 80
TVGM can interfere with the implanted electronic medical devices circuitry. T/F
T
What is the cause of the acoustic noise generated during an MRI exam?
Lorentz forces
According to the reading, OSHA recommends that exposure to noise should be maintained below a level equivalent to ____ dB over an 8 hour period to minimize the risk of hearing loss.
a. 20
b. 60
c. 85
d. 100
e. 115
c. 85
What is required by the ICNIRP to reduce the likelihood of hearing loss during an MRI exam?
Protection for noise levels above 80 db
What are the four primary safety concerns associated with cryogens?
Thermal sensitivity, asphyxia, quench, and explosion
Liquid helium as a cryogen has low temperatures of ___________.
4k above absolute 0
What is the oxygen concentration sensor set at to detect helium gas reducing the oxygen in an MRI suite?
a. 10.5%
b. 19.5%
c. 23.5%
d. 50%
b. 19.5%
What are some risks should the helium leak into the room vs through the quench pipe during a quench?
Asphyxiation, frost bite, cause ear damage, impairer motors kill.
According to Faraday's Law of Electromagnetic Induction, if two of the essential variables are present the third will naturally occur. Choose the three variables.
Magnetism
Magnetic Flux
Charge
Motion
Magnetism
Charge
Motion
Magnetic flux lines are created by two poles. What are they?
North
South
East
West

1 and 2
2 and 3
1 and 4
3 and 4
1 and 2
The X and Y gradient coils are known as:
Opposing Coils
Transmit Coils
Saddle Coils
Receive Coils
Saddle Coils
Identify the calculation used to measure the Maximum Spatial Magnetic Gradient Field.
d= changing in
B= field strength
x= distance

dB+dx/B
dB/dx * B
dB x dx
dB/dx
dB/dx * B
All of the properties of Magnetic Flux Lines are true, except:

Lines are closed loops and continuous
Lines never cross
Lines that are FARTHER apart indicate a STRONG magnetic field
Lines are directed from north to south
Lines that are FARTHER apart indicate a STRONG magnetic field
__________ are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore. When a current is run through these, a secondary magnetic field is created.
RF Coils
Gradient coils
Transmit coils
Birdcage coils
Gradient coils
A basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF) is known as:
Larmor Equation
Ohm's Law
Faraday's Law of Induction
Nyquist Theorem
Faraday's Law of Induction
According to rule 2 of the right hand rule, the thumb will indicate?

none- there is only one right hand rule
the direction of the magnetic field
the direction of the current
the force on the magnetic field
the force on the magnetic field
Identify the factors that alter the strength of the magnetic field.

Changing the current passing through the wires.
Changing the distance or spacing between the windings.
Changing the number of windings in the coil
Changing the diameter of the wire used in the windings.
Changing the current passing through the wires.

Changing the distance or spacing between the windings.

Changing the number of windings in the coil

Changing the diameter of the wire used in the windings.
What does the arrow of the Net Magnetic Vector (NMV) indicate?

The longer the arrow, the higher the signal-to-noise ratio (SNR)
The length indicates the field strength of the main magnetic field.
Direction of the main magnetic field
The speed of the magnetic moments
The longer the arrow, the higher the signal-to-noise ratio (SNR)

The length indicates the field strength of the main magnetic field.

Direction of the main magnetic field
An MRI technologist is laying a patient on the table to prepare for an exam. The patient's bobbyepins fly out of her hair into the magnet and become stuck to the side. The object created a missile effect. What is the most likely magnetic property?

Diamagnetism
Superparamagnetism
Ferromagnetism
Paramagnetism
Ferromagnetism
An object that demonstrates a slight repulsion from the static magnetic field, such as water is known as

Diamagnetism
Superparamagnetism
Ferromagnetism
Paramagnetism
Diamagnetism
What type of magnet uses a cryogen bath to reduce the amount of resistance in the electromagnet?

Superconducting magnets
Solenoid magnets
Permanent magnets
Resistive magnets
Superconducting magnets
Iron, steel, and gadolinium (in its native state) are all examples of:
Ferromagnetism
Diamagnetism
Superparamagnetism
Paramagnetism
Ferromagnetism
The most commonly used material to produce a permanent magnet is an alloy of:

Steel
Nickel
Aluminum
Cobalt
Nickel
Aluminum
Cobalt
Nuclei that have a weak net magnetic vector and easily influenced by the static magnetic field is known as:
Nuceli are not influenced by the magnet
Net magnetic vector
Spin-down
Spin-up
Spin-up
What zone is the quench vent pipe when it enters the ceiling?
zone 3
zone 2
zone 1
zone 4
zone 3
A device used to keep helium in a liquid state by keeping the hollow tubes inside thermally insulated is known as
Cryopins
Cryogen
Bobbins
Cryostat
Cryostat
Identify the hazards of a failed quench when the helium leaks into the MRI room.
Frostbite
Ear drum rupture
Hypothermia
Asthma attack
Frostbite
Ear drum rupture
Hypothermia
Asthma attack
Identify the hazards of a failed quench.

Asthma attack
Asphyxiation
Cold burns/Frostbite
Hyperthermia
Asthma attack
Asphyxiation
Cold burns/Frostbite
A sudden loss of magnet superconductivity is known as:

MRI does not ever have a loss of magnet superconductivity
Hydrogen Boil-off
Quench
Helium Boil-off
Quench
The process of energizing an MRI solenoid to create an electromagnetic force is called:

Sloping
Dampening
Ramping
Camping
Ramping
What element is the main source used in cryogens?
Carbon dioxide
Oxygen
Nitrogen
Helium
Helium
Recondenses the helium gas to liquid to prevent it from burning off entirely.
Cold Head
Responsible for circulating the helium through the magnet. Should it fail, the magnet starts to lose liquid and the ability to keep the magnets cool.
Compressor
This component is responsible for monitoring the temperature.
Chiller Temperature
This component is responsible for circulating the chiller unit to the heat exchanger on the cold head.
Chill water flow
When a quench occurs, it may take up to 30 seconds before a technologist knows a quench is occurring. (T/F)
T
What happens to liquid helium if it reaches room temperature?

It will change to a solid state
Nothing will happen
It will change to the element hydrogen.
It will change to a gaseous state
It will change to a gaseous state
Identify the standard refrigeration system used in modern MRI scanners that reduces the need for helium refills as frequently.
Cold Head
Compressor
Zero Boil Off (ZBO)
Chiller
Zero Boil Off (ZBO)
A Creatinine level 1.8 with a calculated eGFR 40 is _______ kidney disease, according to the ACR on Chronic Kidney Disease (CKD).

Severe (CKD 4,5)
Mild (CKD 2)
Normal (CKD 1)
Moderate (CKD 3)
Moderate (CKD 3)
According to the ACR Manual on Contrast Media 2018, what contrast agent has been labeled "contraindication" by the FDA for patients that have experienced allergic-like reactions to GBCM?

Multihance
Eovist
Gadovist
Prohance
Multihance
According to the ACR Manual on Contrast Media 2018, nearly all life-threatening contrast reactions occur within the first ___ after contrast medium injection.
15 minutes
20 minutes
5 minutes
10 minutes
20 minutes
A breastfeeding mother is having an MRI with contrast. She is concerned about the baby's exposure to the contrast media through the breast milk.

According to the ACR Manual on Contrast Media 2018, what should the instructions be to the breastfeeding mother?
1. There is minimal excretion to the infant's gut and studies show it is safe to continue breastfeeding.
2. A concerned mother should be told to abstain from breastfeeding for 12 to 24 hours.
3. Stop breastfeeding the baby indefinitely
4. Abstain from breastfeeding for 1-week post-contrast.

2 and 3 only
1, 2, 3, and 4
1 and 4 only
1 and 2 only
1 and 2 only
To date, there have been studies showing mutagenic and/or teratogenesis effects on fetuses post GBCM.
False
True
False
All of the properties of Magnetic Flux Lines are true, except:

Lines never cross
Lines are closed loops and continuous
Lines that are FARTHER apart indicate a STRONG magnetic field
Lines are directed from north to south
Lines that are FARTHER apart indicate a STRONG magnetic field
According to rule 2 of the right hand rule, the thumb will indicate?

the direction of the current
the force on the magnetic field
none- there is only one right hand rule
the direction of the magnetic field
the force on the magnetic field
The direction of the force from a magnetic field on a current running through a wire will be _________ to both the magnetic field and the current.

Perpendicular
At an angle
Parallel
None are correct
Perpendicular
What type of magnet uses a cryogen bath to reduce the amount of resistance in the electromagnet?

Solenoid magnets
Permanent magnets
Superconducting magnets
Resistive magnets
Superconducting magnets
An object that demonstrates a slight repulsion from the static magnetic field, such as water is known as

Paramagnetism
Ferromagnetism
Superparamagnetism
Diamagnetism
Diamagnetism
Nuclei that have a weak net magnetic vector and easily influenced by the static magnetic field is known as:

Spin-down
Nuceli are not influenced by the magnet
Spin-up
Net magnetic vector
Spin-up
Identify the properties of objects with Paramagnetic properties.

A small positive magnetic susceptibility

Iron, Nickel, Cobalt, and Gadolinium (in its natural state) are examples

Oxygen, Calcium, Aluminum, Titanium, and Platinum are examples

Weak attraction to the external magnetic field

The lines of magnetic flux converge toward the object
Oxygen, Calcium, Aluminum, Titanium, and Platinum are examples
A small positive magnetic susceptibility
The lines of magnetic flux converge toward the object
Weak attraction to the external magnetic field
__________ are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore. When a current is run through these, a secondary magnetic field is created.

Gradient coils
RF coils
Birdcage coils
Transmit coils
Gradient coils
Identify the type of coil with the following properties:
Extended FOV results in better SNR advantages
Small surface coils each have their own channel through which detected signal is carried to the signal processing components.
Different sections can be turned on to target a specific region of interest.
Below is an example.

Volume RF receive coil
Basic single loop surface RF receive coil
Phased array surface RF receive coil
Birdcage coil
Phased array surface RF receive coil
Surface coils are typically receive-only coils because of their poor RF homogeneity.
T/F
T
Permanent magnets exhibit all of the following properties except:

The magnetic field is created by the inherent ferromagnetism of the alloy.

They are equipped with large discs of a ferromagnetic alloy such as neodymium, boron, and iron, or aluminum, nickel, and cobalt (ALNICO).

Uses solenoid windings to produce a direction of current creating an electromagnet.

Does not require electrical power or cryogenic cooling.
Uses solenoid windings to produce a direction of current creating an electromagnet.
Identify the term:
The strength of the gradient over distance.

Gradient amplitude
Duty cycle
Slew rate
Rise time
Not
Gradient amplitude
What is the boiling point of the cryogen liquid helium?

15 K
10 K
5 K
4.2 K
4.2 K
This type of MRI system generates the main magnetic field using toroidal superconducting solenoid electromagnets positioned in circumference to the cylindrical bore.

Extremity systems
Closed systems
Open systems
Closed systems
Identify the properties of objects with Diamagnetic properties.

These types of material does not retain any net magnetism when removed from the external magnetic field.

Exhibit a weak repulsion to an external magnetic field.

Has a small negative magnetic susceptibility

Oxygen, Calcium, Aluminum, Titanium, and Platinum are examples

This type of magnetism increases the strength of the external magnetic field because of the unpaired electrons.
These types of material does not retain any net magnetism when removed from the external magnetic field.

Exhibit a weak repulsion to an external magnetic field.

Oxygen, Calcium, Aluminum, Titanium, and Platinum are examples

0.33/1 right
The time it takes a gradient to switch on, achieve the required gradient slope, and switch off again.


Gradient amplitude
Slew rate
Rise time
Duty cycle
Rise time
What element is the main source used in cryogens?

Oxygen
Nitrogen
Carbon dioxide
Helium
Helium
Identify the standard refrigeration system used in modern MRI scanners that reduces the need for helium refills as frequently.

Zero Boil Off (ZBO)
Compressor
Chiller
Cold Head
Zero Boil Off (ZBO)
The greatest energy where heat may occur can be found

None are correct
Antinode
Anywhere along the pacing wire
Node
Antinode
Identify the principle safety hazards associated with RF fields.

Antennae Effect
Tissue heating/burns
Implant malfunction
Hearing damage
Rotaion/Torque
Antennae Effect
Tissue heating/burns
Implant malfunction
All of the statements are TRUE concerning Specific Absorption Rate (SAR) EXCEPT:

SAR is measured in W/kg

SAR is affected by the patient's weight.

All statements are true.

SAR is a quantity that depends on the RF pulse characteristics
All statements are true.
MR Safe
An item that poses no known hazards in all MRI environments
MR Unsafe
An item that is known to pose hazards in all MRI environments
MR Conditional
An item that has been demonstrated to pose no knonw hazards in a specified MRI environment with specified conditions of use.
Magneto-phosphenes
Changing magnetic fields
Specific absorption rate (SAR)
A way of measuring the USA FDA limit for RF exposure
Time-varying magnetic fields
Visual effects stimulating the retinal phosphates due to Time-Varying Magnetic Fields
Quenching
Sudden loss of the superconductivity of the magnet coils so that the magnet becomes resistive
Zone 4
This zone is only suitable for screened patients under direct constant supervision of MRI staff as there is a risk of patient heating, RF antenna effects, missile effects and anoxia due to quench pipe failure
Translational force
The spatial gradient of the magnetic field produces an attractive displacement force on a ferromagnetic object placed into the static magnetic field is known as:
Rotational Force
The force on a ferromagnetic object that causes the object to turn and align with the direction of the Bo.
All of the following will reduce the RF deposition in the patient, except:

Reducing the flip angle.
Decrease the field strength of the scanner
Decreasing the TR
Decreasing the number of slices.
Decreasing the TR
A sudden loss of magnet superconductivity is known as:

Hydrogen boil-off
MRI does not ever have a loss of magnet superconductivity
Quench
Helium boil-off
Quench
A quench can be used to:

Satisfy the thirst of the technologist
Rapidly remove superconductivity and the magnetic field
Improve image quality in MRI
Maintain magnetic field homogeneity
Rapidly remove superconductivity and the magnetic field
Which of the following are risk factors for adverse IV Contrast reactions?
Asthma
Renal Insufficiency
Renal Calculi
Heart disease
1, 2, & 4
1, 3, &4
1 & 2
3 & 4
1, 2, & 4
Identify the organs responsible for eliminating the GBCM from the system.
Liver
Lung
Spleen
Kidneys
Liver
Kidneys
What is the half-life of Gadolinium-Based Contrast Agents?
1 hr
24 hrs
2 hrs
10 hrs
2 hrs
Iron, steel, and gadolinium (in its native state) are all examples of:

Ferromagnetism
Superparamagnetism
Diamagnetism
Paramagnetism
Ferromagnetism
The most commonly used material to produce a permanent magnet is an alloy of:
Steel
Nickel
Cobalt
Aluminum
Nickel
Cobalt
Aluminum
Identify the effects of the Magnetic Field strength increasing.

Signal increases
Chemical shift increases
SNR decreases
Noise increase
Signal increases
Noise increase

.67/1 so 1 more must be select (maybe Chemical shift increases)
This type of shielding uses two larger diameter solenoids, bucking coils, positioned at each end of the bobbin to shield the local environment by constraining the 5G footprint of the fringe field to a shorter distance from the scanner.
Armor Shielding
Passive Shielding
Plated Shielding
Active Shielding
Active Shielding
What does the thumb determine by the "right-hand grip rule"?
The current direction
The field strength
The amplitude of the gradient
The magnetic field direction
NOT The magnetic field direction MAYBE The current direction
If a gradient field is permitted to extend into the main magnet solenoids, what might occur?
Aliasing
Chemical shift
Eddy currents
Ghosting artifact
Eddy currents
The speed and strength of the gradient measured in mT/m/s is known as _________.

Gradient amplitude
Gradient speed
Duty cycle
Slew rate
NOT Gradient amplitude
The slew rate is measured in
mT/m
T/m/s
G/cm
Gauss
T/m/s
All of the following contribute to the gradient amplitude, except:

Field of View
Phase resolution
Slice thickness
Echo Train Length
Echo Train Length
What 3 things are needed to create MR images? (choose 3)

Static Magnetic Field
Gradient Field
Coil
RF Field
Static Magnetic Field
Gradient Field
RF Field
The _____ sends radio waves with enough energy to disturb the protons within the magnet.

Shimming
RF Transmitter
Radio Frequency
Gradient
RF transmitter
Permanent magnets exhibit all of the following properties except:

Uses solenoid windings to produce a direction of current creating an electromagnet.

The magnetic field is created by the inherent ferromagnetism of the alloy.

They are equipped with large discs of a ferromagnetic alloy such as neodymium, boron, and iron, or aluminum, nickel, and cobalt (ALNICO).

Does not require electrical power or cryogenic cooling
Uses solenoid windings to produce a direction of current creating an electromagnet.
Identify the standard refrigeration system used in modern MRI scanners that reduces the need for helium refills as frequently.

Zero Boil Off (ZBO)
Compressor
Cold Head
Chiller
Zero Boil Off (ZBO)
The Spatial Magnetic Gradient field is responsible for _____.

Rotational Force
Translational Force
Tissue heating
Translational Force
List at least two techniques you have used in the field or learned from the reading to help patients with the psychological issues of an MRI exam.
Explaining that it is normal to have fears and we are watching them at all times during the scan.
Asking the physician to prescribe medication is also a huge help in getting through scans.
The greatest energy where heat may occur can be found

Node
Antinode
None are correct
Anywhere along the pacing wire
Antinode
The limits set by the IEC/FDA for the head should be:

Scan in Normal Mode Limit.
All are correct
The limits for the head should not be greater than 38 degrees
The limits for the head should not be greater than 3.2 W/kg averaged.
All are correct
All of the following are results of transient biological effects, except:

Tissue heating
Vertigo
Nausea
Nystagmus
Tissue heating
Identify the risks to the patient for time-varying gradient magnetic fields (TVGM).

Peripheral nerve stimulation
Tissue heating
Hearing damage
Missile effect
Peripheral nerve stimulation

Hearing damage
Patients on hemodialysis must undergo treatment within what time period post-contrast administration?

No longer than 24 hours
2-3 days
Immediately
One week
No longer than 24 hours
What temperature should gadolinium be kept prior to injection?

Room temperature
98.6 degrees Farenheit
0 degrees Celsius
37 degrees Celsius
37 degrees Celsius

0/1 pts
A patient is showing moderate hives. Identify the treatment.

Call 911 and start CPR

Administer benadryl by mouth, intramuscular, OR through the IV.

Monitor vitals

Preserve the IV access
Administer benadryl by mouth, intramuscular, OR through the IV.

Monitor vitals

Preserve the IV access
A set of resistive windings that all MR systems are equipped with is known as what?

Gradient coils
Surface coils
Volume coils
Phased array coils
Gradient coils
All of the following are properties of the RF receive system except:

The receiver coil is responsible for the amplification, filtering, and digitization of analog signals.

The receiver coil detects noise.

The receiver coil samples the signal directly.

The signal is received by setting the factor TR
The signal is received by setting the factor TR
This MRI system is commonly used for scanning large animals, humans with large body habitus, claustrophobic patients, etc. The sideways table movement allows for more convenient imaging of lateral body structures. These types of scanners use large permanent magnets or superconducting solenoids to generate the main magnetic field.

Closed systems
Extremity systems
Open systems
Open systems
The stray magnetic field outside the bore of the magnet is known as what?

Static field
Fringe field
The main field
The torque field
Fringe field
Permanent magnets exhibit all of the following properties except:

Does not require electrical power or cryogenic cooling.

They are equipped with large discs of a ferromagnetic alloy such as neodymium, boron, and iron, or aluminum, nickel, and cobalt (ALNICO).

Uses solenoid windings to produce a direction of current creating an electromagnet.

The magnetic field is created by the inherent ferromagnetism of the alloy.
Uses solenoid windings to produce a direction of current creating an electromagnet.
Shim system
Used to improve the homogeneity of the magnetic field
Gradient system
Creates linear slopes in field strength in any direction.
RF Transmission Systems
Generating and transmitting pulses of electromagnetic radiation.
Rf receiver coils
Used to detect signal from the patient
Computer system
Allows input of parameters and displaying images.
Identify the hazards of a failed quench when the helium leaks into the MRI room.
Frostbite
Asthma attack
Hypothermia
Ear drum rupture
Superconducting magnets use cryogens to reduce the temperature of the niobium-titanium wires to a temperature of ____.

400-degrees Celsius
40- degrees Fahrenheit
4,000 Kelvins
4 Kelvins
4 Kelvins
Which of the following government agencies are responsible for setting limits for tissue heating and modes? (choose all that apply)

Joint Review Committee on Education in Radiologic Technology
International Electrotechnical Commission
U.S. Food & Drug Administration
Nuclear Regulatory Commission
NOT
Joint Review Committee on Education in Radiologic Technology
and
U.S. Food & Drug Administration

NOT
Nuclear Regulatory Commission
International Electrotechnical Commission
Identify the objective symptoms indicating an air embolism may be occurring.
Group of answer choices

Cough
Tachycardia
Hypotension
Dyspnea
Cough
Tachycardia
Hypotension
Dyspnea
Gradient amplitude is measured in:
G/cm
T/m/s
Tesla
mT/m
G/cm
mT/m
All are true concerning Faraday cages with the exception of:

Modern scan rooms use aluminum panels for the walls, floor, ceiling, and doors.

Wave guides are used to allow small items to pass through into the magnet room, but the RF waves of the frequencies used in MRI cannot.

Scan rooms have lead lined walls to prevent ionizing radiation from the MRI scanner from passing through.

Areas where a breach may occur, such as windows and air conditioning systems, are lined with wire mesh or honeycomb filters
Scan rooms have lead lined walls to prevent ionizing radiation from the MRI scanner from passing through.
All of the following are properties of Resistive MRI scanners except:

Employs copper-wound solenoids

ALNICO bricks are used to create a magnetic field.

A current over 10 kW is required to produce a maximum flux density used for scanning humans.

The field strength can be adjusted and the magnet switched off safely after use.
ALNICO bricks are used to create a magnetic field.
Gadolinium Based Contrast Agents (GBCAs) do not cross intact blood-brain barriers so normal brain tissue is unenhanced by its use unless there is a disruption
True
False
True
All of the following are methods to managing SAR and patient warming except:

Increase the TR

Pause between sequences

Scan in 1st or 2nd level mode

Use Gradient sequences before Spin Echo/Fast Spin Echo
Scan in 1st or 2nd level mode
The FDA limit for temperature is an increase of ___ degree Celsius.

5
-1
1
10
1
Shielding that requires the scanner to be surrounded by large steel plates is known as:

Active Shielding
Plated Shielding
Passive Shielding
Armor Shielding
Passive Shielding
What should be documented in the pregnant patient's medical record if contrast is deemed necessary?

The examination cannot wait until post pregnancy.
All are correct and should be documented
The MRI exam can not be acquired without contrast.
There are not any other imaging modalities to utilize
All are correct and should be documented
According to the ACR Manual on Contrast Media 2018, what is the recommended flow rate when using peripheral veins for venipuncture?
3 - 4 ml/sec
> 5 ml/sec
< 1 - 2 ml/sec
< 1 - 2 ml/sec
According to the ACR Manual on Contrast Media 2018, what catheter gauge is preferred for flow rates greater than 3 ml/sec?
12- gauge
16-gauge
20-gauge
18-gauge
20-gauge
The MRI system has ____ individual pairs of electromagnets in the gradient system.
2
1
4
3
Not 2
I think 3
The force exerted on a charged particle moving with velocity through an electric and magnetic field is known as:
Lorentz Force
Ohm's Law
Faraday's Law
Oersted's Law
Lorentz Force
The resistivity of the electromagnetic coils is ___ because of the cryogen bath reducing the temperature.
200
100
0
15
0
Identify the term that results in contact point tissue damage described in the image below.

Antenna effect
Time-varying gradient effect
Coil effect
Acoustic effect
NOT Coil effect

(Picture with arms touching)
Match the following SAR limits to the appropriate letter in the chart.
A 2
B 4
C 20
D Greater than 4
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