Instrumentation

What is the typical order (from inside to outside) of the instrumentation that composes the MRI scanner's gantry?

RF coils, gradient coils, shim coils, primary magnet

Which fundamental force governs the interactions between electric charges and magnetic fields?

Electromagnetism

Which two energy fields are involved in MRI image generation?

Radiofrequency field and magnetic field

Faraday's Law is also known as the law of:

Electromagnetic induction

Which law states that a changing magnetic field in the presence of a conductor can induce an electromotive force (EMF) and current?

Faraday's law

According to Faraday's law, which of the following must be present for electromagnetic induction to occur?

All answers are correct

According to Faraday's law, which of the following factors do have a significant impact on electromagnetic induction? (Select two)

- Angle of interaction between the magnetic field and conductor

- Strength of the magnetic field

- Number of coil windings in the conductor

- Speed of the motion between the magnetic field and conductor

According to Faraday's law, as magnetic field strength increases, the current produced within the conductor generally increases. (True or False)

True

According to Faraday's law, as the speed of motion between the magnetic field and the conductor increases, the current produced within the conductor generally decreases. (True or False)

False

According to Faraday's law, as the angle of interaction between the magnetic field and the conductor nears ____, the current produced within the conductor is generally maximized.

90°

According to Faraday's law, as the number of coil windings in the conductor increases, the current produced within the conductor generally decreases. (True or False)

False

A law in electromagnetism stating that an induced current opposes the magnetic field that produced it is also known as:

Lenz's law

Lenz's law states that an induced current creates a(n) ____ opposing the magnetic field that induced the current.

Magnetic field

According to Lenz's law, what are the induced currents that oppose the magnetic field that created them commonly called?

Eddy currents

The ____ is typically located within the fourth layer of instrumentation inside the MRI system's gantry (from inside to outside).

Primary static magnet

The abbreviation that commonly represents the static magnetic field is:

B₀

All of the following are types of magnets employed in MRI systems EXCEPT:

Hyperbaric magnets

MRI superconductive electromagnets are composed of superconductive materials, such as:

Niobium (Nb) and titanium (Ti)

What type of MRI magnet is capable of maintaining a high current without additional power input when cooled below 4 kelvin?

Superconductive electromagnets

In order to achieve superconductivity, the materials used in the magnet coils of superconductive electromagnets are cooled below approximately ____.

4 K

Which type of MRI magnet is capable of producing strong magnetic fields amongst the most powerful available?

Superconductive electromagnets

What unit is commonly used to represent magnetic field homogeneity in MRI systems?

ppm (parts per million)

The homogeneity of magnetic fields produced by superconductive electromagnets is typically:

< 1-3 ppm

MRI superconductive electromagnets are:

Always active

In order to eliminate the magnetic field produced by MRI superconductive electromagnets, what must typically occur?

A quench

Which type of MRI magnet is often the costliest due to its complexity, high-performance characteristics, and cooling requirements?

Superconductive electromagnet

Cryogens are chemical substances used to cool what type of MRI magnet?

Superconductive electromagnets

A cryogen commonly used in modern-day superconductive electromagnets is:

Liquid helium

The cylindrical steel tank that houses the main magnetic coils and cryogens is known as the:

Cryostat

What is another common term for cryostat?

Dewar

What type of MRI magnet requires a constant power supply to directly power its magnetic field?

Resistive electromagnets

What is the source of power for a resistive electromagnet MRI system?

Electricity

What type of MRI magnet is generally less expensive to purchase and install, but can lead to elevated operational costs?

Resistive electromagnets

In order to eliminate the magnetic field produced by MRI resistive electromagnets, what must typically occur?

The external power supply to magnet coils must be terminated

What type of MRI magnet is comprised of ferromagnetic material and can sustain a magnetic field indefinitely without needing electrical power or a cryogenic cooling system?

Permanent magnets

Which of the following ferromagnetic substances commonly compose MRI permanent magnets?

All answers are correct

ALNICO is a ferromagnetic material composed of which substances?

All answers are correct

NdFeB is a ferromagnetic material composed of which substances?

All answers are correct

SmCo is a ferromagnetic material composed of which substances? (Select all that apply)

Cobalt; Samarium

Which type of MRI magnet has significantly lower operating costs due to not requiring electrical power or cryogenic cooling?

Permanent magnets

Which type of MRI magnet generally has the least magnetic field homogeneity?

Permanent magnets

In order to remove the magnetic field produced by permanent MRI magnets, what must typically occur?

The magnetic field cannot be removed

Permanent magnets generally provide the least magnetic field homogeneity and possess non-removable magnetic fields. (True or False)

True

A magnetic field strength of 1 tesla is equal to:

10,000 G (gauss) or 10 kG (kilogauss)

A magnetic field strength of 10,000 gauss is equal to:

1 T (tesla) or 10 kG (kilogauss)

A magnetic field strength of 10 kilogauss is equal to:

1 T (tesla) or 10,000 G (gauss)

Which of the following are commonly used unofficial classifications for MRI systems based on magnetic field strength? (Select all that apply)

High-field; Mid-field; Low-field; Ultra-high field

Which of the following best describes a low-field MRI system?

Magnetic field strength of approximately 0.35 T or lower

Which of the following best describes a high-field MRI system?

Typically utilizes superconducting electromagnets

What is the primary purpose of shim coils in an MRI system?

To optimize the magnetic field by correcting inhomogeneities

Shim coils can enhance the ____ of the magnetic field.

Homogeneity

The ____ is typically located within the third layer of instrumentation inside the MRI system's gantry (from inside to outside).

Shim coil

Which of the following best describes how shim coils function in an MRI system?

Shim coils generate small, additional magnetic fields that fine-tune the main static magnetic field to make it as homogeneous as possible

Why is the use of shim coils important for techniques like fat saturation in MRI?

Shim coils ensure a more homogeneous magnetic field, which is crucial for uniform fat saturation

Shim coils generate the main static magnetic field. (True or False)

False

The abbreviation that commonly represents the radiofrequency field is:

B₁

The RF field is typically oriented ____ to the main magnetic field (B₀).

Perpendicular

Smaller RF coils typically provide:

A smaller coverage area and better SNR

Larger RF coils typically provide:

A larger coverage area and worse SNR

The ____ is typically located within the first layer of instrumentation inside the MRI system's gantry (from inside to outside).

RF coil (body coil)

What type of coil is generally designed to only send radiofrequencies into the body?

Transmit coils

The body coil typically acts as the primary RF transmitter in closed-bore MRI systems. (True or False)

True

What type of coil is generally designed to only accept radiofrequencies emitted by the body?

Receiver coils

During standard sequences, maximum signal is typically produced in receiver coils when the net magnetization vector (NMV) is flipped by:

90 degrees

Which type of receiver coil is typically small and designed to be placed directly on the patient's body to improve signal reception in a localized area?

Surface coil

Surface coils typically provide a ____ coverage area and a ____ signal-to-noise ratio (SNR).

Small / good

Surface coils are generally only sensitive to tissue depths of approximately 50-75% of the coil's diameter. (True or False)

True

A surface coil that is 8 inches in diameter will generally be sensitive to tissue approximately ____ deep.

4 inches

If imaging a body part that is approximately 6 inches thick, which surface coil diameter would generally be suitable?

10 inches

Which type of coil consists of multiple small coil elements that can be used independently or together?

Multichannel coils

Another term commonly used for "multichannel coil" is:

Phased-array coil

The use of a multichannel coil typically provides a ____ coverage area and ____ signal-to-noise ratio (SNR).

Large / good

The use of phased-array coils typically provides the high SNR associated with small coils, and the large coverage area associated with large coils. (True or False)

True

Which technique is commonly employed to effectively make use of a multichannel coil's multiple small coil elements?

Parallel imaging

What type of coil is generally designed to both transmit and receive radiofrequencies to and from the body?

Transceiver coils

Which of the following best describes a transceiver coil used to accommodate a large volume of tissue?

Volume coil

Which of the following best describes a transceiver coil consisting of a simple loop of wire?

Linear coil

Linear coils, extremity coils, and head coils are examples of coils that may function as transceivers.

Linear coils (among other dedicated coils)

Which of the following best describes the transceiver coil built into the MRI system's gantry?

Body coil

The body coil is commonly built into the MRI scanner. (True or False)

True

The body coil is capable of:

Both transmitting and receiving radiofrequencies

The body coil typically provides high SNR. (True or False)

False

The primary RF transmitter used in closed-bore MRI systems is the:

Body coil

The body coil generally provides a ____ coverage area and ____ SNR.

Large / poor

Linear coils tend to provide decent SNR due to their small size. (True or False)

True

Which of the following best describes a transceiver coil that uses two coils offset from each other by 90 degrees?

Quadrature coil

Quadrature coils generally offer increased SNR compared to linear coils. (True or False)

True

What term describes the range of frequencies that the system sends in an RF pulse?

Transmit bandwidth

The transmit bandwidth is directly adjustable at the MR console. (True or False)

False

The transmit bandwidth is indirectly controlled through settings such as slice thickness. (True or False)

True

What term describes the entire range of frequencies that the system samples?

Receiver bandwidth

The receiver bandwidth is directly adjustable at the MR console. (True or False)

True

Changes to the receiver bandwidth commonly affect the signal-to-noise ratio (SNR) and the likelihood of chemical shift artifacts. (True or False)

True

Decreasing the receiver bandwidth generally results in a(n) ____ in SNR and a(n) ____ in chemical shift artifact.

Increase / increase

Increasing the receiver bandwidth generally results in a(n) ____ in SNR and a(n) ____ in chemical shift artifact.

Decrease / decrease

Which receiver bandwidth would typically provide the highest SNR: 8, 16, 64, or 120?

8

Which receiver bandwidth would typically have the greatest risk of creating chemical shift artifacts: 8, 16, 64, or 120?

8

What term generally describes the characteristics of the RF pulses, which are often displayed visually for analysis?

Pulse profile

When performing a pre-scan, the center frequency of the transmitted RF pulse is typically tuned to match the:

Larmor frequency of hydrogen protons

All radiofrequencies displayed in an RF pulse profile are sampled during readout. (True or False)

False