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8-10 Flashcards

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1
Q

What are the three major components of an MRI system?

A
  1. The Gantry (Magnet)
  2. Operating console
  3. System Electronics Cabinet
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2
Q

What is the function of the Gantry in an MRI system?

A

The Gantry has no moving parts (except for the patient couch) and is composed of many subsystems and electromagnetic coils.

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3
Q

What are the three types of magnets used in MRI systems?

A
  1. Permanent
  2. Resistive
  3. Superconducting
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4
Q

How is the magnetic field produced in a Permanent Magnet Imaging System?

A

It is produced by two assemblies of bricklike magnets attached to a massive iron yoke.

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5
Q

What defines a Resistive Magnet Imaging System?

A

It uses coils of wire wound in four to six rings, conducting large electrical currents ranging from 30 to 50 amperes.

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6
Q

What is unique about the Superconducting Magnet Imaging System?

A

It requires supercooled temperatures and is submerged in liquid helium to maintain superconductivity.

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7
Q

What temperature must a superconducting magnet reach to attain superconductivity?

A

Below 120 K or -153 degrees Celsius.

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8
Q

What are the three subassemblies of the gantry in a Superconducting Magnet Imaging System?

A

1) Patient Couch
2) Primary Electromagnet Assembly
3) Secondary Electromagnets and Coils

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9
Q

What is the primary function of the Patient Couch in MRI?

A

To support and position the patient during the scan.

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10
Q

What is the role of the Primary Electromagnetic Assembly?

A

It is housed in a cryostat and is not visible from the outside.

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11
Q

What types of coils are included in the Secondary Electromagnets and Coils?

A

1) Radiofrequency Coil
2) Gradient Coil
3) Shim Coils

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12
Q

What is the function of the Radiofrequency Coil?

A

It produces a magnetic field that oscillates at the resonant frequency of the hydrogen nucleus.

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13
Q

What are Homogeneous Coils?

A

RF coils enclosing the area of anatomy to be imaged, such as Head, Body, and Extremity Coils.

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14
Q

What is the purpose of Inhomogeneous Coils?

A

Also known as surface coils, they provide better contrast and spatial resolution but cover a smaller field of view.

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15
Q

What are Gradient Coils used for in MRI?

A

They produce pulsed gradient magnetic fields and are responsible for the thumping sound of the MRI machine.

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16
Q

What are the three types of Gradient Coils?

A

1) Z Gradient
2) X Gradient
3) Y Gradient

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17
Q

What is the function of Shim Coils?

A

To ensure a uniform static magnetic field for a strong, coherent FID signal.

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18
Q

What are the two main control sets in the MRI Operating Console?

A

1) Image Acquisition
2) Image Processing

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19
Q

What are the key functions of the Image Acquisition?

A

To select pre-selected protocols for imaging and adjust parameters that affect image quality.

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20
Q

What components are included in the MRI System Electronics?

A
  1. Frequency synthesizer
  2. Radio Frequency Amplifier
  3. Gradient Coil Power Supply
  4. Magnet Power Supply
  5. Sequencing System
  6. Digital Signal Acquisition System
  7. Digital Image Processing System
  8. Ancillary Equipment
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21
Q

What is the role of the Frequency Synthesizer in MRI?

A

It generates the fundamental resonance frequency used to excite magnetic nuclear spins.

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22
Q

What does the Radiofrequency Amplifier do?

A

It increases the signal output from the frequency synthesizer for adequate RF power application.

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23
Q

What is the purpose of the Gradient Coil Power Supply?

Study These Flashcards
A

To provide power to the gradient coils in modern MRI systems.

24
Q

What is the function of the Sequencing System?

Study These Flashcards
A

It sets up the proper parameters for MRI signal acquisition based on instructions from the operator’s console.

25
What does the Digital Signal Acquisition System do?
It detects the NMR signal, amplifies it, digitizes it, and processes it for image creation.
26
What are the types of Pulse Sequences in MRI?
1) One-pulse 2) Two-pulse 3) Multi-Pulse
27
What is the One Pulse Sequence?
The most basic pulse, producing a single FID signal and creating one line of data.
28
What are the three types of pulse sequences?
1) One-pulse 2) Two-pulse 3) Multi-Pulse
29
What is the one-pulse sequence?
It is the most basic of all pulses, producing an FID signal with a single RF pulse. ## Footnote Saturation Recovery pulse sequence was the first of the one-pulse sequence.
30
What does a one-pulse sequence create?
A one-pulse sequence creates one line of data.
31
What is Repetition Time (TR)?
The time delay between pulses in a one-pulse sequence.
32
What is the partial flip pulse sequence?
It reduces the flip angle to α < 90 degrees, flipping only part of the longitudinal magnetization, MZ, into the XY plane.
33
What is a spin echo?
An echo signal generated when a 180° RF pulse follows a 90° RF pulse at a later time.
34
What is the time-to-echo (TE)?
The time between the initial 90° RF pulse and the spin echo.
35
What is Inversion Recovery?
An RF pulse sequence using a 180° RF pulse before a 90° RF pulse to invert the net magnetization.
36
What is the inversion-delay-time (TI)?
The delay after the 180° RF pulse before applying the 90° RF pulse.
37
What is a stimulated echo?
An echo signal produced when three RF pulses are used and the time between the pulses is less than T2.
38
What are the tissue imaging parameters?
1) Proton Density (Spin Density) 2) T1 Relaxation 3) T1ρ Relaxation 4) T2 Relaxation 5) T2* Relaxation
39
What is Proton Density?
The measure of the concentration of mobile hydrogen nuclei available to produce an MR signal.
40
How does bound hydrogen appear on an MRI image?
Bound Hydrogen appears Dark, while Mobile Hydrogen appears Bright.
41
What is T1 Relaxation Time?
The time constant that describes the rate at which MZ returns to M0, also known as longitudinal or spin lattice relaxation time.
42
How does T1 differ in diseased tissue compared to healthy tissue?
Generally, the T1 of diseased and damaged tissue is longer than that for corresponding healthy tissue.
43
What does T1W imaging show?
Tissue with short T1 appears bright; tissue with long T1 appears dark.
44
What is T1ρ Relaxation Time?
The T1 relaxation in the rotating frame, always less than T1.
45
What is T2 Relaxation Time?
The transverse relaxation time representing a loss of net XY magnetization and phase coherence.
46
How does T2W imaging represent tissue?
Tissue with long T2 appears bright; tissue with short T2 appears dark.
47
What is T2* Relaxation Time?
Results from a less-than-perfect magnet causing variations in magnetic field and phase coherence loss.
48
are liquefied gases that produce super cold temperatures near absolute zero
Cryogens
49
a large insulating container in which liquid helium and the superconducting magnet coils reside
Cryostat
50
Usually used for Head imaging but it can be used also in attachment with the spine coil to produce image of the Neck and Upper Thorax
Head Coils
51
used for Knee MRI Imaging
Extremity Coil
52
- It is the most robust type of RF Coil, because it can be used on any part of the human anatomy. - It is embedded inside the MRI Gantry and inside the Gradient Coil - It is a transmit/receive coil.
Body coil
53
Composed of Small or Large Flex, Usually used for Hand, Wrist and Elbow Imaging
Flex coils
54
Patient is placed prone while the breast of the patient are placed on the two openings on the coil
Breast coil
55
- Utilization of multiple coils to produce a complete image of the patient's anatomy. - This setup is primarily used for imaging of the Spine
Phased Array and Matrix Coil
56
where post-scan processing is done
image processing console
57
* The magnet power supply for a superconducting magnet is used when the system is first installed. This process is known as “ramping up to field.” *Process, Current is introduced to the Persistent switch to attain the designated B0, (remember it is still submerged in the superconducting cryogen/cryostat), then when the machine attained B0, the current is then stopped, and the switch is now cooled down to superconducting temperatures and B0 is maintained.
magnetic power supply

MRI (2 decks)

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