MRI: Magnets, RF Coils, and Gradient Coils Flashcards

1
Q

However, most existing human MRI scanners have strengths up to

A

3.0 Tesla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

The FDA approved what strength of human MRI scanners for clinical diagnosis?

A

7.0 Tesla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

10,000 gauss is equivalent to

A

1 Tesla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

The magnetic field of the earth ranges from ____ to ____ gauss, with an average of ____ gauss

A

0.25 to 0.65, average of 0.5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What substance is associated with maintaining superconducting magnets that is generally expensive

A

Helium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What difficulty is associated with the high costs of MRI scans?

A

Difficulty of making the magnetic field uniform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Type of MRI magnet that has a strength limited to about 1 Tesla. Maintenance costs are negligible

A

Permanent magnet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Type of MRI magnet that can achieve high magnetic field, has high maintenance costs, and is most popular in hospitals

A

Superconducting magnet

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

The main function of a magnet is to cause proton spins to rotate/precess at a frequency proportional to the magnetic field, also known as

A

Resonance frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

In Tx RF coils, the transmission of homogenous energy is important, so the transmission is often performed with a

A

Large RF coil (a body coil premounted on the scanner)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

In Tx RF coils, the proton spins that have the same frequency as the frequency in the transmission coil will receive energy and get excited. This is also called

A

Magnetic resonance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Aside from using a single RF coil, what are the two separate RF coils that also can be used for MR signals?

A

Transmission (Tx) and reception (Rx) RF coils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

MRI is an integration of many ____ _____ that makes it expensive

A

Hardware equipment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

The main magnetic fields are along what direction?

A

Z direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How can we get spatial information in MRI?

A

Gradient coils

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Positional information of detectors (RF coils) cannot be used to get these information in MRI except in parallel imaging

A

Spatial information

17
Q

High sensitivity to the object is important, so the reception of MR signals is performed with a

A

Small RF coil (close to the object)

18
Q

In Rx RF coils, when the transmission RF energy is off, MR signals will be _____ and _____ in the receiver RF coil

A

Induced and detectable

19
Q

What makes MRI safe?

A

No ionizing radiation

20
Q

These gradient coils are to modulate the main magnetic field strengths along the X and Y but not to generate any fields along X or Y

A

X and Y gradient coils

21
Q

Magnetic field induced by a gradient coil is superimposed on the

A

MRI magnet field

22
Q

Spatially different precession frequencies allow us to get

A

Spatial information

23
Q

Varying magnetic field or gradient causes this to be a function of spatial location

A

Precession frequency (omega)

24
Q

Typical MRI has a field strength of up to _____ Tesla, 60,000x greater than the earth’s magnetic field

25
Unit of SAR
Watts per kilogram (W/kg)
26
A measure of the rate at which energy is absorbed by the human body when exposed to an RF electromagnetic field. These have upper limits in clinical scanners for safety
SAR or specific absorption rate
27
What particular material is not allowed in MRI that involve pacemakers, artificial limbs, or most devices
Metal
28
Modulate the resonance frequency depending on the spatial location along X, Y, and Z
Gradient coils
29
Transmits and/or receives signals at the resonance frequency
Radio frequency (RF) coils
30
Generates magnetic fields that causes protons to precess at a frequency proportional to the strength of the magnetic fields (resonance frequency)
Magnet
31
A noninvasive biomedical imaging device with a relatively high spatial resolution, various soft tissue contrast, and integration of many different imaging modalities in one single scanner
MRI