MRI: Magnets, RF Coils, and Gradient Coils

Question 1

However, most existing human MRI scanners have strengths up to

Answer 1

3.0 Tesla

Question 2

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

Answer 2

7.0 Tesla

Question 3

10,000 gauss is equivalent to

Answer 3

1 Tesla

Question 4

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

Answer 4

0.25 to 0.65, average of 0.5

Question 5

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

Answer 5

Helium

Question 6

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

Answer 6

Difficulty of making the magnetic field uniform

Question 7

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

Answer 7

Permanent magnet

Question 8

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

Answer 8

Superconducting magnet

Question 9

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

Answer 9

Resonance frequency

Question 10

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

Answer 10

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

Question 11

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

Answer 11

Magnetic resonance

Question 12

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

Answer 12

Transmission (Tx) and reception (Rx) RF coils

Question 13

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

Answer 13

Hardware equipment

Question 14

The main magnetic fields are along what direction?

Answer 14

Z direction

Question 15

How can we get spatial information in MRI?

Answer 15

Gradient coils

Question 16

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

Answer 16

Spatial information

Question 17

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

Answer 17

Small RF coil (close to the object)

Question 18

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

Answer 18

Induced and detectable

Question 19

What makes MRI safe?

Answer 19

No ionizing radiation

Question 20

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

Answer 20

X and Y gradient coils

Question 21

Magnetic field induced by a gradient coil is superimposed on the

Answer 21

MRI magnet field

Question 22

Spatially different precession frequencies allow us to get

Answer 22

Spatial information

Question 23

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

Answer 23

Precession frequency (omega)

Question 24

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

Answer 24

3.0 Tesla

Question 25

Unit of SAR

Answer 25

Watts per kilogram (W/kg)

Question 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

Answer 26

SAR or specific absorption rate

Question 27

What particular material is not allowed in MRI that involve pacemakers, artificial limbs, or most devices

Answer 27

Metal

Question 28

Modulate the resonance frequency depending on the spatial location along X, Y, and Z

Answer 28

Gradient coils

Question 29

Transmits and/or receives signals at the resonance frequency

Answer 29

Radio frequency (RF) coils

Question 30

Generates magnetic fields that causes protons to precess at a frequency proportional to the strength of the magnetic fields (resonance frequency)

Answer 30

Magnet

Question 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

Answer 31

MRI