Deck 26: Magnetic Resonance Imaging

Question 1

Which of these pairs describes how a T1-weighted spin echo image is produced using a pulse sequence?

A)long TE and long TR
B)long TE and short TR
C)short TE and long TR
D)short TE and short TR

Answer 1

short TE and short TR

Question 2

The nuclear magnetic resonance (NMR) effect exploits the behaviour of one of these types of particles. Which type of particle is it?

A)protons
B)neutrons
C)electrons
D)photons

Answer 2

protons

Question 3

Biological tissues are made predominantly of ¹²C, ¹⁶O, ¹H, and ¹⁴N. Which of these isotopes is useful for nuclear magnetic resonance?

A)(¹²C)
B)(¹⁶O)
C)(¹H)
D)(¹⁴N)

Answer 3

(¹H)

Question 4

Which of the following does NOT describe a spin-spin relaxation time (T2) in nuclear magnetic resonance?

A)T2 is a constant that describes the return to equilibrium of transverse magnetization.
B)T2 is always smaller than spin lattice relaxation time (T1).
C)T2 is the time to reduce transverse magnetization by a factor of E)
D)T2 is different for different samples and biological tissues.

Question 5

One of the methods for improving MRI resolution is the gradient field method. Which of these results does a stronger gradient make possible?

A)faster imaging, but at the cost of lower resolution
B)slow imaging, but with the benefit of high resolution
C)faster imaging with high resolution
D)better resolution, and the speed of imaging is not related

Question 6

In nuclear magnetic resonance imaging, we are interested in tissue composition.

Question 7

In nuclear magnetic resonance, the time constants associated with the relaxation process of excited nuclei depend on tissue composition.

Question 8

Which of these statements accurately describes features of the gradient field method used for improving MRI image resolution?

A)The magnetic field is set to vary by three coils in three dimensions, producing very large changes of the field with gradients reaching up to 20 T.
B)The magnetic field is set to vary by three coils in three dimensions, producing changes of the field with gradients in the range of millitesla.
C)The magnetic field is set to vary by rotating fast in a circular path, producing very large changes of the field with gradients reaching up to 20 T.
D)The magnetic field is set to vary by rotating fast in a circular path, producing changes of the field with gradients in the range of millitesla.

Question 9

In nuclear magnetic resonance, only a nucleus with spin reacts to the magnetic field. Which of these statement describes a property of such a nucleus?

A)The nucleus has to have an odd number of protons.
B)The nucleus has to have an even number of protons.
C)The nucleus has to have an even number of both protons and neutrons.
D)The reaction depends on the atom.

Question 10

Which of these pairs describes how a spin density-weighted signal is produced using a pulse sequence?

A)long TE and long TR
B)long TE and short TR
C)short TE and long TR
D)short TE and short TR

Question 11

High energy electromagnetic radiation is used to stimulate nuclei in the nuclear magnetic resonance (NMR) effect. Which range of the electromagnetic spectrum does this energy belong to?

A)infrared
B)ultraviolet
C)radio
D)X-ray

Question 12

Nuclei, as dipoles with magnetic spins, all rotate in the external magnetic field's Larmor frequency.

Question 13

A nuclear magnetic resonance (NMR) spectrum results from the emission of photons when nuclear spin alignment is flipped.

Question 14

In nuclear magnetic resonance (NMR), what is the change that nuclei experience when they are exposed to the external magnetic field and electromagnetic radiation?

A)All nuclei assume the direction of the external magnetic field.
B)Some nuclei assume the direction of the external magnetic field, and some the opposite.
C)The nuclei assume random orientations.
D)All nuclei are oriented in the direction opposite to the external magnetic field.

Question 15

Which of the following is NOT an accurate description of nuclear magnetic resonance (NMR)?

A)The energy difference between the two spin states depends on the strength of the external magnetic field.
B)The nuclei are in resonance with electromagnetic radiation when they absorb energy.
C)When a proton is aligned in the direction of an external magnetic field, its energy is lower than when it is aligned against the direction of an external magnetic field.
D)The high energy radiation needed for protons to flip the spin is in the ultraviolet domain of the electromagnetic spectrum.

Question 16

Which of these pairs describes how a T2-weighted spin echo image is produced using a pulse sequence?

A)long TE and long TR
B)long TE and short TR
C)short TE and long TR
D)short TE and short TR

Question 17

Which of the following statements is an accurate description of spin lattice relaxation time (T1) in nuclear magnetic resonance?

A)T1 is always larger than or equal to spin-spin relaxation time (T2).
B)T1 is a constant that describes the return to equilibrium of transverse magnetization.
C)T1 is the time to reduce transverse magnetization by a factor of E)
D)T1 is the same for different samples and biological tissues.

Question 18

The high frequency electromagnetic radiation used in nuclear magnetic resonance is from the ultraviolet part of the spectrum.

Question 19

In nuclear magnetic resonance (NMR), nuclei are changing spin orientation as they occupy excited states. This is obtained by exposing nuclei only to an external magnetic field.

Question 20

Magnetization is different for various tissues. With many tissues involved in magnetic resonance imaging, we need to obtain the best possible contrast. Magnetic resonance imaging is, for this reason, done in three modes. Which of the following is NOT one of the modes?

A)a mode that emphasizes contrast due to proton density
B)a mode that emphasizes contrast due to photon density
C)a mode that emphasizes contrast due to relaxation time T1
D)a mode that emphasizes contrast due to relaxation time T2

Question 21

Describe the reasons why direct measurements of T1 and T2 are not used for magnetic resonance imaging.

Question 22

Magnetic field gradient causes different magnetic fields at different positions and different Larmor frequencies. This frequency variation can be used to determine the location of different anatomical features during reconstruction of an image.

Question 23

Show that, in order to obtain 100 MHz for the Larmor frequency of the protons in a magnetic field, a NMR magnet with a magnetic field of 2.349 T has to be used.
[Note: Take the gyromagnetic ratio for the proton as ã = 42.58 MHz/T.]

Question 24

What is a physical cause of spin echo?

Question 25

Why is the nuclear magnetic resonance (NMR) effect useful for structural analysis of pure organic molecules in organic chemistry?

Question 26

Which of the MRI modes is the most similar to a CT scan? What are the similarities, and what are the differences between the two?

Question 27

In nuclear magnetic resonance imaging, we do not use direct measurements of time constants T1 and T2.

Question 28

Briefly explain the nuclear magnetic resonance (NMR) effect.

Question 29

Why is the nuclear magnetic resonance (NMR) effect useful for structural analysis of human tissue?

Question 30

Describe briefly the problem that arises from the use of a real magnet as opposed to an ideal magnet in NMR, and what technique helps to overcome this and make very sensitive measurements possible.