Question 1

The quantity of resonating spins in a tissue expressed as a percentage of the proton density of water is

Accepted Answer

The choice that corresponds to the quantity of resonating spins in a tissue expressed as a percentage of the proton density of water is spin density, which is represented by the equation F1F1F1S1F1F1F10.

Question 2

The time between a 180-degree pulse and a 90-degree inversion pulse in an inversion recovery pulse system is

Accepted Answer

The time between a 180-degree pulse and a 90-degree inversion pulse in an inversion recovery pulse system is known as the inversion time (TI). TI controls the amount of longitudinal magnetization that recovers and is available to produce signal. It is usually measured in milliseconds (ms) and can range from a few ms to several seconds.

Question 3

When gradient coils are referred to, the y axis coil is referred to as the ____ gradient.

Accepted Answer

The y axis coil is responsible for phase encoding, which is a gradient used to spatially encode the signal along the y axis. Selection and frequency encoding refer to the x and z gradient coils, respectively.

Question 4

When gradient coils are referred to, the z axis coil is referred to as the ____ gradient.

Accepted Answer

The z axis coil in MRI is referred to as the selection gradient because it is used to select the slice to be imaged by varying the magnetic field along the body's length, allowing for the selection of a specific slice thickness and location.

Question 5

The source of magnetic fields within the body

Accepted Answer

The spinning nucleus of an atom, specifically the protons and neutrons, are the source of magnetic fields within the body. The stationary electrons also contribute to the magnetic field, but to a lesser extent.

Question 6

The Larmor frequency is the ____ frequency.

Accepted Answer

The Larmor frequency is the precessional frequency, which is the frequency at which a spinning magnetic dipole precesses around a magnetic field. It is not related to quantum or linear frequencies.

Question 7

The time between a 90-degree pulse and the echo during a spin-echo pulse sequence is

Accepted Answer

The time between a 90-degree pulse and the echo during a spin-echo pulse sequence is known as the echo time (TE). This is the time that it takes for the signal to be emitted by the excited protons and then return to the receiver coil. Choices A, B, and D are not correct, as spin density, repetition time, and inversion time respectively, all refer to different aspects of the pulse sequence.

Question 8

The time required after precessing spins have aligned at an angle to the external field due to an RF pulse losing 63% of their coherence is

Accepted Answer

The time required for spins to lose 63% of their coherence is the spin-lattice relaxation time (T1). None of the other options represent T1, so the answer is D.

Question 9

The time required for precessing spins to align with the constant external field to 63% of the maximum possible strength is

Accepted Answer

The time required for precessing spins to align with the constant external field to 63% of the maximum possible strength is governed by the spin-lattice relaxation time (T1). Option D represents T1, which is the correct answer. Option A refers to spin density, which is the number of spins per unit volume, and is not relevant to the question. Options B and C refer to the timing parameters in MRI, but do not relate to the time it takes for precessing spins to align with the external field.

Question 10

The rotation of the axis of rotation is termed

Accepted Answer

The rotation of the axis of rotation is called precession. This phenomenon is observed in the rotation of the Earth around its axis and also in the motion of spinning objects such as tops and gyroscopes.

Question 11

The gyromagnetic ratio is the ratio of the magnetic

Accepted Answer

The gyromagnetic ratio is the ratio of the magnetic moment to the angular momentum or moment of inertia. It is denoted by γ and is a fundamental property of a given nucleus or particle. Therefore, option C is the correct choice.

Question 12

When gradient coils are referred to, the x axis coil is referred to as the ____ gradient.

Accepted Answer

The gradient coil along the x-axis is referred to as the frequency encoding gradient. This gradient is responsible for creating the spatial encoding of the MR signal, which is essential for image formation. In addition to the frequency encoding gradient, there are also phase encoding and slice selection gradients, which are responsible for controlling the position and orientation of the imaging slice.

Question 13

Each of the following is an example of an RF pulse sequence EXCEPT

Accepted Answer

"Stationary" is not a type of RF pulse sequence. The other options listed (spin-echo, gradient, and inversion recovery) are all examples of RF pulse sequences commonly used in MRI.

Question 14

The gradient coils determine the

Accepted Answer

The gradient coils in an MRI machine are responsible for determining the section thickness, resolution, and plane of the image. Therefore, option D "all of the above" is the correct answer.

Question 15

Protons will alternate from

Accepted Answer

Protons have a magnetic moment due to their spin. When placed in a magnetic field, this causes them to either align (parallel) or oppose (antiparallel) the field. Therefore, protons will alternate between these two orientations in a magnetic field.

Question 16

The primary variable in the data collection procedure during MRI is the

Accepted Answer

The primary variable in MRI data collection is the sequence of RF (radiofrequency) pulses, which are used to excite and detect signals from the protons in the body. The stationary magnet is a constant factor in MRI imaging, and repeats may be used to improve the signal-to-noise ratio, but do not determine the primary variable in data collection. Therefore, choice C, the sequence of RF pulses, is the best answer.

Question 17

The time interval between pulse sequences is

Accepted Answer

The time interval between pulse sequences is called repetition time (TR). This is the time period between the start of one excitation pulse and the start of the next pulse. It is measured in milliseconds and determines the time between two successive RF pulses.

Question 18

The actual response of proton spin to an RF pulse is to

Accepted Answer

The actual response of proton spin to an RF pulse is to change the magnetic moment in a precessing corkscrew motion.

Question 19

To produce magnetic field gradients in MRI, electromagnetic coils are oriented in

Accepted Answer

Magnetic field gradients must be produced in three dimensions to allow for spatial encoding and localization in MRI. By introducing gradients in the x, y, and z directions, the MRI signal can be used to generate images with high spatial resolution.

Question 20

The MHz frequency magnetic field for MRI is produced by a/an

Accepted Answer

The MHz frequency magnetic field for MRI is produced by a radio transmitter coil. This coil generates a strong and uniform magnetic field, which allows for the manipulation of the alignment of the protons in the body's tissues. This alignment provides the signals necessary for MRI imaging. Therefore, the correct choice is A, radio transmitter coil.

Quiz 42: Magnetic Resonance Imaging