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MRI in Practice > Ch. 1 Basic Principles > Flashcards

Ch. 1 Basic Principles Flashcards

1
Q

The most abundant atom in the body is…

A

hydrogen

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2
Q

The sum of the protons in the nucleus.

A

atomic number

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3
Q

The sum of the protons and neutrons in the nucleus.

A

mass number

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4
Q

Atoms of elements with the same number of protons but a different number of neutrons are called.

A

isotopes

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5
Q

Electrons are particles that spin around the…

A

nucleus

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6
Q

There are 3 types of motion present within the atom.

A
  1. electrons spinning on their own axis
  2. electrons orbiting the nucleus
  3. the nucleus itself spinning about its own axis
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7
Q

The principles of MRI rely on the spinning motion of…

A

specific nuclei present in biological tissues.

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8
Q

Nuclei with odd mass numbers, i.e where the # of neutrons is slightly more or less than the number of protons, spin directions are not equal and opposite, so the nucleus itself has a net spin or________. These are known as what?

A

Angular Momentum

MR active nuclei

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9
Q

The law of Electromagnetic Induction refers to which three individual forces. (Faradays Law)

A
  1. motion
  2. magnetism
  3. charge
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10
Q

If two of the 3 forces of Faradays Law are present then the third is____

A

automatically induced

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11
Q

The isotope of the hydrogen nucleus is called? and is the MR active nucleus used in clinical MRI.

A

Protium

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12
Q

This describes the properties of electromagnetic radiation in terms of discrete quantities of energy called quanta.

A

quantum physics

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13
Q

Applying quantum theory to MRI, hydrogen nuclei posses energy in two discrete quantities or populations termed what?

A

Low and High

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14
Q

Low energy nuclei align their magnetic moments _____ to the external field and is termed______.

A

Parallel

spin-up nuclei

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15
Q

High energy nuclei align their magnetic moments ___ ____ _____ and are termed_____

A

anti-parallel direction

spin down nuclei

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16
Q

The factors affecting which hydrogen nuclei align parallel and which align anti-parallel are determined by what?

A
  1. the strength of the external magnetic field

2. the thermal energy level of the nuclei

17
Q

This determines the relative quantities of spin-up and spin-down nuclei.

A

The strength of the external field.

18
Q

In thermal equilibrium, there are always ____ high energy nuclei than low energy nuclei, therefore the magnetic moments of the nuclei aligned parallel to the magnetic field cancel out the smaller number of magnetic moments aligned anti-parallel.

19
Q

The net magnetic moment of hydrogen produces a significant magnetic vector that is used in clinical MRI and thisreflects the balance between spin-up and spin-down nuclei. This is called?

A

Net Magnetization Vector (NMV)

20
Q

The static external magnetic field is called?

21
Q

The interaction of the NMV with the Bo is the…

A

Basis of MRI

22
Q

The unit of Bo is?

A

Tesla or gauss.

23
Q

1 Tesla (T) is the equivalent of ____ gauss (G)

24
Q

The secondary spin is called?

A

precession

25
Q

Precession causes the magnetic moments to follow a circular path around what? and is called what?

A

Bo

Precessional path

26
Q

The speed at which the hydrogen nucleus wobble around Bo is called?

A

Precessional frequency

27
Q

The unit of precessional frequency is called?

A

Megahertz (MHz)

28
Q

1 Hz is one cycle or rotation per second and 1 MHz is?

A

one million cycles or rotations per second

29
Q

The value of the precessional frequency is governed by?

A

The Larmor equation

30
Q

The Larmor equation states that?

A

wo=Bo x /|

wo= the precessional frequency
Bo=the magnetic field strength
/|= the gyromagnetic ratio.

31
Q

This expresses the relationship between the angular momentum and the magnetic moment of each MR active nucleus.

A

The gyromagnetic ratio.

32
Q

What is the gyromagnetic ratio of hydrogen?

A

42.57 MHz/T

33
Q

At 1.5T the precessional frequency of hydrogen is?
1.0T?
.5T?

A
  1. 86 MHz
  2. 57 MHz
  3. 28 MHz
34
Q

This is a phenomenon that occurs when an object is exposed to an oscillating perturbation that has a frequency close to its own natural frequency of oscillation?

35
Q

When a nucleus us exposed to an external perturbation that has an oscillation similar to its own natural frequency, then the nucleus does what?

A

Gains energy from the external force if the energy is delivered at the exact same precessional frequency.

36
Q

Energy at the precessional frequency of hydrogen at all field strengths in clinical MRI corresponds to the?

A

radio frequency (RF) band of the electromagnetic spectrum

37
Q

For resonance of hydrogen to occur, and RF pose at exactly the ____ of hydrogen must be applied.

A

Larmor frequency

38
Q

The application of an RF pulse that causes resonance to occur is termed ______.

A

excitation

MRI in Practice (1 decks)

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