EXAM #12 — PHYSICS UNIT 05 Flashcards

1
Q

RF pulse.

A

a burst of radio frequency energy

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2
Q

net magnetization relaxation.

A

the return of net magnetization to equilibrium as it releases absorbed RF (Tl) and loses energy (T2)

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3
Q

free induction decay.

A

the simple signal given off by the relaxation of net magnetization to equilibrium

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4
Q

spin density or proton density.

A

the relative number of protons (spins) in a sample

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5
Q

spin echo.

A

the signal given off by the relaxation of net magnetization to equilibrium after a refocusing pulse- is a mirror image of the FID

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6
Q

Tl relaxation.

A

regrowth of net magnetization along the Z axis

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7
Q

longitudinal recovery.

A

regrowth of net magnetization along the Z axis

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8
Q

spin-lattice relaxation?

longitudinal recovery and spin-lattice relaxation are terms for ___ _____

A

spin-lattice relaxation. the process of RF being dissipated into the lattice surrounding the proton

longitudinal recovery and spin-lattice relaxation are terms for Tl relaxation

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9
Q

T2 relaxation.

A

the decay of transverse magnetization

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10
Q

transverse decay.

A

the decay of transverse magnetization

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11
Q

spin-spin relaxation?

transverse decay and spin-spin relaxation are terms for ___ _____

A

spin-spin relaxation. the process of spins interacting with each other, which causes phase changes, and loss of transverse magnetization

transverse decay and spin-spin relaxation are terms for T2 relaxation

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12
Q

T2* relaxation.

A

transverse decay in the presence of magnetic field inhomogeneities- spin-spin interaction plus magnetic field inhomogeneity

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13
Q

phase.

A

the degree to which spins are precessing at the same position at a specific point in time- T2 relaxation is also known as phase coherence

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14
Q

explain why T2* relaxation is shorter than T2 relaxation.

A

magnetic field inhomogeneities increase de-phasing and increase decay of transverse magnetization

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15
Q

identify the type of relaxation most affected by magnetic field inhomogeneity. T2*

A

identify the type of relaxation most affected by magnetic field inhomogeneity.

T2*

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16
Q

identify the amount of longitudinal regrowth that defines true Tl relaxation time.

A

Tl relaxation is defined as the time it takes for 63% of longitudinal magnetization to regrow

17
Q

identify the amount of transverse decay that defines true T2 relaxation time.

A

T2 relaxation is defined as the time it takes for 63% of transverse magnetization to decay

18
Q

explain the state of phase of all spins immediately after RF excitation.

A

all spins are in phase immediately after RF excitation

19
Q

recognize a diagram of longitudinal regrowth and the relative relaxation times of tissues on the diagram.

20
Q

recognize a diagram of transverse decay and the relative relaxation times of tissues on the diagram.

21
Q

describe the relative Tl and T2 relaxation times of fat and water.

A

fat has short Tl and short T2 relaxation times (relative to water) water has long Tl and T2 relaxation times (relative to fat)

22
Q

describe the relative brightness of fat and water on Tl and T2 weighted MR images.

A

Tl weighted images- fat is bright and water is dark T2 weighted images- fat is dark and water is bright

23
Q

describe the relative local magnet fields experienced by fat and water nuclei, and their resulting relative resonant frequencies.

A

nuclei of fat molecules experience a lower local magnetic field and therefore have a lower resonant frequency

24
Q

describe the effect of long and short Tl times on MR signal intensity and appearance on Tl weighted images.

A

tissues with long Tl times have low signal intensity, and appear dark; tissues with short Tl times have high signal intensity, and appear bright on Tl weighted images

25
describe the effect of long and short T2 times on MR signal intensity and appearance on T2 weighted images.
tissues with long T2 times have high signal intensity and appear bright; tissues with short T2 times have low signal intensity and appear dark on T2 weighted images
26
describe the relationship between M0 to M2 at equilibrium.
at equilibrium, M0 = Mz
27
identify what flip angle RF pulse creates an FID.
90° or less
28
identify what flip angle RF pulse creates a spin echo.
180°
29
identify which type of relaxation is caused by spin-spin interaction and magnetic field inhomogeneity.
T2*
30
identify which type of relaxation is caused by spin-spin interaction only.
T2