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C5 > MAGNETIC RESONANCE IMAGING > Flashcards

MAGNETIC RESONANCE IMAGING Flashcards

1
Q

What is MRI?

A

A computer-based imaging modality using magnetic fields and radio waves.

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2
Q

What was MRI originally called?

A

Nuclear Magnetic Resonance.

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3
Q

What is the main advantage of MRI?

A

Best low contrast resolution.

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4
Q

Why is MRI non-invasive?

A

It does not use ionizing radiation.

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5
Q

How does MRI differ from conventional radiography in contrast?

A

MRI contrasts depend on electromagnetic interaction, not x-ray attenuation.

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6
Q

Who discovered the properties of magnetic resonance in the 1940s?

A

Felix Bloch and Edward Purcell.

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7
Q

What year did Paul Lauterbur publish the first MRI cross-sectional image?

A

1973

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8
Q

What was the name of the first MRI machine?

A

Indomitable.

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9
Q

A spurious finding or distortion in the image.

A

ARTIFACT

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10
Q

What is “free induction decay”?

A

Signal emitted by tissue after RF excitation.

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11
Q

What is the gyromagnetic ratio of hydrogen?

A

43 MHz/T.

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12
Q

What does the Larmor frequency describe?

A

The frequency at which a nucleus precesses in the magnetic field.

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13
Q

indicates power absorbed during RF irradiation.

A

Specific Absorption Rat (SAR)

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14
Q

What is T1 relaxation time also called?

A

Spin-lattice relaxation time.

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15
Q

What does T2 relaxation time represent?

A

Spin-spin or transverse relaxation time.

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16
Q

What is the SI unit of magnetic field strength?

A

Tesla (T).

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17
Q

Why is hydrogen used in MRI?

A

It is the most abundant element in the body and creates the strongest MRI signal.

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18
Q

What is the purpose of spin echo sequences?

A

To produce T1-weighted images and proton-density-weighted images.

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19
Q

What is the function of FLAIR sequences?

A

Suppressing signals from cerebrospinal fluid (CSF).

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20
Q

What is the primary use of T1-weighted images (T1W)?

A

Showing anatomical detail.

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21
Q

What are T2-weighted images (T2W) useful for?

A

Highlighting pathology.

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22
Q

Localizes the MRI signal, enabling slice selection and spatial encoding.

A

gradient magnetic field

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23
Q

Produces gradient magnetic fields for imaging.

A

gradient coils

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24
Q

What is the main function of the operating console in MRI?

A

To control the computer and imaging parameters.

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25
Q

What type of storage is used for raw MRI data?

A

Magnetic tape or optical disk for permanent storage.

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26
Q

What are the three groups of MRI magnets?

A

Permanent, resistive, and superconducting magnets.

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27
Q

What is an advantage of permanent magnets in MRI?

A

Low operating cost.

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28
Q

What is a disadvantage of resistive magnets in MRI?

A

High power consumption.

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29
Q

What are superconducting magnets cooled with?

A

Cryogens like liquid helium and liquid nitrogen.

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30
Q

Improves the homogeneity of the magnetic field.

A

shim coils

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31
Q

What are the three types of gradient coils in MRI?

A

Z (transaxial slice), X (coronal slice), and Y (sagittal slice) gradients.

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32
Q

What is the main function of RF coils in MRI?

A

Transmitting RF signals and/or receiving the MR signal.

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33
Q

Imaging small body parts like the spine or shoulders.

A

surface coils

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34
Q

Head imaging due to its excellent RF homogeneity.

A

birdcage coil

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35
Q

shields the MRI system from external radio frequency interference.

A

faraday cage

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36
Q

What is the effect of increasing slice thickness in MRI?

A

Reduced spatial resolution but less grainy images.

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37
Q

How does decreasing slice thickness affect pathology visualization?

A

It improves visualization of small pathologic lesions.

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38
Q

The ability to differentiate tissues with small differences in spin density or relaxation times.

A

contrast resolution

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39
Q

What is the principal biological effect of RF emissions in MRI?

A

Tissue heating, measured as Specific Absorption Rate (SAR).

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40
Q

What are the three physical fields in MRI that might cause biological effects?

A

Strong static magnetic field (B0)
time-varying gradient magnetic field (B1)
RF emissions.

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41
Q

A rapid release of cryogens caused by a fault or manual deactivation of the magnet.

A

quenching

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42
Q

What are gadolinium-based contrast agents used for in MRI?

A

Enhancing signal in specific tissues for better imaging.

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43
Q

reduces motion artifacts by synchronizing image acquisition with a specific phase of motion.

A

gating

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44
Q

An image wrap-around effect caused by anatomy outside the FOV appearing in the image.

A

aliasing artifact

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45
Q

A bright signal in tendons caused by their alignment at 55° to the magnetic field.

A

magic angle artifact

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46
Q

What causes a metal artifact in MRI?

A

Field inhomogeneity due to the presence of metal in the scan area.

47
Q

An artifact caused by thick slices or lack of overlap between slices.

A

staircase artifact

48
Q

What is the primary solution for RF overflow artifacts in MRI?

A

Reducing the receiver gain manually.

49
Q

What is the appearance of CSF on T2-weighted images?

A

Very bright signal (white).

50
Q

What is the principal component of MRI systems responsible for creating the magnetic field?

A

magnet

51
Q

How does the Fourier Transform function in MRI?

A

It converts raw MRI signal data into an image spectrum.

52
Q

Calculates the precession frequency of nuclei in a magnetic field.

A

Larmor equation

53
Q

What is the role of the net magnetization vector (M0) in MRI?

A

It represents the overall magnetic moment in equilibrium, contributing to MRI signal intensity.

54
Q

What type of tissues produce high signal intensity on T1-weighted images?

A

Fatty tissues and structures with short T1 relaxation times.

55
Q

How does flow phenomena affect MRI signals?

A

Moving blood produces weak signals, while stagnant blood produces stronger signals.

56
Q

What is the purpose of phase-encoding gradients in MRI?

A

To determine spatial location in the Y-axis.

57
Q

determines spatial location in the X-axis.

A

frequency-encoding gradients

58
Q

What is the main advantage of superconducting magnets in MRI?

A

High field strength and field homogeneity.

59
Q

What is the disadvantage of permanent magnets in MRI?

A

Limited and fixed field strength.

60
Q

cools the magnet coils and maintain superconductivity.

A

cryogens

61
Q

What is the purpose of surface coils in MRI?

A

For high-resolution imaging of small body parts like the spine or joints.

62
Q

What is a neurovascular coil used for?

A

Imaging the brain and neck regions.

63
Q

How does increasing MRI signal acquisition affect spatial resolution?

A

It improves spatial resolution.

64
Q

What is the significance of spatial resolution in MRI?

A

It determines the clarity of anatomical detail in images.

65
Q

What effect does a stronger magnetic field have on the precession rate?

A

It increases the precession rate.

66
Q

creates gradient magnetic fields for slice selection and spatial encoding.

A

gradient coils

67
Q

What is the main role of RF pulses in MRI?

A

To excite hydrogen nuclei and create an MRI signal.

68
Q

What is spin density in MRI?

A

The concentration of hydrogen nuclei in tissue, affecting signal strength.

69
Q

What is the relationship between T1 relaxation time and tissue type?

A

T1 relaxation time varies depending on the tissue’s molecular environment.

70
Q

What type of images are most useful for identifying pathologies in MRI?

A

T2-weighted images.

71
Q

How does fat appear on T1-weighted images?

A

Bright (high signal intensity).

72
Q

What is the primary biological hazard associated with RF emissions in MRI?

A

Tissue heating.

73
Q

What is the significance of a Faraday cage in MRI facility design?

A

It prevents external radiofrequency interference from affecting imaging.

74
Q

suppresses specific tissue signals, like fat or fluid.

A

inversion recovery sequences

75
Q

What causes phase wrapping artifacts in MRI?

A

Anatomy outside the field of view being misrepresented in the image.

76
Q

What is the purpose of short tau inversion recovery (STIR) sequences?

A

To suppress fat signals in MRI images.

77
Q

What causes partial volume artifacts in MRI?

A

Insufficient resolution leading to mixing of signals from adjacent tissues.

78
Q

How does cerebrospinal fluid (CSF) appear on T1-weighted images?

A

Dark (low signal intensity).

79
Q

How is a high signal intensity on T2-weighted images interpreted?

A

It often indicates the presence of pathology or fluid.

80
Q

What is the significance of echo time (TE) in MRI?

A

It determines the time for signal acquisition after the RF pulse.

81
Q

What does repetition time (TR) affect in MRI?

A

The contrast between tissues and the overall signal strength.

82
Q

What is a typical use of fat suppression techniques in MRI?

A

To enhance contrast between fat and adjacent tissues, such as in breast or musculoskeletal imaging.

83
Q

What does the term “spin-spin relaxation” refer to?

A

The process of signal decay due to loss of phase coherence among spins.

84
Q

reconstructs images from raw data, though it is rarely used today.

A

back-projection reconstruction

85
Q

It allows rigorous mathematical reconstruction of images.

A

2D Fourier transformation

86
Q

What does the term “signal-to-noise ratio” (SNR) refer to in MRI?

A

The ratio of useful signal to background noise in an image.

87
Q

What is the principal advantage of increasing the magnetic field strength?

A

Higher SNR and better resolution.

88
Q

How can aliasing artifacts be reduced in MRI?

A

By increasing the field of view or using oversampling techniques.

89
Q

What is the function of shimming in MRI?

A

What is the function of shimming in MRI?

90
Q

How does slice thickness affect spatial resolution in MRI?

A

Thinner slices improve spatial resolution.

91
Q

What is the typical strength of clinical superconducting magnets?

A

1.5T to 3T.

92
Q

What is the appearance of fat on T2-weighted images?

A

Bright but not as intense as fluid.

93
Q

What is the impact of longer echo times (TE) on T2 contrast?

A

It enhances T2 contrast, making fluid and pathology more visible.

94
Q

What is a common application of gradient echo sequences?

A

3D imaging and vascular studies.

95
Q

What is the function of fast spin echo (FSE) sequences?

A

To acquire T2-weighted images quickly.

96
Q

What is the principal hazard of strong static magnetic fields in MRI?

A

Interaction with metallic implants or devices in the patient.

97
Q

How does gadolinium enhance MRI imaging?

A

By shortening T1 relaxation times, increasing signal intensity in affected areas.

98
Q

What type of artifact is common with turbulent blood flow in MRI?

A

Flow-related artifacts or signal voids.

99
Q

What is the purpose of ramping up the magnet in MRI?

A

To gradually increase the magnetic field strength to its operating level.

100
Q

How does increasing receiver bandwidth affect image quality?

A

It reduces chemical shift artifacts but may lower SNR.

101
Q

What are common uses of fluid-attenuated inversion recovery (FLAIR) sequences?

A

Imaging brain lesions or conditions like multiple sclerosis.

102
Q

What is the significance of repetition time (TR) in MRI pulse sequences?

A

It affects image contrast and acquisition time.

103
Q

What is the purpose of paired saddle coils in MRI?

A

For knee imaging and providing uniform gradients.

104
Q

converts time-domain signals into frequency-domain images.

A

fourier transform

105
Q

What is the advantage of short repetition times (TR) in T1-weighted imaging?

A

Faster imaging with higher T1 contrast.

106
Q

What is the function of saturation pulses in MRI?

A

To suppress specific tissue signals.

107
Q

What is the main limitation of resistive magnets in MRI?

A

High power consumption and limited field strength.

108
Q

What are the typical field strengths for permanent magnets in MRI?

A

Up to 0.3T.

109
Q

What does “homogeneity” of the magnetic field affect in MRI?

A

The accuracy and quality of image acquisition.

110
Q

What is the typical appearance of gray matter on T1-weighted images?

A

Gray (lower signal intensity than white matter).

111
Q

What is the role of neurovascular coils?

A

Imaging brain and neck vasculature.

112
Q

What is the main advantage of birdcage coils in MRI?

A

Superior RF homogeneity, ideal for head imaging.

113
Q

What is the role of echo-planar imaging (EPI) in MRI?

A

Rapid acquisition of images, commonly used in functional MRI (fMRI).

C5 (5 decks)

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