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MRI Flashcards

1
Q

What is MRI based on?

A
  • Signal from hydrogen nuclei in water molecules. (hydrogen protons)
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2
Q

Describe the 6 step process of attainment of an MRI.

A
  • Patient placed in scanner with coils that produce a very strong magnetic field
  • Protons align either parallel to the magnetic field, or in the opposite direction creating a net magnetization called LONGITUDINAL MAGNETIZATION
  • Pulse of RF waves applied at right angle to magnetization
  • Protons realign transversely, absorbing energy
  • RF pulse removed, and aided by 180 degree RF pulse, protons realign longitudinally
  • Absorbed energy is released, inducing a current in the receiver coil, which acts as the basis for MRI imaging
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3
Q

What does realignment and decay refer to?

A
  • Realignment from transverse magnetization, and the release of energy.
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4
Q

Does T1 recovery refer to protons gaining longitudinal magnetization, or losing their transverse magnetization?

A
  • Regaining longitudinal magnetization, and losing their energy.
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5
Q

Does T2 decay refer to regain of longitudinal magnetization, or the loss of transverse magnetization?

A
  • Loss of transverse magnetization toward equilibrium
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6
Q

How is T1 relaxation related to imaging?

A

The time of return to longitudinal magnetization differs for separate tissues

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7
Q

How is T2 decay related to imaging?

A
  • A slow decay leads to a stronger signal
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8
Q

What differences in tissues create the contrast seen in MRI images?

A
  • T1
  • T2
  • Proton density
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9
Q

What 2 parameters are most important in creating contrast in an image?

A
  • TE

- TR

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10
Q

What is TE?

A

The time at which the signal is captured.

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11
Q

What is TR?

A

The time at which the RF pulse is repeated to again displace the protons.

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12
Q

Does T1 imaging have long or short TE/TR times?

A

Short.

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13
Q

Does T2 have long or short TE/TR times?

A

Long.

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14
Q

What type of tissue is captured in T1-weighted imaging?

A

Tissues that rapidly return to longitudinal magnetization.

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15
Q

What type of tissue is captured in T2-weighted imaging?

A

Tissues that are more reluctant to give up energy.

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16
Q

Which type of weighted imaging has a grainier display?

A

T2.

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17
Q

Which type of imaging provides good anatomic detail?

A

T1.

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18
Q

Which type of imaging provides detail of structures with free water?

A

T2.

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19
Q

What are the patient information markers in an MRI?

A
  • Patient name
  • DOB
  • Case number
  • Date of exam
  • Facility
  • Body part
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20
Q

What technical information markers are present on an MRI?

A
  • Sequence used (TR/ TE time)
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21
Q

What is a fast SE sequence?

A
  • 90 degree pulse
  • Multiple 180 degree pulses
  • Several images in same slice position without increasing imaging time
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22
Q

What is a proton density sequence? What does the image look like?

A
  • Long TR (>2,000ms)
  • Short TE (20 - 30 ms)
  • Image based on proton density
  • Similar in appearance to T1, but provides greater anatomic detail
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23
Q

What is the most common type of inversion recovery sequence?

A

Short tau inversion recovery (STIR)

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24
Q

What are the TR and TE lengths in STIR?

A
  • Long TR

- Short TE, but not as short as in T1 or PD

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25
Q

What type of tissue is suppressed in STIR imaging?

A
  • Fat
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26
Q

How is the image quality affected by the use of STIR?

A

Poor and grainy.

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27
Q

What is STIR particularly adept at imaging?

A

Bone marrow edema.

28
Q

What differentiates GRE distinctly from SE?

A
  • RF pulse only partly flips the next magnetization vector in the transverse plane.
29
Q

How quickly does GRE sequences generate images?

A
  • Very quckly
30
Q

What is the image quality of a GRE image?

A
  • High quality
31
Q

How thick are the slices of GRE images?

32
Q

What tissues does GRE images create a high contrast between?

A
  • Fluid

- Cartilage

33
Q

What are the 5 elements of an MRI scanner?

A
  • Main magnet
  • Gradient coils
  • RF coils
  • Workstation
  • Computer(s)
34
Q

What is the strength of an MRI magnet in terms of tesla?

35
Q

How many times greater than the strength of the earth’s magnetic field is one tesla?

A

20,000 times.

36
Q

How many gradient coils are there?

A

3; one for each orthogonal plane.

37
Q

What are the 2 functions of an RF field?

A
  • Transmit RF pulses to alter proton alignment

- Receive signals from protons

38
Q

What are 3 advantages of open scanners?

A
  • Scan claustrophobic or obese patients
  • Reduce scanning noise
  • Can perform tests/procedures during scanning
39
Q

What are 3 disadvantages of open scanners?

A
  • Lower field strength, requiring adjustment of sequences
  • Lower signal to noise ratio (worse image)
  • Longer scanning times
40
Q

From which direction are coronal MRI images viewed?

A

From the front. (facing patient)

41
Q

From which direction are axial images viewed?

A

From below.

42
Q

From which direction are sagittal images viewed?

A

From left to right for either side of the body.

43
Q

In radiographic images, anatomy and pathology is identified by radiodensity; what is the equivalent for MRI?

A

Signal intensity.

44
Q

What is the signal intensity of fat on T1 and T2?

A

T1: High
T2: Low

45
Q

What is the signal intensity of free water on T1 and T2?

A

T1: Very low
T2: High

46
Q

What is the signal intensity of tendons, ligaments, and menisci on T1 and T2?

A

T1: Low
T2: Low

47
Q

What is the signal intensity of cortical bone on T1 and T2?

A

T1: Low
T2: Low

48
Q

What is the signal intensity of red bone marrow on T1 and T2?

A

T1: Intermediate/low
T2: Intermediate

49
Q

What is the signal intensity of yellow bone marrow on T1 and T2?

A

T1: High
T2: Low

50
Q

What is the signal intensity of muscle in T1 and T2?

A

T1: Intermediate
T2: Intermediate

51
Q

What is the signal intensity of cartilage in T1 and T2?

A

T1: Intermediate
T2: Intermediate

52
Q

On which weighted image is signal intensity high for inflammation?

53
Q

On which weighted image is signal intensity high for hemmorage?

54
Q

On which weighted image is signal intensity high for fractures?

A

T2. (with a dark band)

55
Q

On which weighted image is signal intensity high for early and late avascular necrosis?

56
Q

On which weighted image is signal intensity high for chronic hemmorage?

57
Q

On which weighted image is signal intensity high for soft tissue tumors?

58
Q

What is the most important intrinsic factor in image creation of MRI?

A

Proton density.

59
Q

What are the 2 most important extrinsic factors in image creation of MRI?

A
  • Magnet strength

- Sequence

60
Q

What 5 things does MRI image best?

A
  • Changes/ variation in bone marrow
  • Soft tissue detail
  • Meniscal tears
  • Differential diagnosis of herniation vs other nerve root problems
  • Staging neoplasms
61
Q

What is the 1 contraindication, and 2 concerns for the use of MRI on patients?

A
  • Surgical clip displacement

Concerns:

  • Pace maker interference
  • Sedating patients who can’t stay still
62
Q

What is the technique used to evaluate joint capsules in MRI?

A

MR Arthrography.

63
Q

What is MR Myelography used to evaluate?

A
  • Subarachnoid space and spinal canal without the use of a contrast medium
64
Q

What are 4 advantages of MRI over CT?

A
  • Greater contrast resolution on soft tissue imaging
  • Greater ability to image organs surrounded by bone
  • No ionizing radiation
  • Less risk of false negatives due to multiple sequences
65
Q

What are 5 advantages of CT over MRI?

A
  • Less expensive
  • Greater availability
  • Faster imaging times
  • Less operator time involved in selecting parameters
  • Thinner slices

Diagnostic Imaging (14 decks)

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