Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > MRI > Flashcards

MRI Flashcards

1
Q

What is the Larmor Equation?

A

Precession Frequency= Gyromagnetic ratio X Field Strength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do protons line up when you enter a MRI?

A

In the Longitudinal direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is T1?

A
  • Recovery of Longitudinal relaxation (Spin-Lattice)
  • Involves the exchange of thermal energy
  • Things are T1 relaxed when they reach 63% of final value
  • Greater the Field strength, the longer the T1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does T1 relaxation changes with magnetic field?

A

-Higher magnetic field= Longer T1 relaxtion time bc the protons are precessing faster (larmor equation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is T2?

A
  • Decay of Transverse relaxation (Spin-Spin)
  • T2 relaxed when decays 63%
  • Decay occurs due to inhomogenieties of external field and internal fields
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is T1 and T2 bright?

A
  • T1 short= Bright

- T2 Long= Bright

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is T2 Star?

A
  • Due to external field inhomogenities

- Always FASTER than T2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is repetition time (TR)?

A

-Time between two RF pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When do you give 180 RF Pulse?

A

-1/2 TE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is Short and Long TR and TE for Spin echo?

A
  • Short TR: 250-700 ms
  • Long TR: >2000 ms
  • Short TE: 10-25
  • Long TE: >60 ms
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is Short and Long TR and TE for Gradient echo

A
  • Short TR <50 ms
  • Long TR >100 ms
  • Short TE 1-5 ms
  • Long TE >10 ms
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does PD do?

A
  • Long TR and Short TE (Excellent SNR)

- Minimizees the difference in contrast between T1 and T2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the Fourier Transform?

A

Converts from the Time Domain to the Frequency Domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is K Space?

A
  • A fourier Plane with MR Signal is stored
  • To convert to image= 1/2 Fourier Tranforms
  • Center of K space has contrast information
  • Peripheral K Space has spatial resolution information
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What determines the duration of Study?

A

TR X Number of Phase encoding Steps X Number of Excitations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is Frequency Encoding gradient applied?

A

Same time as read out

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is Slice Selection Gradient (SSG)?

A
  • Selects the area of interest and determines the view

- Perpendicular to the desired slice plane

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How to do you create a Spin Echo Sequence

A
  1. Select SSG and apply 90 RF Pulse
  2. Apply phase and frquency encoding
  3. Apply 180 RF pulse and SSG
  4. At Echo, apply the frequency encoding
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How do you select for a thinner slice?

A

Thinner Slicer= Thin Transducer Bandwidth = Large Slice Selection Gradient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What determines the duration of a 3 D Study?

A

TR X Number of Phase encoding Steps X Number of Excitations X Slice Thickness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What determines study time for Fast Spin Echo Sequence

A

1/Echo Train Length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How does TR affect number of slices?

A

Longer TR= Can Select more Slices

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is Phase Matrix?

A
  • Number of Phase Encoding steps (lines you need to fill)

- 1 Line= 1 TR

24
Q

What is Number of Excitations?

A
  • Number of times you sample the data

- More= Better image quality but more scan time

25
Q

How do you Increase SNR?

A
  • Higher Magnet
  • Increase TR
  • Decrease TE
  • Large Pixel Size (Large FOV and Small Matrix)
  • Increase slice thickness
  • Increase Transmit Bandwidth
  • Decrease receiver bandwidth
  • Decrease (Small) SSG
  • Small RF Coil
  • Increase Number of Excitations
26
Q

How do you improve spatial resolution?

A
  • Small FOV
  • Large Matrix
  • Thinner Slices
  • Thinner Transmit bandwidth
  • Steeper SSG
27
Q

What is Fast Spin Echo?

A
  • Applying Multiple 180 RF pulses per 90 RF pulse (get multiple echos)
  • Echo train length= Number echos per RF Pulse
  • Acquisition Time= 1/ETL
  • T2 Blurring= Loss of transverse magnetization with each echo
  • Longer T2 FAT signal due to J coupling
28
Q

What is inversion recovery?

A
  • Give 180 Pulse first, then 90 RF at the null point, and then another 180
  • TI= Inversion time between first 180 RF and 90 RF
  • STIR is less susceptible to artifact and you CANNOT use GAD with it
  • Increased scan time due to increase TR from addition of TI
29
Q

What is GRE?

A
  • Uses flip angle less than 90 and No 180 (makes it at T2*)
  • Short TR/TE with fast recovery and shorter scan
  • Lower Specific absorption Rate (SAR)= less heating
30
Q

What is Echo PLanar Imaging?

A
  • Fastest way to acquire sequence (DWI)
  • One 90 RF and one 180 RF pulse, then turning Phase and frequncy encoding on and off very frequently= fills K space very fast
  • very susceptible to Susceptibility artifact
31
Q

How do you fat sat?

A
  1. Give a prepartory RF pulse narrow pulse at the resonance of fat
  2. Add spoiler gradient that dephases the protons primed by RF pulse (no long able to produce signal)
  3. Procedd with normal scan
32
Q

What is In and Out of Phase?

A
  • Drop out of microscopic fat signal on out of phase
  • 1.5 T: Out @ 2.2, In @ 4.4, out @ 6.6
  • 3T: Out @ 1.1, In @ 2,2, Out @3.3
  • Set set of in/out matters for Liver hemochromatosis
33
Q

What is Type 1 Chemical Shift?

A
  • Bright on one side and Dark on the other
  • Occurs on SE and GRE
  • Occurs in the Frequency encoding direction
  • Increase with Higher Magnetic field strength
  • Decrease with increased gradient strength and WIDER readout bandwidth
34
Q

What is Type 2 Chemical Shift?

A
  • India ink artifact that occurs on Fat/Water interaface

- Fix by switching to SE sequences

35
Q

What is Aliasing and how do you fix it

A
  • Undersampling
  • Switch the Phase and Frequency encoding direction (more time)
  • Increase FOV (Loss of spatial resolution)
  • Saturation bands and Surface Coils
36
Q

How to you fix Type 1 chemical shift artifact?

A
  • Switch Phase and Frequency encoding direction
  • Increase RECEIVER BANDWIDTH
  • Use STIR or fat suppression
37
Q

How do you fix Type 2 Chemical Shift Artifact?

A
  • Shorter TE

- Use Spin echo instead of GRE

38
Q

How do you fix partial volume averaging?

A
  • Smaller Pixels

- More Slices

39
Q

What is Truncation/Gibbs Artifact?

A
  • Ripples in data when transferring from the K Space through inverse fourier transform
  • Seen at high contrast interfaces (CSF and Cord)
  • Seen in Phase and Frequency encoding but more common in Phase.
  • Better with Larger Matrix, Decreased pixel, and decreased bandwidth.
40
Q

How do you fix motion Artifact?

A
  • Breath Holding
  • Respiratory Gating (increases acquisition time)
  • ROPE (Respiratory Ordered Phase Encoding)
  • Breathing Navigator: Echo from the Diaphragm that helps to time images
  • Switch phase and frequency encoding direction
  • BLADER/PROPELLER: Over sample the center of the K space so you have redundant material
  • Apply fat sat band to the abdomen
41
Q

What is magic angle artifact?

A
  • loss of signal at 55 degrees on short TE sequences (T1 and GRE/PD)
  • resolves with T2 and higher magnet strength
42
Q

What is cross talk and how do you fix it?

A
  • Overlap from non ideal slice profiles
  • Improve with interleave (odd then even) and increasing gap between sections
  • Does not occur with 3 D
43
Q

What is zipper artifact?

A
  • Stray RF Signal

- Improve by fixing RF shielding, closing door, taknig electronics out of room

44
Q

What is inhomogenous fat sat due to?

A
  • Fat prescesses at different frequencies so may not be suppressed
  • Switch to STIR
  • Shim the magnet (Passive done at installation, Active done wth a coil after aech sequence)
45
Q

What is Susceptibility?

A
  • Ability to be magnetized by an external field
  • More severe with GRE than SE
  • Fix by switching to SE, reduce field strength, thinner slices, Align longitudinal axis of metal with the axis of the main field.
  • Worse with longer scan times (In versus out of phase0
46
Q

What are Eddy Currents?

A
  • Due to rapid turning on and off the gradient

- Seen on DWI as smearing at the edges

47
Q

What is the dielectric effect?

A
  • Tissues have inherent dielectric constant that results in reduction of wavelength by some inverse constant which result in eddy current.
  • Worse in Fat People, ascites and stronger magnet
  • Ex: Dark signal over center of liver.
  • Fix by applying dielectric pads or Parallel RF transmission with each coil sending an independent RG Pulse
48
Q

What is crisscross/herringbone artfact?

A

-Error in Data processing or reconstruction

49
Q

What is signal flair (breast)?

A

-Breast positioned to close to the coil

50
Q

What is the 5 G line?

A

Implantable devices will be OK outside the line

51
Q

What is the limit on Noise for MR?

A

140dB for MRI

52
Q

What is neurostimulation?

A
  • Induced Electric currents that lead to painful neural stimulation
  • Due to High Receiver Bandwidth and Switching Gradients quickly
  • Reduce reader bandwidth and Increase TR
53
Q

What is Specific Absorption Rate (SAR)?

A

-Ability to cook a patient with a RF Pulse
=Field Strength^2 X Alpha ^2 X Duty Cycle
-Field Strength of Magnet
-Alpha is the Flip Angle
-Duty cycle is the inverse of TR
FDA Limits: 4W/kg over 15 min or 3W/kg over 30 min

54
Q

What are Weekly QC for MRI scanners?

A

AC FGH STV

  • Artifact Analysis
  • Center Frequency
  • Film Quality Control
  • Geometric Accuracy
  • High and Low contrast resolution
  • Set up and scanning
  • Table Positioning
  • Visual Checklist
55
Q

What are Annual QC for MRI scanners?

A

MD SSR

  • Magnetic Field Imhomogenities
  • Display monitor Checks
  • Slice Thickness Accuracy
  • Slice Position Accuracy
  • Radiofrequency Coil Check
56
Q

What are the 4 MRI Zones?

A

1: General Public
2: Waiting room, where you get screened
3. Restricted, control rooom
4. MRI scanner Room

57
Q

What is a spoiled Gradient Echo?

A
  • Gradient used to get rid of transverse magnetization

- Shorter TR (basically T1)

Physics (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions