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Applied Medical Imaging > Fundamentals of MRI > Flashcards

Fundamentals of MRI Flashcards

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USMLE® Step 1 flashcards
1
Q

What is the source and type of energy used in MRI?

A

Hydrogen

Electromagnetic radiation

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2
Q

What is a t1 weighted image?

A

Fluid black

Fat white

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3
Q

What is a t2 weighted image?

A

Fluid white

Fat black

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4
Q

What does a magnetic field exert to line up magnets?

A

Torque

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5
Q

What is the direction alignment?

A

In the direction of the magnetic field Btheta

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6
Q

What is torque proportional to?

A

Size of magnetic field

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7
Q

What is the typical magnetic field strength?

A

0.5-2 Tesla

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8
Q

Why is the magnet continuously rotating?

A

Superconducting magnet
Immersed in liquid nitrogen
at 77K no resistance

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9
Q

What happens when you put protons into a magnetic field?

A

Align with the magnetic field (lower energy state) or cancel go against (higher energy state) will oscillate between
slight excess will align with the field

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10
Q

What is precession?

A

Wobbling or rotation of a proton about the axis of Btheta

large gravity large magnetic field= fast precession

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11
Q

What is larmor ‘s equation?

A

Speed of precession=gyro magnetic ratio*magnetic field

1T=42 MHz/s

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12
Q

How do you tip protons out of alignment?

A

Apply RF pulse from RF coil energy depends on Larmor frequency
Causes protons to precess in phase and flips to transverse magnetisation

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13
Q

What happens when RF is turned off?

A

Absorbed RF energy is retransmitted
t1 Recovery-excited spins return to original orientation
T2 relaxation-protons dephase

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14
Q

What does a rotating magnetic field produce?

A

EM radiation- RF signal is retransmitted to MR signal

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15
Q

What is T1 relaxation?

A

Process of giving of RF energy as protons go from a high to low state energy
Some energy goes to heating up surrounding tissue
Relaxes back to longitudinal phase (along Z)

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16
Q

What is T2 relaxation/ decay?

A

Decay or dephasing in transverse plane

Protons begin to interact with each other magnetic field (x)

17
Q

What is quicker T2 decay or T1 relaxation?

A

T2

18
Q

How is an image formed?

A

At a point TE/2 a 180 RF current is sent flipping protons into xy plane another TE/2 passes and at TE vectors have rephrased and signal produced.

19
Q

What are the contraindications for MRI?

A 
Pacemakers
Projectiles
Aneurysm clips
Cryogen leak
Defibs
Foreign bodies
20
Q

What are artefacts?

A

Zipper
RF entering room
Corduray
Motion

21
Q

issues with MRI?

A 
Expensive
Noisy
Claustrophopic
Lack of electron density
Geometric distortion
22
Q

What are patient related artefacts?

A 
Implants
Surgical
Bones
Make up
Clothing

Applied Medical Imaging (10 decks)

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