fMRI and Long-term Memory

Question 1

What did the development of MRI depend on?

Answer 1

• computers: for equipment control and data analysis
• superconductivity: for the high field-strength magnet
• nuclear magnetic resonance/quantum mechanics: for absorption and release of electromagnetic energy

Question 2

What machinery/parts does fMRI require?

Answer 2

• 1.5 Tesla MRI machine
• 4 MRI magnets
• B0 magnet is superconducting and always on
• cooling system in magnets to keep them running
• head coil: radio frequency coil

Question 3

What are some safety issues that need to be considered for fMRI?

Answer 3

• the strong magnetic field can cause projectiles
• superconductor quench
• changing magnetic fields
• radio frequency coil
• claustrophobia
• noise

Question 4

What is superconductor quench?

Answer 4

• when turning off the liquid helium turns to gas and pushes the air out of the room

Question 5

What is the issue of changing magnetic fields?

Answer 5

• if you lie with hands together instead of by your side, this creates a closed circuit loop and may generate current

Question 6

What are some things to screen for when recruiting participants for fMRI?

Answer 6

• claustrophobia

- metals: job, pacemakers, hearing aids, piercings, tattoos

Question 7

What is nuclear magnetic resonance?

Answer 7

• energy at specific radio frequencies is absorbed and reemitted by nuclei with non-zero spin
• matter has a specific resonance frequency

Question 8

What is the equation for nuclear magnetic resonance? What does this mean?

Answer 8

• resonant frequency = gyromagnetic ratio x magnetic field strength
• the resonant frequency can be adjusted by changing the magnetic field strength

Question 9

What molecule is used in fMRI?

Answer 9

• hydrogen because it is in body and brain as water

- 42.576 MHz in a 1 Tesla field

Question 10

How does the MRI signal work?

Answer 10

• radio frequency energy/pulse in

- radio frequency emitted back out for data acquisition

Question 11

How do we measure a single part of the brain if the whole brain is able to emit?

Answer 11

• produce a gradient of magnetic field applied to the brain
• can now pick a piece of brain
• gradient x to produce front to back slice
• gradient y to produce top to bottom slice
• phase to distinguish left from right

Question 12

What is the pulse sequence?

Answer 12

• rapid sequence of different coils turning on and off

Question 13

What is the k-space?

Answer 13

• the raw image of activation

- this is translated to real space by 2D Fourier Transform

Question 14

What does the amount of signal depend on?

Answer 14

• properties of the tissue:
• proton density
• T2 decay (dephasing)
• T1 recovery (return to resting state)

Question 15

How does the researcher manipulate the properties of tissue?

Answer 15

• experimenter has control over how long they wait to record and how long they wait to send the next pulse
• changes which properties matters

Question 16

What is another factor that determines the strength of signal?

Answer 16

• timing of the RF pulse (TR) and data acquisition (TE)