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Principles > fMRI > Flashcards

fMRI Flashcards

1
Q

What is the primary purpose of fMRI?

A

To follow brain functioning over time by measuring physiological activity correlated with neuronal activity.

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2
Q

What does BOLD contrast stand for?

A

Blood Oxygenated Level Dependent contrast.

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3
Q

What is the relationship between blood flow and oxygen consumption in the brain?

A

There is a disparity; an increase in cerebral blood flow does not proportionally match oxygen consumption.

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4
Q

What is the primary energy currency for cells in the human body, including the brain?

A

Adenosine Triphosphate (ATP).

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5
Q

What is the role of ATP in brain cells?

A

It supports various brain processes, especially the activity of Na-K pumps.

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6
Q

Which artery supplies blood to the medial frontal and parietal lobes of the brain?

A

Anterior Cerebral Artery (ACA).

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7
Q

What is the function of the Middle Cerebral Artery (MCA)?

A

It supplies two-thirds of the lateral surface of the brain hemispheres.

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8
Q

How is Positron Emission Tomography (PET) imaging mainly used?

A

To measure the relationship between metabolic needs and neuronal activity in clinical settings.

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9
Q

What are some cons of PET imaging?

A

Limited spatial and temporal resolution, ionizing radiations, high costs, and logistic challenges.

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10
Q

What does BOLD contrast measure in fMRI?

A

The difference in signal on T2* weighted images as an inverse function of the amount of deoxyhemoglobin.

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11
Q

What is the primary role of hemoglobin in fMRI signal changes?

A

Hemoglobin’s magnetic properties, specifically deoxyhemoglobin, affect the MR signal in the transverse plane.

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12
Q

How was the BOLD signal discovered according to Ogawa et al. in 1990?

A

By scanning anesthetized rodents with T2* sensitive MRI sequences and manipulating oxygen levels.

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13
Q

At what point does an action potential occur in a neuron?

A

When the electric potential at the axon hillock reaches -55mV (depolarization).

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14
Q

What is Neurovascular Coupling?

A

The relationship between local neural activity and changes in cerebral blood flow.

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15
Q

What is the principal energy currency for brain cells?

A

Adenosine Triphosphate (ATP).

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16
Q

How is Regional Cerebral Blood Flow (rCBF) measured?

A

With techniques like Arterial Spin Labeling or radioactive tracers in PET imaging.

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17
Q

What is the role of Hemodynamic Response Function (HRF) in fMRI?

A

It represents the change in MR signal following neuronal activity and has a characteristic shape.

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18
Q

What is the initial dip in HRF associated with?

A

A transient increase in oxygen consumption before changes in blood flow.

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19
Q

How does the BOLD signal change with neural activity?

A

It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.

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20
Q

What is the significance of the discovery of BOLD signal?

A

It provided a basis for understanding the relationship between neural and hemodynamic activity.

21
Q

What does the Balloon model propose about neuronal activation?

A

Neuronal activation increases blood flow, initially greater inflow than outflow, causing an initial dip and later BOLD signal increase.

22
Q

Why is the static field strength critical in BOLD activation?

A

Susceptibility differences have a greater signal dephasing effect at higher fields.

23
Q

What is the purpose of choosing a balanced Echo Time (TE) in fMRI?

A

It ensures a balance between T2* differences in rest and activation conditions for the same brain region.

24
Q

When were the first fMRI experiments conducted?

A

In 1992.

25
Q

What type of paradigms were primarily used in the first fMRI experiments?

A

Mostly block designs.

26
Q

What is the primary limitation of contrast agents in fMRI studies?

A

The worse time course of signal change compared to BOLD.

27
Q

What is the potential side effect of using Gadolinium-DTPA as a contrast agent?

A

Nausea, headache, and dizziness a few minutes after injection.

28
Q

What is the common percentage range of signal change in BOLD activation?

A

Between 0.1% and 5% of background signal.

29
Q

What does HRF stand for in the context of fMRI?

A

Hemodynamic Response Function.

30
Q

How does HRF change with different stimuli durations?

A

The width increases with longer stimuli, and the amplitude increases with a higher rate of neuronal firing.

31
Q

What is the relationship between neural firing and HRF amplitude?

A

Increasing the rate of neuronal firing increases HRF amplitude.

32
Q

How much variance can subject-specific HRF models account for?

A

92%

33
Q

What does Logothetis et al. (2001) combine to study neurovascular coupling in monkeys?

A

BOLD and electrophysiology.

34
Q

What is the significance of the Sustained response in HRF?

A

It is important for block design analyses, reflecting prolonged activity.

35
Q

How is BOLD related to Local Field Potential (LFP)?

A

BOLD is mostly related to afferent signals in neurons, while LFP is related to local processing.

36
Q

What does Model 1 suggest about the spatial resolution of fMRI?

A

It suggests limited spatial resolution, especially for the initial dip.

37
Q

How does the initial dip in the BOLD signal relate to the onset of neuronal activity?

A

It is associated with the initial activity of active neurons using available oxygen.

38
Q

What is the role of the undulating balloon in the Balloon model?

A

It represents the expansion of the venous system due to increased blood volume from oxygen-rich blood.

39
Q

What is the primary disadvantage of using contrast agents in fMRI?

A

The worse time course of signal change compared to BOLD.

40
Q

How does the BOLD signal change with neural activity?

A

It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.

41
Q

What is the role of Hemodynamic Response Function (HRF) in fMRI?

A

It represents the change in MR signal following neuronal activity and has a characteristic shape.

42
Q

What is the initial dip in HRF associated with?

A

A transient increase in oxygen consumption before changes in blood flow.

43
Q

How does the BOLD signal change with neural activity?

A

It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.

44
Q

What is the significance of the discovery of BOLD signal?

A

It provided a basis for understanding the relationship between neural and hemodynamic activity.

45
Q

What does the Balloon model propose about neuronal activation?

A

Neuronal activation increases blood flow, initially greater inflow than outflow, causing an initial dip and later BOLD signal increase.

46
Q

Why is the static field strength critical in BOLD activation?

A

Susceptibility differences have a greater signal dephasing effect at higher fields.

47
Q

What is the purpose of choosing a balanced Echo Time (TE) in fMRI?

A

It ensures a balance between T2* differences in rest and activation conditions for the same brain region.

48
Q

When were the first fMRI experiments conducted?

A

In 1992.

49
Q

What type of paradigms were primarily used in the first fMRI experiments?

A

Mostly block designs.

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