fMRI Flashcards
What is the primary purpose of fMRI?
To follow brain functioning over time by measuring physiological activity correlated with neuronal activity.
What does BOLD contrast stand for?
Blood Oxygenated Level Dependent contrast.
What is the relationship between blood flow and oxygen consumption in the brain?
There is a disparity; an increase in cerebral blood flow does not proportionally match oxygen consumption.
What is the primary energy currency for cells in the human body, including the brain?
Adenosine Triphosphate (ATP).
What is the role of ATP in brain cells?
It supports various brain processes, especially the activity of Na-K pumps.
Which artery supplies blood to the medial frontal and parietal lobes of the brain?
Anterior Cerebral Artery (ACA).
What is the function of the Middle Cerebral Artery (MCA)?
It supplies two-thirds of the lateral surface of the brain hemispheres.
How is Positron Emission Tomography (PET) imaging mainly used?
To measure the relationship between metabolic needs and neuronal activity in clinical settings.
What are some cons of PET imaging?
Limited spatial and temporal resolution, ionizing radiations, high costs, and logistic challenges.
What does BOLD contrast measure in fMRI?
The difference in signal on T2* weighted images as an inverse function of the amount of deoxyhemoglobin.
What is the primary role of hemoglobin in fMRI signal changes?
Hemoglobin’s magnetic properties, specifically deoxyhemoglobin, affect the MR signal in the transverse plane.
How was the BOLD signal discovered according to Ogawa et al. in 1990?
By scanning anesthetized rodents with T2* sensitive MRI sequences and manipulating oxygen levels.
At what point does an action potential occur in a neuron?
When the electric potential at the axon hillock reaches -55mV (depolarization).
What is Neurovascular Coupling?
The relationship between local neural activity and changes in cerebral blood flow.
What is the principal energy currency for brain cells?
Adenosine Triphosphate (ATP).
How is Regional Cerebral Blood Flow (rCBF) measured?
With techniques like Arterial Spin Labeling or radioactive tracers in PET imaging.
What is the role of Hemodynamic Response Function (HRF) in fMRI?
It represents the change in MR signal following neuronal activity and has a characteristic shape.
What is the initial dip in HRF associated with?
A transient increase in oxygen consumption before changes in blood flow.
How does the BOLD signal change with neural activity?
It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.
What is the significance of the discovery of BOLD signal?
It provided a basis for understanding the relationship between neural and hemodynamic activity.
What does the Balloon model propose about neuronal activation?
Neuronal activation increases blood flow, initially greater inflow than outflow, causing an initial dip and later BOLD signal increase.
Why is the static field strength critical in BOLD activation?
Susceptibility differences have a greater signal dephasing effect at higher fields.
What is the purpose of choosing a balanced Echo Time (TE) in fMRI?
It ensures a balance between T2* differences in rest and activation conditions for the same brain region.
When were the first fMRI experiments conducted?
In 1992.
What type of paradigms were primarily used in the first fMRI experiments?
Mostly block designs.
What is the primary limitation of contrast agents in fMRI studies?
The worse time course of signal change compared to BOLD.
What is the potential side effect of using Gadolinium-DTPA as a contrast agent?
Nausea, headache, and dizziness a few minutes after injection.
What is the common percentage range of signal change in BOLD activation?
Between 0.1% and 5% of background signal.
What does HRF stand for in the context of fMRI?
Hemodynamic Response Function.
How does HRF change with different stimuli durations?
The width increases with longer stimuli, and the amplitude increases with a higher rate of neuronal firing.
What is the relationship between neural firing and HRF amplitude?
Increasing the rate of neuronal firing increases HRF amplitude.
How much variance can subject-specific HRF models account for?
92%
What does Logothetis et al. (2001) combine to study neurovascular coupling in monkeys?
BOLD and electrophysiology.
What is the significance of the Sustained response in HRF?
It is important for block design analyses, reflecting prolonged activity.
How is BOLD related to Local Field Potential (LFP)?
BOLD is mostly related to afferent signals in neurons, while LFP is related to local processing.
What does Model 1 suggest about the spatial resolution of fMRI?
It suggests limited spatial resolution, especially for the initial dip.
How does the initial dip in the BOLD signal relate to the onset of neuronal activity?
It is associated with the initial activity of active neurons using available oxygen.
What is the role of the undulating balloon in the Balloon model?
It represents the expansion of the venous system due to increased blood volume from oxygen-rich blood.
What is the primary disadvantage of using contrast agents in fMRI?
The worse time course of signal change compared to BOLD.
How does the BOLD signal change with neural activity?
It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.
What is the role of Hemodynamic Response Function (HRF) in fMRI?
It represents the change in MR signal following neuronal activity and has a characteristic shape.
What is the initial dip in HRF associated with?
A transient increase in oxygen consumption before changes in blood flow.
How does the BOLD signal change with neural activity?
It increases due to a decrease in deoxyhemoglobin as oxygenated blood is supplied to active neurons.
What is the significance of the discovery of BOLD signal?
It provided a basis for understanding the relationship between neural and hemodynamic activity.
What does the Balloon model propose about neuronal activation?
Neuronal activation increases blood flow, initially greater inflow than outflow, causing an initial dip and later BOLD signal increase.
Why is the static field strength critical in BOLD activation?
Susceptibility differences have a greater signal dephasing effect at higher fields.
What is the purpose of choosing a balanced Echo Time (TE) in fMRI?
It ensures a balance between T2* differences in rest and activation conditions for the same brain region.
When were the first fMRI experiments conducted?
In 1992.
What type of paradigms were primarily used in the first fMRI experiments?
Mostly block designs.
