Quiz: BOLD Signal/Physiology, Bright

1. What magnetic property of blood oxygenation is the primary driver of BOLD contrast?

A) Increasing the amount of oxygen carried in blood plasma enhances the diffusion of oxygen to the tissue, which increases tissue R₂*
B) The concentration of oxygen-carrying erythrocytes in the blood (hematocrit) affects intravascular R₂*, and increases significantly during brain activation
C) Although it is diamagnetic when oxygenated, hemoglobin is paramagnetic when it becomes deoxygenated, which increases the R₂* dephasing of local spins near the vessel
D) The recruitment of capillaries increases total blood volume, which decreases R₂*

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2. When we model BOLD signal changes in the tissue around the capillary bed, what assumption do we need to make?

A) The vessels are mostly oriented parallel to the main magnetic field of the scanner
B) The total blood volume is very small compared to the tissue volume
C) The total amount of deoxygenated hemoglobin does not change during vasodilation
D) The vessel radius is large compared to its length

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3. During neurovascular coupling, how big is the blood flow response relative to the increase in tissue oxygen metabolism?

A) The blood flow response is twice as large as the metabolic change, to promote oxygen diffusion to tissue that is furthest from the vessel
B) The blood flow response matches the metabolic change, providing efficient supply of oxygen that matches the local demand
C) The blood flow response is half as large as the metabolic change, which causes oxygen extraction to decrease
D) The blood flow response is not coupled to the change in tissue oxygen metabolism, but is inversely coupled to changes in glucose metabolism

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4. What is true of the Hemodynamic Response Function?

A) Increased vascular transit times result in a reduction in the FWHM of the HRF
B) The HRF is stable across brain regions for one individual, but not across individuals
C) The shape of the HRF reflects near-instantaneous, time-locked changes in blood flow, blood volume, and metabolism
D) Impaired pericyte function results in reduced amplitude of the HRF

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5. In fMRI, how can we isolate signal changes related to R2* rather than S0?

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