Week 9 Flashcards
What is spatial resolution?
The level of detail in the spatial dimension of an image, important for both structural and functional imaging
What is temporal resolution?
The level of detail in the temporal (time) dimension of an image, important for functional imaging.
How does a CT scan work?
Uses X-rays from multiple angles to create a detailed image based on tissue density.
What tissues appear white, gray, and black in CT scans?
White: Dense tissues like bone.
Gray: Brain matter.
Black: Low-density tissues like cerebrospinal fluid.
What are the limitations of CT scans?
Lower spatial resolution than MRI and involves radiation exposure.
What is the principle behind MRI scans?
Based on the behavior of hydrogen atoms in a magnetic field.
What do T1-weighted MRI scans show?
Grey matter: Dark grey.
White matter: Lighter grey.
Cerebrospinal fluid: Black.
Why is MRI preferred over CT?
No radiation exposure.
Superior spatial resolution.
Can distinguish white and grey matter and be adapted for functional imaging.
What is functional imaging based on?
Changes in neural activity reflected by physiological changes like blood flow or oxygenation.
What does fMRI measure?
Blood oxygen-level-dependent (BOLD) signals indicating brain activity.
What is the hemodynamic response function (HRF)?
Changes in the BOLD signal over time, with three phases:
Initial Dip: Oxygen consumption rises, reducing the BOLD signal.
Overcompensation: Blood flow increases, boosting the BOLD signal.
Undershoot: Blood flow dips before returning to baseline.
What are the strengths of fMRI?
High spatial resolution (~1 mm).
What are the limitations of fMRI?
Poor temporal resolution (15–20 seconds).
What does fNIRS measure?
Blood oxygenation and deoxygenation using optical absorption.
How does fNIRS work?
Near-infrared light shines through the scalp, and detectors measure how much light is absorbed to infer oxygen levels.
What are the strengths of fNIRS?
Good temporal resolution, non-invasive.
What are the limitations of fNIRS?
Limited to cortical activity, cannot measure deeper brain structures.
What does PET measure?
Biochemical changes in the brain using a radioactive tracer.
How does PET work?
Radioactive isotope is injected into the bloodstream.
Positrons from the tracer emit gamma rays.
Gamma rays indicate areas of greater brain activity.
What are the strengths of PET?
Detects metabolic activity and early disease onset.
What are the limitations of PET?
Expensive, involves radiation, lower temporal (~30 sec) and spatial (~10 mm) resolution.
What are the two main types of imaging techniques?
Structural (CT, MRI) and Functional (fMRI, fNIRS, PET).
What is the main advantage of MRI over CT?
MRI provides better spatial resolution and does not involve radiation.
How do fMRI and fNIRS differ?
Both measure blood oxygenation, but fMRI uses BOLD signals, while fNIRS uses optical absorption.
