Week 9

Question 1

What is spatial resolution?

Answer 1

The level of detail in the spatial dimension of an image, important for both structural and functional imaging

Question 2

What is temporal resolution?

Answer 2

The level of detail in the temporal (time) dimension of an image, important for functional imaging.

Question 3

How does a CT scan work?

Answer 3

Uses X-rays from multiple angles to create a detailed image based on tissue density.

Question 4

What tissues appear white, gray, and black in CT scans?

Answer 4

White: Dense tissues like bone.
Gray: Brain matter.
Black: Low-density tissues like cerebrospinal fluid.

Question 5

What are the limitations of CT scans?

Answer 5

Lower spatial resolution than MRI and involves radiation exposure.

Question 6

What is the principle behind MRI scans?

Answer 6

Based on the behavior of hydrogen atoms in a magnetic field.

Question 7

What do T1-weighted MRI scans show?

Answer 7

Grey matter: Dark grey.
White matter: Lighter grey.
Cerebrospinal fluid: Black.

Question 8

Why is MRI preferred over CT?

Answer 8

No radiation exposure.
Superior spatial resolution.
Can distinguish white and grey matter and be adapted for functional imaging.

Question 9

What is functional imaging based on?

Answer 9

Changes in neural activity reflected by physiological changes like blood flow or oxygenation.

Question 10

What does fMRI measure?

Answer 10

Blood oxygen-level-dependent (BOLD) signals indicating brain activity.

Question 11

What is the hemodynamic response function (HRF)?

Answer 11

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.

Question 12

What are the strengths of fMRI?

Answer 12

High spatial resolution (~1 mm).

Question 13

What are the limitations of fMRI?

Answer 13

Poor temporal resolution (15–20 seconds).

Question 14

What does fNIRS measure?

Answer 14

Blood oxygenation and deoxygenation using optical absorption.

Question 15

How does fNIRS work?

Answer 15

Near-infrared light shines through the scalp, and detectors measure how much light is absorbed to infer oxygen levels.

Question 16

What are the strengths of fNIRS?

Answer 16

Good temporal resolution, non-invasive.

Question 17

What are the limitations of fNIRS?

Answer 17

Limited to cortical activity, cannot measure deeper brain structures.

Question 18

What does PET measure?

Answer 18

Biochemical changes in the brain using a radioactive tracer.

Question 19

How does PET work?

Answer 19

Radioactive isotope is injected into the bloodstream.
Positrons from the tracer emit gamma rays.
Gamma rays indicate areas of greater brain activity.

Question 20

What are the strengths of PET?

Answer 20

Detects metabolic activity and early disease onset.

Question 21

What are the limitations of PET?

Answer 21

Expensive, involves radiation, lower temporal (~30 sec) and spatial (~10 mm) resolution.

Question 22

What are the two main types of imaging techniques?

Answer 22

Structural (CT, MRI) and Functional (fMRI, fNIRS, PET).

Question 23

What is the main advantage of MRI over CT?

Answer 23

MRI provides better spatial resolution and does not involve radiation.

Question 24

How do fMRI and fNIRS differ?

Answer 24

Both measure blood oxygenation, but fMRI uses BOLD signals, while fNIRS uses optical absorption.

Question 25

Why is PET used despite its limitations?

Answer 25

It detects biochemical changes and disease onset before structural changes appear.