Brain Imaging

Question 1

CAT - Function

Answer 1

Differential absorption of X-ray

Question 2

CAT - Procedure

Answer 2

○ The subject lies on a table tat slides inside a cylindrical apparatus where a moving source of X-rays scan around the patient’s head.
○ After passing through the head the ray beam is picked up and mapped from the opposite side.
§ Reveals the structure of the brain

Question 3

CAT - evaluation

Answer 3

§ Quick
			§ Non-invasive
			§ Records
				□ Hard tissue
				□ Soft tissue
				□ Blood
			§ Friendly with implanted devices.
		○ Cons
Involves a level of radiation exposure.

Question 4

MRI - Function

Answer 4

○ Atomic nuclei can emit energy when placed in an external magnetic field.

Question 5

MRI - Procedure

Answer 5

○ Patients are placed in a cylindrical apparatus.
○ Magnetic field allows the hydrogen atoms in the body to emit energy.
○ Pulses of energy are picked up by the scanner.
○ Allows to map out hydrogen atom distribution in the brain.
○ Different tissues have different concentrations.
○ After excitation the tissues return to equilibrium state.
§ The time to equalize is different.
§ Hence the time is analyzed.
○ This is why it’s necessary to change parameters and rapidly turn it on and off.

Question 6

MRI - Evaluation

Answer 6

○ Pros
§ No radiation
§ Better resolution for detecting abnormalities.
○ Cons
§ Not metal transplant friendly
§ Tube is narrow and claustrophobic inducing
§ Lying for a long time is not child friendly.
§ MRI’s more expensive than CAT
§ High resolution may lead to overrepresentation of abnormalities.
□ Lead to patient anxiety

Question 7

FMRI - Function

Answer 7

○ BOLD:
			§ Blood
			§ Oxygen 
			§ Level
			§ Dependent  
		○ The flow of oxygenated blood correlates with the energy used by blood cells and this directly corresponds to brain activity in the region.

Question 8

FMRI - Procedure

Answer 8

○ Patients are placed in a cylindrical apparatus.
○ Magnetic field allows the hydrogen atoms in the body to emit energy.
○ Pulses of energy are picked up by the scanner.
○ Allows to map out hydrogen atom distribution in the brain.
○ Different tissues have different concentrations.
○ After excitation the tissues return to equilibrium state.
§ The time to equalize is different.
§ Hence the time is analyzed.
○ This is why it’s necessary to change parameters and rapidly turn it on and off.

Question 9

FMRI - Evaluation

Answer 9

○ Pros
§ Excellent spatial resolution (1-2mm)
§ Unlike structural brain imaging it can see brain processes.
○ Cons
§ Poor temporal resolution.
§ Not metal transplant friendly
§ Tube is narrow and claustrophobic inducing
§ Lying for a long time is not child friendly.
§ Expensive cost
§ High resolution can lead to overrepresentation of abnormality.
□ Lead to patient anxiety.

Question 10

PET - FUnction

Answer 10

○ Uses blood flow for indication of activity through radiactive tracer.

Question 11

PET - Procedure

Answer 11

○ A radioactive tracer is injected to bind to certain molecules.
§ Such as glucose
○ It has a short half life.
○ The scanner picks up radio waves emitted by the radioactive substances.
○ The distribution of the tracer allows the scanner to see brain activity.

Question 12

PET - Evaluation

Answer 12

○ Pros
§ Decent spatial resolution of 4 mm
§ Useful for detecting tumours and metastases
§ Useful in diagnosing causes of dementias
§ They are small enough to be worn on a rat’s head.
○ Cons
§ Temporal resolution is 30-40 seconds so quick changes can’t be detected.
§ Invasive procedure.
§ Radiation exposure.

Question 13

Electrophenography - Function

Answer 13

○ Measures electric potentials generated by neural circuits.

Question 14

Electroencephalography - Procedure

Answer 14

○ Neurons communicate by sending electrical impulses along their axons.
○ An impulse fired in an individual neuron is “invisible”
§ Too tiny to be detected outside of skull
○ Large groups of neurons firing become detectable.
○ Electrodes attached to the scalp in predetermined points
§ Pick up changes in electrical potential.

Question 15

Electroencephalography - Evaluation

Answer 15

○ Perfect temporal resolution
○ Low cost
○ Mobile service
§ Good ergonomics
○ Silent so auditory simuli can be observed.
○ Completely non-invasive.
• Cons
○ Weak spatial resolution
§ Crude pictures of localisation.
○ Good for measuring electrical activity in the crtex but not good for detecting in subcostal areas.
○ Further away from the scalp is harder to pick up.