EEG brain for medical investigation and

management แพทยหญง กาญจนา พทกษวฒนานนท

อายรแพทยผเชยวชาญระบบประสาท แพทยประจำาศนยสมอง โรงพยาบาลสมตเวชศรราชา

The activity recorded in the EEG originates mainly from the superficial layers of the cerebral cortex.

Current is believed to flow between cortical cell dendrites and cell bodies

As a result of the synchronous activation of axodendritic synapses on many neurons , summed electrical currents flow through the extracellular space , creating the waves recorded as the EEG

Clinical applications Seizure Sleep disorder Encephalopathy

Electroencephalography : EEG

Scalp EEG

Epidural EEG / Subdural EEG

Electrocorticography

EEG – Photic stimulation

Evoked potential : EPRecording in response to a variety of sensory stimuli

SSEPVEPAERPBERP

Measured in terms of latency and amplitude

Visual evoked potentials : VERP

The most common stimulus involves alternating light and dark checkerboard squares

P100 or P1 latency refers to a positive deflection recorded over the occiput , normally occurring around 100 millisecs

Clinical applications

• Optic neuritis ( highly sensitive )• Anterior ischemic optic neuropathy• Sarcoidosis• Leber’s hereditary optic neuropathy• Papilledema• Chiasmal tumors ( eg.,pituitary adenoma )• Psychogenic visual loss ??

Brainstem auditory evoked potentials : BAEP

BAEP + AERP

Clinical applications

• brain death• coma from ??• cortical dysfunction• brainstem dysfunction

• acoustic neuromas ??• early detection subclinical MS

Auditory evoked potential : AERP

Somatosensory evoked potentials : SSEP

From peripheral nerve to sensory cortex

Nerve conduction studies : NCS

Motor nerve & sensory nerveamplitudelatencyconduction velocity

Blink reflex

Afferently CN V ( sensory )

Efferently CN VII ( motor )

Electromyography : EMG

Neuromuscular transmissionPeripheral neuropathyPlexopathyNerve rootSpinal cord lesion

Insertion activitySpontaneous activityMuscle contraction activity

Needle electromyographyFor diagnosis and treatment

Repetitive nerve stimulation test : RNS

MG

Normal / LEMS

Single fiber EMG : SFEMG

MRI scan

MRI involves first alingning the protons within human tissues in a strong magnetic field

The alinment is briefly interrupted via generation of a radiofrequency pulse.

The relaxation characteristics of protons in various tissues are then recorded as they recover magnetization.◦ T1 : spin-lattice relaxation◦ T2 : spin-spin relaxation◦ TR : repetition time◦ TE : echo time

MRI scan

Short TR Short TE Best displays anatomy Bright Dark

Fat , flowing blood , White matter , Gray matter , CSF , Bone , Air , Calcium , Hemosiderin , Flow void , Infarct

T1- weighted images

Long TR Long TE Best highlights pathology Bright Dark

CSF , Edema , Neoplasms , Abcess , Demyelination , Infarct , Gray matter , White matter , Bone , Air , Calcium , Hemosiderin , Flow void , Fat

T2 weighted images

MRI – Brain tumor

MRI – Brain metastasis

An image sensitive to local changes in the concentration of deoxyhemoglobin.

MRI can provide maps that show regions of increased neural activity within the brain.◦ Motor activity ( eg., tapping of fingers )◦ Sensory activity ( eg., stimulation part of body surface )◦ Cognitive activity ( eg., calculation , reading , recalling )◦ Affective activity ( eg., responding mentally to a fearful stimulus

)

fMRI ( functional magnetic resonance

imaging )

fMRI

Diffusion tensor imaging : DTI

Tractography

SPECT ( Single photon emission computed tomography ) Studies the uptake of gamma-releasing

radionucleotides ( eg., hexamethylpropyleneamineoxime : HMPAO ) as a measure of blood flow

PET ( Positron emission tomography ) A functional imaging study that correlates

activity to glucose uptake and metabolism by measuring ( most commonly ) 18F-deoxy-glucose , a positron-emitting nucleotide

Functional neuroimaging

Clinical applications

1. Epilepsy : SPECT increase in ictal period2. Neoplasm : high rate of metabolism3. Dementia : hypometabolism4. Brain death

Functional neuroimaging

Single photon emission computed tomography : SPECT

Positron emission tomography : PET