Week 3 & 4 - Brain Imaging

COW

Circle of Willis

MCA

Middle cerebral artery

EAM

External acoustic meatus

GCS

Glasgow coma scale

SOL

Space occupying lesion (abnormal mass: tumour, cyst, haematoma)

OML

Orbitomeatal line

Name this plane

Axial

Name this plane

Coronal

Name this plane

Sagittal

What happens at gestational week 3 in regards to brain development?

• Brain development begins

• Ectoderm thickens to form the neural plate

• Neural plate folds inwards to form neural groove

What happens at gestational week 4 in regards to brain development?

• Neural groove fuses together creating the neural tube

When does the neural tube differentiate into primary and secondary vesicles?

GW4 - 5

What happens at gestational week 7 - 13 in regards to brain development?

The vesicles fold and the brain begins to take shape

What is the size of a new born brain?

About 25% of the adult brain size

Why is the skull unfused at birth?

To allow for the delivery through the birth canal

Name this section

Fontanelle

What is an epoch?

Stage of brain development

What are the 5 epochs of brain growth?

• Birth - 9

• Adolescence (9 - 32)

• Adulthood (32 - 66)

• Early aging (66 - 83)

• Late aging (83+)

What does the grey matter in brain consist of?

Dendrites and cell bodies

What does the white matter in brain consist of?

Myelinated axons

What are the 3 main parts of the brain and their main functions

• Cerebrum (Higher functions and cognition)

• Cerebellum (Coordination, balance, fine motor skills)

• Brain stem (life support functions, PNS, CNS)

What are the lobes of the brain?

• Frontal

• Parietal

• Occipital

• Temporal

Function of frontal lobe

• Decision making

• Judgement

• Voluntary movement (primary motor cortex)

• Speech production (Broca’s area)

Function of parietal lobe

• Processing and integrating somatosensory information

• Perceive touch, pressure, pain, temperature

• Spatial awareness

• Proprioception (knowing where your body parts are)

• Coordinating visual motor skills

Function of occipital lobe

• Visual processing

• Receiving and decoding raw signals from the eyes

• Spatial processing

• Depth perception

• Colour determination

• Recognition or objects and faces

Function of temporal lobe

• Processing sound

• Language comprehension

• Forming and retrieving memories

• Linking sensory input with emotion and meaning

Function of the basal ganglia

• Smooths involuntary movement

• Cortical functions

• Habit formation

• Limbic system

• Dysfunction = parkinson’s

Describe the function of the limbic system

• Emotional regulation and memory

• Amygdala: source of fight or flight

• Hippocampus: converts short term memories into long term, memory storage, effected by Alzheimer’s

Describe the function of ventricles

• 4 ventricles that synthesise and circulate CSF through the nervous system

• Shock absorbency

• Delivers nutrients and flushes cellular waste

What’re the sections of the brain stem?

• Midbrain

• Pons

• Medulla oblongata (point of left-right crossover)

• Spinal cord

Describe the role of the blood brain barrier

• Protects brain from systematic risks

• Capillary endothelial cells = selectively permeable membrane

• Prevents passage of toxins into the brain but allows oxygen and nutrients by active transport

What contrast is administered in patients with suspected BBB failure?

BBB failure = no ICM!!!

The carotid arteries

• Arises from aortic arch

• CCA branches into ECA and ICA

• ICA branches into MCA - supplies oxygenated blood to cerebrum

The carotid siphon

• S shape bend at the end of the ICA

• Dampens pulsation (reduces changes in blood flow pressure)

• Prevents turbulent blood flow arriving to the COW

Vertebral arteries

• Arise from the subclavian arteries and travel through the transverse foramina of the cervical vertebrae

• 20% of the brains blood supply, supplies the brainstem and cerebellum

• Susceptible to trauma

Meninges of the brain

• Dura mater

• Arachnoid mater

• Pia mater

List some indications for brain imaging

• Trauma

• Neurological changes

• Seizure

• Stroke

• SOL

What is the correct patient positioning for CT brain protocol?

• Head first

• Supine

• Head immobilised in cradle

• EAM is perpendicular to the OML

What is the correct patient scan range (collimation) for CT brain protocol?

C2/C3 vertebra to above head

What is the correct patient breathing instruction for CT brain protocol?

Suspended breathing

What is the window width/level for a soft tissue (brain) reformat?

WW: 80

WL: 40

What is the window width/level for a bone reformat?

WW: 2800

WL: 600

Name the pathology

Intracerebral haemorrhage (bleed)

Name the pathology

Name the pathology

MCA infarct (necrosis)

What dies this indicate?

• Hyperdense MCA sign

• Patient is actively having a stroke

Name the pathology

Skull #

Name the pathology

Mass

Name the pathology

Hypodense mass

Contrast scanning protocol of brain

• 50mL ICM IV, 1mL/sec

• 5min delay before scan

Name the pathology

Glioma

What is a stoke?

Interruption of blood supply to the brain, leading to rapid cell death (infraction - tissue death)

What is SMuRFs?

Standard modifiable cardiovascular risk factors

• Hypertension

• Diabetes

• Hyperlipidaemia

• Smoking

What is FAST?

Symptoms of a stroke

• Face: facial asymmetry, mouth drooping

• Arms: discoordination of motor function

• Speech: slurring

• Time: golden hour (hour to save patient, call for help immediately)

Not all symptoms need to be present to indicate stroke

Describe an ischaemic stroke

• Clot

• Brain not getting enough oxygen

• Caused by blockage of arteries which supply/are in the COW

• Blockage caused by clot (embolisation - clot in bloodstream travels)

• Commonly caused by atherosclerotic plaque rupture in carotid arteries

• 80% of strokes are ischaemic

Describe atherosclerosis

• Chronic disease

• Plaque growth in the arterial vessel wall

• Caused by vascular inflammation, cholesterol accumulation and stress

• Leading cause of ischaemic strokes

Describe an haemorrhagic stroke

• Bleed

• Can be caused by AVM rupture, hypertension, blood thinners, head trauma

• Previous ischaemic stroke can turn into a haemorrhagic stroke

• Caused by damage to damage to micro vessel during infarction

Describe the 2 types if haemorrhagic strokes

Subarachnoid haemorrhage: blood between the arachnoid membrane and pita mater

Subdural haematoma: blood between dura and arachnoid layers

Describe endovascular clot retrieval (ECR)

• 6 - 24 hours after symptom onset

• Catheter passed from thigh to brain to retrieve the clot and reverse stroke

Describe thrombolysis

• Clot busting and blood thinning drugs to rapidly dissolve clot

• Only in ischaemic stroke not haemorrhagic

Describe a craniostomy

Holes are drilled into the skull to drain haematoma and reduce intracranial pressure

Describe decompressive craniectomy

• Reduce intracranial pressure after malignant MCA stroke

• Bone flap is removed until swelling is reduced

Describe CT perfusion

• IV ICM at a fast rate (18 gauge)

• Shuttle scanning (oscillating in and out of machine)

• Heatmap generated to show mean transit time, time to peak and cerebral blood flow

• Used to confirm stroke location (ECR and prognosis)

What is the common nucleus used in MRI medical imaging?

Hydrogen atom

What are the main electromagnetic components of an MRI?

• Main magnet coils

• 3 gradient coils

• Integral radiofrequency (RF) transmitter coil

What is the function of the main magnet coils?

They create a strong constant magnetic field (B₀)

What is the function of the three gradient coils?

• Create changeable magnetic fields for spatial encodings

• Acts as a GPS to help identify the location of the protons within the magnetic field

What is the function of the RP transmitter coil?

• Creates oscillating RF field

• Sends signals to protons in the body from the machine to collect returning signals

What is the strength of MRI machines used in clinical imaging?

0.2T - 3.0T

What is the isocentre?

• The point within the scanner where the magnetic field is the strongest

• ROI should be centred here

What are the 3 gradient coils and their axis?

• Gx (X-axis)

• Gy (Y-axis)

• Gz (Z-axis)

Which gradient coils are on the transverse plane?

Gx (X-axis) and Gy (Y-axis)

Which gradient coils is on the longitudinal plane?

Gz (Z-axis)

Describe how hydrogen in the body reacts to B₀

B₀ is applied across the body → majority of hydrogen atoms align with the main magnetic field (spin up direction) → some will align anti-parallel to B₀

What is Zeeman Splitting?

Assesses the number of protons aligning parallel/anti-parallel to the main magnetic field

What is net magnetisation vector (NMV) in MRI?

• Sum of the number of excess hydrogen protons aligned parallel to B₀

• Paired parallel and unpaired hydrogen protons cancel each other out, since majority of protons align parallel with B₀, the sum of the left over unpaired parallel protons form NMV

• These unpaired protons produce a longitudinal signal that is the basis of the MRI signal

• NVM points in the same direction as the main magnetic field, Gz (longitudinal)

How is the NMV affected by the RF pulse in MRI?

The RF pulse tips the NMV from the longitudinal plane (Gz) to the transverse plane (Gxy)

What happens to the NMV immediately after the RF pulse?

• The longitudinal magnetization (Mz) becomes zero

• Transverse magnetization (Mxy) reaches its maximum and generates signal

• Rotating transverse vector creates oscillating magnetic field → detected by RF receiver coil

What are the 2 processes of the 2 components of net magnetisation?

• Longitudinal (T1 relaxation, recovery)

• Transverse (T2 relaxation, decay)

What does T2 relaxation mean in MRI?

• Happens after the RF signal

• T2 relaxation is the process by which the transverse components of magnetization (Mxy) decay

• Loss of phase coherence among proton spins (loss of synchronisation, losing rhythm)

• Faster than T1

What does T1 recovery mean in MRI?

• Happens after the RF signal

• Protons release absorbed energy to their surrounding environment to realign with the main magnetic field (B₀)

• Along the longitudinal plane