BLOCK 12 WEEK 6 Flashcards
NON INVASIVE BRAIN IMAGING
ULTRASOUND
Pros:
- live images
- no radiation
- Cross sectional images allow for the visualisation of structures
- Relatively portable imaging modality
Con:
- Low spacial resolution
ULTRASOUND
- you know what your looking at by seeing where the probe is placed but its not very clear hence the low ‘spacial resolution’
X- RAYS used for:
- Skull fractures
- Sutures
- Haemorrhage
X -rays:
- Normally a erect PA image is taken and a abdominal supine AP.
- You need at least 2 projections to determine anatomic placement.
X RAYS
CT SCANS
- CT scans are used to image structures associated with the brain but not the brain itself e.g. odema, bone fractures and HAEMORRHAGE
CT SCANS
- CT scans are measured on a HOUNSFIELD SCALE normal X-Rays are not
PROS:
- Cross sectional images which allow for the easy visualisation of structures
- Easy to tell the differences between tissues
CONS:
- Relatively high radiation dose
- Relatively high cost
MRI
MRI are to do with water
- Bone and air have no water so appear black
- Tissues with water appear white to grey
- Tissues with a high amount of signal will appear white
- Tissues with a low level of signal will appear grey
What can we see:
An MRI scanner can be used to examine almost any part of the body including:
Brain and spinal chord / bones and joints / breasts / heart and blood vessels / internal organs such as the liver, womb or prostate gland.
MRIs
MRI Imaging can be:
-T1
-T2
-Fat Saturated Images
-Vascular Contrast Images
How does MRI scan work?
-The human body is about 70% water
-Water molecules are made up of hydrogen and oxygen atoms
At the centre of each hydrogen atom is an even smaller particle called a proton. Protons are tiny magnets and are very sensitive to magnetic fields.
When you lie under a powerful scanner magnet, the protons in your body line up in the same direction, in the same way that a magnet can pull the needle of a compass.
Short bursts of radio waves are then sent to certain areas of the body, knocking the protons out of the alignment.
When the radio waves are turned off, the protons realign. This sends out radio signals, which are picked up by receivers.
These signals give information about the exact location of the protons in the body.
They also help to distinguish between various types of tissues in the body, because the protons in different types of tissues realign at different speeds and produce distinct signals.
In the same way that millions of pixels con a computer can produce complex pictures, the signals from the millions of protons in the body are combines to create a detailed image.
Magnets on – atoms align
Radiofrequency on – atoms disperse
Radiofrequency off – the atoms re-align releasing energy ( different for each tissue type).
Pros:
- good spatial resolution
T1 weighted image
- The timing of radiofrequency pulse sequences used to make T1 images results in images which highlight FAT tissue within the body.
-T1 – ONE tissue is bright: fat
T2 weighted image
- The timing of radiofrequency pulse sequences used to make T2 images results in images which highlight FAT and WATER within the body.
-T2 – TWO tissues are bright: fat and water
T1 and T2 images
Fluid attenuated inversion recovery (FLAIR) MRI
- FLAIR is also similar to T2, however, the CSF signal is nullified. This is particularly useful for evaluating structures in the central nervous system (CNS), including the periventricular areas, sulci, and gyri.
- For example, FLAIR can be used to identify plaques in multiple sclerosis, subtle oedema after a stroke, and pathology in other conditions whereby CSF may interfere with interpretation
MRI (ANGIOGRAPHY)
Clinical use:
- Artherosclerosis (plaques)
- Stenosis (narrowing)
- Aneurysms
- Atriovenous malformations
- Interventional radiology - guide stent placement
DIFFUSION WEIGHTED IMAGING (DWI)
DWI is an imaging modality that combines T2 images with the diffusion of water.
-With DWI scans, ischaemia can be visualised within minutes of it occurring (Figure 5).
- This is because DWI has a high sensitivity for water diffusion, thereby detecting the physiological changes that happen immediately after a stroke.
PET SCAN
- Positron emission tomography (PET) scans produce detailed 3-dimensional images of the inside of the body.
- PET scans are often combined with CT scans to produce even more detailed images. This is known as a PET-CT scan. With MRI its a PET-MRI.
-
Why PET scans are used?
A PET scan can show how well certain parts of your body are working, rather than simply showing what they look like.
PET scans are particularly helpful for investigating confirmed cases of cancer to determine how far the cancer has spread and how well it’s responding to treatment.
PET scans are sometimes used to help plan operations, such as a coronary artery bypass graft or brain surgery for epilepsy.
HOW PET SCANS WORK?
- PET scanners work by detecting the radiation given off by a substance injected into your arm called a radiotracer as it collects in different parts of your body.
- In most PET scans a radiotracer called fluorodeoxyglucose (FDG) is used, which is similar to naturally occurring glucose (a type of sugar) so your body treats it in a similar way.
- By analysing the areas where the radiotracer does and does not build up, it’s possible to work out how certain body functions are working.
- For example, using FDG in the body’s tissues can help identify cancerous cells because they use glucose at a much faster rate than normal cells.
PROCESS OF A PET SCAN
- The radiotracer is injected into a vein in your arm or hand about an hour before your scan, as it takes time for it to reach the right cells in your body.
- During the scan, you lie on a flat bed that’s moved into a large, cylindrical scanner.
-The scan usually takes 30 to 60 minutes.
- ut the amount of radiation you’re exposed to in a standard PET scan is safe.
-The radiotracer becomes quickly less radioactive over time and will usually be passed out of your body naturally within a few hours.
- Drinking plenty of fluid after the scan can help flush it from your body.
PET PHYSICS
- The radioisotope decays as it is in the body from carbon to boron, as the radioisotope decays it releases a positively charged particle a positron
- The positron hits an electron which emits two gamma rays in opposite directions, which are detected simultaneously by opposite sides of the scanner
- Detectors are composed of scintillation crystals and photomultipliers
- Gamma rays are detected and converted to signal intensity, which the computer transforms into a spatial image.
SPECT - SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY
- Similar to PET but uses different radioactive tracers
- Lower spacial resolution
- Less expensive than PET
- Can use long lived radioisotopes which are easier to obtain
EEG
- Electroencephalography
- To find where to put the electrodes, first the technician marks four points on your head - the nasion (indentation between the forehead and the nose), the inion (ridge that can be felt in the middle of the back of the skull, over the occipital area), and the preauricular points on both sides of the head (indentations above the outer part of the ear openings).
-The electrode are then placed in many areas on the head, at specific locations and distances from these landmarks or points listed above.
- Sometimes other electrodes (sphenoidal and suboccipital, for instance) are placed to increase the chance of recording EEG waves from areas that may be too small or too deep to be recorded by the usual electrodes.
-Epilepsy is the fourth most common neurological disorder in the world. If you have epilepsy, surges of electrical activity in your brain can cause recurring seizures.
-
ECoG
What is electrocorticography used for?
Electrocorticogram (ECoG), obtained by placing macroelectrodes (typically 2–3 mm diameter) on the exposed surface of the cortex, is widely used by neurosurgeons to identify the source of seizures in drug-resistant epileptic patients. The brain area responsible for seizures is subsequently surgically removed.
MEG
What is Magnetoencephalography used for?
Magnetoencephalography (MEG) is a noninvasive test that neurologists and neurosurgeons use to help plan brain surgeries for epilepsy and tumor removal. MEG maps out the sensory areas of your brain and can pinpoint the exact location where seizures originate.
WHERE ARE THE SCANNERS?
FMRI image
FUNCTIONAL MRI
- Monitors the brains activity in real time
- Measures the Blood Oxygen Level Dependent (BOLD) response
- Rapid neuron firing needs more energy
- Blood delivers more energy to active neurons than inactive neurons
- This imaging technique is mainly used for research not clinically
- can be used to see brain plasticity
NEUROPLASTICITY
- Neuroplasticity, also known as neural plasticity or brain plasticity, is the ability of neural networks in the brain to change through growth and reorganization. It is when the brain is rewired to function in some way that differs from how it previously functioned.
- neuroplasticity include learning a new language, practicing music, or memorizing how to navigate around your city. It can also occur if you lose a sense, such as hearing or sight.
FUNCTIONAL NEAR INFRARED SPECTROSCOPY (fNIRS)
-100,00 people in the UK suffer from a stroke each year in the UK
- Stroke is the single biggest cause of severe disability in the UK
TIA Diagnosis
- TIA diagnosis is always made using a RETROSPECTIVE history because symptoms resolve by the time a patient is seen by a doctor
FOCAL NEUROLGICAL DEFECIT
- A focal neurologic deficit is a problem with nerve, spinal cord, or brain function.
-It affects a specific location, such as the left side of the face, right arm, or even a small area such as the tongue.
-Speech, vision, and hearing problems are also considered focal neurological deficits
NEUROLOGICAL DEFICIT
A neurologic deficit refers to abnormal function of a body area. This altered function is due to injury of the brain, spinal cord, muscles, or nerves.
Examples include:
-Abnormal reflexes
-Inability to speak
-Decreased sensation
-Loss of balance
-Mental function problems, such as memory loss
-Vision changes
-Walking problems
-Weakness of the arms or legs
WHAT ARE MIMICS OF STROKE
- SEIZURES
- MIGRAINES
- METABOLIC ENCEPHALOPATHY
- PERIPHERAL VESTIBULOPATHY
- FUNCTIONAL
TINNITUS
-Tinnitus is the term for hearing sounds that come from inside your body, rather than from an outside source.
- It’s often described as “ringing in the ears”, although several sounds can be heard, including: buzzing. humming. grinding
- HISTORY cannot differentiate ischemic from hemorrhagic stroke
- 30-50 % of patients referred to a TIA clinic end up having something else instead TIA
ASSESMENT METHODS
- FAST
- BE FAST (balance loss, eyesight changes)
HOSPITAL ASSESSMENT TOOLs:
- The ROSIER tool (Recognition Of Stroke In the Emergency Room) gives a score based on the clinical features and duration. Stroke is possible in patients scoring one or more.
ROSIER
WHAT ARE WE IMAGING?
IMAGING ENABLES:
- intiation of appropriate treatment
- provision of information about prognosis
- information on stroke aetiology
What are we imaging 4Ps?
- PARENCHYMA - assess the early signs of acute stroke, rule out haemorrhage and some stroke mimmics
- PIPES (blood vessels): Assess the extracranial and intercranial circulation
- PERFUSION: assess the cerebral blood volume, cerebral blood flow and mean transit time
- PENUMBRA: Assess tissue at risk of dying if ischemia continues without repruscussion
ADVANTAGES AND DISADVANTAGES OF CT
Advantages:
- sensitive to haemorage
- non invasive
- inexpensive
- rapid image aqcuisition
Disadvantages:
- difficult to distinguish from chronic infarction
- poor imaging of the posterior fossa
- less sensitive for acute infarction
ADVANTAGES and DISADVANTAGES OF MRI
ADVANTAGES:
- no radiation
- more sensitive than CT for detection of ischaemia
- high soft tissue resolution
- you can diffrentiate old from acute infarction
DISADVANTAGES:
- more limited availability particularly out of hours
- more expensive
- less rapid image acqusition
- patient related factors like pacemakers and metal fragments
WHAT HAPPENS TO FRONTAL AND PARIETAL LOBES?
FUNCTION OF PARIETAL AND OCCIPITAL LOBE
FUNCTION OF CEREBELLUM
Heamorrhagic stroke accounts for about 50% of disability and mortality to do with stroke.
- ICH has a 40% to 50% mortality rate within 30 days,
WHAT CAUSES HAEMORRHAGIC STROKE
- HYPERTENSION
- ARTERO-VENOUS MALFORMATION (AVM)
- ANEURYSM
- CEREBRAL AMYLOID ANGIOPATHY (CAA)
- COAGULATION DISORDERS OR MEDICATION RELATED
HEMIPLEGIA
- paralysis which only affects one side of your body
HEMANOPIA
is a loss of vision or blindness in half the visual field, to either the right or left side
Homonymous hemianopsia (or homonymous hemianopia, HH) is a field loss deficit in the same halves of the visual field of each eye.
STROKE LARGE VESSEL OCCLUSION
BAMFORD CLASSIFICATION OF ISCHAEMIC STROKE
- The most commonly used classification system for ischaemic stroke is the Bamford classification system (also known as the Oxford classification system).
- This system categorises stroke based on the initial presenting symptoms and clinical signs.
- This system does not require imaging to classify the stroke, instead, it is based on clinical findings alone.
STROKE CLASSIFICATION:
-TACS ( total anterior circulation stroke)
- PACS (Partial anterior circulation stroke)
- LACS (Lacunar stroke)
- POCS ( Posterior circulation stroke)
INTIALLY WHEN TREATING STROKE WHAT ARE THE GOALS?
- preservation of brain tissue
-restoration of blood flow - prevention of recurrent stroke
THROMBOLYISIS and THROMBECTOMY
- THROMBOLYSIS with a Alteplase is considered once haemorrhage is excluded (after the CT scan).
- Alteplase is a tissue plasminogen activator that rapidly breaks down clots.
- It may be given within 4.5 hours of the symptom onset, based on local protocols and by an appropriately trained team.
- Patients need close monitoring for complications, particularly intracranial or systemic haemorrhage, with access to immediate imaging if bleeding is suspected.
- THROMBECTOMY is a surgery to remove a blood clot from a blood vessel (artery or vein).
- Thrombectomy is considered in patients with a confirmed blockage of the proximal anterior circulation or proximal posterior circulation. It may be considered within 24 hours of the symptom onset and alongside IV thrombolysis.
What causes the blood supply to the brain to be distrupted?
-A thrombus or embolus
-Atherosclerosis - arteries narrow
-Shock - a drop in blood pressure
- Vasculitis
INTRACEREBRAL HAEMMORRHAGES
Intracerebral haemorrhage involves bleeding within the brain secondary to a ruptured blood vessel.
Intracerebral haemorrhages can be intraparenchymal (within the brain tissue) and/or intraventricular (within the ventricles).
SUBARACHANOID HAEMORRAHGES
Subarachnoid haemorrhage is a type of stroke caused by bleeding outside of the brain tissue, between the pia mater and arachnoid mater.
VASCULAR AUTOREGUALTION
TRAUMATIC BRAIN INJURY
PRIMARY INJURIES
INTERCRANIAL BLEEDS
-Extradural haemorrhage (bleeding between the skull and dura mater)
-Subdural haemorrhage (bleeding between the dura mater and arachnoid mater)
-Intracerebral haemorrhage (bleeding into brain tissue)
-Subarachnoid haemorrhage (bleeding in the subarachnoid space)
EXTRADURAL HAEMORRHAGE and SUBDURAL HAEMATOMA
- Extradural haemorrhage occurs between the skull and dura mater and is usually caused by a rupture of the MIDDLE MENINGEAL ARTERY in the temporoparietal region.
- It can be associated with a fracture of the temporal bone. On a CT scan, they have a bi-convex shape and are limited by the cranial sutures (they do not cross the sutures, which are the points where the skull bones join together).
A typical history is a young patient with a traumatic head injury and an ongoing headache. They have a period of improved neurological symptoms and consciousness, followed by a rapid decline over hours as the haematoma gets large enough to compress the intracranial contents.
SUBDURAL HAEMOATOMMA:
- Subdural haemorrhage occurs between the dura mater and arachnoid mater and is caused by a rupture of the bridging veins in the outermost meningeal layer.
- On a CT scan, they have a crescent shape and are not limited by the cranial sutures (they can cross over the sutures).
- Subdural haemorrhages may occur in elderly and alcoholic patients, who have more atrophy in their brains, making the vessels more prone to rupture.
INTRACEREBRAL AND INTRAVENTRICULAR
SUBARACHNOID HAEMORRAHGE
Subarachnoid haemorrhage involves bleeding in the subarachnoid space, where the cerebrospinal fluid is located, between the pia mater and the arachnoid membrane. This is usually the result of a ruptured cerebral aneurysm
COUP and COUNTERCOUP INJURIES
Contrecoup injuries classically occur when the moving head (brain) strikes a stationary object; whereas, a coup injury is associated with a moving object impacting a stationary head
PENETRATING HEAD INJURIES
CONCUSSION and DIFFUSE AXONAL INJURY
Concussion: is a mild traumatic brain injury (mTBI) that affects brain function. Effects are often short term and can include headaches and trouble with concentration, memory, balance, mood and sleep.
- Concussions usually are caused by an impact to the head or body that is associated with a change in brain function.
- CAUSE: falls, road crashes, assaults and sports accidents
CONCUSSION criteria:
- lose conciousness for less than 30 mins or not at all. Only 10% people who have a concussion lose consiousness
- Post-traumatic amnesia (PTA) of less than 24 hours after injury (this is a period where people are confused, act strangely and are unable to remember what has just happened)
DIFFUSE AXONAL INJURY:
- characterised by extensive, generalised damage to the white matter of the brain
Cause: rotational forces or sudden forceful stopping that stretches or tears the axon bundles
SECONDARY INJURY
RAISED INTRACRANIAL PRESSURE
CAUSES OF RAISED INTRACRANIAL PRESSURE
- Intercranial haemorrahge
- Tumours
- Brain odema
- Hydrocephalus
- Idiopathic
SYMPTOMS OF RAISED INTRACRANIAL PRESSURE
SYMPTOMS:
- headache
- vomiting
- papilledema
- The severity of a traumatic brain injury increases due to heightened ICP, especially if the pressure exceeds 40mmHg
- ICP monitoring involves placement of an invasive probe to measure the ICP.
BRAIN HERNIATION
- Brain herniation is the shifting of the brain tissue from one space in the skull to another through various folds and openings
- Brain herniation occurs when something inside the skull produces pressure that moves brain tissues. This is most often the result of brain swelling or bleeding from a head injury, stroke, or brain tumor.
Brain herniation can be a side effect of tumors in the brain, including:
-Metastatic brain tumor
- Primary brain tumor
Herniation of the brain can also be caused by other factors that lead to increased pressure inside the skull, including:
- Collection of pus and other material in the brain, usually from a bacterial or fungal infection (abscess)
- Bleeding in the brain (hemorrhage)
- Buildup of fluid inside the skull that leads to brain swelling (hydrocephalus)
- Strokes that cause brain swelling
CLINICAL MANAGEMENT OF HEAD INJURY
- The glasgow coma scale is used to measure levels of consiousness
MANAGMENT OF MILD HEAD INJURY
HYPERTENSION
ATRIAL FIBRILATION
