Neuroimaging Flashcards
What are some of the uses of brain imaging techniques and factors to consider?
- Locating cysts and tumours
- finding oedema and haemorrhage
- Identifying the facts of a stroke
- some show structure, function and some both
Factors to consider;
- Availability
- Practicality and cost
- Side effects
What are the different orientations/slices of the brain that we can get?
Sagittal
Transverse
Coronal
What are the features of CT (computerised tomography)?
Uses x-rays and a computer to create detailed images of the body
Advantages;
Fast - takes about 0.3 seconds to image a single slice, get up to 64 slices pr rotation with 64 slice CT scanner
Widely available !
Disadvantages;
- Ionizing radiation
Why is radiation an issue in CT and what its the radiation risk factor?
CT head dose = 200 x CXR dose
Radiation risk factor = total lifetime risk of radiation-induced fatal cancer for the general population
0.05% per mSv (1 in 20,000)
There is also new photon-counting CT which reduces radiation and gives better imaging - not been made into routine yet
What plane are CT images given in?
Orbitomeatal plane, now in the supraorbitomeatal plane.
Images are acquired in the axial plane but can be reconstructed
Caudal view: axial slices viewed ‘as if from the foot of the bed’ - Right side of image is the Left side of the patient and vice versa
What colours would you see in CT images?
Grey scale from black to white (opposite of MRI)
Generated by absorption;
- Tissues differ in absorption of x-rays
- Corresponds to ‘shade of grey’ on image
- Narrow range for soft tissues - poor differentiation
Bone absorbs so white, air doesn’t so black
How does MRI work?
Clinical MRI relies on hydrogen;
- Has a single proton in its atom
- Found in abundance in the body -> good source of signal
Uses a combination of magnetic fields and radio waves to produce images
RF pulse used in MRI is non-ionising but may cause heating effect (same radiation as phones)
What planes can you acquire MRI’s in?
Oblique
Axial: Viewed as if from the foot of the bed - Right side of image is left side of patient vice versa
Coronal images: Viewed as if you are looking at the face of the patient - Right side of image is left side of patient vice versa
What are the different MRI scans that you can get?
Contrast between different tissues/structures/pathologies is needed
Three properties of tissue affect contrast:
- T1 time (T1 recovery)
- T2 time (T2 decay)
- Proton density (PD)
A series of RF and magnetic field applications is called a pulse (MR) sequence
Pulse sequence, therefore the images can be T1-, T2- or PD-weighted
What are the different weighted images good for?
T1-weighted image: good for anatomy and contrast
- Water (CSF) is dark, grey matter is dark grey, white matter is off white, fat is white
T2 - weighted image: good for identifying pathology - inflammation, oedema
- Water is white, white matter is darker than grey matter
(WW2 - Water is White on T2)
What is magnetic resonance angiography ?
Makes vessel visible for scan
Can be done with our without contrast - Might not want to use contrast in patients who are allergic or have kidney disease will struggle to eliminate as heavy
Inflow angiography (aka time-of-flight) and phase contrast
Can over-exaggerate stenoses, underestimate true lumen size
When else can contrast agents be used?
Not only for angiography but also to enhance contrast between tissues
Positive contrast agents produce an increase in signal intensity in affected tissues
Gadolinium - Most commonly used - not easily eliminated from body but some instances is needed
- Potential to build up in body
Negative contrast agents produce a decrease in signal intensity in affects tissues - contain iron oxide
What do diffusion wighted imaging (DWI) rely on and what can these show?
Diffusion weighted imaging (DWI) relies on diffusion of water molecules. (T2)
Areas of cerebral infarction t(issue death or necrosis due to inadequate blood supply to the affected area) have decreased diffusion, which results in increased signal intensity (more white)
Is now the standard imaging for early detection of ischemia / infarct / stroke, differentiation of brain tumours and intracranial infections
What is the apparent diffusion coefficient (ADC)?
The apparent diffusion coefficient (ADC) is a measure of the magnitude of diffusion of water molecules within the tissue.
Commonly calculated using diffusion-weighted imaging (DWI)
ADC values are calculated automatically by the software and then displayed as a parametric map
The images contrast on ADC maps is opposite to that of DWI (water was white now black)
What is tractography?
A 3D reconstruction technique to show / assess axons / tracts using data related to diffusion of water collected by diffusion MRI
What is function MRI and its use (fMRI)?
Used to obtain functional information buy visualising cortical activity
Detects subtle alteration in blood flow or blood oxygen in response to stimuli or actions
There are limitations
What are the contraindications of using MRI?
Projectiles (attraction of metal objects)
Implanted devices;
- Pacemakers, cochlear implants, non-MRI compatible heart valves, stents
- Foreign bodies (shrapnel) - torque or malfunction
Claustrophobia
What is nuclear imaging: SPECT and PET
Perfusion techniques that requires intravenous contrast agent
They show the metabolic or biochemical function by measuring radio tracer uptake (usually glucose) by the tissues (cancer, infection, coronary artery disease, brain disorders)
PET offers better spatial resolution, higher diagnostic accuracy and lower dosimetry then SPECT but it is very expensive
What is the system we use for interpreting images?
ABC’S
A;
- Adequacy
- Alignment
- Artefact
B;
- Bones
- Blood
- Brain
C;
- CSF filled spaces (cisterns & ventricles)
S;
- Subcutaneous
- Surfaces
- Symmetry
What does part A in ABC’s cover?
Adequacy - Can you see all 7 cervical vertebrae + the top of T1 (as well as occipital bone)
Alignment - Draw three vertical “parallel” lines along the anterior + posterior border of the 7 vertebral bodies and a third line through the base of each spinous process
Asymmetry - Look for abnormal asymmetry between the 7 cervical vertebrae
Artefact;
- Motion/confused patient, children
- Beam hardening - posterior fossa
- Medical - metal clips, intraventricular shunts
- Aliasing
What does part B in ABC’s cover?
Bones;
- Bone window on CT when parameters are preset correctly
- MRI shows bones indirectly by showing structures around bone to give bone appearance
Blood; (white in T2, not as white as bone tho)
Subdural hematoma;
- Crescent-shaped
- blood collection between dura and arachnoid matter
- Tear in bridging veins
- Alcoholics and elderly are prone
Epidural hematoma;
- Biconvex (lens) shaped
- Blood between dura and skull
- Tearing of middle meningeal artery
- Adolescents and young adults (Trauma)
Subarachnoid haemorrhage;
- blood in circle of Willis, cisterns, and fissures
- Rupture of berry aneurysm
- polycystic kidney disease is a risk factor
- Rupture of cerebral arteries
Intracerebral haemorrhage;
- Blood in parenchyma and ventricles
- Hypertensive vasculopathy
- Terriotry between penetrator arteries (between brain mass)
Brain;
- Mass
- Poor grey-white matter differentiation
- Loss of sulci / atrophy
What does part C in ABC’s cover?
CSF - filled spaces;
Check cisterns, has blood collected in them? - Subarachnoid haemorrhage
Obstructive hydrocephalus - blockage in ventricular system leads to enlargement of lateral ventricles - very large black cross shape
What does part S in ABC’s cover?
Subcutaneous and soft tissues;
- Skin / subcutaneous lesions (or mass)
- Orbit
- Sinuses
- Nasopharynx and oropharynx
What type of heamorrhage is this? (See image)
Subdural hematoma;
- Crescent shapd
- Blood collection between dura and arachnoid matter
- Tear in briding veins
- Alcohlics and elderly are prone
What would a Subdural haematoma look like ?
Subdural hematoma;
- Crescent shaped
- Blood collection between dura and arachnoid matter
- Tear in briding veins
- Alcohlics and elderly are prone
(See image)
What type of haemorrhage is this? (See image)
Subarachnoid Haemorrhage;
- Blood in circle of Willis, cisterns and fissures
- Rupture of berry aneurysm
- Polycistic kidney disease (risk factor)
What type of heamorrhage is this? (See image)
Epidural haematoma;
- Biconvex (lens) shaped
- Blood between dura and skull
- Tearing of middle meningeal artrey (hit in pterion?)
- Adolescents and young adults (trauma)
What type of heamorrhage is this? (See image)
Intracerebral haemorrhage;
- Blood in parenchyma and venticles
- Hypertensive vasculopathy
- Territory of penetrator arteries
What would a Subarachnoid Haemorrhage look like?
Subarachnoid Haemorrhage;
- Blood in circle of Willis, cisterns and fissures
- Rupture of berry aneurysm
- Polycistic kidney disease (risk factor)
(See image)
What would a Epidural haematoma look like?
Epidural haematoma;
- Biconvex (lens) shaped
- Blood between dura and skull
- Tearing of middle meningeal artrey (hit in pterion?)
- Adolescents and young adults (trauma)
(See image)
What would a Intracerebral Haemorrhage look like ?
Intracerebral haemorrhage;
- Blood in parenchyma and venticles
- Hypertensive vasculopathy
- Territory of penetrator arteries
(See image)
