Neuroimaging Techniques Flashcards
What is the function of the frontal lobe? What is contained within the frontal lobe?
- Executing Behaviour – The ‘Action’ Cortex
- Skeletal Movement, Ocular Movement, Speech Control, Expression of Emotions
- Contains most of the dopamine neurons in the cerebral cortex – reward, attention and short term memory tasks
- Contains the Primary Motor Cortex, Premotor cortex and the Prefrontal cortex
What is the motor cortex in the frontal lobe made up of? What starts here? What model is in the top right of the motor cortex?
- Made up of 1. Primary Motor Cortex 2. Premotor Cortex 3. Supplementary Motor Area.
- Plans, controls and executes voluntary movement.
- Corticospinal tracts start here.
- The ‘Homonculous’ model in the top right demonstrates the area of the primary motor cortex responsible for movement of that body part. It also shows the proportion of neurons devoted to these area.
What is the function of the parietal lobe?
- Integrates sensory information
- Also manages localising touch, visuospatial navigation/awareness, assessing numerical relationships and coordinating hand/arm/eye movements
- Contains the primary somatosensory cortex and the posterior parietal cortex
Where and what is the primary somatosensory cortex in the parietal lobe?
- Located in the postcentral gyrus
- Responsible for processing somatic sensations
- Divided into 3 Brodmann Areas:
o Area 1 – Sensing Texture
o Area 2 – Perception of size/shape
o Area 3 – Receives majority of somatosensory input - Receives input from the Dorsal Column and Spinothalamic Tract primarily
Where is the temporal lobe and what is its function?
- Located beneath the lateral fissure
- Involved in processing sensory input in terms of forming memory
- Receives Auditory and Visual stimuli
- Integral in language recognition
What does the occipital lobe contain and what does it do?
- Contains the primary visual cortex
- It is the visual processing center of the human brain.
- Made up of lots of ‘Visual Areas’ defined on their role within visual processing eg what aim I seeing, where is it, how am I seeing it.
What does the cerebellum do and how is it connected to the rest of the brain?
- Means ‘little brain’ in Latin
- Important role in Motor Control – Contributes to coordination, precision and timing
- Connected to the rest of the brain via the Pons
What are the three parts of the brainstem and what is their function?
- 3 parts – Midbrain + pons + medulla oblongata
- Critical role in regulating cardiac and respiratory function
- Provides the main motor and sensory nerve supply to the face/neck via the cranial nerves
- Very important in conveying motor and sensory pathways between the body and brain
What are the deep brain structures and what do they do?
- Basal Ganglia = Group of Subcortical Nuclei
- Deep grey matter structures
- Interconnected with the cerebral cortex, thalamus + brainstem
- Involved with control of voluntary motor movements, procedural learning, habit learning, eye movements, cognition and emotion
What are the ventricles and what is their function?
- 4 Interconnecting cavities
- Each one contains choroid plexus – which produces CSF
- Function is to produce, store and circulate CSF – the substance required to protect the brain/CNS by providing buoyancy.
How is X-ray used to image the cranium?
- Skull XR is now almost obsolete
- Can only reliably detect a depressed skull fracture or penetrating injury
- Bony information only – does not give much information about the consequence of these types of injury.
How are CT scans used to image the cranium?
- Mainstay of acute neuroimaging
- Gives information about the bony and soft tissue structures.
- Gives reasonable information about the perfusion of the structures as well
- Cross sectional imaging
How is CT performed?
- Tomography is derived from Greek – Tomos = Slice, Graphein = to write
- Uses X-Rays
- Instead of this being a static process (as per a Plain XR), in a CT the XR source and XR detectors are rotating incredibly quickly in a helical motion around the site of imaging
- A computer processed combination of the images obtained produces a series of virtual ‘slices’ of the site imaged.
- Takes a few seconds to minutes (depends on complexity of images taken)
- IV or Oral contrast can be used to highlight certain structures during the scan.
- REMEMBER: CT is a significant dose of radiation
What value is CT a digital representation of? What is this measured in?
CT is a digital representation of attenuation coefficient
- Attenuation Coefficient = Quantification of how much an XR beam is weakened by material passing through it
- Measured in Houndsfield Units and then converted into greyscale
(See conversion table in lecture notes)
In which plane are CT scans most commonly viewed? How can you gain a sense of structures in 3D?
- Most commonly viewed in the TRANSVERSE (Axial) plane
- Like you are stood at the feet of the patient, with them lying on their back, looking up at their brain
- Series of slices are produced that allow you to generate a sense of structures in three dimensions
What are the 4 possible types of head CT?
Plain CT Head (non-contrast)
CT Angiography (Circle of Willis) (IV Contrast)
CT Perfusion (IV Contrast)
CT Venogram (IV Contrast)
(IV contrast makes it a bit more complicated to carry out)
What are the clinical uses of plain CT head?
Clinical use of Plain CT Head = TRAUMA AND/OR BLOOD
Clinical use of Plain CT Head: Subarachnoid Haemorrhage
- Blood in the Subarachnoid Space – between the arachnoid mater and the pia mater
Clinical use of Plain CT Head: Subdural Haemorrhage
- Blood between the inner layer of the Dura mater and the Arachnoid mater (crescent shaped)
Clinical use of Plain CT Head: Extradural Haemorrhage
- Blood between the dura mater and the skull (usually due to middle meningeal artery)
Clinical use of Plain CT Head: Intraparenchymal Haemorrhage
- Bleeding within the brain parenchyma
Clinical use of Plain CT Head: Intraventricular Haemorrhage
- Bleeding within the ventricles
See lecture notes for images of haemorrhages
Summarise brain haemorrhages in CT scans.
- Blood becomes less dense as it ages so can start to look similar to parenchyma – therefore CT should be performed quickly to check for damage
What is the role of plain CT head in acute ischaemic strokes?
- Plain CT Head also has role in acute ischaemic stroke (interruption in blood supply).
- It is quick and easy to perform – vital in the acute setting
- HOWEVER
- It is not the most sensitive imaging tool for ischaemia.
What are the clinical uses of CT angiography?
Clinical use of CT Angiography = Visualising the arteries of the brain
Clinical use of CT Angiography (Cerebral Arteries): Ischaemic Stroke
- To detect the site of occlusion and thrombosis
Clinical use of CT Angiography (Cerebral Arteries): Aneurysm
- Localised dilation or ballooning of an cerebral artery – Can rupture and cause a Subarachnoid Haemorrhage
Clinical use of CT Perfusion = Differentiating salvageable ischaemic brain from infarcted brain
See lecture notes for images
What are the advantages of CT?
- Excellent bone detail
- Good for blood
- Limited soft tissue detail
- Combined with contrast – Vascular + Perfusion
- 3D Reconstruction possible
- Used as technique for guiding procedures (biopsy/stents/drains)
- Relatively quick
What are the disadvantages of CT?
- LARGE RADIATION DOSE
- Limited soft tissue resolution
- Can’t be done at the bedside
What is magnetic resonance imaging (MRI)? How does it work?
- Relatively new technique
- Developed in the 1970’s
- Clinical use from the 1980’s
- Does not use radiation
- Requires a very strong magnet (1.5 -3 Teslas)
- MRI works by applying a huge static magnetic field to the body
- This magnetic field aligns all the protons in the body on the axis of the magnetic field
- Radiofrequency pulses are then applied to the body, causing these protons to spin
- When the radiofrequency pulse stops, the protons relax again.
- The energy released on relaxation is measured
- The protons behave differently depending on their environment, and the sequence of radiofrequency pulses – from this an image of these different proton environments can be made.
What are the safety implications of using a very strong magnet in an MRI?
- We must make sure that the person undergoing the MRI has no ferrous metal inside them.
- Older joint replacements/implants can metal that is not safe for MRI
- The vast majority of modern implants are MRI Safe
- Pacemakers have to be turned off
- No one other metal items should be left in the room whilst the MRI is undertaken.
