task 4 Flashcards
invasive / non-invasive procedure
invasive:
> procedure that invades (enters) the body
-> usually by cutting / puncturing the skin or inserting instruments into the body
–> it interrupts normal bodily functions
non-invasive:
> procedure that does not require incision into the body or removal of tissue
-> to break in the skin is created and there is no contact with the mucosa
contrast X-ray techniques
involves injecting into one compartment of the body a substance that absorbs X-ray either less or more than the surrounding tissue
> injected substance heightens contrast between compartment and surrounding tissue during X-ray photography
> angiography:
-> brain-imaging technique in which a specialised X-ray image of head is taken shortly after cerebral blood vessels have been filled with radioactive dye by means of a catheter
creation of brain images
all techniques do not produce actual images of the brain but computer -generated composites based in measurements of:
> density - reflects structure of brain
blood flow - reflects metabolism of brain
electromagnetic activity - reflects electrical activity of brain
computerised axial tomography (CAT or CT)
definition / advantages / disadvantages / characteristics
Noninvasive technique for examining brain structure in humans through computer analysis of X-ray absorption at several positions around the head.
Advantages:
> Quick – Only a few minutes, done in a day;
> Affordable;
> Accommodates large patients;
> It offers the option to perform a 3D reconstruction.
Disadvantages:
> Since CAT scans use X-ray, which produce ionizing radiation, it can damage our DNA and lead to cancer but the risk is very small.
-> Because radiation effect adds up over our lifetime, the risk increases with every CAT we get.
> lesions do not disappear after treatment
> Potential source of error in the evaluation of the diseases.
Characteristics: > spatial resolution: high > temporal resolution: medium > functional: no > invasive: no
positron emission tomography (PET)
definition / advantages / disadvantages / characteristics
Technique for examining brain function by combining tomography with injections of radioactive substances used by the brain.
Advantages:
> Short waiting period;
> It shows how our body is working;
> It can show what is actually happening in our cells – Important because some diseases don’t cause change early on, only in how our cells are working;
> Results can be obtained within 24 hours.
Disadvantages:
> It takes longer than the previous one – We have to wait for the 2-DG to kick in, which takes up to 30 minutes and then lie on the scan for up to one hour.
> Although the scan is painless, some people find that staying still for so long causes discomfort.
> We need to drink plenty of fluids to flush the tracer out of the body – We stay radioactive for a short time.
> Does not provide images of brain structure -> Resolved by combining PET with MRI.
Characteristics: > spatial resolution: intermediate > temporal resolution: low > functional: yes > invasive: yes
transcranial magnetic stimulation (TMS)
definition / advantages / disadvantages / characteristics
Localized, noninvasive stimulation of an area of the cortex through the application of strong magnetic fields.
Advantages:
> Can be used to map behaviour related with spatial and temporal precision.
> It might help with stroke rehabilitation, Parkinson’s, migraine, pain management and auditory hallucination
Disadvantages:
> Patients experience discomfort during the procedure and some might faint or have a seizure undergoing stimulation.
> Other side effects include confusion related to disruptions in cognition, hearing or vision.
> Safety, depth of effect and mechanisms of neural disruption are still being questioned.
Characteristics: > spatial resolution: intermediate > temporal resolution: intermediate > functional: yes > invasive: no
magnetoencephalography (MEG)
definition / advantages / disadvantages / characteristics
Passive and noninvasive functional brain-imaging technique that measures the tiny magnetic fields produced by active neurons, in order to identify regions of the brain that are particularly active during a given task.
Advantages:
> Three-dimensional.
> MEG fields pass through the head without any distortion.
-> Advantage over EEG.
> Direct measure of brain function.
-> Advantage over fMRI (indirect).
> Most advanced method of recording and evaluating the brain while it is actively functioning.
Disadvantages:
> Only magnetic signals near the surface of the brain can be recorded.
Characteristics: > spatial resolution: low > temporal resolution: high > functional: yes > invasive: no
magnetic resonance imaging (MRI)
definition / advantages / disadvantages / characteristics
Noninvasive technique that uses magnetic energy to generate high-resolution images that reveal some structural details in the living brain.
Advantages:
> Good detail – More detailed than CT scan. Can create 3-D images.
> No radiation.
> It can produce images in three dimensions.
> It provides higher-resolution images of the brain than does CT.
> Painless and fast – Can last from 15 minutes to a bit more than one hour.
Disadvantages:
> Difficult with people having metal in body
> Size limits
Characteristics: > spatial resolution: high > temporal resolution: low > functional: no > invasive: no
diffusion tensor imaging / fibre tracking (DI/DWI/DTI)
definition / advantages / disadvantages / characteristics
Modified form of MRI in which the diffusion of water in a confined space is exploited to produce images of axonal fiber tracts (white matter tracts).
Advantages:
> Physiological and quantitative analysis for early stage disease.
> Provides image of major tracts.
Characteristics: > spatial resolution: high > temporal resolution: low > functional: no > invasive: no
functional magnetic resonance imaging (fMRI)
definition / advantages / disadvantages / characteristics
Magnetic resonance imaging that detects changes in blood flow and therefore identifies regions of the brain that are particularly active during a given task.
Advantages:
> It reflects activity of different parts of the brain – Synaptic inputs and local processing.
> Very good details.
> Shows correlation between brain activity and cognitive activity.
> Differentiation of diseased tissue from normal tissues is better than with other imaging such as X-ray, CT and ultrasound.
Disadvantages:
> It reflects brain activity indirectly -> Signals show relative neuronal activity.
-> Its signal analysis must always be compared to reference neuronal activity.
> Presence of metal in body may affect a portion of the MRI image.
> It cannot prove that the brain activity caused cognitive activity.
Characteristics: > spatial resolution: high > temporal resolution: low > functional: yes > invasive: no
electroencephalography (EEG)
definition / advantages / disadvantages / characteristics
Scanning technique that detects electrical activity in our brain using small, metal discs (electrodes) attached to the scalp.
Advantages:
> Continuous EEG monitoring provides dynamic information that allows for the early detection of functional changes – May improve clinical outcome.
> One of the main diagnostic tests for epilepsy.
> Can also diagnose other brain disorders – Tumors, injury, dysfunction, inflammation, stroke and sleep disorders.
> Safe, no discomfort and painless
> Short procedure – Up to 1 hour.
Disadvantages:
> If we use a sedative, it will take time for the medication to begin to wear off.
Characteristics: > spatial resolution: low > temporal resolution: high > functional: yes > invasive: no
psychophysiological recording methods
Methods of recording physiological activity from the surface of the human body.
EMG & EOG
electromyogram (EMG)
> An electrical potential recorded from an electrode placed on or in a muscle.
electrooculogram (EOG)
> An electrical potential from the eyes, recorded by means of electrodes placed on the skin around them; detects eye movements.
lesion methods
More direct technique, commonly employed on laboratory animals. In lesion methods, a part of the brain is removed, damaged, or destroyed in order to assess the behaviour of the subject to determine the functions of the lesioned structure.
> Stereotaxis surgery:
Means by which experimental devices are positioned in the depths of the brain. It has two requirements:
- Stereotaxic atlas: Used to locate brain structures
- Stereotaxic instrument: It consists of a head holder and an electrode holder
characteristics: > spatial resolution: intermediate > temporal resolution: intermediate > functional: yes > invasive: yes
aspiration lesions
> Method of choice when lesion is to be made in area of cortical tissue that is accessible to the eyes and instruments of the surgeon.
Cortical tissue is drawn off by suction through a pipette.
-> White matter is resistant to suction – Surgeon has to peel off the layers of cortical tissue from the surface of the brain -> White matter and major blood vessels undamaged.
