Imaging of the Brain Flashcards
Four ways to image brain activity
Brain stimulation, electrical recording, structural imaging, and dynamic imaging
Brain stimulation
- you stimulate a neuron
- inter-cranial brain stimulation, and transcranial magnetic stimulation (TMS)
Electrical recording
- you record information of a neuron
- single cell recording, EEG, ERP, and MEG
Structural imaging
- looking at the structure of the brain
- Conventional radiography, pneumoencephalography, angiography, and CT
Dynamic Imaging
- you look at what a brain does, as it is doing it
- we are able to look at what is happening, where it is happening and how much activity is going on as it is happening
- PET, MRI, fMRI, MRS, and DTI
Single Cell Recording
- looks at one single neuron
- probes an electrode into the skull, into the particular neuron. After you wait for an action potential (i.e. electrical activity)
- invasive and requires precision
- usually done on animals
Electroencephalography (EEG)
- uses a cap of electrodes to look at multiple neurons in the brain
- places cap on head, and monitors different action potentials across the brain
- usually an on-going recording until the specific activity is done being performed
- can tell us when the patient is happy, sad, sleepy, or in a coma (i.e. the drowsier an individual feels, the larger the waveform)
- can be used to diagnose epilepsy (can tell us where and when it started)
Event-related Potential
- uses a cap of electrodes to look at multiple neurons in the brain
- presents a specific stimuli repeatedly, and recorded responses are averaged
- we are able to tell the location and time of processing
- can also tell us the readiness potential (electrical activity showing us the time before she/he is about to give a motor response)
Magnetoencephalography (MEG)
- uses magnets
- detects electrical activity around the neurons
- instead of producing in waveform it produces a map to detect areas of greater magnetic intensity
- basically how closely connected the lines are means how intensely active that part of the brain is
Intracranial Brain Stimulation
- otherwise known as Deep Brain Stimulation (DBS)
- electrodes are implanted into the brain to stimulate tissue
- unlike single cell recording, we will be looking at number of different neurons
- this procedure is extremely invasive, and so is only used when absolutely necessary
- it is used to treat extremely difficult diseases, like Parkinson’s
Transcranial Magnetic Stimulation (TMS)
- uses a magnetic stimulator
- transcranial = around and on top of skull
- stimulator sends a current through the cord/wire to the TMS coil, where a magnetic field is generated around the coil. The coil is then moved around the skull - when it gets closer to the neurons, the magnetic field causes the neurons to fire
- noninvasive approach
Conventional Radiography
- basically an X-ray
- X-rays are absorbed to different degrees by different tissues
- helps with seeing fractures and abnormalities
Pneumonencephalography
- a form of X-ray that helps us determine any abnormalities in the ventricles
- a patient is asked to lie down, remove CSF and replace it with air, as the patient sits up, since air is lighter than water the air moves to the top and hence into the ventricles
- invasive procedure
Angiography
- a form of X-ray imaging technique that produces an image of blood vessels
- a substance that absorbs X-rays is injected into the bloodstream and then flows to the brain
Computed Tomography (CT)
- a form of X-ray imaging technique in which a bunch of 2D images are taken from various angles and then these images are computed together to form a 3D image of the brain
Hemiparesis
- when half of their body isn’t functioning properly or is completely paralyzed
PET scan
- a radioactive substance is injected into the bloodstream to indirectly measure neural activity through imaging of blood flow in the brain
How does PET scan work?
Radioactive substance is injected into the bloodstream. Since it is extremely unstable, when it gets into the body, the substance breaks off into positrons. These positrons then join freely floating electrons which annihilates the positrons. Photons are released which can be picked up by the machine
Magnetic Resonance Imaging (MRI)
basically involves the aligning of hydrogen atoms with a magnetic field. Hydrogen atoms contain a North and South pole, which are usually not aligned. The first magnetic field causes the poles to align. They are then placed in a second magnetic field which acts like a pulse (i.e turns on and off). This magnetic field causes the poles to turn in a different direction. MRI measures the relaxation rate (i.e. time it takes for the poles to re-align with the first magnetic field once the pulse is turned off). This rate can then be transformed into an image.
Relaxation rate
term used to describe what is looked for in MRI. In particular, the relaxation rate is the time it takes for hydrogen atoms to re-align with the first magnetic field after the magnetic pulse is turned off for the second magnet. This rate is different for different tissues.
fMRI
When neurons are active in the brain, oxygen will be used up, and so more oxygen will be carried into that particular area. This imaging technique observes the change in the ratio of oxyhemoglobin and deoxyhemoglobin. In resting state, the amount of deoxyhemoglobin and oxyhemoglobin would be the same, but in an activated state, when the neurons are active, there will be an increase in deoxyhemoglobin and a rush of oxyhemoglobin. This difference is what changes the signal that is detected by the fMRI machine.
MRS
- technique used to detect the types of compounds present in different tissues
- produces a graph rather than an image
- different compounds have different waveforms, and so by the waveform you can establish what compound is present in the tissue
DTI
is an MRI method that images fiber pathways by looking at the direction of water molecule movement. Water moves in the brain, and when it comes towards an axon (which acts like a wall) it moves in that direction which is how we are able to see the pathways.
