What is electroencephalography (EEG)?
Non-invasive test of brain electrical activity
Measures small changes in voltage within the cells when active
Direct measure of brain function
Brain cells are always active and communicate via electrical pulses
Better temporal resolution than CT, MRI, and PET (does not replace CT or MRI)
Limited spatial resolution (signals distorted by CSF)
Directly measures brain activity through electrodes
What is magnetoencephalography (MEG)?
Non-invasively test that records and analyses the magnetic fields produced by electrical currents in the brain
Similar to EEG but uses magnetic fields instead of electrical potentials
Maps the location of neuromagnetic brain activity
Direct measure of brain function
No machine noise (extraneous noise will interfere with the test)
Complementary with MRI image to locate specific areas of activity
Excellent spatial resolution and good temporal resolution
Signals are extremely small, making the signal easily obscured
Require superconducting sensors to amplify the signal and liquid helium to cool the sensors
Used in neurological or psychiatric disorders
Usually used in research only
What is ultrasound?
Non-invasive test using high frequency sound waves to create real-time images of organs, tissues, or blood vessels
A transducer/probe is used to generate sound waves that are reflected by the tissues to produce an image
Used for visualizing subcutaneous body structures and internal organs for possible pathology
Not good for imaging bone, or tissues underlying bone
Not good for imaging air (i.e. Lungs, Mastoid air cells)
Is patient sitting upright for MEG?
Yes
Is MEG usually used in research only?
Yes
What can be measured with ultrasound?
Tendons, ligaments, muscles, cartilage, joints, blood vessels, organs, etc.
How do ultrasounds work
Probe converts electrical current to high-frequency sound waves
Piezoelectric ceramic material generates the sound waves
Ultrasound waves refer to acoustical waves above human hearing (>20 kHz)
Medical ultrasonography is typically between 2MHz and 10MHz
Piezoelectric ceramic transducer EMITS ultrasound waves through tissues of the body
Transducer DETECTS ultrasound echoes reflected back from the boundaries of tissue in the path of the beam
Echoes received by the transducer are converted to electrical current
A computer analyzes the electrical energy to create images in real time
What is the doppler effect?
In ultrasonography
Shows blood moving through blood vessels (not just the boundaries)
Measures sound waves that are reflected from moving objects, such as red blood cells
Show speed and direction of blood flow in real time
Blood moving towards or away from the transducer has a different frequency
Different color based on direction of blood flow
