It is a branch of medical imaging that concentrates on the brain and is used to diagnose disease and assess the health of the brain. It can also be useful in the study of the brain, how it works, and how different activities affect the brain.
NeuroImaging includes the use of various techniques to either directly or indirectly image the structure function/phamacology of the nervous system. It falls into two categories: structural imaging and functional imaging.
Structural imaging deals with the structure of the nervous system and the diagnosis of intracranial diseases. As for functional imaging, is used to diagnose metabolic diseases to research neurological and cognitive phycology.
Neuroimaging Techniques
Electroencephalography (EEG) - Technique used to record brain's spontaneous electrical activity. It uses non-invasive methods by placing multiple electrodes along the scalp and is often used to diagonose certain brain problems such as Epilepsy.
Magnetoencephalography (MEG) - Functional neuroimaging tecnique for mapping brain activity by recording magnetic fields that uses very sensitive magnetometers
Electrocoticography (ECoG) - Brain mapping tecnique that in practice uses electrods that are place directly on the exposed surface of the brain.
Magnetic Resonance Imaging (MRI) - Medical imaging tecnique used in radiology to investigate the anatomy and physiology of the body in both health and disease.
Positron Emission Tomography (PET) - Functional imaging tecnique that produces three dimensional image of functional processes in the body.
Functional Near-Infrared Spectroscopy (fNIR) - Spectroscopic method that uses the near-infrared region of the electromagnetic spectrum for medical diagnostic such as blood sugar and pulse oximetry.
MEG can be applied by resorting to both non-invasive and semi-invasive techniques such as:
- Superconducting Quantum Interference Devices (SQUIDS):
Non-Invasive technique based on very sensitive magnetometer used to measure extremely sensitive magnetic fields based on superconducting loops that are based on Josephoson junctions that are sensitive enough to measure fields as low as 5 aT (attoTesla).
This technique Has a high acquisition rate which is higher than the highest temporal frequency of interest in the signals emitted by the brain, and a good temporal resolution.
- Spin Exchange Relaxation Free Magnetometer (SERF):
It is non-invasive technique still being studied, that uses lasers in order to detect the interaction between akali metal atoms in a vapor and magnetic fields. In some cases can exceed performances of SQUID detectors of equivalent sizes.
However, SERF techniques can only operate near zero magnetic fields and the sensor vapor cell must be heated.
- Magnetoresistive Sensors Integrated in Micromachined Probe Needles:
Semi-Invasive technique that combines an electrophysiological system with a magnetoresistive chip to measure the magnetic field created by the synaptic/action potential currents. The chip, with 15 spin valve sensors, was designed to be integrated in a recording chamber for submerged mice brain slices used for synaptic potential measurements.
Even though it was developed for studying mice brains, it presents itself with the ability to measure magnetic fields as low as nT (nanoTesla) and for that reason is a technique that should be further studied and developed for human brain study.
ECoG
Electrocorticography (ECoG), or intracranial EEG (iEEG), uses electrodes placed directly on the exposed surface of the brain. The sensors arrays typically consist of 16 electrodes, disposed in a matrix. The grids are transparent and flexible. Standard spacing between the electrodes is 10 mm. In order to access the cortex, a surgeon must first perform a craniotomy. The invasive technique of ECoG provides brain signals that have a high signal-to-noise ratio (SNR) and high spatial and temporal resolution. Most of this information is captured in the frequencies between 70 Hz and 110 Hz.
Innovation
ECoG uses new invasive techniques and sensors such as:
- Wireless ECoG:
One problem of traditional ECoG is the large number of wires required to acquire the signals. The solution is to use a wireless multiplexing system. This system has 16 sensors, a rechargeable battery of 20 mA, and a RF antenna. The system was tested in a mouse on laboratory. The prototype for humans being developed by Neurotech.
- Micro-ECoG:
One of the disadvantages of the traditional system is that it has a low resolution (10 mm) and that the implants occupy a large volume. One solution is to use a micro-ECoG implants, which is thinners. This system has been developed at the University of Utah and 16 individual microelectrodes occupy the space of one traditional electrode. The main advantage is the increase in spatial resolution.
- Flexibles implants:
Some of the sensors are made from silicon, become degraded in the brain and must be replaced. The new sensor will be made of a flexible polymer and have 252-channel. Its size is approximately 35 mm by 60 mm and it is designed to cover large parts of a hemisphere. The system has tested in a monkey’s cortex.