Frontiers of functional brain imaging

Modern neuroimaging techniques provide a wealth of information to study brain function, injury and disease. Clinical diagnosis of large-scale head injury is well-established using structural imaging tools such as x-ray computed tomography (CT) and magnetic resonance imaging (MRI). Technologies including functional MRI (fMRI), positron emission tomography (PET) and single-photon emission computed tomography (SPECT) may detect lesions on a finer scale and offer some insights into metabolic diseases. Highlighting differences in blood oxygen levels to infer brain activity has become a popular technique in dementia research.

MEG – Uniquely high temporal and spatial resolution

Unlike the imaging methods of the slow blood-oxygen response, electroencephalography (EEG) and magnetoencephalography (MEG) are direct measurements of the electrical activity of neurons in the brain on the timescale of milliseconds. They enable the study of rhythmic brain activity in real-time over a wide frequency range. MEG offers superior localisation to EEG and is clinically prescribed in a few countries for specific indications such as presurgical functional mapping of drug-resistant epilepsy and brain tumours.

The evidence for the clinical utility of MEG is compelling. It can provide non-invasive insight into the underlying brain activity and injury which no other method can.

Magnetic field sensors

The techniques of biomagnetism depend critically on the ability to measure tiny time-varying magnetic fields. YI is pioneering the development of quantum sensors to enable new applications.

HyQUIDs offer unique sensitivity to slow-wave biomarkers of brain injury

The HyQUID is a novel development of the superconducting quantum interference device (SQUID) with improved signal-to-noise performance and dynamic range. It is robust to environmental upset, has simplified calibration and superior low-frequency performance making it particularly sensitive to the slow-wave biomarkers of brain injury.

OPMs may enable compact devices

The emerging technology of the optically pumped magnetometer (OPM) promises to free measurements from bulky cooling apparatus. OPMs exploit the interaction of resonant light with atomic vapor to detect magnetic fields. Although outperformed by low-temperature devices, OPMs may eventually compete with high temperature superconductors to enable compact systems with fewer restrictions on subject movement.

Low noise, high speed electronics

The quantum sensors used in MEG collect magnetic signals as a result of neuronal activity and can sense signals as small as 10-15 Tesla—many orders of magnitude smaller than the earth’s magnetic field. Consequently, eliminating extraneous noise in electronics or cabling is of paramount importance.

York Instruments have designed a state-of-the-art set of control electronics to run their MEGSCAN MEG system. Modular, flexible and modern, this set of electronics allows York Instruments to expand MEG into hitherto untapped areas of clinical and research utility, exploring brain data in both ultra-low and ultra-high frequency bands. The modular electronics design in each of the sensor assemblies means interfaces are exchangeable allowing for futureproofing as new quantum sensors (eg OPMs) become commercially available.

Research laboratories looking into applications for quantum sensors from industrial, medical to outer space are working with York Instruments electronics to drive their devices. The ultra high speed ( currently at 81kHz at 24 bits) and low noise characteristics of our electronics design make them ideal for high spec sensor applications.

Hyperpolarization

The sensitivity of NMR and MRI techniques is very low. They exploit the fact that nuclei with the property of spin show a small magnetic signal in an external magnetic field. The signal depends on the small population differences between the direction of spin called polarization. Inside the 1.5T magnetic field of an MRI scanner the signal comes from a small polarization of just 1 in 200,000. In the earth's field of 50microTesla the polarisation is incredibly small at 1 in 10^8. This low sensitivity limits the practical routine use of MRI to long measurement times of the proton-spin signals from water and lipid tissues.

Hyperpolarizing, such that more spins line up together, gives bigger signals. MRI using hyperpolarized agents has begun to influence clinical imaging, for example the use of noble gases to reveal lung structure and 13C to observe prostate cancer metabolism. These are powerful yet arguably niche methods impractical for more widespread application.

ParaHydrogen-induced polarization is an emerging signal amplification technique with great potential. Unlike other methods it promises to deliver a wide range of benign, long-lived agents that are quick to prepare and with sufficient signal strength to observe metabolic function at low-magnetic field. It promises the sensitivity to studying disease models in real-time.