Biology subjects

Kalaboukhov, A.

Publications and source records attributed to Kalaboukhov, A..

3 recordsLinked to original sources

bioRxiv2019

Detection of interictal epileptiform discharges:A comparison of on-scalp MEG and conventional MEGmeasurements

Magnetoencephalography (MEG) is an important part of epilepsy evaluations because of its unsurpassed ability to detect interictal epileptiform discharges (IEDs). This ability may be improved by next-generation MEG sensors, where sensors are placed directly on the scalp instead of in a fixed-size helmet, as in todays conventional MEG systems. In order to investigate the usefulness of on-scalp MEG measurements we performed the first-ever measurements of on-scalp MEG on an epilepsy patient. The measurement was conducted as a benchmarking study, with special focus on IED detection. An on-scalp high-temperature SQUID system was utilized alongside a conventional low-temperature "in-helmet" SQUID system. EEG was co-registered during both recordings. Visual inspection of IEDs in the raw on-scalp MEG data was unfeasible why a novel machine learning-based IED-detection algorithm was developed to guide IED detection in the on-scalp MEG data. A total of 24 IEDs were identified visually from the conventional in-helmet MEG session (of these, 16 were also seen in the EEG data; eight were detected only by MEG). The on-scalp MEG data contained a total of 47 probable IEDs of which 16 IEDs were co-registered by the EEG, and 31 IEDs were on-scalp MEG-unique IEDs found by the IED detection algorithm. We present a successful benchmarking study where on-scalp MEG are compared to conventional in-helmet MEG in a temporal lobe epilepsy patient. Our results demonstrate that on-scalp MEG measurements are feasible on epilepsy patients, and indicate that on-scalp MEG might capture IEDs not seen by other non-invasive modalities.

neuroscience↗

bioRxiv2019

Sensor localization using magnetic dipole-like coils: A method for highly accurate co-registration in on-scalp MEG

Source modelling in magnetoencephalography (MEG) requires precise co-registration of the sensor array and the anatomical structure of the measured individuals head. In conventional MEG, positions and orientations of the sensors relative to each other are fixed and known beforehand, requiring only localization of the head relative to the sensor array. Since the sensors in on-scalp MEG are positioned on the scalp, locations of the individual sensors depend on the subjects head shape and size. The positions and orientations of on-scalp sensors must therefore be measured at every recording. This can be achieved by inverting conventional head localization, localizing the sensors relative to the head - rather than the other way around.\n\nIn this study we present a practical method for localizing sensors using magnetic dipole-like coils attached to the subjects head. We implement and evaluate the method in a set of on-scalp MEG recordings using a 7-channel on-scalp MEG system based on high critical temperature superconducting quantum interference devices (high-Tc SQUIDs). The method provides accurate estimates of individual sensor positions and orientations with short averaging time ([≤] 2 mm and < 3 degrees, respectively, with 1-second averaging), enabling continuous sensor localization. Calibrating and jointly localizing the sensor array can further improve the localization accuracy (< 1 mm and < 2.5 degrees, respectively, with 1-second coil recordings).\n\nWe demonstrate source localization of on-scalp recorded somatosensory evoked activity based on co-registration with our method. Equivalent current dipole fits of the evoked responses corresponded well (within 5.3 mm) with those based on a commercial, whole-head MEG system.

neuroscience↗

bioRxiv2019

A 7-channel high-Tc SQUID-based on-scalp MEG system

Due to their higher operating temperature, high-Tc superconducting quantum interference devices (SQUIDs) require less thermal insulation than the low-Tc sensors that are utilized in commercial magnetoen-cephalography (MEG) systems. As a result, they can be placed closer to the head, where neuromagnetic fields are higher and more focal, potentially leading to higher spatial resolution. The first such on-scalp MEG measurements using high-Tc SQUIDs have shown the potential of the technology. In order to be useful for neuroscience and clinical applications, however, multi-channel systems are required. Herein, we present a 7-channel on-scalp MEG system based on high-Tc SQUIDs. The YBCO SQUID magnetometers are arranged in a dense, head-aligned hexagonal array inside a single, liquid nitrogen-cooled cryostat. The spacing between the magnetometers and the head is adjustable down to 1 mm. The sensors are side-mounted on the cryostat that is mounted on an articulated armature for recordings on arbitrary head locations of a seated subject. We demonstrate white noise levels of 50-130 fT/Hz1/2 at 10 Hz, sensor-to-sensor crosstalk values of <0.6%, and single-fill operation times of 16 hours. We validate the system with MEG recordings of visual alpha modulation and auditory evoked fields. The system is thus useful for densely and sensitively sampling neuromagnetic fields over any[~] 10 cm2 patch of the scalp surface over the course of a day.

neuroscience↗