scholarly journals Low-frequency dominant electrical conductivity imaging of in vivo human brain using high-frequency conductivity at Larmor-frequency and spherical mean diffusivity without external injection current

NeuroImage ◽  
2021 ◽  
Vol 225 ◽  
pp. 117466
Author(s):  
Geon-Ho Jahng ◽  
Mun Bae Lee ◽  
Hyung Joong Kim ◽  
Eung Je Woo ◽  
Oh-In Kwon
Keyword(s):  
Electrical Conductivity ◽  
Human Brain ◽  
High Frequency ◽  
Mean Diffusivity ◽  
Low Frequency ◽  
Larmor Frequency ◽  
Injection Current ◽  
Spherical Mean ◽  
External Injection

scholarly journals A THREE-PHASE INDUCTIVE SENSOR FOR IN VIVO MEASUREMENT OF ELECTRICAL ANISOTROPY OF BIOLOGICAL TISSUES

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Yukio Kosugi ◽  
Tadashi Takemae ◽  
Hiroki Takeshima ◽  
Atsushi Kudo ◽  
Kazuyuki Kojima ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
High Frequency ◽  
Reference Signal ◽  
Biological Tissues ◽  
Electrical Anisotropy ◽  
Conductivity Anisotropy ◽  
In Vivo Measurement ◽  
Surgical Operations

Biological tissue will have anisotropy in electrical conductivity, due to the orientation of muscular fibers or neural axons as well as the distribution of large size blood vessels. Thus, the in vivo measurement of electrical conductivity anisotropy can be used to detect deep-seated vessels in large organs such as the liver during surgeries. For diagnostic applications, decrease of anisotropy may indicate the existence of cancer in anisotropic tissues such as the white matter of the brain or the mammary gland in the breast. In this paper, we will introduce a new tri-phase induction method to drive rotating high-frequency electrical current in the tissue for the measurement of electrical conductivity anisotropy. In the measurement, three electromagnets are symmetrically placed on the tissue surface and driven by high-frequency alternative currents of 0 kHz, modulated with 1 kHz 3-phase signals. In the center area of three magnets, magnetic fields are superimposed to produce a rotating induction current. This current produces electrical potentials among circularly arranged electrodes to be used to find the conductivity in each direction determined by the electrode pairs. To find the horizontal and vertical signal components, the measured potentials are amplified by a 2ch lock-in amplifier phase-locked with the 1 kHz reference signal. The superimposed current in the tissue was typically 45 micro Amperes when we applied 150 micro Tesla of magnetic field. We showed the validity of our method by conducting in vitro measurements with respect to artificially formed anisotropic materials and preliminary in vivo measurements on the pig’s liver. Compared to diffusion tensor MRI method, our anisotropy sensor is compact and advantageous for use during surgical operations because our method does not require strong magnetic field that may disturb ongoing surgical operations.

scholarly journals High frequency photoacoustic detection of red blood cell aggregation

2021 ◽  
Author(s):  
Fayruz Kibria
Keyword(s):  
Blood Cell ◽  
Red Blood Cell ◽  
High Frequency ◽  
Photoacoustic Imaging ◽  
Low Frequency ◽  
Cell Aggregation ◽  
Center Frequency ◽  
Photoacoustic Detection ◽  
Rbc Aggregation

Red blood cell (RBC) aggregation was correctly reported in early 1768 as the increased deposition for blood to form spots of red in pathological conditions. However only recently have there been advances in technology to allow possible detection of RBC aggregation in vivo. Photoacoustic imaging (PA) shows a promising future in the detection of simultaneous in vivo RBC aggregation and oxygen saturation. This work presents, for the first time, the results of investigating aggregated RBCs using high frequency (> 20 MHz) photoacoustic (PA) imaging. Aggregation was induced by using 3% w/v concentration of 70 kDa Dextran and PA measurements were taken by a 25 MHz center frequency transducer. It was found that the spectral slope (SS) of the photoacoustic signals decreased by ~0.25 dB/MHz with RBC aggregation. The results are consistent with the findings of low frequency PA RBC aggregation study which also reported decrease in SS with increased aggregation.

scholarly journals A statistical framework to assess cross-frequency coupling while accounting for confounding analysis effects

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Jessica K Nadalin ◽  
Louis-Emmanuel Martinet ◽  
Ethan B Blackwood ◽  
Meng-Chen Lo ◽  
Alik S Widge ◽  
...  
Keyword(s):  
High Frequency ◽  
Statistical Power ◽  
Brain Activity ◽  
Low Frequency ◽  
Modeling Framework ◽  
Frequency Coupling ◽  
Phase Amplitude ◽  
Cross Frequency Coupling ◽  
Frequency Phase

Cross frequency coupling (CFC) is emerging as a fundamental feature of brain activity, correlated with brain function and dysfunction. Many different types of CFC have been identified through application of numerous data analysis methods, each developed to characterize a specific CFC type. Choosing an inappropriate method weakens statistical power and introduces opportunities for confounding effects. To address this, we propose a statistical modeling framework to estimate high frequency amplitude as a function of both the low frequency amplitude and low frequency phase; the result is a measure of phase-amplitude coupling that accounts for changes in the low frequency amplitude. We show in simulations that the proposed method successfully detects CFC between the low frequency phase or amplitude and the high frequency amplitude, and outperforms an existing method in biologically-motivated examples. Applying the method to in vivo data, we illustrate examples of CFC during a seizure and in response to electrical stimuli.

scholarly journals Minimal basilar membrane motion in low-frequency hearing

2016 ◽  
Vol 113 (30) ◽  
pp. E4304-E4310 ◽  
Author(s):  
Rebecca L. Warren ◽  
Sripriya Ramamoorthy ◽  
Nikola Ciganović ◽  
Yuan Zhang ◽  
Teresa M. Wilson ◽  
...  
Keyword(s):  
High Frequency ◽  
Music Perception ◽  
Basilar Membrane ◽  
Stimulus Frequency ◽  
Low Frequency ◽  
Laser Interferometry ◽  
Outer Hair Cells ◽  
Sound Stimulation

Low-frequency hearing is critically important for speech and music perception, but no mechanical measurements have previously been available from inner ears with intact low-frequency parts. These regions of the cochlea may function in ways different from the extensively studied high-frequency regions, where the sensory outer hair cells produce force that greatly increases the sound-evoked vibrations of the basilar membrane. We used laser interferometry in vitro and optical coherence tomography in vivo to study the low-frequency part of the guinea pig cochlea, and found that sound stimulation caused motion of a minimal portion of the basilar membrane. Outside the region of peak movement, an exponential decline in motion amplitude occurred across the basilar membrane. The moving region had different dependence on stimulus frequency than the vibrations measured near the mechanosensitive stereocilia. This behavior differs substantially from the behavior found in the extensively studied high-frequency regions of the cochlea.

scholarly journals Low and high frequency intracranial neural signals match in the human associative cortex

2022 ◽  
Author(s):  
Corentin Jacques ◽  
Jacques Jonas ◽  
Sophie Colnat-Coulbois ◽  
Louis Maillard ◽  
Bruno Rossion
Keyword(s):  
Human Brain ◽  
High Frequency ◽  
Brain Function ◽  
Large Scale ◽  
Temporal Cortex ◽  
High Signal ◽  
Associative Cortex ◽  
The Relationship ◽  
Intracranial Recordings

In vivo intracranial recordings of neural activity offer a unique opportunity to understand human brain function. Intracranial electrophysiological (iEEG) activity related to sensory, cognitive or motor events manifests mostly in two types of signals: event-related local field potentials in lower frequency bands (<30 Hz, LF) and broadband activity in the higher end of the frequency spectrum (>30 Hz, High frequency, HF). While most current studies rely exclusively on HF, thought to be more focal and closely related to spiking activity, the relationship between HF and LF signals is unclear, especially in human associative cortex. Here we provide a large-scale in-depth investigation of the spatial and functional relationship between these 2 signals based on intracranial recordings from 121 individual brains (8000 recording sites). We measure selective responses to complex ecologically salient visual stimuli – human faces - across a wide cortical territory in the ventral occipito-temporal cortex (VOTC), with a frequency-tagging method providing high signal-to-noise ratio (SNR) and the same objective quantification of signal and noise for the two frequency ranges. While LF face-selective activity has higher SNR across the VOTC, leading to a larger number of significant electrode contacts especially in the anterior temporal lobe, LF and HF display highly similar spatial, functional, and timing properties. Specifically, and contrary to a widespread assumption, our results point to nearly identical spatial distribution and local spatial extent of LF and HF activity at equal SNR. These observations go a long way towards clarifying the relationship between the two main iEEG signals and reestablish the informative value of LF iEEG to understand human brain function.

scholarly journals Phase-amplitude coupling supports phase coding in human ECoG

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Andrew J Watrous ◽  
Lorena Deuker ◽  
Juergen Fell ◽  
Nikolai Axmacher
Keyword(s):  
Human Brain ◽  
High Frequency ◽  
Low Frequency ◽  
Phase Coding ◽  
Neural Representations ◽  
Simultaneous Acquisition ◽  
Categorical Information ◽  
High Frequency Activity ◽  
Phase Amplitude ◽  
Intracranial Recordings

Prior studies have shown that high-frequency activity (HFA) is modulated by the phase of low-frequency activity. This phenomenon of phase-amplitude coupling (PAC) is often interpreted as reflecting phase coding of neural representations, although evidence for this link is still lacking in humans. Here, we show that PAC indeed supports phase-dependent stimulus representations for categories. Six patients with medication-resistant epilepsy viewed images of faces, tools, houses, and scenes during simultaneous acquisition of intracranial recordings. Analyzing 167 electrodes, we observed PAC at 43% of electrodes. Further inspection of PAC revealed that category specific HFA modulations occurred at different phases and frequencies of the underlying low-frequency rhythm, permitting decoding of categorical information using the phase at which HFA events occurred. These results provide evidence for categorical phase-coded neural representations and are the first to show that PAC coincides with phase-dependent coding in the human brain.

scholarly journals High frequency photoacoustic detection of red blood cell aggregation

2021 ◽  
Author(s):  
Fayruz Kibria
Keyword(s):  
Blood Cell ◽  
Red Blood Cell ◽  
High Frequency ◽  
Photoacoustic Imaging ◽  
Low Frequency ◽  
Cell Aggregation ◽  
Center Frequency ◽  
Photoacoustic Detection ◽  
Rbc Aggregation

Red blood cell (RBC) aggregation was correctly reported in early 1768 as the increased deposition for blood to form spots of red in pathological conditions. However only recently have there been advances in technology to allow possible detection of RBC aggregation in vivo. Photoacoustic imaging (PA) shows a promising future in the detection of simultaneous in vivo RBC aggregation and oxygen saturation. This work presents, for the first time, the results of investigating aggregated RBCs using high frequency (> 20 MHz) photoacoustic (PA) imaging. Aggregation was induced by using 3% w/v concentration of 70 kDa Dextran and PA measurements were taken by a 25 MHz center frequency transducer. It was found that the spectral slope (SS) of the photoacoustic signals decreased by ~0.25 dB/MHz with RBC aggregation. The results are consistent with the findings of low frequency PA RBC aggregation study which also reported decrease in SS with increased aggregation.

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