Objective: Acoustoelectric Brain Imaging (ABI) is a potential method for mapping brain electrical activity with high spatial resolution (millimeter). To resolve the key issue for eventual realization of ABI, testing that recorded acoustoelectric (AE) signal can be used to decode intrinsic brain electrical activity, the experiment of living rat SSVEP measurement with ABI is implemented. Method: A 1-MHz ultrasound transducer is focused on the visual cortex of anesthetized rat. With visual stimulus, the electroencephalogram and AE signal are simultaneously recorded with Pt electrode. Besides, with FUS transducer scanning at the visual cortex, corresponding AE signals at different spatial positions are decoded and imaged. Results: Consistent with the directly measured SSVEP, decoded AE signal presents a clear event-related spectral perturbation (ERSP). And, decoded AE signal is of high amplitude response at the base and harmonics of the visual stimulus frequency. What's more, for timing signal, a significant positive amplitude correlation is observed between decoded AE signal and simultaneously measured SSVEP. In addition, the mean SNRs of SSVEP and decoded AE signal are both significantly higher than that of background EEG. Finally, with one fixed recording electrode, the active area with an inner diameter of 1mm is located within the 4 mm×4 mm measurement region. Conclusion: Experimental results demonstrate that the millimeter-level spatial resolution SSVEP measurement of living rat is achieved through ABI for the first time. Significance: This study confirms that ABI should shed light on high spatiotemporal resolution neuroimaging.

In this paper, wafer-scale dense and meosoporous TiO ₂ films are fabricated via spin-coating and thermal treatment. A photo-curable resin, acrylated polytitanoxane tetramer (Ti-resin), is synthesized as the precursor of TiO ₂ to deposit dense films. The refractive index of TiO ₂ films at 500 nm is tuned from 2.17 (dense) to 1.49 (porous) by changing film porosity via adding different amount of polystyrene (PS) to the precursor solvent. A reactive compatibilizer containing one mercapto group and three benzyl rings is synthesized to reduce phase separation and prevent film crack of porous films during the calcinations. The deposition protocol is optimized to prevent infiltration of dense TiO ₂ layers into porous TiO ₂ layers. Film thicknesses of both dense and porous TiO ₂ films can be linearly tuned by changing deposition number. All-TiO ₂ 1D photonic crystals with different structural colors are successfully fabricated on quartz and silicon wafers with reflectivity of at least 90%, covering the spectrum from 400 to 800 nm.

Objective: Based on the acoustoelectric (AE) effect, transcranial acoustoelectric brain imaging (tABI) is of potential for brain functional imaging with high temporal and spatial resolution. With nonlinear and non-steady-state, brain electrical signal is microvolt level which makes the development of tABI more difficult. This study demonstrates for the first time in vivo tABI of different steady-state visual stimulation paradigms. Method: To obtain different brain activation maps, we designed three steady-state visual stimulation paradigms, including binocular, left eye and right eye stimulations. Then, tABI was implemented with one fixed recording electrode. And, based on decoded signal power spectrum (tABI-power) and correlation coefficient between steady-state visual evoked potential (SSVEP) and decoded signal (tABI-cc) respectively, two imaging methods were investigated. To quantitatively evaluate tABI spatial resolution performance, ECoG was implemented at the same time. Finally, we explored the performance of tABI transient imaging. Results: Decoded AE signal of activation region is consistent with SSVEP in both time and frequency domains, while that of the nonactivated region is noise. Besides, with transcranial measurement, tABI has a millimeter-level spatial resolution (< 3mm). Meanwhile, it can achieve millisecond-level (125ms) transient brain activity imaging. Conclusion: Experiment results validate tABI can realize brain functional imaging under complex paradigms and is expected to develop into a brain functional imaging method with high spatiotemporal resolution.

Acoustoelectric brain imaging (ABI) is a potentially noninvasive neuroimaging method with high spatiotemporal resolution. Until now, ABI has been limited to intracerebral measurement, which restricts its application in brain science research. This paper firstly implements in vivo brain activated sources measurement with transcranial ABI. A binocular steady-state visual stimulation paradigm was designed and presented to living rats. Brain electrical signal and acoustoelectric (AE) signal of multi-cortexes were simultaneously detected by intracerebral and transcranial ABI. The AE signal measured by transcranial ABI was then decoded and imaged. The power-enhancement and SNR of transcranial AE signal were 15.51dB and 39.04dB, which were sufficient to ensure its accuracy and distinguishability. With different visual stimuli and pulse repetition frequencies, the decoded AE (dec-AE) signals were always significantly consistent with SSVEP in spectrum response, power change, and waveform change. Within the 3mm × 3mm and 5mm × 3mm scan areas, brain activation areas were located in the visual cortex, mapped by the amplitudes of multi-position dec-AE signals. The diameters of the activation regions were less than 1.5mm. In addition, the transient strength change of the activated area was revealed, which is consistent with the temporal evolution of SSVEP. Experiment results demonstrate that ABI is able to transcranial measure brain electrical signal and locate brain activation source with milli meter spatial and millisecond temporal resolution. This study extends ABI to transcranial measurement, which makes a critical step forward towards the noninvasive detection of high spatiotemporal brain electrical activity.

Objective. Acoustoelectric brain imaging (ABI) is a potential noninvasive electrophysiological neuroimaging method with high spatiotemporal resolution. At the focal spot of the focused ultrasound, with the couple of acoustic and electric fields, high-frequency acoustoelectric (HF AE) signal is generated. Because the brain is a volume conductor, HF AE signal can be detected in other brain cortex. The processing of HF AE signal is critical for improving decoding precision, further improving the spatial resolution performance of ABI. This study investigates the processing network of HF AE signal in the living rat brain. Approach. When HF AE generated on the left primary visual cortex (V1-L), low-frequency (LF) electroencephalography and HF AE signals on different cortex were recorded at the same time. Firstly, AE signal on different sides of the brain cortex were compared, including prefrontal cortex (FrA) and primary somatosensory cortex (S1FL). Then, we constructed and analyzed functional networks of two signals. Main results. In the same cortex, HF AE signal on the right side had stronger intensity. And compared with LF networks, HF AE network had larger global efficiency and shorter characteristic path length, denoting the stronger processing and transmission of AE signal. Additionally, in HF AE network, the node had significantly increased local properties and the connection were concentrated in the occipital lobe, reflecting the occipital lobe plays an important role in the processing. Significance. Experiment results demonstrate that, compared with LF network, HF AE network is more efficient and had stronger transmission capabilities. And the connection of HF AE network is concentrated in the occipital lobe. This work preliminarily reveals the HF AE signal processing, which is significant for improving the ABI quality and provides a new insight for understanding the brain HF signal.

Based on the acoustoelectric (AE) effect, acoustoelectric brain imaging (ABI) is a potential neuroimaging method that can be used to map brain electrical activity with high spatiotemporal resolution. Brain electrical activity is non-stationary, with time-varying frequency and amplitude. However, the current ABI mainly focuses on the current source with stationary current source characteristics. To make a step towards developing ABI as a clinical imaging technique, time-varying ABI with non-stationary current source characteristics is evaluated and verified. A decoded algorithm based on wavelet transform was adopted for AE signal to extract non-stationary current sources characteristics. To test the performance of time-varying ABI, three phantom experiments were designed with a time-varying current source, including one source with time-varying frequency, one source with time-varying amplitude, and two sources of different amplitudes with time-varying frequency. For the experiment of source with time-varying frequency, the time-frequency diagrams of the decoded signal presented clear power enhancements at specific frequencies, which was consistent with the frequency change of the current source. For the experiment of source with time-varying amplitude, the correlation coefficient between the decoded signal and the current source was 0.90. In addition, the SNRs of the decoded signal of current source positions were significantly higher than that of non-current source positions. Finally, the positions of sources with time-varying characteristics could be accurately located at different moments. These results validate the feasibility of time-varying ABI with non-stationary current source characteristics, which make a key step toward its application in neuroimaging.