Towards optimal visual presentation design for hybrid EEG-fTCD brain-computer interfaces.

OBJECTIVE: In this paper, we introduce a novel hybrid brain-computer interface (BCI) system that measures electrical brain activity as well as cerebral blood velocity using electroencephalography (EEG) and functional transcranial Doppler ultrasound (fTCD) respectively in response to flickering mental rotation (MR) and flickering word generation (WG) cognitive tasks as well as a fixation cross that represents the baseline. This work extends our previous approach, in which we showed that motor imagery induces simultaneous changes in EEG and fTCD to enable task discrimination; and hence, provides a design approach for a hybrid BCI. Here, we show that instead of using motor imagery, the proposed visual stimulation technique enables the design of an EEG-fTCD based BCI with higher accuracy. APPROACH: Features based on the power spectrum of EEG and fTCD signals were calculated. Mutual information and support vector machines were used for feature selection and classification purposes. MAIN RESULTS: EEG-fTCD combination outperformed EEG by 4.05% accuracy for MR versus baseline problem and by 5.81% accuracy for WG versus baseline problem. An average accuracy of 92.38% was achieved for MR versus WG problem using the hybrid combination. Average transmission rates of 4.39, 3.92, and 5.60 bits min-1 were obtained for MR versus baseline, WG versus baseline, and MR versus WG problems respectively. SIGNIFICANCE: In terms of accuracy, the current visual presentation outperforms the motor imagery visual presentation we designed before for the EEG-fTCD system by 10% accuracy for task versus task problem. Moreover, the proposed system outperforms the state of the art hybrid EEG-fNIRS BCIs in terms of accuracy and/or information transfer rate. Even though there are still limitations of the proposed system, such promising results show that the proposed hybrid system is a feasible candidate for real-time BCIs.

A random phased-array for MR-guided transcranial ultrasound neuromodulation in non-human primates.

Transcranial focused ultrasound (FUS) is a non-invasive technique for therapy and study of brain neural activation. Here we report on the design and characterization of a new MR-guided FUS transducer for neuromodulation in non-human primates at 650 kHz. The array is randomized with 128 elements 6.6 mm in diameter, radius of curvature 7.2 cm, opening diameter 10.3 cm (focal ratio 0.7), and 46% coverage. Simulations were used to optimize transducer geometry with respect to focus size, grating lobes, and directivity. Focus size and grating lobes during electronic steering were quantified using hydrophone measurements in water and a three-axis stage. A novel combination of optical tracking and acoustic mapping enabled measurement of the 3D pressure distribution in the cortical region of an ex vivo skull to within ~3.5 mm of the surface, and allowed accurate modelling of the experiment via non-homogeneous 3D acoustic simulations. The data demonstrates acoustic focusing beyond the skull bone, with the focus slightly broadened and shifted proximal to the skull. The fabricated design is capable of targeting regions within the S1 sensorimotor cortex of macaques.

Transcranial focused ultrasound to the thalamus is associated with reduced extracellular GABA levels in rats.

OBJECTIVE: Transcranial focused ultrasound (FUS), with its ability to non-invasively modulate the excitability of region-specific brain areas, is gaining attention as a potential neurotherapeutic modality. The aim of this study was to examine whether or not FUS administered to the brain could alter the extracellular levels of glutamate and γ-aminobutyric acid (GABA), which are representative excitatory and inhibitory amino acid neurotransmitters, respectively. METHODS: FUS, delivered in the form of a train of pulses, was applied to the thalamus of Sprague-Dawley rats transcranially. Glutamate and GABA were directly sampled from the frontal lobe of the rat brain via a direct microdialysis technique before, during, and after the sonication. The dialysate concentrations were determined by high-performance liquid chromatography. RESULTS: The individual levels of the neurotransmitters sampled were normalized to the baseline level for each rat. In terms of the changes in extracellular glutamate levels, there was no difference between the FUS-treated group and the unsonicated control group. However, extracellular GABA levels started to decrease upon sonication and remained reduced (approximately 20% below baseline; repeated-measures ANOVA, p < 0.05, adjusted for multiple comparisons) compared to the control group. CONCLUSION: The ability to modulate region-specific brain activity, along with the present evidence of the ability to modulate neurotransmission, demonstrates the potential utility of FUS as a completely new non-invasive therapeutic modality.

Peroperative transcranial sonography for electrode placement into the targeted subthalamic nucleus of patients with Parkinson disease: technical note.

BACKGROUND: In the search for a better preoperative knowledge of the position of probes and electrodes, we assessed the feasibility and the usefulness of transcranial sonography during surgery for the implantation of stimulation electrodes into the subthalamic nucleus (STN) of patients with Parkinson's disease. METHODS: Transcranial sonography was carried out during stereotactic surgery in 8 patients with Parkinson's disease who had a suitable temporal bone window on the side receiving the electrode. Test stimulation parameters were 130 Hz, 0.1 ms, up to 0 to 4.5 V. RESULTS: The test probe with a diameter of 0.8 mm was visualized through the temporal preauricular window. The correct anatomic position of the electrode tip could be indirectly assessed thanks to the topographic relationship of the STN with the hyperechogenic substantia nigra and the nucleus ruber. The tip position of the final electrode was easily documented. A laterality of 10.5 to 11.5 mm, verified by teleradiographic ventriculography and plain films, was correlated with the best response of symptoms of Parkinson's disease to electrical impulses delivered to the STN. CONCLUSIONS: Transcranial sonography is easily feasible during stereotactic surgery. In combination with the clinical effects of electrostimulation on the symptoms of Parkinson's disease and with stereotactic x-ray images, it enables the assessment and the documentation of the correct position of implanted STN electrodes in real time.

Differentiating vascular pathophysiological states by objective analysis of flow dynamics.

BACKGROUND AND PURPOSE: There is an unmet need to classify cerebrovascular conditions physiologically and to assess cerebrovascular system performance. The authors hypothesized that by simultaneously considering the dynamic parameters of flow velocity, acceleration, and pulsatility index (PI) (impedance) in individual Doppler spectrum waveforms, they could develop an objective method to elucidate the pathophysiology of vascular conditions and classify cerebrovascular disorders. This method, dynamic vascular analysis (DVA), is described. METHODS: First, a theoretical model was developed to determine how any vascular segment and the ensemble of intracranial vascular segments could be defined according to its dynamic physiological characteristics. Next, the DVA method was applied to 847 anonymous serial complete clinical transcranial Doppler (TCD) studies of patients without regard for their diagnosis to ascertain actual reference ranges and the normality of the distribution curves for each dimension of the 3-parameter nomogram. The authors applied DVA to 2 clinical cases to see if they could track the changes in vascular performance of 2 known progressive diseases. RESULTS: The theoretical analysis identified 295,245 possible vascular states for the ensemble of vascular segments in the cerebral circulation. When applied to clinical TCD data, DVA revealed continuous, normally distributed data for the velocity, PI, and logarithm of the acceleration. CONCLUSIONS: DVA is proposed as a method for monitoring the physiological state of each cerebral artery segment individually and in ensemble. DVA evaluates the relationship among acceleration (force or pressure), velocity, and PI and provides an objective means to evaluate intracranial vascular segments using the paradigm of the well-described pressure-perfusion autoregulation relationship. DVA may be used to study cerebrovascular pathophysiology and to classify, evaluate, and monitor cerebrovascular disorders or systemic disorders with cerebrovascular effects.

Reliability of semiquantitative ultrasonic perfusion imaging of the brain.

BACKGROUND AND PURPOSE: Contrast burst depletion imaging (CODIM) visualizes cerebral perfusion by destruction of microbubbles and observation of image intensity course. Because of its complexity, artifacts occur. Criteria of reliability to improve diagnostic significance were created and validated. METHODS AND RESULTS: Eighteen healthy volunteers were examined with 2 echo contrast agents (ECAs) and 3 frame rates in 3 regions of interest (ROIs). Perfusion coefficient (PC), Tmin (time to decrease intensity to 10% of its max), and relative error (RE) (deviation of measured data from fitted model) were determined. PC differed significantly neither between CA nor between frame rates (overall mean = 1.60 +/- 0.21 x 10(-2) s-1). Tmin differed significantly between frame rate groups (P < .001, 33.4 +/- 11.2 s/0.5 Hz; 3.6 +/- 2.5 s/5 Hz) since it is related to destruction of microbubbles that occurs with each frame and to the perfusion rate. RE was higher in the Optison group and tended to decrease in ROIs closer to the probe. CONCLUSIONS: PC was independent of frame rate and ECA. Tmin was shorter with higher frame rates. Due to a very rapid decay at 5 Hz, the ideal frame rate should be about 1 Hz, that is, because the number of frames acquired within Tmin and therefore signal-to-noise ratio is higher at 1 Hz. Since the algorithm is complex (high RE) and more artifacts should occur in patients (insufficient bone window, etc), a triggering of the insonations by, for example, heart rate could decrease artifacts and increase diagnostic power of CODIM.

Robotic transcranial Doppler sonography probes and acupuncture.

The present study shows with a sophisticated quantitative method a change in blood flow velocity in a cerebral artery in response to acupuncture. Monitoring of transcranial Doppler sonography (TCD) was examined in 12 healthy volunteers (mean age: 35.2+/-4.4 years; 26-41 years; 4 female, 8 male) before, during and after acupuncture. In all persons the same unspecific scheme of acupuncture with a "general increase of Qi-energy" was used. The measurements were performed with new robotic TCD-probes allowing three-dimensional imaging by using multi-scan methods. The results showed a significant (p < 0.01; ANOVA; Tukey test) increase in mean blood flow velocity, which was measured at different depths of the right middle cerebral artery. Quantitative determination of the physiological effects during acupuncture can lead to a better acceptance of this unconventional complementary medical method.

Effects of acupuncture on the oxygenation of cerebral tissue.

Monitoring of regional cerebral oxygen saturation (r. cereb. O2 satn.) was carried out continuously in 12 healthy subjects (mean age 35.2 +/- 4.4 years; range 26-41 years; 4 women, 8 men), prior to, during and following acupuncture. Measurements were obtained with the INVOS 3100 cerebral oximeter (Somanetics Corp., Troy, USA). In addition new robotic transcranial Doppler sonography (TCD) probes enabling three-dimensional imaging of the middle cerebral artery by the use of multi-scan techniques were used simultaneously. The results showed small increases in r. cereb. O2 satn. mean values (69.9% before, 70.3% during and 70.2% after acupuncture) and a significant (p < 0.01; ANOVA, Tukey test) increase in mean bloodflow velocity during acupuncture measured simultaneously at different depths within the right middle cerebral artery. There are reports in the literature about the effects of acupuncture on the oxygenation of cerebral tissue in a study with animals. An increase in the cerebral oxygen saturation could be registered with the help of microelectrodes in the cortex. This is parallel evidence to the present results with near infrared spectroscopy and transcranial Doppler sonography. Quantifiable changes in the physiological effects of acupuncture may contribute to improved acceptance of this unconventional complementary medical procedure.

[Transcranial Doppler ultrasound--robotics-controlled transducers for quantifying the effect of acupuncture]. / Transkranielle Doppler-Sonographie--Robotergesteuerte Sonden zur Quantifizierung des Einflusses der Akupunktur.

Transcranial Doppler Sonography (TCD) monitoring was carried out in 12 healthy subjects (mean age: 35.2 +/- 4.4 years; range: 26-41 years; 4 women, 8 men), prior to, during and following acupuncture. In all subjects an identical acupuncture scheme with a "general increase in Qi energy" setting was employed. Measurements were obtained with new robotic TCD probes enabling three-dimensional imaging of the middle cerebral artery by the use of the multi-scan technique. The results showed a significant (p < 0.01; ANOVA; Tukey test) increase in mean bloodflow velocity measured simultaneously at different depths within the right middle cerebral artery. Quantifiable changes in the physiological effects of acupuncture may contribute to improved acceptance of this unconventional complementary medical procedure.