Improved Localization of Implanted Subdural Electrode Contacts on MRI Using an Elastic Image Fusion Algorithm in Invasive EEG Recording

BACKGROUND: Accurate projection of implanted subdural electrode contacts in presurgical evaluation of pharmacoresistant epilepsy cases by invasive EEG is highly relevant. Linear fusion of CT and MRI images may display the contacts in the wrong position due to brain shift effects. OBJECTIVE: A retrospective study in five patients with pharmacoresistant epilepsy was performed to evaluate whether an elastic image fusion algorithm can provide a more accurate projection of the electrode contacts on the pre-implantation MRI as compared to linear fusion. METHODS: An automated elastic image fusion algorithm (AEF), a guided elastic image fusion algorithm (GEF), and a standard linear fusion algorithm (LF) were used on preoperative MRI and post-implantation CT scans. Vertical correction of virtual contact positions, total virtual contact shift, corrections of midline shift and brain shifts due to pneumencephalus were measured. RESULTS: Both AEF and GEF worked well with all 5 cases. An average midline shift of 1.7mm (SD 1.25) was corrected to 0.4mm (SD 0.8) after AEF and to 0.0mm (SD 0) after GEF. Median virtual distances between contacts and cortical surface were corrected by a significant amount, from 2.3mm after LF to 0.0mm after AEF and GEF (p<.001). Mean total relative corrections of 3.1 mm (SD 1.85) after AEF and 3.0mm (SD 1.77) after GEF were achieved. The tested version of GEF did not achieve a satisfying virtual correction of pneumencephalus. CONCLUSION: The technique provided a clear improvement in fusion of pre- and post-implantation scans, although the accuracy is difficult to evaluate.

Compact low-power cortical recording architecture for compressive multichannel data acquisition

This paper introduces an area- and power-efficient approach for compressive recording of cortical signals used in an implantable system prior to transmission. Recent research on compressive sensing has shown promising results for sub-Nyquist sampling of sparse biological signals. Still, any large-scale implementation of this technique faces critical issues caused by the increased hardware intensity. The cost of implementing compressive sensing in a multichannel system in terms of area usage can be significantly higher than a conventional data acquisition system without compression. To tackle this issue, a new multichannel compressive sensing scheme which exploits the spatial sparsity of the signals recorded from the electrodes of the sensor array is proposed. The analysis shows that using this method, the power efficiency is preserved to a great extent while the area overhead is significantly reduced resulting in an improved power-area product. The proposed circuit architecture is implemented in a UMC 0.18 [Formula: see text]m CMOS technology. Extensive performance analysis and design optimization has been done resulting in a low-noise, compact and power-efficient implementation. The results of simulations and subsequent reconstructions show the possibility of recovering fourfold compressed intracranial EEG signals with an SNR as high as 21.8 dB, while consuming 10.5 [Formula: see text]W of power within an effective area of 250 [Formula: see text]m × 250 [Formula: see text]m per channel.

Optical recording of calcium currents during impulse conduction in cardiac tissue

We explore the feasibility of obtaining a spatially resolved picture of Ca2+Ca2+ inward currents (ICaICa) in multicellular cardiac tissue by differentiating optically recorded Ca2+Ca2+ transients that accompany propagating action potentials. Patterned growth strands of neonatal rat ventricular cardiomyocytes were stained with the Ca2+Ca2+ indicators Fluo-4 or Fluo-4FF. Preparations were stimulated at 1 Hz, and Ca2+Ca2+ transients were recorded with high spatiotemporal resolution (50  μm50  μm, 2 kHz analog bandwidth) with a photodiode array. Signals were differentiated after appropriate digital filtering. Differentiation of Ca2+Ca2+ transients resulted in optically recorded calcium currents (ORCCs) that carried the temporal and pharmacological signatures of L-type Ca2+Ca2+ inward currents: the time to peak amounted to ∼2.1  ms∼2.1  ms (Fluo-4FF) and ∼2.4  ms∼2.4  ms (Fluo-4), full-width at half-maximum was ∼8  ms∼8  ms, and ORCCs were completely suppressed by 50  μmol/L50  μmol/LCdCl2CdCl2. Also, and as reported before from patch-clamp studies, caffeine reversibly depressed the amplitude of ORCCs. The results demonstrate that the differentiation of Ca2+Ca2+ transients can be used to obtain a spatially resolved picture of the initial phase of ICaICa in cardiac tissue and to assess relative changes of activation/fast inactivation of ICaICa following pharmacological interventions.

Sural nerve conduction studies using ultrasound-guided needle positioning: Influence of age and recording location.

INTRODUCTION The aim of this study was to compare orthodromic sural nerve conduction study (NCS) results using ultrasound-guided needle positioning (USNP) to surface electrode recordings. METHODS 51 healthy subjects aged 24 - 80 years, divided into 5 age groups, were examined. Electrical stimuli were applied behind the lateral malleolus. Sensory nerve action potentials (SNAPs) were recorded 8 and 15 cm proximally with surface and needle electrodes. RESULTS Mean SNAP amplitudes in µV (surface/needle electrodes) averaged 12.7 (SD 7.6)/40.6 (SD 20.8), P<0.001, for subjects aged 20-29 years, and 5.0 (SD 2.4)/19.8 (SD 9.8), P<0.01, for subjects aged > 60 years. SNAP amplitudes were smaller at the proximal recording location. DISCUSSION NCS using USNP yield higher amplitude responses than surface electrodes in all age groups at all recording sites. SNAP amplitudes are smaller at proximal recording locations due to sural nerve branching. This article is protected by copyright. All rights reserved.

Autonomous recording current meter measurements at the Håkon Mosby mud volcano (LOOME)

The deployment of LOOME was performed by lowering the LOOME frame by winch, followed by positioning of the surface sensors across the most active site by ROV. The frame was placed on an inactive slab of hydrates, eastwards and adjacent to the hot spot. To the frame autonomous recording current meter was mounted, recording physical oceanography variables approximately two to three meter above the seafloor.