A tool for monitoring cell type-specific focused ultrasound neuromodulation and control of chronic epilepsy.

Focused ultrasound (FUS) is a powerful tool for noninvasive modulation of deep brain activity with promising therapeutic potential for refractory epilepsy; however, tools for examining FUS effects on specific cell types within the deep brain do not yet exist. Consequently, how cell types within heterogeneous networks can be modulated and whether parameters can be identified to bias these networks in the context of complex behaviors remains unknown. To address this, we developed a fiber Photometry Coupled focused Ultrasound System (PhoCUS) for simultaneously monitoring FUS effects on neural activity of subcortical genetically targeted cell types in freely behaving animals. We identified a parameter set that selectively increases activity of parvalbumin interneurons while suppressing excitatory neurons in the hippocampus. A net inhibitory effect localized to the hippocampus was further confirmed through whole brain metabolic imaging. Finally, these inhibitory selective parameters achieved significant spike suppression in the kainate model of chronic temporal lobe epilepsy, opening the door for future noninvasive therapies.

Comparison between MR and CT imaging used to correct for skull-induced phase aberrations during transcranial focused ultrasound.

Transcranial focused ultrasound with the InSightec Exablate system uses thermal ablation for the treatment of movement and mood disorders and blood brain barrier disruption for tumor therapy. The system uses computed tomography (CT) images to calculate phase corrections that account for aberrations caused by the human skull. This work investigates whether magnetic resonance (MR) images can be used as an alternative to CT images to calculate phase corrections. Phase corrections were calculated using the gold standard hydrophone method and the standard of care InSightec ray tracing method. MR binary image mask, MR-simulated-CT (MRsimCT), and CT images of three ex vivo human skulls were supplied as inputs to the InSightec ray tracing method. The degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. Targets at the geometric focus and 5 mm lateral to the geometric focus were investigated. There was no statistical difference between any of the metrics at either target using either MRsimCT or CT for phase aberration correction. As opposed to the MRsimCT, the use of CT images for aberration correction requires registration to the treatment day MR images; CT misregistration within a range of ± 2 degrees of rotation error along three dimensions was shown to reduce focal spot intensity by up to 9.4%. MRsimCT images used for phase aberration correction for the skull produce similar results as CT-based correction, while avoiding both CT to MR registration errors and unnecessary patient exposure to ionizing radiation.

Improving Transcranial Acoustic Targeting: The Limits of CT-Based Velocity Estimates and the Role of MR.

Transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) enables the noninvasive treatment of the deep brain. This capacity relies on the ability to focus acoustic energy through the in-tact skull, a feat that requires accurate estimates of the acoustic velocity in individual patient skulls. In current practice, these estimates are generated using a pretreatment computed tomography (CT) scan and then registered to a magnetic resonance (MR) dataset on the day of the treatment. Treatment safety and efficacy can be improved by eliminating the need to register the CT data to the MR images and by improving the accuracy of acoustic velocity measurements. In this study, we examine the capacity of MR to supplement or replace CT as a means of estimating velocity in the skull. We find that MR can predict velocity with less but comparable accuracy to CT. We then use micro-CT imaging to better understand the limitations of Hounsfield unit (HU)-based estimates of velocity, demonstrating that the macrostructure of pores in the skull contributes to the acoustic velocity of the bone. We find evidence that detailed T2 measurements provide information about pore macrostructure similar to the information obtained with micro-CT, offering a potential clinical mechanism for improving patient-specific estimates of acoustic velocity in the human skull.

Transcranial focused ultrasound phase correction using the hybrid angular spectrum method.

The InSightec Exablate system is the standard of care used for transcranial focused ultrasound ablation treatments in the United States. The system calculates phase corrections that account for aberrations caused by the human skull. This work investigates whether skull aberration correction can be improved by comparing the standard of care InSightec ray tracing method with the hybrid angular spectrum (HAS) method and the gold standard hydrophone method. Three degassed ex vivo human skulls were sonicated with a 670 kHz hemispherical phased array transducer (InSightec Exablate 4000). Phase corrections were calculated using four different methods (straight ray tracing, InSightec ray tracing, HAS, and hydrophone) and were used to drive the transducer. 3D raster scans of the beam profiles were acquired using a hydrophone mounted on a 3-axis positioner system. Focal spots were evaluated using six metrics: pressure at the target, peak pressure, intensity at the target, peak intensity, positioning error, and focal spot volume. For three skulls, the InSightec ray tracing method achieved 52 ± 21% normalized target intensity (normalized to hydrophone), 76 ± 17% normalized peak intensity, and 0.72 ± 0.47 mm positioning error. The HAS method achieved 74 ± 9% normalized target intensity, 81 ± 9% normalized peak intensity, and 0.35 ± 0.09 mm positioning error. The InSightec-to-HAS improvement in focal spot targeting provides promise in improving treatment outcomes. These improvements to skull aberration correction are also highly relevant for the applications of focused ultrasound neuromodulation and blood brain barrier opening, which are currently being translated for human use.

Acoustic Attenuation: Multifrequency Measurement and Relationship to CT and MR Imaging.

Transcranial magnetic resonance-guided focused ultrasound (tcMRgFUS) is gaining significant acceptance as a noninvasive treatment for motion disorders and shows promise for novel applications such as blood-brain barrier opening for tumor treatment. A typical procedure relies on CT-derived acoustic property maps to simulate the transfer of ultrasound through the skull. Accurate estimates of the acoustic attenuation in the skull are essential to accurate simulations, but there is no consensus about how attenuation should be estimated from CT images and there is interest in exploring MR as a predictor of attenuation in the skull. In this study, we measure the acoustic attenuation at 0.5, 1, and 2.25 MHz in 89 samples taken from two ex vivo human skulls. CT scans acquired with a variety of X-ray energies, reconstruction kernels, and reconstruction algorithms, and MR images acquired with ultrashort and zero echo time sequences are used to estimate the average Hounsfield unit value, MR magnitude, and T2* value in each sample. The measurements are used to develop a model of attenuation as a function of frequency and each individual imaging parameter.

Anatomic and Thermometric Analysis of Cranial Nerve Palsy after Laser Amygdalohippocampotomy for Mesial Temporal Lobe Epilepsy.

BACKGROUND: Laser interstitial thermal therapy (LITT) is a minimally invasive therapy for treating medication-resistant mesial temporal lobe epilepsy. Cranial nerve (CN) palsy has been reported as a procedural complication, but the mechanism of this complication is not understood. OBJECTIVE: To identify the cause of postoperative CN palsy after LITT. METHODS: Four medial temporal lobe epilepsy patients with CN palsy after LITT were identified for comparison with 22 consecutive patients with no palsy. We evaluated individual variation in the distance between CN III and the uncus, and CN IV and the parahippocampal gyrus using preoperative T1- and T2-weighted magnetic resonance (MR) images. Intraoperative MR thermometry was used to estimate temperature changes. RESULTS: CN III (n = 2) and CN IV palsies (n = 2) were reported. On preoperative imaging, the majority of identified CN III (54%) and CN IV (43%) were located within 1 to 2 mm of the uncus and parahippocampal gyrus tissue border, respectively. Affected CN III and CN IV were more likely to be found < 1 mm of the tissue border (PCNIII = .03, PCNIV < .01; chi-squared test). Retrospective assessment of thermal profile during ablation showed higher temperature rise along the mesial temporal lobe tissue border in affected CNs than unaffected CNs after controlling for distance (12.9°C vs 5.8°C; P = .03; 2-sample t-test). CONCLUSION: CN palsy after LITT likely results from direct heating of the respective CN running at extreme proximity to the mesial temporal lobe. Low-temperature thresholds set at the border of the mesial temporal lobe in patients whose CNs are at close proximity may reduce this risk.

A rapid beam simulation framework for transcranial focused ultrasound.

Transcranial focused ultrasound is a non-invasive therapeutic modality that can be used to treat essential tremor. Beams of energy are focused into a small spot in the thalamus, resulting in tissue heating and ablation. Here, we report on a rapid 3D numeric simulation framework that can be used to predict focal spot characteristics prior to the application of ultrasound. By comparing with magnetic resonance proton resonance frequency shift thermometry (MR thermometry) data acquired during treatments of essential tremor, we verified that our simulation framework can be used to predict focal spot position, and with patient-specific calibration, predict focal spot temperature rise. Preliminary data suggests that lateral smearing of the focal spot can be simulated. The framework may also be relevant for other therapeutic ultrasound applications such as blood brain barrier opening and neuromodulation.

Measurements of the Relationship Between CT Hounsfield Units and Acoustic Velocity and How It Changes With Photon Energy and Reconstruction Method.

Transcranial magnetic resonance-guided focused ultrasound continues to gain traction as a noninvasive treatment option for a variety of pathologies. Focusing ultrasound through the skull can be accomplished by adding a phase correction to each element of a hemispherical transducer array. The phase corrections are determined with acoustic simulations that rely on speed of sound estimates derived from CT scans. While several studies have investigated the relationship between acoustic velocity and CT Hounsfield units (HUs), these studies have largely ignored the impact of X-ray energy, reconstruction method, and reconstruction kernel on the measured HU, and therefore the estimated velocity, and none have measured the relationship directly. In this paper, 91 ex vivo human skull fragments from two skulls are imaged by 80 CT scans with a variety of energies and reconstruction methods. The average HU from each fragment is found for each scan and correlated with the speed of sound measured using a through transmission technique in that fragment. As measured by the -squared value, the results show that CT is able to account for 23%-53% of the variation in velocity in the human skull. Both the X-ray energy and the reconstruction technique significantly alter the -squared value and the linear relationship between HU and speed of sound in bone. Accounting for these variations will lead to more accurate phase corrections and more efficient transmission of acoustic energy through the skull.

Semiquinone intermediates are involved in the energy coupling mechanism of E. coli complex I.

Complex I (NADH:quinone oxidoreductase) is central to cellular aerobic energy metabolism, and its deficiency is involved in many human mitochondrial diseases. Complex I translocates protons across the membrane using electron transfer energy. Semiquinone (SQ) intermediates appearing during catalysis are suggested to be key for the coupling mechanism in complex I. However, the existence of SQ has remained controversial due to the extreme difficulty in detecting unstable and low intensity SQ signals. Here, for the first time with Escherichia coli complex I reconstituted in proteoliposomes, we successfully resolved and characterized three distinct SQ species by EPR. These species include: fast-relaxing SQ (SQNf) with P1/2 (half-saturation power level)>50mW and a wider linewidth (12.8 G); slow-relaxing SQ (SQNs) with P1/2=2-3mW and a 10G linewidth; and very slow-relaxing SQ (SQNvs) with P1/2= ~0.1mW and a 7.5G linewidth. The SQNf signals completely disappeared in the presence of the uncoupler gramicidin D or squamotacin, a potent E. coli complex I inhibitor. The pH dependency of the SQNf signals correlated with the proton-pumping activities of complex I. The SQNs signals were insensitive to gramicidin D, but sensitive to squamotacin. The SQNvs signals were insensitive to both gramicidin D and squamotacin. Our deuterium exchange experiments suggested that SQNf is neutral, while SQNs and SQNvs are anion radicals. The SQNs signals were lost in the ΔNuoL mutant missing transporter module subunits NuoL and NuoM. The roles and relationships of the SQ intermediates in the coupling mechanism are discussed.

Semiquinone and cluster N6 signals in His-tagged proton-translocating NADH:ubiquinone oxidoreductase (complex I) from Escherichia coli.

NADH:ubiquinone oxidoreductase (complex I) pumps protons across the membrane using downhill redox energy. The Escherichia coli complex I consists of 13 different subunits named NuoA-N coded by the nuo operon. Due to the low abundance of the protein and some difficulty with the genetic manipulation of its large ~15-kb operon, purification of E. coli complex I has been technically challenging. Here, we generated a new strain in which a polyhistidine sequence was inserted upstream of nuoE in the operon. This allowed us to prepare large amounts of highly pure and active complex I by efficient affinity purification. The purified complex I contained 0.94 ± 0.1 mol of FMN, 29.0 ± 0.37 mol of iron, and 1.99 ± 0.07 mol of ubiquinone/1 mol of complex I. The extinction coefficient of isolated complex I was 495 mM(-1) cm(-1) at 274 nm and 50.3 mM(-1) cm(-1) at 410 nm. NADH:ferricyanide activity was 219 ± 9.7 µmol/min/mg by using HEPES-Bis-Tris propane, pH 7.5. Detailed EPR analyses revealed two additional iron-sulfur cluster signals, N6a and N6b, in addition to previously assigned signals. Furthermore, we found small but significant semiquinone signal(s), which have been reported only for bovine complex I. The line width was ~12 G, indicating its neutral semiquinone form. More than 90% of the semiquinone signal originated from the single entity with P½ (half-saturation power level) = 1.85 milliwatts. The semiquinone signal(s) decreased by 60% when with asimicin, a potent complex I inhibitor. The functional role of semiquinone and the EPR assignment of clusters N6a/N6b are discussed.