Duration Tp Research Articles

Advancing Boiling Histotripsy Dose in Ex Vivo And In Vivo Renal Tissues Via Quantitative Histological Analysis and Shear Wave Elastography

ObjectiveIn the context of developing boiling histotripsy (BH) as a potential clinical approach for non-invasive mechanical ablation of kidney tumors, the concept of BH dose (BHD) was quantitatively investigated in porcine and canine kidney models in vivo and ex vivo. MethodsVolumetric lesions were produced in renal tissue using a 1.5-MHz 256-element HIFU-array with various pulsing protocols: pulse duration tp = 1–10 ms, number of pulses per point ppp = 1–15. Two BHD metrics were evaluated: BHD1 = ppp, BHD2 = tp × ppp. Quantitative assessment of lesion completeness was performed by their histological analysis and assignment of damage score to different renal compartments (i.e., cortex, medulla, and sinus). Shear wave elastography (SWE) was used to measure the Young's modulus of renal compartments in vivo vs ex vivo, and before vs after BH treatments. ResultsIn vivo tissue required lower BH doses to achieve identical degree of fractionation as compared to ex vivo. Renal cortex (homogeneous, low in collagen) was equal or higher in stiffness than medulla (anisotropic, collagenous), 5.8–12.2 kPa vs 4.7–9.6 kPa, but required lower BH doses to be fully fractionated. Renal sinus (fatty, irregular, with abundant collagenous structures) was significantly softer ex vivo vs in vivo, 4.9–5.1 kPa vs 9.7–15.2 kPa, but was barely damaged in either case with any tested BH protocols. BHD1 was shown to be relevant for planning the treatment of renal cortex (sufficient BHD1 = 5 pulses in vivo and 10 pulses ex vivo), while none of the tested doses resulted in complete fractionation of medulla or sinus. Post-treatment SWE imaging revealed reduction of tissue stiffness ex vivo by 27–58%, increasing with the applied dose, and complete absence of shear waves within in vivo lesions, both indicative of tissue liquefaction. ConclusionThe results imply that tissue resistance to mechanical fractionation, and hence required BH dose, are not solely determined by tissue stiffness but also depend on its composition and structural arrangement, as well as presence of perfusion. The SWE-derived reduction of tissue stiffness with increasing BH doses correlated with tissue damage score, indicating potential of SWE for post-treatment confirmation of BH lesion completeness.

Simulation of femtosecond laser-induced periodic surface structures on fused silica by considering intrapulse and interpulse feedback

The formation of laser-induced periodic surface structures (LIPSSs) on fused silica upon irradiation with plane wave, double pulse, spot processing, and scanning processing (pulse duration tp = 35 fs, center wavelength λ = 800 nm, low repetition rate ≈1 kHz) is studied theoretically with an improved three-dimensional finite-difference time-domain plasma model. The model covers both intrapulse feedback under single shot and interpulse feedback under multi-shots, thus enabling better prediction of transient responses during laser–material interaction and the evolution of the ablated morphology and accumulated defects’ density with more shots. In simulations of a single plane wave, a double pulse can modulate LIPSS periodicity. In simulations of spot processing with Gaussian beam, an increase in the number of shots results in a noticeable ablation pattern where high-spatial-frequency LIPSS surrounds low-spatial-frequency LIPSS at a fluence of 2.8 J/cm2. Moreover, simulations of scanning processing with Gaussian beam showcase the broad applicability of this model, revealing that the orientation of the LIPSS depends on the polarization direction rather than the scanning path. This new model provides a powerful tool to simulate the formation of LIPSS on silica, particularly when temporally modulated laser is involved or predicting the evolution of morphology dependent on the number of shots.

Abstract 13129: Human in vitro Study on Pulsed Electric Field Cardiac Ablation Cell Sensitivity

Introduction: Catheter cardiac ablation is a standard treatment for atrial fibrillation for patients that do not respond to drugs. Pulsed electric field (PEF) cardiac ablation has been proposed as a nonthermal technology to cause cell death by irreversible electroporation (IRE). IRE has shown to minimize off target damage. The lack of systematic studies to inform optimal PEF ablation parameters has significantly slowed down device development and regulatory process. Hypothesis: As part of a larger effort to develop a standard laboratory assay for PEF parameter optimization, in this study we investigate tissue specificity of IRE cardiac ablation treatments. Methods: Human induced pluripotent stem cell cardiomyocytes derived (hiPSC-CMs, Fujifilm Cellular Dynamic, Inc.), human esophageal muscle cells (HESMC, ScienCell Research Laboratories), and human bronchial epithelial cells (HBEC3-KT, ATCC) were cultured in monolayer formats on 96-well NanoFiber plates. PEF were delivered by an FID pulse generator connected to two needle electrodes (1.7 mm center-to-center distance). PEF parameters investigated in this study are: phase duration tp=1, 5, 10 μs; phase intensity Vp=284, 372, 568V; pulse repetition frequency PRF=10, 100, 1000 Hz, pulse number p#=100. We quantified IRE areas 4 hours post-treatment by propidium iodide (PI). Results: Preliminary results show that increasing the tp, Vp and decreasing the PRF resulted in a larger IRE area in all the cell types studied. For the range of PEF parameters investigated, a treatment with same tp, p# and PRF required higher Vp to induce IRE in HESMC and HBEC3-KT than hiPSC-CMs, i.e., 100 pulses with tp=5 μs and PRF=1000 Hz, to achieve the same IRE area, hiPSC-CMs needed half Vp than HESMC and HBEC3-KT. Conclusions: Our data suggests that same PEF treatments induced larger IRE areas in hiPSC-CM than in HESMC and HBEC3-KT. Future work will focus on validating these results in tissues to assess safety of IRE cardiac ablation devices.

A robust adiabatic constant amplitude spin-lock preparation module for myocardial T1ρ quantification at 3T.

T1ρ quantification has the potential to assess myocardial fibrosis without contrast agent. However, its preparation spin-lock pulse is sensitive to B1 and B0 inhomogeneities, resulting in severe banding artifacts in the heart region, especially at high magnetic field such as 3T. We aimed to design a robust spin-lock (SL) preparation module that can be used in myocardial T1ρ quantification at 3T. We used the tan/tanh pulse to tip up and tip down the magnetization in the spin-lock preparation module (tan/tanh-SL). Bloch simulation was used to optimize pulse shape parameters of the tan/tanh with a pulse duration (Tp ) of 8, 4, and 2ms, respectively. The designed tan/tanh-SL modules were implemented on a 3-T MR scanner. They were evaluated in phantom studies under three different cases of B0 and B1 inhomogeneities, and tested in cardiac T1ρ quantification of healthy volunteers. The performance of the tan/tanh-SL was compared with the composite SL preparation pulses and the commonly used hyperbolic secant pulse for spin-lock (HS-SL). Feasible pulse shape parameters were obtained using Bloch simulation. Compared with HS-SL, the quantification error of tan/tanh-SL was reduced by 27.7% for Tp = 8ms (mean ∆Q = 126.15 vs. 174.42) and 75.6% for Tp = 4ms (mean ∆Q = 136.65 vs. 559.53). In the phantom study, tan/tanh-SL was less sensitive to B1 and B0 inhomogeneity compared with composite SL pulses and HS-SL. In cardiac T1ρ quantification, the T1ρ maps using tan/tanh-SL showed fewer banding artifacts than using composite SL pulses and HS-SL. The proposed tan/tanh-SL preparation module greatly improves the robustness to B0 and B1 field inhomogeneities and can be used in cardiac T1ρ quantification at 3T.

Laser decontamination microscopic process study on radioactive contaminations with Cs+ ion of 304 stainless steel surface

The decommissioning of contaminated metal equipment in nuclear facilities may produce a wide range of radioactive waste. For metallic equipment like the primary loop, the radioactivity is mainly located in the oxide surface. Laser decontamination was performed on 304 stainless steel specimens with a stable isotope Cs contamination layer. Laser melting was used to create oxide layer on the surface of polished specimen for enhancing the penetration of Cs+ ion. The interaction between laser and matter (contamination, oxide and substrate) was studied by the stratification theory considering the difference in the thickness of contamination layer. At higher pulse duration (τp = 5ns), laser decontamination is mainly caused by thermal effects. The metal near oxide layer melts and vaporizes to form a molten pool and crater. For short pulse duration (τp = 1ns), the removal of surface contaminations mainly depends on thermal effect and stress wave, CsCl particles were removed by vaporization; however, oxide layer was stripped from the substrate in the form of solid fragment. For ultra-short pulse duration (τp = 150ps), the oxide layer has been partially ablated. Most of the heat absorbed by γ (austenite) is used for heating and evaporation to form porous structure, while the great mass of heat absorbed by M (martensite) is used for thermal diffusion. Therefore, the M regions only form a dynamic molten pool on its surface without vaporization.

A Compact Circuit for Boosting Electric Field Intensity in Repetitive Transcranial Magnetic Stimulation (rTMS).

The concept of a portable, wearable system for repetitive transcranial stimulation (rTMS) has attracted widespread attention, but significant power and field intensity requirements remain a key challenge. Here, a circuit topology is described that significantly increases induced electric field intensity over that attainable with similar current levels and coils in conventional rTMS systems. The resultant electric field is essentially monophasic, and has a controllable, shortened duration. The system is demonstrated in a compact circuit implementation for which an electric field of 94 V/m at a depth of 2 cm is measured (147 V/m at 1 cm depth) with a power supply voltage of 80 V, a maximum current of 500 A, and an effective pulse duration (half amplitude width) of 7 µsec. The peak electric field is on the same order as that of commercially available systems at full power and comparable depths. An electric field boost of 5x is demonstrated in comparison with our system operated conventionally, employing a 70 µsec rise time. It is shown that the power requirements for rTMS systems depend on the square of the product of electric field Ep and pulse duration tp, and that the proposed circuit technique enables continuous variation and optimization of the tradeoff between Ep and tp. It is shown that the electric field induced in a medium such as the human brain cortex at a specific depth is proportional to the voltage generated in a given loop of the generating coil, which allows insights into techniques for its optimization. This rTMS electric field enhancement strategy, termed 'boost rTMS (rbTMS)' is expected to increase the effectiveness of neural stimulation, and allow greater flexibility in the design of portable rTMS power systems.Clinical Relevance- This study aims to facilitate a compact, battery-powered rTMS prototype with enhanced electric field which will permit broader and more convenient rTMS treatment at home, in a small clinic, vessel, or field hospital, and potentially, on an ambulatory basis.

Hyporheic exchange mechanism driven by flood wave

AbstractTo study the hyporheic exchange driven by a single peak flood‐induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real‐time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine‐type) and its change rate v (cosine‐type), and was proportional to the polynomial of them q ∝ (ω∙h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.

Critical kinetic parameters and rate constants representing lipid peroxidation as affected by temperature

This study aimed to comparatively investigate the temperature effect on the kinetic parameters and rate constants representing lipid hydroperoxides (LOOH) formation and decomposition during initiation and propagation peroxidations. The initiation phase was characterized by induction period IP, overall initiation rate constant kIP, initiation oxidizability Oi, and the critical reverse micelle concentration of LOOH, CMCL. The propagation phase was characterized by its duration tp, the maximum rate of LOOH accumulation Rmax, maximum LOOH concentration [LOOH]max, propagation oxidizability Rn, composite rate constant kc, and LOOH decomposition rate constant kd. Oi and Rn indicated relatively high dependencies on temperature, respectively. Among the rate constants, kd better highlighted oxidizabilities as affected by temperature. The oxidizabilities had good correspondences with the Arrhenius kinetic (A and Ea) and Eyring thermodynamic (ΔS++ and ΔH++) parameters. The most endergonic reactions (ΔG++>0) were LOOH decompositions, followed by LOOH formations during the propagation and initiation phases, respectively.

General Regularities and Differences in the Behavior of the Dynamic Magnetization Switching of Ferrimagnetic (CoFe2O4) and Antiferromagnetic (NiO) Nanoparticles

In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe2O4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH/dt, and the value of applied field H0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.

Relayed nuclear Overhauser enhancement imaging with magnetization transfer contrast suppression at 3 T.

To develop a pulsed CEST magnetization-transfer method for rapidly acquiring relayed nuclear Overhauser enhancement (rNOE)-weighted images with magnetic transfer contrast (MTC) suppression at clinical field strength (3 T). Using a pulsed CEST magnetization-transfer method with low saturation powers (B1 ) and long mixing time (tmix ) to suppress contributions due to strong MTC from solid-like macromolecules, a low B1 also minimized direct water saturation. These MTC contributions were further reduced by subtracting the Z-spectral signals at two or three offsets by assuming that the residual MTC is a linear function between -3.5 ppm and -12.5 ppm. Phantom studies of a lactic acid (Lac) solution mixed with cross-linked bovine serum albumin show that strong MTC interference has a significant impact on the optimum B1 for detecting rNOEs, due to lactate binding. The MTC could be effectively suppressed using a pulse train with a B1 of 0.8 μT, a pulse duration (tp ) of 40 ms, a tmix of 60 ms, and a pulse number (N) of 30, while rNOE signal was well maintained. As a proof of concept, we applied the method in mouse brain with injected hydrogel and a cell-hydrogel phantom. Results showed that rNOE-weighted images could provide good contrast between brain/cell and hydrogel. The developed pulsed CEST magnetization-transfer method can achieve MTC suppression while preserving most of the rNOE signal at 3 T, which indicates the potential for translation of this technique to clinical applications related to mobile proteins/lipids change.

Stimulated Raman scattering of light in suspension of diamond microparticles in ethanol and in water.

The spectra of stimulated Raman scattering of light in ethanol and in water suspensions containing diamond microparticles with sizes 0.2-0.3μm were investigated. An excitation radiation source was a pulsed ruby laser with a generation wavelength λ0=694.3nm, a pulse duration τp≈20ns, a maximum beam energy of Emax=0.6J, a spectral width Δν=0.015cm-1, and a beam divergence 3.5·10-4rad. For the first time, the observation of stimulated Raman scattering of light at a boson peak in suspension of diamonds microcrystals with close sizes (0.2-0.3μm) in a liquid is reported. The corresponding spectra were recorded using a Fabry-Perot interferometer. In this case, the frequency shift of the stimulated Stokes Raman scattering depended on the size of the diamond microparticles introduced into the liquid and amounted to ~1cm-1. In addition, stimulated Raman scattering by a fundamental optical mode with a frequency shift ν=1331cm-1 was observed. In this case, the Raman spectra were recorded using a small-sized spectrometer with a multi-element receiver, detecting radiation in the range of 200-1000nm. At a sufficiently high intensity of the exciting radiation, the Stokes and anti-Stokes satellites were simultaneously present in the spectrum of stimulated Raman scattering. The obtained results on stimulated scattering of diamond microparticles in liquids are of interest for estimating the sizes of microcrystals from scattering spectra at a boson peak, as well as for creating a frequency comb of emitters based on stimulated Raman scattering with a large frequency shift.

Characteristics of Bubble Oscillations During Laser-Activated Irrigation of Root Canals and Method of Improvement.

Background and ObjectivesLaser‐activated irrigation of dental root canals is being increasingly used as its efficacy has been shown to be superior compared with conventional techniques. The method is based on laser‐initiated localized fluid evaporation and subsequent rapid bubble expansions and collapses, inducing microfluid flow throughout the entire volume of the cavity. The irrigation efficacy can be further improved if optimally delayed “SWEEPS” double laser pulses are delivered into the canal. This study aims to show that the irrigation efficacy, as measured by the induced pressure within the canal, is related to the double pulse delay, with the maximal pressure generated at an optimal delay. The second aim is to find a method of determining the optimal delay for different cavity dimensions and/or laser parameters.Study Design/Materials and MethodsExperiments were made in transparent models of root canals where Er:YAG laser (λ = 2.94 μm, pulse duration t p = 25 or 50 microseconds, and pulse energies up to E L = 40 mJ) was used with a combination of cylindrical and conical fiber‐tip geometries (diameters 400 and 600 µm). High‐speed photography (60,000 fps) and average pressure measurements inside the canal were used for process characterization.ResultsThe results show that a pressure amplification of more than 1.5 times occurs if the laser pulse delay approximately coincides with the bubble oscillation time. Correlations between normalized oscillation time and canal diameter for a wide range of laser pulse energies (R 2 = 0.96) and between the average pressure within the canal and the bubble oscillation periods (R 2 = 0.90) were found. A relationship between the bubble oscillation time and the diameter of the treated cavity was found depending on the bubble oscillation time in an infinite fluid reservoir.ConclusionsThe bubble oscillation time within a constrained volume can be determined based on the known oscillation time in infinite space, which offers a fast and simple solution for optimization of the laser parameters. These findings enable determination of optimal conditions for shock wave generation, and improvement of root canal irrigation at the same dose of laser energy input, leading to improved treatment efficacy and safety. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals, Inc.

Methods for reducing write error rate in voltage-induced switching having prolonged tolerance of voltage-pulse duration

Simulating the magnetization dynamics in a perpendicularly-magnetized free layer with Langevin equation, we investigated methods for reducing write error rate (WER) in voltage-induced switching with long tolerance of voltage-pulse duration (tp). The simulation results show that WER can be reduced by increasing the perpendicular anisotropy (Ku) before and after the application of voltage or by increasing both Ku and the in-plane external magnetic field.

Spike-shape dependence of the spike-timing dependent synaptic plasticity in ferroelectric-tunnel-junction synapses

Resistive switching (RS) devices have attracted increasing attention for artificial synapse applications in neural networks because of their nonvolatile and analogue resistance changes. Among the neural networks, a spiking neural network (SNN) based on spike-timing-dependent plasticity (STDP) is highly energy efficient. To implement STDP in resistive switching devices, several types of voltage spikes have been proposed to date, but there have been few reports on the relationship between the STDP characteristics and spike types. Here, we report the STDP characteristics implemented in ferroelectric tunnel junctions (FTJs) by several types of spikes. Based on simulated time evolutions of superimposed spikes and taking the nonlinear current-voltage (I-V) characteristics of FTJs into account, we propose equations for simulating the STDP curve parameters of a magnitude of the conductance change (ΔGmax) and a time window (τC) from the spike parameters of a peak amplitude (Vpeak) and time durations (tp and td) for three spike types: triangle-triangle, rectangular-triangle, and rectangular-rectangular. The power consumption experiments of the STDP revealed that the power consumption under the inactive-synapse condition (spike timing |Δt| > τC) was as large as 50–82% of that under the active-synapse condition (|Δt| < τC). This finding indicates that the power consumption under the inactive-synapse condition should be reduced to minimize the total power consumption of an SNN implemented by using FTJs as synapses.

A fast measurement of Warburg-like impedance spectra with Morlet wavelet transform for electrochemical energy devices

Fast impedance measurement via complex Morlet wavelet transform (CMWT) offers a valuable way for real-time diagnosis and in-situ monitoring on electrochemical energy devices. However, it normally suffers from a dilemma: how to set CMWT parameters such as sampling duration Tp, sampling frequency fs, scale factor range A, central frequency fc, and band factor fb? Especially for a fast measurement of Warburg-like impedance spectra. Thus, optimal theories are needed in order to acquire Warburg-like impedance spectra rapidly under a required precision and a given frequency range. In this paper, the optimal rules for a fast impedance measurement are developed based on the uncertainty principle: 1) 2.5/fL ≤ Tp ≤ 3.0/fL; 2) fs ≥ 20fU; 3) 1.0/fc≤fb≤1.4/fc where fL and fU are the lower-limit and upper-limit frequencies of the impedance spectra, respectively. Subsequently, measurement errors are quantitatively evaluated for the reconstructed impedance spectra via CMWT algorithm. Through the derived optimal rules, a fast measurement with Tp = 28.0 s and fs = 20.0 kHz is implemented for Warburg-like impedance spectra from 0.1 Hz to 1.0 kHz and with the average errors of 0.7% and 2.6% for magnitude and phase, respectively. The developed method creates a higher possibility for real-time diagnosis and in-situ monitoring of electrochemical energy devices in electric vehicles (EVs).

AFM-tip written normal and anomalous domains in PMN-0.4PT crystals

At present, crystals of the solid solutions Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) are under intensive investigation due to their excellent piezoelectric characteristics. Studies in domain engineering are of importance for an insight into the contribution from the domain formation and resulting domain-wall density to piezoelectric coefficients. In this work, the fabrication of domains by dc AFM-tip voltages was studied in the tetragonal PMN-0.4PT crystals. Two types of domains were observed, either uniformly polarized along the poling field (the “normal” ones), or, following the commonly accepted term, “anomalous” ones containing a small area with the polarization directed oppositely to the poling field. In this work, for the first time, the correlation between the domain shape and the local piezoelectric hysteresis loops Hω−Utip was found, namely, the larger is the local bias voltage Ub, the higher is the tip voltage Utip at which the anomalous domains appear. This finding relates the observed scatter in the exposure conditions corresponding to the anomalous domains formation, to the nonuniform spatial distribution of the local bias fields. The domain diameter D vs Utip and pulse duration tp were investigated for Utip ≤ 50 V and tp from 10 ms to 10 s. The exposure characteristics are independent of the domain shape. For a given tp, D(Utip) is described by a unified linear function in the whole Utip range. The curves D(tp) follow a power law D∼tpk with the exponent k varying very weakly with Utip. The relaxation kinetics of anomalous domains depends on the writing conditions. The normal domains are found to decay significantly faster than the anomalous ones, with the decay kinetics depending on the domain spacing.

Voltage-induced switching with long tolerance of voltage-pulse duration in a perpendicularly magnetized free layer

The voltage-induced magnetization switching with the long tolerance of voltage-pulse duration (tp) is theoretically investigated. This method does not require the voltage-pulse to be turned off at around half-period of precessional motion of magnetization, and it can be realized by the energy dissipation through the damping torque. Numerical simulations show that this method is applicable in perpendicularly magnetized free layer at room temperature. The results provide a method for designing a voltage-controlled MRAM which ensures the reliability in writing against the distribution of tp from pulsed power supply and the distribution of precession periods among the MRAM cells.

The Role of Myofibroblasts and Mast Cells in Oral Mucosa Repair After Fractional Laser Treatment

The aimof this study was to clarify the features of the reparative process of the rat's oral mucosa in the later periods after fractional laser treatment with an analysis of the possible involvement of mast cells and myofibroblasts in this process.Material and methods.The samples of the oral mucosa of male Wistar rats (n=9) were used as a material for this study. Fractional laser treatment was carried out using stLase (DentalPhotonics, USA) with power P=7–10 W and pulse duration tp=100–200 ms (wavelength 980 nm). Histological sections of the oral mucosa from the control zones (unaffected) and zones treated with laser radiation were stained with hematoxylin and eosin and with Masson’s aniline blue. To identify mast cells, toluidine blue was used. For the detection of blood vessels and myofibroblasts, immunohistochemical reaction to smooth-muscle α-actin was performed.Results.On the 28th day after fractional laser treatment in rat oral mucosa the signs of incomplete repair were present. At this period in laser treated areas within the lamina propria rows of densely adjacent myofibroblasts were found. In the rows of myofibroblasts the mast cells are not visualized, while in the similar areas of the intact mucosa mast cells are present in large numbers.Conclusion.Fractional laser treatment stimulates the prolongation of regeneration process of rat oral mucosa while formation of myofibroblasts occurs in the laser treated zone. During this process mast cells may be involved. The ability to degranulate under laser radiation was shown.

Realization of uniform transverse gain in an edge-pumped multislab pulsed amplifier with a gradient profile doping

Gradient doping ensures uniform transverse gain in an edge-pumped multislab pulsed amplifier, and a 1D iterative method is developed to generate the proper doping profile. Our investigations show that uniform gain under short pump duration tp = 0.25 ms can be readily achieved, where the modulation of the gain distribution is lower than 1.05 even if the diagonal transverse gain-length product (DTGLP) increases up to 5. For tp = 1.0 ms, comparable modulation of the gain distribution is achieved for a much lower DTGLP value of 2.3. To extend the DTGLP range for long pump duration, a modified 1D iterative method with an effectively “shortened” lifetime of the active ions is developed. With the modified method, the gain uniformity for both pumping conditions is greatly improved, and specifically, the DTGLP increases from 2.3 to 3.0 for tp = 1.0 ms. In addition, degradation of the gain uniformity resulting from deviations of the doping concentration is discussed. The deviations should be at least lower than 1% and 5% for tp = 1.0 ms and tp = 0.25 ms to maintain the gain uniformity, respectively. Our investigations might provide a useful way to design the amplifier with uniform gain in the beam aperture of a high average power pulsed laser.

3D gradient echo snapshot CEST MRI with low power saturation for human studies at 3T.

PurposeFor clinical implementation, a chemical exchange saturation transfer (CEST) imaging sequence must be fast, with high signal‐to‐noise ratio (SNR), 3D coverage, and produce robust contrast. However, spectrally selective CEST contrast requires dense sampling of the Z‐spectrum, which increases scan duration. This article proposes a compromise: using a 3D snapshot gradient echo (GRE) readout with optimized CEST presaturation, sampling, and postprocessing, highly resolved Z‐spectroscopy at 3T is made possible with 3D coverage at almost no extra time cost.MethodsA 3D snapshot CEST sequence was optimized for low‐power CEST MRI at 3T. Pulsed saturation was optimized for saturation power and saturation duration. Spectral sampling and postprocessing (B0 correction, denoising) was optimized for spectrally selective Lorentzian CEST effect extraction. Reproducibility was demonstrated in 3 healthy volunteers and feasibility was shown in 1 tumor patient.ResultsLow‐power saturation was achieved by a train of 80 pulses of duration tp = 20 ms (total saturation time tsat = 3.2 seconds at 50% duty cycle) with B1 = 0.6 μT at 54 irradiation frequency offsets. With the 3D snapshot CEST sequence, a 180 × 220 × 54 mm field of view was acquired in 7 seconds per offset. Spectrally selective CEST effects at +3.5 and –3.5 ppm were quantified using multi‐Lorentzian fitting. Reproducibility was high with an intersubject coefficient of variation below 10% in CEST contrasts. Amide and nuclear overhauser effect CEST effects showed similar correlations in tumor and necrosis as show in previous ultra‐high field work.ConclusionA sophisticated CEST tool ready for clinical application was developed and tested for feasibility.