Ablation Region Research Articles

Effects of differenta mitomycin C concentrations on laser-assisted subepithelial keratectomy.

The aim of the present study was to determine the effect of different concentrations of mitomycin C (MMC) administered intraoperatively during laser-assisted subepithelial keratectomy (LASEK) surgery. A total of 261 patients (496 eyes) were randomly divided into two groups: 0.04% MMC treatment group consisting of 133 patients (245 eyes) and the 0.02% MMC treatment group consisting of 128 patients (251 eyes). The MMC solutions were dropped intraoperatively onto the ablation region and the duration was dependent on the preoperative refractive power of the patient’s cornea: ≤−3.00 diopters (D), 30 sec; between −3.25 D and −6.00 D, 60 sec; between −6.25 D and −9.00 D, 90 sec and ≥−9.25 D, 110 sec. Postoperative observations included haze formation, visual acuity, changes in refractive power, corneal endothelial cell density and incidence of complications. The one year postoperative incidence of haze differed significantly between the groups (P<0.05). The one week and one year comparisons of postoperative visual acuity also differed significantly between the groups (P<0.05). Postoperative changes in corneal refractive power at one, six and 12 months following surgery significantly differed between the groups (P<0.05). No statistically significant difference was identified between the density of corneal endothelial cells prior to surgery and the density at one, six and 12 months following surgery (P>0.05). Thus, the intraoperative application of 0.04% MMC solution effectively inhibited haze formation and markedly improved the efficacy of LASEK surgery, when compared with that of 0.02% MMC.

Femtosecond laser micromachining with extended depth of focus by using diffractive lenses

We show that a simple diffraction focusing element can alleviate mechanical tolerances in ultrafast laser microprocessing. In particular, we experimentally demonstrate that, in comparison with a conventional refractive lens (RL), focusing light pulses of 30fs onto a stainless steel sample with a diffractive lens (DL) can increase twice the useful axial ablation region. This is thanks to the combination of the broadband spectrum of ultrashort pulses, and the huge longitudinal chromatic aberration associated with DLs. We believe that our results might be useful for reducing the complexity and cost of ultrafast microprocessing systems.

Microelectrode patterning of metal films using pulsed UV-laser system

This study presents a maskless method to conduct microelectrode patterning of metal films using pulsed UV-laser-writing technology. The experimental procedures involved designing the ablation region of a glass substrate, ablation path planning, and determining detailed laser-writing parameters. The various parameters used in a UV-laser-writing system were investigated and analyzed using an optical microscope and a three-dimensional confocal laser scanning microscope. This technique was successfully applied in patterning aluminum (Al) thin film on a glass substrate for use in microheater devices. The measurements of electrical resistance and temperature distribution on the substrate demonstrated that no short circuiting occurred in the microheater, confirming the quality of the electrical isolation values.

Ablation mechanism and properties of SiCf/SiBCN ceramic composites under an oxyacetylene torch environment

Ablation mechanism and properties of SiCf/SiBCN ceramic composites under an oxyacetylene torch ablation environment were investigated. Ablation products mainly consist of amorphous SiO2 glass and cristobalite. Four time-dependent ablation actions contribute to the various ablation regions: oxidations of SiC fibers and SiBCN matrix, erosion of SiC fibers in the center region, evaporation of SiO(g) and B2O3(g), and high-viscosity SiO2 liquid flowing with ablation gas-stream. Meanwhile, the mass ablation rate and linear ablation rate of SiCf/SiBCN are notably lower than those of Cf/SiBCN.

A Nanoengineered Embolic Agent for Precise Radiofrequency Ablation

The purpose of the work is to investigate whether the electromagnetic properties of multi-walled carbon nanotubes (MWCNT) in the presence of radiofrequency (RF) energy is (1) safe, and (2) improves the precision of the therapeutic efficiency of the RF-ablation (RFA) procedure. An in vitro phantom was created for evaluating temperature near RF treated nanotubes. For the in vivo study, three baboons and six pigs were submitted for RFA procedure in superior/inferior kidney poles embolized with a non-adherent, lipophilic embolic agent (marsembol) with or without MWCNT. Tissue damage in the surrounding kill zone was assayed through caspase-3 activation. The in vitro results showed marked heat increase only in the region of the nanotubes. In vivo, necrosis/ischemic damage resulted from RFA therapy alone, RFA plus marsembol only. In marsembol+MWCNT condition, dramatic disruption of cell membranes and sub-cellular organelles was found whereas the nuclear membranes and basal cell membranes remained largely intact. The marsembol vaporized under RFA and tissue fluid filled the space. This caused the MWCNT to cluster within the new aqueous environment. RFA plus marsembol+MWCNT created a well-defined demarcation between healthy and apoptotic cells as evidenced by a marked reduction of caspase-3 expression. By contrast, there was a much less defined ablation zone in the absence of MWCNT. In conclusion, the combination of RFA plus marsembol+MWCNT embolization delineated the kill zone in vitro and in vivo. We demonstrate that MWCNTs remain in the ablation region thus minimizing their migration to the systemic circulation.

OS1126 超短パルスレーザによるマイクロドリルの数値シミュレーション

The purpose of this study is to estimate the shape of ablated crater with sufficient accuracy when the multi-shot of the ultra-short pulse laser are irradiated to glasses. In this analytical model, the complex dielectric function of the Lorentz model is applied, in order to consider that glasses are dielectrics and to evaluate the damage by the laser ablation. Simultaneously, the time evolutions of free electrons density for distinguishing the ablation region and the damage region are calculated, and finally the threshold fluences are able to be computed quantitatively to various laser irradiation conditions. The absorption coefficients and threshold fluences which were obtained by this analysis were applied to the Beer-Lambert law, and it was well in agreement with the crater depth obtained from this analysis. Moreover, the crater shapes over the multi-shot channels in consideration of the laser fluence dependences of the absorption coefficients and the threshold fluences at the first shot were well in agreement with experimental results.

Considering angle selection when using ultrasound electrode displacement elastography to evaluate radiofrequency ablation of tissues.

Percutaneous radiofrequency ablation (RFA) is a minimally invasive treatment to thermally destroy tumors. Ultrasound-based electrode-displacement elastography is an emerging technique for evaluating the region of RFA-induced lesions. The angle between the imaging probe and the RFA electrode can influence electrode-displacement elastography when visualizing the ablation zone. We explored the angle effect on electrode-displacement elastography to measure the ablation zone. Phantoms embedded with meatballs were fabricated and then ablated using an RFA system to simulate RFA-induced lesions. For each phantom, a commercial ultrasound scanner with a 7.5 MHz linear probe was used to acquire raw image data at different angles, ranging from 30° to 90° at increments of 10°, to construct electrode-displacement images and facilitate comparisons with tissue section images. The results revealed that the ablation regions detected using electrode-displacement elastography were highly correlated with those from tissue section images when the angle was between 30° and 60°. However, the boundaries of lesions were difficult to distinguish, when the angle was larger than 60°. The experimental findings suggest that angle selection should be considered to achieve reliable electrode-displacement elastography to describe ablation zones.

Bubble formation induced by nanosecond laser ablation in water and its diagnosis by optical transmission technique

In this paper, bubble formation and ablation rate in laser ablation of a thin-film aluminum target are studied. The target was an aluminum thin-film coated on a quartz substrate and interacted by a nanosecond Nd:YAG laser beam in ambient air and distilled water. Measuring optical transmission of a He-Ne beam through the ablation region shows that the ablation rate in water is higher than that in ambient air. The results also show that an initial peak appears in the transmission signal which is an evi- dence for bubble formation in water. Analyzing the data is useful for monitoring the bubble formation in water and relatively estimating the ablation rate.

Treatment planning for prostate focal laser ablation in the face of needle placement uncertainty

To study the effect of needle placement uncertainty on the expected probability of achieving complete focal target destruction in focal laser ablation (FLA) of prostate cancer. Using a simplified model of prostate cancer focal target, and focal laser ablation region shapes, Monte Carlo simulations of needle placement error were performed to estimate the probability of completely ablating a region of target tissue. Graphs of the probability of complete focal target ablation are presented over clinically relevant ranges of focal target sizes and shapes, ablation region sizes, and levels of needle placement uncertainty. In addition, a table is provided for estimating the maximum target size that is treatable. The results predict that targets whose length is at least 5 mm smaller than the diameter of each ablation region can be confidently ablated using, at most, four laser fibers if the standard deviation in each component of needle placement error is less than 3 mm. However, targets larger than this (i.e., near to or exceeding the diameter of each ablation region) require more careful planning. This process is facilitated by using the table provided. The probability of completely ablating a focal target using FLA is sensitive to the level of needle placement uncertainty, especially as the target length approaches and becomes greater than the diameter of ablated tissue that each individual laser fiber can achieve. The results of this work can be used to help determine individual patient eligibility for prostate FLA, to guide the planning of prostate FLA, and to quantify the clinical benefit of using advanced systems for accurate needle delivery for this treatment modality.

Single shot depth sensitivity using femtosecond Laser Induced Breakdown Spectroscopy

Depth profiling measurement using multiple pulse Laser Induced Breakdown Spectroscopy (LIBS) can be used to determine the characteristics of buried layers. However for femtosecond pulses the emission spectra does not necessarily reflect the average depth composition for the single shot case and instead has much higher sensitivity for the surface layer of the ablation region. We introduce a concept of “depth sensitivity” to characterize this behavior for single shot LIBS depth profiling. Experiments were carried out using 800nm femtosecond laser pulses irradiating layered targets while monitoring the plasma emission with a spectrometer system. Laser induced plasma formed at the surface layer exhibits a strong LIBS signature while deeper ablated region contributes very little to the emission spectrum. The sensitive depth region, the source of the major part of the emission, is much less than the ablation crater depth and is shown to be of the order of 3nm in the case of actual crater depths of 100's of nm. A two temperature model has been used to determine the lattice temperature profile versus depth which qualitatively predicts the observed behavior.

Formation of laser jet thrust in the supersonic regime

Basic methods for obtaining laser jet thrust in the supersonic regime corresponding to the supersonic flow in the jet nozzle are analyzed. It is shown that the method based on the interaction of a laser ablative jet with the supersonic flow is promising. In this case, laser thrust is formed due to additional acceleration of the flow behind the ablation region. Numerical simulation of the flow in a parabolic nozzle is employed to demonstrate the possibility of effective formation of laser thrust at a level of 3 × 10−3 N/W.

Enhancement of detection by selective modification of silicon nanobelt field-effect transistors via localized Joule heating

We utilized localized Joule heating to ablate methoxy-poly (ethylene-glycol)-silane (mPEG-sil) modified on the p− region of an n+–p−–n+ silicon nanobelt field-effect transistor (SNFET). SNFETs with selective modifications of 3-aminopropyltrimethoxysilane (APTMS) and NHS-biotin on the ablated region exhibited a faster sensing response rate and a higher sensitivity in real-time detection of Streptavidin (SA). Characterization of the ablated region via lateral force microscopy and the fluorescence image show that the ablation region occurs only in the p− region near the drain side and is believed to be a result of the impact ionization mechanism during Joule heating. Moreover, a bias of 20V pulse voltage for 1ms successfully ablates mPEG-sil and reduces the device off leakage current by 1 order after Joule heating. However, Joule heating with a pulse voltage larger than 20V (1ms) yielded an increase of device off leakage owing to damage to gate dielectrics during Joule heating. A comparison of real-time detection of SA between selectively and non-selectively modified chips shows that selectively modified ones exhibit a better limit of detection (LOD) that is one order lower than non-selectively modified ones, and a sensing response rate twice as fast as the non-selectively modified one for every target concentration.

FIB/TEM/EELS micro/nanometric investigations of the effects of laser ablation on the diamond/binder structure in polycrystalline diamond composites

Laser ablation of diamond composites is of high interest for a wide range of industries for making high wear resistant tools/components. In this context, the paper studies the effects of pulsed laser ablation on a polycrystalline diamond composite (CMX850, average grain size 2μm, Cobalt binder volume, circa 15%) by identifying the residual carbonic allotropes and metallic binder traces in the ablation region. For this study, grooves were first laser (DMG LASERTEC 60 HSC Q-switched Nd:YAG, pulse duration 20μs, frequency 10kHz) ablated into the surface of the polycrystalline diamond structure, then, by using Focused Ion Beam (FIB) techniques, a thin section across the groove was extracted, which allowed the identification of the distinct microstructural characteristics below the ablated surfaces at sites that experienced high and low laser fluence. Using Transmission Electron Microscopy (TEM) imaging and Electron Energy Loss Spectroscopy (EELS) scans, the extracted lamella revealed that amorphous carbon and graphitic structures were formed as a consequence of the ablation process and an abrupt interface graphite to polycrystalline diamond was evident showing an undisturbed polycrystalline diamond (PCD) composite substructure below the graphitic boundary. Furthermore partially evacuated pockets containing traces of the Cobalt binder were identified within the amorphic/graphitic regions of the lamella. The examination of local high and low laser fluence ablated sites has revealed that the extent of residual deposits (amorphic and graphitic carbon) is related to the level of fluence/thermal activity during ablation.

Cyclic ablation behavior of C/C–ZrC–SiC composites under oxyacetylene torch

Cyclic ablation behavior of C/C–ZrC–SiC composites prepared by precursor infiltration and pyrolysis process was studied using oxyacetylene torch. After repeated 30s ablation for four times, the composites exhibited better ablation properties than those under single ablation for 120s because of the lower surface temperature, and their linear and mass ablation rates were −3×10–4mm/s and −2.29×10–3g/s, respectively. A continuous ZrO2–SiO2 layer formed on the surface of center ablation region and acted as an effective barrier to the transfer of heat and oxidative gases into the inner material. Thermal stress induced by repeated impact of oxyacetylene led to some cracks on the ZrO2–SiO2 layer; however its destructive power was weaker than that of higher temperature. Stick like silica as grown silica nanowires were generated in the transition ablation region due to the evaporation of silicon oxide at appropriate temperature.

In vitro parameter optimization for spatial control of focused ultrasound ablation when using low boiling point phase-change nanoemulsions.

BackgroundPhase-shift nanoemulsions (PSNEs) provide cavitation sites when the perfluorocarbon (PFC) nanodroplets (ND) are vaporized to microbubbles by acoustic energy. Their presence lowers the power required to ablate tissue by high-intensity focused ultrasound (HIFU), potentially making it a safer option for a broader range of treatment sites. However, spatial control over the ablation region can be problematic when cavitation is used to enhance heating. This study explored relationships between vaporization, ablation, and the PSNE concentration in vitro to optimize the acoustic intensity and insonation time required for spatially controlled ablation enhancement using a PSNE that included a volatile PFC component.MethodsHIFU (continuous wave at 1 MHz; insonation times of 5, 10, 15, and 20 s; cool-down times of 2, 4, and 6 s; peak negative pressures of 2, 3, and 4 MPa) was applied to albumin-acrylamide gels containing PFC agents (1:1 mix of volatile decafluorobutane and more stable dodecafluoropentane at 105 to 108 PFC ND per milliliter) or agent-free controls. Vaporization fields (microbubble clouds) were imaged by conventional ultrasound, and ablation lesions were measured directly by calipers. Controlled ablation was defined as the production of ‘cigar’-shaped lesions corresponding with the acoustic focal zone. This control was considered to be lost when ablation occurred in prefocal vaporization fields having a predominantly ‘tadpole’ or oblong shape.ResultsChanges in the vaporization field shape and location occurred on a continuum with increasing PSNE concentration and acoustic intensity. Working with the maximum concentration-intensity combinations resulting in controlled ablation demonstrated a dose-responsive relationship between insonation time and volumes of both the vaporization fields (approximately 20 to 240 mm3) and the ablation lesions (1 to 135 mm3) within them.ConclusionsHIFU ablation was enhanced by this PSNE and could be achieved using intensities ≤650 W/cm2. Although the ablation lesions were located within much larger microbubble clouds, optimum insonation times and intensities could be selected to achieve an ablation lesion of desired size and location for a given PSNE concentration. This demonstration of controllable enhancement using a PSNE that contained a volatile PFC component is another step toward developing phase-shift nanotechnology as a potential clinical tool to improve HIFU.

Er:YAG Laser Ablation of Bone versus Conventional Burrs in Otologic Surgery

Objectives: The Er:YAG laser (EYL) provides an efficient means of precise and predictable bone ablation, without intense thermal injury associated with CO2 laser use. Use of the EYL in otology is possible, but must be undertaken with caution as ablation is associated with brief intense acoustic transients up to 120 dB. This study details the use of the EYL in otologic and neuro-otologic surgery and compares ablation using a commercially available EYL with customizable glass fiber tips versus diamond and cutting burrs by means of infrared thermal imaging (IRT) and environmental scanning electron microscopy (ESEM). Methods: Five 0.6 mm diameter cylindrical cuts to a depth of 0.6 mm were made in formalin fixed human squamous temporal bone using a 300 µs EYL with pulse energies of 250 and 400 mJ (corresponding fluence levels of 175 and 280 mJ/cm2) and 0.6 mm diameter cutting and diamond burrs. Copious irrigation was used for all cuts. IRT was used to determine temperature rise. Ablation regions were inspected with ESEM. Results: Peak temperature rises were similar for all methods of ablation, none exceeding the 12 °C threshold required for irreversible bone injury. ESEM revealed rough margins for cuts made using the cutting burr and smooth edges with no sign of microfracture for those made with EYL and diamond burr. Conclusions: EYL ablates bone efficiently and predictably with smooth margins without microfractures or clinically significant temperature rise. When used appropriately, EYL may be a valuable tool for the otologic surgeon.

The Effects of Metallic Implants on Electroporation Therapies: Feasibility of Irreversible Electroporation for Brachytherapy Salvage

Electroporation-based therapies deliver brief electric pulses into a targeted volume to destabilize cellular membranes. Nonthermal irreversible electroporation (IRE) provides focal ablation with effects dependent on the electric field distribution, which changes in heterogeneous environments. It should be determined if highly conductive metallic implants in targeted regions, such as radiotherapy brachytherapy seeds in prostate tissue, will alter treatment outcomes. Theoretical and experimental models determine the impact of prostate brachytherapy seeds on IRE treatments. This study delivered IRE pulses in nonanimal, as well as in ex vivo and in vivo tissue, with and in the absence of expired radiotherapy seeds. Electrical current was measured and lesion dimensions were examined macroscopically and with magnetic resonance imaging. Finite-element treatment simulations predicted the effects of brachytherapy seeds in the targeted region on electrical current, electric field, and temperature distributions. There was no significant difference in electrical behavior in tissue containing a grid of expired radiotherapy seeds relative to those without seeds for nonanimal, ex vivo, and in vivo experiments (all p > 0.1). Numerical simulations predict no significant alteration of electric field or thermal effects (all p > 0.1). Histology showed cellular necrosis in the region near the electrodes and seeds within the ablation region; however, there were no seeds beyond the ablation margins. This study suggests that electroporation therapies can be implemented in regions containing small metallic implants without significant changes to electrical and thermal effects relative to use in tissue without the implants. This supports the ability to use IRE as a salvage therapy option for brachytherapy.

Underwater-laser drilling of aluminum

Pulsed-laser ablation of an aluminum bulk sample was performed both in water and air with a Q-switched Nd:YAG 1,064-nm laser over a range of high-output energies from 100 to 500 mJ. The effect of laser drilling in terms of produced crater volumes as a function of water-layer thickness was studied. The water-layer thickness was varied from 1 to 20 mm. In a special case, water droplets were added to the ablation region of the dry target in order to support ablation. Water-layer thickness in that case was estimated to be 0.5 mm. A comparison of the results obtained in air and underwater was performed. It is found that the aluminum target may be drilled more efficiently under the confinement of water compared to drilling in air environment. Further drilling efficiency can be achieved by varying the thickness of water. The optimized water thickness under the conditions of our experiment was found to be 3 mm. In that case, a 28-fold increase in crater volume and 18-fold increase in crater depth was achieved as compared to ablation in air. In underwater ablation, the formation of irregular surface structures of re-deposited material around the crater (rim) is avoided and the crater surface is smoother. In an air environment, the drilling is suppressed due to an immediate re-solidification and re-deposition of ablated material. This leads to a better characteristics of craters obtained underwater in terms of roughness, shape, volumes, and reproducibility.

Method for Detecting Ablation Damage Using Sensor Integration of Hot Biopsy Forceps

Method for Detecting Ablation Damage Using Sensor Integration of Hot Biopsy Forceps

Evolution of the Ablation Region After Magnetic Resonance–Guided High-Intensity Focused Ultrasound Ablation in a Vx2 Tumor Model

Volumetric magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) is a completely noninvasive image-guided thermal ablation technique. Recently, there has been growing interest in the use of MR-HIFU for noninvasive ablation of malignant tumors. Of particular interest for noninvasive ablation of malignant tumors is reliable treatment monitoring and evaluation of response. At this point, there is limited evidence on the evolution of the ablation region after MR-HIFU treatment. The purpose of the present study was to comprehensively characterize the evolution of the ablation region after volumetric MR-HIFU ablation in a Vx2 tumor model using MR imaging, MR temperature data, and histological data. Vx2 tumors in the hind limb muscle of New Zealand White rabbits (n = 30) were ablated using a clinical MR-HIFU system. Twenty-four animals were available for analyses. Magnetic resonance imaging was performed before and immediately after ablation; MR temperature mapping was performed during the ablation. The animals were distributed over 7 groups with different follow-up lengths. Depending on the group, animals were reimaged and then killed on day 0, 1, 3, 7, 14, 21, or 28 after ablation. For all time points, the size of nonperfused areas (NPAs) on contrast-enhanced T1-weighted (CE-T1-w) images was compared with lethal thermal dose areas (ie, the tissue area that received a thermal dose of 240 equivalent minutes or greater [EM] at 43°C) and with the necrotic tissue areas on histology sections. The NPA on CE-T1-w imaging showed an increase in median size from 266 ± 148 to 392 ± 178 mm(2) during the first day and to 343 ± 170 mm(2) on day 3, followed by a gradual decrease to 113 ± 103 mm(2) on day 28. Immediately after ablation, the NPA was 1.6 ± 1.4 times larger than the area that received a thermal dose of 240 EM or greater in all animals. The median size of the necrotic area on histology was 1.7 ± 0.4 times larger than the NPA immediately after ablation. After 7 days, the size of the NPA was in agreement with the necrotic tissue area on histology (ratio, 1.0 ± 0.2). During the first 3 days after MR-HIFU ablation, the ablation region increases in size, after which it gradually decreases in size. The NPA on CE-T1-w imaging underestimates the extent of tissue necrosis on histology in the initial few days, but after 1 week, the NPA is reliable in delineating the necrotic tissue area. The 240-EM thermal dose limit underestimates the necrotic tissue area immediately after MR-HIFU ablation. Reliable treatment evaluation techniques are particularly important for noninvasive, image-guided tumor ablation. Our results indicate that CE-T1-w imaging is reliable for MR-HIFU treatment evaluation after 1 week.