Coagulation Zone Research Articles

Study on microwave ablation temperature prediction model based on grayscale ultrasound texture and machine learning.

Temperature prediction is crucial in the clinical ablation treatment of liver cancer, as it can be used to estimate the coagulation zone of microwave ablation. Experiments were conducted on 83 fresh ex vivo porcine liver tissues at two ablation powers of 15 W and 20 W. Ultrasound grayscale images and temperature data from multiple sampling points were collected. The machine learning method of random forests was used to train the selected texture features, obtaining temperature prediction models for sampling points and the entire ultrasound imaging area. The accuracy of the algorithm was assessed by measuring the area of the hyperechoic area in the porcine liver tissue cross-section and ultrasound grayscale images. The model exhibited a high degree of accuracy in temperature prediction and the identification of coagulation zone. Within the test sets for the 15 W and 20 W power groups, the average absolute error for temperature prediction was 1.14°C and 4.73°C, respectively. Notably, the model's accuracy in measuring the area of coagulation was higher than that of traditional ultrasonic grey-scale imaging, with error ratios of 0.402 and 0.182 for the respective power groups. Additionally, the model can filter out texture features with a high correlation to temperature, providing a certain degree of interpretability. The temperature prediction model proposed in this study can be applied to temperature monitoring and coagulation zone range assessment in microwave ablation.

In Vivo Histological Study Evaluating Non-Ablative Fractional 1940-nm Laser.

Non-ablative fractional lasers (NAFL) have increased in demand compared to ablative laser treatments as they provide lesser down time, fewer side-effects, and are safer to use. Non-ablative fractional treatment with lasers ranging from 1320 to 1927-nm have been shown to be safe and effective for skin resurfacing procedures. The objective of this study is to investigate healing of the 1940-nm NAFL-induced microthermal treatment zones (MTZs) in human skin from a histologic perspective. Three subjects received 1940-nm NAFL treatment to test areas on the abdomen at various timepoints during the study. The minimum 5 mJ/MTZ and maximum 20 mJ/MTZ energy settings were used at 20% coverage. Biopsies were taken coinciding with immediately posttreatment, 1, 3, 7 days, and 6 weeks posttreatment. Blinded analysis of hematoxylin and eosin stained slides was performed to measure the width and depth of the MTZs and evaluate the inflammatory and healing response of the skin over time (immediately to 6 weeks posttreatment). Safety was evaluated by assessing local skin responses and adverse events immediately after treatment and at all study visits. Histological analysis of tissue following NAFL 1940-nm treatments showed mild early inflammatory response (presence of lymphotic infiltrate) in some test areas and zones of necrosis and coagulation having widths and depths (immediately-3 days posttreatment) that scaled with the 1940-nm pulse energy. Signs of healing such as presence of dermal mucin, evidence of fibrosis, and absence of necrosis were observed long-term (7 days to 6 weeks posttreatment). Evidence of the MTZ persisted beyond the 6-week study and was predicted to last for 100 days. All local clinical skin responses healed within 6 weeks and were limited to mild, transient erythema and edema which resolved in less than 12-24 h following treatment. No serious adverse events occurred during the study. NAFL 1940-nm treatments are safe for inducing small fractional coagulation and necrosis zones in abdominal skin. NAFL 1940-nm laser creates fractional columns of injury with sufficient depth and coverage that suggest effective skin resurfacing, like other non-ablative fractional lasers.

Comparison of holmium:yttrium-aluminium-garnet (YAG), thulium fiber laser, and pulsed thulium:YAG lasers on soft tissue: an ex vivo study.

To assess laser-tissue interactions through ablation, coagulation, and carbonisation characteristics in a non-perfused porcine kidney model between three pulsed lasers: holmium (Ho): yttrium-aluminium-garnet (YAG), thulium fiber laser (TFL), and pulsed thulium (p-Tm):YAG. A 150-W Ho:YAG, a 60-W TFL, and a 100-W p-Tm:YAG lasers were compared. The laser settings that can be set identically between the three lasers and be clinically relevant for prostate laser enucleation were identified and used on fresh, unfrozen porcine kidneys. Laser incisions were performed using stripped laser fibers of 365 and 550 μm, set at distances of 0 and 1 mm from the tissue surface at a constant speed of 2 mm/s. Histological analysis evaluated shape, depth, width of the incision, axial coagulation depth, and presence of carbonisation. Incision depths, widths, and coagulation zones were greater with Ho:YAG and p-Tm:YAG lasers than TFL. Although no carbonisation was found with the Ho:YAG and p-Tm:YAG lasers, it was common with TFL, especially at high frequencies. The shapes of the incisions and coagulation zones were more regular and homogeneous with the p-Tm:YAG laser and TFL than with Ho:YAG laser. Regardless of the laser used, short pulse durations resulted in deeper incisions than long pulse durations. Concerning the distance, we found that to be effective, TFL had to be used in contact with the tissue. Finally, 365-μm fibers resulted in deeper incisions, while 550-μm fibers led to wider incisions and larger coagulation zones. Histological analysis revealed greater tissue penetration with the p-Tm:YAG laser compared to the TFL, while remaining less than with Ho:YAG. Its coagulation properties seem interesting insofar as it provides homogeneous coagulation without carbonisation, while incisions remained uniform without tissue laceration. Thus, the p-Tm:YAG laser appears to be an effective alternative to Ho:YAG and TFL lasers in prostate surgery.

Coagulation depth estimation using a line scanner for depth-resolved laser speckle contrast imaging.

Partial-thickness burn wounds extend partially through the dermis, leaving many pain receptors intact and making the injuries very painful. Due to the painfulness, quick assessment of the burn depth is important to not delay surgery of the wound if needed. Laser speckle imaging (LSI) of skin blood flow can be helpful in finding severe coagulation zones with impaired blood flow. However, LSI measurements are typically too superficial to properly reach the full depth of the adult dermis and cannot resolve the flow in depth. Diffuse correlation spectroscopy (DCS) uses varying source-detector separations to allow differentiation of flow depths but requires time-consuming 2D scanning to form an image of the burn area. We here present a prototype for a hybrid DCS and LSI technique called speckle contrast diffuse correlation spectroscopy (scDCS) with the novel approach of using a laser line as a source and using the speckle contrast of averaged images to obtain an estimate of static scattering in the tissue. This will allow for fast non-contact 1D scanning to perform 3D tomographic imaging, making quantitative estimates of the depth and area of the coagulation zone from burn wounds. Simulations and experimental results from a volumetric flow phantom and a gelatin wedge phantom show promise to determine coagulation depth. The aim is to develop a method that, in the future, could provide more quantitative estimates of coagulation depth in partial thickness burn wounds to better estimate when surgery is needed.

Microwave ablation on ex vivo porcine pancreas: The influence of ablation parameters on ablation results and fat liquefaction.

The pancreas is adjacent to critical organs; excessive microwave ablation (MWA) can result in serious complications. The purpose of this paper is to provide the reference data of pancreas MWA for clinicians, analyze the ablation outcomes under different ablation parameters, and determine the critical temperature of pancreatic surface fat liquefaction outflow. Combinations of two power levels (30 W and 55 W), three antenna diameters (1.3 mm, 1.6 mm, and 1.9 mm), and three ablation times (1 min, 1.5 min, and 2 min) were applied to an ex vivo pig pancreas. Temperature measurements were taken at four thermocouple points. The center point is located 5 mm horizontally from the antenna slot, with a temperature measurement point located 5 mm above, below, and to the right of the center point. Main effect analysis and variance analysis were used to quantify the influences of each factor on the ablation outcomes. At 30 W, the antenna diameter contributing the most at 48.5%. At 30 W-1.3 mm-1 min, the spherical index (1.41) is closest to 1. At 55 W, the coagulation zone size was almost only affected by the ablation time, with a contribution rate of 28.7%, the temperature at point C exceeds point B. On the surface of the ex vivo porcine pancreas, the fat outflow temperature was 54ã. Ablation combinations with low power, short duration, and small antenna diameter results in a more nearly spherical coagulation zone. When performing MWA on the pancreas, it is advisable to avoid areas with higher fat content, while keeping the pancreatic surface temperature below 54°C.

Impact of surrounding tissue-type and peri-electrode gap in stereoelectroencephalography guided (SEEG) radiofrequency thermocoagulation (RF-TC): a computational study

Purpose To use computational modeling to provide a complete and logical description of the electrical and thermal behavior during stereoelectroencephalography-guided (SEEG) radiofrequency thermo­coagulation (RF-TC). Methods A coupled electrical-thermal model was used to obtain the temperature distributions in the tissue during RF-TC. The computer model was first validated by an ex vivo model based on liver fragments and later used to study the impact of three different factors on the coagulation zone size: 1) the difference in the tissue surrounding the electrode (gray/white matter), 2) the presence of a peri-electrode gap occupied by cerebrospinal fluid (CSF), and 3) the energy setting used (power-duration). Results The model built for the experimental validation was able to predict both the evolution of impedance and the short diameter of the coagulation zone (error < 0.01 mm) reasonably well but overestimated the long diameter by 2 − 3 mm. After adapting the model to clinical conditions, the simulation showed that: 1) Impedance roll-off limited the coagulation size but involved overheating (around 100 °C); 2) The type of tissue around the contacts (gray vs. white matter) had a moderate impact on the coagulation size (maximum difference 0.84 mm), and 3) the peri-electrode gap considerably altered the temperature distributions, avoided overheating, although the diameter of the coagulation zone was not very different from the no-gap case (<0.2 mm). Conclusions This study showed that computer modeling, especially subject- and scenario-specific modeling, can be used to estimate in advance the electrical and thermal performance of the RF-TC in brain tissue.

Multimodality quantitative ultrasound envelope statistics imaging based support vector machines for characterizing tissue scatterer distribution patterns: Methods and application in detecting microwave-induced thermal lesions

Ultrasound envelope statistics imaging, including ultrasound Nakagami imaging, homodyned-K imaging, and information entropy imaging, is an important group of quantitative ultrasound techniques for characterizing tissue scatterer distribution patterns, such as scatterer concentrations and arrangements. In this study, we proposed a machine learning approach to integrate the strength of multimodality quantitative ultrasound envelope statistics imaging techniques and applied it to detecting microwave ablation induced thermal lesions in porcine liver ex vivo. The quantitative ultrasound parameters included were homodyned-K α which is a scatterer clustering parameter related to the effective scatterer number per resolution cell, Nakagami m which is a shape parameter of the envelope probability density function, and Shannon entropy which is a measure of signal uncertainty or complexity. Specifically, the homodyned-K log10(α), Nakagami-m, and horizontally normalized Shannon entropy parameters were combined as input features to train a support vector machine (SVM) model to classify thermal lesions with higher scatterer concentrations from normal tissues with lower scatterer concentrations. Through heterogeneous phantom simulations based on Field II, the proposed SVM model showed a classification accuracy above 0.90; the area accuracy and Dice score of higher-scatterer-concentration zone identification exceeded 83% and 0.86, respectively, with the Hausdorff distance <26. Microwave ablation experiments of porcine liver ex vivo at 60–80 W, 1–3 min showed that the SVM model achieved a classification accuracy of 0.85; compared with single log10(α),m, or hNSE parametric imaging, the SVM model achieved the highest area accuracy (89.1%) and Dice score (0.77) as well as the smallest Hausdorff distance (46.38) of coagulation zone identification. We concluded that the proposed multimodality quantitative ultrasound envelope statistics imaging based SVM approach can enhance the capability to characterize tissue scatterer distribution patterns and has the potential to detect the thermal lesions induced by microwave ablation.

Histological analysis of laser-enabled tissue coring with a novel 2910 nm erbium-doped fluoride glass fiber laser.

There remains an unmet need for a laser-enabled tissue coring device that can effectively improve face and neck skin laxity and rhytides. We investigate a novel 2910 nm erbium-doped fluoride glass fiber laser (2910 nm fiber laser) (UltraClear; Acclaro Medical) for laser-coring of submental tissue. Five subjects, Glogau scale III-IV, were treated with a single pulse of the laser-coring mode of the 2910 nm fiber laser in the submentum. A 4 mm punch biopsy was immediately performed. Biopsy specimens were sectioned and stained with hematoxylin and eosin and placed on glass slides. All sections were reviewed, and sections containing the center of the transected core were analyzed for depth and diameter of the ablative microchannel and width of the surrounding zone of coagulation. A total of 15 intact micro-cores were analyzed. Histological analysis revealed an average ± standard deviation microchannel diameter of 242.5 ± 65.2 µm, an average ablative depth of 980 ± 318.8 µm, and an average zone of coagulation of 104 ± 32 µm. Laser-enabled tissue coring with a novel 2910 nm fiber laser can safely achieve a wider microchannel diameter with ablative depth extending to the mid and deep dermis, which has the potential for collagen contraction and tissue tightening. Laser-coring to this ablation diameter and depth and with the surrounding zone of coagulation was found to be safe without adverse effects of post-inflammatory erythema or scarring in our study.

Effective Management of Recurrent Trauma-Induced Neck Pain With Radiofrequency Neurotomy Using the Nimbus Electrosurgical Radiofrequency Multitined Expandable Electrode: A Case Report

BACKGROUND: Radiofrequency neurotomy (RFN) can be an effective treatment for patients with chronic neck pain and cervicogenic headaches resistant to conservative care. However, the degree and duration of pain relief after RFN is dependent upon the thoroughness of target nerve coagulation. CASE REPORT: This is a case of a 37-year-old patient with debilitating neck pain and headaches following a motor vehicle accident. Successful local anesthetic block of the third occipital nerve (TON) confirmed pain of C2-C3 facet joint origin. An initial RFN treatment of the TON, using standard 18G electrodes in bipolar mode, resulted in complete symptom amelioration for 8 months. Repeat RFN, using the same electrode configuration, was unsuccessful in alleviating the severe neck pain and headaches, and produced no demonstrable sensory loss in the distribution of the TON. RFN was then performed using the Nimbus® electrosurgical RF multitined expandable electrode, which provides a larger zone of coagulation in volume than standard RFN electrodes even when used in bipolar configuration. CONCLUSIONS: The Nimbus procedure resulted in successful coagulation of the TON with sensory loss in the TON distribution and reinstatement of palliative relief. KEY WORDS: Cervical pain, radiofrequency neurotomy, third occipital nerve, Nimbus, case report

Novel 40 µm spot size 3050/3200 nm DFG laser versus CO2 laser for laser-assisted drug delivery.

The use of ablative fractional lasers to enhance the delivery of topical drugs through the skin is known as laser-assisted drug delivery. Here, we compare a novel 3050/3200 nm difference frequency generation (DFG) fiber laser (spot size: 40 µm) to a commercially used CO2 laser (spot size: 120 µm). The objective is to determine whether differences in spot size and coagulation zone (CZ) thickness influence drug uptake. Fractional ablation was performed on ex-vivo human abdominal skin with the DFG (5 mJ) and CO2 (12 mJ) lasers to generate 680 µm deep lesions. To evaluate drug delivery, 30 kDa encapsulated fluorescent dye was topically applied to the skin and histologically analyzed at skin depths of 100, 140, 200, 400, and 600 µm. Additionally, transcutaneous permeation of encapsulated and 350 Da nonencapsulated dye was assessed using Franz Cells. The DFG laser generated smaller channels (diameter: 56.5 µm) with thinner CZs (thickness: 22.4 µm) than the CO2 laser (diameter: 75.9 µm, thickness: 66.8 µm). The DFG laser treated group exhibited significantly higher encapsulated dye total fluorescence intensities after 3 h compared to the CO2 laser treated group across all skin depths (p < 0.001). Permeation of nonencapsulated dye was also higher in the DFG laser treated group vs the CO2 laser treated group after 48 h (p < 0.0001), while encapsulated dye was not detected in any group. The DFG laser treated skin exhibited significantly higher total fluorescence uptake compared to the CO2 laser. Additionally, the smaller spot size and thinner CZ of the DFG laser could result in faster wound healing and reduced adverse effects while delivering similar or greater amount of topically applied drugs.

Impact of skin hydration on patterns of microthermal injury produced by fractional CO2 laser.

The impact of skin hydration on patterns of thermal injury produced by ablative fractional lasers (AFLs) is insufficiently examined under standardized conditions. Using skin with three different hydration levels, this study assessed the effect of hydration status on microchannel dimensions generated by a fractional CO2 laser. A hydration model (hyperhydrated-, dehydrated- and control) was established in ex vivo porcine skin, validated by changes in surface conductance and sample mass. After, samples underwent AFL exposure using a CO2 laser (10,600 nm) at two examined pulse energies (10 and 30 mJ/mb, fixed 10% density, six repetitions per group). Histological assessment of distinct microchannels (n = 60) determined three standardized endpoints in H&E sections: (1) depth of microthermal treatment zones (MTZs),(2) depth of microscopic ablation zones (MAZs), and (3) coagulation zone (CZ) thickness. As a supplemental in vivo assessment, the same laser settings were applied to hyperhydrated- (7-h occlusion) and normohydrated forearm skin (no pretreatment) of a human volunteer. Blinded measurement of MAZ depth (n = 30) was performed using noninvasive optical coherence tomography (OCT). Modest differences in microchannel dimensions were shown between hyperhydrated, dehydrated and control skin at both high and low pulse energy. Compared to controls, hyperhydration led to median reductions in MTZ and MAZ depth ranging from 5% to 8% (control vs. hyperhydrated at 30 mJ/mb; 848 vs. 797 µm (p < 0.003) (MAZ); 928 vs. 856 µm (p < 0.003) (MTZ)), while 14%-16% reductions were shown in dehydrated skin (control vs. dehydrated at 30 mJ/mb; MAZ: 848 vs. 727 µm (p < 0.003); MTZ: 928 vs. 782 µm (p < 0.003)). The impact of skin hydration on CZ thickness was in contrast limited. Corresponding with ex vivo findings, hyperhydration was similarly associated with lower ablative depth in vivo skin. Thus, median MAZ depth in hydrated skin was 10% and 14% lower than in control areas at 10 and 30 mJ/mb pulse energy, respectively (10 mJ: 210 vs. 180 µm (p < 0.001); 30 mJ: 335 vs. 300 µm (p < 0.001)). Skin hydration status can exert a minimal impact on patterns of microthermal injury produced by fractional CO2 lasers, although the clinical implication in the context of laser therapy requires further study.

Enlarging the thermal coagulation volume during thermochemical ablation with alternating acid-base injection by shortening the injection interval: A computational study

Background and objectivesThermochemical ablation (TCA) is a cancer treatment that utilises the heat released from the neutralisation of acid and base to raise tissue temperature to levels sufficient to induce thermal coagulation. Computational studies have demonstrated that the coagulation volume produced by sequential injection is smaller than that with simultaneous injection. By injecting the reagents in an ensuing manner, the region of contact between acid and base is limited to a thin contact layer sandwiched between the distribution of acid and base. It is hypothesised that increasing the frequency of acid-base injections into the tissue by shortening the injection interval for each reagent can increase the effective area of contact between acid and base, thereby intensifying neutralisation and the exothermic heat released into the tissue. MethodsTo verify this hypothesis, a computational model was developed to simulate the thermochemical processes involved during TCA with sequential injection. Four major processes that take place during TCA were considered, i.e., the flow of acid and base, their neutralisation, the release of exothermic heat and the formation of thermal damage inside the tissue. Equimolar acid and base at 7.5 M was injected into the tissue intermittently. Six injection intervals, namely 3, 6, 15, 20, 30 and 60 s were investigated. ResultsShortening of the injection interval led to the enlargement of coagulation volume. If one considers only the coagulation volume as the determining factor, then a 15 s injection interval was found to be optimum. Conversely, if one places priority on safety, then a 3 s injection interval would result in the lowest amount of reagent residue inside the tissue after treatment. With a 3 s injection interval, the coagulation volume was found to be larger than that of simultaneous injection with the same treatment parameters. Not only that, the volume also surpassed that of radiofrequency ablation (RFA); a conventional thermal ablation technique commonly used for liver cancer treatment. ConclusionThe numerical results verified the hypothesis that shortening the injection interval will lead to the formation of larger thermal coagulation zone during TCA with sequential injection. More importantly, a 3 s injection interval was found to be optimum for both efficacy (large coagulation volume) and safety (least amount of reagent residue).

Multi-Probe RFA vs. Single-Probe MWA in an Ex Vivo Bovine Liver Model: Comparison of Volume and Shape of Coagulation Zones.

To compare the volumes and shapes of the coagulation zone (CZ) of a multi-probe RFA system (three RFA electrodes) and a single-probe MWA system from the same vendor in an ex vivo bovine liver model. A total of 48 CZs were obtained in bovine liver specimens with three different ablation system configurations (single-probe MWA vs. multi-probe RFA with 20 mm inter-probe distance [confluent CZ] vs. multi-probe RFA with 50 mm inter-probe distance [three individual CZs]) at 4, 6, 8, and 10 min ablation time using a fixed ablation protocol. Ablation diameters were measured and ellipticity indices (EIs) and volumes calculated. Calculations for all systems/configurations were compared. Volumes and diameters increased with ablation time for all configurations. At 4 and 6 min ablation time volumes obtained with the RFA 50 mm setup, and at 8 and 10 min with the RFA 20 mm setup were the largest at 26.5 ± 4.1 mL, 38.1 ± 5.8 mL, 46.3 ± 4.9 mL, 48.4 ± 7.3 mL, respectively. The single-probe MWA could not reach the volumes of the RFA setups for any of the ablation times evaluated. EI were very similar and almost round for RFA 20 mm and single-probe MWA, and differed significantly to the more ovoid ones for the RFA 50 mm configuration. The multi-probe RFA system employing three electrodes achieved significantly larger ablation volumes in both configurations (confluent CZ and three individual CZs) per time as compared with a single-probe MWA system in this ex vivo bovine liver model.

Comparative study of soft tissue surgery by visible and infrared laser radiation.

To compare the cutting properties of lasers with different wavelengths (445nm, 532nm and 808nm) used in cutting blood-rich tissues.Porcine myocardial tissue was cut using 2.3-15 W laser radiation in contact and non-contact modes with an optical fiber or focusing handpiece. The cut depth and coagulation zone width were determined histologically.The 445-nm laser achieved the greatest cut depth for all cutting parameters (p < 0.01). The blue laser gave the smallest coagulation width to cut depth ratio.Results of the study are consistent with the assumption that a 445nm blue laser may have better cutting properties than green and infrared lasers due to the high absorption of radiation at this wavelength in hemoglobin and, consequently, in the biological blood-rich tissue.

Histological damage characteristics and quantitive analysis of porcine skin with non-insulated microneedle radiofrequency.

In recent years, the microneedle radiofrequency (MRF) has been widely used for skin rejuvenation, but histological studies on the immediate trauma caused by different parameters of non-insulated RF microneedles METHODS: The skin of three pigs was treated with different needle depths, pulse widths and energy levels of non-insulated microneedle RF. Samples were collected before, immediately, and 2 weeks after treatment. The immediate histological response of each group was assessed and quantified by hematoxylin and eosin staining, Masson staining and Victoria Blue staining. In the treatment of non-insulated microneedle RF, different energy levels affected mainly the range of thermal damage (p=0.044), and different needle depths affected mainly the depth of the cavity (p=0.022). But the width of the coagulation zone width was determined by different factors. There was no significant difference in the histology of immediate damage caused by different pulse widths. Reepithelialization of the epidermis and basic wound repair can be completed within 2weeks. Non-insulated RF microneedle therapy is an effective and safe treatment that can stimulate dermal wound healing with less thermal coagulation and a wide range of reversible thermal damage. However, it should be noted that the set needle depth may not correspond to the actual penetration depth, nor to the actual depth of histologic trauma.

Morphological substantiation of laser exposure parameters and modes for surgical treatment of intrauterine pathology

Introduction No data on experimentally substantiated parameters and modes of diode laser radiation allowing a minimally traumatic surgical treatment of intrauterine pathology have been found in the literature.The aim of the investigation was to substantiate experimentally the optimum parameters and modes of diode laser radiation in the treatment of intrauterine pathology based on the study of morphological changes in the endometrium.Materials and methods 48 endometrial samples were exposed to 10-40 W diode laser power in a constant mode and 15 samples - in a pulsed mode with 3 different sets of laser exposure parameters. The data were statistically processed using Microsoft Excel spreadsheets, version 16.49. The differences were considered statistically significant at р&lt;0.05.Results Width of the ablation zone, lateral coagulation and hyperthermic exposure zone was calculated at the most optimal parameters of laser energy (20 W), achieving adequate cutting and bleeding properties of the laser. The most effective in the pulsed mode of laser operation was 30 W amplitude power of radiation, the pulse duration of 100 ms, the duration of the interval between pulses of 50 ms, the average power of 20 W.Discussion Comparative analysis of morphometric parameters in the action of laser radiation in the constant mode with a radiation power of 20 W and in the pulsed mode with an average laser power of 20 W has shown that the structural parameters have significantly lower values in the pulsed laser mode.Conclusion Optimal cutting properties of the laser are observed when constant laser irradiation with a power of 20 W is used. The best cutting and bleeding properties were demonstrated by the pulsed laser mode with an average power of 20 W, amplitude power of 30 W, pulse duration of 100 ms, and inter-pulse interval of 50 ms.

A Computational Study Evaluating the Effects of Diffuser Length and Pullback Distance on the Ablation Zone During Laser Ablation Treatment of Liver Cancer

Abstract Although laser ablation is not commonly used for liver cancer treatment, there are several benefits that make it an appealing alternative. Nevertheless, investigations on the efficacy of laser ablation for liver cancer have been limited to few clinical trials. Therefore, not much is known regarding the efficacy of the technique especially when operating under different protocols and device parameters. In this study, we performed a numerical study to investigate the effects of diffuser length, power density, and the pullback technique on the coagulation zone formation during laser ablation of spherical liver cancer. The objective is to demarcate the influence of diffuser length from power density and to compare their performance to that when pullback is implemented. Four diffuser lengths (10, 15, 20, and 25 mm), and three pullback distances (5, 10, and 15 mm), were considered. Results showed that laser power density is a factor that limits the coagulation zone size when the diffuser length increases. A longer diffuser must be accompanied by an increase in laser power to achieve the desired treatment outcome. The pullback technique increases the effective diffuser length, but the coagulation volume obtained was smaller than that of a longer diffuser at the same power density. This suggests that increasing both the diffuser length and laser power is better at increasing the coagulation zone than the pullback technique. To obtain coagulation zone that is sufficiently large to cover the entire tumor, careful selection of the diffuser length, power density, and pullback distance is critical.

Verhoeff van Gieson staining in laser-irradiated gingival tissues

ABSTRACT There have been several studies on the use of the Verhoeff van Gieson staining method to demonstrate thermal effects on tissues. However, this method has rarely been used for the analysis of periodontal tissues. This study was undertaken to compare the quality and effectiveness of the Verhoeff van Gieson (VVG) staining method with conventional hematoxylin & eosin (H&E) in measuring the thermal effects in gingival tissues. Periodontal tissues around bovine mandibular teeth were treated using different surgical lasers (wavelengths of 10,600 nm, 970 nm, and 445 nm) at 2 W power setting. Measurements of the depth of the coagulation zone were recorded for all treatment groups in sample tissues stained with H&E as well as the VVG-staining method. Measures were interpreted by a trained pathologist. A statistical analysis was performed using the Wilcoxon signed-rank test to determine if there was a statistically significant difference between values recorded for the light penetration depth on tissues stained with each of the two staining methods. It was determined that there was no significant difference in the recorded values (P = 0.23). We have concluded that the VVG-stained tissues were better able to visualize the depth of thermal damage and thus may make it easier for someone not well trained to interpret the depth of light penetration in these tissues.

Ultrasound Homodyned-K Contrast-Weighted Summation Parametric Imaging Based on H-scan for Detecting Microwave Ablation Zones.

The homodyned-K (HK) distribution is a generalized model of envelope statistics whose parameters α (the clustering parameter) and k (the coherent-to-diffuse signal ratio) can be used to monitor the thermal lesions. In this study, we proposed an ultrasound HK contrast-weighted summation (CWS) parametric imaging algorithm based on the H-scan technique and investigated the optimal window side length (WSL) of the HK parameters estimated by the XU estimator (an estimation method based on the first moment of the intensity and two log-moments, which was used in the proposed algorithm) through phantom simulations. H-scan diversified ultrasonic backscattered signals into low- and high-frequency passbands. After envelope detection and HK parameter estimation for each frequency band, the α and k parametric maps were obtained, respectively. According to the contrast between the target region and background, the (α or k) parametric maps of the dual-frequency band were weighted and summed, and then the CWS images were yielded by pseudo-color imaging. The proposed HK CWS parametric imaging algorithm was used to detect the microwave ablation coagulation zones of porcine liver ex vivo under different powers and treatment durations. The performance of the proposed algorithm was compared with that of the conventional HK parametric imaging and frequency diversity and compounding Nakagami imaging algorithms. For two-dimensional HK parametric imaging, it was found that a WSL equal to 4 pulse lengths of the transducer was sufficient for estimating the α and k parameters in terms of both parameter estimation stability and parametric imaging resolution. The HK CWS parametric imaging provided an improved contrast-to-noise ratio over conventional HK parametric imaging, and the HK αcws parametric imaging achieved the best accuracy and Dice score of coagulation zone detection.

An in silico assessment on the potential of using saline infusion to overcome non-confluent coagulation zone during two-probe, no-touch bipolar radiofrequency ablation of liver cancer.

No-touch bipolar radiofrequency ablation (bRFA) is known to produce incomplete tumour ablation with a 'butterfly-shaped' coagulation zone when the interelectrode distance exceeds a certain threshold. Although non-confluent coagulation zone can be avoided by not implementing the no-touch mode, doing so exposes the patient to the risk of tumour track seeding. The present study investigates if prior infusion of saline into the tissue can overcome the issues of non-confluent or butterfly-shaped coagulation. A computational modelling approach based on the finite element method was carried out. A two-compartment model comprising the tumour that is surrounded by healthy liver tissue was developed. Three cases were considered; i) saline infusion into the tumour centre; ii) one-sided saline infusion outside the tumour; and iii) two-sided saline infusion outside the tumour. For each case, three different saline volumes were considered, i.e. 6, 14 and 22 ml. Saline concentration was set to 15% w/v. Numerical results showed that saline infusion into the tumour centre can overcome the butterfly-shaped coagulation only if the infusion volume is sufficient. On the other hand, one-sided infusion outside the tumour did not overcome this. Two-sided infusion outside the tumour produced confluent coagulation zone with the largest volume. Results obtained from the present study suggest that saline infusion, when carried out correctly, can be used to effectively eradicate liver cancer. This presents a practical solution to address non-confluent coagulation zone typical of that during two-probe bRFA treatment.