Thermal Coagulation Of Tissue Research Articles

Spray coagulation as an alternative to argon plasma coagulation for bleeding portal hypertensive gastropathy

Spray coagulation as an alternative to argon plasma coagulation for bleeding portal hypertensive gastropathy

Optical Coherence Tomography Feedback System for Infrared Laser Sealing of Blood Vessels.

Infrared (IR) lasers have recently been tested as an alternative to electrosurgical and ultrasonic laparoscopic devices for optical sealing of blood vessels. IR laser technology previously demonstrated faster sealing times, reduced thermal spread, and lower device temperatures during experimental studies. However, current commercial laparoscopic devices incorporate electrical impedance and/or temperature sensors as real-time, closed-loop, feedback to indicate successful blood vessel seals. This preliminary study explores an infrared laser system for sealing and optical coherence tomography (OCT) as a potential feedback system for successful vessel seal verification. A 1470-nm diode laser delivered an incident power of 30 W for an irradiation time of 5 s using an 8 × 2 mm linear beam, for creating strong seals in porcine renal blood vessels under compression. After sealing the blood vessels, OCT was performed on unsealed and sealed vessel regions for comparison. Standard vessel burst pressure (BP) measurements confirmed successful seals after OCT. Integrated reflectance intensity in OCT A-scans decreased by an average of 20 ± 6% in sealed versus native vessels of 2.4 ± 0.4 mm diameter. Vessel BP measured 532 ± 239 mmHg, with all vessels (n = 25) recording a successful BP > 180 mmHg (hypertensive blood pressure). Unsealed vessels demonstrated significantly deeper imaging marked by a continuous decay in reflected intensity, while sealed vessels showed subsurface reflectance intensity peaks, immediately followed by a rapid decay in reflectance intensity. These markers are consistent with increased light scattering and decreased optical penetration depth upon thermal coagulation of tissues. A-line OCT data consistently differentiated between sealed and unsealed blood vessel regions. Future work will involve OCT integration into the laparoscopic device for real-time optical feedback during IR laser sealing.

CT-based quantification of short-term tissue shrinkage following hepatic microwave ablation in an in vivo porcine liver model.

Microwave ablation (MWA) is a minimally invasive treatment option for solid tumors and belongs to the local ablative therapeutic techniques, based on thermal tissue coagulation. So far there are mainly ex vivo studies that describe tissue shrinkage during MWA. To characterize short-term volume changes of the ablated zone following hepatic MWA in an in vivo porcine liver model using contrast-enhanced computer tomography (CECT). We performed multiple hepatic MWA with constant energy parameters in healthy, narcotized and laparotomized domestic pigs. The volumes of the ablated areas were calculated from venous phase CT scans, immediately after the ablation and in short-term courses of up to 2 h after MWA. In total, 19 thermally ablated areas in 10 porcine livers could be analyzed (n = 6 with two volume measurements during the measurement period and n = 13 with three measurements). Both groups showed a statistically significant but heterogeneous volume reduction of up to 12% (median 6%) of the ablated zones in CECT scans during the measurement period (P < 0.001 [n = 13] and P = 0.042 [n = 6]). However, the dimension and dynamics of volume changes were heterogenous both absolutely and relatively. We observed a significant short-term volume reduction of ablated liver tissue in vivo. This volume shrinkage must be considered in clinical practice for technically successful tumor treatment by MWA and therefore it should be further investigated in in vivo studies.

Thermal Therapy With a Fully Electronically Steerable HIFU Phased Array Using Ultrasound Guidance and Local Harmonic Motion Monitoring.

The focus of this paper is to study the performance of LHM monitoring in vivo in order to assess the tissue coagulation during ultrasound surgery of bone metastases. This is done through a pre-clinical study on large scale animals (pigs) as well as a first-in-human pilot study, using a hand held ultrasound-guided HIFU phased array. A flat, fully steerable HIFU phased array system (1024 elements, 100mm diameter, 516kHz), in combination with a co-aligned 64 element imaging system, is used to perform thermal surgery and monitor tissue coagulation using the LHM technique. The in vivo experiments are conducted using thirteen animals, followed by a first-in-human pilot study in which nine patients are enrolled. The pre-clinical results show that the LHM monitoring method is able to detect about 80% of the observed coagulated tissue volumes visible in dissection. In the pilot study, six out of nine patients have durable pain reduction with good correlation observed from LHM detections. In general, the results suggest that the LHM monitoring performance is promising in detecting thermal tissue coagulation during focused ultrasound surgery in tissues close to the bone. The LHM technique can offer a very accessible and cost-efficient monitoring solution during ultrasound surgery within a clinical setting.

WE‐H‐209‐00: Carson/Zagzebski Distinguished Lectureship: Image Guided Ultrasound Therapy

Focused ultrasound has been shown to be the only method that allows noninvasive thermal coagulation of tissues and recently this potential has been explored for image‐guided drug delivery. In this presentation, the advances in ultrasound phased array technology for energy delivery, exposure monitoring and control will be discussed. Experimental results from novel multi‐frequency transmit/receive arrays will be presented. In addition, the feasibility of fully electronically focused and steered high power arrays with many thousands of transducer elements will be discussed. Finally, some of the recent clinical and preclinical results for the treatment of brain disease will be reviewed. Learning Objectives: Introduce FUS therapy principles and modern techniques Discuss use of FUS for drug delivery Cover the technology required to deliver FUS and monitor therapy Present clinical examples of the uses of these techniquesThis research was supported by funding from The Canada Research Chair Program, Grants from CIHR and NIH (no. EB003268).; K. Hynynen, Canada Foundation for Innovation; Canadian Institutes of Health Research; Focused Ultrasound Surgery Foundation; Canada Research Chair Program; Natural Sciences and Engineering Research Council of Canada; Ontario Research Fund; National Institutes of Health; Canadian Cancer Society Research Institute; The Weston Brain Institute; Harmonic Medical; Focused Ultrasound Instruments

WE‐H‐209‐01: Advances in Ultrasound Therapy

Focused ultrasound has been shown to be the only method that allows noninvasive thermal coagulation of tissues and recently this potential has been explored for image‐guided drug delivery. In this presentation, the advances in ultrasound phased array technology for energy delivery, exposure monitoring and control will be discussed. Experimental results from novel multi‐frequency transmit/receive arrays will be presented. In addition, the feasibility of fully electronically focused and steered high power arrays with many thousands of transducer elements will be discussed. Finally, some of the recent clinical and preclinical results for the treatment of brain disease will be reviewed. Learning Objectives: Introduce FUS therapy principles and modern techniques Discuss use of FUS for drug delivery Cover the technology required to deliver FUS and monitor therapy Present clinical examples of the uses of these techniquesThis research was supported by funding from The Canada Research Chair Program, Grants from CIHR and NIH (no. EB003268).; K. Hynynen, Canada Foundation for Innovation; Canadian Institutes of Health Research; Focused Ultrasound Surgery Foundation; Canada Research Chair Program; Natural Sciences and Engineering Research Council of Canada; Ontario Research Fund; National Institutes of Health; Canadian Cancer Society Research Institute; The Weston Brain Institute; Harmonic Medical; Focused Ultrasound Instruments

Entrance and propagation pattern of high‐frequency electrical currents in biological tissues as applied to fractional skin rejuvenation using penetrating electrodes

Fractional resurfacing of the skin using radiofrequency devices has been used for collagen remodeling and rejuvenation. To determine how radiofrequency current enters and propagates through tissue, and the pattern of the resulting effect. An electrosurgical device with a 0.4 MHz frequency output was used as the source of radiofrequency current. Current was applied via a metallic needle introduced into a large piece of cow liver, with different amounts of energy delivered at multiple points. Cross-sections of the liver were then studied for tissue effect. Thermal coagulation of tissue started from the tip of the electrode. With higher energy, a rim of coagulated tissue formed around the entire length of the needle. This rim of coagulated tissue was thicker around the tip of the electrode. Radiofrequency currents have a tendency to move toward the center of the bulk of tissue. When an electrode of a fractional radiofrequency device enters the skin, maximum heating effect will be around the tip of the electrode in the dermis. This phenomenon can preserve epidermis from injury during dermal heating, reducing post-procedural skin surface side effects seen with many skin rejuvenation procedures.

Advances in ultrasound methods for therapy

Focused ultrasound has been shown to be the only method that allows noninvasive thermal coagulation of tissues and recently this potential has been explored for noninvasive image-guided drug delivery. In this presentation, the advances in ultrasound phased array technology for well controlled energy delivery will be discussed. In addition, some of the recent preclinical results for the treatments of brain tumors, stroke, and Alzheimer's disease will be reviewed. As conclusion, the advances in the image-guided focused ultrasound for the treatment of disease has been rapid and the future potential appears very promising.

An integrated system to deliver impulsive radiation force and to image induced transient strain for monitoring focused ultrasound surgery

Thermal coagulation of tissue causes an approximate three‐fold increase in stiffness, which can be easily detected by various elasticity imaging methods. Advantages have been reported, for application to breast cancer diagnosis, of an elasticity imaging method that applies a highly localised transient stress deep within the tissue using a low frequency focused ultrasound radiation force impulse, and uses relatively high frequency echo imaging to measure the transient strain generated in the tissue placed between the transducers. In this paper we describe a new system that implements this concept using a focused ultrasound surgical transducer to apply the transient (<10 ms) load, synchronized by a customised field programmable gate array to a Zonare C5‐2 probe to image the strain. Both transducers are on the same side of the tissue and locked together for scanning to create transient strain elastograms. Performance measurements, obtained using gelatine phantoms and ex vivo thermally ablated liver tissue, i...

Clinical Applications of Argon Plasma Coagulation in Endoscopy

The argon plasma coagulator is a device used for noncontact thermal coagulation of tissue. The device was first used in open and laparoscopic surgical procedures and in 1991 was adapted for use in endoscopy. Since then, argon plasma coagulation has expanded its clinical applications in the treatment of various gastrointestinal conditions. The endoscopy nurse plays an important role in the care of patients before, during, and after argon plasma coagulation treatment. This article reviews the principles and components of the argon plasma coagulator, and provides a summary of the various clinical applications, patient safety practices, and potential complications of argon plasma coagulation therapy.

Mechanism of Porphyrin-Induced Sonodynamic Effect: Possible Role of Hyperthermia

The biological effects of ultrasound have been investigated vigorously for various applications including the thermal coagulation of tissues, the opening of tight junctions, and localized gene or drug introduction. The synergistic cell killing effect of ultrasound and porphyrin derivatives, the so-called sonodynamic effect, holds promise for cancer treatment. Although several models to explain the sonodynamic effect have been proposed, its exact mechanism, especially in vivo, remains unknown. We examined the effect of a porphyrin derivative, protoporphyrin IX, on ultrasound-induced killing of HeLa cells. In some experiments, the intracellular protoporphyrin IX concentration was increased by 5-aminolevulinic acid treatment of the cells. Although extracellular protoporphyrin IX showed an enhanced cell killing effect by microbubble-enhanced ultrasound, intracellular protoporphyrin IX did not. On the other hand, intracellular protoporphyrin IX enhanced the cell killing effect of hyperthermia, which can be produced by ultrasound exposure, in a moderately acidic environment (pH 6.6). Because porphyrin derivatives are generally imported into the intracellular component in vivo, our results suggest that hyperthermia caused by ultrasound may play an important role in the sonodynamic effect induced by porphyrin derivatives.

Colorectal tumors and hepatic metastases differ in their optical properties—relevance for dosimetry in laser-induced interstitial thermotherapy

The therapeutic application of laser light is a promising alternative to surgical resection of colorectal liver metastases. The extent of tumor destruction achieved by this strategy depends primarily on light distribution in the target tissue. Knowledge about optical properties is necessary to predict light distribution in the tissue for careful irradiation planning. The aim of this study was to compare the optical behavior of healthy colon tissue with that of colorectal carcinomas and their hepatic metastases in the native and coagulated state in order to test the effect of malignant degeneration, metastasis, and thermal coagulation on optical parameters. Ninety tissue samples were taken from patients with a colorectal carcinoma and concomitant liver metastases: healthy colon tissue (n = 30); colon carcinoma (n = 30); liver metastases (n = 30). Optical properties were measured according to the single integrating sphere principle in the native state and after thermal coagulation in the wavelength range of 800-1,100 nm and analyzed by inverse Monte Carlo simulation. The highest optical penetration depth for all tissue types was obtained at the end of the spectral range investigated. The highest penetration depths of 4.13 mm (healthy colon), 7.47 mm (colon carcinoma tissue), and 4.08 (liver metastases) were at 1,060 nm, although the values decreased significantly after thermal coagulation. Comparing healthy colon-to-colon carcinoma always revealed a significantly lower absorption and scattering coefficient in the tumor tissue. This resulted in a higher optical penetration depth of the laser light in the colon carcinoma tissue (P < 0.05). A direct comparison disclosed no agreement between the optical properties of the primary tumor and the liver metastases. In the native state, colon carcinoma tissue had a lower scattering coefficient (P < 0.05), higher anisotropy factor, and optical penetration depth than liver metastases (P < 0.05). The absorption coefficient did not differ significantly. The differences in the native state were equalized by tissue coagulation. Colon carcinoma tissue has a higher optical penetration depth than healthy colon tissue, which speaks in favor of tumor selectivity for interstitial laser application, since large treatment volumes can be obtained in the tumor. The lack of agreement between primary tumors and their concomitant liver metastases indicates a modification of optical behavior through metastasis. Thermal coagulation of tissue leads to changes in the optical properties, which are clearly less pronounced in carcinoma tissue. The data obtained in this study clearly show that an individual irradiation schedule is necessary for effective and safe dosimetry in laser-induced thermotherapy (LITT).

Simulations of thermal tissue coagulation and their value for the planning and monitoring of laser-induced interstitial thermotherapy (LITT).

MRI information is widely used for the monitoring of thermal therapies, such as laser-induced interstitial thermotherapy (LITT). However, a detailed knowledge about the relationship between time/temperature exposure and resulting tissue thermal damage is needed to estimate the lesion extent. The aims of this work were to model the thermal response of laser-irradiated tissue and to assess the value of Monte Carlo simulation (MCS) for tumor therapy planning and monitoring. MCS yielded true 3D distributions of laser-induced temperature and thermal damage. These results were compared with 2D MR thermometry data from in vitro experiments performed on animal liver tissue over an ordinary range of laser powers (10-25 W) and irradiation times (5-25 min). Clinical reference data were available from MR-guided liver LITT procedures. MCS correctly predicted the shape of temperature and damage distributions. The quantitative agreement between simulated and measured lesion diameters was within 10% and 15% for the in vitro and in vivo cases, respectively. The simulated 53 degrees C isotherm best estimated the boundary of the final thermal damage (6% variance). This study shows that MCS of interstitial laser coagulation provides unique information that can be of use in the empirical correlation of temperature with thermal damage, and can assist greatly in thermal treatment planning and monitoring.

B-scan ultrasound imaging of thermal coagulation in bovine liver: log envelope slope attenuation mapping

Thermal therapy is an experimental procedure to treat localised tumours in the prostate, liver, kidney or breast. Monitoring is important to ensure complete tumour destruction while sparing adjacent sensitive structures. Previous work demonstrated that, when biological tissues are heated above 65°C, ultrasound (US) attenuation increases due to thermal coagulation of tissue. This study examined the feasibility of a B-scan, envelope-based attenuation estimation method to monitor thermal therapy. The slope of the log of the signal envelope was used to estimate attenuation. It is shown that this method is able to demonstrate, from simulated and phantom data, a limited ability to differentiate attenuation levels that correspond to thermally coagulated and uncoagulated beef liver. In ex vivo bovine liver, however, issues due to signal-to-noise ratio (SNR) of the signal envelope prevented the visulisation of a 2-cm diameter thermally coagulated inclusion. The limitations of this method are extended to the multinarrow-band (MNB) technique. (E-mail:sherar@oci.utoronto.ca)

Intrastromal Holmium Laser Keratostomy: Long-Term Results

A new filtering procedure, the Intrastromal Holmium Laser Keratostomy (ILK) has been developed. A laser canal is created intrastromally in the cornea anterior to Schwalbe's line in the floor of a corneo-scleral tunnel incision made with a knife from the corneal site. Theoretically, the complications of the conventional Subconjunctival Holmium Laser Sclerostomy (SLS) can thus be avoided. Experimental and clinical evaluation of the new procedure, as well as clinical long-term results are presented. The ILK was evaluated experimentally on bank eyes and clinically using postoperative Ultrasound Biomicroscopy (UBM). The clinical long-term effect was evaluated by a follow-up of the first 22 ILK performed on 17 eyes in 17 consecutive patients with complicated, refractory primary and secondary open angle glaucoma. Preoperative subconjunctival mitomycin-C injection (0.02 mL of 0.2 mg/mL) was used. The experimental and clinical evaluations show that the collateral thermal tissue coagulation made by the Holmium laser in ILK probably is an advantage, because the subsequent shrinkage prevents postoperative self sealing of the laser canal. Complete surgical success without medication and reoperations was reached in 63% of the eyes with a mean observation time of 22.5 months (range: 16.6-26.7 mos.). Any failure appeared within the first 10 months. Only 13% of the eyes had early iris incarcerations, there were no late incarcerations. Twenty-five percent had temporary shallow anterior chambers. The mitomycin-ILK procedure has shown obvious better results than the conventional SLS technique due to a considerable reduction in postoperative complications. Since the present material further developments in the ILK technique has made this procedure still more attractive.

Angular directivity of thermal coagulation using air-cooled direct-coupled interstitial ultrasound applicators

The performance characteristics and thermal coagulation of tissue produced by directional air-cooled, direct-coupled interstitial ultrasound (US) applicators were evaluated. Prototype applicators (2.2 mm o.d.) were constructed using cylindrical transducers sectored into angular active zones of 90 o, 200 o, 270 o, and 360 o. Acoustic characterization of the applicators showed the beam output to be angularly directed from the active sector of the transducer and collimated within the axial extent. Empirical determination of the average convective heat transfer coefficient, resulting from airflow cooling the inner surface of the transducer, showed significantly high levels of transfer (> 700 W m −2 oC −1) with a flow rate of 5.6 L min −1. Thermal performance of the applicators was characterized through high temperature heating in vivo (porcine thigh muscle, 11 trials) and in vitro (bovine liver, 46 trials). Results demonstrated directional coagulation of tissue, with good correlation between the angular extent of the lesions and the active acoustic sector. Radial depth of coagulation with a 200 o applicator extended 8–17 mm, with a heating time of 1–10 min, respectively. Angular and axial lesion shape remained similar over the course of 1–10 min heating trials. Implementation of air-cooling within direct-coupled interstitial US applicators provided enhanced directivity of heating in angular and axial dimensions, and significantly increased the power handling and radial depth of tissue coagulation.

Measurement of thermal effects on the optical properties of prostate tissue at wavelengths of 1,064 and 633 nm

Background and Objective The extent of thermal injury during laser prostatectomy is dependent on the light distribution in laser-irradiated tissue. As tissue is irradiated, the optical properties change as a function of temperature due to an alteration of molecular and cellular structure. The purpose of the present study was to determine how the exposure of both fresh and previously frozen canine prostate tissue to elevated temperatures affects the optical properties. Study Design/Materials and Methods Optical properties were measured by using a double integrating sphere spectrophotometer with an inverse adding-doubling algorithm. Measurements were made at two wavelengths (1,064 nm and 633 nm) on samples heated in a waterbath in 5°–10° increments for 10 min through a 50°C temperature range. Results Upon coagulation, the absorption coefficient of fresh tissue decreased from the baseline measurement for both wavelengths (0.027 ± 0.003 to 0.019 ± 0.002 for λ = 1,064 nm; 0.073 ± 0.007 to 0.061 ± 0.006 for λ = 633 nm). However, the scattering coefficient increased sharply from the baseline measurement following coagulation (3.06 ± 0.26 to 6.05 ± 0.29 for λ = 1,064 nm; 4.89 ± 0.23 to 7.22 ± 0.30 for λ = 633 nm). Thermal coagulation occurred during exposure to temperatures between 60°C and 70°C. Conclusion Data obtained in this study indicate that thermal coagulation of tissue alters the optical properties. The extent to which these changes occur was found to be dependent on wavelength and freshness of tissue. These results are significant because they suggest how thermally induced changes in the optical properties may limit the depth of light penetration in tissue thus compromising treatment. Lasers Surg. Med. 24:38–47, 1999. © 1999 Wiley-Liss, Inc.

Time and temperature dependence of MR parameters during thermal coagulation of ex vivo rabbit muscle.

Detailed measurements of the T1-weighted, T2-weighted, and MT-weighted signal were performed for ex vivo muscle samples heated to various temperatures for different times. Consistent, monotonic increases in signal intensity were observed with progressive thermal coagulation, corresponding to an increase in T2 relaxation time and an increase in MT-weighted signal for temperatures above 60 degrees C. The relationship for T1 relaxation was more complex, showing a decrease in T1 relaxation from 40 to 60 degrees C and an increase above 60 degrees C. These techniques provide a more direct measure of tissue thermal coagulation than that provided by MR thermometry and suggest MR imaging strategies for the optimization and monitoring of thermal coagulation therapy protocols that create thermal damage in target tissues.

Temperature monitoring of interstitial thermal tissue coagulation using MR phase images.

The temperature-dependent water proton frequency shift was investigated for temperature monitoring of interstitial thermal coagulation. A procedure for on-line temperature calculation was developed, and errors due to temperature-dependent susceptibility were investigated by finite element analysis and reference measurements. The temperature coefficient of magnetic susceptibility and proton chemical shift were determined for brain tissue and other substances. With the proposed procedure, the location of isotherms could be well visualized during laser-induced interstitial coagulation in vitro and in vivo. Systematic errors caused by magnetic susceptibility changes with temperature depend strongly on the characteristics of the heat source and can exceed susceptibility effects caused by physiologic tissue changes. For the laser applicators discussed here, however, a first order compensation for this effect was found to be satisfactory, because it reduces the absolute error to the range of +/- 1 degrees C. The proposed method represents a very promising approach for monitoring of the interstitial thermal coagulation.

Effect of steroids or tissue precooling on edema and tissue thermal coagulation after CO2 laser implant

Effect of steroids or tissue precooling on edema and tissue thermal coagulation after CO2 laser implant