Water-jet-cooled Nd:YAG laser coagulation: selective destruction of rat liver metastases

Experimental Study on Surface Erosion of Grade A Marine Steel by Ultrahigh-Pressure Water Jet

To investigate the interaction and erosion mechanisms between an ultrahigh-pressure water jet and the surface of Grade A marine steel, this study used the ANSYS FLUENT software to simulate the hydrodynamic characteristics of an ultrahigh-pressure water jet. To erode the Grade A marine steel, a water jet with ultrahigh-pressure (200 MPa, 40 L/min) was used. An ASMC2-4 resistance strain gauge collected the dynamic strain signal at the back of the sample during jet impingement, and the simulation results were compared to experimental results. A scanning electron microscope (SEM), X-ray diffractometer (XRD), energy dispersive spectrometer (EDS), and other equipment were used to observe and analyze the phase before impact and the material surface morphology and element distribution after impact. The results reveal that as the wall shear stress increased with the target distance, the energy loss of the jet could be reduced by changing the jet incidence angle, and the peak value of the wall shear stress increased. Under the pressure of 200 MPa, the average microstrain at the back side of the impact center area of the Grade A marine steel was 180 × 10−6, and the microstrain amplitude was 35 × 10−6–50 × 10−6. The impact force of the water jet on the Grade A marine steel produced alternating stress with cyclic fluctuation. The experimental results are consistent with the simulation results. Under the alternating jet stress action, fatigue failure and cavitation failure occurred on the sample surface, which was characterized by a spalling pit, layer erosion, and cavitation hole morphology. The surface stripping model of the Grade A marine steel under an ultrahigh-pressure water jet was established, and the interaction mechanism and erosion mechanism between the ultrahigh-pressure water jet and the surface of the Grade A marine steel were elucidated.

Laser ablation for small hepatocellular carcinoma: State of the art and future perspectives

During the last two decades, various local thermal ablative techniques for the treatment of unresectable hepatocellular carcinoma (HCC) have been developed. According to internationally endorsed guidelines, percutaneous thermal ablation is the mainstay of treatment in patients with small HCC who are not candidates for surgical resection or transplantation. Laser ablation (LA) represents one of currently available loco-ablative techniques. In this article, the general principles, technique, image guidance, and patient selection are reported. Primary effectiveness, long-term outcome, and complications are also discussed. A review of published data suggests that LA is equivalent to the more popular and widespread radiofrequency ablation in both local tumor control and long-term outcome in the percutaneous treatment of early HCC. In addition, the LA technique using multiple thin laser fibres allows improved ablative effectiveness in HCCs greater than 3 cm. Reference centres should be equipped with all the available techniques so as to be able to use the best and the most suitable procedure for each type of lesion for each patient.

Multiple fiber laser-induced thermotherapy for ablation of large intrahepatic tumors

OBJECTIVE

The aim of this study was to test three techniques used simultaneously to increase lesion size.

BACKGROUND DATA

Laser-induced thermotherapy (LITT) is a method of local tumor ablation, which may prolong survival in patients with unresectable liver metastases. The main limitation has been the production of lesions with sufficient tumor-free margin.

METHODS

LITT treatment was performed with water-cooled, multiple fiber application and hepatic blood flow occlusion in six patients with unresectable intrahepatic metastases. Response was measured by computed tomography scan.

RESULTS

In all patients, tumors were effectively ablated. In two patients with colorectal metastases, lesions up to 8.6 cm could be created.

CONCLUSION

The use of watercooled multiple fiber application and hepatic inflow occlusion makes LITT an effective ablative method, expanding the treatment options for patients with large intrahepatic masses.

Synergistic effect of interstitial laser coagulation and doxorubicin in a murine tumor recurrence model of solitary colorectal liver metastasis

BACKGROUND

Interstitial laser coagulation (ILC) is gaining acceptance for treatment of unresectable colorectal liver metastases. However, local recurrence rates are still high. To overcome this problem, we investigated the potential of additional systemic therapy after ILC in a murine model.

METHODS

Single C26 colon carcinoma nodules (approximately 1 mm3) expressing firefly luciferase were implanted in the left liver lobe of 32 BALB/c mice. Seven days after implantation, tumors were treated with either ILC alone (neodymium-yttrium aluminum garnet; 6 W/cm; 800 J/cm) or ILC followed by 1 mg/kg of doxorubicin intravenously. Controls received either doxorubicin alone or sham treatment. Tumor load was measured by in vivo bioluminescent imaging.

RESULTS

Solitary colorectal liver metastases developed over 7 days after tumor implantation in the liver. Extrahepatic disease was not observed. The ILC dose was set to ablate the liver metastases with recurrent tumor growth in 9 of 16 mice after 7 days. After ILC plus doxorubicin, complete tumor destruction occurred without recurrence (0 of 14). Sham treatment or treatment with doxorubicin alone showed an exponential increase in tumor load.

CONCLUSIONS

A murine tumor recurrence model after local ablative treatment of solitary liver metastasis was developed. The combination of ILC and doxorubicin had a strong synergistic effect that led to complete tumor remission in all animals treated.

Interstitial laser thermotherapy for liver tumours

BACKGROUND

Primary hepatocellular carcinoma (HCC) and metastases from colorectal cancer are the most common malignant liver tumours. Surgical resection is the optimum treatment in suitable patients. Interstitial laser thermotherapy (ILT) is gaining acceptance for the treatment of irresectable liver tumours and as a potential alternative to surgery. An understanding of the principles of therapy and review of clinical outcomes may allow better use of this technology.

METHOD

An electronic search using the Medline database was performed for studies on the treatment of hepatic malignancy published between January 1983 and February 2003.

RESULTS

Current information on the efficacy of ILT is based on prospective studies. ILT appears to be a safe and minimally invasive technique that consistently achieves tumour destruction. The extent of destruction depends on the fibre design, delivery system, tumour size and tumour biology. Real-time magnetic resonance imaging provides the most accurate assessment of laser-induced tumour necrosis. In selected patients with HCC and colorectal cancer liver metastases, ILT achieves complete tumour necrosis, provides long-term local control, and improves survival, compared with the natural history of the disease. In addition, ILT has survival benefits for patients with other tumour types, especially those with isolated liver metastases from a breast cancer primary.

CONCLUSION

ILT improves overall survival in specific patients with liver tumours. Advances in laser technology and refinements in technique, and a better understanding of the processes involved in laser-induced tissue injury, may allow ILT to replace surgery as the procedure of choice in selected patients with liver malignancies.

[Model construction for reperfusion of the isolated pig liver]

In recent years thermal ablation of liver tumors as a minimally invasive method became a promising alternative to conventional strategies such as chemotherapy or resection of liver tissue. Thereby an electrode is placed inside the tumor delivering energy in the form of high frequency current into the target volume to achieve and maintain a tissue temperature between 60 and 100 degrees C. Cells exposed to this thermic stress undergo coagulation necrosis and are irreversibly damaged. To protect vital liver structures from heat, it is necessary to develop an online temperature monitoring system. An experimental setup perfusing isolated pig livers under physiological conditions with 0.9% NaCl solution was established to develop and evaluate the measuring technique.

Thermo-controlled device for inducing deep coagulation in the liver with the Nd:YAG laser

BACKGROUND AND OBJECTIVE

To increase the effectiveness of laser-induced interstitial thermotherapy (LITT), a new thermo-controlled application system for minimal invasive intervention was designed. Our system consists of a laser applicator of 2.5 mm in diameter, insertion equipment, and a Nd:YAG-laser source.

STUDY DESIGN/MATERIALS AND METHODS

A cylindrical light emitting fiber (1-6 cm in length) was placed in the center of the applicator. The surrounding tissue was irradiated through a Duran window at the distal end of the applicator. The power of the laser source was controlled dynamically by thermosensors in a water-cooling system of the laser applicator. The temperature at the surface of the Duran window was kept constant at approximately 60 degrees C, without charring the surrounding tissue.

RESULTS/CONCLUSION

We obtained homogeneous coagulation zones. In in vitro experiments with pig livers, we reached ellipsoid coagulation volumes of 3 and 5 cm in diameter within 10 minutes, corresponding to a volume of approximately 25 cm3.

Nd: YAG interstitial laser thermotherapy in the treatment of breast cancer

BACKGROUND AND OBJECTIVE

"Minimal treatment strategy" is desirable in certain breast cancer patients. The main objective of the present study is to examine the use of interstitial laser thermotherapy (laserthermia) for this purpose.

STUDY DESIGN/MATERIALS AND METHODS

Thirty-five patients with primary breast cancer were treated with laserthermia using the Nd:YAG (1,064 nm) pulse-wave laser. In 28 patients, laserthermia was performed before radical resection, and in seven patients it was the only invasive treatment.

RESULTS

One gaseous rupture of tumor occurred at 3 Watts. The diameter of single focus of laser-induced damage after 1-2 Watts was less than 1 cm, and after 2.5-6 Watts it reached 1.5-2.5 cm. Of seven patients treated without surgery, local tumor control was achieved in five, and in three stage I-III patients disease-free survival followed for 19-60 months. After laserthermia plus surgery, 3-year disease-free survival was 27% in premenopausal and 92% in menopausal patients.

CONCLUSIONS

It seems that laser destruction of relatively small primary breast cancer is possible. Provisionally, laserthermia should not be used in premenopausal patients.

The effects of CO2 laser and Nd:YAG with and without water/air surface cooling on tooth root structure: correlation between FTIR spectroscopy and histology

Morphologic and chemical characterization of root surfaces treated with either the CO2 laser, Nd:YAG, or Nd:YAG with water/air surface cooling (Nd:YAG-C) was completed using scanning electron microscopy (SEM) and FTIR photoacoustic spectroscopy (FTIR/PAS). Specimens for morphologic analysis consisted of 20 extracted single rooted teeth unaffected by periodontal disease. The specimens were exposed at varying energy densities to a single pass of the laser. SEM examination revealed, for all lasers, a direct correlation between increasing energy densities and depth of tissue ablation and width of tissue damage. The Nd:YAG-C required higher energy densities than either the CO2 or Nd:YAG lasers to achieve the same relative depth of tissue ablation. Regardless of energy density, and in contrast with other laser types, areas treated with the Nd:YAG-C did not exhibit collateral zones of heat damage. Specimens for spectroscopic examination consisted of 12 disks, 6 x 2 mm, cut from debrided root surfaces of extracted, unerupted human molars. The spectral results indicate a substantial reduction in the absorption bands attributable to protein and an additional band at 2015 cm-1 in specimens exposed to the Nd:YAG without water. In the presence of water/air coolant, the band at 2015 cm-1 appears only at a substanially higher energy density. The spectra of the CO2 treated specimens, with the char layer present, show a significant reduction in the protein bands and additional bands at 2015 and 2200 cm-1, that are tentatively assigned to the cyanamide and cyanate ions, respectively. These results suggest a reaction of the organic matrix and mineral with laser exposure.

Effects of surface irrigation on the thermal response of tissue during laser irradiation

Effects of surface irrigation on the thermal response of tissue during laser irradiation are investigated. In particular, influence of temperature and flow rate of the irrigation fluid on the resulting temperature distributions and coagulation depths are studied. Intraluminal Nd:YAG laser irradiation of bovine muscle is performed in vitro for a fixed value of the irrigation flow rate while the irrigation temperature is varied, and for a fixed irrigation temperature while the irrigation flow rate is kept constant. Thermocouples are used to measure the temperatures within the tissue for various irradiation and irrigation conditions. Higher temperatures and deeper coagulation depths are achieved as the temperature of the irrigation fluid is increased. For sufficiently low values of irradiance and exposure time, the use of cold irrigation is shown to prevent or delay tissue carbonization. Beyond a critical irradiance and an exposure time, use of cold irrigation does not prevent tissue carbonization. Coagulation depths and temperature distributions are not affected by a change in the flow rate of laminar irrigation. Application of stagnant irrigation, however, results in an increase in coagulation depth. Results of this study suggest that the dominating mechanism of heat transfer during application of laminar irrigation is thermal diffusion as compared to the bulk motion of the fluid.

Comparison of the thermal tissue effects produced by aged sapphire and silica hemispherical tips

This study evaluated the performance of sapphire and fused silica hemispherical tips under the same exposure conditions. Lesions produced in the chicken breast and a blood field were sectioned for light and transmission polarizing microscopy. Lesion size and thermal damage area were recorded as a function of the tips accumulated exposure. The tips transmission was measured after every 1,000 J of exposure. Fused silica tips lasted for approximately 5,000 J and experienced significant surface and transmission deterioration. The sapphire hemispherical tips lasted for > 12,000 J with no surface and transmission deterioration. Lesions produced with the fused silica tips generally increased in depth with use, and depths of 6 mm were common. Lesions produced by the sapphire tips were subsurface spherical areas of coagulation with the tissue surface relatively intact. This difference in resulting lesions may be attributed to the higher thermal conductivity of sapphire.

Interstitial Nd:YAG laser coagulation with a cylindrical diffusing fiber tip in experimental liver metastases

Interstitial laser coagulation as a means of destructing hepatic metastases was investigated. Colon carcinoma CC531 was implanted in the liver of 42 Wag/Rij rats; 20 days later, tumors (5.5 +/- 0.2 mm) were exposed to 1,064 nm Nd:YAG laser light at 4 W/cm and either 600, 1,200, 2,400, 3,400, or 4,800 J/cm from a 0.5 cm Helioseal coated cylindrical diffuser. Temperature and fluence rate were measured at the tumor boundary. Lesions were studied on day 2 and 36 posttreatment by light microscopy. Tumor proliferative activity was assessed by bromodeoxyuridine incorporation. Liver damage and function were determined by serum liver enzymes and antipyrine clearance. Fluence rate increased during laser treatment up to 170%; mean temperature increased logarithmically up to 69.7 degrees C. Short-term light microscopy showed coagulation necrosis of 7-11 mm without charring. Lesion size and liver enzymes increased logarithmically with laser energy applied. No deterioration in liver function was found. At 4,800 J/cm complete tumor remission occurred in three of four animals. This study shows the ability of interstitial laser coagulation to produce selective destruction of colonic tumor within the liver.

Optical properties of rat liver and tumor at 633 nm and 1064 nm: photofrin enhances scattering

Predicting the effects of photodynamic therapy (PDT) and Nd: YAG laser coagulation requires knowledge of the light distribution in tumor and surrounding tissue. Therefore, absorption and scattering coefficients and the average cosine of the scattering angle (the anisotropy factor) were measured in rat liver and tumor at 632.8 and 1064 nm. A syngenic colon adenocarcinoma CC531 was implanted subcutaneously in two groups of 7 Wag/Rij rats. In one group Photofrin was administered 5 mg/kg intravenously 48 h before determination of optical properties. Two months after inoculation, samples were taken from tumor and liver and optical properties determined using indirect methods with two integrating spheres. The absorption coefficient was larger in liver than in tumor at 632.8 nm (P < 0.0005), whereas the scattering coefficient was larger in tumor than in liver at 1,064 nm (P < 0.05). Addition of Photofrin increased the scattering coefficient in liver and in tumor at both wavelengths (P < 0.025) and decreased the anisotropy in tumor (P < 0.025), suggesting that for modelling the dosimetry of PDT the optical properties of photosensitized tissue should be used.

Water-jet-cooled Nd:YAG laser coagulation of experimental liver metastases: correlation between ultrasonography and histology

To establish the value of ultrasonography in imaging laser coagulation of tumor and surrounding tissue, the relation between measurements on ultrasound and histology was determined in a rat tumor model. A piece of colon carcinoma CC531 was implanted in the liver of 21 Wag/Rij rats; 20 days later, tumors (mean diameter 5.3 mm) were treated with a water-jet-cooled Nd:YAG laser at 10 W and either 150 J, 300 J, 600 J, 1,200 J, 1,700 J, or 2,400 J. Ultrasonography was done just pre- and immediately post-laser treatment. The animals were sacrificed and livers removed for light microscopical evaluation. Depth and width of coagulation were measured directly on ultrasound, and on histological samples by computer-assisted image analysis. Laser treatment did not change the echogenic aspect of the tumor on ultrasound. However, liver damage appeared hypoechoic compared to normal liver. A significant correlation was found between the total size of the lesion on ultrasound and histology (P = 0.015, r = 0.57 for depth; P = 0.012, r = 0.58 for width), suggesting that laser induced tumor destruction may be derived from the amount of surrounding hepatic damage on ultrasound.

Interstitial photodynamic therapy in a rat liver metastasis model

Photodynamic therapy (PDT) of hepatic tumours has been restricted owing to the preferential retention of photosensitizers in liver tissue. We therefore investigated interstitial tumour illumination as a means of selective PDT. A piece of colon carcinoma CC531 was implanted in the liver of Wag/Rij rats. Photofrin was administered (5 mg kg-1 i.v.) 2 days before laser illumination. Tumours with a mean (+/- s.e.) diameter of 5.7 +/- 0.1 mm (n = 106, 20 days after implantation) were illuminated with 625 nm light, at 200 mW cm-1 from a 0.5 cm cylindrical diffuser and either 100, 200, 400, 800 or 1600 J cm-1. Control groups received either laser illumination only, Photofrin only or diffuser insertion only. Short-term effects were studied on the second day after illumination by light microscopy and computer-assisted integration of the circumference of damaged areas. Long-term effects were studied on day 36. To determine the biochemistry of liver damage and function, serum ASAT and ALAT levels were measured on day 1 and 2, and antipyrine clearance on day 1. Tumour and surrounding liver necrosis increased with light dose delivered (P < 0.001). Best long-term results were obtained at 800 J cm-1 with complete tumour remission in 4 out of 6 animals. No deterioration in liver function was found. The results of this study show the ability of interstitial PDT to cause major destruction of tumour tissue in the liver combined with minimal liver damage.

Optical property changes as a result of protein denature in albumen and yolk

Heat-induced changes in the scattering and absorbing properties of tissue begin with the denaturation of protein. Using egg albumen and egg yolk as tissue phantoms, the changes in absorption and scattering coefficients and the average cosine of the scattering angle have been quantified from 350 to 850 nm for heating corresponding to an empirical damage parameter from 3.7 to 1430 (albumen) and from 0.067 to 28 (yolk). In addition to being useful for modelling the response of tissue to laser light, the changes in optical properties yield information on the particle size distribution in the phantoms. For a low damage parameter the albumen has a large percentage of small, so-called Rayleigh scattering, particles owing to the initial denaturation of the protein. As the damage parameter increases, the percentage of these particles decreases. In the yolk, the effect of denaturation of proteins on the scattering characteristics is still present but less pronounced, because of the initial highly scattering nature of the tissue and perhaps to other rate processes that also occur.

A new liver-tumor model in the rat

A new tumor model for testing and comparing the effect of different forms of treatment on liver tumors is described. Single tumors were induced in the liver of rats by the implantation of small pieces taken from a subcutaneously growing tumor. Tumor growth was determined by measuring the weight of the implanted tumors after the animals had been killed. In this way, weight curves for treated and untreated tumors could be defined. The weight of untreated liver tumors increased exponentially with time (tumor weight in milligrams = 1 + e(t-0.31)/5). In addition, tumor growth defined as the geometric mean of three perpendicular diameters was determined. Tumor-diameter curves showed a linear increase with time in the untreated groups (tumor diameter in millimeters = 0.4 t + 1.90). The model was tested by assessing the effect of intraperitoneally injected cisplatin. The dose chosen produced a marked delay in tumor growth. On the basis of the weight gain shown by the treated animals and tumor growth delay, a therapeutic index can be defined, thus enabling to compare quantitatively different forms of treatment according to their antitumor effect and toxicity.