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Background and Objectives Proliferation and synthesis of hepatocellular tissue after tissue damage are promoted by specific growth factors such as hepatic tissue growth factor (HGF) and connective growth factor (CTGF). Laser-induced thermotherapy (LITT) for the treatment of liver metastases is deemed to be a parenchyma-saving procedure compared to hepatic resection. The aim of this study was to compare the impact of LITT and hepatic resection on intrahepatic residual tumor tissue and expression levels of mRNA HGF/CTGF within liver and tumor tissue. Study Design/Materials and Methods Two independent adenocarcinomas (CC531) were implanted into 75 WAG rats, one in the right (untreated tumor) and one in the left liver lobe (treated tumor). The left lobe tumor was treated either by LITT or partial hepatectomy. The control tumor was submitted to in-situ hybridization of HGF and CTGF 24–96 hours and 14 days after intervention. Results Volumes of the untreated tumors prior to intervention were 38±8 mm3 in group I (laser), 39 ± 7 mm3 in group II (resection), and 42 ± 12 mm3 in group III (control) and did not differ significantly (P > 0.05). Fourteen days after the intervention the mean tumor±SEM volume of untreated tumor in group I (laser) [223 ± 36] was smaller than in group II (resection) [1233.28 ± 181.52; P

Background and Objectives 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. Materials and Methods 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. Results 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

Background and Objectives In contrast to hepatic resection, thermally destroyed autologous tumor cells remain in situ after laser-induced thermotherapy (LITT). The aim of the study was to evaluate the effect of LITT and hepatic resection on the immune response to residual intrahepatic tumor tissue and the growth of untreated liver metastases. Study Design/Materials and Methods Two independent adenocarcinomas (CC531) were implanted into 60 WAG rats, one in the right (control tumor) and one in the left liver lobe (treated tumor). The left lobe tumor was treated either by LITT or partial hepatectomy. The control tumor was submitted to further investigation 24 hours, 96 hours, 7 days, and 10 days after treatment. Results Ten days after treatment, control tumor volumes were 296±46 mm_ after LITT and 1,181±192 mm_, 1,387±200 mm_ after hepatic resection and no treatment, respectively (P

Background and Objective The aim of this study was to evaluate the accuracy of Gd-DTPA MRI in the detection of recurrent tumor after laserinduced thermotherapy (LITT) of experimental liver metastases. Study Design/Materials and Methods LITT was performed at different energy levels in VX-2 tumor-bearing rabbits (n = 80). MRI and histology were placed at 0, 24, 96 hours, and 14 days. Signal intensities were calculated of the transition between thermally damaged and undamaged tissue (transition zone = TZ) and of the surrounding tissue (reference zone = RZ). Results Tumor recurrence was seen in 47 animals. At 24 hours sensitivity, specificity and accuracy was 92, 100, and 95% in TZ and 23, 100, and 50% in RZ. At 14 days sensitivity, specificity and accuracy was 100, 11, and 60% in TZ and 100, 89, and 95% in RZ. Conclusions Recurrence is best excluded in TZ at 24 hour and in RZ at 14 day with an accuracy up to 95%. Lasers Surg. Med. 30:280–289, 2002. © 2002 Wiley-Liss, Inc.

Background and Objective Laser induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. For predicting the effects of laser applications and optimizing irradiation planning in LITT, knowledge about light distribution in tissue, optical tissue properties (absorption, scattering, anisotropy, penetration depth) and their changes due to thermal denaturation is indispensable. Study Design/Materials and Methods The optical parameters in healthy porcine liver were determined in the native state and after thermal coagulation using a double integrating sphere system in the wavelength range of 400–2400 nm. Results Optical parameters showed significant fluctuations in the examined wavelength range mainly due to the water and hemoglobin content in the tissue. The greatest optical penetration depth of 7.46 mm was achieved at 1070 nm. After thermal coagulation, a clear increase in scattering and a slight decrease in absorption was found, which results in a decreased optical penetration depth. Conclusions In order to ensure a safe and effective procedure, an adjustment of the laser power to the decreasing penetration depth is recommended during therapy. These results provide a better understanding of laser-tissue interaction and may be helpful to investigators in the field of light dosimetry in liver tissue. Lasers Surg. Med. 29:205–212, 2001. © 2001 Wiley-Liss, Inc.

Background and Objective Laser-induced thermotherapy (LITT) is a promising treatment for irresectable liver tumors. To predict the effects of laser applications and to optimize treatment planning in LITT, it is essential to gain knowledge about light distribution in tissue, tissue optical properties (absorption, scattering, anisotropy, penetration depth), and their continuous changes during therapy. Study Design/Materials and Methods Measurements of optical properties were performed with a double integrating-sphere system and a laser diode (830 nm). Porcine liver tissue samples were examined in a native state (35°C) and after exposure to different temperatures (45°C to 80°C). Results Rising temperature was accompanied by a decrease in the absorption coefficient and anisotropy factor and an increase in the scattering coefficient. These changes were only significant in the temperature range of 50° to 65°C (P

The feasibility and safety of percutaneous laser-induced thermotherapy (LITT) of liver metastases in an open low-field magnetic resonance imaging (MRI) system combined with microsphere-modulated blood flow reduction were tested. Nd:YAG laser therapy with an internally cooled laser applicator was performed under local anesthesia on 20 patients with 34 liver metastases. To increase the effectiveness of LITT, degradable starch microspheres were injected into the proper hepatic artery through an MR-visible catheter initially inserted under fluoroscopy. Near real-time imaging was used for positioning the laser applicator. A T1-weighted gradient-echo breath-hold sequence was used for catheter localization and temperature monitoring. The volumes of the liver metastases and the thermonecroses were determined. MRI-guided LITT could be performed in all patients with no clinically relevant complications. Intraprocedural imaging underestimated the extent of thermonecrosis. In conclusion, percutaneous LITT of liver metastases after injection of starch microspheres is both technically feasible and safe in an open MRI system. J. Magn. Reson. Imaging 2001;13:31-36.

25 Angefangen beim gepulsten UV-Laser, der die Fehlsichtigkeit des Auges korrigiert, bis hin zum kontinuierlichen Infrarotlaser zur Zerstorung von Tumoren: Aus vielen Bereichen der Medizin sind Laser heute nicht mehr wegzudenken. Neben Wellenlange und Pulsdauer interessiert man sich zunehmend auch fur die Koharenz des Laserlichts. Sie wird ausgenutzt, um bildgebende Verfahren in der medizinischen Diagnostik zu unterstutzen.

Background and Objective: Knowledge about optical parameters and the resultant light distribution in laser-treated tissue is important for predicting the effects of laser-induced thermotherapy of liver metastases (LITT). Materials and Methods: The absorption and scattering coefficients as well as the anisotropy factors and the optical penetration depths of human liver tissue and colorectal liver metastases were determined at 850, 980, and 1,064 nm under native and thermocoagulated conditions. Results: Liver metastases had a lower anisotropy factor, absorption, and scattering coefficient than healthy liver (P < 0.01), resulting in a significantly higher optical penetration depth in metastatic tissue. Coagulation significantly changes the optical parameters by reducing the optical penetration depth in both tissue types (P < 0.01). Conclusions: A greater optical penetration depth in metastatic tissue is advantageous for LITT, since larger tumor volumes can be coagulated. At the same time, an adjustment of the application parameters during LITT is necessary to achieve optimal therapeutic success. Lasers Surg. Med. 23:194‐203, 1998. © 1998 Wiley-Liss, Inc.

Background and Objective Interstitial laser therapy (ILT) is a minimally invasive treatment method for congenital vascular malformations (CVM). This study was intended to show whether or not open magnetic resonance imaging (MRI) offers a means of on-line thermometry and procedure control. Study Design/Patients and Methods ILT using a bare fiber and an Nd:YAG laser was applied in 20 children with CVM under open MR-control. Results With the open MR-systems, needle placement and advancement was excellent in all cases. On-line thermometry was possible in 90% of the therapy spots. The 6 week MR follow-up revealed a 76% reduction in tumor size in 14 patients. Clinical symptoms improved in 85% of the patients. Conclusion MR-guided ILT could become a safe method to treat selected types or selected regions of CVM. Lasers Surg. Med. 23:250–257, 1998. © 1998 Wiley-Liss, Inc.

BACKGROUND AND OBJECTIVE: The effect of temporarily interrupted hepatic blood flow and multiple-fiber application on necrosis volume in interstitial laser coagulation (ILC) was investigated. STUDY DESIGN/MATERIALS AND METHODS: Single- and multiple-fiber ILC were performed in porcine livers with normal as well as interrupted perfusion. Temperatures were determined. Lesions were measured and studied by light microscopy 4 hours post-treatment. RESULTS: ILC with multiple-fiber application led to significantly greater individual lesion volumes (3.7 +/- 0.5 cm3) than single-fiber application (2.5 +/- 0.5 cm3) (P < .01). The interruption of hepatic perfusion led to a significant increase in lesion volume with single- (7.5 +/- 1.0 cm3) as well as multiple-fiber application (12.6 +/- 2.2 cm3) (P < .01). Superposition of the lesions in the multiple-fiber application mode was only determined with interrupted perfusion (total volume: 50.3 +/- 6.6 cm3). CONCLUSION: Interruption of hepatic perfusion increases lesion volumes significantly. ILC for treating liver tumors should preferably be performed by application routes that permit temporary interruption of hepatic perfusion.

Background and Objective : This study investigated the feasibility of 850 nm diode laser-induced thermotherapy (LITT), a new procedure providing local hyperthermia and photocoagulation, a minimally invasive treatment of tumors, and other disorders such as benign prostate hyperplasia. Study Design/Material and Methods : An improved fiber optic diffuser inserted through a catheter was used to irradiate prostate, liver, and kidney tissue in-vitro. Experimental results were compared with predictions from mathematical simulations based on measured optical tissue parameters. Results : After 10 minutes of irradiation with 2-4.6 W CW laser power, sizable coagulation diameters had been achieved. In prostate and kidney tissue, temperature rises and coagulation diameters after laser irradiation were found to be smaller than in liver tissue. Those tissues also had a higher threshold for carbonization, thus reducing the risk of damage to the delivery system. Conclusion : The data suggest that a low power diode laser can be recommended for use in LITT to treat prostate and kidney tissue.