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Knowledge about the changes in the electric conductivity during the coagulation process of radiofrequency ablation of the liver is a prerequisite for the predictability of produceable thermonecrosis in the liver.Continuous measurements of the electric conductivity sigma in ex vivo porcine liver (n = 25) were done during the coagulation and cooling process at the temperature range of the radiofrequency ablation at a frequency of 470 kHz relevant for the radiofrequency ablation. Measurements of the electric conductivity were performed in both perfused porcine liver (n = 3) and a human surgical specimen from a colorectal liver metastasis.At a body temperature of 37 degrees C, conductance sigma was 0.41 siemens per metre (0.32 S/m; 0.52 S/m). Conductance sigma increased continuously and uniformly at a temperature of 77 degrees C. Maximum conductance sigma with 0.79 S/m (0.7 S/m; 0.87 S/m) was reached at 80 degrees C. A continuous reduction of conductance was observed during the cooling phase. At 37 degrees C, the specific conductance sigma in the healthy perfused porcine liver was 0.52 S/m, 0.55 S/m and 0.57 S/m (mean 0.55 S/m). The electric conductivity of the human colorectal liver metastasis was clearly higher.Changes in the specific conductivity during the coagulation and the cooling phase play an important role for the produceable size of a coagulation necrosis and necessitates an adaptation of the therapy parameters during radiofrequency ablation.

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

Institutional review board approval and patient informed consent were obtained. Use of a multipolar radiofrequency (RF) ablation device in patients with hepatic malignancy was prospectively evaluated with regard to feasibility, achieved ablation zone size and shape, technical effectiveness, and complications. Nineteen malignant liver tumors were treated with the multipolar resistance-controlled RF ablation system, with which up to three internally cooled bipolar coagulation electrodes can be operated simultaneously. Postinterventional imaging was performed with dynamic contrast material-enhanced magnetic resonance (MR) imaging and MR imaging-based three-dimensional planimetry. Complete tumor destruction was achieved in 18 of 19 tumors. Mean ablation zone volume was 52 mL +/- 45 (standard deviation). Thirteen patients were treated with a percutaneous approach; six, with an intraoperative approach. Maximum ablation size was 91 x 62 x 79 mm with the percutaneous and 73 x 98 x 74 mm with the intraoperative approach. Of the 18 completely evaluable ablation zones, 13 were concentric, two were moderately eccentric, two were eccentric, and one was wedge-shaped. The multipolar RF ablation device achieves large ablation zones and has high technical effectiveness in treating hepatic tumors.

Recently, it has been shown that coagulation volumes of interstitial laser therapy (ILT) can be enlarged by introducing a diffuser tip applicator into a cooling catheter system in the treatment of liver, breast and lung neoplasm. The aim of this study was to prove if coagulation volumes in ILT of congenital vascular malformations (CVMs) can also be enlarged by using this system. Cooled laser applicators were used in eight patients with CVM. The procedures were executed with an Nd:YAG laser 1064 nm. The laser power was 25 W. The applicator was introduced into a thermostable Teflon cooling catheter. Cooling flow was 50 ml/min. For online thermo-monitoring, we used three time-optimized MR sequences in an open magnetic resonance imaging (MRI) unit. The volume of MRI-changes ranged from 12 up to 36 ml (mean: 20.5 ml). In comparison with previous results in 600 μm bare fibre treatment (mean spot volume 1.9 ml), treatment spots were 10 times higher in the cooled applicator system. In certain large and deep seeded CVM, ILT becomes more effective with cooled laser applicator systems.

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

We describe a software system that helps both to determine anatomically correct and surgically realizable resection territories and to plan minimally invasive interventions for cases that are impracticable for surgery.

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.

A newly developed diffusing laser applicator was examined for interstitial laser coagulation (ILC) of liver tumours. The applicator consisted of a matted quartz core and a quartz glass dome, also matted on its inner surface and sealed to the fibre. The applicator provided a homogeneous light intensity distribution over an active length of about 20 mm. Lesions were created in an ex-vivo porcine liver model using a Nd-YAG laser comparing the new diffusing tip with a Ringmode(®)-ITT applicator in order to find optimal laser parameters and damage thresholds. The lesions were investigated using macroscopic size measurement, volume calculation and histological examination (HE, NADPH-dehydrogenase). The damage threshold of the diffusing tip was 6 W at 14 min exposure time whereas the Ringmode(®)-ITT applicator had its limit at 5 W and 12 min exposure. Comparing various exposure times showed that treatment over a time of more than 840 s did not significantly increase the lesion volume. At 5 W and 720 s the mean lesion volume was 6.9±1.1 cm(3) with the diffusing tip and 6.3±0.6 cm(3) with the Ringmode(®)-ITT applicator, both having a slight ellipsoidal shape. Hence, the created lesions were not significantly different for both applicators when the same laser parameters were applied. On the other hand, the new diffusing tip had a higher damage threshold and was therefore capable of producing maximal coagulation volumes of up to 7.9±0.5 cm(3) at 5 W and 20 min. The experiments showed that lesions with a dimension of 31×22 mm can be achieved with the diffusing applicator which seem suitably sized for treating small human liver metastases in a single laser session.

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.

Purpose: The aim of this study was to determine the energy (J/mm3 tumor volume) and temperature required for a complete laser-induced thermotherapy (LITT) of experimental liver tumors, and to find out causes and areas of local recurrence followed by incomplete treatment. Methods: In VX-2 tumor-bearing rabbits LITT was performed using neodymium:yttrium-aluminum-garnet (Nd:YAG) laser (1064 nm) with a diffuser-tip applicator and a temperature feedback system. The animals were randomized into four groups (n = 20) that differed in the target temperature at the tumor border as follows: 45°C, 50°C, 55°C and 60°C. The target temperature was held for 10 min constant. Histologic examination (hematoxylin and eosin [H&E], nicotinamide adenine dinucleotide phosphate [NADPH]-dehydrogenase) was performed at 0 h, 24 h, 96 h, and 14 days after LITT. Results: The pretreatment tumor volume of 2191 ± 61 mm3 was the same for all groups (p > 0.05). Energy up to target temperature and total energy required, lesion size, and the rate of incomplete tumor ablation (recurrences) are listed below (ap < 0.05, Kruskal-Wallis test). Histologically, two forms of local recurrences could be differentiated intralesionary and extralesionary. Conclusions: To achieve complete in situ ablation under the given conditions, it is necessary to apply laser energy of 3 J/mm3 tumor volume. A minimum temperature of 60°C on the tumor border presumed an application of 10 min. Recurrence was found outside the coagulation zone (extralesionary) and in high vascularized areas within the coagulation zone (intralesionary).

For effective small-volume tissue ablation in clinical and experimental settings, smaller laser-induced interstitial thermotherapy (LITT) applicator designs are required. The aim of this study was to compare the ablation properties of recently developed ultrasmall and small to standard LITT applicators.Laser-induced interstitial thermotherapy was performed on liver samples using ultrasmall, small, and standard LITT applicators. Thermotherapy was monitored by magnetic resonance imaging, and lesion sizes were measured for each image. True lesion sizes were then determined macroscopically and by histology.For continuous laser application over 5 minutes, maximum power settings were 5 W for the ultrasmall and small applicators and 10 W for the standard applicator. Given identical LITT settings, lesion volume measured by magnetic resonance imaging was significantly larger and histological tissue damage was more severe with the ultrasmall and small applicators than with the standard applicator.Small and ultrasmall LITT applicators can be used for effective tissue ablation of small target volumes in experimental and clinical applications.

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

Summary Introduction: Extratruncular, infiltrating congenital vascular malformations (CVM) are found in all organ systems. Large substance defects and diffuse blood loss may occur during surgical removal. Thus, conservative and interventional procedures are also applied, one of them being interstitial laser therapy (ILT). Patients and methods: Forty children with deep CVM underwent interstitial laser therapy with open MRI. The laser light guide was introduced into the malformation with a titan puncture needle and the tissue was thermically damaged by adequate selection of the physical parameters of the Nd:YAG 1064-nm laser. Beside the high soft-tissue contrast, MRI has the advantage of thermosensibility. For online thermomonitoring, we used 3 time-optimized MR sequences with a maximal velocity of 1 image in 3 seconds. Results: Positioning of the puncture needle was excellent in all applications and thermomonitoring was successful in 89%. A reduction of the tumor volume was observed in 36 patients at the 6-week follow-up. The volume of the malformations was reduced to 76%, on the average. Clinical improvement was seen in 78% of the cases. One fifth of the children are presently without symptoms. Thermic skin damage in 2 cases and intracorporal bare fiber tip loss in 1 case was found to be a complication. Discussion: Process control is decisive for successful interstitial laser therapy. Beside the high soft tissue contrast, MRI is characterized by a thermosensibility which does not allow invasive registration of temperature changes provoced by ILT inside the body. Summary: The introduction of open MR systems has enabled access to patients and interactive management directly in the magnetic field. MR-controlled interstitial laser therapy has to be included in the differential treatment of complicated congenital vascular malformations.

Summary A new scattering applicator for use in laser-induced thermotherapy (LITT) is presented. The applicator is mounted in front of a 400 μm quartz fiber and consists of a temperature stable plastic material with deposited scattering particles. The applicator provides a homogeneous axial scattering profile over an active length of 30 mm. The maximum power settings in porcine liver (in vitro) using a Nd:YAG-Laser and a cooled protective catheter were 31 W over an exposure period of 10 minutes. The resulting thermal lesions showed axial extensions of up to 50 mm and diameters of up to 33 mm, representing a total volume of 28.6 cm 3 .

Summary A dosimetry model was developed for the thermal laser treatment of biological tissue and applied to laser-induced thermotherapy of organ tumors. This model combines a Monte Carlo simulation for calculating photon distribution in the target volume, a finite difference method for computing heat dissipation and the Arrhenius formalism for predicting protein denaturation and subsequent tissue damage. Implementation was carried out on a Windows-based platform and enabled the three-dimensional control of the target volume. An in vitro evaluation in porcine liver revealed a difference of less than 7% with regard to the ablation volume.

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.

Summary The Nd:YAG laser (1064 nm) is still the most commonly used laser system for interstitial LITT. However, high-power diode lasers are gaining a foothold in medical treatment by virtue of their compactness, reliability, and portability. This study investigates the feasibility of the 940 nm diode laser application for LITT procedures and enables a comparison of tissue effects using both laser systems. An in-vitro study was performed on porcine liver and muscle tissue using a bare fiber and a cooled, diffusely scattering applicator. Different power settings and exposure time combinations were chosen depending on the applicator type. Five applications were performed for each parameter combination. As a result, a clearly demarcated coagulation could be easily identified in each experiment. Carbonization effects were found to occur earlier in diode laser applications, while Nd:YAG laser applications allowed the use of higher power levels. The diode laser allows the creation of a certain volume of coagulation in a short period of time due to the lower optical penetration depth and this is usually accompanied by carbonization. Our results have shown that the 940 nm diode laser could be a possible alternative for the Nd:YAG laser especially in the interstitial treatment of pale tissue. Besides this it can be successfully applied even for the treatment of high absorbing tissue if small coagulation volumes are needed.

Summary Introduction: For prediction of the effectiveness of laser-induced thermotherapy (LITT) of liver metastases and for the Planning of laser treatment it is indispensable to achieve knowledge about the intrahepatic light and temperature distribution in order to obtain data for an optimally adapted dosimetry. Material and methods: We evaluated the optical properties of normal and tumorous rabbit-liver ex-vivo using a double integrating sphere technique as well as a Monte-Carlo-simulation. These data were correlated with the measurement of the intrahepatic temperature ditrsibution in-vivo during LITT. Results: In our study we were able to show a positive correlation between ex-vivo results of optical properties and in-vivo results in temperature distribution. The absorption coefficient and scattering coefficients were significantly smaller in tumor tissue than in normal liver. This resulted in a higher optical penetration depth of the laser light into the tumor tissue (p Conclusions: 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.

Zusammenfassung Mit zunehmender Anwendung der interstitiellen Thermotherapie als Methode zur lokalen Behandlung tiefliegender Tumore ergibt sich die Notwendigkeit, geeignete Monitoringverfahren zur Uberwachung dieser Therapie zur Verfugung zu stellen. Die Behandlung von Mammatumoren zeigte, dass speziell fur das Online-Monitoring in dieser Korperregion, die beiden bislang am haufigsten eingesetzten Verfahren (Sonographie und MRT) nur bedingt geeignet sind. Im Rahmen der vorgestellten Arbeiten wurde daher die Eignung der intensitatsmodulierten optischen Durchleuchtung zur Online-Uberwachung untersucht. Mit Hilfe von Phantom- und In-vitro-Untersuchungen konnte gezeigt werden, dass die Identifikation von Koagulationen im umgebenden Gewebe moglich ist. Dazu wurde eine Auswertemethodik entwickelt, die unter In-vitro-Bedingungen eine Bestimmung der Koagulationszone auf ±1,4 mm erlaubt. Damit konnte die Eignung des Verfahrens nachgewiesen und die Grundlagen fur weitere, klinisch orientierte Untersuchungen geschaffen werden.

Objective: To test the feasibility and safety of the laser-induced thermotherapy (LITT) for liver metastases in open MR imaging system operating at 0.2 Tesla. Method: Laser therapy using the Nd:YAG laser was performed on 25 patients with a total of 41 liver metastases. An open low-field MRI scanner was used for puncture, positioning of the laser applicator, and monitoring the therapy. A true FISP sequence was used to track the puncture in close to real-time. Localization diagnostics and temperature monitoring were aided by T 1 -weighted gradient echo sequences in the breath-holding technique. In the first follow up after 24-48 hours, a contrast-enhanced T 1 -weighted gradient-echo sequence was performed in an MRI scanner at 1.5 T. The pre-, intra- and post-interventional volumes of the liver metastases as well as the thermolesions and the thermonecroses were determined. Results: LITT in an open MRI system was technically feasible in all patients with no clinically relevant complications. The mean volumes of the thermolesions measured during intervention in low-field MRI were lower than the volumes of the thermonecroses measured after intervention in high-field MRI. Conclusion : The technique presented here of laser-induced thermotherapy for liver metastases in an open MRI system is technically feasible and safe.

Purpose Description of local ablative techniques such as laser-induced thermotherapy (LITT) and radiofrequency ablation in the percutaneous interstitial thermotherapy for malignant liver tumors. Patients and methods MR-guided LITT is currently performed by means of implantable percutaneous catheter systems. CT is used to control the insertion of the catheter. Irrigated administration systems are available both for LITT and for radiofrequency therapy. Results At present LITT enables a local tumor control of 97.2% for localized liver metastases without extrahepatic spreading patterns. In a group of 381 patients the average survival times were 45.7 months for patients with liver metastasis, 42.7 months for those with colorectal liver metastases, and 32 months for HCC tumors. The data for radiofrequency ablation confirm the high value for tumor control of hepatocellular carcinomas with poorer results for liver metastases. Conclusions Percutaneous, MR-guided LITT permits good tumor control of liver metastases smaller than 5 cm and less than 5 in number. For HCC, at present percutaneous injection of alcohol, radiofrequency ablation, and LITT are equally effective.

Zusammenfassung Es wurde ein Dosimetriemodell fur die thermische Therapie von biologischem Gewebe mittels Laserstrahlung erarbeitet und auf die interstitielle laserinduzierte Thermotherapie von Organtumoren angewendet. Das Modell kombiniert eine Monte-Carlo-Simulation zur Berechnung der Photonenverteilung im Zielvolumen, ein Finite-Differenzen-Verfahren zur Berucksichtigung von Warmetransportprozessen und den Arrhenius-Formalismus zur Bestimmung der Proteindenaturierung und finalen Gewebedestruktion. Die Implementierung der Algorithmen erfolgte auf einer Windows™-basierten Plattform und ermoglicht die dreidimensionale Kontrolle des Zielvolumens. Die In-vitro-Evaluierung in Schweineleber zeigte eine Ubereinstimmung von besser 7 % bezuglich des Destruktionsvolumens. Die Anwendung des Modells fur eine klinisch relevante Situation machte deutlich, dass Masnahmen zur Perfusionsminderung die Effizienz der LITT um ein Vielfaches steigern konnen.

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.

To evaluate gadolinium (Gd)-diethylenetriamine-pentaacetic-acid (DTPA)-enhanced magnetic resonance imaging (MRI) for follow-up monitoring of laser-induced thermotherapy (LITT) and to determine a useful examination schedule.LITT of the liver was performed in 55 rabbits using a neodymium: yttrium-aluminum-garnet (Nd:YAG) laser (4-W power output, 840-s exposure time). Gd-DTPA MRI and histologic examinations were performed at different times (0-168 days).Laser-induced lesions underwent regeneration and volume size reduction (69% after 168 days). The correlation coefficient (MR vs. macroscopic analysis) for the mean lesion diameter was r = 0.96. Histology of lesions comprised the four zones that correlated best with MRI findings. Coagulation necroses immediately after LITT was seen as an area of no enhancement on Gd-DTPA MRI. Circular enhancement was first seen 72-96 h after LITT, which was due to early mesenchymal proliferation.Gd-DTPA MRI is a good monitoring procedure for LITT. MRI should be performed 24 and 96 h after LITT.

To evaluate experimentally and clinically an internally cooled power laser system for percutaneous treatment of liver metastases, with magnetic resonance (MR) imaging guidance, to increase the volume of coagulative necrosis with single laser beam applications.The power laser system consisted of standard cannulation paraphernalia and a specially designed 7-F protective catheter for cooling the laser tip during treatment to avoid carbonization. A microdome laser beam applicator with a laser tip diameter of 0.95 mm kept the entire device as small as possible. After the unit was tested in 40 porcine livers, 532 laser beam applications (mean power, 27.5 W [range, 22.1-30.0 W]; mean application time, 19.8 minutes [range, 14-30 minutes]) were performed with MR guidance in 127 patients with 318 liver metastases. The safety of the procedure and the volume of induced necrosis were evaluated.In vitro, cuboid areas of coagulative necrosis with a mean greatest diameter of 4.3 cm +/- 0.5 (SD) were demonstrated after single applications. In vivo, MR thermometry allowed accurate demarcation of changes induced by heat, with a mean diameter of necrosis of 3.3 cm +/- 1.4. No carbonization or vaporization of tissue or damage of equipment occurred during treatment.This power laser system can increase the volume of laser-induced necrosis in liver metastases with a single application, thereby simplifying and accelerating the treatment of larger lesions.

The technical requirements have been fulfilled for the reliable clinical application of laser-induced thermotherapy for treating liver tumors. Laparotomy as well as percutaneous and laparoscopic access modes are available for this method. Thus, laser-induced thermotherapy is a true minimally invasive procedure for treating liver metastases. Presently, it is not possible to make a final assessment on the prognostic value of laser-induced thermotherapy in the treatment of liver tumors. However, recently published data justify the scheduling of a randomized study comparing laser-induced thermotherapy with standard surgical liver resection. In this article, thermobiological and technical principles as well as the different types of application modes for this method are described. Copyright ©1998 by W B. Saunders Company

Laser-induced thermotherapy is an in situ ablation method for the local treatment of liver tumors. The basic prerequisite for induction of adequate treatment volumes for clinical use was the development of a thermostable application system. In an ex vivo test series, the specially developed application system (diffuser tip) with 5760 J had a higher thermic loading capacity than the Ringmode applicator with 4200 J, thus enabling the induction of significantly larger lesions with a volume of 7.6 cm3. The results of a further in vivo test series demonstrated that the lesions were subject to a four-phase connective-tissue organization within a 6-month period. Furthermore, the same laser energy (4200 J) was associated with a significantly lower lesion volume of 2.5 cm3 in the in vivo than in the ex vivo test series. The influence of liver perfusion on the inducible lesion volume was examined in a further animal experimental study. By temporarily interrupting hepatic blood perfusion (Pringle's maneuver) during laser application, the effective volume could be increased to 50.3 cm3 (P < 0.01) using an optical beam splitter. These results show that the technical prerequisites for reliable clinical application of laser-induced thermotherapy have been fulfilled.

PURPOSE To evaluate the correlation of MR-measured changes of signal intensity and invasive fluoroptic temperature measurements during MR-guided LITT of liver metastases. MATERIALS AND METHODS In 15 patients with proven liver metastases of colorectal carcinoma, MR-guided LITT was performed with a percutaneous approach in a multiapplicator technique. Two temperature sensitive T1-weighted sequences (FLASH-2D- and TurboFLASH-sequences) were used to map the spatial and temporal distribution of Nd:YAG laser effects. Parallel fluoroptic temperature measurements were carried out by means of an inserted probe in a distance of 5-26 mm (mean: 14 mm) from the laser applicator. RESULTS In both sequences a gradually increasing signal loss could be documented during laser application which proved to be reversible after cessation of energy deposition. the percentage of decrease in signal intensity correlated directly with the measured increase of temperature. Invasive fluoroptical evaluation of temperature distribution after 10 min exposure time showed at 5 mm distance from the applicator an increase of temperature of 35 degrees C, in 10 mm distance a mean increase of 9 degrees C +/- 1.7, in 15 mm a mean increase of 7 degrees C +/- 1.6 and in 20 mm a mean increase of 3 degrees C +/- 0.5. This is evidence of thermal tissue damage up to 3 cm in diameter with laser monoapplication. The qualitative evaluation revealed a reproducible correlation of the extent of signal loss around the applicator and the finally induced degree of necrosis. CONCLUSION Invasive fluoroptical temperature measurements prove the diagnostic reliability of MR thermometry for the online monitoring of LITT of liver metastases.

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.

PURPOSE To optimize the MR sequences parameter for monitoring hyperthermic effects in the tissue during laser induced thermotherapy (LITT). MATERIAL AND METHODS Experimental studies were performed for the evaluation of MR-thermometry using a contrast-agent-water solution and a pig-liver. A T1-weighted TurboFLASH sequence and a FLASH-2D sequence were used. The TurboFLASH sequence was used with various T1 settings (between 100 and 1250 ms). MR findings were correlated with temperature measurements using a fluoride optical temperature measuring system in a distance of 1, 2, and 5 cm from the laser applicator. RESULTS Using the contrast-agent-water solution demonstrated the temperature sensitivity of both sequences. In vitro evaluations using pig liver demonstrated a near linear increase of signal versus increasing tissue temperatures in a distance of 1 cm to the tip of the laser applicator. Optimal visualization of the temperature effects was obtained using a T1 between 100 ms and 400 ms. Using the FLASH-2D sequence a signal loss was documented at a TR of 110 ms. CONCLUSION MR-thermometry using sequentially TurboFLASH and FLASH-2D sequences allowed a non-invasive monitoring of the laser induced temperature changes.

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.

In the medical setting, scattering dome applicators are used in various therapeutic and diagnostic procedures, e.g. laser-induced interstitial thermotherapy. The present study reports on the development of an automatic measuring system for determining the light distribution along the active end of scattering dome applicators. Using a stepper motor, the applicator is gradually moved into an integrating sphere, in which the light intensity is measured with a photodetector. It was shown the light distribution is determined mainly by the conditions under which the laser beam is coupled to the transmission fiber. The results made it possible to optimize the production of applicators, and showed that the set-up was suitable for quality control use.

Purpose To analyse the value of MR-guided laser-induced thermotherapy (LITT) for palliative treatment of recurrent tumours of the head and neck region. Material and methods 8 patients with recurrent tumours of the head and neck region (squamous cell carcinomas n = 6, pleomorphic adenomas n = 2) underwent MR-controlled LITT. A 7 French laser applicator was inserted under local anaesthesia into the centre of the recurrent tumour. A Nd:YAG laser with a wavelength of 1064 nm was used. Therapy was monitored on-line using special MR thermosequences. Results Preinterventional contrast-enhanced MRI revealed a recurrent tumour of the head and neck region for all eight patients. All patients tolerated the procedures well under local anaesthesia, with no clinically relevant side effects. The MR thermosequences depicted up to 15 mm diameter areas of less signal near the laser tip. Postinterventional contrast-enhanced MRI revealed hypovascularized areas due to the resulting coagulative necrosis. Coagulative necrosis of 4 cc to 28 cc occurred in all patients, and a reduction of clinical symptoms was achieved in five. Conclusion The results obtained indicate that minimal invasive LITT can be a therapeutic alternative for palliative treatment of head and neck tumours.

PURPOSE: To evaluate magnetic resonance (MR) imaging-controlled laser-induced thermotherapy (LITT) in the treatment of recurrent head and neck tumors. MATERIALS AND METHODS: Six patients with recurrent nasopharyngeal tumors (squamous cell carcinoma [n = 4], pleomorphic adenoma [n = 2]) underwent LITT with local anesthesia. A 7-F introducing sheath was inserted into the center of the tumor followed by a specially designed laser emitter. Therapy was monitored on-line with MR thermometry, and the amount of necrosis was estimated with dynamic and static contrast material-enhanced sequences. RESULTS: All procedures were well tolerated with use of local anesthesia, with no clinically relevant side effects. MR thermometry depicted up to 15-mm-diameter areas of less signal intensity near the laser tip. Coagulative necrosis was achieved in all patients (volume range, 4-28 cm3), and clinical symptoms were reduced in four. CONCLUSION: MR imaging-controlled LITT may be a safe, minimally invasive alternative in the tr...

Knowledge about the optical properties μa,μs, and g of human blood plays an important role for many diagnostic and therapeutic applications in laser medicine and medical diagnostics. They strongly depend on physiological parameters such as oxygen saturation, osmolarity, flow conditions, haematocrit, etc. The integrating sphere technique and inverse Monte Carlo simulations were applied to measure μa,μs, and g of circulating human blood. At 633 nm the optical properties of human blood with a haematocrit of 10% and an oxygen saturation of 98% were found to be 0.210±0.002 mm-1 for μa,77.3±0.5 mm-1 for μs, and 0.994±0.001 for the g factor. An increase of the haematocrit up to 50% lead to a linear increase of absorption and reduced scattering. Variations in osmolarity and wall shear rate led to changes of all three parameters while variations in the oxygen saturation only led to a significant change of the absorption coefficient. A spectrum of all three parameters was measured in the wavelength range 400-2500 nm for oxygenated and deoxygenated blood, showing that blood absorption followed the absorption behavior of haemoglobin and water. The scattering coefficient decreased for wavelengths above 500 nm with approximately λ-1.7; the g factor was higher than 0.9 over the whole wavelength range. © 1999 Society of Photo-Optical Instrumentation Engineers.

The absorption coefficient mu(a), scattering coefficient mu(s), and anisotropy factor g of diluted and undiluted human blood (hematocrit 0.84 and 42.1%) are determined under flow conditions in the wavelength range 250 to 1100 nm, covering the absorption bands of hemoglobin. These values are obtained by high precision integrating sphere measurements in combination with an optimized inverse Monte Carlo simulation (IMCS). With a new algorithm, appropriate effective phase functions could be evaluated for both blood concentrations using the IMCS. The best results are obtained using the Reynolds-McCormick phase function with the variation factor alpha = 1.2 for hematocrit 0.84%, and alpha = 1.7 for hematocrit 42.1%. The obtained data are compared with the parameters given by the Mie theory. The use of IMCS in combination with selected appropriate effective phase functions make it possible to take into account the nonspherical shape of erythrocytes, the phenomenon of coupled absorption and scattering, and multiple scattering and interference phenomena. It is therefore possible for the first time to obtain reasonable results for the optical behavior of human blood, even at high hematocrit and in high hemoglobin absorption areas. Moreover, the limitations of the Mie theory describing the optical properties of blood can be shown.

Background and Objectives Laser-induced thermotherapy (LITT) is a promising method for local treatment of liver metastases. The aim of this study was to compare the effect of LITT on lesion size when combined with hepatic arterial microembolization or complete hepatic blood flow occlusion. Study Design/Materials and Methods In a porcine liver model, LITT (30 W 15 minutes) was performed with either normal (n = 12), partially interrupted (arterial microembolization via a hepatic artery catheter n = 12) or completely interrupted hepatic perfusion (Pringle's maneuver, n = 12). LITT lesions were macro- and microscopically assessed after liver dissection. Results Hepatic inflow occlusion led to a fourfold increase in lesion volume after arterial microembolization and a ninefold increase after complete interruption (6.3. cm3 vs. 27.1 cm3 vs. 58.8 cm3, P

Ziele: Eine homogene, ausreichend hohe Energieverteilung im Zielgewebe ist von entscheidender Bedeutung bei der in-situ Thermoablation. Zu diesem Zweck wurden in der Vergangenheit zahlreiche mono- und bipolare Sondensysteme entwickelt. Letztere haben theoretische Vorteile hinsichtlich der Energieverteilung, wurden aber bisher aufgrund der kleinen Ablationszonen klinisch nicht eingesetzt. Es werden erste Erfahrungen mit einem System vorgestellt, bei dem bis zu 3 bipolare, intern gekuhlte Sonden im Abstand von 2–3cm appliziert werden konnen. Methode: Das System wurde bisher bei 12 Patienten mit 16 malignen Lebertumoren (mittlere Grose 33mm, 20–55mm) perkutan Ultraschall- oder CT-gesteuert (9 Patienten) und intraoperativ IOUS-gesteuert (3 Patienten) eingesetzt. Das Ablationsergebnis wurde mittels CT vor und 1 Woche nach Ablation sowie MRT am Tag 2 nach Ablation kontrolliert. Die Ablationszonen wurden in allen 3 Ebenen ausgemessen und hinsichtlich persistierenden Tumorgewebes untersucht. Die applizierte Energie wurde dokumentiert. Ergebnis: 15 der 16 Lasionen wurden vollstandig erfasst. Bei einer Lasion von 2cm Grose verblieb trotz erneuter Ablation ein kleiner Tumorrest unmittelbar subkapsular. Die Grose der Ablationszonen war abhangig von der Anzahl der Sonden und der applizierten Energie und betrug durchschnittlich 42×43×58mm (23×34×40mm, 2 Sonden perkutan, bis 85×65×65mm, 3 Sonden intraoperativ unter Pringle-Manover). Bei 11 der 12 Patienten traten keine relevanten Komplikationen auf. Bei einem voroperierten Patienten kam es zu einer Dunndarmverletzung, die eine operative Therapie erforderte. Schlussfolgerung: Nach unseren bisherigen Erfahrungen konnen mit dem neuen bipolaren System Ablationslasionen am Patienten bis gut 5cm Grose erreicht werden.

In general, medical laser systems consist of a source of laser light, a shutter and control units, a beam-handling system and the optical end unit (Fig. 1).

Introduction Thermal in situ ablation techniques like radiofrequency interstitial thermotherapy (RFITT) become increasingly important in the treatment of liver tumors. The aim of this study was to develop a computer-simulated 3-D irradiation model for predicting the ablation volume and to evaluate RFA in vivo in porcine liver with normal and interrupted perfusion.

Introduction The goal of this study was to compare the optical properties (o.p.) of colorectal primary tumors with that of synchronous hepatic metastases to ascertain whether the o.p of the primary tumor can be used to determine suitable application parameters and dosimetry for metastases.