Quantitative microspectrophotometry in turbid media.

We present a new technique to determine the scattering coefficient, the absorption coefficient, and the anisotropy factor in turbid media on a microscopic level. To this end, a microspectrophotometer was used to obtain transmission measurements at different solid angles. To extract the optical properties from phantom materials (liquid and solid) and biological tissue (bovine liver) an inverse Monte Carlo algorithm was used.

Effect of the scattering delay on time-dependent photon migration in turbid media.

We modified the diffusion approximation of the time-dependent radiative transfer equation to account for a finite scattering delay time. Under the usual assumptions of the diffusion approximation, the effect of the scattering delay leads to a simple renormalization of the light velocity that appears in the diffusion equation. Accuracy of the model was evaluated by comparison with Monte Carlo simulations in the frequency domain for a semi-infinite geometry.

[Survival after laser-induced interstitial thermotherapy of colorectal liver metastases--a comparison of first clinical experiences with current therapy results].

Purpose: Laser-induced interstitial thermotherapy (LITT) is a minimally invasive procedure for local tumor ablation. This report discusses the long-term results of this therapy in non-surgical patients with colorectal liver metastases.

Materials And Methods: In total, we treated 163 colorectal liver metastases in 85 patients by MR-guided LITT.

MR-guided laser-induced interstitial thermotherapy of recurrent glioblastoma multiforme: preliminary results in 16 patients.

We investigated the survival after laser-induced interstitial thermotherapy in 16 patients suffering from recurrent glioblastoma multiforme. The concept underlying the intervention is the cytoreduction of the tumor tissue by local thermocoagulation. All patients received standard chemotherapy (temozolomide).

[Stereotactic body radiotherapy (SBRT) -- an overview under special consideration of SBRT and LITT in the therapy of liver metastases].

Stereotactic body radiotherapy (SBRT) is a high dose radiotherapy, the radiation dose is applicated one-time or in a few fractions exactly to the tumor or metastases under maximal separation from the normal tissue. Because of this a major expenditure of medical and technical efforts are necessary, a detailed description of the proceedings is following in the methodic part of this article. Indications of SBRT are especially medical irresectable lung tumors of early stages, primary liver/biliary tumors and pulmonary or liver metastases if there is an oncological benefit for the patients.

MR-guided laser irradiation of recurrent glioblastomas.

We treated two patients with recurrent glioblastoma multiforme using Nd:YAG laser irradiation in the framework of a salvage therapy. The underlying concept is to achieve cytoreduction by partial coagulation of the tumor. Magnetic resonance imaging (MRI) follow-up examinations revealed a volume reduction of the laser-irradiated areas, while the untreated parts of the tumor exhibited a progression.

Measurement of the coagulation dynamics of bovine liver using the modified microscopic Beer-Lambert law.

Background And Objectives: During heating, the optical properties of biological tissues change with the coagulation state. In this study, we propose a technique, which uses these changes to monitor the coagulation process during laser-induced interstitial thermotherapy (LITT).

Study Design/materials And Methods: Untreated and coagulated (water bath, temperatures between 35 degrees C and 90 degrees C for 20 minutes.

Small-volume frequency-domain oximetry: phantom experiments and first in vivo results.

We describe a new method to determine the oxygen saturation and the total hemoglobin content of tissue in vivo absolutely at small source-detector separations (<10 mm). Phase and mean intensity of modulated laser light of various wavelengths was measured at several predetermined source-detector separations in the frequency domain. From these measured quantities, the absorption coefficient was derived using the modified time-integrated microscopic Beer-Lambert law (MBL).

Optical properties of selected native and coagulated human brain tissues in vitro in the visible and near infrared spectral range.

Medical laser applications require knowledge about the optical properties of target tissue. In this study, the optical properties of selected native and coagulated human brain structures were determined in vitro in the spectral range between 360 and 1100 nm. The tissues investigated included white brain matter, grey brain matter, cerebellum and brainstem tissues (pons, thalamus).

Laser-induced interstitial thermotherapy of liver metastases in an interventional 0.5 Tesla MRI system: technique and first clinical experiences.

Laser-induced interstitial thermotherapy (LITT) surveyed by magnetic resonance imaging (MRI) has been shown to be effective in various applications. The laser treatment of colorectal liver metastases usually requires a separate device (e.g.

Scattering delay time of Mie scatterers determined from steady-state and time-resolved optical spectroscopy.

We have determined the scattering delay time of Mie scatterers (r = 255 nm quartz spheres in polyester resin) from a combination of steady-state (integrating-sphere) and time-resolved (frequency-domain) measurements performed in the multiple-scattering regime. The effective transport velocity of light was derived from intensity and phase measurements at four different wavelengths by using the time-integrated microscopic Beer-Lambert law. We could demonstrate a systematic underestimation of the effective transport velocity compared with the phase velocity in the medium.

Influence of the scattering phase function approximation on the optical properties of blood determined from the integrating sphere measurements.

We investigated the impact of the scattering phase function approximation on the optical properties of whole human blood determined from integrating sphere measurements using an inverse Monte Carlo technique. The diffuse reflectance Rd and the total transmittance Tt(λ=633 nm) of whole blood samples (Hct=38%) were measured with double-integrating sphere equipment. The scattering phase functions of highly diluted blood samples (Hct=0.

[Interventional MR tomography. Current status and future perspectives].

The concept of MR guidance of invasive diagnostic and minimally invasive therapeutic procedures is based on the excellent morphologic and functional properties of MR imaging. Prerequisites are adequate patient monitoring and adherence to safety guidelines. Fast and ultrafast sequences, temperature quantification, visualization of intravascular devices, thermal stability of contrast media and thermosensitive contrast media are discussed.

In vivo MRI thermometry using a phase-sensitive sequence: preliminary experience during MRI-guided laser-induced interstitial thermotherapy of brain tumors.

The purpose of this study was the application of the proton-resonance-frequency method to monitor laser-induced interstitial thermotherapy (LITT) in a patient with an astrocytoma WHO II. A phase-sensitive two-dimensional (2D) fast low-angle shot (FLASH) sequence was used to determine the temperature-related phase shifts during LITT. Temperature maps were displayed during therapy with a temporal resolution of 20 seconds.

Treatment planning for MRI-guided laser-induced interstitial thermotherapy of brain tumors--the role of blood perfusion.

MR techniques have been demonstrated to allow a reliable monitoring of laser-induced interstitial thermotherapy (LITT). However, an adequate on-line control of this coagulation technique requires an exact therapy planning. The latter is mandatory to interpret the MR-monitoring data correctly to guarantee a precise laser irradiation.

Laser-induced thermal lesions in the human brain: short- and long-term appearance on MRI.

Purpose: The purpose of our study was to investigate with MRI the development of thermal lesions in the human brain up to almost 4 years after laser-induced interstitial thermotherapy (LITT).

Method: Eighteen patients with brain tumors who underwent LITT entered the study.

Results: In all patients the acute lesion comprised five concentric zones that showed reverse signal intensities on T1- versus T2-weighted images.

[MR tomographic temperature quantification at 1.5 T in vitro: a comparison of fast T1 maps and a phase-sensitive sequence].

Purpose: To determine the value of fast T1-maps and a phase-sensitive sequence for temperature quantification with MR imaging.

Material And Methods: The experimental setup allowed both homogeneous heating as well as laser-induced interstitial thermotherapy (Nd:YAG, 1064 nm) of tissue specimens (pig brain, liver and muscle) in vitro. A total of 60 experiments were performed.

Determination of laser-induced temperature distributions using echo-shifted TurboFLASH.

An echo-shifted TurboFLASH sequence implemented on a clinical whole body MR scanner was used to determine thermal changes in tissue. With this snapshot-like data acquisition, temperature-related phase shifts were measured with a temporal resolution of 1.3 s.

Preliminary experience with the application of gadolinium-DTPA before MR imaging-guided laser-induced interstitial thermotherapy of brain tumors.

The purpose of this study was to investigate the potential value of i.v. gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) applied before MRI-guided laser-induced interstitial thermotherapy (LITT) of brain tumors without original enhancement, especially in defining total lesion size during therapy.

Inverse hybrid technique for determining the optical properties of turbid media from integrating-sphere measurements.

We have combined the Monte Carlo method with the small-angle approximation of the radiative transfer theory to derive the optical properties (the absorption coefficient, the scattering coefficient, and the anisotropy factor) of turbid materials from integrating-sphere measurements (the total transmittance and the diffuse reflectance) and the collimated transmittance. Unlike one-dimensional models, the technique accounts for the side losses of light at the edges of the sample. In addition, it enables the correction of the measured collimated signal for the contribution of multiply scattered light.

[Laser-induced interstitial induced hyperthermia of cerebral tumors with nuclear magnetic resonance tomography control].

Purpose: The purpose of our study was to determine the value of MRI in monitoring laser-induced interstitial thermotherapy (LITT) of cerebral neoplasms.

Materials And Methods: Sixteen patients with brain tumors were treated with LITT. The laser irradiation was performed within the MR unit and monitored with a temperature-sensitive T1-weighted 2D-FLASH sequence.

Mapping of the cortical motor hand area with functional MR imaging and MR imaging-guided laser-induced interstitial thermotherapy of brain tumors. Work in progress.

Purpose: To localize the cortical motor hand area with functional magnetic resonance (MR) imaging before and after MR imaging--guided laser-induced interstitial thermotherapy of tumors in the precentral brain region to control energy delivery and to improve safety.

Materials And Methods: Functional MR images were obtained in eight patients (five men, three women; aged 27-63 years) while they flexed their fingers. MR imaging--guided laser-induced interstitial thermotherapy was terminated when there was less than 8-12 mm between the border of the laser-induced lesion and the motor hand area anterior aspect.

Magnetic resonance imaging of microwave induced tissue heating.

MR-guided interstitial thermotherapy offers a minimally invasive treatment for localized tumors and tissue structures exhibiting functional abnormalities. In this study, microwaves (2.45 GHz) were used for tissue irradiation to overcome some limitations of the heating sources used so far.

Optical properties of human articular tissue as implication for a selective laser application in arthroscopic surgery.

Background And Objective: Optical density of normal and pathological hyaline cartilage, meniscus, and synovium is determined using native and laser-irradiated tissue samples in order to examine potentials for a selective laser ablation.

Study Design/materials And Methods: One hundred forty-four autopsy specimens were irradiated in a direct contact mode using a XeCl excimer laser (lambda = 308 nm; 20 ns; 40 Hz; 40 +/- 2.1 J/mm2; 800 microns fused silica fiber) and a continuous-wave Nd:YAG laser (lambda = 1,064 nm; 1 s; 124 +/- 5.