Juergen Beuthan

Two- and three-dimensional optical tomography of finger joints for diagnostics of rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common diseases of human joints. This progressive disease is characterized by an inflammation process that originates in the inner membrane (synovalis) of the capsule and spreads to other parts of the joint. In early stages the synovalis thickness and the permeability of this membrane changes. This leads to changes in the optical parameters of the synovalis and the synovial fluid (synovia), which occupies the space between the bones. The synovia changes from a clear yellowish fluid to a turbid grayish substance. In this work we present 2 and 3-dimensional reconstruction schemes for optical tomography of the finger joints. Our reconstruction algorithm is based on the diffusion approximation and employs adjoint differentiation techniques for the gradient calculation of the objective function with respect to the spatial distribution of optical properties. In this way, the spatial distribution of optical properties within the joints is reconstructed with high efficiency and precision. Volume information concerning the synovial space and the capsula are provided. Furthermore, it is shown that small changes of the scattering coefficients can be monitored. Therefore, optical tomography has the potential of becoming a useful tool for the early diagnosis and monitoring of disease progression in RA.

Diagnosis of inflammatory rheumatic diseases with photon density waves

Rheumatoid arthritis (RA) is a common inflammatory disease of interphalangeal joints. The utilization of conventional imaging systems (e.g. x-rays) for non invasive diagnostics at an early stage of the disease is difficult, since pathologically induced changes do not occur at this stage in hard tissue. Use of MR and ultrasound methods are both methodically problematic and expensive. Therefore investigations for optical diagnostics using photon density waves (PDW) were carried out. The PDW was realized with an intensity modulated laser diode (825 nm, fmod: 110 MHz) and an ac- and phase detection in a 2D transillumination scanner. Measurements of optical properties of synovia and synovialis of healthy and early RA stages were performed and indicated a significant pathological increase of (mu) s. The detected PDW-pictures provided corresponding results. Further investigations regarding the object- variation of the modulation transfer function provide a sufficient spatial resolution in order to assign functional changes to anatomical structures. The results are presented using photos.

RA diagnostics applying optical tomography in frequency domain

Our aim is to reconstruct the optical parameters in a slice of a finger joint phantom for further investigations about rheumatoid arthritis (RA). Therefore, we have developed a flexible NIR scanning system in order to collect amplitude and phase delay of photon density waves in frequency-domain. A cylindrical finger joint phantom was embedded in a container of Intralipid solution due to the application of an inverse method for infinite geometry. The joint phantom was investigated by a laser beam obtaining several projections. The average optical parameters of each projection was calculated. Using different reconstruction techniques, e.g. ART and SIRT with a special projection operator, we reconstructed the optical parameters in a slice. The projection operator can be heuristically described by a photon path density function of a homogeneous media with infinite geometry. Applied to an object with an unknown distribution of optical parameters it calculates the expectation value of the investigated object. The potentials and limits of these fast reconstruction methods will be presented.

Fiber design for interstitial laser treatment

The interstitial laser tumor treatment and the local coagulation of malignant tumors with Nd:YAG laser radiation are approved procedures in minimal invasive medicine. The hyperthermic effects in tissue cause irreversible tissue damage. An advanced but simple disposable plastic introducer has been developed which is designed for volume coagulation by inserting a frosted bare fiber. If the desired size of the coagulation is reached, an alert signal to stop the treatment is derived from an on-line monitoring of NADH concentration by laser induced fluorescence measurements.

Investigations concerning the determination of NADH concentrations using optical biopsy

The intrinsic NADH autofluorescence intensity of biological tissue depends on the local, cellular concentration of this coenzyme. It plays a dominant role in the Krebs-Cycle and therefore serves as indicator for the vitality of the observed cells. Due to individually and locally varying boundary conditions and optical tissue properties, which are scattering coefficients, absorption coefficients and g-factors the fluorescence signal needs to be rescaled. One possible rescaling method is the theoretical derived Photon Migration Theory. Our new rescaling method is partly based on measurements and partly theoretical derived. By using the 4 information channels: LIF time-resolved signal, biochemical concentration measurements, Monte Carlo simulations with optical parameters and microscopic investigations we demonstrate that simultaneous detection of the fluorescence and the backscattering signal can easily and accurately provide rescaled, quantitative values for the NADH concentrations.

In-vivo investigations on the detection of chronical polyarthritis (c.P.) using a cw-transillumination method at interphalangeal joints

This paper presents first results of an in-vivo-experimental study on the detection of pathological changes of chronical polyarthritis (c.P.) performed by a near infrared cw- transillumination method in interphalangeal joints. The inflammation of a joint system when caused by c.P. leads to changes in the synovial membrane, synovia composition and content, and anatomic geometrical variations. Measurements have shown that these rheumatic induced inflammation processes result in a variation in optical properties ((mu) a, (mu) s, g) of the joint system. Using a scanning system the interphalangeal joint is transilluminated with diode lasers (788 nm, 831 nm) perpendicular to the articular cavity in order to use the entire distribution of the transmitted radiation intensity for diagnostic purposes. The study includes results of in-vivo-measurements on healthy and c.P. patients and the evaluation of different distribution properties for detection of chronical polyarthritis.

Development of an application set for intraoperative and percutaneous laser-induced interstitial thermotherapy (LITT)

A variable application-set was developed to enable a safe and effective LITT treatment. The set consists of various laser applicators, a protecting catheter and an introducing equipment. The laser applicator was developed with different radiation patterns to match the topological conditions of the diseased area. For MRI-controlled LITT treatments a special marker is mounted at the distal end of the glass fiber which facilitates its localization. To increase the patients safety a special protecting catheter was designed which is temperature stable up to 250 degree(s)C and transparent for NIR-radiation. The catheter can be placed into the diseased area using the introducing equipment which consists of modified parts of standard interventional radiology equipment. The laser applicator is finally guided through the protecting catheter so that there is no direct contact between applicator and tissue. The system can be used both for intraoperative and for percutaneous treatments.

Infrared diaphanoscopy in medicine

This paper will deal with a band-limited cw-transillumination and illustrates that the differences between scattering distributions of tissues determines the functional status of body parts and thus enables an adequate diagnosis with a minimal technical expenditure.

Mathematical model of heat transfer in tissue compared with results from thermography, MRI and laser fluorescence spectroscopy

The use of laser radiation of 1064 nm (Nd:YAG laser) in interstitial laser therapy is coming of age. It is important to realize that the irradiation of tissue contributes to optical changes of the tissue. Consequently, the coefficients of the heat transfer function and the thermodynamic description of the energy balance budget in tissue are not constant. Regarding laser-induced regional hyperthermia non-linear behavior is observed. The heat transfer is estimated to be at multi parameter process. As a first result, a mathematical model is being introduced. The parameters of the model are derived from thermal and spectroscopic in vitro- and in vivo- measurements. Experimental findings of MRI and LIF correspond with the hyperthermal process of the mathematical model.

Evaluation of scattered light distributions of cw-transillumination for functional diagnostic of rheumatic disorders in interphalangeal joints

This paper presents in-vitro-studies using the scattered intensity distribution obtained by cw- transillumination to examine the condition of rheumatic disorders of interphalangeal joints. Inflammation of joints, due to rheumatic diseases, leads to changes in the synovial membrane, synovia composition and content, and anatomic geometrical variations. Measurements have shown that these rheumatic induced inflammation processes result in a variation in optical properties of joint systems. With a scanning system the interphalangeal joint is transilluminated with diode lasers (670 nm, 905 nm) perpendicular to the joint cavity. The detection of the entire distribution of the transmitted radiation intensity was performed with a CCD camera. As a function of the structure and optical properties of the transilluminated volume we achieved distributions of scattered radiation which show characteristic variations in intensity and shape. Using signal and image processing procedures we evaluated the measured scattered distributions regarding their information weight, shape and scale features. Mathematical methods were used to find classification criteria to determine variations of the joint condition.