Viravuth Prapavat

In vitro studies and computer simulations to assess the use of a diode laser (850 nm) for laser‐induced thermotherapy (LITT)

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.

Effects of continuous-wave laser systems on stapes footplate

The aim of the present study was to clarify which of the presently available continuous‐wave laser systems are best suited for application in stapes surgery.

Effects of pulsed laser systems on stapes footplate.

The aim of the present study was to investigate the tissue ablation capacity of various pulsed lasers at the stapes footplate.

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.

Thermic effects in the "vestibule" during laser stapedotomy with pulsed laser systems.

Apart from the ablation properties at the stapes footplate, the degree of thermic loading in the inner ear is important in determining the suitability of pulsed lasers for stapedotomy. The aim of the study is to compare the thermic effects in the vestibule with different pulsed laser systems.

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.

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.

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.

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.

Phase demodulation imaging of coagulation-necrosis in biological tissue

Laser-induced coagulation in biological tissue leads to a significant change of the reduced scattering coefficient (mu) s. This change can be monitored by phase-demodulation imaging and cw-transillumination techniques in bulk tissue. First results are presented using a 2D optical tomography and a linear scanning system.