Objective: Develop a representative calcium target model to evaluate penetration of calcified plaque lesions during
atherectomy procedures using 308 nm Excimer laser ablation.
Materials and Methods: An in-vitro model representing human calcified plaque was analyzed using Plaster-of-Paris and
cement based composite materials as well as a fibrinogen model. The materials were tested for mechanical consistency.
The most likely candidate(s) resulting from initial mechanical and chemical screening was submitted for ablation testing.
The penetration rate of specific multi-fiber catheter designs and a single fiber probe was obtained and compared to that
in human cadaver calcified plaque. The effects of lasing parameters and catheter tip design on penetration speed in a
representative calcified model were verified against the results in human cadaver specimens.
Results: In Plaster of Paris, the best penetration was obtained using the single fiber tip configuration operating at 100
Fluence, 120 Hz. Calcified human lesions are twice as hard, twice as elastic as and much more complex than Plaster of
Paris. Penetration of human calcified specimens was highly inconsistent and varied significantly from specimen to
specimen and within individual specimens.
Conclusions: Although Plaster of Paris demonstrated predictable increases in penetration with higher energy density and
repetition rate, it can not be considered a totally representative laser ablation model for calcified lesions. This is in part
due to the more heterogeneous nature and higher density composition of cadaver intravascular human calcified
occlusions. Further testing will require a more representative model of human calcified lesions.
Periodontal disease is a term used to describe an inflammatory disease affecting the tissues surrounding and supporting the teeth. Periodontal diseases are some of the most common chronic disorders, which affect humans in all parts of the world. Treatment usually involves the removal of plaque and calculus by scaling and polishing the tooth. In some cases a surgical reduction of hyperplastic tissue, may also be required. In addition, periodontitis is a risk factor for systemic disorders such as cardiovascular disease and diabetes. Current detection methods are qualitative, inaccurate, and often do not detect the periodontal disease in its early, reversible stages. Therefore, an early detection method should be implemented identifying the relationship of periodontal disease with erythema. In order to achieve this purpose we are developing an optical erythema meter to diagnose the periodontal disease in its reversible, gingival stage. The discrimination between healthy and diseased gum tissue was made by using the reflection of two illuminating wavelengths provided by light emitting diodes operating at wavelengths that target the absorption and reflection spectra of the highlights of each particular tissue type (healthy or diseased, and what kind of disease). Three different color gels could successfully be distinguished with a statistical significance of P < 0.05.
When irradiating particular biological media in general there will be a range of optical properties to deal with, with respect to the irradiating wavelength, and the respective tissues that make up the organ under treatment or being imaged. In addition to this we saw changing optical properties under influence of denaturization, dehydration and carbonization. We also observed optical nonlinearities that are irradiance dependent, in addition to the birefringence which affects the light distribution throughout the tissue differently than the polarization birefringence used in optical polarization microscopy. In the treatment of ventricular tachycardia with laser photocoagulation the success of the procedure depends on whether sufficient energy has been directed to the relevant region of the myocardium to ablate the entire arrhythmogenic focus. A new high power diode laser operating in the near infrared was used in an animal infarct model and in human arrhythmia ablation. The light distribution measured for Chagasic heart tissues at the diode laser wavelength demonstrated the key potential to create controlled deep photocoagulation lesions. From our observations we may conclude that the diode laser - catheter combination offers significant potential for the elimination of arrhythmia's resulting from Chagas disease.
Medical therapeutic applications using lasers involves understanding the
light tissue interaction, in particular the rate ofphotochemical and thermal
reactions. Tissue is composed ofa mix ofturbid media. Light propagation in
turbid media can be described by the so-called Equation of Radiative Transfer, an
integro-differential equation where scattering, absorption and internal reflection
are significant factors in determining the light distribution in tissue. The Equation
of Radiative Transfer however can not commonly be solved analytically.'
In order to visualize and simulate the effects of laser light on heart
tissues (myocardium) in relation to the treatment of irregular heart rates or so
called arrhythmias, a fast interactive computer program has been developed in
Java.
The effect of anomalous optical behavior of biological tissue at high-intensity laser irradiation can be caused by heat- induced changes in optical properties of consisting components, mainly muscle tissue and blood. We registered the spectral transmission of fresh human whole blood and serum samples in the wavelength range of 300 - 700 nm at the heating of samples in the temperature range of 35 - 65 degrees Celsius. The results showed an increase of 10 - 15% in the transmission of blood serum at the temperature rising up to 50 - 60 degrees Celsius. In the case of diluted whole blood a sharply enhanced transmission was observed at the temperature of 56 - 60 degrees Celsius, while further heating resulted in a decreased transmission down to the initial level. The significant changes (of a three orders of magnitude) in the transmission of whole blood at the wavelength of Nd:YAG laser (1064 nm) were observed. The obtained results can be considered as one of the possible explanations of the anomalous light distribution in certain tissues.
In medical experimental and clinical treatment modalities of light, laser photocoagulation of ventricular tachycardia amongst others, the success of the application relies on whether or not the procedure operates in the optical window of the light-tissue interaction. The optical window of biological tissues can be determined by spectral scans of the optical properties. Optical anomalies may result from the irradiance, the wavelength, or from the tissue composition itself. The transmission of cw Nd:YAG laser light on myocardial tissue showed a nonlinearity in the transmission curve at approximately 3 kW/mm2 irradiance. The total attenuation coefficient dropped sharp from 1.03 plus or minus 0.04 mm-1 to 0.73 plus or minus 0.05 mm-1 at this point in the curve. On the other hand, aneurysm tissue has a highly organized fiber structure, which serves as light-guides, since the transmission of light along the length of the collagen fibers is approximately 50% higher than the transmission perpendicular to the fiber orientation. In addition, changes in optical properties due to tissue phase changes also influence the penetration depth. These phenomena can be utilized to manipulate the optical penetration to an advantage.
A broadband interferometer is used to acquire scattered light as a function of depth in biological media. The `tissue-light-signature' that is obtained by this depth scan can be correlated with the computer simulated light distributions for well defined tissue parameters, and wavelengths of specific interest. In theory, the collimated irradiation of heart tissue, by low coherence light will generate a statistically significant different light signature for respective myocardial tissues, and pathological tissue conditions. Interferometric axial scanning of in vitro myocardial tissues confirmed the statistically significant difference between normal, coagulated myocardium, and aneurysm at the 790 nm wavelength. The scanning depth however is presented limited by the intensity of the illumination and the choice of detection scheme. Identification of the local optical characteristics as a function of depth directly underneath the target zone will provide discrimination between healthy and pathological conditions in addition to real time assessment of laser dosimetry. Theoretically the scanning depth is limited to a maximum of 4 mm. The beam profile of the irradiation source significantly affects the ability to distinguish between certain tissues. Broadband interferometric axial tissue scanning, will provide a tool for an accurate light energy delivery guided by the desired outcome, while being able to verify the appropriate target location, in real time.
Although non-invasive methods for in-situ analysis of laser-tissue interaction are not available yet, it continues to be an area of increased interest owing to its potential. This paper describes the development of an integrated diagnostic and therapeutic laser procedure through in-situ monitoring of the optical tissue characteristics in a non-invasive manner. Biological tissues are highly scattering media. The system under development uses a broadband (white-light) interferometer that derives the scattered signals obtained from different depths of the biological medium. The tissue light signature obtained in this manner will be curve fitted to the appropriate computer simulation resulting from the optical properties particular to well defined tissues, resulting from simulations within a range of optical parameters. The beam profile of the irradiation source appears to affect the ability to distinguish between certain tissues. A single mode fiber in tissue contact produces a statistically significant different light signature for at least three myocardial tissues. However, the theoretical resolution is limited to 4 to 8 mm depth. Identification of the local optical characteristics will provide discrimination between healthy and pathological conditions in addition to real time assessment of dosimetry.
A Ti:Sapphire CW laser operating at room temperature provides an output power of 6.7 W, limited by available pump power. A Z-configuration oscillator (LEXEL laser) was modified to operate in dual pump mode. The Ti:Sapphire laser was pumped by two independent 13 watt CW Ar-ion lasers. The two Ar-ion lasers were focussed on each end of the Ti:Sapphire crystal. The Ti:Sapphire laser covers the visible red to the near infrared regime (690-1100 nm) with four sets of mirrors. A three plate birefringent filter was used for wavelength tuning, with a 0.5 nm bandwidth. The spectral analysis was performed with a monochromator with a resolution of 0.2 nm. A maximum output of 6.7 Watt was achieved at 790 nm, in TEM00 mode, corresponding to a conversion efficiency of 26%. The Ti:Sapphire was operating below saturation levels at 26 W total pump. Laser output without the birefringent filter resulted in spontaneous mode hopping leading to output wavelength fluctuations between several resonant wavelengths. Double pumping resulted in higher output powers than single pumping with corresponding total input power. The flat tuning curve in combination with the high output powers makes this laser an ideal source for spectral investigations of laser tissue interaction.
Local tissue optical parameters are of principal importance in determining the ideal dosage of laser energy and choosing the most suitable therapeutic wavelength for a specific organ. We have developed a non-invasive method for the determination of optical parameters of whole tissue in-situ. Backscattered laser light from a pencil beam incident on the tissue surface was measured using a CCD camera interfaced with a personal computer. Backscatter measurements were performed on in-vitro canine myocardium and on phantoms, with optical properties predetermined by the integrating sphere method. Backscattering radiance proved to be a function of the distance to the incident beam. Regression analysis of the backscatter showed that the backscatter can be expressed as an exponential function of the distance to the beam with a regression coefficient ((mu) r) resembling the tissue diffusion coefficient ((mu) eff), for tissue thickness much greater than optical free path. The CCD derived backscatter radiance exponent showed excellent agreement with the diffusion coefficient, with a correlation coefficient of 0.91. The backscattering technique might prove to be a simple, non-invasive, accurate new technique in the determination of in-vivo optical properties.
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