Vladimir Blazek

Chirp Optical Coherence Tomography of Layered Scattering Media

A new noninvasive technique that reveals cross sectional images of scattering media is presented. It is based on a continuous wave frequency modulated radar, but uses a tunable laser in the near infrared. As the full width at half maximum resolution of 16 μm is demonstrated with an external cavity laser, the chirp optical coherence tomography becomes an alternative to conventional short coherence tomography with the advantage of a simplified optical setup. The analysis of two-layer solid phantoms shows that the backscattered light gets stronger with decreasing anisotropic factor and increasing scattering coefficient, as predicted by Monte Carlo simulations. By introducing a two-phase chirp sequence, the combination of lateral resolved perfusion and depth resolved structure is shown.

Photoplethysmography imaging: a new noninvasive and noncontact method for mapping of the dermal perfusion changes

This paper presents the experimental setup and preliminary results of a CCD based Photoplethysmographic Imager (PPGI) which has been shown to be capable to assess various disorders of the peripheral venous system by standard test methods derived from the classical photophethysmographic practice in a noninvasive and non-contact way. The PPGI is a computer- based CCD imaging system to visualize the skin vessels and analyze the local changes of dermal blood volume. Our results show that this system performs as well as the currently available commercial PPG system by adding information of spatial distribution which allows the investigation of locations and causes of vascular disorders. Both the venous hemodynamics and arterial perfusion can be mapped in two dimensions.

Near-infrared CCD imaging : Possibilities for noninvasive and contactless 2D mapping of dermal venous hemodynamics

This paper presents the experimental setup and first results of a near infrared CCD based Photoplethysmographic Imager (PPGI) which has been shown to be suitable for contactless assessing various disorders of the peripheral venous system by standard test methods derived from the classical photoplethysmographic practice. The PPGI is a computer-based CCD near-infrared imaging system to visualize the skin vessels and analyze the local changes in dermal blood volume. Our current results show that this system performs as well as the available commercial PPG system by adding information of spatial distribution which allows the investigation of locations and causes of vascular disorders.

High-resolution imaging with advanced chirp optical coherence tomography

Chirp optical coherence tomography (Chirp OCT) has been introduced as an alternative solution for imaging scattering media or biotissues. The basic principle of Chirp OCT is well-known by the FMCW radar technique and is adapted to the optical regime. This method uses a frequency modulated laser source in the near IR frequency range. Fast imaging can be performed by an electrical tuned diode laser without the disadvantage of any mechanical moved elements but retaining the properties of optical tomographic tools for contact less, non-ionizing, non-invasive and high depth resolved scanning. The demand of high resolution imaging for media application requires a large frequency tuning range. Covering the whole lasing bandwidth of an external cavity laser by the frequency Chirp, non-linear terms as well as mode-hopping reduce the depth resolution and the dynamic range, if equidistant sampling in the time domain is performed. To restore the resolution given by the Chirp bandwidth a reference detector has been implemented, which allows the detection of mode-hopping quantitatively and the correction of the non-linearity. The reference detector can be used for real-time laser frequency measurements and offers the possibility to determine the location of discrete reflectors more accurate. Images with a high dynamic range demonstrate an increased penetration depth.

Modeling and visualization of photon migration in tissue by Monte Carlo simulation

A Monte Carlo simulation program with graphic user interface has been developed under Windows environment by Visual C++. The parameters of media and certain type of source-detector geometry can be set flexibly for different simulation conditions and purposes. Through graphical user interface, Monte Carlo modeling of photon migration process in tissue is displayed during simulation. Also the computation results can be visualized directly after simulation. The aims of work is to develop an integrated Monte Carlo Simulation environment which makes the computation of the complex process of photon-tissue interaction more intuitive and understandable.

Investigations on the influence of breathing on brain activity using optical sensors

In recent years investigation and understanding of the brain activity is receiving much attention. Such investigations are generally confined to few select premier research institutions where expensive and sophisticated facilities like EEG, PET, FMRI, etc. are available. Of late optical sensors are receiving much attention for biomedical applications because they are relatively simple in construction, easy to use and comparatively inexpensive. Among the biomedical optical sensors, photophlethysmographic (PPG) measuring systems have a unique position. They function as transcutaneous registration of blood volume changes in the near skin blood vessels. By recording the signals from the supply to the left and right lobes of the brain in the cerebral cortex. The oxygen content in the arterary blood flow to the brain will naturally have an important role to play in the activity of the brain. It is suggested that by positioning sensitive temperature sensors in the nostrils of a subject, one could monitor his breathing activity. By recording the outputs rom these temperature sensor for several hours, it has been noticed that the breathing activity of a subject will change from one nostril to another periodically. Besides, it has also been observed that any sudden fluctuations in the breathing pattern is accompanied by changes in the blood flow to the brain as monitored by PPG optical sensors mounted on the temples of a subject. An attempt is made to understand such events.