Previously, we analyzed the classical theory for oxygen saturation in blood. We proposed a novel model to reduce noise
effects, and a methodology based on standard deviation oxygen saturation maps to select the optimal wavelength zones
to improve oximetry measurements. We evaluate the oxygen saturation measurement for different wavelength pairs in
the spectral range from 650 to 1050 nm looking for accurate saturation values. We perform a cross-talk analysis in
hemoglobin absorbance spectra in order to find out the optimum center wavelength for light sources of extended
spectrum like a led. We compare the oxygen saturation results obtained with different peak wavelengths considering the
cross-talk effect between oxy- and deoxy-hemoglobin signals.
We describe a systematic procedure to arrive at the optimal wavelengths for monitoring oxygen delivery to and its
consumption in an organ. On the basis of the signal-to-noise optimization study, we propose several high
performance 2-D wavelength intervals within the therapeutic window. Furthermore, we find that at least one of the
traditional wavelength choices falls near the interval of decreased performance, providing a possible explanation for
the occasional failure of currently used devices.
Pulse oximetry technique is a non invasive method useful to monitor the quantity of oxygen in hemoglobin, used in
medical diagnosis and clinical decision-making. It is based on the ratio between the red and infrared light absorbance
corresponding to the oxygenated (HbO<sub>2</sub>) and non-oxygenated (Hb) state of the hemoglobin. We develop the
mathematical model to obtain the oxygen saturation value observing that it depends on four known parameters: two
transillumination values assessed at the common pulse oximetry wavelengths (λ<sub>1</sub> = 660 nm y λ<sub>2</sub> = 940 nm), and the
extinction coefficients for the oxy- and deoxy-hemoglobin at these given wavelengths.
Analyzing the extinction curves for oxy- and deoxy-hemoglobin we note that at λ equal to 660 nm the HbO<sub>2</sub> component
almost does not contribute to the attenuation of incidance when we transilluminate tissue (7.479x10<sup>-5</sup> cm<sup>-1</sup>M<sup>-1</sup>). In this
case is the Hb component that gives the significant attenuation value (7.863x10<sup>-4</sup> cm<sup>-1</sup>M<sup>-1</sup>). In 940 nm the extinction
coefficient of the Hb is 2.589x10<sup>-5</sup> cm<sup>-1</sup>M<sup>-1</sup> and we can ignore it when we count attenuation. At this λ we assume that the
pulsate component is only affected by the HbO<sub>2</sub> (2.099x10<sup>-4</sup> cm<sup>-1</sup>M<sup>-1</sup>). This analysis of hemoglobin extinction
coefficients in the absorption curves highlights the signal to noise ratio between these two oxygen dependent elements.
We are interested in accentuate the better contrast interval (λ pair), where this signal-to-noise ratio is higher, looking for
more transillumination information and more precise SO<sub>2</sub> value.
We propose to use a transillumination waveform simulator to study the different effects (respiration, artifact body
movement, absorption, low perfusion, etc) presented in complex physiological signals and to know the optical path-integrated
behavior when we transilluminate tissue. This is practical for acquisition and processing transillumination
signals. The present work is the first part of a λ selection method to guaratee the optimum <i>S/N</i> for measurements in blood
using pulse oximetry and spectroscopic techniques at near infrared.
We describe a new method to separate ballistic from the scattered photons in a tissue characterization study. It is
based on the concept that the scattered photons acquire a phase delay whose magnitude depends on the number of
scatterings and the resulting path increment for photons transmitted in the direction of incidence. All other photons are
eliminated with physical apertures in his scanning arrangement. We propose a Mach-Zehnder experimental setup
where the ballistic photons pass through the sample with the delay caused uniquely by the sample indices of refraction,
assuming multiple layers. The method is based on the capability of the photons, passing through the sample without
scattering or absorption to preserve their coherence. With the incorporation of a movable mirror on the piezoelectric
actuator in the reference arm, this method allows measuring only those photons that suffer no phase delay upon
passing through the sample. We present the theory that predicts the feasibility of this method to differentiate between
classes of tissues. The method is feasible for samples with transmission of ballistic photons down to 10<sup>-18</sup>.
We use an IR camera to record and visualize the ignition process in a domestic gas stove during the first second after
the electrical spark has initiated the combustion. The measurement and visualization of the flame growth and
distribution process resulted in an improved design of thermo-mechanical properties and ventilation characteristics of
the ignition chamber. We report recording and the actual visualization of the real-time ignition process, incorporating
frame interpolation and other image processing and subtraction schemes to play back the temporal evolution of the
fire-propagation process at a rate suitable for human inspection and visual processing at about 30 frames per second.
We evaluate the degree of oxygen saturation for several explicit wavelengths in the spectral interval from 650 to 1050
nm (therapeutic window). We analyze the effect of selecting a particular wavelength pair to calculate oxygen saturation
considering the known absorption specific coefficients of oxy- and deoxy-hemoglobin. Also, we design a heart simulator
to determine the most useful wavelength couple for oxygen saturation for all wavelengths in the therapeutic window. We
present a selection map to facilitate wavelength choice. Furthermore, we examine the random noise sensitivity of the
trans-illuminated irradiance. This information will be used to determine accurately the illumination sources for NIR
spectroscopy and oximetry.
We examine the feasibility of applying oximetry for the assessment of the degree of brain activity. Changes in concentration of oxygenated and deoxygenated hemoglobin may be used to determine the activity levels through differential attenuation in red and infrared (IR) spectral lines. We extend the classical mathematical model for oxygen saturation to include multiplicative and additive noises, signal gain, and detector responsivity. We perform temporal correlation between two signals (red and IR) to increase immunity to noise. This is particularly important when we consider dynamic biological processes and that the movement is always present. In the literature the difficulty of movement (differences in optical paths) is resolved with electronic solutions. We improve the effect of time displacement between signals at the level of equations. The considerations of noise in the saturation expression are significant when the signal levels approach zero.