To achieve the quantitative optical non-invasive diagnosis of blood during extracorporeal circulation therapies, the
instrumental technique to extract extracellular spectra from whole blood was developed. In the circuit, the continuous
blood flow was generated by a centrifugal blood pump. The oxygen saturation was maintained 100% by an oxygenator.
The developed glass optical flow cell was attached to the outlet tubing of the oxygenator. The halogen lamp including
the light from 400 to 900 nm wavelength was used for the light source. The light was guided into an optical fiber. The
light emitted by the fiber was collimated and emitted to the flow cell flat surface at the incident angle of 45 degrees. The
light just reflected on the boundary between inner surface of the flow cell and plasma at 45 degrees was detected by the
detection fiber. The detected light was analyzed by a spectral photometer. The obtained spectrum from 400 to 600nm
wavelength was not changed with respect to the hematocrit. In contrast, the signal in the spectral range was changed
when the plasma free hemoglobin increased. By using two spectral range, 505±5 nm and 542.5±2.5 nm, the differential
spectrum was correlated with the free hemoglobin at R2=0.99. On the other hand, as for the hematocrit, the differential
spectrum was not correlated at R2=0.01. Finally, the plasma free hemoglobin was quantified with the accuracy of
22±19mg/dL. The result shows that the developed plasma surface reflectance spectroscopy (PSRS) can extract the
plasma spectrum from flowing whole blood.
Optical properties of flowing blood were analyzed using a photon-cell interactive Monte Carlo (pciMC) model with the physical properties of the flowing red blood cells (RBCs) such as cell size, shape, refractive index, distribution, and orientation as the parameters. The scattering of light by flowing blood at the He-Ne laser wavelength of 632.8 nm was significantly affected by the shear rate. The light was scattered more in the direction of flow as the flow rate increased. Therefore, the light intensity transmitted forward in the direction perpendicular to flow axis decreased. The pciMC model can duplicate the changes in the photon propagation due to moving RBCs with various orientations. The resulting RBC's orientation that best simulated the experimental results was with their long axis perpendicular to the direction of blood flow. Moreover, the scattering probability was dependent on the orientation of the RBCs. Finally, the pciMC code was used to predict the hematocrit of flowing blood with accuracy of approximately 1.0 HCT%. The photon-cell interactive Monte Carlo (pciMC) model can provide optical properties of flowing blood and will facilitate the development of the non-invasive monitoring of blood in extra corporeal circulatory systems.
We have sought for non-invasive diagnosis of blood during the extracorporeal circulation support. To achieve the goal,
we have newly developed a photon-cell interactive Monte Carlo (pciMC) model for optical propagation through blood.
The pciMC actually describes the interaction of photons with 3-dimentional biconcave RBCs. The scattering is described
by micro-scopical RBC boundary condition based on geometric optics. By using pciMC, we modeled the RBCs inside
the extracorporeal circuit will be oriented by the blood flow. The RBCs' orientation was defined as their long axis being
directed to the center of the circulation tube. Simultaneously the RBCs were allowed to randomly rotate about the long
axis direction. As a result, as flow rate increased, the orientation rate increased and converged to approximately 22% at
0.5 L/min flow rate and above. And finally, by using this model, the pciMC non-invasively and absolutely predicted Hct
and hemoglobin with the accuracies of 0.84±0.82 [HCT%] and 0.42±0.28 [g/dL] respectively against measurements by
a blood gas analyzer.
A photon-cell interactive Monte Carlo (pciMC) that tracks photon migration in both the extra- and intracellular spaces is developed without using macroscopic scattering phase functions and anisotropy factors, as required for the conventional Monte Carlos (MCs). The interaction of photons at the plasma-cell boundary of randomly oriented 3-D biconcave red blood cells (RBCs) is modeled using the geometric optics. The pciMC incorporates different photon velocities from the extra- to intracellular space, whereas the conventional MC treats RBCs as points in the space with a constant velocity. In comparison to the experiments, the pciMC yielded the mean errors in photon migration time of 9.8±6.8 and 11.2±8.5% for suspensions of small and large RBCs (RBCsmall, RBClarge) averaged over the optically diffusing region from 2000 to 4000 μm, while the conventional random walk Monte Carlo simulation gave statistically higher mean errors of 19.0±5.8 ( p < 0.047) and 21.7±19.1% (p < 0.055), respectively. The gradients of optical density in the diffusing region yielded statistically insignificant differences between the pciMC and experiments with the mean errors between them being 1.4 and 0.9% in RBCsmall and RBClarger, respectively. The pciMC based on the geometric optics can be used to accurately predict photon migration in the optically diffusing, turbid medium.
A photon-cell interactive Monte Carlo ("pciMC") model was developed to quantify the intracellular optical
propagation in a 3-dimensional biconcave red blood cell (RBC) model having a finite volume and intracellular
hemoglobin. The orientation of RBCs with respect to the incident photons was randomized to allow either extra- or
intra-cellular propagation depending on the incident point and angles where the photon propagation at the plasma-cell
interface was determined by the Snell's law and Fresnell's law. In this study, the photon propagation through single RBC
using the pciMC was compared against the Henyey-Greenstein phase function. The absorption dependent intracellular
optical path length was evaluated in comparison to Mie theory. Both results showed good agreement. The pciMC can
contribute to photo-spectroscopy of blood and tissues by quantifying both extra- and intra-cellular optical propagation.
Cardiovascular devices such as heart-lung machine generate un-physiological level of shear stress to damage red blood
cells, leading to hemolysis. The diagnostic techniques of cell damages, however, have not yet been established. In this
study, the time-resolved optical spectroscopy was applied to quantify red blood cell (RBC) damages caused by the
extracorporeal circulation system. Experimentally, the fresh porcine blood was subjected to varying degrees of shear
stress in the rotary blood pump, followed with measurement of the time-resolved transmission characteristics using the
pico-second pulses at 651 nm. The propagated optical energy through the blood specimen was detected using a streak
camera. The data were analyzed in terms of the mean cell volume (MCV) and mean cell hemoglobin concentration
(MCHC) measured separately versus the energy and propagation time of the light pulses. The results showed that as the
circulation time increased, the MCV increased with decrease in MCHC. It was speculated that the older RBCs with
smaller size and fragile membrane properties had been selectively destroyed by the shear stress. The time-resolved
optical spectroscopy is a useful technique in quantifying the RBCs' damages by measuring the energy and propagation
time of the ultra-short light pulses through the blood.
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