Photoplethysmographic imaging and analysis of pulsatile pressure wave in palmar artery at 10 wavelengths.

Significance: As a noncontact method, imaging photoplethysmography (iPPG) may provide a powerful tool to measure pulsatile pressure wave (PPW) in superficial arteries and extract biomarkers for monitoring of artery wall stiffness. Aim: We intend to develop a approach for extraction of the very weak cardiac component from iPPG data by identifying locations of strong PPW signals with optimized illumination wavelength and determining pulse wave velocity (PWV). Approach: Monochromatic in vivo iPPG datasets have been acquired from left hands to investigate various algorithms for retrieval of PPW signals, distribution maps and waveforms, and their dependence on arterial location and wavelength. Results: A robust algorithm of pixelated independent component analysis (pICA) has been developed and combined with spatiotemporal filtering to retrieve PPW signals. Spatial distributions of PPW signals have been mapped in 10 wavelength bands from 445 to 940 nm and waveforms were analyzed at multiple locations near the palmar artery tree. At the wavelength of 850 nm selected for timing analysis, we determined PWV values from 12 healthy volunteers in a range of 0.5 to 5.8 m/s across the hand region from wrist to midpalm and fingertip. Conclusions: These results demonstrate the potentials of the iPPG method based on pICA algorithm for translation into a monitoring tool to characterize wall stiffness of superficial artery by rapid and noncontact measurement of PWV and other biomarkers within 10 s.

Resolving power of diffraction imaging with an objective: a numerical study.

Diffraction imaging in the far-field can detect 3D morphological features of an object for its coherent nature. We describe methods for accurate calculation and analysis of diffraction images of scatterers of single and double spheres by an imaging unit based on microscope objective at non-conjugate positions. A quantitative study of the calculated diffraction imaging in spectral domain has been performed to assess the resolving power of diffraction imaging. It has been shown numerically that with coherent illumination of 532 nm in wavelength the imaging unit can resolve single spheres of 2 µm or larger in diameters and double spheres separated by less than 300 nm between their centers.

Comparison study of distinguishing cancerous and normal prostate epithelial cells by confocal and polarization diffraction imaging.

Accurate classification of malignant cells from benign ones can significantly enhance cancer diagnosis and prognosis by detection of circulating tumor cells (CTCs). We have investigated two approaches of quantitative morphology and polarization diffraction imaging on two prostate cell types to evaluate their feasibility as single-cell assay methods toward CTC detection after cell enrichment. The two cell types have been measured by a confocal imaging method to obtain their three-dimensional morphology parameters and by a polarization diffraction imaging flow cytometry (p-DIFC) method to obtain image texture parameters. The support vector machine algorithm was applied to examine the accuracy of cell classification with the morphology and diffraction image parameters. Despite larger mean values of cell and nuclear sizes of the cancerous prostate cells than the normal ones, it has been shown that the morphologic parameters cannot serve as effective classifiers. In contrast, accurate classification of the two prostate cell types can be achieved with high classification accuracies on measured data acquired separately in three measurements. These results provide strong evidence that the p-DIFC method has the potential to yield morphology-related "fingerprints" for accurate and label-free classification of the two prostate cell types.

Bulk optical parameters of porcine skin dermis at eight wavelengths from 325 to 1557 nm.

We introduce a method with which to obtain accurately the bulk optical parameters of fresh biological tissues in vitro by combining measurements of the sample surface profiles, reflectance, and transmittances with Monte Carlo-based inverse calculations. The bulk optical parameters of fresh porcine dermis tissue were determined at eight wavelengths from 325 to 1557 nm and were found to be much different from those determined without consideration of surface roughness.

Effect of surface roughness on determination of bulk tissue optical parameters.

Monte Carlo simulations have been conducted to investigate the effect of surface roughness on the inverse determination of bulk optical parameters. Results show that mus, mua, and g can be overestimated by an order of magnitude for thin slab tissue samples with a moderate index mismatch at the interfaces if typical surface roughness is neglected. Measurements of Intralipid samples between glass windows with smooth and rough surfaces have been carried out and agreement was found between the numerical and the experimental data. This study suggests that the surface roughness should be taken into account for both in vitro and in vivo determination of bulk tissue optical parameters.