Measurement of morphology thickness and refractive index in a melanoma A375 cell line using digital holographic microscopy.

Digital holographic microscopy (DHM) is a technique that has high potential for analyzing biological samples and has been successfully applied to the study of cells and cell lines providing information about important parameters such as refractive index, morphology, and dry mass, among others; it has also found applicability to study the effects of therapeutic treatments. Finding the size and shape of cells is important since they tend to change in the presence of some pathologies. In this research work, we obtain the morphology thickness and refractive index of the A375 melanoma cell line through a slight tilting of the cell in a DHM setup. Further, the development of a novel mathematical expression based on this tilt and in the optical phase difference is presented. We show images of melanoma cells with the refractive index information included, and their morphology thickness as rendered from the holographic phase maps recorded with DHM.

Motion of the surface of the human tympanic membrane measured with stroboscopic holography.

Sound-induced motion of the surface of the human tympanic membrane (TM) was studied by stroboscopic holographic interferometery, which measures the amplitude and phase of the displacement at each of about 40,000 points on the surface of the TM. Measurements were made with tonal stimuli of 0.5, 1, 4 and 8 kHz. The magnitude and phase of the sinusoidal displacement of the TM at each driven frequency were derived from the fundamental Fourier component of the raw displacement data computed from stroboscopic holograms of the TM recorded at eight stimulus phases. The correlation between the Fourier estimates and measured motion data was generally above 0.9 over the entire TM surface. We used three data presentations: (i) plots of the phasic displacements along a single chord across the surface of the TM, (ii) phasic surface maps of the displacement of the entire TM surface, and (iii) plots of the Fourier derived amplitude and phase-angle of the surface displacement along four diameter lines that define and bisect each of the four quadrants of the TM. These displays led to some common conclusions: at 0.5 and 1kHz, the entire TM moved roughly in-phase with some small phase delay apparent between local areas of maximal displacement in the posterior half of the TM. At 4 and 8 kHz, the motion of the TM became more complicated with multiple local displacement maxima arranged in rings around the manubrium. The displacements at most of these maxima were roughly in-phase, while some moved out-of-phase. Superposed on this in- and out-of-phase behavior were significant cyclic variations in-phase with location of less than 0.2 cycles or occasionally rapid half-cycle step-like changes in-phase. The high frequency displacement amplitude and phase maps discovered in this study can not be explained by any single wave motion, but are consistent with a combination of low and higher order modal motions plus some small traveling-wave-like components. The observations of the dynamics of TM surface motion from this study will help us better understand the sound-receiving function of the TM and how it couples sound to the ossicular chain and inner ear.

Finding the position of tumor inhomogeneities in a gel-like model of a human breast using 3-D pulsed digital holography.

3-D pulsed digital holography is a noninvasive optical method used to measure the depth position of breast tumor tissue immersed in a semisolid gel model. A master gel without inhomogeneities is set to resonate at an 810 Hz frequency; then, an identically prepared gel with an inhomogeneity is interrogated with the same resonant frequency in the original setup. Comparatively, and using only an out-of-plane sensitive setup, gel surface displacement can be measured, evidencing an internal inhomogeneity. However, the depth position cannot be measured accurately, since the out-of-plane component has the contribution of in-plane surface displacements. With the information gathered, three sensitivity vectors can be obtained to separate contributions from x, y, and z vibration displacement components, individual displacement maps for the three orthogonal axes can be built, and the inhomogeneity's depth position can be accurately measured. Then, the displacement normal to the gel surface is used to find the depth profile and its cross section. Results from the optical data obtained are compared and correlated to the inhomogeneity's physically measured position. Depth position is found with an error smaller than 1%. The inhomogeneity and its position within the gel can be accurately found, making the method a promising noninvasive alternative to study mammary tumors.

Detection of biological tissue in gels using pulsed digital holography.

An out of plane optical sensitive configuration for pulsed digital holography was used to detect biological tissue inside solid organic materials like gels. A loud speaker and a shaker were employed to produce a mechanical wave that propagates through the gel in such a way that it generates vibrational resonant modes and transient events on the gel surface. Gel surface micro displacements were observed between the firing of two laser pulses, both for a steady resonant mode and for different times during the transient event. The biological tissue sample inserted approximately 2 cm inside the gel diffracts the original mechanical wave and changes the resonant mode pattern or the transient wave on the gel surface. This fact is used to quantitatively measure the gel surface micro displacement. Comparison of phase unwrapped patterns, with and without tissue inside the gel, allows the rapid identification of the existence of tissue inside the gel. The results for the resonant and transient conditions show that the method may be reliably used to study, compare and distinguish data from inside homogeneous and in-homogeneous solid organic materials.