Mariana C. Potcoava

Optical tomography for biomedical applications by digital interference holography

We present results of imaging experiments using digital interference holography (DIH). Calibration experiments using a resolution target demonstrate an improvement of signal-to-noise ratio (SNR) with increasing number of holograms consistent with theoretical prediction. Imaging experiments on retinal tissue reveal the topography of blood vessels as well as the optical thickness profile of the retinal layer. The SNR of tissue images is comparable to that of the resolution target, implying that the imaging system is operating close to theoretical optimum.

Fingerprint biometry applications of digital holography and low-coherence interferography

We use several holographic and interferographic methods for two- and three-dimensional imaging of fingerprints. Holographic phase microscopy is used to produce images of thin-film patterns left by latent fingerprints. Two or more holographic phase images with different wavelengths are combined for optical phase unwrapping of images of thicker patent prints or a plastic print. Digital interference holography uses scanned wavelengths to synthesize short-coherence interference tomographic images of a plastic print. We also demonstrate light-emitting-diode-based low-coherence interferography for imaging plastic as well as latent prints. These demonstrations point to significant contributions to biometry by the emerging technology of digital holography and interferography.

In vitro imaging of ophthalmic tissue by digital interference holography

We used digital interference holography (DIH) for in vitro imaging of human optic nerve head and retina. Samples of peripheral retina, macula, and optic nerve head from two formaldehyde-preserved human eyes were dissected and mounted onto slides. Holograms were captured by a monochrome CCD camera (Sony XC-ST50, with 780 × 640 pixels and pixel size of ∼9 µm). Light source was a solid-state pumped dye laser with tunable wavelength range of 560–605 nm. Using about 50 wavelengths in this band, holograms were obtained and numerically reconstructed using custom software based on NI LabView. Tomographic images were produced by superposition of holograms. Holograms of all tissue samples were obtained with a signal-to-noise ratio of approximately 50 dB. Optic nerve head characteristics (shape, diameter, cup depth, and cup width) were quantified with a few micron resolution (4.06–4.8 µm). Multiple layers were distinguishable in cross-sectional images of the macula. To our knowledge, this is the first report of DIH use to image human macular and optic nerve tissue. DIH has the potential to become a useful tool for researchers and clinicians in the diagnosis and treatment of many ocular diseases, including glaucoma and a variety of macular diseases.

Three-Dimensional Tracking of Optically Trapped Particles by Digital Gabor Holography

A new technique for 3-D position detection of optically trapped particle by digital Gabor holography is demonstrated with accuracy of ~100 nm. The particle complex optical field is reconstructed via the angular spectrum method.

Fingerprint scanner using digital interference holography

We present three-dimensional imaging of artificial fingerprints using the Digital Interference Holography (DIH) scanner. DIH is based on a multiwavelength optical sensing technique that can be used to build holographically the three dimensional structure of the fingerprints. Many holograms (~50) were acquired by a CCD camera by scanning a range of wavelengths. Each hologram was numerically reconstructed and then superposed yielding tomographic images which represented the artificial fingerprint structure. The axial resolution is a parameter that depends on the wavelength scanning range and is about 5 μm. The light source was a solid state pumped dye laser with a tunable wavelength range of 550 nm to 600 nm. Holograms were captured by a monochrome CCD camera (Sony XC-ST50, with 780 × 640 pixels and a pixel size of ~ 9 μm). An image acquisition board (NI IMAQ PCI-1407) digitized the image with 8 bit resolution. All software was developed in house with the NI LabView. We used a Michelson interferometer in a backscattering geometry and the reconstruction of the optical field was done using the angular spectrum algorithm. Our goal is to identify and quantify, Level 1 (pattern), Level 2 (minutia points), and Level 3 (ridge contours) features from the amplitude images, using the DIH technique and fingerprints recognition. The results could be used in the two fingerprint matching phases, identification and verification.

Wavelength scanning digital interference holography for high-resolution ophthalmic imaging

An improved digital interference holography (DIH) technique suitable for fundus images is proposed. This technique incorporates a dispersion compensation algorithm to compensate for the unknown axial length of the eye. Using this instrument we acquired successfully tomographic fundus images in human eye with narrow axial resolution less than 5μm. The optic nerve head together with the surrounding retinal vasculature were constructed. We were able to quantify a depth of 84μm between the retinal fiber and the retinal pigmented epithelium layers. DIH provides high resolution 3D information which could potentially aid in guiding glaucoma diagnosis and treatment.

3-D Representation of Retinal Blood Vessels through Digital Interference Holography

This paper presents a 3D amplitude model of a pig retina sample with micron-scale resolution using Digital Interference Holography. We concentrate on the retinal vessels visualization and the retinal vessels width estimation.