Digital in-line holography: influence of the shadow density on particle field

Abstract

We have used a digital in-line holography system with numerical reconstruction for 3D particle field extraction. In this system the diffraction patterns (holograms) are directly recorded on a charge-coupled device (CCD) camera. The numerical reconstruction is based on the wavelet transformation method. A sample volume is reconstructed by computing the wavelet components for different scale parameters. These parameters are related to the axial distance between a particle and the CCD camera. The particle images are identified and localized by analyzing the maximum of the wavelet transform modulus and the equivalent diameter of the particle image. The general process for the 3D particle location and data processing method are presented. As in classical holography we found that the signal to noise ratio depends only on the shadow density. Nevertheless, we show that both the volume depth and the shadow density affect the percentage of extracted particles.

The ePetri dish, an on-chip cell imaging platform based on subpixel perspective sweeping microscopy (SPSM)

“…In the past few years, these sensor chips enabled the development of new microscopy implementations that are significantly more compact and cheaper than traditional microscopy designs. The optofluidic microscope (1)(2)(3) and the digital in-line holographic microscope (4)(5)(6)(7)(8)(9) are two examples of these new developments. Both of these technologies are designed to operate without lenses and, therefore, circumvent their optical limitations, such as aberrations and chromaticity.…”

“…There have been two major types of algorithms that have been reported (10)(11)(12). In both cases, the image quality depends critically on the extent of the target, the scattering property and the signal-to-noise ratio (SNR) of the measurement processes (5,7,8,(13)(14)(15). The method works well for well-isolated targets, such as diluted blood smear slides.…”

“…However, for digital in-line holography, light field in the object domain is complex valued and, therefore, the phase recovery is possible only if the support of the object is sufficiently isolated (i.e., sparsity constrains) (14,15,17,18) or the edges are sharply defined (true boundary) (14,15,18). Furthermore, the interference nature of the technique implies that coherence-based noise sources, such as speckles and cross-interference, would be present and would need to be addressed (7,8,19). While methods for mitigating these have been reported (13,14,20), the generated images are, nevertheless, identifiably different from images acquired with conventional microscopes due to coherence based noise sources.…”

Wavelet-based tracking of bacteria in unreconstructed off-axis holograms

“…Out of focus particles in a hologram are commonly found by matching characteristic light scattering simulations to real data [8] or by segmentation of particles via edge detection in reconstructed planes [9][10][11]. Matching real light scattering via Lorenz-Mie and RayleighSommerfeld scattering approximations provides depth information [6,8,12,13].…”

Influence of virtual images on the signal-to-noise ratio in digital in-line particle holography

“…This estimate is an upper limit based on the fact that it is impossible to get more measurements of particle position than there are measurements of the (complex) scattered field; it did not involve the physical nature of the holographic recording process. In another study numerical simulations were used to show that the SNR depends on the shadow density, a parameter that relates to the number of particles and the particle size [4]. However, the study did not involve the number of pixels, and as such no quantitative relation between SNR, the number of pixels, and the number of particles was found.…”