Basic Research For Applications Of Digital Holography In Biomedical Imaging

In terms of diagnostics for human disease and bio-medical research, biomedical imaginghas become a widely used method. The traditional imaging instrument is optical microscope. Themicrobody which is invisible to the naked eyes can be imaged by the microscope. However, theconventional microscopes can not meet the development trend of the scientific research, becauseonly the intensity of the light can be detected to obtain its distribution of two-dimensional imagesinstead of3-D images by the traditional optical microscope. Therefore, for the active demand oflife sciences research, it is necessary to grope for a novel imaging technique that can achievereal-time, non-interference and quantitative analysis. In this paper, a basic research forapplications based on digital holography is proposed.The digital holography is based on the classic holographic principle with the differencebeing that the hologram recording is performed by a photoelectric sensor (such as CCD orCMOS camera), and the hologram is transferred to a computer as an array of numbers. In digitalholography, the reconstruction process calling numerical reconstruction is accomplished via acomputer using numerical calculation method to obtain the quantitative intensity image andphase image of the object light simultaneously. Digital holograph has following advantagescomparing with the classic holographic imaging methods: Continuous real-time hologram can berecorded online. The amplitude and phase information of the object can be analysedquantitatively via numerical reconstruction. Image processing methods can be used to therecorded digital holography, which can reduce or remove the influences of the noises and theastigmation in the digital holographic recording process. For these unique advantages, digitalholography has been considered a powerful tool to analyze sample quantitatively and to studyliving organisms. The technology has become a hot international research in recent years.In this dissertation, the recording and reconstruction process of digital holography aredescribed based on the traditional optical holographic principle. A setup of digital holography isbuilded for fundamental experiment study in dynamic organism imaging. The main contentsinclude the following aspects:(1) To solve the problems of the difficult imaging and the bigdisturbance to the imaging object through turbid media, and the problem that the3-D information of the imaging object can not be dynamically obtained, an imaging method for thedynamic objects through turbid media based on digital holography was proposed. The Lightpropagation in turbid media was introduced firstly. For the characteristics of the continuousvariation of the optical field caused by the dynamic objects, the cw laser with longer coherencelength was used as recording source for the holographic recording. A digital filtering technologyis employed to extract the the first order term of the Fourier transform spectrum of theholography. With the method, the holography can be reconstructed, the twin image and thebackground effect of the zero order term can be eliminated and the most of the noise caused bythe diffuse light can be weakened. With digital auto-focus technology, the problem that the objectcannot be directly focused through turbid media is solved. Combining spatial filtering technique,the effect of the diffuse noise can be further eliminated. The dynamic imagings for living lifesthrough turbid media based on digital holography has successfully achieved by the experiment.The imaging method is expected to be used in dynamics imagings for living lifes through turbidmedia.(2) To solve the problems of high-throughput analysis of biological chip by the surfacePlasmon resonance imaging (SPRI), a study for high-throughput analysis of biological chip usingthe surface plasmon resonance imaging based on digital holography was carried out. To realizehigh-throughput analysis, it must solve the problems of the narrow detection range inbiochemical analysis. In this dissertation, a new surface plasmon resonance imaging technologywith simultaneous amplitude-contrast and phase-contrast is proposed. With the intensity and thephase information, the detection range can be broadened and the numbers of analyzes throughputcan be improved. A theoretical model is established to characterize the biomolecular interactionsby using simultaneously amplitude and phase information. A sigle wavelength experimentsystem of SPRI is builded to obtain simultaneously amplitude and phase images. Theexperiments have demonstrated the feasibility of this technology. The method is expected to usein the high-throughput analysis by the surface plasmon resonance imaging.(3) Water is the maincomponent of a variety of life forms. The liquid lies in all organisms. It is conducive to explorevarious life processes associated with the liquid to understand the various properties of the liquid.In this paper, a study of dynamic imaging for a small water droplet and a saline water droplet inthe evaporation process is carried out by use of digital holography. The technology is expected tobe applied in the aspects of moisting research on a variety of biological surface and the evaporation mechanism.(4) The detection range can be broadened by use of dual-wavelengthmultiplexing digital holography. In this paper, a simple experiment setup of dual-wavelengthdigital holography based on the principle of the dispersiveprism was improved. The phase of theUSAF1951resolution target corresponding to a single wavelength can be isolated successfullyby demultiplexing digital reconstruction method of dual-wavelength digital holography. Thefeasibility of the improved experimental setup has been validated successfully. The experimentaldevice provides technical support for application of the dual wavelength-multiplexed digitalholography in biomedical imaging.