Balasigamani Devaraj

Two-dimensional Imaging of Ultraweak Photon Emission from Germinating Soybean Seedlings with a Highly Sensitive CCD Camera

A novel application of a highly sensitive charge-coupled device (CCD) camera for imaging of spontaneous ultraweak photon emission from living organisms (biophoton emission) is described. The performance of the CCD camera for low-level light imaging is theoretically compared to a conventionally used two-dimensional photon counting tube, and we deduce that in the wavelength region above 700 nm and for measurement periods over 2000 s, the CCD camera is advantageous over the twodimensional photon counting tube. Experimental results on the two-dimensional biophoton imagery of germinating soybean seedlings also suggest that the wide-range spectral sensitivity of the CCD camera is effective for low-level light imaging from living organisms that have a predominant emission spectrum in the red and near-IR wavelength region.

Recent advances in coherent detection imaging (CDI) in biomedicine: laser tomography of human tissues in vivo and in vitro

We review the advantages of the optical heterodyne detection-based coherent detection imaging system, for transillumination laser computed tomography (CT) in biomedicine using CW and single-frequency lasers as light sources. The unique properties of the coherent detection imaging system such as excellent directionality, selectivity, and high sensitivity are exploited to differentiate and detect the minimally deviated on-axis/near-axis photons emerging from a tissue enabling the reconstruction high-resolution laser CT images. Our recent progress on the applications of the coherent detection imaging system to laser CT of human fingers in vivo and calcified tissues in vitro at different wavelengths in the visible and near-infrared regions are described. The laser CT images are obtained with low incident power of a few milliwatts and are comparable to conventional imaging techniques. The internal layers of the imaged tissues could be clearly differentiated and identified with submillimeter resolution. We propose that further refinements in the coherent detection imaging system could lead to a novel and potential diagnostic tool in dentistry, osteology, and bone and joint related diseases and disorders.

Optical imaging through highly scattering media by use of heterodynedetection in the 1.3-μm wavelengthregion

Optical imaging through highly scattering media was studied in the 1.3-microm wavelength region by use of a continuous-wave Nd:YAG laser and an optical heterodyne detection technique. We measured and compared the extinction coefficients of the fat emulsion Intralipid-10% at 0.80, 1.064, and 1.319 microm and demonstrated that the low scattering at 1.319 microm will permit optical imaging through highly scattering media, which otherwise may not be achieved. A possible use of water absorption at 1.319 microm to image the interior structure of biological tissues is also presented and discussed.

Coherent detection techniques in optical imaging of tissues

To form optical images from the transmitted or reflected light that is multiply scattered inside biological tissue, several detection techniques that extract the least-scattered photons or path-resolved photons have been developed. This paper reviews the coherent detection techniques. Emphasis is put on coherent detection imaging methods based on optical heterodyning, whose attractive features include quantum-noise-limited sensitivity, wide dynamic range, and excellent directionality and selectivity. Coherent detection methods have been implemented to achieve laser computed tomography and micrometre-resolution cross-sectional images in both in vivo and in vitro biological systems. Imaging works by ourselves and others are described, and an experimental study on coherent photon migration through highly scattering media is described to aid the understanding of the coherent detection method in selectively detecting the signal-carrying photons.

Fundamental imaging properties of transillumination laser CT using optical fiber applicable to bio-medical sensing

We proposed and developed a novel transillumination laser CT imaging system, using optical fibers, based on the optical heterodyne detection method for biomedical use. The use of optical fibers enables portability and robustness against environmental changes such as varying temperature, air-flow shifts, and unexpected vibrations. In addition, motion-artifact-free images can be obtained with the present system as measurements can be performed with the object fixed. We experimentally investigate in detail the fundamental imaging properties of the system, that has a spatial resolution of 500 /spl mu/m, a dynamic range of approximately 110 dB, and a minimum-detectable-optical power of 10/sup -14/ W as a result of the excellent properties of the heterodyne detection. Based on experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the transillumination mode, similar to X-ray CT, at sub-millimeter spatial resolution and can derive quantitative information from the images. Finally, we experimentally demonstrate the first in-situ tomographic images of plants using the fiber-optic-based laser CT system.

Transillumination computed tomography of high scattering media using laser linewidth broadening projections

Optical tomographic images of highly scattering media reconstructed with the amplitude of the transmitted light have poor contrast and do not accurately describe the small variations in the optical properties. We propose a new method for transillumination optical computed tomography (CT) of highly scattering media using the broadening of laser linewidth as projection data. Reconstructed images using amplitude projection data and linewidth projection data are compared and it is shown that scattering coefficients of target structures can be quantitatively determined in the reconstructed CT images using laser linewidth broadening even at optical thickness exceeding 50 scattering mean free paths.

Enhancement of laser CT image contrast by correction of artifacts due to surface effects

Mismatched boundary conditions such as air-sample interface introduce artifacts that obscure internal information in the reconstructed laser computed tomographic (CT) images. Here, we demonstrate enhancement of target structure in the laser CT images by correcting the projection data using the experimentally determined angle dependence of sample surface attenuation. The images reconstructed with the corrected projection data are shown to have improved image contrast. Our proposed correction to laser CT reconstruction is effective for visualizing internal structure with small variations in the attenuation coefficients that would otherwise be masked by the dominant surface attenuation.

Prototype system of laser transillumination computed tomography for early diagnosis of rheumatoid arthritis

So far we have shown, through various preliminary imaging experiments with small-animal ankle’s and human finger’s joints both healthy and joint-diseased, that early diagnosis for joint disease such as rheumatoid arthritis (RA) is feasible using a transillumination laser CT. For a practical purpose, we have recently proposed and developed a transillumination laser CT imaging system using optical fibers based on the optical heterodyne detection method for a clinical use. In the proposed system, motion-artifact free images can be obtained because measurements can be performed with the object fixed. In addition, use of fiber-optics enables portability, and robustness against environmental changes in a room, such as variable temperature, air-flow shifts, and unexpected vibrations. The imaging system has the following sensing properties: spatial resolution of 500 μm, a dynamic range of approximately 120 dB, and a minimum-detectable-optical power of 10-14 W as a result of the excellent properties of the heterodyne detection technique. In the present paper, we describe a prototype laser CT imaging system using optical fibers for early diagnosis of joint disease such as rheumatoid arthritis by demonstrating the first in vivo tomographic image of a volunteer’s index finger joint as well as the fundamental imaging properties.

New biochemical material laser emission in microdroplets using ribo-flavin and its enhancement by mixing highly scattering intralipid medium

New laser emission from a biochemical material, ribo-flavin (vitamin B2), at 570 nm was observed for the first time in liquid microdroplets pumped at 475 nm using a pulsed optical parametric oscillator. Laser emission spectra from microdroplets containing ribo-flavin in water and glycerol solution exhibit periodic mode structures depending on the microdroplet diameter demonstrating the morphology-dependent resonances. Magnitude enhancement of lasing emission is confirmed experimentally from liquid microdroplets of ribo-flavin solution with appropriate mixture of the fat emulsion Intralipid-10% suspension as highly scattering medium. We believe that such biochemical-soft multiple light scatterer systems may allow a wide range lasing of other bio-materials and even lead to the discovery of some novel species as well as highly sensitive analysis and diagnosis for future applications.

Coherent detection imaging of absorption and scattering in tissues and tissuelike phantoms

This paper presents measurement results of absorption and scattering in tissues and tissuelike phantoms by using coherent detection imaging (CDI) technique. CDI measurements are carried out in 0.8 - 1.3 micrometer wavelength region by using several continuous wave, single frequency lasers, including a tunable Ti:sapphire laser and laser diode-pumped Nd:YAG lasers. A 120 dB dynamic range achieved with less than 10 mW incident power and a detection time of 0.1 msec enables spectroscopic measurements through attenuation of as much as exp(-27). Measurement results using cw lasers are also compared to the temporal scattering profiles of coherent photon migration in highly scattering media. For this purpose, a modified CDI system using low-coherence super luminescent diodes has been developed. The results from the laser and low coherence CDI measurements are found to be consistent.