Optical properties of flavin adenine dinucleotide (FAD) moiety are nowadays widely used for biotechnological applications. Given the fundamental role played by FAD, having additional information about this complex can be extremely useful to get a deeper insight in structural properties and functional role of this enzymatic co-factor. For this purpose, we investigated FAD behaviour in aqueous solutions at two pH values by means of complementary optical spectroscopic techniques (circular dichroism, infrared spectroscopy and time-resolved fluorescence). The results confirm that pH influences circular dichroism spectra. An innovative Maximum Entropy Method was adopted for time-resolved fluorescence signal analysis allowing us to evidence a three-components decay for FAD in aqueous solution with pH-depending lifetimes and relative amplitudes. All the results here reported give a more complete view of FAD’s properties that can be exploited in designing new biotechnological devices.
Visible and near-infrared dyes are largely used in diagnostics and sensing. For this reason, it is very important to
study their time-resolved fluorescence in presence or in absence of proper scattering medium in order to simulate
the optical characteristics of biological tissues. Moreover, if one- or two-photon excitation processes are available
also visible dyes will be employed taking advantages from using exciting sources in the diagnostic window (red
and near IR) of the electromagnetic spectrum, where the photons are rarely absorbed and more often scattered.
Visible and near IR fluorescent samples (Indocyanine Green and Rhodamine 6G) in absence and in presence of
scattering agents (different Intralipid concentrations) and one- and two- photon time-resolved experiments have
been performed. As expected, the presence of scattering agents modified time-resolved spectra and the related
lifetime components. The experimental results have been used to preliminarly test different theoretical approaches
describing the propagation of fluorescence signals in scattering media.
Intralipid is a material widely employed for the preparation of phantoms simulating optical properties of tissues in the
field of optical imaging. Two main assumptions underlie the theoretical predictions of their scattering properties: the
occurrence of single scattering for any concentrations of Intralipid, thus enabling the use of Mie theory, and a highly
anisotropic g-factor giving a forward preferential direction of photon propagation. The importance of precisely
estimating the optical properties of such phantoms requires that the accuracy of these assumptions and their range of
applicability are very well-assessed. In this paper, we report the first step of an experimental investigation on the
scattering properties of Intralipid suspensions at different concentrations. The study is carried out by the joined use of
Time-Resolved Transmittance and Dynamic and Static Light Scattering techniques. By the analysis of the angular and
temporal dependence of light scattered by Intralipid suspensions, a more reliable description of the scattering process
occurring in the samples could be obtained. The results allow us to better elucidate the dependence of scattering
properties of suspensions on Intralipid concentrations and composition. This will help in the design and realization of
tissue phantoms with more and more reliable optical properties.
In the framework of perturbation approach to diffusion equation analytical expressions are derived to describe
the effects on the time-resolved transmittance due to the presence of an inclusion that can be purely absorptive
or diffusive. The formula assume the optical properties of the inclusion are spatially Gaussian distributed. The
accuracy and the application range of the perturbed transmittance are investigated through comparisons with
the numerical solutions of the time-dependent diffusion equation given by using the Finite Element Method. A
case of practical interest for two-dimensional breast imaging is considered.
The intrinsic quality of an image is related to the concepts of spatial resolution, noise and contrast. A common method to measure these parameters is by using Edge Response Function measurements with a black mask. We investigated these parameters using an experimental apparatus mainly composed by a an argon pumped Ti:Sa laser working in femtosecond regime and a time-correlated single photon-counting system. The investigated samples were suspensions of Intralipid 10% with distilled water in which a black mask was inserted and bidimensional scanning were performed at different depths ( z = L/2, L/4, 3L/4). The experimental data were analyzed in order to get information on the above-mentioned image quality parameters. A comparison with similar results obtained with a streak camera has been done and for spatial resolution a comparison with random walk predictions has been performed. The results of this study can be particularly useful in identifying the best working conditions and in improving the performance of image reconstruction algorithms since the clinical prototypes of optical mammographers nowadays under pre-clinical investigation adopt time-correlated single photon-counting technique.
Theoretical and experimental investigations on image quality are extremely important in optical imaging in order to better define the role of optical techniques in medical diagnostics. Today time-resolved laser transillumination can be considered a good candidate as an alternative and/or auxiliary technique in medical diagnostic field. The intrinsic quality of an image is related to the concepts of spatial resolution, noise and contrast. A common method to measure these parameters is by using Edge Response Function measurements with a black mask. We investigated these parameters using an experimental apparatus mainly composed by a picosecond solid-state laser and a time-correlated single photon-counting system. The investigated samples were suspensions of Intralipid 10% with distilled water in which a black mask was inserted and bidimensional scanning were performed. The experimental data were analyzed in order to get information on the above-mentioned image quality parameters. For spatial resolution a comparison with random walk predictions has been attempted. The results of this study can be particularly useful in identifying the best working conditions and in improving teh performance of image reconstruction algorithms since the clinical prototypes of optical mammogrpahers nowadays under pre-clinical investigation adopt time-correlated single photon-counting technique.
We have performed a detailed analysis for the problem of photon migration through a scattering slab containing a single absorptive inclusion whose absorption coefficient is characterized by a spatially varying Gaussian distribution law. The analysis has been performed within the framework of the first-order perturbation approach to the diffusion theory for a slab geometry and a coaxial measurements arrangement. An analytical expression has been derived that account for the change in the time-resolved transmittance in presence of the absorptive Gaussian inclusion. We present experimental results of time-resolved measurements that have been performed on absorptive phantoms with the aim to investigate and to validate the ability of this model to predict the optical properties of absorptive inhomogeneities hidden inside a scattering medium.
Results on image quality parameters of a time-resolved imaging system are reported. Spatial resolution has been investigated by using the edge response function method (ERF) whereas a small absorbing inclusion hidden inside a turbid slab has been adopted to analyze the contrast and noise of images obtained by different reconstruction algorithms.
The possibility of obtaining images of human organs by optical techniques for diagnostic purposes is still under intense investigation. Useful information for devising the most efficient data acquisition procedures and reconstruction algorithms can be obtained by imaging well-controlled small inhomogeneities using different reconstruction procedures. For this purpose we performed time-resolved imaging experiments by embedding in a turbid slab small inclusions with different absorption coefficients. The ability of the imaging system to detect these hidden objects strongly depends on its optical properties and on the method that is adopted to reconstruct images. To this regard, in order to construct images different procedures can be adopted. The efficiency of these different procedures has been valuated by investigating the contrast, the noise and the effective signal-to-noise ratio of constructed images. Furthermore, this data analysis has been used to study the role of the inclusion’s object contrast on the efficiency of the adopted reconstruction algorithm.
Well-characterized phantom objects are necessary for investigating the performances of optical imaging systems based on time-resolved transmittance and fluorescence. For this purposes we have prepared inhomogeneous phantoms made of gelatinous objects placed in aqueous solutions of 10% Intralipid with different concentrations. The gelatinous objects have been prepared using a mixture of 10% Intralipid with agar at which absorbing ink have been added for transmittance based optical imaging system. For fluorescence measurements proper fluorescent dyes (rhodamine6G and IR125) have been added. Conventional optical characterization by spectrophotometric and spectrofluorimetric measurements have been performed. In addition, time-resolved transmittance and fluorescence measurements have been carried out. In particular, time-correlated single photon counting system has been used for time-resolved transmittance measurements. For time-resolved fluorescence measurements an optical imaging system based on a Ti:Sa laser and streak camera has been employed.
First order perturbation approach to the diffusion equation provides a more realistic model to describe inhomogeneous structures. To this regard, we obtained a general expression of the time-resolved transmittance relatively to a homogeneous turbid medium with an embedded inclusion. This expression was further approximated in the case of a small volume object. Then, we studied the limit and accuracy of this approach concerning on a cubic absorber placed in the centre of the source-detector line of a turbid slab.
A multichannel time-resolved system for medical optical tomography has been developed. Its main components are an eight channel single-photon counting detector and an ultrafast picosecond solid state laser. Several instrumental aspects concerning the optical coupling between the MCP-PMT and the optical fiber bundles, the electronic components and the roto-translation stages control have been examined. Moreover the accuracy limits in the determination of optical properties of phantom objects have been largely investigated taking into account the role played by the theoretical description of light propagation, the instrumental response function (by means of a convolution procedure) and the fitting algorithm. Information on image quality parameters (spatial resolution, contrast and SNR) have been also obtained by measuring Edge Response Function in different experimental conditions. In such a work, aqueous Intralipid solutions have been used as phantom objects. Furthermore, experimental investigations on well controlled inhomogeneous with different optical properties embedded in Intralipid solutions have been carried on. As last step of the work, preliminary imaging of cylindrical objects has been performed and a Linux version of TOAST code has been used in the imaging reconstruction.
The image quality in optical imaging is actually under intense investigation in order to ultimately define the role of optical techniques for medical diagnosis purposes. In this work we have investigated the spatial resolution, noise and contrast parameters by using edge response function measurements with masks having well-controlled optical properties. The experimental set-up mainly consisted of an Argon pumped Titanium-Sapphire laser working in femtosecond regime and a streak camera with a few picosecond of temporal resolution. The investigated samples were solutions of Intralipid 10% with distilled water in order to approximate optical properties of biological tissues. The experimental data were analyzed with different imaging algorithms and compared with theoretical predictions about the above- mentioned image quality parameters. The use of spatial resolution, contrast and signal-to-noise ratio allowed us in identifying the best working conditions for optical imaging systems and in evaluating the efficiency of different image reconstruction algorithms.
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