It is well known that the reconstruction problem in fluorescence diffuse optical tomography is badly conditioned and
requires the knowledge of medium optical properties. Its principle is to measure the fluorescence light emerging at
different positions of the surface when the biological medium is excited with point sources. In this paper, we evaluate the
influence of the medium optical properties and the noise on the fluorescence reconstruction, and we introduce a new
regularized fluorescence reconstruction method using an a priori on contours. The fluorescence reconstruction
improvement is studied when using this method.
This work is first a description of a statistical simulation algorithm developed for simulating the spectral absorption and emission of several fluorophores in an absorbing and diffusing multilayer model. Second, a detailed experimental validation of the simulation program is conducted on two sets of liquid and solid multilayer phantoms, containing one, two, or three fluorophores, within absorbing and scattering media. Experimental spatially resolved reflectance spectra are acquired in the wavelength band 400 to 800 nm and compared to corresponding simulated spectra. The degree of similarity between experimentation and simulation data is quantified. The results obtained underline good correlations with mean errors varying from 2 to 10%, depending on the number of layers and on the complexity of the phantom's composition.
Skin cancer full resection implies an evaluation of safety margins around the visible tumour. For melanomas such
margins are proportional to tumour's thickness also known as "Breslow Index". In order to see if Diffuse Reflectance
Spectroscopy (DRS) could be used to non-invasively evaluate Breslow Index, an in vitro study as well as numerical
simulations were performed. Bilayered phantoms were made : a lower layer mimicking dermis underneath an absorbing
layer mimicking a melanoma. Five groups of phantoms each having a specific top layer's thickness were made : 2, 3, 4, 5
or 6 mm. For wavelengths longer than 600 nm, Diffuse Reflectance spectra were significantly different (p<0.05) for each
thickness at every Collecting to Excitation Fibre Separations (CEFS) : 271, 536, 834, 1076 and 1341 &mgr;m. Monte Carlo
simulations were performed to check if DRS could detect smaller (i.e. 0.5 mm) thickness variations. Both experimental
and numerical results showed the DR signal intensity linearly (R2>0.9) decreases as CEFS increases. The thicker the
melanic layer was the smaller the slope (absolute value) was. These in vitro results will help setting up a clinical trial to
non invasively evaluate Breslow Index : the bandwidth should be the NIR one (wavelengths longer than 600 nm) and
CEFS should be shorter than 1 mm. Calibration will have to be made in order to relate slope to Breslow Index.
Cryopreservation is the only method for conserving blood vessels as future allografts with biological immunity controls. Although it affects vessels mechanical structure, no biomechanical integrity simple test is available today.
Biological tissues optical properties characterization by spectroscopic methods is of interest due to their types or natures variations. Collected data complementarity contributes to "photodiagnosis" applicative prospects (cancer, vascular...).
Pig carotid artery rings were tested after excision and after one month cryopreservation. An uniaxial mechanical testing device was used for ring stretching, and elongation and axial forces measurement. Circumferential large strains and stresses were calculated. Simultaneously, each artery ring optical characteristics was measured using fibered autofluorescence and elastic scattering spectrometers.
Mechanical results showed nonlinear strain/stress curves and large deformations in good agreement with other referenced works. Significant differences (p<0.05) between fresh and cryopreserved rings mechanical properties were noticed. Elastic scattering spectra intensity variations were well correlated with artery mechanical properties. The standardized autofluorescence spectra were more clearly correlated with anatomo-histological changes due to cryopreservation, providing rather accurate differentiation between fresh and cryopreserved samples.
This study offers a new perspective to detect changes of cryopreserved arterial samples mechanical properties. Coupling mechanical tests (uniaxial traction of arterial rings) and optical spectroscopic measurements (autofluorescence, elastic scattering) is the driving point: it allows correlating mechanical modifications and spectral variations of artery rings before and after cryopreservation. Ultimately, this new approach could help developping a device allowing non-invasive, atraumatic and contactless optical examinations of arterial graft to assess its mechanical state before reimplantation.
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