Current efforts in tissue engineering target the growth of 3D volumes of tissue cultures in bioreactor conditions.
Fluorescence optical tomography has the potential to monitor cells viability and tissue growth non-destructively
directly within the bioreactor via bio-molecular fluorescent labelling strategies. We currently work on developing
the imaging instrumentation for tissue cultures in bioreactor conditions. Previously, we localized in 3D
thin fluorescent-labelled capillaries in a cylindrically shaped bioreactor phantom containing a diffusive medium
with our time-of-flight localization technique. Here, we present our first reconstruction results of the spatial
distribution of fluorophore concentrations for labelled capillaries embedded in a bioreactor phantom.
Fluorescence optical diffuse tomography (fDOT) is of much interest in molecular imaging to retrieve information
from fluorescence signals emitted from specifically targeted bioprocesses deep within living tissues. An exciting
application of fDOT is in the growing field of tissue engineering, where 3D non-invasive imaging techniques are
required to ultimately grow 3D engineered tissues. Via appropriate labelling strategies and fluorescent probes,
fDOT has the potential to monitor culture environment and cells viability non-destructively directly within
the bioreactor environment where tissues are to be grown. Our ultimate objective is to image the formation
of blood vessels in bioreactor conditions. Herein, we use a non-contact setup for small animal fDOT imaging
designed for 3D light collection around the sample. We previously presented a time of flight approach using a
numerical constant fraction discrimination technique to assign an early photons arrival time to every fluorescence
time point-spread function collected around the sample. Towards bioreactor in-situ imaging, we have shown the
capability of our approach to localize a fluorophore-filled 500 μm capillary immersed coaxially in a cylindrically
shaped bioreactor phantom containing an absorbing/scattering medium representative of experiments on real
tissue cultures. Here, we go one step further, and present results for the 3D localization of thinner indocyanine
green labelled capillaries (250 μm and 360 μm inner diameter) immersed in the same phantom conditions and
geometry but with different spatial configurations (10° and 30° capillary inclination).
Currents eorts in tissue engineering (TE) are directed towards growing 3D volumes of tissues. In response to TE
needs, we are developing a non-invasive technique based on fluorescence diuse optical tomography (FDOT) to
image in 3D, via fluorescence labelling, the formation of micro-blood vessels in tissue cultures grown on biodegradable
scaolds in bioreactor conditions. In the present work, we use a non-contact FDOT setup developed for
small animal imaging for our measurements. We present experimental results showing the feasability to localize
a fluorophore-filled 500μm capillary immersed in a scattering medium contained in a cylindrically-shaped glass
tube. These conditions are representative of experiments to be carried on real tissue cultures. Time-resolved
scattering-fluorescence measurements are made via Time-Correlated Single Photon Counting (TCSPC) and we
use numerical constant fraction discrimination (NCFD) to obtain primary localization information from our
time-resolved data.
Recent advances in tissue engineering (TE) aim to grow 3D volumes of tissue in bioreactor conditions. This has
proved to be a difficult task thus far, notably due to the lack of non-invasive diagnostic tools to monitor the
growth of a tissue and ensure its appropriate development. To fulfill part of this need, we currently develop a
non-invasive imaging technique based on fluorescence diffuse optical tomography (FDOT) to image in 3D, via
fluorescent tracers, processes relevant to tissue growth in a bioreactor. More particularly, here we are interested
in imaging the formation of micro-blood vessels in tissue cultures grown on biodegradable scaffolds. Blood vessels
are thought to play a fundamental role in tissue growth. Since a bioreactor possesses a known geometry (by
design), we propose an FDOT configuration that uses fiber optics brought in contact with the boundary of the
bioreactor to collect tomographic optical data. We describe an optical fibers-based set-up and experimental
measurements that demonstrate the possibility of localizing a fluorophore-filled 500&mgr;m capillary immersed in
a scattering medium contained in a cylindrically-shaped glass tube. These conditions are representative of
experiments to be carried on real tissue cultures. In our particular implementation, time-resolved scattering-
fluorescence measurements are made via time-correlated single photon counting. Numerical constant fraction
discrimination applied to our time-resolved data allows to extract primary localization information.
Positron Emission Tomography (PET) scanners dedicated to small animal studies have seen a swift development in recent years. Higher spatial resolution, greater sensitivity and faster scanning procedures are the leading factors driving further improvements. The new LabPETTM system is a second-generation APD-based animal PET scanner that combines avalanche photodiode (APD) technology with a highly integrated, fully digital, parallel electronic architecture. This work reports on the performance characteristics of the LabPET quad detector module, which consists of LYSO/LGSO phoswich assemblies individually coupled to reach-through APDs. Individual crystals 2×2×~10 mm3 in size are optically coupled in pair along one long side to form the phoswich detectors. Although the LYSO and LGSO photopeaks partially overlap, the good energy resolution and decay time difference allow for efficient crystal identification by pulse-shape discrimination. Conventional analog discrimination techniques result in significant misidentification, but advanced digital signal processing methods make it possible to circumvent this limitation, achieving virtually error-free decoding. Timing resolution results of 3.4 ns and 4.5 ns FWHM have been obtained for LYSO and LGSO, respectively, using analog CFD techniques. However, test bench measurements with digital techniques have shown that resolutions in the range of 2 to 4 ns FWHM can be achieved.
Detectors working in photon counting mode offer an interesting alternative to the common charge integrating detectors for computed tomography (CT), because they can potentially measure the energy of every detected X-ray photons and achieve better image contrast sensitivity for a given dose. Unfortunately, most current X-ray detectors suffer from limited count rate capability, due either to a long charge migration time in semiconductor and gas detectors, or to a slow decay time in ceramic scintillators. To overcome these difficulties, we propose to use pixel detectors based on fast light emitting inorganic scintillators individually coupled to avalanche photodiodes with parallel, low-noise, fast digital processing electronics to provide real time single event detection and recording. The proposed detector was investigated with 2 × 2 × 10 mm3 Lu1.9Y0.1SiO5 (LYSO), a fast decay time (40 ns), heavy (7.19 g/cc) scintillator that is also suitable for coincidence detection of annihilation radiation (511 keV) in positron emission tomography (PET). Therefore, the detector characteristics make it a good candidate for implementation in a combined PET/CT dual-modality scanner. Although only coarse spectral analysis is possible in the X-ray energy range, it is demonstrated that appropriate CT images for anatomical localization can be obtained at very low dose in counting mode using a PET/CT simulator set up for small animal imaging. Data are reported on CT image resolution, noise, contrast and dose.
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