To increase prostate cancer diagnosis sensibility, we propose to add an optical modality to an US biopsy tool to localize
fluorophore marked tumors. Optical signals are acquired on a time-resolved acquisition chain composed by a 770 nm
femtosecond laser source and a four channels TCSPC device. The fluorescence concentration is reconstructed by using
intensity and mean time of flight acquired from each time-resolved source-detector signal. Validation experiments are
performed on a phantom mimicking prostate both on its optical and ultrasound properties with 10 μmol/L ICG 1 cm deep double fluorescent inclusions to simulate marked tumors. An exhaustive search algorithm succeeded in reconstructing the two distinct fluorescence dots with correct locations.
Finding a way to combine ultrasound and fluorescence optical imaging on an endorectal probe may improve early detection of prostate cancer. The ultrasound provides morphological information about the prostate, while the optical system detects and locates fluorophore-marked tumors. A tissue-mimicking phantom, which is representative of prostate tissues both on its optical (absorption µa and diffusion µ) and its ultrasound properties, has been made by our team. A transrectal probe adapted to fluorescence diffuse optical tomography measurements was also developed. Measurements were taken on the prostate phantom with this probe based on a pulsed laser and a time-resolved detection system. A reconstruction algorithm was then used to help locate and quantify fluorescent inclusions of different concentrations at fixed depths.
Fluorescence is a very promising radioactive-free technique for functional imaging in small animals and, in the future, in humans. However, most commercial near-infrared dyes display poor optical properties, such as low fluorescence quantum yields and short fluorescence lifetimes. In this paper, we explore whether the encapsulation of infrared cyanine dyes within the core of lipid nanoparticles (LNPs) could improve their optical properties. Lipophilic dialkylcarbocyanines DiD and DiR are loaded very efficiently in 30-35-nm-diam lipid droplets stabilized in water by surfactants. No significant fluorescence autoquenching is observed up to 53 dyes per particle. Encapsulated in LNP, which are stable for more than one year at room temperature in HBS buffer (HEPES 0.02 M, EDTA 0.01 M, pH 5.5), DiD and DiR display far improved fluorescence quantum yields (respectively, 0.38 and 0.25) and longer fluorescence lifetimes (respectively, 1.8 and 1.1 ns) in comparison to their hydrophilic counterparts Cy5 (=0.28, =1.0 ns) and Cy7 (=0.13, =0.57 ns). Moreover, dye-loaded LNPs are able to accumulate passively in various subcutaneous tumors in mice, thanks to the enhanced permeability and retention effect. These new fluorescent nanoparticles therefore appear as very promising labels for in vivo fluorescence imaging.
Prostate cancer diagnosis is based on PSA dosage and digital rectal examination. In case of positive test, a biopsy is
conducted and guided by ultrasound imaging. Today, however, as ultrasound imaging is not able to precisely detect
tumors, some biopsies have to be performed in the prostate and the only way to improve detection is to increase the
number of those uncomfortable biopsies. In order to decrease this number and to improve the patient wellness, we are
studying a way to couple ultrasound and fluorescence optical imaging on an endorectal probe. The ultrasounds are used
to get morphological information on the prostate and the optical system to detect and to localize fluorophore marked
tumors. To support the development of such a system, we have carried out a new tissue-mimicking phantom which
represents the three different kind of tissue concerned during prostate endorectal examination: prostate, rectum,
surrounding tissues. It was imaged by ultrasound and by fluorescence diffuse optical imaging. We have proved that the
optical system is able to detect and to localize a fluorescing inclusion at different depth inside the phantom which has
then been superimposed to the morphological image provided by the ultrasounds.
Fluorescence Diffuse Optical Tomography is an optical non-invasive molecular technique for cancer imaging.
Depending on the accessibility of the organ two main geometries might be considered, reflection or transmission. We
will present first experimental and reconstruction comparison between these two geometries, on a laboratory time
resolved bench. Both acquisitions were made using a fluorophore inclusion positioned in a liquid phantom, with breast
comparable optical properties. We successfully reconstructed all fluorophore positions examined in both geometries.
Reflection geometry suffers of many drawbacks that we have to deal with. We will present all challenges it implies, and
also what are the advantages to use time resolved techniques in both geometries.
We investigated femtosecond pump-repump depletion excitation in biological fluorescent molecules (tryptophan and flavins) in solutions and in organic fluorescent interferents such as polycyclic hydrocarbons (naphthalene, diesel fuel). If the repump pulse induces in both flavins and Trp a depletion of the excited state, populated by the pump pulse, which leads to a drastic decrease of the fluorescence, such mechanism is ineffective in organic fluorescent interferents. The repump induced depletion is still observed for bacteria containing solutions. This opens interesting perspectives to discriminate biological from non-biological fluorescent particles in air.