André Studzinski

A network of disdrometers to quantify the small-scale variability of the raindrop size distribution

Insight into the spatial variability of the (rain) drop size distribution (DSD), and hence rainfall, is of primary importance for various environmental applications like cloud/precipitation microphysical processes, numerical weather modeling, and estimation of rainfall using remote sensing techniques. In order to quantify the small-scale variability of the DSD, a network of 16 optical disdrometers has been designed and deployed over a typical operational weather radar pixel (about 1 x 1 km(2)) in Lausanne, Switzerland. This network is fully autonomous in terms of power supply as well as data transmission and storage. The combination of General Radio Packet Service and radio communication allows a real-time access to the DSD measurements. The network is sampling at a temporal resolution of 30 s. A period representative of frontal precipitation is analyzed to illustrate the measurement capabilities of the network. The spatial variability is quantified by the coefficient of variation of the total concentration of drops, the mass-weighted diameter, and the rain rate between the 16 stations of the network. The sampling uncertainty associated with disdrometer measurements is taken into account, and the analysis of a 1.5 month rainy period shows a significant variability of these quantities, which cannot be explained by the sampling uncertainty alone, even at such a small scale.

Instrumentation for real-time fluorescence lifetime imaging in endoscopy

The fluorescence lifetime of living tissues is, in certain cases, related to their pathologic state and is therefore of interest for cancer detection. Measuring fluorescence lifetime in vivo during an endoscopic examination has thus been a challenging objective for several years. The present article deals with the development and first clinical trails of an instrumentation producing fluorescence lifetime images in real time. The acquisition of such fast phenomenon (nanosecond time scale) on an image has been made possible by using the homodyne detection approach, in which the excitation light and the detection gain are modulated in a phase-coherent way. Based on images acquired at different phase between the excitation and detection modulation, the fluorescence lifetime is calculated for each pixel of the image. Different configurations of excitation modulation characteristics (pulse train versus sine-wave amplitude modulation) have been investigated and compared using Fourier transforms. Interestingly, a...

An endoscopic fluorescence imaging system for simultaneous visual examination and photodetection of cancers

We describe the design and performance tested during six years of clinical trials of a fluorescence endoscope for the detection and delineation of cancers in several hollow organs. The apparatus is based on the imaging of the laser-induced fluorescence that differs between a tumor and its surrounding normal tissue. The tests are carried out in the upper aerodigestive tract, the tracheobronchial tree, the esophagus, and the colon. In the three former cases an exogenous dye is used (Photofrin II), whereas in the latter case fluorescein molecules conjugated with monoclonal antibodies directed against carcinoembryonic antigen are injected. The decrease of native tissue autofluorescence observed in early cancers is also used for detecting lesions in the tracheobronchial tree. The fluorescence contrast between the tumor and surrounding normal tissue is enhanced by real time image processing. This is done by simultaneously recording the fluorescenceimage in two spectral domains, after which these two images are digitized and manipulated with a mathematical operator (look-up table) at video frequency. Moreover, the device that is described below allows for an immediate observation of the endoscopic area under white light illumination during fluorescence detection in order to localize the origin of the “positive” fluorescence signals. Typical results obtained in the tracheobronchial tree and in the colon are presented and the sources of false positives and false negatives are evaluated in terms of the fluorescent dye, tissue optical properties, and illumination optics.

Frequency-domain fluorescence lifetime imaging for endoscopic clinical cancer photodetection: Apparatus design and preliminary results

We describe a new fluorescence imaging device for clinical cancer photodetection in hollow organs in which the tumor/normal tissue contrast is derived from the fluorescence lifetime of endogenous or exogenous fluorochromes. This fluorescence lifetime contrast gives information about the physicochemical properties of the environment which are different between normal and certain diseased tissues. The excitation light from a CW laser is modulated in amplitude at a radio frequency by an electrooptical modulator and delivered by an optical fiber through an endoscope to the hollow organ. The image of the tissue collected by the endoscope is separated in two spectral windows, one being the backscattered excitation light and the other the fluorescence of the fluorochrome. Each image is then focused on the photocathode of image intensifiers (II) whose optical gain is modulated at the same frequency as the excitation intensity, resulting in homodyne phase-sensitive images. By acquiring stationary phase-sensitive frames at different phases between the excitation and the detection, it is possible to calculate in quasi-real time the apparent fluorescence lifetime of the corresponding tissue region for each pixel. A result obtained by investigating the endogenous fluorochromes present in the mucous membrane of an excised human bladder is presented to illustrate this method and most of the optical parameters which are of major importance for this photodetection modality have been evaluated.

Clinical imaging fluorescence apparatus for the endoscopic photodetection of early cancers by use of Photofrin II

A fluorescence imaging device applied to the detection of early cancer is described. The apparatus is based on the imaging of laser-induced fluorescence of a dye that localizes in a tumor with a higher concentration than in the surrounding normal tissue after iv injection. Tests carried out in the upper aerodigestive tract, the tracheobronchial tree, and the esophagus with Photofrin II (1 mg/kg of body weight) as the fluorescent agent are reported as examples. The fluorescence is induced by violet (410-nm) light from a continuous-wave (cw) krypton-ion laser. The fluorescence contrast between tumor and surrounding tissue is enhanced by real-time image processing. This is done by the simultaneous recording of the fluorescence image in two spectral domains (470-600 and 600-720 nm), after which these two images are digitized and manipulated with a mathematical operator (look-up table) at video frequency. Among the 7 photodetections performed in the tracheobronchial tree, 6 were successful, whereas it was the case for only 5 of the 15 lesions investigated in squamous mucosa (upper aerodigestive tract and esophagus). The sources of false positives and false negatives are evaluated in terms of the fluorescent dye, tissue optical properties, and illumination optics.

Endoscopic frequency-domain fluorescence lifetime imaging for clinical cancer photodetection: apparatus design

We describe a new fluorescence imaging device for clinical cancer photodetection in hollow organs in which the image contrast is derived from the fluorescence lifetime of the fluorochrome at each point in a 2D image. Lifetime images are created from a series of images obtained from two gain-modulated image intensifiers. One of them (II-1) detects the light-induced tissue fluorescence, whereas the other (II-2) detects the backscattered fluorescence excitation light. This light is modulated at the same frequency as the detectors, resulting in homodyne phase-sensitive image. These stationary phase-sensitive images are collected using two CCD cameras, digitized and manipulated with a mathematical operator in real time. A series of such images, obtained with both image intensifiers at various phase shifts between their gain modulation and the modulation of the excitation light, is used to determine phase angle and/or the modulation of the fluorescence emission at each pixel. The reference values of these phase angles and modulations are obtained with II-2, whereas II-1 enables the measurement of the phase and modulation of the fluorescence. Phase and modulation are related to the fluorescence lifetime of the fluorochrome. An advantage of the experimental method proposed here is that pixel-to-pixel scanning is not required to obtain the fluorescence lifetime image, as the information from all pixels is obtained at the same time.

Endoscopic tissue fluorescence life-time imaging by frequency doamin light-induced fluorescence

An instrumentation is being developed to draw a fluorescence life-time map of tissue endoscopically. This fluorescence life-time of an endogenous or exogenous fluorochrome gives information about the physico-chemical environment which is thought to vary between normal and diseased tissue. The excitation light from a cw laser is modulated in amplitude at high frequencies by an electro-optic modulator and delivered to the endoscopic site through an optical fiber. The image of the tissue is spectrally split in two parts, the one being the backscattered excitation light, the other the fluorescence of the fluorochromes. Each image is focused on the photocathode of an image intensifier whose gain is modulated at the same frequency. By acquiring frames at different phases between the excitation and the emission, it is possible to calculate pixel by pixel the apparent fluorescence life-time of the corresponding tissue region.