Compact fiber-optic fluorosensor using a continuous-wave violet diode laser and an integrated spectrometer

A compact fluorosensor with a fiber-optic measurement probe was developed, employing a continuous-wave violet diode laser as an exciting source and an integrated digital spectrometer for the monitoring of fluorescence signatures. The system has the dimensions 22x13x8 cm(3), and features 5 nm spectral resolution and an excellent detectivity. Results from measurements on vegetation and human premalignant skin lesions are reported, illustrating the potential of the instrument. (C) 2000 American Institute of Physics. [S0034-6748(00)04508-1]

‘Paging Podiatry!’: an audit of acute inpatient podiatry referrals

For the analysis of small concentrations of organics in aqueous solutions, a novel add-on accessory for dual-beam / optical subtraction spectroscopy has been built for a commercial Fourier transform infrared spectrometer. A standard FT-IR instrument requires a sample measurement and a separate reference measurement, whereas the optical subtraction instrument directly measures the difference between sample and reference. This has a number of advantages. The time delay between the two measurements is eliminated, and the effective measurement time is improved by a factor of two. Moreover, the optical subtraction provides a large reduction in dynamic range of the measured signal, which prevents detector saturation, and enables effective use of dynamic range of the analog to digital converter in the FT-IR spectrometer. This results in an increased signal to noise ratio, compared to the standard FT-IR instrument. By changing detector and light source the instrument may be used for both near- and mid.-infrared spectroscopy. The increased sensitivity and stability of the optical subtraction instrument compared to the standard instrument is demonstrated by transmission measurements of aqueous urea solutions in the combination band region 4000 to 5000cm(-1) (2000 to 2500nm)

Photodynamic therapy using intravenous delta-aminolaevulinic acid-induced protoporphyrin IX sensitisation in experimental hepatic tumours in rats.

The efficacy of photodynamic therapy (PDT) using delta-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) sensitisation and laser light at 635 nm was investigated in the treatment of experimental hepatic tumours. The model of liver tumours was induced either by local inoculation or by administration of tumour cells through the portal vein in rats. ALA at a dose of 60 mg kg(-1) b.w. was intravenously administered 60 min before PDT. PpIX accumulation in tumour, normal liver and abdominal wall muscle was detected by means of laser-induced fluorescence (LIF). Laser Doppler imaging (LDI) was used to determine changes in the superficial blood flow in connection with PDT. Histopathological examinations were performed to evaluate the PDT effects on the tumour and the surrounding liver tissue, including pathological features in the microvascular system. The accumulation of PpIX, as monitored by LIF, showed high fluorescence intensities at about 635 nm in both the hepatic tumour tissue and normal liver and low values in the abdominal wall. LDI demonstrated that the blood flow in the treated tumour and its surrounding normal liver tissue decreased immediately after the PDT, indicating an effect on the vascular system. A large number of thrombi in the irradiated tumour were found microscopically 3 h after the PDT. The tumour growth rate showed a marked decrease when evaluated 3 and 6 days after the treatment. These results show that the ALA-PDT is effective in the inhibition of growth of experimental hepatic tumours

Time and wavelength resolved spectroscopy of turbid media using light continuum generated in a crystal fiber

We report a novel system for time-resolved diffuse remission spectral measurements, based on short light continuum pulses generated in an index-guided crystal fiber, and a spectrometer-equipped streak camera. The system enables spectral recordings of absorption and reduced scattering coefficients of turbid media in the wavelength range 500 - 1200 nm with a spectral resolution of 5 nm and a temporal resolution of 30 ps. The optical properties are calculated by fitting the solution of the diffusion equation to the time-dispersion curve at each wavelength. Example measurements are presented from an apple, a finger and a pharmaceutical tablet. (C) 2004 Optical Society of America

Evaluation of a Fiber-Optic Based Pulsed Laser System for Fluorescence Spectroscopy

A fiber optic based continous wave laser setup has been developed to record the 5-aminolevulinic (5-ALA) induced Protoporfyrin IX (PpIX) fluorescence signals from cerebral gliomas. To reduce the energy delivered to the tissue as well as suppression of the ambient lamp artifact from the recorded spectra, a pulsed laser setup has been developed and evaluated. This setup has been calibrated and first evaluations were performed on the 5-ALA treated skin showing PpIX fluorescence peaks from the ALA treated skin at 635 and 704 nm wavelengths. The system controls laser pulses through a computer interface and labview software package. Pulses as short as 50 ms over a period time of 500 ms are generated and optimally detected. The results from primary measurements on skin show an effective suppression of room fluorescent lamp artifact from the recorded spectra

Autofluorescence insensitive imaging using upconverting nanocrystals in scattering media

Autofluorescence is a nuisance in the field of fluorescence imaging and tomography of exogenous molecular markers in tissue, degrading the quality of the collected data. In this letter, we report autofluorescence insensitive imaging using highly efficient upconverting nanocrystals (NaYF4: Yb3+ /Tm3+) in a tissue phantom illuminated with near- infrared radiation of 85 mW/cm(2). It was found that imaging with such nanocrystals leads to an exceptionally high contrast compared to traditional downconverting fluorophores due to the absence of autofluorescence. Upconverting nanocrystals may be envisaged as important biological markers for tissue imaging purposes. c 2008 American Institute of Physics. [DOI: 10.1063/1.3005588

Scatter correction of transmission near-infrared spectra by photon migration data: Quantitative analysis of solids

The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model

Time-resolved NIR/Vis spectroscopy for analysis of solids: Pharmaceutical tablets

Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals. The objective of the experiments was to study the interaction of light with pharmaceutical solids and to investigate the usefulness of the method as an analytical toot for spectroscopic analysis. In these experiments, a pulsed Ti:sapphire laser and white light generation in water was utilized to form a pulsed light source in the visible/NIR region. The light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera. Two types of measurements were performed. First, a spectrometer was put in front of the streak camera for spectral resolution. Secondly, the signal originating from different locations of the sample was collected. Time-resolved and wavelength/spatially resolved data were generated and compared for a number of different samples. The most striking result from the experiments is that the typical optical path length through a 3.5-mm-thick tablet is about 20-25 cm. This indicates very strong multiple scattering in these samples. Monte Carlo simulations and comparison with experimental data support very high scattering coefficients on the order of 500 cm(-1). Furthermore, the data evaluation shows that photons with a particular propagation time through the sample contain a higher chemical contrast than other propagation times or than steady-state information. In conclusion, time-resolved NIR spectroscopy yields more information about solid pharmaceutical samples than conventional steady-state spectroscopy

Fiber-optic probe for noninvasive real-time determination of tissue optical properties at multiple wavelengths

We present a compact, fast, and versatile fiber-optic probe system for real-time determination of tissue optical properties from spatially resolved continuous-wave diffuse reflectance measurements. The system collects one set of reflectance data from six source-detector distances at four arbitrary wavelengths with a maximum overall sampling rate of 100 Hz. Multivariate calibration techniques based on two-dimensional polynomial fitting are employed to extract and display the absorption and reduced scattering coefficients in real-time mode. The four wavelengths of the current configuration are 660, 785, 805, and 974 nm, respectively. Cross-validation tests on a 6 x 7 calibration matrix of Intralipid-dye phantoms showed that the mean prediction error at, e.g., 785 nm was 2.8% for the absorption coefficient and 1.3% for the reduced scattering coefficient. The errors are relative to the range of the optical properties of the phantoms at 785 nm, which were 0-0.3/cm for the absorption coefficient and 6-16/cm for the reduced scattering coefficient. Finally, we also present and discuss results from preliminary skin tissue measurements. (C) 2001 Optical Society of Americ