No Difference in Muscle Basal Oxygenation in a Bedridden Population Pre and Post Rehabilitation

Long periods of bed rest for elderly population, due to a femur fracture event, can cause a deterioration in the muscular capacity. Therefore, monitoring of the muscle oxidative capacity in this fragile population is necessary to define the muscular oxidative metabolism state before and after a rehabilitation period. The time-domain near-infrared spectroscopy (TD-NIRS) technique enables the absolute values to be calculated for hemodynamic parameters such as oxy- (O2Hb), deoxy- (HHb), total- (tHb) haemoglobin, and tissue oxygen saturation (SO2) of the muscular tissue. In this work, we have characterized vastus lateralis muscle hemodynamics during a baseline period at two different time points: after the surgery (PRE) and after 15 days of rehabilitation (POST). The mean values for the absolute values of the hemodynamic parameters were: O2Hb_PRE = 49.1 ± 14.1 μM; O2Hb_POST = 47.1 ± 13.4 μM; HHb_PRE = 28.3 ± 10.3 μM; HHb_POST = 26.7 ± 9.9 μM; tHb_PRE = 77.3 ± 23.6 μM; tHb_POST = 73.8 ± 21.4 μM; SO2_PRE = 63.9 ± 4.0% and SO2_POST = 64.9 ± 5.6%. The hemodynamic parameters did not show significant differences at both group and single subject level. These results suggest that for this kind of population, the baseline of the hemodynamic parameters is not the best one to consider to assess the rehabilitation progresses in terms of muscular oxidative metabolism.

Monitoring the haemodynamic response to visual stimulation in glaucoma patients

In this paper, we used time-domain functional near infrared spectroscopy (TD-fNIRS) to evaluate the haemodynamic response function (HRF) in the occipital cortex following visual stimulation in glaucomatous eyes as compared to healthy eyes. A total of 98 subjects were enrolled in the study and clinically classified as healthy subjects, glaucoma patients (primary open-angle glaucoma) and mixed subjects (i.e. with a different classification for the two eyes). After quality check data were used from HRF of 73 healthy and 62 glaucomatous eyes. The amplitudes of the oxygenated and deoxygenated haemoglobin concentrations, together with their latencies with respect to the stimulus onset, were estimated by fitting their time course with a canonical HRF. Statistical analysis showed that the amplitudes of both haemodynamic parameters show a significant association with the pathology and a significant discriminating ability, while no significant result was found for latencies. Overall, our findings together with the ease of use and noninvasiveness of TD-NIRS, make this technique a promising candidate as a supporting tool for a better evaluation of the glaucoma pathology.

Determination of reference values for optical properties of liquid phantoms based on Intralipid and India ink

A multi-center study has been set up to accurately characterize the optical properties of diffusive liquid phantoms based on Intralipid and India ink at near-infrared (NIR) wavelengths. Nine research laboratories from six countries adopting different measurement techniques, instrumental set-ups, and data analysis methods determined at their best the optical properties and relative uncertainties of diffusive dilutions prepared with common samples of the two compounds. By exploiting a suitable statistical model, comprehensive reference values at three NIR wavelengths for the intrinsic absorption coefficient of India ink and the intrinsic reduced scattering coefficient of Intralipid-20% were determined with an uncertainty of about 2% or better, depending on the wavelength considered, and 1%, respectively. Even if in this study we focused on particular batches of India ink and Intralipid, the reference values determined here represent a solid and useful starting point for preparing diffusive liquid phantoms with accurately defined optical properties. Furthermore, due to the ready availability, low cost, long-term stability and batch-to-batch reproducibility of these compounds, they provide a unique fundamental tool for the calibration and performance assessment of diffuse optical spectroscopy instrumentation intended to be used in laboratory or clinical environment. Finally, the collaborative work presented here demonstrates that the accuracy level attained in this work for optical properties of diffusive phantoms is reliable.

Non-contact time-resolved diffuse reflectance imaging at null source-detector separation

We report results of the proof-of-principle tests of a novel non-contact tissue imaging system. The system utilizes a quasi-null source-detector separation approach for time-domain near-infrared spectroscopy, taking advantage of an innovative state-of-the-art fast-gated single photon counting detector. Measurements on phantoms demonstrate the feasibility of the non-contact approach for the detection of optically absorbing perturbations buried up to a few centimeters beneath the surface of a tissue-like turbid medium. The measured depth sensitivity and spatial resolution of the new system are close to the values predicted by Monte Carlo simulations for the inhomogeneous medium and an ideal fast-gated detector, thus proving the feasibility of the non-contact approach for high density diffuse reflectance measurements on tissue. Potential applications of the system are also discussed.

Study of neurovascular and autonomic response in a divided attention test by means of EEG, ECG and NIRS signals

We evaluated neurovascular and autonomic response to a Divided Attention task within a group of 16 healthy subjects, by means of Electroencephalography, Electrocardiography, functional Near Infrared Spectroscopy techniques, acquired simultaneously. We exctracted Alpha (8-13,5 Hz) and Beta (13,5-30 Hz) power rhythms with a spectral autoregressive residual model, and inter-beat-interval (RR series) and separated superficial (extracortical) and depth NIRS contribution. Cross Correlation Function at different time lags was then calculated between each signal and the task, modeled as a square wave and among couples of signals, in order to evaluate the sequence of activation of the different physiological districts involved and the common information shared. Results showed the presence of a cascade of responses and a strong influence by the block task on each signal, representative of the neurovascular coupling elicited by the cognitive cerebral activation.

Bandpass effects in time-resolved diffuse spectroscopy

This paper discusses the spectral distortions occurring when time-resolved spectroscopy of diffusive media is performed illuminating with a wide bandpass. It is shown that the spectral region within the bandpass that exhibits the lowest absorption will dominate the resulting time-resolved curve, leading to significant underestimations of absorption as well as distortions in the spectral shape (including shifts in peak positions). Due to the nonlinear behavior of absorption, this effect becomes even more pronounced when including longer and longer photon path lengths. First, a theoretical treatment of the problem is given, and then the distortion is described by time-resolved reflectance simulations and experimental measurements of lipid and water samples. A spectrally constrained data analysis is proposed that takes into account the spectrum of the light injected into the sample, used to overcome the distortion and improve the accuracy of the estimation of chromophore concentrations from absorption spectra. Measurements on a lipid sample show a reduction of the error from 30% to 6%.

Time-resolved optical spectroscopy of wood

We have proposed and experimentally demonstrated that picosecond time-resolved optical spectroscopy in the visible/near-infrared (NIR) region (700-1040 nm) is a useful technique for noninvasive characterization of wood. This technique has been demonstrated on both softwood and hardwood samples treated in different ways simulating the aging process suffered by waterlogged woods. In all the cases, alterations of absorption and scattering spectra were observed, revealing changes of chemical and structural composition.

Time-resolved spectrally constrained method for the quantification of chromophore concentrations and scattering parameters in diffusing media

We have devised and experimentally validated, on tissue-simulating phantoms and in vivo, a time-resolved spectral fitting analysis for direct assessment of chromophore concentrations and scattering parameters. Experimental data have been acquired with a time-resolved broadband system based on supercontinuum light generated in a photonic crystal fiber and a 32 channel Time Correlated Single Photon Counting system. The novel method is more robust than conventional techniques, especially at low signal-to-noise ratio.

Analyzing integrated circuits at work with a picosecond time-gated imager

A system based on a picosecond time-gated image intensifier is proposed for non-contact testing of CMOS circuits. The apparatus allows one to record the temporal evolution of the luminescence emitted during transistor switching as a function of the position inside the chip. The system is characterized by an intrinsic parallelism in the spatial dimensions. This feature is noticeable for studying wide sections of complex circuits, like microprocessors and random access memories, where multiple electrical events occur simultaneously. Experiments on a CMOS inverter chain and on a static memory have been carried out, in order to demonstrate the applicability of a picosecond time-gated imager to circuit analysis.

Multi-wavelength time domain optical mammography

A time-resolved optical mammograph operating at 7 wavelengths (637, 683, 785, 832, 905, 916, and 975 nm) in compressed breast geometry was developed. Its clinical application was started on patients bearing malignant and benign lesions. Late gated intensity images are used to obtain information on the spatial distribution of the absorption properties of breast. Scattering images derived from the diffusion theory are also applied for lesion detection and characterization. Cancers are identified in intensity images at short wavelengths, due to the high blood content, while cysts are typically characterized by low scattering at all wavelengths. The increase (from 4 to 7) in the number of wavelengths as compared to the previous versions of the instrument aims at improving the robustness of the fitting procedures for a better estimate of tissue composition and structure and of physiological parameters. Moreover, the new wavelengths contribute to the qualitatively identify tissue composition from intensity images, and could assist lesion detection.

Determination of visible near-IR absorption coefficients of mammalian fat using time- and spatially resolved diffuse reflectance and transmission spectroscopy

In-vivo optical spectroscopy and the determination of tissue absorption and scattering properties have a central role in the development of novel optical diagnostic and therapeutic modalities in medicine. A number of techniques are available for the optical characterization of tissue in the visible near-IR region of the spectrum. An important consideration for many of these techniques is the reliability of the absorption spectrum of the various constituents of tissue. The availability of accurate absorption spectra in the range 600 to 1100 nm may allow for the determination of the concentration of key tissue constituents such as oxy- and deoxy-hemoglobin, water, and lipids. The objective of the current study is the determination of a reliable absorption spectrum of lipid(s) that can be used for component analysis of in-vivo spectra. We report the absorption spectrum of a clear purified oil obtained from pig lard. In the liquid phase above 36 degrees C, the oil is transparent and thus suitable for collimated transmission measurements. At room temperature, the oil is a solid grease that is highly scattering. The absorption and scattering properties in this solid phase are measured using time- and spatially resolved diffuse reflectance spectroscopy. Using these three independent measurement techniques, we have determined an accurate estimate for the absorption spectrum of mammalian fat.

Liquid phantom for investigating light propagation through layered diffusive media

A liquid phantom for investigating light propagation through layered diffusive media is described. The diffusive medium is an aqueous suspension of calibrated scatterers and absorbers. A thin membrane separates layers with different optical properties. Experiments showed that a material with scattering properties should be used for the membrane to avoid the perturbation due to the guided propagation that occurs through a transparent layer. Examples of measurements on a three-layered medium are reported both in the cw and in the time domain.

Do shorter wavelengths improve contrast in optical mammography?

The detection of tumours with time-resolved transmittance imaging relies essentially on blood absorption. Previous theoretical and phantom studies have shown that both contrast and spatial resolution of optical images are affected by the optical properties of the background medium, and high absorption and scattering are generally beneficial. Based on these observations, wavelengths shorter than presently used (680-780 nm) could be profitable for optical mammography. A study was thus performed analysing time-resolved transmittance images at 637, 656, 683 and 785 nm obtained from 26 patients bearing 16 tumours and 15 cysts. The optical contrast proved to increase upon decreasing wavelengths for the detection of cancers in late-gated intensity images, with higher gain in contrast for lesions of smaller size (<1.5 cm diameter). For cysts either a progressive increase or decrease in contrast with wavelength was observed in scattering images.

Reconstruction of absorber concentrations in a two-layer structure by use of multidistance time-resolved reflectance spectroscopy

The characterization of a two-layer structure was investigated by use of time-resolved reflectance over a wide spectral range. We exploited the nonlinear dependence of the measured spectra on the upper-and lower-layer properties to formulate an algorithm for the recovery of absorber concentrations in both layers. The method assumes that the spectral features of the key absorbers are known, but it does not rely on a priori knowledge of the layer thickness. Phantom tests confirmed the accuracy of the estimate of the absorber concentrations to within 10% for thickness values ranging from 0.3 to 1.2 cm. Multidistance absorption spectra from 610 to 1000 nm were obtained in vivo from the forearms of human subjects, allowing us to estimate the concentration of key tissue constituents in a two-layer approximation. Good agreement between the reconstructed spectra and the experimental data taken from two volunteers with opposite predominance of adipose and muscular tissues demonstrated the validity of this approach.

In vivo optical characterization of human tissues from 610 to 1010 nm by time-resolved reflectance spectroscopy

A fully automated system for time-resolved reflectance spectroscopy based on tunable mode-locked laser sources and on time-correlated single-photon counting for the detection of time-resolved reflectance data was applied to the evaluation of the optical properties of biological tissues (arm, abdomen and forehead) in vivo from 610 to 1010 nm. The scattering decreases progressively with increasing wavelength, while the absorption line shapes show the typical spectral features of the principal tissue components (haemoglobin, water and lipid), with different weights depending on the tissue type. The best fit of the absorption spectra measured in vivo with the spectra of the pure constituents yielded information on the percentage composition of the different tissues. The interpretation of transport scattering spectra with Mie theory provided information on tissue structure.

Effects of photodynamic therapy on the absorption properties of disulphonated aluminum phthalocyanine in tumor-bearing mice

Time-resolved reflectance spectroscopy was performed on tumor-bearing mice, administered with disulphonated aluminum phthalocyanine (AlS(2)Pc, 5 mg/kg body weight), before, during and after photodynamic therapy. This allowed us to evaluate the absorption spectrum of AlS(2)Pc in vivo from 610 to 700 nm, and to investigate how the therapeutic irradiation affects it. Two tumor locations (intraderma on the back and intramuscular in the leg), and two uptake times (3 and 12 h) were considered. As already observed previously, the absorption spectrum of AlS(2)Pc in vivo is centered at 680-685 nm. The irradiation causes a blue-shift of the measured line shape, more or less marked depending on the experimental conditions. A reduction in absorption is also often observed upon illumination with therapeutic light doses.

Nondestructive quantification of chemical and physical properties of fruits by time-resolved reflectance spectroscopy in the wavelength range 650-1000 nm

Time-resolved reflectance spectroscopy can be used to assess nondestructively the bulk (rather than the superficial) optical properties of highly diffusive media. A fully automated system for time-resolved reflectance spectroscopy was used to evaluate the absorption and the transport scattering spectra of fruits in the red and the near-infrared regions. In particular, data were collected in the range 650-1000 nm from three varieties of apples and from peaches, kiwifruits, and tomatoes. The absorption spectra were usually dominated by the water peak near 970 nm, whereas chlorophyll was detected at 675 nm. For all species the scattering decreased progressively with increasing wavelength. A best fit to water and chlorophyll absorption line shapes and to Mie theory permitted the estimation of water and chlorophyll content and the average size of scattering centers in the bulk of intact fruits.

Time-resolved DNA-microarray reading by an intensified CCD for ultimate sensitivity

We describe a novel technique for DNA-microarray reading based on time-resolved fluorescence measurements. We used an intensified CCD camera with picosecond resolution to acquire a set of time-delayed fluorescence images from a mutation DNA microarray marked with cyanine 3. We measured the fluorescence lifetimes of the marker and the background separately, and we used this information to calculate the amplitude map of the marker, starting from the time-delayed images. This procedure allowed us to identify hybridized spots that are not visible in fluorescence images acquired with continuous-wave detection.

Fluorescence imaging during photodynamic therapy of experimental tumors in mice sensitized with disulfonated aluminum phthalocyanine

A fluorescence imaging system was used to monitor the emission of disulfonated aluminum phthalocyanine (AlS2Pc) during the photodynamic therapy (PDT) of murine tumors. Cells of the MS-2 fibrosarcoma were injected in mice in two compartments in order to cause the development of tumors in different host tissues. Two drug doses and two uptake times were considered. Moreover, the fluorescence of the AlS2Pc was excited using two wavelengths on the opposite sides of the absorption peak to detect a possible change in the absorption spectrum of the sensitizer induced by the PDT. In the tumors, the treatment induces a variation of the fluorescence intensity: in some mice a mild photobleaching takes place, in others a fluorescence enhancement occurs. Which effect predominates depends on the experimental conditions, even though a large spread of data was found amongst mice of the same group. In all mice, independently of the drug dose, uptake time or tumor compartment, a marked increase in the fluorescence signal takes place at the borders of the irradiated area. To quantify this effect we evaluated the ratio between the fluorescence intensities in the peritumoral area and in the tumor itself. This ratio increases monotonically during the PDT, showing a different behavior with the two excitation wavelengths. This indicates that the AlS2Pc absorption spectrum shifts toward shorter wavelengths as a result of the irradiation.

Effects of the menstrual cycle on the red and near-infrared optical properties of the human breast

Time-resolved reflectance and transmittance spectroscopy was applied to measure in vivo the absorption and transport scattering spectra of the female breast from 610 to 1010 nm. Three measurement configurations were used to probe different breast regions, and data were collected two or three times in each of the five phases of the menstrual cycle. The absorption spectra were best-fitted with a linear combination of the spectra of the main tissue constituents (water, lipids, oxy- and deoxyhemoglobin). This allowed us to evaluate percentage contents of water and lipids, total hemoglobin content and hemoglobin oxygen saturation. The scattering spectra were interpreted with a function derived from Mie theory, providing information on the density and average size of the tissue scatterers. Significant changes in the estimated variables were observed with measurement geometry, reflecting the heterogeneous nature of the breast, and with time, in agreement with expected physiological changes over the menstrual cycle.

Nitric oxide and salt sensitivity

Studies in laboratory animals suggest that altered nitric oxide (NO) production may be associated with salt sensitivity. In this investigation we determined whether the endogenous NO production was altered in salt-sensitive human subjects when salt intake was changed. Salt sensitivity was assessed from the magnitude of the blood pressure (BP) lowering obtained when the salt intake was reduced from high to a low intake. The combined urinary excretion of nitrites and nitrates, the major metabolites of NO, was employed as an index of endogenous NO production. Salt-sensitive subjects (n = 23) were older, heavier, and had greater waist-to-hip ratios and higher baseline BP than salt-resistant individuals (n = 25). In salt-sensitive subjects, mean blood pressure (MBP) decreased 11.8+/-0.7 mm Hg, and NO metabolite excretion increased from 823+/-102 to 1530+/-148 mmol/24 h, when salt intake was reduced from 316 to 28 micromol/day. NO metabolite excretion was 45% lower during high salt (0.66+/-0.1 micromol/mg creatinine) than during low salt intake (1.12+/-0.1 micromol/mg creatinine) (P < .001). In contrast, when salt intake was reduced, salt-resistant subjects exhibited no significant mean changes in BP or NO metabolite excretion. During low salt intake, NO metabolite excretion (micromol/ day) was significantly higher in salt-sensitive individuals. The magnitude of decrease of systolic blood pressure, diastolic blood pressure, or MBP induced by reducing salt intake was not related to the increase in urinary excretion of NO metabolite levels (r2 = 0.009; P = .66). In summary, to the extent that urinary NO metabolite levels reflect the activity of the endogenous NO system, our results support the view that salt sensitivity may in part be determined by an inability to increase or to sustain NO production in response to high salt. Insufficient NO production during high salt may in turn lead to altered pressure-natriuresis relationships and to an increase in BP. The possibility that the increase in BP induced by high salt intake in salt-sensitive individuals could be the key factor in reducing NO metabolite levels can not be ruled out.

Quantification by random walk of the optical parameters of nonlocalized abnormalities embedded within tissuelike phantoms

We have extended a random-walk theory that uses time-dependent contrast functions to quantify the cross section and the corrected scattering and absorption coefficients of abnormal nonlocalized targets from time-of-flight (TOF) data obtained in time-resolved transillumination experiments. Experimental TOF's are used to show that this newly developed random-walk method is able to quantify the size and the optical properties of embedded nonlocalized targets in with an error rate of </=25%.

Preliminary evaluation of two fluorescence imaging methods for the detection and the delineation of basal cell carcinomas of the skin

BACKGROUND AND OBJECTIVE

Fluorescence techniques can provide powerful noninvasive means for medical diagnosis, based on the detection of either endogenous or exogenous fluorophores. The fluorescence of delta-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) has already shown promise for the diagnosis of tumors. The aim of the study was to investigate the localization of skin tumors after the topical application of ALA, by detecting the PpIX fluorescence either in the spectral or in the time domain. STUDY DESIGN/MATERIALS N AND METHODS: Two fluorescence imaging systems were used to identify basal cell carcinomas of the skin in humans, after topical application of 20% ALA ointment. Both systems rely on the comparison between the exogenous and the endogenous fluorescence, performed either in the spectral domain or in the time domain. The first system works by using three images acquired through different spectral filters, whereas the second one measures the spatial map of the average fluorescence lifetime of the sample.

RESULTS

A clear demarcation of skin malignancies was successfully performed in vivo noninvasively with both fluorescence imaging systems.

CONCLUSION

The two complementary approaches considered in the present study show promise for skin tumor detection and delineation based on specific fluorescence features.

Photophysical studies of A2-E, putative precursor of lipofuscin, in human retinal pigment epithelial cells

With age, human retinal pigment epithelial cells accumulate lipofuscin that can absorb photons in the visible range leading to light-induced damage and impaired vision. A putative precursor of lipofuscin, 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E, 5E,7E- octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-trimethyl-1 - cyclohexen-1-yl)-1E,3E,5E-hexatrienyl]-pyridinium (A2-E), has recently been isolated and characterized from aged human retinal pigment epithelial cells. We have found that A2-E inhibits the growth of human retinal pigment epithelial cells at concentrations greater than 1 microM. Time-resolved fluorescence measurements of 1 microM A2-E in solution, performed under 413 nm excitation, showed that fluorescence wave forms integrated across the spectrum (450-600 nm) were best-fitted with three decay times in the nanosecond and subnanosecond time scale: 6.6, 1.9 and 0.33 ns. Untreated retinal pigment epithelial cells were characterized by three fluorescence lifetimes: 6.3, 1.7 and 0.35 ns. In retinal pigment epithelial cells treated with 1 microM A2-E, the fluorescence decay was significantly faster, with the marked presence (approximately equal to 30%) of a fourth short lifetime (0.12 ns). These fluorescence decay times for A2-E bound to human retinal pigment epithelial cells are similar to those of lipofuscin granules isolated from aged human retinal pigment epithelial cells. This similarity supports the hypothesis that A2-E is a precursor of lipofuscin and suggests that A2-E may play a role in the overall light damage associated with age-related retinal diseases.

Compact tissue oximeter based on dual-wavelength multichannel time-resolved reflectance

We developed a compact dual-wavelength multichannel tissue oximeter based on the time-correlated single-photon counting (TCSPC) technique. The light sources are two pulsed diode lasers (output wavelengths of 672 and 818 nm, an average power of 1 mW, a pulse duration of 100 ps, and a pulse-repetition rate as high as 80 MHz). The time-resolved reflectance photons are detected by a multianode photomultiplier, and the output signals are redirected by a router to different memory blocks of the TCSPC personal computer board. The system's accuracy in determining the absorption microa and the reduced-scattering micros' coefficients and in reconstructing absorber concentrations in diffusive media was tested on phantoms. Preliminary in vivo tissue-oxygenation measurements were performed on healthy volunteers under different physiological conditions with a minimum acquisition time of 100 ms and an injected power of less than 100 microW.

Imaging with diffusing light: an experimental study of the effect of background optical properties

The overall image quality and diagnostic potential of time-resolved transmittance imaging depend on sensitivity to optical contrast, capacity to discriminate scattering from absorption contributions, and spatial resolution. We have investigated experimentally the effects of the optical properties of the background medium on the overall image quality of optical imaging based on fitting the experimental data to the solution of the diffusion equation and on time gating. Images were acquired from phantoms with different background optical properties, while the optical contrast between inhomogeneities and background is kept constant. Data were collected every 0.2 cm over a 6 cm x 6 cm area from realistic tissue phantoms containing cylindrical inhomogeneities (1 cm high and 1 cm in diameter) embedded in a 5-cm-thick turbid slab. The optical coefficients of the background were varied in the ranges of 5-15 cm(-1) for transport scattering and 0.02-0.08 cm(-1) for absorption. The optical contrast for the inclusions was kept at values of -50% and +50% for the scattering and -75% and +300% for the absorption. The results show that both high scattering and high absorption are beneficial.

Antitumor efficacy of the combination of photodynamic therapy and chemotherapy in murine tumors

Photodynamic therapy (PDT) is based on the administration of tumor-localizing photosensitizers followed by light exposure of the tumor mass. The photocytotoxic effects are mainly caused by the generation of singlet oxygen. Recently, PDT has been proposed for use in combination with anticancer chemotherapy with a view to exploiting any additive antitumor effect. We investigated the effect of PDT with photoactivated aluminum disulfonated phthalocyanine (AlS2Pc) combined with the antiblastic drugs Adriamycin (ADR) and cisplatinum (CDDP) on murine tumors. Mice bearing L1210 leukemia and P388 lymphoma were treated with ADR or CDDP and subsequently treated with PDT. Low chemotherapy doses were ineffective, but the combination of antiblastic drugs + PDT had a significantly additive antitumor effect. In conclusion, with this combined therapy we were able to greatly reduce the effective doses of antiblastic drugs, thus lowering their toxic effects on normal host tissues.

A solid tissue phantom for photon migration studies

A solid tissue phantom made of agar, Intralipid and black ink is described and characterized. The preparation procedure is fast and easily implemented with standard laboratory equipment. An instrumentation for time-resolved transmittance measurements was used to determine the optical properties of the phantom. The absorption and the reduced scattering coefficients are linear with the ink and Intralipid concentrations, respectively. A systematic decrease of the reduced scattering coefficient dependent on the agar content is observed, but can easily be managed. The phantom is highly homogeneous and shows good repeatability among different preparations. Moreover, agar inclusions can be easily embedded in either solid or liquid matrixes, and no artefacts are caused by the solid-solid or solid-liquid interfaces. This allows one to produce reliable and realistic inhomogeneous phantoms with known optical properties, particularly interesting for studies on optical imaging through turbid media.

Fluorescence lifetime imaging of experimental tumors in hematoporphyrin derivative-sensitized mice

Tumor detection has been carried out in mice sensitized with hematoporphyrin derivative (HpD) by measuring the spatial distribution of the fluorescence lifetime of the exogenous compound. This result has been achieved using a time-gated video camera and a suitable mathematical processing that led to the so-called "lifetime images." Extensive experimental tests have been performed on mice bearing the MS-2 fibrosarcoma or the L1210 leukemia. Lifetime images of mice show that the fluorescence decay of HpD is appreciably slower in the tumor than in healthy tissues nearby, allowing a reliable detection of the neoplasia. The lengthening of the lifetime in tumors depends little on the drug dose, which in our experiments could be lowered down to 0.1 mg/kg body weight, still allowing a definite tumor detection. In order to ascertain the results achieved with the imaging apparatus, high-resolution spectroscopy, based on a time-correlated single photon counting system, has also been performed to measure the fluorescence lifetime of the drug inside the tumor and outside. The outcomes obtained with two techniques are in good agreement.

Hb Osler [beta 145(HC2)Tyr-->Asp] results from posttranslational modification

We studied two members of an African American family with erythrocytosis. An abnormal hemoglobin variant with an electrophoretic pattern on cellulose acetate similar to Hb J was identified. The oxygen dissociation curve using whole blood was biphasic, dramatically left-shifted, and hyperbolic. Sequence analysis of DNA from the proband showed heterozygosity for a T-->A change at the first position of codon 145 in the beta-globin gene which results in the substitution of an asparagine residue for normal tyrosine. The second cycle of C-terminal amino acid sequence analysis of a mixture of alpha- and beta-globin chains showed tyrosine, aspartic acid, and small amounts of asparagine. Collectively, these results indicate the existence of a mutation at codon 145 of the beta-globin gene which encodes for asparagine instead of tyrosine, and that asparagine then undergoes a partial posttranslational deamidation to aspartic acid. This amino acid substitution corresponds to Hb Osler, which is a high oxygen affinity hemoglobin variant, initially described to be caused by a substitution of Tyr-->Asp at beta 145. Posttranslational amino acid modification may constitute an important component in the pathophysiology of hemoglobinopathies.

Experimental test of theoretical models for time-resolved reflectance

Four different expressions, derived from the diffusion theory or the random walk model, were used to fit time-resolved reflectance data for the evaluation of tissue optical properties. The experimental reflectance curves were obtained from phantoms of known optical parameters (absorption and transport scattering coefficients) covering the range of typical values for biological tissues between 600 and 900 nm. The measurements were performed using an instrumentation for time-correlated single-photon counting. The potential of the four methods in the assessment of the absorption and transport scattering coefficients was evaluated in terms of absolute error, linearity error, and dispersion of data. Each method showed different performances depending on the optical properties of the sample and the experimental conditions. We propose some criteria for the optimal choice of the fitting method to be used in different applications.

Time-resolved imaging on a realistic tissue phantom: μ(s)' and μ(a) images versus time-integrated images

A method is proposed by which we construct images through turbid media, plotting directly either the transport-scattering coefficient μ(s) ' or the absorption coefficient μ(a). These optical parameters are obtained from the best fit of the time-resolved transmittance curves with a diffusion model. Measurements were performed with a time-correlated single-photon counting system on realistic tissue phantoms simulating a tumor mass within a breast. Images were obtained with an incident power of <1 mW and an acquisition time of 1 s/point. Comparison of μ(s) ' and μ(a) images with time-integrated images constructed from the same experimental data shows that the fitting method discriminates between scattering and absorption inhomogeneities and improves image quality for scattering but not for absorption inhomogeneities.

In vivo absorption spectrum of disulphonated aluminium phthalocyanine in a murine tumour model

The absorption spectrum of aluminum phthalocyanine with an average disulphonation of 2.1 (hereafter called disulphonated aluminum phthalocyanine, A1S2Pc) was measured in vivo in a murine tumour model by means of time-resolved reflectance. Mice bearing the L1210 leukaemia were administered 2.5 or 5 mg/kg body weight (b.w.) of A1S2Pc intraperitoneally. Reflectance measurements were performed in the 650-695 nm range before and 1, 4 and 7 h after the drug administration. Fitting of the data with the diffusion theory allowed us to assess the absorption coefficient in both conditions (i.e. before and after). As a difference between the latter and the former data, the in vivo absorption spectrum of A1S2Pc was evaluated. 1 h after the administration of 2.5 mg/kg b.w. A1S2Pc, the absorption peak was centred at 685 nm, red-shifted about 15 nm with respect to the spectrum in aqueous solution. For the lower dose, the absorption line shapes 4 and 7 h after the administration remained very similar. The red shift of the absorption spectrum is consistent with the therapeutic efficacy of the photodynamic therapy which was measured at 672, 685 and 695 nm, and proved to be maximum at 685 nm for both the L1210 leukaemia and the MS-2 fibrosarcoma. With the higher drug dose, the absorption spectra taken from different animals showed significant differences. In particular, in some mice the line shape was similar to that measured with 2.5 mg/kg b.w., while in other subjects it showed a broadening or a second peak at shorter wavelengths. Measurements on some animals were performed also 18 and 24 h after the injection of 5 mg/kg b.w., leading to no time evolution or to a progressive line shape narrowing.

Study of photoablation of rabbit corneas by Er:YAG laser

BACKGROUND AND OBJECTIVE

This work studied the ablation mechanisms of rabbit corneas by the Erbium:YAG laser. The occurrence of thermal and mechanical damages in the tissue as a function of the laser fluence was also investigated.

STUDY DESIGN/MATERIALS AND METHODS

The experiments were performed both on enucleated eyes and in vivo. An ultrafast imaging technique was used to investigate the dynamic evolution of the ablation. The treated samples underwent histological and ultrastructural study.

RESULTS

A single high fluence laser shot led to the complete removal of the epithelium by a photomechanical effect. In eyes whose epithelium was manually removed, high fluence pulses resulted in evident tears in the stroma, whereas low fluence pulses led to few microns deep incisions, characterized by limited mechanical and thermal damages.

CONCLUSION

The photomechanical action plays a significant role in the ablation of the cornea by Erbium laser. Precise control of the fluence is required to avoid cracking phenomena in the stroma.

delta-Aminolevulinic acid induced fluorescence in tumour-bearing mice

The potential of protoporphyrin IX fluorescence induced by the systemic administration of delta-aminolevulinic acid (ALA) for the detection of tumours was tested in three different murine models (MS-2 fibrosarcoma, L1210 leukaemia, and Lewis lung carcinoma). Time-gated fluorescence images were acquired up to 4 h after the intraperitoneal injection of ALA (200 mg (kg body mass (BM))-1). For comparison images were acquired also after the administration of 25 mg (kg BM)-1 of haematoporphyrin derivative. The latter drug was characterized by better localization in the tumour area, leading to higher fluorescence contrast between neoplastic mass and surrounding healthy tissue, and consequently was preferable for tumour diagnosis in all the models under study.

Study of porphyrin fluorescence in tissue samples of tumour-bearing mice

A time-gated fluorescence-imaging technique was applied to study the distribution of sensitizer in porphyrin-treated tumour-bearing mice. The animals were administered with either haematoporphyrin derivative (HpD) or Photofrin and sacrificed 4 or 12 h later. Fluorescence images were acquired from tumour, skin, muscle, fat, brain, lymph node, bowel and bone of both treated and untreated mice. The results obtained with HpD and Photofrin are similar. In images acquired 30 ns after excitation a bright exogenous fluorescence allows clear detection of the tumour. Nevertheless, the images show that porphyrins localize with different concentrations in all the examined tissues except the brain. Moreover, an appreciable long-living endogenous emission was observed in the bone.