Time-domain diffuse optics with 8.6 mm2 fast-gated SiPM for extreme light harvesting.

Fast time-gated single-photon detectors demonstrated high depth sensitivity in the detection of localized absorption perturbations inside scattering media, but their use for in vivo clinical applications-such as functional imaging of brain activation-was impaired by their small (<0.04mm2) active area. Here, we demonstrate, both on phantoms and in vivo, the performance of a fast-gated digital silicon photomultiplier (SiPM) that features an overall active area of 8.6mm2, overcoming the photon collection capability of established time-gated single-pixel detectors by orders of magnitude, enabling deep investigations within scattering media and high signal-to-noise ratios at late photon arrival times.

Enhanced diffuse optical tomographic reconstruction using concurrent ultrasound information.

Multimodal imaging is an active branch of research as it has the potential to improve common medical imaging techniques. Diffuse optical tomography (DOT) is an example of a low resolution, functional imaging modality that typically has very low resolution due to the ill-posedness of its underlying inverse problem. Combining the functional information of DOT with a high resolution structural imaging modality has been studied widely. In particular, the combination of DOT with ultrasound (US) could serve as a useful tool for clinicians for the formulation of accurate diagnosis of breast lesions. In this paper, we propose a novel method for US-guided DOT reconstruction using a portable time-domain measurement system. B-mode US imaging is used to retrieve morphological information on the probed tissues by means of a semi-automatical segmentation procedure based on active contour fitting. A two-dimensional to three-dimensional extrapolation procedure, based on the concept of distance transform, is then applied to generate a three-dimensional edge-weighting prior for the regularization of DOT. The reconstruction procedure has been tested on experimental data obtained on specifically designed dual-modality silicon phantoms. Results show a substantial quantification improvement upon the application of the implemented technique. This article is part of the theme issue 'Synergistic tomographic image reconstruction: part 2'.

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.

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.

Characterization of the fluorescent morphological structures in human arterial wall using ultraviolet-excited microspectrofluorimetry.

In this study, the fluorescent morphological structures in normal coronary artery, normal aorta, and atherosclerotic aorta were histochemically identified and spectroscopically characterized in situ using ultraviolet-excited microspectrofluorimetry. Excitation wavelengths of 290 nm and 310/312 nm were employed to observe two distinct fluorescence bands, with peak emission wavelengths near 335 nm and 380 nm, respectively. Emission of the short wavelength 335 nm band, previously assigned to tryptophan residues in tryptophan-containing proteins, was observed from all the morphological structures in the vessel walls and was isolated in groups of smooth muscle cells in aorta and coronary artery media. The long wavelength 380 nm band was assigned to distinct fluorophores associated with the structural proteins collagen and elastin and was observed in collagen fibers and elastic fibers, respectively. The corresponding morphological structures in normal aorta, normal coronary artery, and atherosclerotic aorta exhibited similar fluorescence lineshapes. In atherosclerotic plaque, a distinct fluorescence band, peaking near 370 nm, was observed in the emission from both ceroid granules and necrotic core. Using a simple, quantitative model, differing contributions of collagen, elastin, and tryptophan-containing protein fluorescence were shown to account for over 95% of the emission from the intima, media, and adventitia layers of non-necrotic aorta and coronary artery.

Efficacy of photodynamic therapy against doxorubicin-resistant murine tumors.

Photodynamic therapy (PDT) is a relatively new cancer treatment modality that employs light excitation of a photosensitizer to yield cytotoxic oxygen-related species. In the present study we explored whether PDT would have therapeutic effect against doxorubicin-resistant murine tumors. We compared the efficacy of PDT with aluminium disulphonated phthalocyanine (A1S2Pc) and laser light on the doxorubicin-sensitive murine tumors, B16 melanoma (B16), L1210 leukemia (L1210), P388 lymphoma (P388) and the corresponding doxorubicin-resistant lines (B16/Dx, L1210/Dx and P388/Dx). Mice bearing L1210-L1210/Dx, P388-P388/Dx and B16-B16/Dx, were treated with 5 mg/kg of A1S2Pc and laser light (100 mW/cm2 x 10 min of exposure) or with doxorubicin (10 or 12 mg/kg i.v.). The results show that PDT is active versus all tumors while doxorubicin is effective only against the three sensitive tumor lines (L1210, P388 and B16). These observations suggest that PDT might be a beneficial alternative treatment for drug-resistant tumors.

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.

Comparative study of the therapeutic effect of photoactivated hematoporphyrin derivative and aluminum disulfonated phthalocyanines on tumor bearing mice.

Although the hematoporphyrin derivative (Hpd) is one of the most studied photosensitisers for photodynamic therapy (PDT), it is far from ideal. Therefore, many laboratories have been investigating a new group of sensitisers, the phthalocyanines. Particularly, in our laboratory we decided to study the aluminum disulfonated phthalocyanines (AlS2PC). They are chemically stable, readily soluble in water and have a strong absorption in the red part of the spectrum at 675 nm. Mice bearing the MS-2 fibrosarcoma treated with 5 mg/kg of AlS2PC survived indefinitely also using a low laser power of 100 mW/cm2 X 10' of exposure time, in contrast to experiments carried out with Hpd where the optical therapeutic laser power was 400 mW/cm2 X 10' and the dose of Hpd was 25 mg/kg. Furthermore, treatment of mice bearing the highly metastatic tumor, B16 melanoma, with 5 mg/kg of AlS2PC and laser light (100 mW/cm2 X 10'), significantly prolonged the survival time in respect to mice treated with 25 mg/kg of Hpd and laser light (400 mW/cm2 X 10').

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.

Pharmacokinetics and safety of iomeprol in healthy volunteers and in patients with renal impairment or end-stage renal disease requiring hemodialysis.

RATIONALE AND OBJECTIVES: To present the results of two studies conducted to evaluate the pharmacokinetics and safety of iomeprol in healthy volunteers and in patients with various degrees of renal impairment. METHODS: In these two open-label, single-dose, phase I studies, a 50-mL dose of iomeprol 400 was administered intravenously to a total of 30 subjects of either sex. In study 1, six healthy volunteers with normal renal function, six patients with mild renal failure, six patients with moderate renal failure, and four patients with severe renal failure were enrolled. In study 2, eight patients with end-stage renal disease requiring hemodialysis were enrolled. Safety was determined by predose and postdose (up to 10 days) measurement of vital signs, hematology, blood chemistry, urinalysis, electrocardiogram, physical examinations, and the incidence of adverse events. Pharmacokinetics was determined by measuring iomeprol levels in plasma, urine, feces, and dialysate samples, by using a validated high-performance liquid chromatography assay, up to 7 days after administration. RESULTS: The plasma concentration of iomeprol declined biexponentially in both healthy subjects and patients. As expected, mean body and renal clearances decreased progressively with increasing renal impairment, with a significant correlation with the glomerular filtration rate. The elimination half-life increased progressively with increasing renal impairment. The extraction efficiency of dialyser was estimated as approximately 40%, and dialysis clearance of iomeprol was approximately 1.26 mL. min-1. kg-1 (80.6 mL/min), slightly less than the body clearance previously observed in healthy subjects. It appears that dialysis is almost as efficient as renal function in healthy subjects in the removal of iomeprol. After a single dialysis session, approximately 58% of the dose was recovered in dialysate. Mild to moderate adverse events were reported by 17 of 30 subjects; none was clinically meaningful. One serious adverse event, unrelated to iomeprol, was reported. No clinically meaningful findings were noted for other safety parameters. CONCLUSIONS: Iomeprol was almost completely eliminated both in patients with renal impairment and in patients receiving dialysis. No dose adjustment appears to be necessary either in patients with renal impairment or with end-stage renal disease requiring hemodialysis. In this risk population, iomeprol 400 was safe and well tolerated.

Clinical experience with iomeprol in myelography and myelo-CT: clinical pharmacology and double-blind comparisons with iopamidol, iohexol, and iotrolan.

RATIONALE AND OBJECTIVES: To evaluate iomeprol, a new nonionic iodinated contrast medium, as a contrast agent for myelography and to compare it with iopamidol, iohexol, and iotrolan. METHODS: An extensive clinical program was conducted on more than 600 patients to assess iomeprol's pharmacokinetics, tolerability, safety, and efficacy after intrathecal injection. RESULTS: Pharmacokinetics study results showed that after intrathecal administration iomeprol is completely absorbed from the cerebrospinal fluid compartment; once absorbed into the systemic circulation, it is rapidly excreted, unmetabolized, by glomerular filtration. Dose-finding studies showed that the opacification produced by iomeprol depends on the injected dose. Although a dose-dependent increase in efficacy was observed, no differences in neurotolerability and safety were detected between the doses tested. Doses of iomeprol greater than 3 g I did not cause a greater incidence of adverse events and produced significantly better contrast efficacy. Comparative clinical trials showed that iomeprol and iopamidol, iohexol, and iotrolan always provided adequate opacification of the subarachnoid space, both in conventional myelography and myelo-CT, with adequate delineation of normal structures and pathologic processes. No serious adverse events occurred up to a total dose of 4.5 g I. No differences between the agents with regard to tolerance, adverse events, and effects on vital signs, physical examination, and neurologic examination were observed. CONCLUSIONS: Iomeprol is safe and effective and can be recommended for myelography and myelo-CT.

Iomeprol: current and future profile of a radiocontrast agent.

RATIONALE AND OBJECTIVES: To review the safety and efficacy profiles of iomeprol by examining the most indicative comparative clinical studies of iomeprol with widely used low-osmolar ionic or nonionic contrast agents, and to illustrate the recent development in iomeprol liposomal formulations for liver imaging and intravascular enhancement. METHODS: Randomized, double-blind, comparative studies were performed of iomeprol versus iopamidol, iopromide, ioxaglate, iopentol, iodixanol, ioversol, and iohexol. In all studies, safety controls included pre- and postadministration physical examinations, monitoring of vital signs, electrocardiography, clinical laboratory investigations, and 24- or 72-hour postadministration monitoring of patients for adverse events. Technically adequate images were rated for diagnostic efficacy by masked assessors. RESULTS: Iomeprol showed similar safety and diagnostic efficacy compared with the nonionic monomers iopamidol, iohexol, and ioversol, and no statistically significant differences were observed. No differences in diagnostic efficacy between iomeprol and iopromide were observed, but in one study on 1,200 patients, the incidence of adverse events and adverse reactions was significantly higher with iopromide than with iomeprol. Iomeprol caused significantly less heat/pain than iopentol in one study; it showed similar safety and tolerability to the nonionic dimer iodixanol, the two agents causing no or modest, superimposable pain and heat sensation at injection and showing similar renal tolerability after intra-arterial injection. A comparison of iomeprol versus ionic dimer ioxaglate in 2,000 patients undergoing percutaneous coronary interventions showed that the incidence of thrombus-related events was similar with the two agents, but ioxaglate caused a significantly higher incidence of allergy-like reactions. First results with iomeprol-containing liposomal formulations show that these agents may facilitate the CT assessment of intrahepatic malignancies and CT angiography procedures. CONCLUSIONS: The overall results of numerous randomized, double-blind, comparative clinical studies in a variety of indications show that the diagnostic efficacy of iomeprol solutions does not differ significantly from that of the low-osmolar contrast media available on the marketplace when similar iodine strengths are used, although iomeprol may have better tolerability and safety than the ionic dimer and some of the nonionic monomers in selective applications. First results obtained with iomeprol-containing liposomal formulations are promising and may foster additional clinical testing.

The cytochrome oxidases of Bacillus subtilis: mapping of a gene affecting cytochrome aa3 and its replacement by cytochrome o in a mutant strain.

A mutant of Bacillus subtilis has been isolated that fails to grow on succinate as the source of carbon, yet grows on glucose. Intact cells of the mutant and cytoplasmic membranes derived therefrom lack cytochromes a and a3 but contain a cytochrome o-like pigment, which forms a photodissociable compound with CO and is reactive with oxygen. The mutation in the genome has been located and lies at about 130 degrees on the chromosomal map between the metC and pyrD loci. The designation cox is suggested for this gene.

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-gated fluorescence imaging for the diagnosis of tumors in a murine model.

A system for time-gated fluorescence imaging was used to perform measurements on tumor-bearing mice treated with hematoporphyrin derivative (HpD). The aim of the study was to define the potential of this technique in the diagnosis of tumors by taking advantage of the long fluorescence lifetime of the exogenous dye with respect to the decay times of the natural fluorescence. After the administration of three different drug doses (5, 10 and 25 mg/kg body weight), fluorescence images were acquired at various uptake times (from 2 h to 10 d), to determine the best instrumental conditions and experimental procedure for the detection of tumors in the murine model considered. The optimal fluorescence contrast between the tumor area and the surrounding healthy tissue was found at 12 h after the administration of either 5 or 10 mg/kg HpD and was anticipated at 8 h for the highest drug dose. In this optimum condition, the tumor region could be identified even after the injection of 5 mg/kg HpD. A better fluorescence contrast was always obtained in 15 ns-delayed images with respect to synchronous ones.

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.

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.

Absorption spectrum of hematoporphyrin derivative in vivo in a murine tumor model.

Time-resolved reflectance was used to measure the absorption spectrum of hematoporphyrin derivative (HpD) in vivo in a murine tumor model. Reflectance measurements were performed in the 600-640 nm range on mice bearing the L1210 leukemia. Then the animals were administered 25 mg/kg body weight of HpD intraperitoneally. One hour later the reflectance measurements were repeated. Fitting of the data using the diffusion theory allowed assessment of the absorption coefficient before and after the administration. As a difference between the latter and the former data, the in vivo absorption spectrum of HpD was evaluated. Maximum absorption was measured at 620-625 nm. Similar spectral behavior was obtained for HpD in solution in the presence of low-density lipoproteins.

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.