Marigo Stavridi

Surface BRDF and texture of bricks

We analyze material properties underlying visual appearance, such as surface bidirectional reflection distribution function (BRDF) and texture. We perform gonioradiometric measurements on bricks and fit the data to sets of models of specular and diffuse reflectance on rough surfaces in order to describe the composite reflection mechanisms, of the surfaces under study. We also acquire images and perform image texture statistical discrimination techniques to determine the textural differences in the surface appearance, resulting from the variation of illumination and viewing.

Differentiation of artery wall lesions using porphyrins and fiberoptic sensor in rabbits

We investigated the ability of fluorescence spectroscopy, and photosensitizers to differentiate normal, hyperplastic and atherosclerotic arterial wall lesions in vivo. Hyperplastic lesions were induced in the abdominal aorta (AB) of 24 rabbits by balloon injury (BI). Atherosclerotic arterial wall lesions were induced by BI and diet. Fluorescence signals from thoracic n equals 16 and AB n equals 15 sites were analyzed by computer. A ratio was used as an index of drug presence. Use of PPS or BPD and LIFS may be a feasible, in vivo method for the differentiation between normal, hyperplastic and atherosclerotic arterial wall lesions.

Blood perfusion and pH monitoring in organs by laser-induced fluorescence spectroscopy

Sensitivity of laser-induced fluorescence spectroscopy (LIFS) in detecting a change in tissue pH, and blood perfusion was determined. Rabbits were anesthetized, paralyzed, and mechanically ventilated. The arterial and venous blood supplies of the kidney were isolated and ligated to alter the perfusion. The femoral artery was cannulated to extract samples for blood gas analysis. A 308-nm XeCl was used as an excitation source. A 600 micrometers core diameter fiber was used for fluorescence acquisition, and the spectra analyzed by an optical multichannel analyzer (EG & G, OMA III). the corresponding intensity ratio R equals INADH / ICOLL was used as an index for respiratory acidosis. Blood perfusion was assessed using the following algorithm: (IELAS minus ICOLL) divided by (INADH minus ICOLL). The intensity ratio linearly decreased with the reduction of blood perfusion. When we totally occluded the artery the ratio decreased tenfold when compared to the ratio of a fully perfused kidney. Results of monitoring blood acidosis by laser-induced fluorescence spectroscopy shows a significant trend between pH and intensity ratio. Since all the slopes were negative, there is an obvious significant correlation between the pH and NADH.COLLAGEN RATIO. Blue-light-induced fluorescence measurements and ratio fluorometry is a sensitive method for monitoring blood perfusion and acidity or alkalinity of an organ.

Biodistribution detection of Photofrin porfimer sodium and benzoporphyrin derivative using a fiber optic sensor and ratio fluorometry

Laser induced fluorescence spectroscopy (LIFS) was used to detect the presence of PHOTOFRINR porfimer sodium and Benzoporphyrin derivative-monoacid, ring A (BPD-MA) in various tissues. Lobund Wistar rats (n equals 49) inoculated with rat prostatic adenocarcinoma (PA-III) were injected with PHOTOFRINR porfimer sodium (7.5 - 0.25 mg/kg) and BPD (0.50 - 25 mg/kg) intravenously. A Helium-Cadmium laser (442 nm) was used as an excitation source. Our study showed that the amount of PHOTOFRINR porfimer sodium and BPD-MA which localizes in the metastatic lymph nodes is higher than in tumor and all other healthy tissues. Laser induced fluorescence spectroscopy may be a feasible method to detect the distribution of photosensitizers or other fluorescent compounds in vivo.

Effectiveness of benzoporphyrin derivative monoacid (BPD-MA) and fiberoptic sensor in detecting metastatic neoplasm in lymph nodes in rats

An intensity ration of the photosensitizing agent to the natural fluorescence was used to determine the condition of lymph nodes (normal, inflammatory, or with metastases). Eighty- one Lobund Wistar rats were inoculated with Pollard rat adenocarcinoma cells. After 40 days the rats were injected with 0.75 mg/kg BPD-MA. A helium-cadmium lasers (442 nm) was used for both light delivery ad fluorescence acquisition. Fluorescence spectra were acquired and analyzed by an optical multichannel analyzer 9 EG&G, OMA III). Unbalanced repeated measures analysis of variance (ANOVA) was done on the mean intensity ratio according to location. Several locations recorded for each rat were modeled as the repeated variable. The fluorescence signal obtained from lymph nodes with metastases indicated high drug amounts, greater than in the skin, tumors, and all other tissues. The lowest fluorescence intensity ratios were observed in the skin. This leads us to the conclusion that the amount of Photofrin porfimer sodium and BPD-MA which localized in the metastatic lymph nodes is higher than in tumor and all other healthy tissues. Among normal lymph nodes there were significant differences according to the site of the node, with the left iliac lymph nodes having higher IR values than either the mesenteric (MC I or MC II) nodes. The geometric means of IR are consistently higher in normal as compared to inflammatory nodes for each location. The optical biopsy needle with laser-induced fluorescence detection and exogenic fluorochrome is a sensitive, novel techniques to localize small boundaries of metastatic neoplasm in lymph nodes.

Light and laser induced fluorescence spectroscopy (LIFS) and their biomedical applications

The signals produced by laser and light induced emission spectroscopy can be used to characterize different components of tissue. This method enables us to identify proteins and different metabolic mediators. Using extensive emission light at a certain wavelength and analyzing it with mathematical algorithms, we can characterize individual anatomical structures in the tooth, tissue alkalinity or acidity, blood perfusion or presence of neoplasm in any tissue. To enhance the sensitivity of our detection method we can use different fluorescence drugs. These drugs can be used to tag malignancy (neoplasm), making this method one of the most rapidly developing area in the diagnosis of cancers. A XeCl (308 nm, nanosecond pulsed) or He-Cd (442 nm, CW) laser output was reflected at a right angle by a dichroic mirror. It was focused at the input of a 400 /spl mu/m core diameter fiber optic probe, The output of the lasers at the distal end of the fiber was 5 mJ/pulse or 17 mW. Fluorescence was collected using the same fiber and transmitted through the dichroic beamsplitter and guided via a fiber bundle to a 0.5 spectrograph. The light was then imaged at the modified output port. A 1024 element linear diode array detector (EG&G 1422G) was attached to the exit port. Final data was displayed on the screen of the optical multichannel analyzer (OMA III, EG&G). We recorded background spectra before excitation. This was subtracted from the resulting data. Calibration was not required because intensity ratios were used instead of absolute intensities. The mean and standard deviation of the designated curve segment was then computed.<<ETX>>

Biodistribution of benzoporphyrin derivative in tumor-bearing rats by laser-induced fluorescence spectroscopy

The goal of this study was to detect the presence of benzoporphyrin derivative-monoacid (BPD-MA) in tissues of a tumor bearing animal model. Eighty one Lobund-Wistar rats, inoculated with Pollard rat adenocarcinoma cells, were used. This animal model exhibits unique predictable, unilateral, metastatic spread. The animals were injected intravenously with 0.75 mg/kg of BPD-MA. A Helium-Cadmium (He-Cd) laser (442 nm, 17 mW) was used as an excitation source and coupled to a 400 micrometers core diameter fiber. Following laparotomy, exploration of the abdominal and inguinal area was performed with laser induced fluorescence. Fluorescence spectra of the primary tumor, bilateral lymph nodes, and various organs were recorded. Fluorescence measurements were conducted four hours post injection. The spectra obtained were characterized by a broadband autofluorescence (approximately 540 nm) and a characteristic peak of BPD-MA (approximately 690 nm). Overall, the BPD-MA concentration was higher in lymph nodes than in the skin, kidney, large bowel, muscle or spleen. Skin exhibited the lowest fluorescence intensity ratio, indicative of a lower drug concentration in this tissue. In summary, our results suggest that laser induced fluorescence spectroscopy may provide an alternative way of assessing the biodistribution of BPD-MA or other photosensitizers.

Detection of dental tissues using fiberoptic sensor

Our goal was to determine the fluorescence aided characterization of teeth. The incisors of 6 farmer pigs were opened with a round bur to expose the pulp. A Helium-Cadmium laser at a wavelength of 442 nm and operating at 17 mW was used as the excitation source. The light was guided through a 400 micrometers core diameter fiber which was used not only for delivery, but for the collection of tissue fluorescence. A spectrometer and an optical multichannel analyzer were used to detect and record the fluorescence signal.