Trung Hau Nguyen

Intravascular ultrasonic-photoacoustic (IVUP) endoscope with 2.2-mm diameter catheter for medical imaging.

Intravascular ultrasound (IVUS) imaging is extremely important for detection and characterization of high-risk atherosclerotic plaques as well as gastrointestinal diseases. Recently, intravascular photoacoustic (IVPA) imaging has been used to differentiate the composition of biological tissues with high optical contrast and ultrasonic resolution. The combination of these imaging techniques could provide morphological information and molecular screening to characterize abnormal tissues, which would help physicians to ensure vital therapeutic value and prognostic significance for patients before commencing therapy. In this study, integration of a high-frequency IVUS imaging catheter (45MHz, single-element, unfocused, 0.7mm in diameter) with a multi-mode optical fiber (0.6mm in core diameter, 0.22 NA), an integrated intravascular ultrasonic-photoacoustic (IVUP) imaging catheter, was developed to provide spatial and functional information on light distribution in a turbid sample. Simultaneously, IVUS imaging was co-registered to IVPA imaging to construct 3D volumetric sample images. In a phantom study, a polyvinyl alcohol (PVA) tissue-mimicking arterial vessel phantom with indocyanine green (ICG) and methylene blue (MB) inclusion was used to demonstrate the feasibility of mapping the biological dyes, which are used in cardiovascular and cancer diagnostics. For the ex vivo study, an excised sample of pig intestine with ICG was utilized to target the biomarkers present in the gastrointestinal tumors or the atherosclerotic plaques with the proposed hybrid technique. The results indicated that IVUP endoscope with the 2.2-mm diameter catheter could be a useful tool for medical imaging.

Circumferential irradiation for interstitial coagulation of urethral stricture

An optical diffuser was developed to achieve radially uniform light irradiation by micro-machining helical patterns on the fiber surface for endoscopically treating urethral stricture. Spatial emission from the diffuser was evaluated by goniometric measurements. A computational model was developed to predict spatio-temporal heat distribution during the interstitial coagulation. The fabricated diffuser yielded circumferential light distribution with slightly concentrated energy at the proximal end. Both simulation and tissue testing demonstrated approximately 1-mm coagulation thickness at 6 W for 10 sec with 1470 nm. The proposed optical diffuser may be a feasible tool to treat the urethral stricture in a uniform manner.

Evaluation of hyper thermal acid hydrolysis of Kappaphycus alvarezii for enhanced bioethanol production.

Hyper thermal (HT) acid hydrolysis of Kappaphycus alvarezii, a red seaweed, was optimized to 12% (w/v) seaweed slurry content, 180mM H2SO4 at 140°C for 5min. The maximum monosaccharide concentration of 38.3g/L and 66.7% conversion from total fermentable monosaccharides of 57.6g/L with 120gdw/L K. alvarezii slurry were obtained from HT acid hydrolysis and enzymatic saccharification. HT acid hydrolysis at a severity factor of 0.78 efficiently converted the carbohydrates of seaweed to monosaccharides and produced a low concentration of inhibitory compounds. The levels of ethanol production by separate hydrolysis and fermentation with non-adapted and adapted Kluyveromyces marxianus to high concentration of galactose were 6.1g/L with ethanol yield (YEtOH) of 0.19 at 84h and 16.0g/L with YEtOH of 0.42 at 72h, respectively. Development of the HT acid hydrolysis process and adapted yeast could enhance the overall ethanol fermentation yields of K. alvarezii seaweed.

Temperature feedback-controlled photothermal treatment with diffusing applicator: theoretical and experimental evaluations.

To minimize thermal injury, the current study evaluated the real-time temperature monitoring with a proportional-integrative-derivative (PID) controller during 980-nm photothermal treatment with a radially-diffusing applicator. Both simulations and experiments demonstrated comparable thermal behaviors in temperature distribution and the degree of irreversible tissue denaturation. The PID-controlled application constantly maintained the pre-determined temperature of 353 K (steady-state error = < 1 K). Due to constant energy delivery, coagulation volumes linearly increased up to 1.04 ± 0.02 cm3 with irradiation time. Integration of temperature feedback with diffuser-assisted photothermal treatments can provide a feasible therapeutic modality to treat pancreatic tumors in an effective manner.

Evaluation of Galactose Adapted Yeasts for Bioethanol Fermentation from Kappaphycus alvarezii Hydrolyzates.

Bioethanol was produced from Kappaphycus alvarezii seaweed biomass using separate hydrolysis and fermentation (SHF). Pretreatment was evaluated for 60 min at 121°C using 12% (w/v) biomass slurry with 364 mM H2SO4. Enzymatic saccharification was then carried out at 45°C for 48 h using Celluclast 1.5 L. Ethanol fermentation with 12% (w/v) K. alvarezii hydrolyzate was performed using the yeasts Saccharomyces cerevisiae KCTC1126, Kluyveromyces marxianus KCTC7150, and Candida lusitaniae ATCC42720 with or without prior adaptation to high concentrations of galactose. When non-adapted S. cerevisiae, K. marxianus, and C. lusitaniae were used, 11.5 g/l, 6.7 g/l, and 6.0 g/l of ethanol were produced, respectively. When adapted S. cerevisiae, K. marxianus, and C. lusitaniae were used, 15.8 g/l, 11.6 g/l, and 13.4 g/l of ethanol were obtained, respectively. The highest ethanol concentration was 15.8 g/l, with YEtOH = 0.43 and YT% = 84.3%, which was obtained using adapted S. cerevisiae.

Enhancement of Ethanol Production via Hyper Thermal Acid Hydrolysis and Co-Fermentation Using Waste Seaweed from Gwangalli Beach, Busan, Korea

The waste seaweed from Gwangalli beach, Busan, Korea was utilized as biomass for ethanol production. Sagassum fulvellum (brown seaweed, Mojaban in Korean name) comprised 72% of the biomass. The optimal hyper thermal acid hydrolysis conditions were obtained as 8% slurry contents, 138 mM sulfuric acid, and 160°C of treatment temperature for 10 min with a low content of inhibitory compounds. To obtain more monosaccharides, enzymatic saccharification was carried out with Viscozyme L for 48 h. After pretreatment, 34 g/l of monosaccharides were obtained. Pichia stipitis and Pichia angophorae were selected as optimal co-fermentation yeasts to convert all of the monosaccharides in the hydrolysate to ethanol. Co-fermentation was carried out with various inoculum ratios of P. stipitis and P. angophorae. The maximum ethanol concentration of 16.0 g/l was produced using P. stipitis and P. angophorae in a 3:1 inoculum ratio, with an ethanol yield of 0.47 in 72 h. Ethanol fermentation using yeast co-culture may offer an efficient disposal method for waste seaweed while enhancing the utilization of monosaccharides and production of ethanol.

Application of novel optical diffuser for urethral stricture treatment (Conference Presentation)

Optical fibers have frequently been used for photothermal laser therapy due to its efficiency to deliver laser energy directly to tissue. The aim of the current study was to develop a diffusing optical fiber to achieve radially uniform light irradiation for endoscopically treating urethral stricture. The optical diffuser was fabricated by micro-machining helical patterns on the fiber surface using CO2 laser light at 5 W. Visible light emission (632 nm) and spatial emissions (including polar, azimuthal, and longitudinal emissions) of the fiber tip were evaluated to validate the performance of the fabricated diffuser. Prior to tissue tests, numerical simulation on heat distribution was developed to estimate the degree of tissue coagulation depth during interstitial coagulation. Due to a high absorption coefficient by tissue water, 1470 nm laser was used for photothermal therapy treatment of urethral stricture to obtain a more precise depth profile. For in vitro tissue tests, porcine liver tissue was irradiated with three different power levels (3, 6, and 9 W) at various irradiation times. Porcine urethral tissue was also tested with the diffuser for 10 sec at 6 W to validate the feasibility of circumferential photothermal treatment. The treated tissue was stained with hematoxylin and eosin (H and E) and then imaged with an optical transmission microscope. The spatial emission characteristics of the diffusing optical fiber presented an almost uniform power distribution along the diffuser tip (less than 10% deviation) and around its circumference (less than 5% deviation). The peak temperature in simulation model at the tissue interface between the glass-cap and the tissue was 373 K that was higher than that at the distal end. The tissue tests showed that higher power levels resulted in lower coagulation thresholds (e.g., 1 sec at 9 W vs 8 sec at 3 W). Furthermore, the coagulation depth was approximately 20% thinner than the simulation results (p<0.001). The extent of coagulation thickness in urethral tissue was measured to be 1.3±0.2 mm, which was slightly thicker (18%) than the liver testing (1.1±0.1 mm) under the same conditions (p < 0.001). The proposed optical diffuser may be a feasible tool to treat the urethral stricture in a uniform manner.

Photoactive dye enhanced tissue ablation for endoscopic laser prostatectomy

Laser light has been widely used as a surgical tool to treat benign prostate hyperplasia with high laser power. The purpose of this study was to validate the feasibility of photoactive dye injection to enhance light absorption and eventually to facilitate tissue ablation with low laser power. The experiment was implemented on chicken breast due to minimal optical absorption Amaranth (AR), black dye (BD), hemoglobin powder (HP), and endoscopic marker (EM), were selected and tested in vitro with a customized 532-nm laser system with radiant exposure ranging from 0.9 to 3.9 J/cm2. Light absorbance and ablation threshold were measured with UV-VIS spectrometer and Probit analysis, respectively, and compared to feature the function of the injected dyes. Ablation performance with dye-injection was evaluated in light of radiant exposure, dye concentration, and number of injection. Higher light absorption by injected dyes led to lower ablation threshold as well as more efficient tissue removal in the order of AR, BD, HP, and EM. Regardless of the injected dyes, ablation efficiency principally increased with input parameter. Among the dyes, AR created the highest ablation rate of 44.2±0.2 μm/pulse due to higher absorbance and lower ablation threshold. Preliminary tests on canine prostate with a hydraulic injection system demonstrated that 80 W with dye injection yielded comparable ablation efficiency to 120 W with no injection, indicating 33 % reduced laser power with almost equivalent performance. In-depth comprehension on photoactive dye-enhanced tissue ablation can help accomplish efficient and safe laser treatment for BPH with low power application.