Impact of interface roughness on the performance of broadband blackbody absorber based on dielectric-metal film multilayers.

We report on factors affecting the performance of a broadband, mid-IR absorber based on multiple, alternating dielectric / metal layers. In particular, we investigate the effect of interface roughness. Atomic layer deposition produces both a dramatic suppression of the interface roughness and a significant increase in the optical absorption as compared to devices fabricated using a conventional thermal evaporation source. Absorption characteristics greater than 80% across a 300 K black body spectrum are achieved. We demonstrate a further increase in this absorption via the inclusion of a patterned, porous anti-reflection layer.

Analysis of reflective Mach-Zehnder interferometry for electro-optic characterization of poled polymer films in multilayer structures.

We consider the Mach-Zehnder interferometer (MZI) method that specifically uses a poled organic thin film as one of the reflective mirrors in order to characterize the two independent electro-optic tensor elements r(13) and r(33). We discuss both a simple analysis based on a three-layer structure and a rigorous method including multiple reflection effects in a multilayer structure. In doing so, we find that the simple analysis of the reflective MZI method yields identical results to the reflection ellipsometric method (simple Teng-Man method), first introduced by Teng and Man as well as Shildkraut in 1990, when the ratio of r(13) to r(33) obtained from the MZI method is used in the analysis of the simple Teng-Man method. Error introduced by ignoring the multilayer nature of the sample structures in the MZI method is discussed and corrections are given for previous expressions in the literature for the simple analysis.

Broadband and mid-infrared absorber based on dielectric-thin metal film multilayers.

We propose a periodic multilayer structure of dielectric and metal interlayers to achieve a near-perfect broadband absorber of mid-infrared radiation. We examine the influence of four factors on its performance: (1) the interlayer metal conductance, (2) the number of dielectric layers, (3) a nanopatterned antireflective layer, and (4) a reflective metallic bottom layer for backreflection. Absorption characteristics greater than 99% of the 300 K and 500 K blackbody spectra are found for the optimized structures. Incident angle and polarization dependence of the absorption spectra are examined. We also investigate the possibility of fabricating a nanopatterned antireflective layer to maximize absorption.

Closed-form Maker fringe formulas for poled polymer thin films in multilayer structures.

We report new closed-form expressions for Maker fringes of anisotropic and absorbing poled polymer thin films in multilayer structures that include back reflections of both fundamental and second-harmonic waves. The expressions, based on boundary conditions at each interface, can be applied to multilayer structures containing a buffer and a transparent conducting oxide layer, which might enhance multiple reflections of fundamental and second-harmonic waves inside a nonlinear thin film layer. This formulation facilitates Maker fringe analysis for a sample containing additional multilayer structures on either side of a poled polymer thin film. Experimental data and numerical simulations are given to indicate the importance of inclusion of such a reflective layer in analyses for reliable characterization of second-harmonic tensor elements.

Gallbladder wall thickening in patients with acute hepatitis.

BACKGROUND: Gallbladder wall thickening (GWT) is often observed in patients with acute hepatitis (AH). However, little is known regarding the relationship between AH and GWT. We analyzed the characteristics of GWT in patients with AH. METHOD: Between April 2002 and April 2007, 232 patients with AH underwent a sonographic examination. The clinical and laboratory findings of patients with GWT were evaluated and compared with patients without GWT. Data were recorded for the following variables: gender, age, laboratory findings, duration of symptom, presence of gallstone, and etiology of GWT. RESULTS: A total of 147 (63%) patients with AH had GWT. GWT in patients with an alanine aminotransferase level more than 500 IU/l (5.2 +/- 3.4 mm) was greater than that in other patients (3.9 +/- 2.3 mm; p < 0.05). Hepatitis A virus infection (odds ratio = 3.17 [1.42-7.09]), female gender (odds ratio = 2.47 [1.34-4.56]), and an elevated total bilirubin level (odds ratio = 1.09 [1.03-1.15]) were positively associated with GWT. CONCLUSION: The incidence of GWT in patients with AH was 63%, and there was an association with hepatitis A virus infection, female gender, and an elevated total bilirubin level.

Angiotensin receptor blockers are superior to angiotensin-converting enzyme inhibitors in the suppression of hepatic fibrosis in a bile duct-ligated rat model.

BACKGROUND: Angiotensin blockade such as with an angiotensin II receptor blocker (ARB) or angiotensinconverting enzyme inhibitor (ACEI) has antifibrotic properties. The aim of this study was to evaluate and compare the antifibrotic effect between ARBs and ACEIs. METHODS: Common bile duct-ligated (BDL) adult Sprague-Dawley rats were allocated to five groups (each group, n = 8) as follows: G1, BDL without drug; G2, BDL + captopril 100 mg/kg per day; G3, BDL + ramipril 10 mg/kg per day; G4, BDL + losartan 10 mg/kg per day; G5, BDL + irbesartan 15 mg/kg per day. Four weeks post-BDL, hepatic fibrosis was analyzed histomorphologically using Batts and Ludwig scores. alpha-Smooth muscle actin (alpha-SMA) expression by immunohistochemical staining, hydroxyproline contents of liver tissue by spectrophotometry, and angiotensin receptor, collagen, procollagen, and transforming growth factor beta (TGF-beta) expressions were evaluated by real-time reverse transcriptase-polymerase chain reaction. Angiotensin receptor expression was also determined by Western blotting. RESULTS: Batts and Ludwig scores were 3.8, 2.6, 2.4, 1.8, and 1.6 in G1, G2, G3, G4, and G5, respectively. Histologically, ARB groups (G4, G5) showed significant suppression of hepatic fibrosis compared with ACEI groups or the control. Expressions of alpha-SMA (%) and the content of hydroxyproline (microg liver tissue) were significantly lower in ARB groups (G4, G5) than in ACEI groups (G2, G3) (P < 0.05). Also, ARB reduced the expression of angiotensin receptor, collagen, procollagen, and TGF-beta1 compared with ACEI. Western blot analysis showed that the expression of angiotensin receptor was inhibited in both ARB and ACEI groups. CONCLUSIONS: Both ARB and ACEI attenuate hepatic fibrosis through inhibiting hepatic stellate cell activation, and the inhibitory effect of ARBs on hepatic fibrosis is superior to that of ACEIs in the BDL rat model.

Thickening of the gastric wall on transabdominal sonography: a sign of gastric cancer.

PURPOSE: To determine the value of a thickened gastric wall detected during transabdominal sonography (TAS) in the diagnosis of gastric cancer. METHOD: This prospective study comprised 312 patients who underwent both TAS and endoscopy. Transverse TAS scanning was performed using a 3.5-MHz curved transducer to measure gastric wall thickness in the antrum and body of the stomach. Based on endoscopic and histologic findings, we classified the patients into 3 groups: normal or benign disease (BD), early gastric cancer (EGC), and advanced gastric cancer (AGC). TAS findings were then compared. RESULTS: The thickness of the gastric wall was 4.9 +/- 1.6 mm in 262 patients with BD, 5.6 +/- 2.4 mm in 21patients with EGC, and 10.3 +/- 4.7 mm in 29 patients with AGC (p < 0.01). A gastric wall thickness of greater than 7 mm had a 75.0% sensitivity, 92.6% specificity, 50.0% positive predictive value, and 97.4% negative predictive value in the diagnosis of AGC. CONCLUSION: Although not suitable as a screening method for gastric cancer, a thickening of the gastric wall of >7 mm may be a marker for AGC.

An adequate level of training for technical competence in screening and diagnostic colonoscopy: a prospective multicenter evaluation of the learning curve.

BACKGROUND: Various training programs in colonoscopy recommend that trainees should perform at least 100 to 200 procedures to be considered technically competent at diagnostic colonoscopy. OBJECTIVE: Our purpose was to determine the adequate level of training for technical competence in screening and diagnostic colonoscopy. DESIGN: A prospective multicenter trial. SETTING: Fifteen tertiary care academic medical centers. PATIENTS: Over 8 months we prospectively evaluated the procedures of 24 first-year GI fellows in 15 tertiary care academic medical centers. A total of 4351 colonoscopies were assessed prospectively with variable clinical factors. INTERVENTION: Cecal intubation was documented by photographing the identified cecal landmarks, including the appendiceal orifice and the ileocecal valve. MAIN OUTCOME MEASUREMENTS: Acquisition of competence (success rate) was evaluated for colonoscopic training on the basis of 2 objective criteria: (1) adjusted completion rate (>90%) and (2) cecal intubation time (<20 minutes). RESULTS: The overall success rate was 83.5% (3635/4351). The mean cecal intubation time was 9.23 +/- 4.63 minutes. The success rate significantly improved and reached the requisite standard of competence after 150 procedures (71.5%, 82.6%, 91.3%, 94.4%, 98.4%, and 98.7%, respectively, for every 50 consecutive blocks). The polyp detection rate did not improve significantly during the 8 months and was not correlated with the learning curve. In addition, mean time to cecal intubation decreased significantly, from 11.16 to 8.39 minutes, after 150 procedures. Logistic regression analysis found that prolonged cecal intubation was caused by the following factors: elderly patients, female sex, low body mass index, poor bowel preparation, poor American Society of Anesthesiologists status, abdominal pain as an indication, instructor's supervision, and low case volume. LIMITATIONS: We did not record final pathologic reports of detected polyps and withdrawal time. CONCLUSIONS: Competence in technically efficient screening and diagnostic colonoscopy generally requires experience with more than 150 cases. Also, factors associated with prolonged cecal intubation for typical trainees did not differ from those for experienced colonoscopists.

Clinicopathologic characteristics and malignant potential of colorectal flat neoplasia compared with that of polypoid neoplasia.

PURPOSE: Because of their potential for malignancy, flat colorectal neoplasias are a current topic of debate. This study was designed to investigate the clinicopathologic features of flat neoplasia and to compare them with those of polypoid neoplasia, as well as to identify the determinants of malignant transformation of both flat and polypoid colorectal neoplasia. METHODS: A prospective, cross-sectional study of 3,360 patients diagnosed with adenomas via total colonoscopy and polypectomy was performed at 11 tertiary medical centers between July 2003 and July 2004. In this study, potential risk factors for malignant transformation were analyzed. If multiple adenomas were identified, then only the adenoma with the most advanced degree of histology was recorded for the patient. RESULTS: Of a total of 3,360 neoplasias identified, we found that the incidence of flat and polypoid neoplasias were 207 (6.2 percent) and 3,153 (93.8 percent), respectively. Patients with flat neoplasias tended to be older (59.6 vs. 57.1, P < 0.01), with the neoplasia located more frequently in the right colon than polypoid neoplasias (49.3 percent vs. 32 percent, P < 0.01). The incidence of high-grade dysplasia or cancer in flat neoplasias was similar to that of polypoid neoplasias (5.4 percent vs. 4.6 percent, P = 0.36). Multivariate analysis revealed that a size of > or =11 mm (odds ratio, 6.8; 95 percent confidence interval, 4.8-9.7) and location in the left colon (odds ratio, 1.6; 95 percent confidence interval, 1.1-2.4) were significant determinants for the malignancy potential of colonic neoplasias. CONCLUSIONS: The clinicopathologic indices for the propensity of malignant transformation in colorectal neoplasias were a size > or =11 mm and location in the left colon rather than flat gross morphology.

Damping index of Doppler hepatic vein waveform to assess the severity of portal hypertension and response to propranolol in liver cirrhosis: a prospective nonrandomized study.

BACKGROUND AND AIMS: Alterations in the Doppler hepatic vein (HV) waveform are associated with cirrhosis and portal hypertension. We prospectively evaluated the correlation between the extent of abnormal Doppler HV waveforms expressed as damping index (DI) and the hepatic venous pressure gradient (HVPG) and response to propranolol in patients with cirrhosis. MATERIAL AND METHODS: In 76 patients with cirrhosis (69 men and seven women), both DI of Doppler HV waveform and HVPG were measured, and the relationship between them was analysed. DI was calculated by the minimum velocity/maximum velocity of the HV waveform. An HVPG>12 mmHg was defined as severe portal hypertension. In a subgroup of 19 patients receiving propranolol, changes in both DI and HVPG were evaluated after propranolol administration for 3 months. One author (S. K. B.) performed all DI of Doppler HV waveform studies. RESULTS: Abnormal HV waveforms were seen in 66 of 76 patients (86.8%). DI significantly correlated with the grade of HVPG, i.e. with higher HVPG increased DI was observed (P<0.01). By logistic regression analysis, DI>0.6 was significantly more likely to be severe portal hypertension (odds ratio: 14.19, 95% confidence interval: 4.07-49.55). Receiver-operating characteristic curve according to the value of 0.6 of DI showed a sensitivity of 75.9% and a specificity of 81.8% for the presence of severe portal hypertension. In 19 patients of the propranolol subgroup, change of DI following propranolol treatment also significantly correlated with that of HVPG (P<0.01). CONCLUSIONS: Damping index of the HV waveform by Doppler ultrasonography might be a non-invasive supplementary tool in evaluating the severity of portal hypertension and in responding to propranolol in patients with liver cirrhosis.

[Inhibitory effect of angiotensin blockade on hepatic fibrosis in common bile duct-ligated rats].

BACKGROUNDS AND AIMS: Angiotensin receptors are found on hepatic stellate cells, which participate in hepatic fibrosis. Therefore, it is presumed that angiotensin has a role in hepatic fibrosis. The aim of this study was to evaluate the effects of angiotensin blockade on inhibition of hepatic fibrosis in cirrhotic rat model. MATERIAL AND METHODS: Cirrhosis with portal hypertension was produced by common bile duct ligation (BDL) in the adult Sprague-Dawley rats. They were classified into 4 groups (each group n=6) as follows; G1: BDL without drug, G2: BDL+captopril 100 mg/kg/day beginning 2 weeks after BDL, G3: BDL+captopril 100 mg/kg/day, starting just after BDL, G4: BDL+losartan 10 mg/kg/day, starting just after BDL. After 4 weeks following BDL, hepatic fibrosis was histomorphologically analyzed by Batts & Ludwig score. alpha smooth muscle actin by immunohistochemical stain, hydroxyproline contents of liver tissue by spectrophotometry and expression of collagen, procollagen, and TGF-beta by real-time PCR were measured. RESULTS: Batts & Ludwig score were 3.8, 3.0, 2.6,and 2.6 in G1, G2, G3, and G4, respectively. The expression of alpha-SMA was significantly lower in G3 and G4 than in G1; 11.9%, 10.9%, 2.6%, and 1.1% in G1, G2, G3, and G4, respectively (p<0.05). The concentration of hydroxyproline (microg/g liver tissue) was lower in G3 and G4 compared with G1 (p<0.05). Also, the administration of angiotensin blockade just after BDL significantly reduced the expression of collagen, procollagen, and TGF-beta mRNA. CONCLUSIONS: Angiotensin blockades are effective in the prevention of hepatic fibrosis in BDL rats.

Effect of propranolol on portal pressure and systemic hemodynamics in patients with liver cirrhosis and portal hypertension: a prospective study.

BACKGROUND/AIMS: Propranolol can prevent variceal bleeding by ameliorating portal hypertension. We conducted this study to determine the effect of propranolol on portal hypertension and the optimal required dose in Korean cirrhotic patients. METHODS: This study prospectively evaluated 50 patients with cirrhosis who exhibited variceal bleeding. The hepatic venous pressure gradient (HVPG), portal venous flow, heart rate (HR), and blood pressure were assessed both at baseline and at 3 months after the treatment. The initial dose of propranolol (20 mg) was subsequently adjusted until the target HR was reached. Patients in whom HVPG reduced by >20% or to less than 12 mmHg were defined as responders. RESULTS: Propranolol significantly (p<0.01) reduced the HVPG (-21+/-26%, mean+/-standard deviation), portal venous flow (-25+/-21%), HR (-20+/-13%), and blood pressure (-3+/-13%). Twenty-nine patients were responders, and the optimal required dose was 154.4 mg. The main complication was dizziness (24%), but this was not serious enough to require medication withdrawal. CONCLUSIONS: Propranolol is safe and effective at reducing portal pressure in Korean cirrhotic patients. An effective improvement in portal hypertension requires the dose to be increased until the target HR is reached.

[Interequipment variability of Doppler ultrasonographic indices in patients with liver cirrhosis].

BACKGROUNDS/AIMS: Doppler ultrasongraphy is used to evaluate hemodynamic alternations in patients with liver cirrhosis. Purpose of this study was to determine the interequipment variability of Doppler indices in portal and splenic vein in cirrhosis. METHODS: Blood velocity, diameter, flow and congestive index in portal and splenic vein were measured by Doppler ultrasonography in 30 patients with cirrhosis using two different machines. RESULTS: Portal venous velocities measured by HDI-5000 and SSD-5000 were 8.72+/-3.69 cm/sec, 12.21+/-2.84 cm/sec, respectively which showed significant difference (P<0.001). Measured portal blood flows and congestive indices also had significant difference between HDI-5000 and SSD-5000 (P<0.01). Splenic venous velocity by HDI-5000 was 8.55+/-2.71 cm/sec, which was lower than that of 12.32+/-3.11 cm/sec by SSD-5000 (P<0.001). Splenic blood flows measured by HDI-5000 and SSD-5000 were 390.73+/-260.98 mL/min, 595.01+/-346.53 mL/min, respectively, showing significant difference (P=0.015). However, no differences were in the diameters of portal and splenic vein between HDI-5000 and SSD-5000. CONCLUSION: Doppler indices in portal and splenic vein showed significant interequipment variability. Therefore, in liver cirrhosis, hemodynamic investigations using different Doppler ultrasonographic machines is inappropriate.

Effectiveness of walking exercise as a bowel preparation for colonoscopy: a randomized controlled trial.

OBJECTIVES: This prospective study was conducted to assess the effect of walking exercise on bowel cleansing before colonoscopy and to define a patient subgroup that would benefit from walking exercise. METHODS: A total of 383 outpatients were randomized into two groups (G1 [n = 196]; walking exercise, G2 [n = 187]; nonexercise). Those randomized to G1 were instructed to drink 250 mL of polyethylene glycol (PEG) solution and then walk at least for 5 min at intervals of 10 min whereas those randomized to G2 were instructed to drink and then take rest in a waiting room until the entire 2.5-3 L volume was consumed. The amount of walking exercise in both groups was estimated using a step counter. A single endoscopist estimated the efficacy of cleansing in a single-blinded manner. Patient's demographics, various parameters related to bowel preparation, and the degree of patients discomfort caused by the walking exercise were assessed. RESULTS: The number of step counts taken was significantly different for the two groups (p < 0.001). The degree of bowel cleansing in the G1 (n = 189) and G2 (n = 177) groups was significantly different (p < 0.01). However, the groups were similar in terms of all other data collected. By univariate analysis, walking exercise was especially beneficial to a subgroup of nonobese patients of age <65 yr, without history of abdominal surgery. Also, multivariate logistic regression analysis demonstrated that nonexercise (OR = 0.49; 95% CI = 0.31-0.79) was an independent risk factor for poor bowel cleansing. Most walking patients (97.3%) considered walking exercise more comfortable than taking the polyethylene glycol solution. CONCLUSION: The walking exercise was found to improve colonoscopic bowel cleansing without significant patient discomfort.

Captopril reduces portal pressure effectively in portal hypertensive patients with low portal venous velocity.

BACKGROUND: The effect of an angiotensin II blockade in lowering the portal pressure in patients with liver cirrhosis and portal hypertension is controversial. This prospective study was undertaken to evaluate the portal hypotensive effect of captopril compared to that of propranolol, and to determine the factors that contribute to a successful reduction in the portal pressure after longterm captopril administration in patients with liver cirrhosis. METHODS: The hepatic venous pressure gradient (HVPG) and portal venous velocity (PVV) were measured both before and 3 months after initiation of the administration of captopril (n = 29) or propranolol (n = 29) in cirrhotic patients with a variceal bleeding episode. Patients who showed a reduction in the HVPG of more than 20% of the baseline were defined as being responders. RESULTS: At 3 months, the mean reduction in the HVPG after captopril was less than that after propranolol (-3.0 +/- 9.3% vs -28.5% +/- 4.1%; P < 0.05). However, of the 29 patients receiving captopril, 9 were classified as being responders. On multivariate analysis with parameters including age, cause, Child-Pugh score, HVPG, and PVV, only low PVV was found to be a significant independent factor for responders (PVV < 12 cm/s; odds ratio [OR], 12.2; 95% confidence interval [CI], 1.47-102.40) in the captopril group. CONCLUSIONS: Longterm captopril administration reduces the portal pressure effectively in cirrhotic patients with a low PVV. This suggests that the reduction in portal pressure after captopril administration is a result of improved portal venous outflow brought about by a decrease in the intrahepatic vascular resistance. When the PVV is below 12 cm/s, a captopril trial might be useful in preventing variceal bleeding in portal hypertensive patients.