An Improved Approach for Terrain Correction: Application to Northeast Asia’s Highest Peak (Mt. Jade, Taiwan)

Mt. Jade (or “Yushan” in Chinese) is the highest peak in northeast Asia. The topography is very rugged and complicated. Such terrain makes it difficult to obtain the correct results for terrain corrections (TCs). This paper developed an improved approach, named cone-section method, to compute the TCs of the Mt. Jade area using a high-resolution digital elevation model (DEM) on a 9″ × 9″ grid. The corrections were calculated to the distance of 100 km with an average rock density of 2.57 × 103 kg·m−3. This investigation compared the results of TCs from the cone-section method with those from the cylinder prism and Gaussian quadrature methods using a 9″ × 9″ elevation grid for the inner zone and a 90″ × 90″ elevation grid for the outer zone. The inner and outer radii were set to 20 and 200 km, respectively. The comparisons showed that the cone-section algorithm is consistent with the Gaussian quadrature. Furthermore, the cone-section method is an appropriate approach for TCs in high elevation areas, yielding results that outperform the cylinder prism method

Study of Alternative GPS Network Meteorological Sensors in Taiwan: Case Studies of the Plum Rains and Typhoon Sinlaku

Plum rains and typhoons are important weather systems in the Taiwan region. They can cause huge economic losses, but they are also considered as important water resources as they strike Taiwan annually and fill the reservoirs around the island. There are many meteorological sensors available for investigating the characteristics of weather and climate systems. Recently, the use of GPS as an alternative meteorological sensor has become popular due to the catastrophic impact of global climate change. GPS provides meteorological parameters mainly from the atmosphere. Precise Point Positioning (PPP) is a proven algorithm that has attracted attention in GPS related studies. This study uses GPS measurements collected at more than fifty reference stations of the e-GPS network in Taiwan. The first data set was collected from June 1st 2008 to June 7th 2008, which corresponds to the middle of the plum rain season in Taiwan. The second data set was collected from September 11th to September 17th 2008 during the landfall of typhoon Sinlaku. The data processing strategy is to process the measurements collected at the reference stations of the e-GPS network using the PPP technique to estimate the zenith tropospheric delay (ZTD) values of the sites; thus, the correlations between the ZTD values and the variation of rainfall during the plum rains and typhoon are analyzed. In addition, several characteristics of the meteorological events are identified using spatial and temporal analyses of the ZTD values estimated with the GPS network PPP technique

Efficacy of gadoxetic acid-enhanced magnetic resonance cholangiography compared with T2-weighted magnetic resonance cholangiography in patients with liver cirrhosis

Background: Gadoxetic acid is one of the hepatobiliary-specific agents and so can be used for contrast-enhanced magnetic resonance cholangiography (CE-MRC). The aim of our study was to compare the performance of CE-MRC with that of T2-weighted magnetic resonance cholangiography (T2W-MRC), and also to ascertain the effectiveness of both modalities combined for visualizing anatomic structures of the biliary tree in patients with liver cirrhosis. Methods: Fifty-six patients underwent CE-MRC and T2W-MRC imaging. In the CE-MRC studies, hepatobiliary phase images were acquired 20 minutes after contrast injection. Two radiologists first evaluated the T2W-MRC and CE-MRC images separately in random order, and then they reviewed both images together 8 weeks later. The readers graded the quality of visualization of each biliary duct and the entire biliary tree (overall rating) using a five-point scale. Images with a grade of 3 or 4 were considered to provide sufficient visualization for clinical application, and those with a grade of 2 or less were considered to provide insufficient visualization. Laboratory data, Child–Pugh classification, and model for end-stage liver disease score were also recorded. Results: The overall rating of T2W-MRC was significantly higher than that of CE-MRC (p < 0.001), although combined T2W/CE-MRC provided better visualization of biliary segments than T2W-MRC alone (p = 0.025). There were no significant differences between liver function and the overall rating of CE-MRC. Conclusion: CE-MRC is not superior to conventional T2W-MRC with respect to biliary visualization in patients with liver cirrhosis. However, a combination of T2W-MRC and CE-MRC provides significantly better visualization of biliary structures than T2W-MRC alone

Flow diagram of patient selection.

<p>HBV = chronic hepatitis B; HCV = chronic hepatitis C; APRI = aspartate aminotransferase to the platelet ratio index; MRE = MR elastography.</p

Box plots.

<p>(a) liver stiffness values measured by MRE and (b) APRI values according to each METAVIR fibrosis stage (F0 to F4). The mean liver stiffness scores and APRI values increased with increasing METAVIR stage of fibrosis. (Spearman’s risk correlation coefficient = 0.85 and 0.42, respectively) The horizontal line through each box represents the median and each box represents data from the 25^th to the 75^th percentile. The separate asterisks and circles represent outliers.</p

Influences of clinical, biological and histolopathological parameters on liver stiffness measurement using MR Elastography.

<p>The results of the univariate and multivariate linear analyses are expressed as unstandardized B coefficients with 95% confidence intervals.</p><p>Influences of clinical, biological and histolopathological parameters on liver stiffness measurement using MR Elastography.</p

Optimal liver stiffness cutoff values measured by MR Elastography for different degrees of liver fibrosis.

<p>kPa, kilopascal; Sn, sensitivity; Sp, specificity; PPV, positive predictive value; NPV, negative predictive value; LR (+), positive likelihood ratio; LR (-), negative likelihood ratio.</p><p>Concordance represents the rate of patients who were classified correctly (true positive + true negative).</p><p>*Sn, 100% sensitivity; Sn+Sp, a maximum sum of sensitivity and specificity; Sp, 100% specificity.</p><p>Optimal liver stiffness cutoff values measured by MR Elastography for different degrees of liver fibrosis.</p

Proposed clinical algorithm of liver stiffness measured by MR Elastography in patients with HBV and those with HCV.

<p>Proposed clinical algorithm of liver stiffness measured by MR Elastography in patients with HBV and those with HCV.</p

Analysis of the effect of liver steatosis on liver stiffness estimated by MR Elastogrpahy for each fibrosis stage.

<p>Values are depicted as mean ± standard deviation. kPa = kilopascal.</p><p>Analysis of the effect of liver steatosis on liver stiffness estimated by MR Elastogrpahy for each fibrosis stage.</p