Jesper Schou

A test statistic in the complex Wishart distribution and its application to change detection in polarimetric SAR data

When working with multilook fully polarimetric synthetic aperture radar (SAR) data, an appropriate way of representing the backscattered signal consists of the so-called covariance matrix. For each pixel, this is a 3/spl times/3 Hermitian positive definite matrix that follows a complex Wishart distribution. Based on this distribution, a test statistic for equality of two such matrices and an associated asymptotic probability for obtaining a smaller value of the test statistic are derived and applied successfully to change detection in polarimetric SAR data. In a case study, EMISAR L-band data from April 17, 1998 and May 20, 1998 covering agricultural fields near Foulum, Denmark are used. Multilook full covariance matrix data, azimuthal symmetric data, covariance matrix diagonal-only data, and horizontal-horizontal (HH), vertical-vertical (VV), or horizontal-vertical (HV) data alone can be used. If applied to HH, VV, or HV data alone, the derived test statistic reduces to the well-known gamma likelihood-ratio test statistic. The derived test statistic and the associated significance value can be applied as a line or edge detector in fully polarimetric SAR data also.

LCAT, HDL Cholesterol and Ischemic Cardiovascular Disease: A Mendelian Randomization Study of HDL Cholesterol in 54,500 Individuals

BACKGROUND Epidemiologically, high-density lipoprotein (HDL) cholesterol levels associate inversely with risk of ischemic cardiovascular disease. Whether this is a causal relation is unclear. METHODS We studied 10,281 participants in the Copenhagen City Heart Study (CCHS) and 50,523 participants in the Copenhagen General Population Study (CGPS), of which 991 and 1,693 participants, respectively, had developed myocardial infarction (MI) by August 2010. Participants in the CCHS were genotyped for all six variants identified by resequencing lecithin-cholesterol acyltransferase in 380 individuals. One variant, S208T (rs4986970, allele frequency 4%), associated with HDL cholesterol levels in both the CCHS and the CGPS was used to study causality of HDL cholesterol using instrumental variable analysis. RESULTS Epidemiologically, in the CCHS, a 13% (0.21 mmol/liter) decrease in plasma HDL cholesterol levels was associated with an 18% increase in risk of MI. S208T associated with a 13% (0.21 mmol/liter) decrease in HDL cholesterol levels but not with increased risk of MI or other ischemic end points. The causal odds ratio for MI for a 50% reduction in plasma HDL cholesterol due to S208T genotype in both studies combined was 0.49 (0.11-2.16), whereas the hazard ratio for MI for a 50% reduction in plasma HDL cholesterol in the CCHS was 2.11 (1.70-2.62) (P(comparison) = 0.03). CONCLUSION Low plasma HDL cholesterol levels robustly associated with increased risk of MI but genetically decreased HDL cholesterol did not. This may suggest that low HDL cholesterol levels per se do not cause MI.

CFAR edge detector for polarimetric SAR images

Finding the edges between different regions in an image is one of the fundamental steps of image analysis, and several edge detectors suitable for the special statistics of synthetic aperture radar (SAR) intensity images have previously been developed. In this paper, a new edge detector for polarimetric SAR images is presented using a newly developed test statistic in the complex Wishart distribution to test for equality of covariance matrices. The new edge detector can be applied to a wide range of SAR data from single-channel intensity data to multifrequency and/or multitemporal polarimetric SAR data. By simply changing the parameters characterizing the test statistic according to the applied SAR data, constant false-alarm rate detection is always obtained. An adaptive filtering scheme is presented, and the distributions of the detector are verified using simulated polarimetric SAR images. Using SAR data from the Danish airborne polarimetric SAR, EMISAR, it is demonstrated that superior edge detection results are obtained using polarimetric and/or multifrequency data compared to using only intensity data.

Genetic inhibition of CETP, ischemic vascular disease and mortality, and possible adverse effects.

OBJECTIVES This study tested whether genetic variation in the CETP gene is consistent with a protective effect of cholesteryl ester transfer protein (CETP) inhibition on risk of ischemic events and on total mortality, without the adverse effects reported for torcetrapib. BACKGROUND Torcetrapib, an inhibitor of CETP, increased risk of death and ischemic cardiovascular disease of those randomized to the drug, despite improving the lipid profile. METHODS The Copenhagen City Heart Study is a prospective cohort study of 10,261 individuals, aged 20 to 93 years, who were followed for up to 34 years (1976 to 2010). Of these, 2,087 developed ischemic heart disease, 1,064 developed ischemic cerebrovascular disease, and 3,807 died during follow-up. We selected 2 common genetic variants in CETP previously associated with reductions in CETP activity, thus mimicking the effect of pharmacological CETP inhibition. RESULTS In individuals carrying 4 versus 0 high-density lipoprotein cholesterol-increasing alleles, there was an increase in levels of high-density lipoprotein cholesterol of up to 14% (0.2 mmol/l), and concomitant decreases in triglycerides, low-density lipoprotein cholesterol, and non-high-density lipoprotein cholesterol of, respectively, 6% (0.1 mmol/l), 3% (0.1 mmol/l), and 4% (0.2 mmol/l) (p for trend 0.004 to <0.001). Corresponding hazard ratios were 0.76 (95% confidence interval [CI]: 0.68 to 0.85) for any ischemic vascular event, 0.74 (95% CI: 0.65 to 0.85) for ischemic heart disease, 0.65 (95% CI: 0.54 to 0.79) for myocardial infarction, 0.77 (95% CI: 0.65 to 0.93) for ischemic cerebrovascular disease, 0.71 (95% CI: 0.58 to 0.88) for ischemic stroke, and 0.88 (95% CI: 0.80 to 0.97) for total mortality. CETP genotypes did not associate with variation in markers of possible side effects previously reported for torcetrapib. CONCLUSIONS Genetic CETP inhibition associates with reductions in risk of ischemic heart disease, myocardial infarction, ischemic cerebrovascular disease, and ischemic stroke, with a corresponding antiatherogenic lipid profile, and with increased longevity, without adverse effects.

The Elasticity and the Tensile Strength of Tunica Albuginea of the Corpora Cavernosa

The aim of this study was to determine the tensile strength and the elasticity of the tunica albuginea (TA), and describe morphological structures in the tissue before and after mechanical deformities. Twenty cadavers of men aged between 33 and 83 were examined. Cavernosometry was performed in all specimens. Afterwards in five cadavers the flow rate was increased until a herniation of the TA appeared. A strength about 1500 mm. Hg was found. Similar results were found in four who had an inflatable prosthesis (AMS 700) inserted, and the intraprosthetic pressure increased until a deformity was noted. Slices of TA (thickness 1.3 to 3.3 mm.) from 11 specimens were tested in a tensiometer. The elasticity coefficient was found to be around 10(8) N/m2, and the tensile strength to be 600 to 750 mm. Hg (10(4) to 10(5) N/m2). The difference between the tensile strength achieved in the tensiometer and during saline infusion is possibly caused by the intracavernous framework. Microscopy showed that TA is mainly composed of collagen fibres which are situated in an undulating arrangement, with a few elastic fibres arranged longitudinally which connect the undulating bundles of collagen fibres. When the tissue is overstretched, the elastic fibres are destroyed and the undulating arrangement disappears.

Restoration of polarimetric SAR images using simulated annealing

Filtering synthetic aperture radar (SAR) images ideally results in better estimates of the parameters characterizing the distributed targets in the images while preserving the structures of the nondistributed targets. However, these objectives are normally conflicting, often leading to a filtering approach favoring one of the objectives. An algorithm for estimating the radar cross-section (RCS) for intensity SAR images has previously been proposed in the literature based on Markov random fields and the stochastic optimization method simulated annealing. A new version of the algorithm is presented applicable to multilook polarimetric SAR images, resulting in an estimate of the mean covariance matrix rather than the RCS. Small windows are applied in the filtering, and due to the iterative nature of the approach, reasonable estimates of the polarimetric quantities characterizing the distributed targets are obtained while at the same time preserving most of the structures in the image. The algorithm is evaluated using multilook polarimetric L-band data from the Danish airborne EMISAR system, and the impact of the algorithm on the unsupervised H-/spl alpha/ classification is demonstrated.

Genetic Variation in ABCG1 and Risk of Myocardial Infarction and Ischemic Heart Disease

Objective—ATP binding cassette transporter G1 (ABCG1) facilitates cholesterol efflux from macrophages to mature high-density lipoprotein particles. Whether genetic variation in ABCG1 affects risk of atherosclerosis in humans remains to be determined. Methods and Results—We resequenced the core promoter and coding regions of ABCG1 in 380 individuals from the general population. Next, we genotyped 10 237 individuals from the Copenhagen City Heart Study for the identified variants and determined the effect on lipid and lipoprotein levels and on risk of myocardial infarction (MI) and ischemic heart disease (IHD). g.−376C>T, g.-311T>A, and Ser630Leu predicted risk of MI in the Copenhagen City Heart Study, with hazard ratios of 2.2 (95% confidence interval: 1.2–4.3), 1.7 (1.0–2.9), and 7.5 (1.9–30), respectively. These results were confirmed for g.−376C>T in a case-control study comprising 4983 independently ascertained IHD cases and 7489 controls. Expression levels of ABCG1 mRNA were decreased by approximately 40% in g.−376C>T heterozygotes versus noncarriers (probability values: 0.005–0.009). Finally, in vitro specificity protein 1 (Sp1) bound specifically to a putative Sp1 binding site at position −382 to −373 in the ABCG1 promoter, and the presence of the −376 T allele reduced binding and transactivation of the promoter by Sp1. Conclusion—This is the first report of a functional variant in ABCG1 that associates with increased risk of MI and IHD in the general population.

ABC Transporter Genes and Risk of Type 2 Diabetes A study of 40,000 individuals from the general population

OBJECTIVE Alterations of pancreatic β-cell cholesterol content may contribute to β-cell dysfunction. Two important determinants of intracellular cholesterol content are the ATP-binding cassette (ABC) transporters A1 (ABCA1) and -G1 (ABCG1). Whether genetic variation in ABCA1 and ABCG1 predicts risk of type 2 diabetes in the general population is unknown. RESEARCH DESIGN AND METHODS We tested whether genetic variation in the promoter and coding regions of ABCA1 and ABCG1 predicted risk of type 2 diabetes in the general population. Twenty-seven variants, identified by previous resequencing of both genes, were genotyped in the Copenhagen City Heart Study (CCHS) (n = 10,185). Two loss-of-function mutations (ABCA1 N1800H and ABCG1 g.-376C>T) (n = 322) and a common variant (ABCG1 g.-530A>G) were further genotyped in the Copenhagen General Population Study (CGPS) (n = 30,415). RESULTS Only one of the variants examined, ABCG1 g.-530A>G, predicted a decreased risk of type 2 diabetes in the CCHS (P for trend = 0.05). Furthermore, when validated in the CGPS or in the CCHS and CGPS combined (n = 40,600), neither the two loss-of-function mutations (ABCA1 N1800H, ABCG1 g.-376C>T) nor ABCG1 g.-530A>G were associated with type 2 diabetes (P values >0.57 and >0.30, respectively). CONCLUSIONS Genetic variations in ABCA1 and ABCG1 were not associated with increased risk of type 2 diabetes in the general population. These data were obtained in general population samples harboring the largest number of heterozygotes for loss-of-function mutations in ABCA1 and ABCG1.

Change detection in polarimetric SAR data and the complex Wishart distribution

When working with multi-look fully polarimetric synthetic aperture radar (SAR) data an appropriate way of representing the backscattered signal consists of the so-called covariance matrix. For each pixel this is a 3/spl times/3 Hermitian, positive definite matrix which follows a complex Wishart distribution. Based on this distribution a test statistic for equality of two such matrices and an associated asymptotic probability for obtaining a smaller value of the test statistic are given and applied to change detection in polarimetric SAR data. In a case study EMISAR L-band data from 17 April 1998 and 20 May 1998 covering agricultural fields near Foulum, Denmark are used. The derived test statistic can be applied as a line or edge detector in fully polarimetric SAR data also.

Polarimetric edge detector based on the complex Wishart distribution

A new edge detector for polarimetric SAR data has been developed. The edge detector is based on a newly developed test statistic for equality of two complex covariance matrices following the complex Wishart distribution and an associated asymptotic probability for the test statistic. The new polarimetric edge detector provides a constant false alarm rate and it utilizes the full polarimetric information. The edge detector has been applied to polarimetric SAR data from the Danish dual-frequency, airborne polarimetric SAR, EMISAR. The results show clearly an improved edge detection performance for the full polarimetric detector compared to single channel approaches.