The basis of phase dominance.

Phase dominance is a phenomenon that has been widely observed in imaging, visual perception, and other technical areas. Here we show for general images that phase dominance, in terms of exchanging the spectral amplitude and phase of two images, is simply explained by the expected mean square error.

Molecular variant M235T of the angiotensinogen gene is associated with essential hypertension in Taiwanese.

OBJECTIVE: To examine the association of the molecular variants of the angiotensinogen (AGT) gene with essential hypertension in Taiwanese. METHODS: We conducted a case-control study concerning 151 subjects, 102 hypertensives and 49 normotensives. We created a rapid mini-sequencing method based on dye-terminator cycle sequencing to simultaneously detect the M235T and T174M variants of the AGT gene for each subject. RESULTS: The genotype and allele distribution of the M235T variant differed significantly in hypertensives and normotensives (chi 2 = 11.106, P = 0.004 and chi 2 = 6.453, P = 0.011, respectively), whereas those of the T174M variant did not differ (chi 2 = 0.004, P = 0.998 and chi 2 = 0.032, P = 0.858, respectively). The odds ratio for hypertension was 3.64 (95% confidence interval 1.56-8.49) for subjects with the C/C genotype of the M235T variant compared with other genotypes of 2.87 (95% confidence interval 1.76-4.68) for those carrying allele C versus those carrying allele T. CONCLUSION: The molecular variant M235T, but not T174M, of the AGT gene is associated significantly with essential hypertension in this Taiwanese population. The genotype C/C or allele C is a risk factor for hypertension. The underlying mechanism of this association needs to be elucidated further.

Newly identified missense mutation reduces lipoprotein lipase activity in Taiwanese patients with hypertriglyceridemia.

Lipoprotein lipase (LPL) plays a crucial role in the regulation of lipoprotein metabolism by hydrolyzing the core triglycerides of circulating chylomicrons and very low-density lipoprotein. Deficiency in this enzyme usually results in disturbances in lipid levels. To understand the molecular defect that leads to a functional deficiency of LPL in patients with hypertriglyceridemia, we looked for mutations of the LPL gene by means of single-strand conformation polymorphism (SSCP) analysis and direct DNA sequencing in 24 patients. A single base C-->G substitution in codon 252 of the LPL gene, encoding a change of a leucine to a valine residue in the mature protein, was found in three women who had hypertriglyceridemia and recurrent pancreatitis. Two of these patients, who were homozygous for the L252V mutation, had variable and occasionally severe hypertriglyceridemia with undetectable or very low LPL activities, respectively. The third woman was heterozygous for this mutation. All three patients had poor post-heparin LPL activity. Site-directed mutagenesis experiments provided in vitro evidence that the mutation of codon 252 was responsible for the loss of LPL activity. In conclusion, we identified a novel LPL mutation that results in decreased LPL activity in Taiwanese patients with hypertriglyceridemia. The assessment of a causative link between the mutation and hyperlipidemia awaits further studies.

The corpus-predominant gastritis index may serve as an early marker of Helicobacter pylori-infected patients at risk of gastric cancer.

BACKGROUND: To eradicate Helicobacter pylori before the occurrence of precancerous changes is important to prevent gastric carcinogenesis. AIM: To validate whether the corpus-predominant gastritis index (CGI) can serve as an early marker to identify the H. pylori-infected patients at risk of gastric carcinogenesis. METHODS: This study enrolled 188 subjects, including 43 noncardiac gastric cancer patients, 63 of their first-degree relatives and 82 sex- and age-matched duodenal ulcer patients as controls. All received endoscopy to provide topographic gastric specimens to test for H. pylori infection and its related histological features, translated into the operative link on gastritis assessment (OLGA), operative link on gastric intestinal metaplasia assessment (OLGIM) stages, and the presence of CGI. Spasmolytic polypeptide-expressing metaplasia (SPEM) was assessed by immunohistochemistry staining of trefoil factor 2. RESULTS: Gastric cancer patients had higher prevalence of CGI and OLGIM stage II-IV, but not OLGA stage II-IV, than the controls (P = 0.001, OR = 3.4[95% CI: 1.4-8.1] for CGI; OR = 5.0[95% CI: 2.0-12.8] for OLGIM). In patients with the combined presence of CGI and OLGIM stage II-IV, the risk of gastric cancer increased to 9.8 (P < 0.001). The first-degree relatives of the gastric cancer patients had a higher rate of the presence of CGI, but not OLGA or OLGIM stage II-IV than the duodenal ulcer controls (P = 0.001). Of the first-degree relatives, the presence of CGI increased the risk of SPEM (P = 0.003, OR = 5.5[95% CI: 1.8-17.0]). CONCLUSION: The corpus-predominant gastritis index, which is highly correlated to SPEM, may serve as an early marker to identify the H. pylori-infected patients at a higher risk of gastric cancer.

Effects of Fourier-plane amplitude and phase errors on image reconstruction. I. Small amplitude errors.

The effects of Fourier-plane, or spectral, amplitude and phase errors on reconstructed images are studied in terms of the expected mean square error in the image. The relationship between the variance of amplitude and phase errors and the expected mean square error is derived for small amplitude errors and arbitrarily large phase errors. This allows "equivalent" amplitude and phase errors to be defined. The effects of large amplitude errors are discussed in general terms. Simulations are used to verify these relationships, and the effects of spectral amplitude and phase errors on reconstructed images are compared.

Image spectral amplitude distributions.

Models for the probability density functions of the Fourier amplitude of images are derived. The densities are based on a simple model of an image made up of independent objects and incorporates the observed behavior of the circularly averaged power spectrum versus spatial frequency. The density function over all spatial frequencies gives a good fit to spectral amplitude data from a variety of images.

Effects of occlusion, edges, and scaling on the power spectra of natural images.

The circularly averaged power spectra of natural image ensembles tend to have a power-law dependence on spatial frequency with an exponent of approximately -2. This phenomenon has been attributed to object occlusion, the presence of edges, and scaling of object sizes (self-similarity) in natural scenes, although the relative importance of these properties is still unclear. A detailed examination of the effects of occlusion, edges, and self-similarity on the behavior of the power spectrum is conducted using a simple model of natural images. Numerical simulations show that edges and self-similarity are necessary for a power-law power spectrum over a wide range of spatial frequencies. Object occlusion is not an essential factor. A theoretical analysis for images containing nonoccluding objects supports these results.

On apparent counterexamples to phase dominance.

Phase dominance refers to the observation that the phase of the Fourier transform of an image carries more information than does the amplitude. We show that apparent counterexamples to phase dominance are not in fact counterexamples since the phase functions used are not independent of the true phase function. Phase dominance appears to be a general phenomenon.