Using computer simulations we examine the ranges of validity of the first Born and first Rytov approximations employed in diffraction tomography. To that end we apply the filtered backpropagation(FBP) algorithm in conjunction with the first Born approximation and the hybrid FBP algorithm in conjunction with the first Rytov approximation. We find that the range of validity of the first Born approximation is approximately 3 times smaller than that of the first Rytov approximation and that the range of validity of each approximation can be expressed in terms of the product of the refractive-index difference between the object and the background and the size of the object. Also, we establish precise criteria for the validity of diffraction tomography within each of these two approximations. For the first Rytov approximation the validity of the hybrid FBP algorithm is found to be limited by phase-unwrapping problems.

No abstract

Accurate numerical simulations based on rigorous radiative transfer theory are used to assess the validity of the diffusion approximation that is frequently used in bio-optical imaging. These simulations show that the error is large for a non-index-matched boundary between air and tissue. This weakness of the diffusion approximation underscores the need to understand how diffusion theory can be used to extract accurate values of tissue optical properties. A validity criterion for the diffusion approximation is established on the basis of the single-scattering albedo a and the asymmetry factor g for a slab with index-matched boundaries.

Current methods for the atmospheric correction of ocean-color imagery rely on the computation of optical properties of a mixture of chemically different aerosol particles through combination of the mixture with it into an effective, single-particle component that has an average refractive index. However, a multi-component approach in which each particle type independently grows and changes its refractive index with increasing humidity is more realistic. Computations based on Mie theory and radiative transfer are used to show that the two approaches result in top-of-the-atmosphere radiances that differ more than the water-leaving radiance. Thus, proper atmospheric correction requires a multicomponent approach for the computation of realistic aerosol optical properties.

Abstract:Decreased glucose tolerance and diabetes are frequently observed in advanced liver cirrhosis patients and may be related to insulin resistance. Glucose transporter-4 (GLUT4), one of the most important glucose transporters, plays a key role in the development of type 2 diabetes. In order to study the mechanism of insulin resistance in liver cirrhosis patients, we measured the insulin sensitivity index and determined the GLUT4 protein and mRNA contents of skeletal muscle by Western blotting and reverse transcription-polymerase chain reaction (RT-PCR), respectively, in normal people and liver cirrhosis patients. The results showed that the levels of glucose, insulin, and C-peptide in two liver cirrhosis groups were higher and the insulin sensitivity index lower than those of the normal control group. The sensitivity of insulin may decrease with the decline of liver function. However, the contents of GLUT4 protein and mRNA in patients with advanced liver cirrhosis were similar to those of normal controls. In conclusion, insulin resistance is observed in patients with advanced liver cirrhosis but may not be correlated with the skeletal contents of GLUT4 protein and mRNA.

No abstract

No abstract

No abstract