Measurements of minimum and average total tissue thicknesses overlying the fetus during the third trimester were taken on 52 patients between 24 and 40 weeks gestation. Minimum total thickness of tissues constantly along the ultrasound path had a mean value of 1.75 cm, ranging from 0.40 to 3.70 cm. This corresponded to a mean attenuation of 0.87 dB MHz-1, ranging from 0.30 to 1.68 dB MHz-1. Ave...

PURPOSE An attenuation correction is necessary to improve quantitative SPECT evaluation. The aim of this study was to evaluate the performance of several different types of commercial attenuation correction algorithms. METHODS We investigated the performance of four attenuation correction algorithms using a simulation phantom with and without scatter. The attenuation correction was performed ...

Attenuation correction is necessary for quantification in micro-single-photon emission computed tomography (micro-SPECT). In general, this is done based on micro-computed tomographic (micro-CT) images. Derivation of the attenuation map from magnetic resonance (MR) images is difficult because bone and lung are invisible in conventional MR images and hence indistinguishable from air. An ultrashor...

BACKGROUND Accurate PET quantification demands attenuation correction (AC) for both patient and hardware attenuation of the 511 keV annihilation photons. In hybrid PET/MR imaging, AC for stationary hardware components such as patient table and MR head coil is straightforward, employing CT-derived attenuation templates. AC for flexible hardware components such as MR-safe headphones and MR radiof...

An improved approach of predicting rain attenuation cumulative distribution (CD) over terrestrial microwave links operating in tropical regions is presented in this article. The proposed method offers a better extrapolation approach for determining the values of rain attenuation at different exceedance probability from the measured attenuation at 0.01% of the time. The experimental data consist...

Compressional waves in heterogeneous permeable media suffer attenuation fiom both scattering and induced pore scale flow of the viscous saturating fluid. Stochastic medium theories are used to describe scattering on multiple length scales, and are validated by numerical examples using a dual length scale sedimentary sequence taken from a producing oil reservoir. The highly variable permeability...

A of seismic waves is sensitive to the physical properties of the subsurface and has been observed in vertical seismic profiling (VSP) and reflection data. De et al. (1994) report measurements of the Pand S-wave quality factors from VSP surveys and sonic logs. Klimentos (1995) measures compressional and shear attenuation from sonic logs in sandstone formations with variable oil, water, and gas...

  The sporozoites of Theileria annulata invade bovine MHC II cells, where they differentiate into schizonts. The later can immortalize and induce fundamental changes in their host cells. Live attenuated vaccine is an important way of controlling T. annulata infection of cattle. Production is by prolonged cultivation of macroschizont-infected cells. The mechanisms underlying this transformation ...

We review theoretical models to show that contrast reduction at a specific wavelength in the horizontal direction depends directly on the beam attenuation coefficient at that wavelength. If a black target is used, the inherent contrast is always negative unity, so that the visibility of a black target in the horizontal direction depends on a single parameter only. That is not the case for any o...

background: attenuation coefficient (μ) plays an important role in calculations of treatment planning systems, as well as determination of dose distributions in external beam therapy, dosimetry, protection, phantom materials and industry. so, its exact measurement or calculation is very important. the aim of this study was to evaluate the μ in different points in the water phantom analytically ...