Measurements of the particulate beam attenuation coefficient at multiple wavelengths in the ocean typically exhibit a power law dependence on wavelength, and the slope of that power law has been related to the slope of the particle size distribution (PSD), when assumed to be a power law function of particle size. Recently, spectral backscattering coefficient measurements have been made using se...

Planar g-scintigraphy is often used to quantify pulmonary deposition patterns from aerosol inhalers. The results are quite different from those obtained using 3-dimensional PET and SPECT. The purpose of this study was to characterize the effects of scatter and tissue attenuation on the distribution of radiolabeled aerosol as measured by planar scintigraphy using Monte Carlo simulations. This st...

Attenuation measurements can be derived from the decay of backscattered signal with depth in an inhomogeneous material. In cases such as liver tissue, where many small inhomogeneities are likely to be included in sample volumes defined by pulse and beam widths, Rayleigh statistics describe the random nature of the magnitude of backscattered pressure. The statistics of speckle underlie the uncer...

Brass compensators for beam modulation present an alternative method for IMRT treatment planning to traditional dynamic leaf modulation. In this work, we present a detailed method to commission the Pinnacle treatment planning system for IMRT using brass compensators. Beam attenuation from various brass thicknesses were measured using an ion chamber, as well as a MapCHECK device, for a represent...

UNLABELLED Planar gamma-scintigraphy is often used to quantify pulmonary deposition patterns from aerosol inhalers. The results are quite different from those obtained using 3-dimensional PET and SPECT. The purpose of this study was to characterize the effects of scatter and tissue attenuation on the distribution of radiolabeled aerosol as measured by planar scintigraphy using Monte Carlo simul...

The qualitative and quantitative accuracy of SPECT images is degraded by physical factors of attenuation, Compton scatter and spatially varying collimator geometric response. This paper presents a 3D ray-tracing technique for modelling attenuation, scatter and geometric response for SPECT imaging in an inhomogeneous attenuating medium. The model is incorporated into a three-dimensional projecto...

In computed tomography (CT), the beam hardening effect has been known to be one of the major sources of deterministic error that leads to inaccuracy and artifact in the reconstructed images. Because of the polychromatic nature of the x-ray source used in CT and the energy-dependent attenuation of most materials, Beer's law no longer holds. As a result, errors are present in the acquired line in...

background: in radiation therapy, the sparing of normal tissues can be performed using either multi-leaf collimators or cerrobend blocks. the current work focuses on the physical characteristics of cerrobend blocks including attenuation coefficient, effective penumbra width and isodose curves undulation in penumbral regions. materials and methods: all measurements were performed using a dual en...

The limitations imposed by Mie scattering and atmospheric-induced beam scintillations on a direct line-of-sight optical link were investigated at 632.8 nm. The experimental investigations were carried out in Kuwait during the summer season when the local climate is characterized by high daily temperatures and frequent dust storms. Beam attenuation and scintillation data coupled with climatologi...

Hot-electron transport in Co/Cu/Co trilayer films has been studied in the energy range from 1.0 to 2.0 eV using ballistic electron magnetic microscopy. Both the spin-dependent attenuation lengths of Co and the cumulative polarizing effects of spin-dependent tunneling and transmission across a Co/Cu interface have been determined. For very thin (a few A) Co layers, the latter effects result in a...