Monte Carlo calculations using the codes PENELOPE and GEANT4 have been performed to characterize the dosimetric parameters of the new 20 mm long catheter based 32 P beta source manufactured by Guidant Corporation. The dose distribution along the transverse axis and the two dimensional dose rate table have been calculated. Also, the dose rate at the reference point, the radial dose function and the anisotropy function were evaluated according to the adapted TG-60 formalism for cylindrical sources. PENELOPE and GEANT4 codes were first verified against previous results corresponding to the old 27 mm Guidant 32 P beta source. The dose rate at the reference point for the unsheathed 27 mm source in water was calculated to be 0.215 ± 0.001 cGy s −1 mCi −1 , for PENELOPE, and 0.2312 ± 0.0008 cGy s −1 mCi −1 , for GEANT4. For the unsheathed 20 mm source these values were 0.2908 ± 0.0009 cGy s −1 mCi −1 and 0.311 ± 0.001 cGy s −1 mCi −1 , respectively. Also, a comparison with the limited data available on this new source is shown. We found non negligible differences between the results obtained with PENELOPE and GEANT4.
The contrast sensitivity function (CSF) of the whole visual system is determined with the use of coherent diffuse illumination. This function provides supplementary data about the effect of speckle on the ability of the visual system to perceive the spatial information contained in an image. The results show that speckle not only prevents perception of the finest details (highest frequencies) but also reduces the visibility of lower frequencies (especially where contrast is low). The difference between the CSF's determined with and without speckle is quantitatively very important. And the ratio between the two CSF's is a measure of the retinal ability to perceive contrast in the presence of speckle noise. The influence of the pupil size and luminance level on the CSF with speckle is studied and compared with the influence of the same parameters on the classical CSF.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.