Biomedical subjects

R Accorsi

Publications and source records attributed to R Accorsi.

3 recordsLinked to original sources

PubMed2006

Non-diverging analytic expression for the on-axis sensitivity of converging collimators: analytic derivation.

The expressions for the sensitivity of converging collimators found in the literature diverge at points near the focal locus of the collimator. In this paper, an analytical formula that does not diverge is derived and compared to that available in the literature. An analysis is provided to predict the cases in which use of the new formula is advisable. Since the first expression derived is rather complex, approximations were made to reach simpler formulae. The formulae derived can be used to define and extend the realm of applicability of the literature expression in the cases identified in their derivation.

Computer Simulation↗

PubMed2006

Non-diverging analytic expression for the on-axis sensitivity of converging collimators: experimental verification.

The previous paper presented the derivation of an analytical formula for the sensitivity of converging collimators that does not diverge at the focal locus of the collimator. Its predictions, those from a simplified version, and those from the most commonly referenced formula are compared to Monte Carlo and experimental data. Agreement is excellent for all formulae far from the focal locus of the collimator, where it is markedly better for the new formula and its approximation. It is inferred that such formulae should be used in the cases identified by theory, namely around the focal locus of collimators of any focal length and over a substantial part of the field-of-view for short focal length collimators.

Calibration↗

PubMed2005

Resolution- versus sensitivity-effective diameter in pinhole collimation: experimental verification.

To account for photon penetration, the formulae used to calculate the geometric resolution of a pinhole collimator use an effective diameter d(e) rather than the physical diameter of the aperture. The expressions commonly used for d(e), however, were originally derived to include penetration in sensitivity calculations. To predict the full width at half maximum (FWHM) resolution of the point-spread function (PSF) of a knife-edge pinhole collimator, we have previously proposed simple expressions for a resolution-effective diameter d(re). Unlike those for d(e), expressions for d(re) predict both a dependence on the polar angle of the source (theta) and a non-isotropic PSF. In this paper, the new theory was tested by measuring experimentally the FWHM of the PSF. Results confirm the theoretical predictions that (a) d(re) provides the best estimates of the experimental FWHM as a function of theta and of the direction in the plane of the pinhole, (b) Paix's expression for d(e) tends to overestimate the FWHM, (c) Anger's is a better approximation, but still cannot predict the dependence on theta, and (d) the FWHM decreases with decreasing theta, i.e. resolution improves for sources at the edge of the field-of-view.

Algorithms↗