In the second part of the paper, the sensitivity expression will be validated with Monte Carlo simulations for both geometric and penetrative cases.Ī. The effective slit width is always at least as large as the geometric width of the slit. It will be shown that the effect of photon penetration on the sensitivity can be handled by the use of an effective slit width, which is defined as the width of an ideal slit (i.e., one that does not allow penetration) that passes the same number of photons as the real slit, which allows penetration. In this paper, we will first derive an analytical expression for the sensitivity of a slit-slit collimator. An analytic expression for sensitivity, for example, is necessary to be able to make the comparison of sensitivity performance with other collimation schemes, such as a pinhole and slit-slat –. An analytic expression for the sensitivity and resolution for a slit-slit collimator are not yet available. However in order to be able to assess the usefulness of the slit-slit collimator in different imaging scenarios, its characteristics such as sensitivity and resolution need to be evaluated. Later, in, the reconstruction algorithm presented in was extended to include a uniform attenuation correction. In, an analytical image reconstruction algorithm based on tilted fan-beam inversion with non-uniform attenuation was developed the authors also showed that the reconstructed images had less severe axial artifacts compared to pinhole collimation. Since its proposal as an alternative to a pinhole collimator, the slit-slit collimator’s characteristics have not been evaluated yet. Since slit-slit collimators can have two independent, axial and transaxial cone angles, the severity of the axial artifacts may be reduced by allowing a smaller cone angle in the axial direction. Slit-slit collimation has been proposed as an alternative to pinhole collimation because of its favorable sampling properties. This leads to axial artifacts in the reconstructed image –. Q is the center of the projection, and γ is the angle between the photon path and the slit 2 plane.Ī pinhole collimator imaging along a circular orbit results in projections that do not fully fill the Radon space. (b) The projection of slit 1 on the plane of slit 2 has width w 1 ′. The polar angle is θ and the azimuthal angle ϕ is measured with the right hand rule about the y–axis with respect to the direction of slit 2. w 1(2) is the slit 1(2) width, and h 1(2) is the perpendicular distance from the source P to the plane of slit 1(2). (a) Schematic drawing showing the slit-slit geometry and the symbols used. The derived expression for the sensitivity was validated by Monte Carlo simulation for both geometric and penetrative cases. When the effective slit width is used instead of the geometric slit width, the derived analytical expression accurately accounts for photon penetration of the aperture. This expression could also be useful for comparing the slit-slit’s sensitivity performance with others. An analytical expression for sensitivity is necessary in order to accurately model the system response. In this paper an analytical expression is derived for the sensitivity of slit-slit collimation including effective slit widths for photon penetration. In addition, since the two slit planes can be placed at different distances with respect to the source, a better detector usage can be achieved, especially in the case of detectors and imaged objects with different aspect ratios. A small axial acceptance angle may help mitigate axial blurring with circular orbits, allowing multiple copies axially. Since the two slits are independent of each other, there can be independent axial and transaxial acceptance angles. A slit-slit collimator consists of two orthogonal slits and can be conceptualized as a generalized pinhole.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |