In order to perform fan-beam reconstruction using projection data collected from a noncircular scanning locus, existing noncircular fan-beam formulas require a derivative of the scanning locus with respect to the rotation angle. A derivative-free noncircular fan-beam reconstruction formula that is based on a geometrical explanation of the circular equispatial fan-beam reconstruction formula is ...

We have developed a prototype imaging system that can perform simultaneous x-ray transmission CT and SPECT phantom studies. This system employs a 23-element high-purity-germanium detector array. The detector array is coupled to a collimator with septa angled toward the focal spot of an x-ray tube. During image acquisition, the x-ray fan beam and the detector array move synchronously along an ar...

A rotatable collimator is proposed for the LHC phase II collimation upgrade. When the beam crosses the collimator, it will excite trapped modes that can contribute to the beam energy loss and power dissipation on the vacuum chamber wall. Transverse trapped modes can also generate transverse kicks on the beam and may thus affect the beam quality. In this paper, the parallel eigensolver code Omeg...

Background: This study aims to investigate radiation beam geometry of Cyberknife beam and change in dosimetric characteristics of six megavoltage (6MV) flattening filter free (FFF) beam after passing through high density cadmium free compensator alloy.Material and Methods: In this experimental study, changes in FFF beam dosimetric characteristics after passing through compensator alloy wa...

In single photon emission computed tomography (SPECT), pinhole and cone-beam collimators are used for small object imaging. It is accepted that a pinhole collimator should be used if the object is very small, and the cone-beam collimator should be used if the object is larger. This paper presents criteria to determine which collimation geometry is more advantageous in terms of spatial resolutio...

Based on realistic Monte-Carlo simulations a two-stage beam collimation system is designed to minimize the beam loss in the Fermilab Tevatron for fixed target and collider Run II. Thin primary collimators are used to increase particle amplitude and their impact parameter on the downstream secondary collimators. This results in a significant reduction of the total beam loss in the machine, decre...

In single photon emission computed tomography (SPECT), a varying-focal-length cone-beam collimator can be used to reduce the truncation problem and to maintain sensitivity when imaging the organ of interest. The collimator is constructed so that the collimator holes focus to a circular symmetric, spatially varying, focal point function. The focal length increases radially from the shortest foca...

The performance of future linear colliders are limited by the effect of short-range collimator wakefields on the beam. The beam quality is sensitive to the positioning of collimators at the end of the linac. The determination of collimator wakefields has been difficult, largely because of the scarcity of measurement data, and of the limitation of applicability of analytical results to realistic...

In this paper, Novikov's inversion formula of the attenuated two-dimensional (2D) Radon transform is applied to the reconstruction of attenuated fan-beam projections acquired with equal detector spacing and of attenuated cone-beam projections acquired with a flat planar detector and circular trajectory. The derivation of the fan-beam algorithm is obtained by transformation from parallel-beam co...