Hole Array Pattern Research Articles

Study of high-energy multihole collimators

Recently, a general theoretical description of multihole collimators has been proposed by one of the authors. In this work, the theory was used to study the artifacts, which are caused by the hole-array pattern of high-energy collimators. The relevant outcomes of the study were that the response to a sheet source does not depend on its distance from the collimator, whereas the response depends on the gap between the collimator and the image plane that is located in the scintillation crystal; the dependence of hole-array artifacts on this gap was assessed and the existence of optimal values for which they are minimized was found. A large field of view camera, equipped with a high-energy general purpose collimator for /sup 131/I with hexagonal holes placed in an hexagonal lattice, was used. A series of images of a flood source placed on the external face of the collimator was acquired. Each image was acquired with a different value of the crystal-collimator distance. The analysis of the images clearly showed the existence of optimal crystal-collimator distances to reduce the hole-array artifacts. These distances have been found in agreement with the values predicted by the theory. This work may be useful for the design of new collimators, for the optimal arrangement of camera-collimator system and it may also foster the study of some artifacts compensation methods.

Geometrical response of multihole collimators

A complete theory of camera multihole collimators is presented. The geometrical system response is determined in closed form in frequency space. This closed form accounts for the known efficiency and resolution formulae for parallel beam, fan beam, cone beam and astigmatic collimators as well as for the most frequent hole array patterns and hole shapes. The point spread function in the space domain for a certain collimator and source position can be calculated via a discrete fast Fourier transform. Beside the complete theoretical definition of the response of multihole collimators, this theory allows the definition of accurate models of the geometrical response for SPECT reconstruction and it is suitable for designing new collimators.