Medical image reconstruction using an exact formula for solid angle of view

Modeling of the tomographic weights usually incorporates angle of view, decay and attenuation. A usual assumption is that the gamma camera is a long way from the object, this leads to the approximation that the angle of view subtending the front of the collimator tube is the same as that subtending the back [6]. If, however, the distance between camera and subject is small then this approximation may not be good enough and artifacts may be produced. In this paper, the derivations of the angle of view and the solid angle of view are analyzed considering distances when the camera is close to the body. The solid angle is explained by an appropriate formula which is defined as the exact solid angle of view. The effect of the solid angle of view for different distances is examined. A comparison between exact solid angle and the approximate solid angle formula of Weir is presented. Finally the effects of the two formulae on reconstruction are studied using simulated data from circular gamma camera rotation systems.