THE EXPERIMENTAL EVALUATION OF A PROTOTYPE ROTATING SLAT COLLIMATOR FOR PLANAR GAMMA-CAMERA IMAGING

A collimator consisting of a series of parallel slats has been constru cted and used in conjunction with a conventional gamma camera to colle ct one-dimensional projections of the radioisotope distribution being imaged. With the camera remaining stationary, the collimator was made to rotate continuously over the face of the detector and the projectio ns acquired were used to reconstruct a planar image by the theory of c omputed tomography. The propagation of noise on image reconstruction w as largely offset by the increased geometric efficiency that resulted from the enlarged solid angle of acceptance afforded by the slat colli mator. For a uniform disc of activity the signal to noise ratio (SNR) at a point in an image reconstructed by convolution and backprojection is shown to be given by where [GRAPHICS] and Q(1)(xi) is the one-dime nsional filter function in Fourier space. Improved noise behaviour was observed for images acquired with the slat collimator compared to tho se acquired with a low-energy high-resolution (LEHR) collimator for sm all distributions of activity. Spatial resolution with the slat collim ator was approximately equal to that obtained with an LEHR collimator and improved contrast was observed in images of small hot regions.