A prototype rotating slat collimator for single photon emission computed tomography.

A collimator consisting of a series of highly attenuating parallel slats has been constructed and used in conjunction with a gamma-camera to approximately measure planar projections of a given radionuclide distribution. The enlarged solid angle of acceptance afforded by the slat collimator gave rise to an increased geometric efficiency of between 12 and 28 times that observed with a low-energy high-resolution (LEHR) parallel-hole collimator. When the slats rotated over the face of the detector and the camera gantry turned about the object, sufficient projections were acquired to reconstruct a three-dimensional (3-D) image using the inversion of the 3-D radon transform. The noise behavior of an algorithm for implementing this inversion was studied analytically and the resulting relationship has been verified by computer simulation. The substantially improved geometric efficiency of the slat collimator translated to improvements in reconstructed signal-to-noise ratio (SNR) by, at best, up to a factor of 2.0 with respect to standard parallel-hole collimation. The spatial resolution achieved with the slat collimator was comparable to that obtained with a LEHR collimator and no significant differences were observed in terms of scatter response. Accurate image quantification was hindered by the spatially variant response of the slat collimator.