Verification of the sensitivity and resolution dependence on the incidence angle for slit-slat collimation.

Single photon emission computed tomography (SPECT) can be performed with various collimator types, which have an inherent tradeoff between the properties of sensitivity, resolution, field of view and complete sampling. Slit-slat collimation, which has seen recent interest in the literature, combines a slit parallel to the axis of rotation of a gamma camera with a set of septa perpendicular to the slit. This collimator geometry exhibits properties that may enhance some SPECT imaging applications, specifically imaging of the breast, limbs and medium-sized animals. However, a complete description of its system response is critical for a comparison to other collimator types and for accurate reconstruction of projection data. Herein, experimental and Monte Carlo methods are used to determine the sensitivity and transaxial and axial resolutions as a function of the incidence angle theta, which is the angle formed by the line from the photon source to the center of the slit and the plane of the slit, to compare to theoretical expectations. Four configurations are investigated by varying the slit width, septal spacing and septal height. Monte Carlo sensitivity data not modeling penetration and scatter exhibit a sin(3)theta dependence. Experimental and Monte Carlo-derived sensitivity data modeling scatter and penetration are consistent with each other and have a sin(x)theta dependence, where x is greater than 3. Transaxial resolution data show a small dependence on theta, and axial resolution data are consistent with no angular dependence.