Axial Movement Parameter Study on Preclinical Slit-Slat SPECT

One challenge to discrete detector slit-slat SPECT is that the system's resolution and sensitivity vary significantly in the axial direction. The objective of this work was to reduce the variation by introducing axial movement and to determine the corresponding parameters, i.e. step size (D) and total length (L). We calculated the system response matrix of the slit-slat SPECT system and evaluated the system's axial-direction resolution and sensitivity as functions of axial positions in the field of view. A series of scan protocols with combined rotational and axial movements, that is, helical scans, were applied to simulated phantom studies to select the preferred L and D values. Introducing axial movement effectively improved the system's axial-direction sensitivity uniformity and reconstructed image resolution in both axial direction and in transverse plane, and it also reduced the artifacts in the transverse plane. The preferred choice of L is the cycle of the periodic pattern formed by the slat collimator's and detector crystals. As about the value of D, a smaller D value is preferred for better uniformity as well as resolution improvement but practical constraints would apply.