Revolving multipinhole SPECT for small animal imaging

Multi-pinhole collimators are often used to obtain the detection sensitivity necessary for small animal SPECT with submillimeter spatial resolution. However, in comparison to pinhole collimators with single aperture, multipinhole acquisitions run the risk of yielding overlapping projection data, which can result in reconstructed images that exhibit multiplexing artifacts. In this work, we study the multiplexing artifacts produced by a nine-pinhole collimator in three different acquisition geometries: (1) circular multipinhole (CMP) in which the nine-pinhole collimator is rotated around the object with a simple circular gantry rotation, (2) helical multipinhole (HMP) that uses a circular gantry rotation combined with a table translation to produce a helical acquisition, and (3) revolving multipinhole (RMP) produced with a circular orbit of the gantry combined with a concurrent revolution of the nine-pinhole collimator. The pinhole configurations were simulated for a SPECT scanner with a 40 40 cm² detector. The reconstructed images obtained using the different imaging geometries were compared by calculating the lesion detectability index, contrast-ratio, normalized standard deviation and percentage error using a series of simulation experiments. The improved sampling obtained with the RMP imaging geometry produced a faithful reconstruction of a larger FOV compared to the single pinhole (SP) case. For example, the contrast ratio for equivalent noise levels obtained from a Defrise phantom were approximately 98%, 92%, 75% and 35% for RMP, HMP, CMP and SP respectively. Results show that the improved angular sampling of the RMP imaging geometry diminishes the effects of multiplexing patterns thereby facilitating the accurate convergence of the resulting SPECT image.