Reconstruction of Phantom SPECT Scans Acquired with a Slit-Slat Collimator

A slit-slat collimator merges the properties of pinhole and fan-beam collimation. The slit allows high sensitivity and fine resolution for points near the slit, as does a pinhole. The slats, which are normal to the axis of rotation, provide axial collimation, resulting in nearly independent axial slices and complete sampling for points for circular orbits. The collimator differs from pinhole in that a circular orbit is sufficient to avoid axial-blurring artifacts from incomplete sampling. It differs from fan-beam in that both the best resolution and best sensitivity are obtained near the collimator, whereas fan-beam´s sensitivity is best at the focal line. In this study, the SPECT performance of an early prototype collimator is evaluated. The collimator was placed on a lead box attached to a gamma camera. Micro hot-rod and cold-rod phantoms and a mini cold-rod phantom were rotated about a line parallel to the slats normal. Two different slit widths, 1.0 mm and 3.0 mm, were used. The projections were reconstructed slice by slice using an MLEM algorithm (50 iterations). The configuration of this early prototype allowed only a large radius of rotation (80 mm), hurting sensitivity and resolution. Despite this, the reconstruction was able to resolve 3.2 mm hot rods and 4.0 mm cold rods when the slit width was 3 mm. Hot rods of diameter 1.6 were resolved using the 1 mm slit, although sensitivity was reduced by a factor of 3. These resolutions are consistent with theoretical expectations for the resolutions at these configurations. The properties of this collimator make it a good choice for scanning mid-size objects.