Experimental evaluation of PET inserts on reducing the acolinearity effect and improving image resolution

Image resolution of a PET scanner is affected by detector intrinsic spatial resolution, positron range, acolinearity, and the depth of interaction (DOI) effect. Typically, one would reduce crystal dimension to improve image resolution. One can reduce crystal width to improve the tangential resolution. One can also reduce crystal length or increase system diameter to reduce the DOI effect and improve the radial resolution, at the cost of reduced sensitivity. Ideally, one would like to use multi-layer DOI detectors to improve both resolution and sensitivity, but that can be quite expensive. In the case of clinical whole-body (WB) PET scanners, the acolinearity effect limits the image resolution to be no better than 2 mm FWHM regardless how small the detector crystal is. We are developing PET insert devices that improve image resolution of existing PET systems by allowing zoom-in imaging within a smaller field of view (FOV). A high-resolution insert positioned near an object magnifies the radioactivity distribution by a fan-beam geometry that is similar to a pinhole camera. Image resolution of insert systems using this "pseudo-pinhole PET" geometry still depend on the detector intrinsic spatial resolution and the acolinearity effect, but in a way that is different from traditional PET systems. This study investigates the factors that affect image resolution of insert systems through a series of experiments