Time-multiplexing using a static full-ring multi-pinhole collimator for brain SPECT

In clinical practice, brain SPECT is usually performed using a dual-head SPECT scanner with fan-beam or parallel-beam collimators rotating around the patient´s head. The resolution of such a system is typically around 8-10 mm. We designed a SPECT system based on a full ring of detectors with a stationary multi-pinhole collimator. The spatial resolution of this brain imaging system is 6 mm. The system is adaptive in the sense that it can be used with different degrees of multiplexing by selecting the number of pinholes that are opened at the same time. The opening and closing of pinholes is controlled with a shutter mechanism. In this study we investigated the potential of combining multiplexed and non-multiplexed data (called time-multiplexing) to increase the sensitivity and the image quality of the system. We simulated and reconstructed a uniform phantom to assess the presence of artifacts, a contrast phantom to quantify the potential improvement in image quality and a Hoffman phantom for visual assessment. We compared different acquisition setups: without multiplexing, with only multiplexing and with time-multiplexing. The reconstructed images with only multiplexed data show severe artifacts. These were reduced by using time-multiplexing and were completely eliminated by using a body support (BS). The simulations of the contrast phantom show an improved image quality for time-multiplexing with BS (5% improvement in CRC at 58% noise compared to non-multiplexed data with BS).