TOF Benefits and Trade-offs on Image Contrast-to-Noise Ratio Performance for a Small Animal PET Scanner

Recently, time-of-flight (TOF) scanners have become a mainstream in positron emission tomography research particularly owing to their ability to improve the image contrast-to-noise ratio (CNR). As the scintillation photon transport directly affects the coincidence time resolution, decreasing crystal length can be considered to improve timing performance even at the cost of sensitivity loss. This would also improve the radial spatial resolution and reduce the cost of the scintillator material, particularly in clinical scanners. Hence, this article investigates the tradeoffs between TOF, crystal length, and scan time with the goal of using TOF to compensate for CNR degradation caused by decreasing the scintillator volume in a highly pixelated scanner. To do this, a TOF model of the LabPET II small animal scanner was developed. The contrast recovery coefficient (CRC) and CNR performance were investigated through a factorial design. This was followed by assessing when TOF gain may be advantageous in small animal imaging. Results show that decreasing crystal length by 2 mm improves CRC performance for such a scanner while CNR can be fully recovered by increasing scan time. It was also observed that the same CNR can be reached for a shorter acquisition time if faster TOF resolution is achieved. This article concludes with a summary of the trade offs to optimize the CNR.