Study of dose reduction in computed tomography using a time-of-flight scatter rejection mechanism in a 3D voxelized...

Objective. Scattered photons are the main source of contrast degradation in x-ray imaging when not filtered out appropriately. Measuring the time-of-flight (ToF) of x-ray photons has recently been revisited as an innovative way to discriminate between primary and scattered photons without significant loss in sensitivity in order to improve the contrast-to-noise ratio (CNR) in radiography and computed tomography (CT). The technique could allow for the removal of the anti-scatter grid (ASG) while still producing a CNR comparable to that of a fan-beam CT, allowing for potential dose reduction and more uniform axial spatial resolution when used in a cone-beam configuration.Approach. This work presents an evaluation study of the potential reduction in absorbed radiation dose in the body during a CT image acquisition when using time-correlated single photon counting CT in a cone-beam geometry. A comparative study is carried out using Monte Carlo simulations in GEANT4 Application for Tomographic Emission of a voxelized body of an adult female for a multi-slice fan beam CT scanner and a cone beam system using ToF measurements with various timing jitters or ASGs.Main results. For CNR equivalent torso images, simulation data in the high contrast region for ToF of 10, 50, 100, 200 ps full width at half maximum (FWHM) timing jitters show a dose reduction of 35%, 28%, 15%, 5% respectively compared to cone-beam CT with an ASG. Compared to a fan-beam setup without an ASG, the cone-beam ToF CT achieved a dose reduction of 13% and 4% for 10 and 50 ps FWHM timing jitter respectively, and an increase of 13% and 26% at 100 and 200 ps timing jitter. In the low contrast region, 10 ps ToF led to a reduction in dose of 15% and 50 ps led to an increase of 5%. Resolutions above 100 ps failed to accurately reject scattered photons and led to a considerable increase in dose.Significance. ToF scatter rejection shows potential for reducing radiation dose while preserving image quality when the timing resolution is 50 ps FWHM or better, but better ToF-based scatter rejection algorithms are required to enable this method for worse timing resolutions and low contrast regions.