Time-of-flight scatter rejection in x-ray radiography

Abstract

Objective 
Time-of-flight (TOF) scatter rejection allows for identifying and discarding scattered photons without the use of an anti-scatter grid (ASG). Although TOF scatter rejection was initially presented for cone-beam CT, we propose, herein, to extend this approach to X-ray radiography. This work aims to evaluate with simulations if TOF scatter rejection can outperform ASGs for radiography.

Approach 
GATE was used to simulate the radiography of a head and a torso and a water cylinder with bone inserts in a system with total timing jitters from 0 ps up to 500 ps full-width-at-half-maximum. The transparency of TOF scatter rejection to primary and scattered photons was evaluated as if it were a virtual ASG.

Main results 
With a total timing jitter of 50 ps, TOF scatter rejection can reach a selectivity of 4.93 with a transparency to primary photons of 99%. Reducing the timing jitter close to 0 ps increases the selectivity up to 15.85 for a head and torso radiography, outperforming typical ASGs which usually have a selectivity from 2.5 to 10 with a transparency to primary photons from 50% to 70%.

Significance 
This suggests that TOF scatter rejection may be suitable to replace ASGs in applications requiring lower radiation exposure if sufficiently low timing jitter is achieved.

Bright Innovations: Review of Next-Generation Advances in Scintillator Engineering

“…It is noteworthy to understand that a single scintillator cannot be ideal for all the applications, and the reader may refer to the following literature for comprehensive information on scintillator requirements for certain applications. ,,,, Here we briefly name some applications that could benefit from the above-mentioned enhancements; e.g., PET was mentioned above as an application that could benefit from enhanced light output, energy resolution, and timing. These parameters are relevant for other modalities of medical imaging as well; e.g., very fast scintillators with high light output may make way to time-of-flight measurements in CT and X-ray radiography, allowing significantly reduced dose load on a patient. , High-energy physics uses high-volume scintillator detectors for calorimetry (particle energy measurement); the sampling calorimeter concept, based on a combination of tiles of fibers of different materials in one detector (shashlik or spaghetti type, correspondingly), presents a prefiguration of energy sharing metamaterials. , At the same time, detectors dedicated to measuring the precise timing of the studied events, particle tracking, or beam characterization utilize thin sensitive layers, so it is the available niche for nanophotonically enhanced materials, and both enhanced timing and light output would play positive roles in these applications. ,, Other rapidly developing applications such as X-ray microtomography and microscopy, including synchrotron-based imaging, demand good spatial resolution, which can be achieved by a photonic approach . Other applications in the areas of security, nondestructive testing, scientific measurements, etc., may benefit from nanophotonic and metamaterials approaches when these underlying technologies are mature enough to allow for volume materials.…”

“…These parameters are relevant for other modalities of medical imaging as well; e.g., very fast scintillators with high light output may make way to time-of-flight measurements in CT and X-ray radiography, allowing significantly reduced dose load on a patient. 133 , 134 High-energy physics uses high-volume scintillator detectors for calorimetry (particle energy measurement); the sampling calorimeter concept, based on a combination of tiles of fibers of different materials in one detector (shashlik or spaghetti type, correspondingly), presents a prefiguration of energy sharing metamaterials. 135 , 136 At the same time, detectors dedicated to measuring the precise timing of the studied events, particle tracking, or beam characterization utilize thin sensitive layers, so it is the available niche for nanophotonically enhanced materials, and both enhanced timing and light output would play positive roles in these applications.…”