Objective characterization of an in-line phase sensitive imaging prototype using a mid-energy beam

Abstract

The goal of this study was to perform a characterization study for an in-line phase contrast x-ray imaging prototype with a mid-energy source. Compared to similar prototypes that use high energies, the mid-energy system offers better balancing between the attenuation and phase induced contrasts. An inline phase sensitive prototype acquired all images for this study. The prototype utilizes a microfocus x-ray tube and a flat panel detector, aligned on an optical rail. The source-to-object distance (SOD) was set to 68.58cm while the source-to-image distance (SID) was set to 150.876cm for a magnification of 𝑀 = 2.2. The modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) were calculated for the prototype with source potentials of 60, 90, and 120kV. The oversampled MTF was calculated for each setting. NPS experiments were conducted with a virtual detector set at the SOD. Exposure at the SID was approximately the same for all NPS experiments. The 90 and 120kVp beams were directed through a 2.5mm Al filter, while 60kVp beams were sent through a 1.2mm Al filter. Results indicate that 60kV imaging yields lower amplitude noise than high energy imaging, while maintaining the same resolving power. The cutoff frequency for each source potential was approximately 14 line pairs per mm (lp/mm). The DQE(0) for 60kV, 90kV, and 120kV were 0.757, 0.564, and 0.571 respectively. The study confirmed the hypothesis that 60kVp phase sensitive x-ray imaging yields a higher DQE than those found at 90 and 120kVp.