CT dose reduction factors in the thousands using X-ray phase contrast

Marcus J Kitchen,Timur E Gureyev,Stuart B Hooper,Kentaro Uesugi,Naoto Yagi,Genevieve A Buckley,Nico Andres-Thio,Megan J Wallace

doi:10.1038/s41598-017-16264-x

Abstract

Phase-contrast X-ray imaging can improve the visibility of weakly absorbing objects (e.g. soft tissues) by an order of magnitude or more compared to conventional radiographs. Combining phase retrieval with computed tomography (CT) can increase the signal-to-noise ratio (SNR) by up to two orders of magnitude over conventional CT at the same radiation dose, without loss of image quality. Our experiments reveal that as the radiation dose decreases, the relative improvement in SNR increases. We show that this enhancement can be traded for a reduction in dose greater than the square of the gain in SNR. Upon reducing the dose 300 fold, the phase-retrieved SNR was still up to 9.6 ± 0.2 times larger than the absorption contrast data with spatial resolution in the tens of microns. We show that this theoretically reveals the potential for dose reduction factors in the tens of thousands without loss in image quality, which would have a profound impact on medical and industrial imaging applications.

Highlights

X-ray radiography and computed tomography (CT) are two of the most common imaging modalities in diagnostic medicine
A newborn rabbit thorax was imaged for this study to show the impact of phase retrieval on improving the image signal-to-noise ratio (SNR) whilst maintaining sufficiently high spatial resolution to resolve individual alveoli
The gain in spatial resolution from Fresnel diffraction has been traded for an increase in the SNR

Summary

Introduction

X-ray radiography and computed tomography (CT) are two of the most common imaging modalities in diagnostic medicine. New techniques have been developed to enhance image contrast by an order of magnitude or more[1,2,3] using phase shifts (i.e. refraction) of X-rays. Propagation-based imaging (PBI) is the simplest phase contrast technique, relying on Fresnel diffraction[4], and is well-suited to commercially available polychromatic, micro-focus X-ray sources[5]. Beltran et al.[13,14] extended TIE-Hom for multi-material samples These algorithms have been shown to improve the signal-to-noise ratio (SNR) by up to 200 fold over conventional CT with minimal loss of spatial resolution[13,14,15]. Since photon number is proportional to radiation dose and, in the case of constant photon rate, η, to exposure time, t, as n = ηt, the gain in SNR provided by phase retrieval is: www.nature.com/scientificreports/. The attenuation coefficient, μ, is the CT signal and z is the object-to-detector propagation distance that enables

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