Phase contrast x-ray velocimetry of small animal lungs: optimising imaging rates.

R P Murrie,D M Paganin,A Fouras,K S Morgan

doi:10.1364/boe.7.000079

Abstract

Chronic lung diseases affect a vast portion of the world's population. One of the key difficulties in accurately diagnosing and treating chronic lung disease is our inability to measure dynamic motion of the lungs in vivo. Phase contrast x-ray imaging (PCXI) allows us to image the lungs in high resolution by exploiting the difference in refractive indices between tissue and air. Combining PCXI with x-ray velocimetry (XV) allows us to track the local motion of the lungs, improving our ability to locate small regions of disease under natural ventilation conditions. Via simulation, we investigate the optimal imaging speed and sequence to capture lung motion in vivo in small animals using XV on both synchrotron and laboratory x-ray sources, balancing the noise inherent in a short exposure with motion blur that results from a long exposure.

Highlights

Imaging the soft tissues of the body, and in particular the lungs and airways, has traditionally been difficult in the x-ray regime due to the similarities in the x-ray absorption properties of muscle, tissues and liquids
Phase contrast x-ray imaging (PCXI) allows us to image the lungs in high resolution by exploiting the difference in refractive indices between tissue and air
We investigate the optimal imaging speed and sequence to capture lung motion in vivo in small animals using x-ray velocimetry (XV) on both synchrotron and laboratory x-ray sources, balancing the noise inherent in a short exposure with motion blur that results from a long exposure

Summary

Introduction

Imaging the soft tissues of the body, and in particular the lungs and airways, has traditionally been difficult in the x-ray regime due to the similarities in the x-ray absorption properties of muscle, tissues and liquids. The variations in density and atomic make-up of different biological tissues create differences in their refractive abilities, and it is these refractive properties that create the contrast seen in phase contrast imaging In such a way, PCXI can prove to be significantly more sensitive than conventional x-ray imaging methods [10]. There are numerous ways to convert these phase variations to observable intensity variations, the simplest of which is propagation-based PCXI This technique differs from the conventional x-ray imaging setup only by the increased distance from the sample to the detector, with no additional optical elements required. As the distorted wavefront propagates towards the detector the rays diverge and interfere, producing a Fresnel diffraction pattern at the imaging plane, resulting in intensity variations in the form of bright-dark fringes These fringes enhance the visibility of material boundaries, allowing subtle features within the sample to have their visibility enhanced. With an increased sample-to-detector propagation distance, R2, the fringes of the Fresnel diffraction pattern initially increase in both width and relative magnitude, creating tuneable increased edge contrast [11]

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Conclusion