Abstract
Tomographic phase contrast imaging using hard X-rays is instrumental in revealing and understanding the three-dimensional (3D) anatomic structure of biological tissues. However, phase contrast imaging is often limited to synchrotron radiation sources to which access is limited and highly competitive. Therefore, it is critical to enable high-quality phase contrast tomography using lab-based X-ray sources. We present a lab-based soft tissue 3D imaging approach through optimised in-line phase contrast computed tomography, building upon and going beyond previous work of Bidola et al. [Opt Express 23(23), 30000-30013 (2015)]. Murine soleus muscle was used as a test specimen to systemically optimise source-to-sample and sample-to-detector distances, exposure time and the critical ratio used for Paganin phase retrieval before tomographic reconstruction. Larger propagation distances combined with longer exposure times resulted in improved image quality. Whilst the contrast-to-noise ratio of lab-based phase contrast imaging was found to be lower than that of synchrotron-based imaging, important microscopic soft tissue features, such as nerves, could well be distinguished in 3D from surrounding tissue for both imaging modalities. This shows that lab-based X-ray sources present a viable alternative to synchrotron radiation sources for tomographic phase contrast imaging of soft tissues.
Highlights
Three-dimensional X-ray tomographic imaging of soft tissues, such as brain, colon, lung, muscle, skin and other organs, can be used to enhance the understanding of the tissue structure and how it is linked to the tissue function in health and disease
The image quality resulting from phase retrieval with different δ/μ ratios was firstly characterised using signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) (Fig. 2 (a)) and by parallel visual assessment of the respective reconstructed tomographic data sets
The standard deviation over each image stack of both SNR and CNR increased with increasing δ/μ ratio (Fig. 2 (a))
Summary
Three-dimensional X-ray tomographic imaging of soft tissues, such as brain, colon, lung, muscle, skin and other organs, can be used to enhance the understanding of the tissue structure and how it is linked to the tissue function in health and disease. Dealing with soft tissues, which are composed primarily of light elements with low atomic numbers, Wu et al observed [12] that soft tissue attenuation cross-sections for hard X-rays can be approximated by incoherent scattering that is proportional to the atomic number Based on these observation, a complementary relationship between phase shift and X-ray attenuation for quasi-homogenous and weakly absorbing objects, a so-called ‘phase-attenuation’ duality, has been suggested by the same researchers [12], stating that the linear absorption coefficient and the phase change are both proportional to the local electron density of the object, which can be exploited for phase retrieval through PPCI using a single propagation distance only [13]
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