# Multi-Modal X-ray Imaging and Analysis for Characterization of Urinary Stones
###### Abstract  
Background: The composition of stones formed in the urinary tract plays an important role in their management over time. The most common imaging method for the non-invasive evaluation of urinary stones is radiography and computed tomography (CT). However, CT is not very sensitive, and cannot differentiate between all critical stone types. In this study, we propose the application, and evaluate the potential, of a multi-modal (or multi-contrast) X-ray imaging technique called speckle-based imaging (SBI) to differentiate between various types of urinary stones. Methods: Three different stone samples were extracted from animal and human urinary tracts and examined in a laboratory-based speckle tracking setup. The results were discussed based on an X-ray diffraction analysis and a comparison with X-ray microtomography and grating-based interferometry. Results: The stones were classified through compositional analysis by X-ray diffraction. The multi-contrast images obtained using the SBI method provided detailed information about the composition of various urinary stone types, and could differentiate between them. X-ray SBI could provide highly sensitive and high-resolution characterizations of different urinary stones in the radiography mode, comparable to those by grating interferometry. Conclusions: This investigation demonstrated the capability of the SBI technique for the non-invasive classification of urinary stones through radiography in a simple and cost-effective laboratory setting. This opens the possibility for further studies concerning full-field in vivo SBI for the clinical imaging of urinary stones. kidney stone; urinary stone; KUB radiography; X-ray computed tomography; X-ray speckle-based imaging; X-ray phase-contrast and dark-field imaging Article  
[PERSON], [PERSON], [PERSON], [PERSON], R. Multi-Modal X-ray Imaging and Analysis for Characterization of Urinary Stones  
The standard imaging methods for the diagnosis and evaluation of urinary stones are ultrasonography (US), kidney-unterter-bladder (KUB) radiography, and non-contrast-enhanced computed tomography (NCCT) of the abdomen and pelvis [5; 6]. US is widely accessible and poses no radiation dose, but suffers from low sensitivity and specificity. For X-ray imaging, one challenge is that only 60% of all renal stones are radiopaque and bear no risk of being missed [5; 6]. Recently, dual-energy CT (DECT) has been suggested to improve the prediction capability for stone-type differentiation, compared to the standard CT [3; 4; 5; 6]. By facilitating low- and high-energy scanning during a single acquisition, DECT has the inherent capability to help differentiate between materials that have similar electron densities but varying photon absorptions [3; 4; 5]. DECT is nearly 100% accurate when characterizing uric acid (UA) stones, both in vitro and in vivo [4]. Recently, some progress has been made to differentiate between non-UA stone types, such as calcium oxalate and hydroxylapatite stones [7]. However, the ability of DECT to discriminate among stone types depends on the difference between the CT number ratio of the materials, which is determined by the difference in the atomic numbers of stone components and the spectral separation [7]. The effective atomic numbers of the UA stone types fall into a narrow range (6.84-7.01); the effective atomic numbers of non-UA stones are higher and more varied (10.78-15.56). The large difference in the effective atomic numbers of UA and non-UA stones explains the ability of DECT to differentiate UA from non-UA stones with higher accuracy. However, the differences in the effective atomic numbers among the common non-UA stones such as cystine, struvite, calcium oxalate, brushite, and apatite are much smaller. Considering that many stones are a combination of two or more of the above compositions, a true differentiation of various stones remains a great challenge [7]. Multi-modal X-ray imaging techniques can potentially be an alternative for urinary stone diagnosis.