Time-lapse nondestructive assessment of shock wave damage to kidney stones in vitro using micro-computed tomography

How reliable is endoscopic stone recognition? A comparison between visual stone identification and formal stone analysis

OBJECTIVE

To assess the diagnostic accuracy and intra-observer agreement of endoscopic stone recognition compared with formal stone analysis.

INTRODUCTION

Stone analysis is a corner stone in the prevention of stone recurrence. Although X-ray diffraction and infrared spectroscopy are the recommended techniques for reliable formal stone analysis, this is not always possible, and the process takes time and is costly. Endoscopic stone recognition could be an alternative as it would give immediate information on stone composition.

MATERIAL AND METHODS

Fifteen endourologists predicted stone composition based on 100 videos from ureterorenoscopy. Diagnostic accuracy was evaluated by comparing the prediction from visual assessment with stone analysis by X-ray diffraction. After 30 days, the videos were reviewed again in a random order to assess intra-observer agreement.

RESULTS

The median diagnostic accuracy for calcium oxalate monohydrate was of 54% in questionnaire 1 (Q1) and 59% in questionnaire 2 (Q2), whereas calcium oxalate dihydrate had a median diagnostic accuracy of 75% in Q1 and 50% in Q2. The diagnostic accuracy for calcium hydroxyphosphate was 10% in Q1 and 13% in Q2. The median diagnostic accuracy for calcium hydrogen phosphate dihydrate and calcium magnesium phosphate was 0% in both questionnaires. The median diagnostic accuracy for magnesium ammonium phosphate was in 20% in Q1 and 40% in Q2. The median diagnostic accuracy for uric acid was 22% in both questionnaires. Finally, there was a diagnostic accuracy of 60% in Q1 and 80% in Q2 for cystine. The intra-observer agreement ranged between 45-72%.

CONCLUSION

Diagnostic accuracy of endoscopic stone recognition is limited and intra-observer agreement is below the threshold of acceptable agreement.

Using micro computed tomographic imaging for analyzing kidney stones

Stone analysis is a critical part of the clinical characterization of urolithiasis. This article reviews the strengths and limitations of micro CT in the analysis of stones. Using micro CT alone in a series of 757 stone specimens, micro CT identified the 458 majority calcium oxalate specimens with a sensitivity of 99.6% and specificity of 95.3%. Micro CT alone was also successful in identifying majority apatite, brushite, uric acid, and struvite stones. For some minor minerals-such as apatite in calcium oxalate or calcium salts in uric acid stones-micro CT enables the detection of minute quantities well below 1%. The addition of a standard for calibrating X-ray attenuation values improves the ability of micro CT to identify common stone minerals. The three-dimensional nature of micro CT also allows for the visualization of surface features in stones, which is valuable for the study of stone formation.

Micro-computed tomography characterization of tissue engineering scaffolds: effects of pixel size and rotation step

Quantitative assessment of micro-structure of materials is of key importance in many fields including tissue engineering, biology, and dentistry. Micro-computed tomography (µ-CT) is an intensively used non-destructive technique. However, the acquisition parameters such as pixel size and rotation step may have significant effects on the obtained results. In this study, a set of tissue engineering scaffolds including examples of natural and synthetic polymers, and ceramics were analyzed. We comprehensively compared the quantitative results of µ-CT characterization using 15 acquisition scenarios that differ in the combination of the pixel size and rotation step. The results showed that the acquisition parameters could statistically significantly affect the quantified mean porosity, mean pore size, and mean wall thickness of the scaffolds. The effects are also practically important since the differences can be as high as 24% regarding the mean porosity in average, and 19.5 h and 166 GB regarding the characterization time and data storage per sample with a relatively small volume. This study showed in a quantitative manner the effects of such a wide range of acquisition scenarios on the final data, as well as the characterization time and data storage per sample. Herein, a clear picture of the effects of the pixel size and rotation step on the results is provided which can notably be useful to refine the practice of µ-CT characterization of scaffolds and economize the related resources.

Micro-CT imaging of Randall's plaques

Micro-computed tomographic imaging (micro-CT) provides unprecedented information on stone structure and mineral composition. High-resolution micro-CT even allows visualization of the lumens of tubule and/or vessels within Randall's plaque, on stones or in papillary biopsies, thus giving a non-destructive way to study these sites of stone adhesion. This paper also shows an example of a stone growing on a different anchoring mechanism: a mineral plug within the lumen of a Bellini duct (BD plug). Micro-CT shows striking structural differences between stones that have grown on Randall's plaque and those that have grown on BD plugs. Thus, Randall's plaque can be distinguished by micro-CT, and this non-destructive method shows great promise in helping to elucidate the different mechanisms by which small stones are retained in the kidney during the development of nephrolithiasis.

Micro-computed tomography for analysis of urinary calculi

Micro-computed tomographic (micro CT) imaging has become an important tool for the study of urinary stones. The method involves the collection of a series of X-ray pictures of the stone as it is rotated, and the internal structure of the stone is computationally reconstructed from these pictures. The entire process takes from 30 min to an hour with present technology. Resulting images of the stone provide unprecedented detail of the mineral composition and its morphological arrangement within the stone. For smaller stones, reconstructions can easily have voxel sizes of <5 μm, making this a truly microscopic view of the stone. The micro CT reconstructions can be viewed with any of a number of existing methods for visualizing the structure of both the surface and internal features of the stone. Because the entire process is non-destructive, traditional analysis methods--such as dissection and spectroscopic examination of portions of the stones--can also be performed. Micro CT adds value to traditional methods by identifying regions of the stone to be analyzed, and also with its ability to scan a cluster of stones or stone fragments at once. Finally, micro CT has become a powerful tool to help investigate events in stone formation that distinguish different kinds of stone disease.

Lithotripsy

Shock wave lithotripsy (SWL) is the process of fragmentation of renal or ureteric stones by the use of repetitive shock waves generated outside the body and focused onto the stone. Following its introduction in 1980, SWL revolutionized the treatment of kidney stones by offering patients a non-invasive procedure. It is now seen as a mature technology and its use is perceived to be routine. It is noteworthy that, at the time of its introduction, there was a great effort to discover the mechanism(s) by which it works, and the type of sound field that is optimal. Although nearly three decades of subsequent research have increased the knowledge base significantly, the mechanisms are still controversial. Furthermore there is a growing body of evidence that SWL results in injury to the kidney which may have long-term side effects, such as new onset hypertension, although again there is much controversy within the field. Currently, use of lithotripsy is waning, particularly with the advent of minimally invasive ureteroscopic approaches. The goal here is to review the state of the art in SWL and to present the barriers and challenges that need to be addressed for SWL to deliver on its initial promise of a safe, effective, non-invasive treatment for kidney stones.

Cavitation bubble cluster activity in the breakage of kidney stones by lithotripter shockwaves

BACKGROUND AND PURPOSE

There is strong evidence that cavitation bubble activity contributes to stone breakage and that shockwave-bubble interactions are involved in the tissue trauma associated with shockwave lithotripsy. Cavitation control may thus be a way to improve lithotripsy.

MATERIALS AND METHODS

High-speed photography was used to analyze cavitation bubble activity at the surface of artificial and natural kidney stones during exposure to lithotripter shockwaves in vitro.

RESULTS

Numerous individual bubbles formed on the surfaces of stones, but these bubbles did not remain independent but rather combined to form clusters. Bubble clusters formed at the proximal and distal ends and at the sides of stones. Each cluster collapsed to a narrow point of impact. Collapse of the proximal cluster eroded the leading face of the stone, and the collapse of clusters at the sides of stones appeared to contribute to the growth of cracks. Collapse of the distal cluster caused minimal damage.

CONCLUSION

Cavitation-mediated damage to stones is attributable, not to the action of solitary bubbles, but to the growth and collapse of bubble clusters.