CT visible internal stone structure, but not Hounsfield unit value, of calcium oxalate monohydrate (COM) calculi predicts lithotripsy fragility in vitro

Recent developments in computed tomography for urolithiasis: diagnosis and characterization

Objective. To critically evaluate the current literature in an effort to establish the current role of radiologic imaging, advances in computed tomography (CT) and standard film radiography in the diagnosis, and characterization of urinary tract calculi. Conclusion. CT has a valuable role when utilized prudently during surveillance of patients following endourological therapy. In this paper, we outline the basic principles relating to the effects of exposure to ionizing radiation as a result of CT scanning. We discuss the current developments in low-dose CT technology, which have resulted in significant reductions in CT radiation doses (to approximately one-third of what they were a decade ago) while preserving image quality. Finally, we will discuss an important recent development now commercially available on the latest generation of CT scanners, namely, dual energy imaging, which is showing promise in urinary tract imaging as a means of characterizing the composition of urinary tract calculi.

Stone clearance after extracorporeal shockwave lithotripsy in patients with solitary pure calcium oxalate stones smaller than 1.0 cm in the proximal ureter, with special reference to monohydrate and dihydrate content

OBJECTIVE

The aim of this study was to assess stone-free rates following extracorporeal shockwave lithotripsy (ESWL) of pure calcium oxalate (CaOx) stones in the proximal ureter.

MATERIAL AND METHODS

The investigators retrospectively examined 53 patients with 5-10 mm pure CaOx stones in the proximal ureter from the medical archives of 593 consecutive patients treated with ESWL. The compositions of calcium oxalate monohydrate (COM) and dihydrate (COD) in a given stone were determined by infrared spectrometry. Stone size, attenuation number and stone-to-skin distance (SSD) were measured using plain radiography and computed tomography (CT). ESWL success was evaluated by stone-free status after the first single session.

RESULTS

On average, calculi were 8.0 × 5.3 mm in size, with an SSD of 11.0 cm. The mean CT attenuation value was 740.1 HU. Attenuation numbers correlated significantly with stone diameter (r = 0.49), but had no correlation with the stone content of COM or COD. A negative correlation was observed between COM and COD content (r = -0.925). With regard to patients' physical characteristics and COM and COD content, no differences were found between study subgroups with stone-free and residual status (n = 38 and 15, respectively). There were also no differences in clinical features between patient subgroups with COM- or COD-predominant stones (n = 22 and 31, respectively).

CONCLUSION

The findings indicated that the differences in COM and COD content of CaOx stones had no impact on stone clearance after ESWL and that a favorable stone-free rate of the stones treated with ESWL may be achieved independently of CaOx hydration.

Stability of the infection marker struvite in urinary stone samples

BACKGROUND AND PURPOSE

Struvite in kidney stones is an important marker for infection. In kidney stone samples, struvite is known to be prone to chemical breakdown, but no data exist on the stability of samples stored in dry form. The objective of this study was to examine stability of struvite under increasingly poor conditions of storage.

MATERIALS AND METHODS

Samples of struvite kidney stones were broken to obtain 38 pieces averaging 67 mg in weight, and these were randomized into four storage conditions: Airtight containers stored in the dark, open containers in the dark, open containers in ambient light, and open containers at elevated temperature (40°C). Pieces were left for 6 months, and then analyzed for changes using micro CT and Fourier transform infrared spectroscopy (FT-IR).

RESULTS

Initial samples proved to be struvite, indicating no transformation in the large specimens that had been stored in airtight containers in the dark for more than 6 years before this study. Pieces of struvite taken from these large specimens appeared unchanged by micro CT and FT-IR after being stored in closed containers for 6 months, but 8 of 9 pieces in open containers showed the presence of newberyite in surface layers, as did 10 of 10 pieces in open containers out in ambient light. All pieces stored at 40°C showed transformation of struvite, with 60% of the pieces showing the presence of amorphous phosphates, indicating complete breakdown of struvite in the surface layers of the pieces.

CONCLUSION

We conclude that struvite in dry kidney stone samples is stable when the specimens are stored in airtight containers at room temperature, even after several years.

The interior structure of breast microcalcifications assessed with micro computed tomography

BACKGROUND

Morphology microcalcification descriptors help stratify the risk of breast malignancy. Micro CT is feasible for visualization of the fine-structure of tissues and may be suitible for high resolution microcalcification analysis.

PURPOSE

To analyze the interior structure of microcalcifications using a micro CT imaging system.

MATERIAL AND METHODS

Core needle breast biopsy specimens from 16 women with clustered microcalcifications were examined with micro CT. The samples measured between 0.8 to 1.2 mm in diameter. Micro CT scans with an isotropic voxel size of 8.4 µm were obtained to generate two- and three-dimensional images of the microcalcifications. The number of microcalcifications were counted on the magnified specimen radiogram and on micro CT. Attenuation values of microcalcifications were measured by drawing a region of interest (ROI) in the center of the microcalcifications. Two blinded observers assessed the morphology and the interior structure of microcalcifications.

RESULTS

Five patients had benign and 11 patients had malignant breast lesions. On micro CT, microcalcifications of benign tissue showed a coarse lamellar or trabecular interior structure, whereas microcalcifications of breast cancer tissue showed a more uniform granular interior structure. There was no correlation between attenuation values of benign compared with malignant microcalcifications.

CONCLUSION

On micro CT, an interior structure of microcalcifications is detectable. Benign and malignant microcalcifications display different patterns of interior structure.

Assessment of stone composition in the management of urinary stones

Several explanations have been suggested to account for the failure of extracorporeal shockwave lithotripsy (ESWL) treatment in patients with urinary stones, including large stone volume, unfavorable stone location or composition and the type of lithotriptor used. Unfavorable stone composition is considered a major cause of failure of ESWL treatment, and consequently knowledge of the stone composition before treatment is initiated is desirable. Plain abdominal radiographs cannot accurately determine either stone composition or fragility, and although the CT attenuation value in Hounsfield units (HU) (that is, normalized to the attenuation characteristics of water) is useful, this parameter has limited value as a predictor of stone composition or the response to ESWL treatment. By contrast, stone morphology as visualized by CT correlates well with both fragility and susceptibility to fragmentation by ESWL. For patients prone to recurrent calculi, analyses of stone composition are especially important, as they may reveal an underlying metabolic abnormality. The development of advanced imaging technologies that can predict stone fragility is essential, as they could provide extra information for physicians, enabling them to select the most appropriate treatment option for patients with urinary stones.

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.

Development of a scoring system from noncontrast computerized tomography measurements to improve the selection of upper ureteral stone for extracorporeal shock wave lithotripsy

PURPOSE

We investigated the role of noncontrast computerized tomography in predicting the treatment outcome of shock wave lithotripsy on upper ureteral stones to formulate a clinical algorithm to facilitate clinical management.

MATERIALS AND METHODS

Adult patients with upper ureteral stones confirmed by noncontrast computerized tomography and scheduled for primary in situ shock wave lithotripsy were prospectively recruited. Standardized treatment was performed on each patient. The primary end point was stone-free status at 3 months. Pretreatment noncontrast computerized tomography was assessed by a single radiologist blinded to the clinical parameters. Predictive values of computerized tomography measurements on the treatment outcome were then assessed.

RESULTS

Between October 2004 and July 2007 a total of 94 patients (60 male and 34 female) were recruited for the study. Logistic regression showed that stone volume, mean stone density and skin-to-stone distance were potential predictors of successful treatment. From ROC curves the optimum cutoff for predicting treatment outcomes for stone volume, mean stone density and skin-to-stone distance was 0.2 cc, 593 HU and 9.2 cm, respectively. A simple scoring system was constructed based on the 3 factors of stone volume less than 0.2 cc, mean stone density less than 593 HU or skin-to-stone distance less than 9.2 cm. The stone-free rate for patients having 0, 1, 2 and 3 factors was 17.9%, 48.4%, 73.3% and 100%, respectively (linear-by-linear association test 22.83, p <0.001).

CONCLUSIONS

Stone volume, mean stone density and skin-to-stone distance were potential predictors of the successful treatment of upper ureteral stones with shock wave lithotripsy. A scoring system based on these 3 factors helps separate patients into outcome groups and facilitates treatment planning.

Protein content of human apatite and brushite kidney stones: significant correlation with morphologic measures

Apatite and brushite kidney stones share calcium and phosphate as their main inorganic components. We tested the hypothesis that these stone types differ in the amount of proteins present in the stones. Intact stones were intensively analyzed by microcomputed tomography (micro CT) for both morphology (including the volume of voids, i.e., space devoid of X-ray dense material) and mineral type. To extract all proteins present in kidney stones in soluble form we developed a three-step extraction procedure using the ground stone powder. Apatite stones had significantly higher levels of total protein content and void volume compared to brushite stones. The void volume was highly correlated with the total protein contents in all stones (r2 = 0.61, P < 0.0001), and brushite stones contained significantly fewer void regions and proteins than did apatite stones (3.2 +/- 4.5% voids for brushite vs. 10.8 +/- 11.2% for apatite, P < 0.005; 4.1 +/- 1.6% protein for brushite vs. 6.0 +/- 2.4% for apatite, P < 0.03). Morphological observations other than void volume did not correlate with protein content of stones, and neither did the presence or absence of minor mineral components. Our results show that protein content of brushite and apatite stones is higher than that was previously thought, and also suggest that micro CT-visible void regions are related to the presence of protein.

Radiographic parameters on noncontrast computerized tomography predictive of shock wave lithotripsy success

PURPOSE

Accurate prediction of shock wave lithotripsy success for given patient and radiographic parameters will lead to improved selection of patients for shock wave lithotripsy vs more invasive treatment. In this study we determined which radiographic parameters are the most predictive of shock wave lithotripsy success, and present a method to incorporate these into current and future models based on nonradiographic parameters.

MATERIALS AND METHODS

A retrospective case-control study was performed to determine average, maximum and standard deviation of stone attenuation values, stone size and skin-to-stone distance on preoperative noncontrast computerized tomography for 220 patients successfully treated with shock wave lithotripsy and 105 patients in whom shock wave lithotripsy failed.

RESULTS

Average stone attenuation is the best independent predictor of shock wave lithotripsy success as determined by the Student t test (p <0.0001) and receiver operating characteristic curves. Odds and likelihood ratios are provided for shock wave lithotripsy success for incremental average HU cutoffs. An average HU cutoff can be established over which the refined probability of success is below an arbitrary minimally acceptable cutoff of a 60% stone-free rate. Using pre-test probabilities of shock wave lithotripsy success from nomograms in the literature, our data suggest that shock wave lithotripsy should be first line therapy for solitary 6 to 10 mm stones with an average stone attenuation of less than 1,000 and 640 HU for the proximal ureter and renal pelvis, respectively.

CONCLUSIONS

Average stone attenuation is a convenient radiographic measure that can be used to refine a known probability of shock wave lithotripsy success. Clinical HU cutoff guidelines can be determined based on current or future predictive nomograms based on other parameters.

The acute and long-term adverse effects of shock wave lithotripsy

Shock wave lithotripsy (SWL) has proven to be a highly effective treatment for the removal of kidney stones. Shock waves (SWs) can be used to break most stone types, and because lithotripsy is the only noninvasive treatment for urinary stones, SWL is particularly attractive. On the downside SWL can cause vascular trauma to the kidney and surrounding organs. This acute SW damage can be severe, can lead to scarring with a permanent loss of functional renal volume, and has been linked to potentially serious long-term adverse effects. A recent retrospective study linking lithotripsy to the development of diabetes mellitus has further focused attention on the possibility that SWL may lead to life-altering chronic effects. Thus, it appears that what was once considered to be an entirely safe means to eliminate renal stones can elicit potentially severe unintended consequences. The purpose of this review is to put these findings in perspective. The goal is to explain the factors that influence the severity of SWL injury, update current understanding of the long-term consequences of SW damage, describe the physical mechanisms thought to cause SWL injury, and introduce treatment protocols to improve stone breakage and reduce tissue damage.