Analysis of stone fragility in vitro and in vivo with piezoelectric shock waves using the EDAP LT-01

Noncontrast computed tomography factors that predict the renal stone outcome after shock wave lithotripsy

OBJECTIVES

Extracorporeal shock wave lithotripsy (ESWL) is a popular treatment for nephrolithiasis. We took advantage of noncontrast abdominal computed tomography (NCCT) to search the possible prognostic factors including abdominal fat distribution influencing stone-free rate.

METHODS

From August 2008 to August 2010, 145 patients who had renal calculus and had undergone ESWL were retrospectively reviewed. All of them received NCCT assessment before ESWL and were followed up after 1 month for stone clearance. These patients were divided into two groups: one was the stone-free group and the other was the residual-stone group. Affecting parameters included stone size, location, stone surface area, Hounsfield unit density (HU density), skin-to-stone distance (SSD), and abdominal fat area as analyzed between these two groups.

RESULTS

Of 145 patients, 70 were stone-free and 75 had residual stone after ESWL treatment and 1-month follow-up. From univariate analysis, stone size, HU density, SSD, and stone surface area were significant predicting factors for ESWL success. On multivariate analysis, the important factors influencing ESWL outcomes were HU density and stone surface area (odds ratio 1.002 vs. 77.18, respectively; P<.05). Abdominal fat accumulation and distribution had no significant difference between these two groups.

CONCLUSION

This study revealed that stone size, HU density, SSD, and stone surface area were associated with stone-free rate after ESWL treatment. Therefore, these factors could be used to assess the feasibility of ESWL before deciding the treatment strategy. Abdominal fat distribution had no significant impact on ESWL outcome for renal stones.

The efficacy of radiographic anatomical measurement methods in predicting success after extracorporeal shockwave lithotripsy for lower pole kidney stones

OBJECTIVES

To assess the impact of lower pole calyceal anatomy on clearace of lower pole stones after extracorporeal shockwave lithotripsy (ESWL) by means of a new and previously defined radiographic measurement method.

MATERIALS AND METHODS

Sixty-four patients with solitary radiopaque lower pole kidney stones were enrolled in the study. Infundibulopelvic angle (IPA), infundibulotransverse angle (ITA), infundibular lenght(IL), and infundibular width (IW) were measured on the intravenous urographies which were taken before the procedure.

RESULTS

48 of 64 patients (75%) were stone-free after a follow-up period of 3 months. The IPA,ITA,IL and IW were determined as statistically significant factors, while age,gender and stone area were found to have no impact on clearance.

CONCLUSION

By the help of radiographic measurement methods related to lower pole kidney anatomy, appropriate patient selection and increment in success after ESWL may be achieved.

Predicting effectiveness of extracorporeal shockwave lithotripsy by stone attenuation value

PURPOSE

The aim of this study was to evaluate the effect of stone attenuation value on the effectiveness of extracorporeal shockwave lithotripsy (SWL) for upper urinary tract stones.

METHODS

In this prospective study, 99 patients underwent SWL for solitary renal and upper ureteral stones from January 2007 to March 2009. All patients underwent CT scan before SWL. The mean attenuation value of stones in our study was 1213.3 +/- 314.5 Hounsfield units (HU). Group A consisted of 42 patients with stones of attenuation value <1200 HU and group B had 57 patients with stones of attenuation value >1200 HU. Stone size, location, requirement of number of shockwaves, shock intensities (power), retreatment rate, complication rate, auxiliary procedure rate, and effectiveness quotient (EQ) ratio were studied.

RESULTS

The mean total number of shocks required to fragment the stones in groups A and B were 1317.1 +/- 345.3 and 1646.5 +/- 610.8, respectively (p = 0.001), with a mean shock intensity of 12.2 +/- 0.7 and 12.4 +/- 0.5 kV, respectively (p = 0.03). Retreatment was not required in patients of group A, but 14.03% patients in group B required retreatment (p < 0.0001). Clearance rate in group A was 88.1%, whereas in group B it was 82.5% (p = 0.35). Auxiliary procedure rates were 9.5% and 10.5% in groups A and B (p = 0.22), respectively. EQ was 80.4% and 66.2% in groups A and B (p = 0.03), respectively. Complication rates were similar with 2.4% and 3.5% in groups A and B, respectively (p = 0.37). Significant correlation was recorded for total number and intensity of shocks with stone attenuation value.

CONCLUSIONS

The EQ of SWL for upper urinary tract stones was significantly better for stones with lower attenuation value. The number and intensity of shocks required to fragment these stones with lower attenuation value were also significantly lower.

Composition and clinically determined hardness of urinary tract stones

OBJECTIVES

To derive hardness factors for crystal phases of urinary tract stones and describe the hardness pattern in a stone population.

MATERIAL AND METHODS

In a retrospective study, recordings from patients treated with extracorporeal shock-wave lithotripsy (ESWL) (stone surface area < or = 100 mm2) were used to derive hardness factors. The number of re-treatments, the number of shock waves and the energy index (the voltage in kilovolts multiplied by the number of shock waves) required for a satisfactory stone disintegration were assumed to reflect the hardness. The stone composition in 2100 patients provided the basis for an average hardness pattern. A hardness index was calculated from the fraction of each crystal phase and its hardness factor.

RESULTS

The hardness factors were as follows: calcium oxalate monohydrate, 1.3; calcium oxalate dehydrate, 1.0; hydroxyapatite, 1.1; brushite, 2.2; uric acid/urate, 1.0; cystine, 2.4; carbonate apatite, 1.3; magnesium ammonium phosphate, 1.0; and mixed infection stones, 1.0. The hardness index for 114 stones (surface area 100-200 mm2) corresponded reasonably well to the ESWL treatment efforts. Calcium oxalate monohydrate, calcium oxalate dihydrate and hydroxyapatite were the most frequently encountered crystal phases in all 2100 stones. Only 21% of the stones were composed of only one crystal phase. There were two, three and more than three crystal phases in 26%, 38% and 15% of the stones, respectively. The hardness index calculated for 2100 stones ranged between 0.70 and 2.33, with a mean (SD) of 1.18 (0.15).

CONCLUSIONS

The hardness factors and hardness index derived in this study might be useful for describing the stone situation in individual patients and groups of patients and for comparison of various treatment strategies.

Effect of skin-to-stone distance on shockwave lithotripsy success

PURPOSE

We evaluated the effect of increased body habitus on stone-free rates after shockwave lithotripsy (SWL), determined by three reproducible skin-to-stone distances (SSDs) on CT.

PATIENTS AND METHODS

We retrospectively reviewed the records of 85 patients with preoperative CT scans available on Stentor Radiology Imaging who underwent SWL with the unmodified Dornier HM3 lithotripter from 2002 to 2007. SSDs were measured at the following angles: 0 degrees (vertical), 30 degrees, and 90 degrees (horizontal). Successful therapy was defined as stone free (residual fragments <2 mm) on follow-up imaging. Data were analyzed using descriptive statistics, Student t test, and the Fisher exact test.

RESULTS

Four hundred and eighty patients underwent SWL at our institution from 2002 to 2007; 85 patients (50.6% men, mean age 50.8 +/- 15.7 years, mean body mass index [BMI] 28.8 +/- 6.6 kg/m2) had preoperative CT scans available for review. On follow-up imaging (142.7 +/- 217.2 days), 49.4% of patients were stone free. Mean SSDs (vertical, 30 degrees, horizontal) in patients who were stone-free v those with residual stone were 104.3 +/- 26.2 mm v 102.6 +/- 29.9 mm (P = 0.79), 103.9 +/- 28.2 mm v 101.0 +/- 31.5 mm (P = 0.66), and 106.6 +/- 25.3 mm v 107.1 +/- 29.3 mm (P = 0.94), respectively.

CONCLUSIONS

Multiple variables have been shown to be associated with SWL success. In our sample of patients with preoperative CT scans, SSD was found to have no effect on SWL success.

Does Lower-Pole Caliceal Anatomy Predict Stone Clearance after Shock Wave Lithotripsy for Primary Lower-Pole Nephrolithiasis?

AIM

In order to have an idea about the success rates after extracorporeal shock wave lithotripsy (SWL) in patients with lower-pole stones, we reviewed the caliceal anatomy of the patients treated in our clinic.

PATIENTS AND METHODS

One hundred and ninety-eight patients having at least a 3-month follow-up period, with a single stone located in the lower pole, were included. Lower infundibulopelvic angle (LIP-A), infundibular width, and infundibular length were measured from standard intravenous urograms taken before initial ESWL.

RESULTS

One hundred and thirty patients (65%) were male, and 68 patients (35%) were female. We found no impact of age, sex, and affected side on the results of ESWL. The overall stone-free rate was 61.1% after 3 months of follow-up. The stone-free rates were 47.8 and 81.4% in patients with an acute (< 70 degrees) and an obtuse (> or = 70 degrees) LIP-A, respectively (p = 0.007). Taking the infundibular width into consideration, the stone-free rates were 85.4 and 43.2% for favorable and unfavorable angles and widths (p = 0.003). However, infundibular length and stone sizes were not found to have important effects on a stone-free status (p = 0.546 and p = 0.283).

CONCLUSION

We conclude that LIP-A (> or = 70 degrees) has the greatest impact on the clearance of residual fragments produced by SWL.

Prediction of shockwave failure in patients with urinary tract stones

PURPOSE OF REVIEW

To evaluate recent developments in predicting the failure of shockwave lithotripsy when treating patients with urinary tract stones.

RECENT FINDINGS

Although the features of patients with stones, as well as of the stones themselves, associated with refractoriness to shockwave lithotripsy are fairly well defined, refining the preoperative detection of these traits and optimizing the efficacy of shockwave lithotripsy are still under investigation. Several studies have recently focused on improving the radiological appraisal of stone size and composition through the use of axial computed tomography and reconstruction software. Other investigators have researched techniques to increase the efficacy of the technology underlying shockwave lithotripsy, such as varying the shockwave delivery rate and method.

SUMMARY

Investigators have demonstrated different factors and predictors that affect shockwave lithotripsy for stone disease. Continued research will better define patient selection and the role of shockwave lithotripsy in the treatment of urolithiasis.

Predictive Factors of Lower Calyceal Stone Clearance after Extracorporeal Shockwave Lithotripsy (ESWL): A Focus on the Infundibulopelvic Anatomy

INTRODUCTION

Controversy exists as to whether ESWL is suitable for lower pole renal stones, given the dependent position of the lower calyces. This study aims to test the effect of lower pole anatomy, namely lower polar infundibulo-pelvic angle, infundibular length and width, on clearance of fragments after ESWL.

PATIENTS AND METHODS

We conducted a retrospective study of 205 renal units with single lower pole stones of not more than 25 mm in their greatest diameter that were treated by ESWL alone. Exclusion criteria included multiple stones, patients requiring stenting or percutaneous drainage for various reasons. Pretreatment IVU was used to measure lower polar dimensions. Post treatment ultrasonography and KUB were used to assess clearance of fragments.

RESULTS

The right kidney was involved in 68% and the left in 42% of cases. Average number of sessions was 1.6 with an average 3277 shockwaves per session. 134 patients (65.3%) required one session, 41 requiring 2 sessions (20%), 18 requiring 3 sessions (8.7%), 6 requiring 4 sessions (2.9%) and 8 requiring 5 sessions (3.9%). Complete clearance was attained in 141 cases, while 64 cases had residual fragments, 20 were asymptomatic and required no further management. The lower pole infundibulo-pelvic angle (LIP-A) was the most significant factor in clearance (p value 0.00001). Infundibular length (IL) was also statistically significant (p value 0.039).

CONCLUSION

Lower pole anatomy has a significant impact on ESWL results. LIP-A not less than 70 degrees and an infundibular length of < 50 mm is preferable to achieve favorable outcome.

Role of computed tomography with no contrast medium enhancement in predicting the outcome of extracorporeal shock wave lithotripsy for urinary calculi

OBJECTIVE

To evaluate the usefulness of urinary calculi attenuation values from non-contrast computed tomography (NCCT) in predicting the outcome of treatment by extracorporeal shock wave lithotripsy (ESWL).

PATIENTS AND METHODS

We evaluated 112 patients with solitary renal and upper ureteric calculi of 0.5-2 cm undergoing ESWL. All patients had NCCT at 120 kV and 240 mA on a spiral CT scanner. During each ESWL session 3000 shock waves were given to a maximum of 3.0 kV. A final X-ray of the kidney, ureters and bladder was taken 12 weeks after the last ESWL session. Fragments of < or = 5 mm were regarded as clinically insignificant residual fragments (CIRF). The calculi retrieved were analysed by X-ray diffraction and the results assessed by comparing the mean density (as measured in Hounsfield units, HU) with the number of ESWL sessions and clearance.

RESULTS

In all, 82 (76%) patients had complete clearance of stones and 26 (24%) had CIRF. There was a linear relationship between the calculus density and number of ESWL sessions required. Of patients with calculi of < or = 750 HU, 41 (80%) needed three or fewer ESWL sessions and 45 (88%) had complete clearance. Of patients with calculi of > 750 HU, 41 (72%) required three or more ESWL sessions, and 37 (65%) had complete clearance. The best outcome was in patients with calculus diameters of < 1.1 cm and mean densities of < or = 750 HU; 34 (83%) needed three or fewer ESWL sessions, and the clearance rate was 90%. The worst outcome was in patients with calculus densities of > 750 HU and diameters of > 1.1 cm; 23 (77%) needed three or more ESWL sessions and the clearance rate was only 60%. The calculus density was a stronger predictor of outcome than size alone.

CONCLUSIONS

The use of NCCT for determining the attenuation values of urinary calculi before ESWL might help to predict the treatment outcome, and so might help in planning alternative treatment in patients with a likelihood of a poor outcome from ESWL.

Calcium stone fragility is predicted by helical CT attenuation values

BACKGROUND AND PURPOSE

Helical CT has become the preferred method for imaging urinary calculi, and so it would be useful if data from helical CT could also be used to predict the number of shockwaves (SWs) needed to break a given stone.

METHODS AND MATERIALS

We measured the number of SWs required to comminute calcium stones in vitro.

RESULTS

The SW requirement correlated with stone size (volume, weight, diameter) and with helical CT attenuation values when the scans were performed at 3-mm collimation. When CT scans were performed at 1-mm collimation, the number of SWs needed for comminution did not correlate with helical CT attenuation values. This result indicates that the correlation with 3-mm scans was attributable to volume-averaging effects, in which smaller stones yield smaller attenuation values. That is, attenuation values from helical CT at larger beam collimation widths contain information about stone size that can be exploited to predict the fragility of calcium stones. We observed that for calcium stones, the number of SWs to comminution was generally less than half the stone CT attenuation value in Hounsfield units. This "half-attenuation rule" predicted the number of SWs needed to complete fragmentation for 95% of calcium stones (24/24 calcium oxalate monohydrate, 13/13 hydroxyapatite, 8/10 brushite stones).

CONCLUSION

This in vitro study suggests that it may be possible to predict effective SW dose using helical CT prior to lithotripsy.

Stone fragmentation pattern of piezoelectric shockwave lithotripsy in vitro

Whole stones (N = 64; largest diameter 5-15 mm) were treated in vitro with piezoelectric shockwaves using the Edap LT-01 lithotripter with 2.5 Hz at either 100% or 54% power. The number of fragments larger than 2 mm was counted after every 30 seconds. The stones were defined as totally broken when all fragments were < 2 mm. Total fragmentation time was correlated with the energy level and the size of the stone. The number of large fragments did not correlate with the energy level but rather with the original size of the stone.