Stone Attenuation Value Research Articles

Preoperative Stone Attenuation Value Predicts Success After Shock Wave Lithotripsy in Children

We determined whether stone attenuation can predict stone fragmentation after shock wave lithotripsy in the pediatric population. Previous studies show that preoperative attenuation in HU on noncontrast computerized tomography predicts shock wave lithotripsy success. To our knowledge study of this parameter in the pediatric population has been lacking to date. We performed a multi-institutional review of the records of 53 pediatric patients 1 to 18 years old who underwent shock wave lithotripsy for 3.8 to 36.0 mm renal calculi. Stone size, average skin-to-stone distance and attenuation value were determined by bone windows on preoperative noncontrast computerized tomography. Success was defined as radiographically stone-free status at 2 to 12-week followup after a single lithotripsy session without the need for further sessions or ancillary procedures. After lithotripsy 33 patients (62%) were stone-free and 20 had incomplete fragmentation or required additional procedures. Mean ± SD stone attenuation in successfully treated patients vs those with incomplete fragmentation was 710 ± 294 vs 994 ± 379 HU (p = 0.007). Logistical regression analysis revealed that only attenuation in HU was a significant predictor of success. When patients were stratified into 2 groups (less than 1,000 and 1,000 HU or greater), the shock wave lithotripsy success rate was 77% and 33%, respectively (p <0.003). Stone attenuation less than 1,000 HU is a significant predictor of shock wave lithotripsy success in the pediatric population. This finding suggests that attenuation values have a similar predictive value in the pediatric population as that previously reported in the adult population.

Predicting Effectiveness of Extracorporeal Shockwave Lithotripsy by Stone Attenuation Value

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. 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. 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. 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.

A Simple Objective Method to Assess the Radiopacity of Urinary Calculi and its Use to Predict Extracorporeal Shock Wave Lithotripsy Outcomes

We describe an objective method to evaluate kidney stone radiopacity for use in selection of cases suitable for ESWL. We recruited 76 adult patients with a solitary 1 to 2 cm renal pelvic stone. All patients underwent routine plain x-ray of the urinary tract but an aluminum step wedge (Gammex) was adapted to the cassette before x-ray exposure. This x-ray was then digitized and analyzed by histogram to calculate the gray level of the stone and of each step of the aluminum step wedge. This allowed radiographic stone density to be expressed in mm aluminum equivalent. All patients also underwent abdominopelvic computerized tomography and then ESWL was started. Stone density on plain x-ray was 1.83 to 5.93 mm aluminum equivalent. There was a positive correlation between these values and stone attenuation values on computerized tomography (r(2) 0.83, p <0.005). The 12 patients in whom ESWL failed were found to have stones of significantly higher density than stones in patients with complete stone fragmentation (mean +/- SD 4.8 +/- 0.74 vs 3.35 +/- 0.88 mm aluminum equivalent, p <0.005). There was also a positive correlation between stone radiopacity in mm aluminum equivalent and the total number of shock waves required to achieve complete fragmentation (r(2) 0.66, p <0.005). The aluminum step wedge with plain x-ray of the urinary tract provides a good reference for objectively assessing the radiopacity of renal calculi.

Radiographic Parameters on Noncontrast Computerized Tomography Predictive of Shock Wave Lithotripsy Success

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. 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. 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. 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.

A Prospective Multivariate Analysis of Factors Predicting Stone Disintegration by Extracorporeal Shock Wave Lithotripsy: The Value of High-Resolution Noncontrast Computed Tomography

ObjectiveTo assess the value of noncontrast computed tomography (NCCT) as a possible predictor of renal stone disintegration by shock wave lithotripsy (SWL). Patients and methodsThe study included 120 consecutive patients (71 males, 49 females; mean age: 42.6 yr) with a solitary renal stone of 0.5–2.5cm in length. NCCT was performed using a multidetector row CT scanner at 120KV and 240mA, with 1.25-mm collimation. A bone window was used to measure stone attenuation values. SWL was performed with an electromagnetic lithotripter. Failure of disintegration was defined as no fragmentation of the stone after three sessions. The impact of patients’ sex, age, and body mass index (BMI) and the stones’ laterality, location, volume, mean attenuation value, and the skin-to-stone distance on disintegration were evaluated by univariate and multivariate analyses. ResultsFailure of disintegration was observed in 15 patients (12.5%). BMI and stone density >1000HU were the significant independent predictors of failure (p=0.04 and 0.02, respectively). The success rate of extracorporeal SWL at 3 mo was 87.5% (105 of 120 patients); 90 patients were stone free and 15 had residual fragments <4mm. The only significant predictor of residual fragments was stone density (p<0.001). ConclusionsObesity and increased stone density as detected by NCCT are significant predictors of failure to fragment renal stones by SWL. An alternative treatment should be devised for obese patients with stone density >1000HU.