Use of Hounsfield Units to Optimize Care for Kidney Stones: New York Urology Specialists.

Innovative physicians at New York Urology Specialists are among the first urologists in NYC specializing in kidney stone care to use hounsfield units to optimize care for kidney stones in New York City.   We present latest research on the topic for your reference.  

BJU Int. 2012 Dec;110(11 Pt B):E438-42. doi: 10.1111/j.1464-410X.2012.10964.x. Epub 2012 Feb 28.

A 970 Hounsfield units (HU) threshold of kidney stone density on non-contrast computed tomography (NCCT) improves patients’ selection for extracorporeal shockwave lithotripsy (ESWL): evidence from a prospective study.


What’s known on the subject? and What does the study add? Stone density on non-contrast computed tomography (NCCT) is reported to be a prognosis factor for extracorporeal shockwave lithotripsy (ESWL). In this prospective study, we determined that a 970 HU threshold of stone density is a very specific and sensitive threshold beyond which the likelihood to be rendered stone free is poor. Thus, NCCT evaluation of stone density before ESWL may useful to identify which patients should be offered alternative treatment to optimise their outcome.


• To evaluate the usefulness of measuring urinary calculi attenuation values by non-contrast computed tomography (NCCT) for predicting the outcome of treatment by extracorporeal shockwave lithotripsy (ESWL).


• We prospectively evaluated 50 patients with urinary calculi of 5-22 mm undergoing ESWL. • All patients had NCCT at 120 kV and 100 mA on a spiral CT scanner. Patient age, sex, body mass index, stone laterality, stone size, stone attenuation values (Hounsfield units [HU]), stone location, and presence of JJ stent were studied as potential predictors. • The outcome was evaluated 4 weeks after the ESWL session by NCCT. • ESWL success was defined as patients being stone-free (SF) or with remaining stone fragments of <4 mm, which were considered as clinically insignificant residual fragments (CIRF).


• Our survey concluded that 26 patients (52%) were SF, 12 (24%) had CIRF and 12 (24%) had residual fragment on NCCT after a one ESWL treatment. • Stones of patients who became SF or had CIRF had a lower density compared with stones in patients with residual fragments [mean (sd) 715 (260) vs 1196 (171) HU, P < 0.001]. • The Youden Index showed that a stone density of 970 HU represented the most sensitive (100%) and specific (81%) point on the receiver-operating characteristic curve. • The stone-free rate for stones of <970 HU was 96% vs 38% for stones of ≥ 970 HU (P < 0.001). A linear relationship between the calculus density and the success rate of ESWL was identified.


• The use of NCCT to determine the attenuation values of urinary calculi before ESWL helps to predict treatment outcome, and, consequently, could be helpful in planning alternative treatment for patients with a likelihood of a poor outcome from ESWL.


J Endourol. 2012 Sep;26(9):1125-30. doi: 10.1089/end.2012.0154. Epub 2012 Jun 12.

Predictive value of attenuation coefficients measured as Hounsfield units on noncontrast computed tomography during flexible ureteroscopy with holmium laser lithotripsy: a single-center experience.



To assess the utility of attenuation coefficients as predictors of surgical outcome after a single flexible ureteroscopy (URS) with holmium laser lithotripsy. Many reports indicate that the efficacy of extracorporeal shockwave lithotripsy (SWL) can be predicted by the target’s radiofrequency attenuation, measured as Hounsfield units (HUs) on noncontrast CT (NCCT). Studies of flexible URS, however, have not assessed the predictive value of attenuation coefficients on NCCT.


Patients with renal stones who were treated by flexible URS with holmium laser lithotripsy between December 2009 and October 2011 at a single institute were retrospectively evaluated. Stone-free (SF) status was determined by kidneys-ureters-bladder (KUB) radiography at postoperative month 3. Correlations of possible predictors with SF status were analyzed using a logistic regression model. The comparison between groups with low and high HUs was examined using the Mann-Whitney U test.


There were 219 eligible procedures. According to the logistic regression model, the maximum attenuation coefficient (P=0.105) and average attenuation coefficient (P=0.175) did not significantly, independently predict SF status. Fragmentation efficiency was significantly different between cases with low and high attenuation coefficients (P=0.001). In groups with less than 20.0-mm diameter stones, overall operative time (P<0.001 and P=0.001) and the time from starting fragmentation (P<0.001 and P=0.002) were significantly high in both attenuation groups. In groups with stones greater than 20.0 mm diameter, the two definitions of operative time revealed no differences between the low and high attenuation groups. The retrospective study design was the major limitation of this study.


We found that both the maximum and average attenuation coefficients on NCCT are significantly related to the fragmentation efficiency. In addition, this study showed that, in patient groups with stone a burden <20.0 mm in diameter, both the maximum and average attenuation coefficients were significantly predictive of operative time.



Urology. 2013 Apr;81(4):880-4. doi: 10.1016/j.urology.2012.12.012. Epub 2013 Feb 6.

Kidney stone size and hounsfield units predict successful shockwave lithotripsy in children.



To define the preoperative kidney and stones characteristics on noncontrast-enhanced computed tomography that affect the success of extracorporeal shockwave lithotripsy (SWL) for treatment of renal calculi in pediatric patients.


From 2005 to 2011, 57 children (age <16 years) with documented preoperative noncontrast-enhanced computed tomography scans underwent SWL for treatment of renal stones and were included in the present study. Stone size, site, multiplicity, average skin-to-stone distance, stone attenuation value, and kidney morphology were determined from the preoperative noncontrast-enhanced computed tomography scans. Success was defined as radiographically stone-free status at the 3-month follow-up examination after a single lithotripsy session without the need for additional sessions or ancillary procedures.


After a single session of SWL, 24 children (42.1%) were stone free on the 3-month follow-up imaging study without the need for additional SWL sessions. Treatment failed in 33 patients (57.9), with residual fragments in 30 children, of whom 29 required repeat SWL, and 3 with stones that were considered unchanged and were finally treated with percutaneous nephrolithotomy. Logistic regression analysis revealed that stone attenuation in Hounsfield units (HU) and stone length were the only significant predictors of success. When the HU were stratified into 2 groups of ≤600 and >600 HU, the SWL success rate was 82.1% and 20%, respectively (P = .023). When length was stratified as ≤12 mm and >12 mm, the stone-free rate was 58.6% and 25.1%, respectively (P = .016).


Stone attenuation ≤600 HU and stone length ≤12 mm were significant independent predictors of SWL success in children.

Copyright © 2013 Elsevier Inc. All rights reserved.

PMID:  23395121



Scand J Urol. 2013 Dec;47(6):509-14. doi: 10.3109/21681805.2013.803261. Epub 2013 Jun 19.

Impact of stone density on outcomes in percutaneous nephrolithotomy (PCNL): an analysis of the clinical research office of the endourological society (CROES) pcnl global study database.


Abstract Objective. This study aimed to explore the relationship between stone density and outcomes of percutaneous nephrolithotomy (PCNL) using the Clinical Research Office of the Endourological Society (CROES) PCNL Global Study database. Material and methods. Patients undergoing PCNL treatment were assigned to a low stone density [LSD, ≤ 1000 Hounsfield units (HU)] or high stone density (HSD, > 1000 HU) group based on the radiological density of the primary renal stone. Preoperative characteristics and outcomes were compared in the two groups. Results. Retreatment for residual stones was more frequent in the LSD group. The overall stone-free rate achieved was higher in the HSD group (79.3% vs 74.8%, p = 0.113). By univariate regression analysis, the probability of achieving a stone-free outcome peaked at approximately 1250 HU. Below or above this density resulted in lower treatment success, particularly at very low HU values. With increasing radiological stone density, operating time decreased to a minimum at approximately 1000 HU, then increased with further increase in stone density. Multivariate non-linear regression analysis showed a similar relationship between the probability of a stone-free outcome and stone density. Higher treatment success rates were found with low stone burden, pelvic stone location and use of pneumatic lithotripsy. Conclusions. Very low and high stone densities are associated with lower rates of treatment success and longer operating time in PCNL. Preoperative assessment of stone density may help in the selection of treatment modality for patients with renal stones.

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