Implementation of a Technique Based on Hounsfield Units and Hounsfield Density to Determine Kidney Stone Composition.

Hounsfield units (HU) are a measure of radiodensity, related to the density of a tissue and the composition of kidney stones. Hounsfield density is what is related to the composition of kidney stones. In the standard acquisition method, these measures are arbitrary and dependent on the operator. This study describes the implementation of a technique based on the HU and Hounsfield density to predict the stone compositions of patients with nephrolithiasis. By conventional percutaneous nephrolithotomy, thirty kidney stone samples corresponding to the cortex, middle, and nucleus were obtained. The HU were obtained by CT scanning with a systematic grid. Hounsfield density was calculated as the HU value divided by the stone's greatest diameter (HU/mm). With that method and after analyzing the samples by IR-spectroscopy, anhydrous uric acid and ammonium magnesium phosphate were identified as the compounds of kidney stones. Additionally, anhydrous uric acid, magnesium ammonium phosphate, and calcium oxalate monohydrate were identified via Hounsfield density calculation. The study identified HU ranges for stone compounds using a systematic technique that avoids bias in its analysis. In addition, this work could contribute to the timely diagnosis and development of personalized therapies for patients with this pathology.

Large database study of urinary stone composition in South Korea: Korean Society of Endourology and Robotics (KSER) research series.

PURPOSE: To evaluate the characteristics of urinary stone composition in a Korean population using a large database of stone composition. MATERIALS AND METHODS: From January 1, 2014, to June 30, 2019, a total of 33,078 urinary stone composition data were analyzed. Stone composition was classified into four main groups: calcium oxalate (CaOx), struvite, uric acid (UA), and calcium phosphate (CaP). We examined the relationship between stone composition and sex, age, geographic region, calendar month, and season. RESULTS: The CaOx group (46.41%) was the largest, followed by the struvite group (29.66%), UA group (19.61%), and CaP group (4.32%). The CaOx group tended to decrease with age, but the UA group increased with age. Also, the CaOx group had the highest percentage in summer and the lowest in spring (p<0.001). The struvite and CaP groups had higher percentages of females than males (struvite: 36.6% vs. 25.7%, p<0.001; CaP: 6.2% vs. 3.3%, p<0.001). Conversely, the UA stones were more common in males than in females (24.5% vs. 11.0%, p<0.001). The UA group had the lowest percentage in the capital region (p<0.001). The total male-to-female ratio decreased over time from 1.95:1 in 2014 to 1.67:1 in 2018 (p<0.001). CONCLUSIONS: There were differences for each stone composition in the percentages according to sex, age, geographic region, month, and season. Identifying these differences based on the stone composition is vital for the treatment and prevention of urinary stones.

Predictors of urosepsis in struvite stone patients after percutaneous nephrolithotomy.

PURPOSE: This study aims to identify clinical factors that may predispose struvite stone patients to urosepsis following percutaneous nephrolithotomy (PCNL). MATERIALS AND METHODS: A retrospective review was conducted on patients who received PCNL for struvite stones. The Systemic Inflammatory Response Syndrome (SIRS) criteria and quick-Sepsis Related Organ Failure Assessment (q-SOFA) criteria were used to identify patients who were at an increased risk for urosepsis. Statistical analysis was performed using Fisher's exactness test, Wilcoxon rank test, and logistic regression. RESULTS: Chart review identified 99 struvite stone patients treated with PCNL. Post-operatively, 40 patients were SIRS positive (≥2 criteria) and/or q-SOFA positive (score ≥2). Using SIRS as an approximation for urosepsis, longer operative times (p<0.001), higher pre-operative white blood cell counts (p=0.01), greater total stone surface area (p<0.0001), and pre-operative stenting (OR, 5.75; p=0.01) were identified as independent risk factors for urosepsis. Multivariate analysis demonstrated pre-operative stenting (OR, 1.46; p=0.01) to be a risk factor. With q-SOFA, univariable analysis found that antibiotic use within 3 months prior to a PCNL (OR, 4.44; p=0.04), medical comorbidities (OR, 4.80; p=0.02), longer operative times (p<0.001), lengthier post-operative hospitalization (p<0.01), and greater total stone surface area (p<0.0001) were risk factors for urosepsis. Multivariate analysis revealed that bladder outlet obstruction (OR, 2.74; p<0.003) and pre-operative stenting (OR, 1.27; p=0.01) significantly increased odds of being q-SOFA positive. CONCLUSIONS: Several risk factors for urosepsis following PCNL for struvite stones have been identified. These risk factors should be taken into consideration in peri-operative care to mitigate the risks of urosepsis.

Association of Impaired Renal Function With Changes in Urinary Mineral Excretion and Stone Composition.

OBJECTIVE: To investigate the effect of kidney function on stone composition and urinary mineral excretion in patients undergoing surgical intervention for nephrolithiasis. METHODS: Using our institutional kidney stone database, we performed a retrospective review of stone patients who underwent surgical intervention between 2004 and 2015. Patients' demographic information, 24-hour urinary mineral excretion, and stone characteristics were reported. The patients' estimated glomerular filtration rates (eGFR) were compared with their stone compositions and 24-hour urine mineral excretions. RESULTS: A statistically significant difference was noted between the groups, with uric acid stones being associated with lower eGFR and calcium phosphate stones associated with higher eGFR. No relationship could be demonstrated between eGFR and calcium oxalate or struvite stones. Patients with lower eGFR also demonstrated a statistically significant association with lower urinary pH as well as lower urinary excretion of calcium and citrate. CONCLUSION: While various factors have been found to play significant roles in kidney stone formation and composition, our findings demonstrate a definite relationship between these and renal function. This paper highlights the fact that renal function evaluation should be considered an important component in the evaluation, counseling, and management of patients with nephrolithiasis.

A novel method for the stabilization of soluble contaminants in electrolytic manganese residue: Using low-cost phosphogypsum leachate and magnesia/calcium oxide.

Electrolytic manganese residue (EMR) contains a large amount of NH4+-N and Mn2+ and can negatively impact the environment. A stabilization treatment of soluble contaminants in the EMR is necessary for its reuse and safe stacking. This study presents experimental results for the stabilization of NH4+-N and Mn2+ in the EMR using phosphogypsum leachate as a low-cost phosphate source and MgO/CaO (PLMC) process. The results demonstrated that the stabilization efficiency of NH4+-N and Mn2+ was 93.65% and 99.99%, respectively, under the following conditions: a phosphogypsum leachate dose of 1.5 mL g-1, an added MgO dose of 0.036 g g-1, an added CaO dose of 0.1 g g-1 and a reaction time of 2 h. The stabilization effect of the PLMC process was higher and more cost effective than that of using Na3PO4·12H2O and MgO/CaO. The concentration of NH4+-N and Mn2+ in the leaching liquor decreased to 80 mg L-1 and 0.5 mg L-1, respectively, after the stabilization under the optimum conditions. The stabilization characteristics indicated that NH4+-N was stabilized to form NH4MgPO4·6H2O (struvite) and that Mn2+ was stabilized to form Mn5(PO4)2(OH)4, Mn3(PO4)2·3H2O and Mn(OH)2. PO43--P, F-, and heavy metal ions of the phosphogypsum leachate were removed from the leaching liquor and stabilized in the treated EMR.

Deep learning computer vision algorithm for detecting kidney stone composition.

OBJECTIVES: To assess the recall of a deep learning (DL) method to automatically detect kidney stones composition from digital photographs of stones. MATERIALS AND METHODS: A total of 63 human kidney stones of varied compositions were obtained from a stone laboratory including calcium oxalate monohydrate (COM), uric acid (UA), magnesium ammonium phosphate hexahydrate (MAPH/struvite), calcium hydrogen phosphate dihydrate (CHPD/brushite), and cystine stones. At least two images of the stones, both surface and inner core, were captured on a digital camera for all stones. A deep convolutional neural network (CNN), ResNet-101 (ResNet, Microsoft), was applied as a multi-class classification model, to each image. This model was assessed using leave-one-out cross-validation with the primary outcome being network prediction recall. RESULTS: The composition prediction recall for each composition was as follows: UA 94% (n = 17), COM 90% (n = 21), MAPH/struvite 86% (n = 7), cystine 75% (n = 4), CHPD/brushite 71% (n = 14). The overall weighted recall of the CNNs composition analysis was 85% for the entire cohort. Specificity and precision for each stone type were as follows: UA (97.83%, 94.12%), COM (97.62%, 95%), struvite (91.84%, 71.43%), cystine (98.31%, 75%), and brushite (96.43%, 75%). CONCLUSION: Deep CNNs can be used to identify kidney stone composition from digital photographs with good recall. Future work is needed to see if DL can be used for detecting stone composition during digital endoscopy. This technology may enable integrated endoscopic and laser systems that automatically provide laser settings based on stone composition recognition with the goal to improve surgical efficiency.

Urinary stone composition analysis of 3684 patients in the eastern Shandong region of China.

OBJECTIVE: There has not been a study that analyzed the composition of urinary stones from patients in the eastern Shandong region of China. Thus, we explored the composition of urinary stones in the eastern Shandong region of China and discuss the clinical significance of the findings. METHODS: A total of 3684 urinary calculi from the eastern Shandong region were collected in our study. Compositions of the stones were analyzed using an Automatic Infrared Spectrum Analysis System (type LIIR-20). The results were verified through manual analysis of the spectrograms, which was accompanied by polarizing microscopy and chemical analysis if necessary. RESULTS: Among the 3684 specimens, there were 1767 single-component stones and 1917 mixed-component stones. According to the main components of the stones, the stones were divided into the following types: calcium oxalate monohydrate stones (1779, 48.3%), anhydrous uric acid stones (1105, 30.0%), carbonate apatite stones (590, 16.0%), ammonium magnesium phosphate hexahydrate stones (143, 3.9%), calcium oxalate dihydrate stones (36, 1.0%), and cystine stones (31, 0.8%). CONCLUSIONS: There was a relatively high rate of uric acid stones in patients from the eastern Shandong region of China.

Phosphorous in the environment: characteristics with distribution and effects, removal mechanisms, treatment technologies, and factors affecting recovery as minerals in natural and engineered systems.

Phosphorus (P), an essential element for living cells, is present in different soluble and adsorbed chemical forms found in soil, sediment, and water. Most species are generally immobile and easily adsorbed onto soil particles. However, P is a major concern owing to its serious environmental effects (e.g., eutrophication, scale formation) when found in excess in natural or engineered environments. Commercial chemicals, fertilizers, sewage effluent, animal manure, and agricultural waste are the major sources of P pollution. But there is limited P resources worldwide. Therefore, the fate, effects, and transport of P in association with its removal, treatment, and recycling in natural and engineered systems are important. P removal and recycling technologies utilize different types of physical, biological, and chemical processes. Moreover, P minerals (struvite, vivianite, etc.) can precipitate and form scales in drinking water and wastewater systems. Hence, P minerals (e.g., struvite, vivianite etc.) are problems when left uncontrolled and unmonitored although their recovery is beneficial (e.g., slow release fertilizers, sustainable P sources, soil enhancers). Sources like wastewater, human waste, waste nutrient solution, etc. can be used for P recycling. This review paper extensively summarizes the importance and distribution of P in different environmental compartments, the effects of P in natural and engineered systems, P removal mechanisms through treatment, and recycling technologies specially focusing on various types of phosphate mineral precipitation. In particular, the factors controlling mineral (e.g., struvite and vivianite) precipitation in natural and engineered systems are also discussed.

Development of phosphorus recovery reactor for enlargement of struvite crystals using seawater as the magnesium source.

Struvite crystallization is an interesting method for the recovery of phosphorus (P) from wastewater. However, the struvite crystals obtained are small, which makes them difficult to separate from wastewater. A continuous reactor for enlarging struvite crystals was developed. Batch-scale experiments were conducted to investigate the optimum factors for the enlargement of struvite crystals. The results of pH experiments showed that P recovery efficiency increased with an increase of pH values (7.6 to 10), while the size of struvite crystals decreased. The results of the Mg:P ratios found that the maximum P recovery efficiency occurred at the maximum ratio of Mg:P. The sizes of struvite crystals were not significantly different. For the variation of temperature values, the results showed that P recovery efficiency and crystal sizes decreased when temperature values increased. Therefore, the optimized conditions for P recovery efficiency and enlargement of struvite crystals for the continuous reactor were pH 8.5 and an Mg:P ratio of 1.2:1 at 30 °C (room temperature). The treated swine wastewater and seawater were continuously fed in at the bottom of the reactor. After 30 days, the size of struvite crystals had increased from 125 µm to 0.83 mm (seven times).

Defining a clinically significant struvite stone: a non-randomized retrospective study.

OBJECTIVE: To study the association between a stone's struvite content and clinical outcomes and to determine a clinically significant cutoff for defining struvite stones. MATERIALS AND METHODS: This was a retrospective study of all patients who underwent ureteroscopy or PCNL at our institution between 2012 and 2017 and had any component of struvite in the stone analysis. Patients were divided into four groups based on percent struvite content: A (1-25%), B (26-50%), C (51-75%), and D (76-100%). Bacterial characteristics were compared between groups. Univariate and multivariate analyses were performed to evaluate the association between struvite content and postoperative SIRS. Log-rank test was used to compare between the four groups' recurrence rates. RESULTS: A total of 123 patients were included in the study. Positive preoperative urine culture was found in 31%, 81%, 87%, and 90% of patients from group A, B, C, and D, respectively. E. Coli was the most common pathogen in group A (54%), while Proteus was the most common pathogen in groups C (53%) and D (47%). Enterococci isolation rates remained similar between groups A-D, ranging from 23 to 33%. Postoperative SIRS occurred in 2.4%, 21.3%, 26.7%and 47.4% of the patients from groups A, B, C, and D, respectively, and was associated with struvite content and age on multivariate analysis. Increasing struvite content was associated with higher 2-year recurrence rate. CONCLUSIONS: Higher struvite content is associated with a higher frequency of traditional urea splitting bacteria in urine culture, higher risk for postoperative SIRS, and higher recurrence rate. Struvite content greater than 25% can be used to define a clinically significant struvite stone.

Comparative study of heavy metal residues in struvite products recovered from swine wastewater using fluidised bed and stirred reactors.

Struvite (MgNH4PO4·6H2O) crystallisation is a promising approach for phosphorus recovery from swine wastewater. Currently, intensive pig feeding has made heavy metals (HMs) extensive in swine wastewater; therefore, significant amounts of HMs have been detected in struvite recovery products. In this study, the HM residues in the struvite products recovered from stirred and fluidised bed reactors were investigated. The results showed that Zn, Mn, and Cu were the most abundant elements in swine wastewater (1,175.3 ± 178.0, 745.4 ± 51.5, and 209.3 ± 54.4 µg L-1, respectively). The HMs, especially Zn (97.0%) and Cu (96.8%), were mainly distributed in the total suspended solids (TSS) of the swine wastewater. Redundancy analysis revealed that the HMs in the struvite products harvested from the fluidised bed reactor were mainly attributable to the aggregation of dissolved matters, because most TSS were elutriated through fluidisation. In contrast, the HMs in the struvite products harvested from the stirred reactor mainly originated from the TSS, which complexed with the HMs, and co-precipitated and settled with the struvite products. Furthermore, chemical fractionation of the HM species confirmed that the presence of HMs in the struvite products was mainly attributable to metal precipitation and organic aggregation.

[Etiological factors for calculus-associated seminal vesiculitis: Analysis of calculus composition in 6 cases].

OBJECTIVE: To explore the etiological factors for calculus-associated seminal vesiculitis by analyzing the composition of seminal vesicle calculus samples. METHODS: This retrospective study included 6 cases of recurrent hematospermia diagnosed with seminal vesicle calculus by non-contrast pelvic CT. The patients were aged 28 to 69 years, with persistent or recurrent hematospermia for 3 months to 6 years, and 5 of them with a history of acute urethritis. All the patients underwent seminal vesiculoscopy, which confirmed calculus-associated seminal vesiculitis. The calculus samples were obtained with a spiral dislodge and their composition was determined with a second-generation infrared calculus composition analyzer. The patients were followed up for 2 to 12 weeks postoperatively, during which non-contrast pelvic CT was employed for observation of recurrent calculus in the reproductive tract. RESULTS: Pelvic CT scanning indicated recurrence of seminal vesicle calculus in 3 cases at 12 weeks postoperatively, of which, 2 were accompanied with recurrent hematospermia, both observed at 4 weeks after operation. As for the composition of the calculus, the infrared calculus composition analyzer revealed struvite (magnesium ammonium phosphate hexahydrate) in 5 cases and a mixture of calcium oxalate dihydrate, calcium oxalate monohydrate, and carbonate apatite in the other one. CONCLUSIONS: Seminal vesicle calculi are most commonly composed of struvite, and infection is the main etiological factor for calculus-associated seminal vesiculitis.

Diagnosis and management of non-calcium-containing stones in the pediatric population.

Compared to adults, urolithiasis is less common in children, with a definite rise in incidence, especially among young adults (Tasian et al. in Clin J Am Soc Nephrol 11:488, 2016). In the last 25 years, the incidence in children has increased by approximately 6-10% annually, for reasons still unknown, with an associated significant increase in related health care-related expenditures (Hyams and Matlaga in Transl Androl Urol 3(3):278-83, 2014). It has been shown that there is twice as high a risk of chronic kidney disease (CKD) or end stage renal disease (ESRD) in stone formers compared to non-stone formers (Tasian et al. 2016). While calcium-containing stones are by far the most common category of stone encountered in both children and adults, non-calcium stones are more common in children than adults and have been shown in several studies to be associated with greater morbidity and lower renal function than calcium stones (Issler et al. in BMC Nephrol 18(1):136, 2017; Gambaro et al. in J Urol 198:268-273, 2017). This could be related to the challenges in the management of non-calcium-containing stones due to associated infection or metabolic derangements, further leading to recurrence and loss of renal function. There is currently a gap in our understanding of how to appropriately and effectively encounter and manage patients with non-calcium-containing stones, as such cases are encountered less frequently. Identification of stone composition and appropriate management is very important to reduce serious complications and recurrence, especially in non-calcium stones. We present a review of diagnosis and management of non-calcium-containing stones in the pediatric population, in hopes of providing more clarity to providers and promoting a consideration of non-calcium stone composition with all children presenting with urolithiasis.

Nutrient recovery from anaerobically digested chicken slurry via struvite: Performance optimization and interactions with heavy metals and pathogens.

The aim of this study was to assess the potential of struvite precipitation to recover nutrients from anaerobically-processed poultry slurry and struvite's interactions with heavy metals (Zn, Cu, Pb, Cr, and Ni) and pathogens (total coliforms and Escherichia coli). The impacts of pH, Mg, N, and P molar proportion, reaction time, and mixing rate and duration were explored to determine the optimal conditions for nutrient recovery through struvite precipitation. A pH range of 9.5 to 10.5, was ideal for P and N removal and recovery, with a molar ratio of 1:1:1 for Mg:N:P. A mixing rate of 150rpm for 10min could allow nutrient recovery with little loss (3.32%) of NH3 through volatilization, and also achieve an optimal struvite crystal size (50-60µm). The results of X-ray diffractometry and scanning electron microscopy confirmed that the precipitates generated at pH9 and 10 were orthorhombic struvite. Moreover, along with the recovery of nutrients, 40, 45, 66, 30, and 20% of Zn, Cu, Pb, Cr, and Ni, respectively, and 70% total coliforms and E. coli were removed by struvite precipitation from poultry slurry. This was observed despite that the levels of contaminants (heavy metals) detected in struvite were well below the permissible limits and free of pathogens. Consequently, it was inferred that the struvite quality was reasonable by virtue of its heavy metal and pathogen content, and therefore appropriate for application in the field. Similarly, struvite precipitation has multiple benefits as it can effectively recover nutrients as well as reducing pathogenic populations.

Outcomes of Ureteroscopic Stone Treatment in Patients With Spinal Cord Injury.

OBJECTIVE: To evaluate the association of clinical factors on outcomes in patients with spinal cord injury (SCI) undergoing ureteroscopy. Immobility, recurrent urinary tract infection, and lower urinary tract dysfunction contribute to renal stone formation in patients with SCI. Ureteroscopy is a commonly utilized treatment modality; however, surgical complication rates and outcomes have been poorly defined. Evidence guiding safe and effective treatment of stones in this cohort remains scarce. METHODS: Records were retrospectively reviewed for patients with SCI who underwent ureteroscopy for kidney stones from 1996 to 2014 at a single institution. Multivariate relationships were evaluated using a general estimating equation model. RESULTS: Forty-six patients with SCI underwent a total of 95 ureteroscopic procedures. After treatment, stone-free rate was 17% and 20% with <2-mm fragments. The complication rate was 21%. On multivariate analysis, SCI in cervical (C) levels was associated with higher risk of complications (C3: odds ratio [OR] 3.83, 95% confidence interval [CI] 2.17-6.98; C6: OR 3.83, 95% CI 1.08-13.53). American Spinal Injury Association Scale A classification was associated with a lower probability of stone-free status (OR 0.16, 95% CI 0.03-0.82). Patients averaged 2.2 procedures yet more procedures were associated with lower stone-free status (OR 0.83, 95% CI 0.03-0.32). Chronic obstructive pulmonary disease and bladder management modality were not associated with stone-free status or complications. CONCLUSION: In patients with SCI, higher injury level and complete SCI were associated with worse stone clearance and more complications. Stone-free rate was 17%. Overall, flexible ureteroscopy is a relatively safe procedure in this population. Alternative strategies should be considered after failed ureteroscopy.

The optimization of microalgal culturing in liquid digestate after struvite precipitation using gray relational analysis.

Liquid digestate (LD) is highly turbid and contains ammonium (NH4+-N), which negatively influences microalgal growth. Therefore, a method of reducing LD turbidity and NH4+-N content is proposed, using struvite precipitation. To obtain struvite precipitation supernatant with an ideal UV transmittance, NH4+-N concentration, and N/P ratio for microalgal growth, the effects of pH and the molar ratio of NH4+/Mg2+/PO43- were studied. Results show that the optimal NH4+/Mg2+/PO43- molar ratio was 1:1.5:1.5, with a pH value of 8.5, following NaOH addition. Gray relational analysis (GRA) was applied to obtain a relative gray scale for the evaluation of multiple outputs. Results show that Chlorella regularis FACHB-1068 was the optimal microalgae species to support growth in the struvite precipitation supernatant. Using struvite precipitation and treatment with cultured C. regularis FACHB-1068 for 7 days, the removal efficiencies of NH4+-N, PO43--P, and COD in LD were 96.52, 99.33, and 35.30%, respectively.

Application of image processing on struvite recovery from swine wastewater by using the fluidized bed.

Fluidized granulation is one of the common methods used in wastewater treatment and resource recovery with harvesting millimeter-scale large particles. Presently, effective methods are lacking to measure the fluidized granules ranging from micro- to millimeter scales, with the consequence of ineffectively controlling and optimizing the granulation process. In this work, recovering struvite (MgNH4PO4·6H2O) from swine wastewater by using a fluidized bed was taken as an example. Image processing was applied to analyze the properties of different types of struvite granules, including morphology, particle size distribution, number density and mass concentration. Four stages of the struvite crystal evolution were therefore defined: aggregation, aggregate compaction, cluster-agglomerating and coating growth. These stages could occur simultaneously or sequentially. Up-flow rates of 30-80 mm/s in the fluidized bed sustained 600-876 g/L granular solids. Results revealed that the coating-growth granules were formed with compact aggregates or cluster-agglomerating granules as the nuclei. The growth rates for the different types of particles, including population growth, mass increase and particle size enlargement, were determined. In final, a schematic illustration for struvite granulation process is also presented.

No stone unturned: The presence of kidney stones in a skeleton from 19th century Peoria, Illinois.

During the excavation of the 19th century Peoria City Cemetery (Peoria, Illinois), a skeleton of a female, aged 20-30 years old, was found with large, bilateral calcified masses in the abdominal region. The masses were analyzed by Fourier transform infrared (FTIR) spectroscopy, and the results compared to published clinical data in an effort to determine the etiology of the stones. The calcified masses were determined to be staghorn struvite uroliths, which commonly result from chronic urinary tract infection and likely impacted the overall health of this individual.

Clinical utility of computed tomography Hounsfield characterization for percutaneous nephrolithotomy: a cross-sectional study.

BACKGROUND: Computed Tomography (CT) is considered the gold-standard for the pre-operative evaluation of urolithiasis. However, no Hounsfield (HU) variable capable of differentiating stone types has been clearly identified. The aim of this study is to assess the predictive value of HU parameters on CT for determining stone composition and outcomes in percutaneous nephrolithotomy (PCNL). METHODS: Seventy seven consecutive cases of PCNL between 2011 and 2016 were divided into 4 groups: 40 (52%) calcium, 26 (34%) uric acid, 5 (6%) struvite and 6 (8%) cystine stones. All images were reviewed by a single urologist using abdomen/bone windows to evaluate: stone volume, core (HUC), periphery HU and their absolute difference. HU density (HUD) was defined as the ratio between mean HU and the stone's largest diameter. ROC curves assessed the predictive power of HU for determining stone composition/stone-free rate (SFR). RESULTS: No differences were found based on the viewing window (abdomen vs bone). Struvite stones had values halfway between hyperdense (calcium) and low-density (cystine/uric acid) calculi for all parameters except HUD, which was the lowest. All HU variables for medium-high density stones were greater than low-density stones (p < 0.001). HUC differentiated the two groups (cut-off 825 HU; specificity 90.6%, sensitivity 88.9%). HUD distinguished calcium from struvite (mean ± SD 51 ± 16 and 28 ± 12 respectively; p = 0.02) with high sensitivity (82.5%) and specificity (80%) at a cut-off of 35 HU/mm. Multivariate analysis revealed HUD ≥ 38.5 HU/mm to be an independent predictor of SFR (OR = 3.1, p = 0.03). No relationship was found between HU values and complication rate. CONCLUSIONS: HU parameters help predict stone composition to select patients for oral chemolysis. HUD is an independent predictor of residual fragments after PCNL and may be fundamental to categorize it, driving the imaging choice at follow-up.