Accuracy of ultrasonography for renal stone detection and size determination: is it good enough for management decisions?

Proof-of-concept for a novel nanotechnology-based treatment for urolithiasis

Proof-of-concept of photonic lithotripsy in an in vitro setting and its ability to fragment the most common stone types is demonstrated. Effectiveness of different classes of photonic nanoparticles in fragmenting human stones is assessed. De-identified human stones were collected after institutional approval. Stones of a size range between 2-4 mm were rehydrated in simulated urine for 24 h. Stones were then coated with a solution of nanoparticles prior to activation with either a 785 nm or 1320 nm near-infrared energy source. Photonic lithotripsy achieved greater than 70% success rate in fragmentating calcium oxalate monohydrate stones using carbon-based nanoparticles for both near-infrared wavelengths. For gold-based nanoparticles, there was a similar success rate with the 785 nm wavelength but a significant decrease when using the 1320 nm wavelength energy source. All stones fragmented with the energy source at a distance ≥ 20 mm from the stone's surface. Limitations include the use of mixed-composition stones, a lack of complete stone immersion in liquid during treatment, and smaller stone size. Different classes of nanoparticles when excited with a near-infrared energy source can fragment common stone types in vitro. This technology has the potential to change the way we approach and treat patients with urolithiasis in a clinical setting.

Machine learning models for screening clinically significant nephrolithiasis in overweight and obese populations

PURPOSES

Our aim is to build and evaluate models to screen for clinically significant nephrolithiasis in overweight and obesity populations using machine learning (ML) methodologies and simple health checkup clinical and urine parameters easily obtained in clinics.

METHODS

We developed ML models to screen for clinically significant nephrolithiasis (kidney stone > 2 mm) in overweight and obese populations (body mass index, BMI ≥ 25 kg/m2) using gender, age, BMI, gout, diabetes mellitus, estimated glomerular filtration rate, bacteriuria, urine pH, urine red blood cell counts, and urine specific gravity. The data were collected from hospitals in Kaohsiung, Taiwan between 2012 and 2021.

RESULTS

Of the 2928 subjects we enrolled, 1148 (39.21%) had clinically significant nephrolithiasis and 1780 (60.79%) did not. The testing dataset consisted of data collected from 574 subjects, 235 (40.94%) with clinically significant nephrolithiasis and 339 (59.06%) without. One model had a testing area under curve of 0.965 (95% CI, 0.9506-0.9794), a sensitivity of 0.860 (95% CI, 0.8152-0.9040), a specificity of 0.947 (95% CI, 0.9230-0.9708), a positive predictive value of 0.918 (95% CI, 0.8820-0.9544), and negative predictive value of 0.907 (95% CI, 0.8756-0.9371).

CONCLUSION

This ML-based model was found able to effectively distinguish the overweight and obese subjects with clinically significant nephrolithiasis from those without. We believe that such a model can serve as an easily accessible and reliable screening tool for nephrolithiasis in overweight and obesity populations and make possible early intervention such as lifestyle modifications and medication for prevention stone complications.

Ultrasound accuracy in evaluating renal calculi in Maysan province

Renal calculi are a common clinical presentation. While ultrasound (US) is a widely used imaging modality for kidney stone diagnosis due to its accessibility and lower cost, its accuracy compared to computerized tomography (CT), the gold standard, remains understudied. This cross-sectional study evaluated the diagnostic accuracy of ultrasound for detecting and characterizing kidney stones compared to computed tomography (CT). Fifty-six patients with suspected kidney stones based on flank pain underwent abdominal ultrasound to assess stone presence, size, location, and the severity of any hydronephrosis (kidney swelling). These findings were then confirmed with a subsequent non-contrast CT scan. There was a fair agreement between US and CT (Kappa = 0.368) for detecting the stone location. The US could not detect 7 (12.5%) stones, being less sensitive in the middle and upper calyx compared to CT. There was a fair agreement between the US and CT (Kappa = 0.394) for detecting the severity of hydronephrosis. The US was less sensitive to moderate and severe hydronephrosis compared to CT. The abdominal ultrasound demonstrated excellent reliability for stone size measurement (intraclass correlation = 0.924), with CT measurements only slightly larger on average (mean difference 0.9 mm). Although abdominal ultrasound provides reliable stone size assessment, its capacity to accurately localize stones and assess hydronephrosis severity is limited.

Prevalence and implications of perinephric fluid on renal point-of-care ultrasound in the emergency department

BACKGROUND

Point-of-care ultrasound (PoCUS) is commonly utilized in the setting of renal colic. The presence of perinephric fluid may be an overlooked finding associated with ureteral obstruction. Our aims were to determine the prevalence of perinephric fluid on emergency physician-performed PoCUS and to determine whether perinephric fluid was associated with stone size or urologic intervention.

METHODS

This was a 12-month cross-sectional study at an academic emergency department (ED) that took place from January 1, 2022, to December 31, 2022. All adult ED patients ≥18 years of age who had a renal PoCUS examination performed were included. Patients with missing or inadequate PoCUS images were excluded. Investigators blinded to PoCUS images and interpretations performed chart review for demographic data and outcome variables, while separate investigators blinded to clinical data reviewed PoCUS images to assess for perinephric fluid and hydronephrosis. A chi-square analysis was used to determine significance of association between perinephric fluid and outcome variables (stone size, urologic intervention).

RESULTS

There were 442 patients screened; 18 were excluded due to inadequate images and 4 were repeat visits of which only the initial visit was analyzed. Of the remaining 420 patients included, the prevalence of perinephric fluid was 6.2% (n = 26). Most patients (23/26) with perinephric fluid had final diagnoses consistent with ureterolithiasis. Hydronephrosis was present in 115 of the 420 patients (27.4%) and of these, 22 (19.1%) had perinephric fluid which was significantly associated with a need for urologic intervention; odds ratio (OR) 10.38 (95% CI 2.70-39.85), p < 0.01. Among the 67 patients with confirmed ureterolithiasis on computed tomography, perinephric fluid was associated with stone size ≥5 mm; OR 4.00 (95% CI 1.01-15.85), p = 0.04.

CONCLUSION

The prevalence of perinephric fluid on emergency physician-performed renal PoCUS was 6.2% of all studies and 19.1% of patients with hydronephrosis. In the setting of ureterolithiasis, perinephric fluid was associated with larger stone size and need for urologic intervention.

Predictive value of single-nucleotide polymorphism signature for nephrolithiasis recurrence: a 5-year prospective study

Background

Genetic variations are linked to kidney stone formation. However, the association of single nucleotide polymorphism (SNPs) and stone recurrence has not been well studied. This study aims to identify genetic variants associated with kidney stone recurrences and to construct a predictive nomogram model using SNPs and clinical features to predict the recurrence risk of kidney stones.

Methods

We genotyped 49 SNPs in 1001 patients who received surgical stone removal between Jan 1 and Dec 31 of 2012. All patients were confirmed stone-free by CT scan and then received follow-up at least 5 years. SNP associations with stone recurrence were analyzed by Cox proportion hazard model. A predictive nomogram model using SNPs and clinical features to predict the recurrence risk of kidney stones was developed by use of LASSO Cox regression.

Results

The recurrence rate at 3, 5, 7 years were 46.8%, 71.2%, and 78.4%, respectively. 5 SNPs were identified that had association with kidney stone recurrence risk. We used computer-generated random numbers to assign 500 of these patients to the training cohort and 501 patients to the validation cohort. A nomogram that combined the 14-SNPs-based classifier with the clinical risk factors was constructed. The areas under the curve (AUCs) at 3, 5 and 7 years of this nomogram was 0.645, 0.723, and 0.75 in training cohort, and was 0.631, 0.708, and 0.727 in validation cohort, respectively. Results show that the nomogram presented a higher predictive accuracy than those of the SNP classifier or clinical factors alone.

Conclusion

SNPs are significantly associated with kidney stone recurrence and should add prognostic value to the traditional clinical risk factors used to assess the kidney stone recurrence. A nomogram using clinical and genetic variables to predict kidney stone recurrence has revealed its potential in the future as an assessment tool during the follow-up of kidney stone patients.

Role of Posterior Acoustic Shadow Width in Ultrasound in Determining Stone Size in Urolithiasis

Introduction Ultrasound (US) is frequently the initial diagnostic tool for urolithiasis, though computed tomography (CT) remains the imaging modality of choice. However, due to potential overestimations, the accuracy of US in gauging stone size has been a point of contention. This study aims to compare the accuracy of stone size measurements in US, specifically evaluating the utility of the posterior acoustic shadow (PAS) width, against the CT measurements. Methods We conducted a cross-sectional study where 120 adult patients (aged >18 years) with confirmed urolithiasis through CT participated. Stone sizes were assessed via both CT and US, with the PAS width also being measured in the latter. Statistical analysis compared stone size discrepancies between both CT and US measurement techniques. Results The study enrolled 73 males and 47 females with various stone locations. The average stone sizes were 15.93 ± 4.59 mm (CT), 18.60 ± 4.80 mm (US), and 16.69 ± 4.61 mm (PAS width). There was a mean difference of 2.67 mm (p < 0.0001) between CT and US sizes, whereas the difference between the PAS width and CT sizes was only 0.75 mm (p = 0.203). Stone size miscalculation by US was 16.77%, whereas it was only 4.77% for PAS width. Conclusion US tends to significantly overestimate stone size when compared to CT. Conversely, the measurement of the PAS width in US presents a more aligned estimation to CT outputs. Integrating PAS width into routine US reporting can enhance the accuracy of stone size estimation, optimizing urolithiasis management and patient counseling.

ACR Appropriateness Criteria® Acute Onset Flank Pain-Suspicion of Stone Disease (Urolithiasis)

Noncontrast CT (NCCT) is the imaging study of choice for initial evaluation of patients with acute onset of flank pain and suspicion of stone disease without known prior stone disease. NCCT can reliably characterize the location and size of an offending ureteral calculus, identify complications, and diagnose alternative etiologies of abdominal pain. Although less sensitive in the detection of stones, ultrasound may have a role in evaluating for signs of obstruction. Radiography potentially has a role, although has been shown to be less sensitive than NCCT. For patients with known disease and recurrent symptoms of urolithiasis, NCCT remains the test of choice for evaluation. In pregnancy, given radiation concerns, ultrasound is recommended as the initial modality of choice with potential role for noncontrast MRI. In scenarios where stone disease suspected and initial NCCT is inconclusive, contrast-enhanced imaging, either with MRI or CT/CT urogram may be appropriate. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision process support the systematic analysis of the medical literature from peer reviewed journals. Established methodology principles such as Grading of Recommendations Assessment, Development, and Evaluation or GRADE are adapted to evaluate the evidence. The RAND/UCLA Appropriateness Method User Manual provides the methodology to determine the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where peer reviewed literature is lacking or equivocal, experts may be the primary evidentiary source available to formulate a recommendation.

Radiologic and pathologic correlation of a renal venous hemangioma

Renal hemangiomas, including the rare subtype of venous hemangioma, are typically non-cancerous, often asymptomatic, and usually discovered incidentally during imaging studies. Here, we report a unique case of a 59-year-old African-American female with a renal venous hemangioma that initially mimicked papillary-type renal cell carcinoma (RCC-pt) on imaging studies. The patient's presentation included a long history of rectal bleeding and an incidental discovery of a hypoattenuating mass in the left kidney during a contrast-enhanced CT scan. Renal MRI revealed a 3.5 cm left renal lower pole mass, presenting as heterogeneously hyperintense on T1-weighted images and hypointense on T2-weighted images, with gradual mild enhancement post-contrast. Subsequent total nephrectomy confirmed the histopathological diagnosis of a venous hemangioma. This case underlines the need for recognizing unique imaging features of renal venous hemangiomas, contributing to the differential diagnosis of T2 dark hypoenhancing renal masses. Correct interpretation may prevent unnecessary invasive procedures and operations, thereby improving patient management and outcomes.

Application of ultrasound imaging in the treatment of urinary tract stones

Urinary tract stones are a common clinical condition that affect millions of individuals worldwide. The management of these stones has evolved significantly over the past 70 years, and ultrasound imaging has emerged as a valuable tool for diagnosis, treatment planning, and follow-up. This review aims to provide an overview of the application of ultrasound imaging in the treatment of urinary tract stones, highlighting its advantages, limitations, and current advancements in the field.

Enhancing sizing accuracy in ultrasound images with an alternative ADMIRE model and dynamic range considerations

Ultrasound imaging can struggle with sizing accuracy, especially when the targets have a significantly different amplitude compared to the surrounding background. In this work, we consider the challenging task of accurately sizing hyperechoic structures, and specifically kidney stones, where accurate sizing is critical for determining medical intervention. AD-Ex, an extended alternative model of our aperture domain model image reconstruction (ADMIRE) pre-processing method, is introduced and is designed to improve clutter removal and improve sizing accuracy. We compare this method against other resolution enhancing methods such as minimum variance (MV) and generalized coherence factor (GCF), and against those methods using AD-Ex as a pre-processing tool. These methods are evaluated among patients with kidney stone disease, with the task of accurately sizing the stones against the gold standard, computed tomography (CT). Stone ROI's were selected using contour maps as reference from which the lateral stone size was estimated. Among the in vivo kidney stone cases we processed, AD-Ex+MV had the overall lowest sizing error among the methods, with an average error of 10.8% compared to the next best method AD-Ex which had an average error of 23.4%. For reference, DAS had an average error of 82.4%. Though dynamic range was evaluated to determine optimal thresholding for sizing applications, variability between stone cases was too high for any conclusions to be drawn at this time.

Imaging in stone diagnosis and surgical planning

PURPOSE OF REVIEW

Radiological imaging techniques and applications are constantly advancing. This review will examine modern imaging techniques in the diagnosis of urolithiasis and applications for surgical planning.

RECENT FINDINGS

The diagnosis of urolithiasis may be done via plain film X-ray, ultrasound (US), or contrast tomography (CT) scan. US should be applied in the workup of flank pain in emergency rooms and may reduce unnecessary radiation exposure. Low dose and ultra-low-dose CT remain the diagnostic standard for most populations but remain underutilized. Single and dual-energy CT provide three-dimensional imaging that can predict stone-specific parameters that help clinicians predict stone passage likelihood, identify ideal management techniques, and possibly reduce complications. Machine learning has been increasingly applied to 3-D imaging to support clinicians in these prognostications and treatment selection.

SUMMARY

The diagnosis and management of urolithiasis are increasingly personalized. Patient and stone characteristics will support clinicians in treatment decision, surgical planning, and counseling.

Ureteropyeloscopic removal of a nephrolith from a 19 year old Hanoverian gelding

OBJECTIVE

To describe the ureteropyeloscopic removal of a nephrolith in a horse.

ANIMALS

A 19 year old Hanoverian gelding with history of urolithiasis requiring surgical intervention.

STUDY DESIGN

Case report METHODS: The horse presented with signs of abdominal straining and stranguria. A proximal urethral calculus was palpable externally within the perineal urethra. Perineal urethrostomy (PU) at the location of the urethral calculi was performed to remove the urethral obstruction. Left nephrolithiasis was then treated by endoscopic retrieval, inserting the endoscope through the PU. The procedures were performed over 2 consecutive days, with the horse standing and sedated. Medical therapy included antimicrobial and anti-inflammatory treatment.

RESULTS

The ureteropyeloscopic removal of a nephrolith from the left renal pelvis was completed. No complications were appreciated following the procedure, and the horse was able to return to athletic activity within 2 weeks. The horse had no further clinical signs referable to urinary dysfunction 7 months later.

CONCLUSION

Ureteropyeloscopic removal of a nephrolith from the renal pelvis is technically feasible in the equine patient and preserves function of the affected kidney. The availability of a treatment that maintains renal function is a distinct benefit over unilateral nephrectomy, particularly when treating a condition that frequently involves both kidneys.

Development and validation of a clinical diagnostic model for pregnant women with renal colic in the emergency department in China: a protocol for a retrospective cohort study

INTRODUCTION

Urolithiasis affects many people throughout their lives. Among the maternal population, although the morbidity of acute urolithiasis in pregnant women is unremarkable, it is the leading cause of hospitalisation during pregnancy. There is no effective clinical diagnostic tool to help doctors diagnose diseases. Our primary aim was to develop and validate a clinical prediction model based on statistical methods to predict the probability of having disease in pregnant women who visited the emergency department because of urolithiasis-induced colic.

METHODS AND ANALYSIS

We will use multivariate logistic regression analysis to build a multivariate regression linear model. A receiver operating characteristic curve plot and calibration plot will be used to measure the discrimination value and calibration value of the model, respectively. We will also use least absolute shrinkage and selection operator regression analysis combined with logistic regression analysis to select predictors and construct the multivariate regression model. The model will be simplified to an application that has been reported before, and users will only need to enter their clinical parameters so that risk probability is automatically derived.

ETHICS AND DISSEMINATION

The review and approval documents of the clinical research ethics committee have been received from the ethics committee of our hospital (The Third Affiliated Hospital of Wenzhou Medical University). We will disseminate research findings through presentations at scientific conferences and publication in peer-reviewed journals.

Spatial Coherence Beamforming With Multi-Line Transmission to Enhance the Contrast of Coherent Structures in Ultrasound Images Degraded by Acoustic Clutter

This work demonstrates that the combination of multi-line transmission (MLT) and short-lag spatial coherence (SLSC) imaging improves the contrast of highly coherent structures within soft tissues when compared to both traditional SLSC imaging and conventional delay and sum (DAS) beamforming. Experimental tests with small (i.e., [Formula: see text]-3 mm) targets embedded in homogeneous and heterogeneous backgrounds were conducted. DAS or SLSC images were reconstructed when implementing MLT with varying numbers of simultaneously transmitted beams. In images degraded by acoustic clutter, MLT SLSC achieved up to 34.1 dB better target contrast and up to 16 times higher frame rates when compared to the more conventional single-line transmission SLSC images, with lateral resolution improvements as large as 38.2%. MLT SLSC thus represents a promising technique for clinical applications in which ultrasound visualization of highly coherent targets is required (e.g., breast microcalcifications, kidney stones, and percutaneous biopsy needle tracking) and would otherwise be challenging due to the strong presence of acoustic clutter.

Resolution of Hydronephrosis and Pain to Predict Stone Passage for Patients With Acute Renal Colic

OBJECTIVE

To study patients who presented to the Emergency Department with acute renal colic to determine if resolution of hydronephrosis and pain accurately predicts stone passage on follow-up CT.

MATERIALS AND METHODS

This is a secondary analysis of a multicenter prospective randomized clinical trial of patients diagnosed by computed tomography (CT) scan with a symptomatic ureteral stone < 9 mm in diameter. Participants were followed after randomization to evaluate for analgesic use and to assess stone passage and hydronephrosis on a repeat CT scan obtained at 29-36 days.

RESULTS

Four-hundred-three patients were randomized in the original study and patients were included in this analysis if they did not have surgery for stone removal and had a CT scan and information on pain medication at follow-up (N = 220). Hydronephrosis was detected in 181 (82%) on initial CT. At follow-up CT, 43 (20%) participants had a persistent ureteral stone. Of these patients, 36 (84%) had no pain, 26 (60%) did not have hydronephrosis, and 23 (53%) had neither pain nor hydronephrosis. Resolution of hydronephrosis was associated with stone passage (RR 4.6, 95% CI 1.9, 11.0), while resolution of pain was not (RR 1.1, 95% CI 0.9, 1.4).

CONCLUSION

In patients with urinary stone disease, stone passage is associated with resolution of hydronephrosis but not resolution of pain. In patients with persistent ureteral stones, neither pain nor hydronephrosis are consistently present. These findings have important implications on follow-up imaging of patients with urinary stone disease.

Can plain film radiography improve the emergency department detection of clinically important urinary stones?

OBJECTIVE

Physicians frequently use ultrasound to assess hydronephrosis in patients with suspected renal colic, but ultrasound has limited diagnostic sensitivity and rarely clarifies stone size or location. Consequently, up to 80% of emergency department (ED) renal colic patients undergo confirmatory CT imaging. Our goal was to estimate x-ray sensitivity for urinary stones and determine whether x-ray substantially improves stone detection (sensitivity) compared to hydronephrosis assessment alone.

METHODS

We reviewed imaging reports from all renal colic patients who underwent x-ray and CT at four EDs. For each patient, we documented stone size, location and hydronephrosis severity on CT and whether stones were identified on x-ray. We considered moderate and severe hydronephrosis (MS-Hydro) as significant positive findings, then calculated the sensitivity (detection rate) of MS-Hydro and x-ray for large stones ≥5 mm and for stones likely to require intervention (all ureteral stones >7 mm and proximal or middle stones >5 mm). We then tested a diagnostic algorithm adding x-ray to hydronephrosis assessment.

RESULTS

Among 1026 patients with 1527 stones, MS-Hydro sensitivity was 39% for large stones and 60% for interventional stones. X-ray sensitivity was 46% for large stones and 52% for interventional stones. Adding x-ray to hydronephrosis assessment increased sensitivity in all stone categories, specifically from 39% to 68% for large stones (gain = 29%; 95%CI, 23% to 35%) and from 60% to 82% for interventional stones (gain = 22%; 95%CI, 13% to 30%). Because CT and ultrasound show strong agreement for MS-Hydro identification, physicians who depend on ultrasound-based hydronephrosis assessment could achieve similar gains by adding x-ray.

CONCLUSIONS

Adding x-ray to hydronephrosis assessment substantially improves diagnostic sensitivity, enabling the detection of nearly 70% of large stones and over 80% of interventional stones. This level of sensitivity may be sufficient to reassure physicians about a renal colic diagnosis without CT imaging for many patients.

Automated radiomic analysis of CT images to predict likelihood of spontaneous passage of symptomatic renal stones

PURPOSE

To evaluate the ability of a semi-automated radiomic analysis software in predicting the likelihood of spontaneous passage of urinary stones compared with manual measurements.

METHODS

Symptomatic patients visiting the emergency department with suspected stones in either kidney or ureters who underwent a CT scan were included. Patients were followed for up to 6 months for the outcome of a trial of passage. Maximum stone diameters in axial and coronal images were measured manually. Stone length, width, height, max diameter, volume, the mean and standard deviation of the Hounsfield units, and morphologic features were also measured using automated radiomic analysis software. Multivariate models were developed using these data to predict subsequent spontaneous stone passage, with results expressed as the area under a receiver operating curve (AUC).

RESULTS

One hundred eighty-four patients (69 females) with a median age of 56 years were included. Spontaneous stone passage occurred in 114 patients (62%). Univariate analysis demonstrated an AUC of 0.83 and 0.82 for the maximum stone diameter determined manually in the axial and coronal planes, respectively. Multivariate models demonstrated an AUC of 0.82 for a model including manual measurement of maximum stone diameter in axial and coronal planes. The same AUC was found for a model including automatic measurement of maximum height and diameter of the stone. Further addition of morphological parameters measured automatically did not increase AUC beyond 0.83.

CONCLUSION

The semi-automated radiomic analysis of urinary stones shows similar accuracy compared with manual measurements for predicting urinary stone passage. Further studies are needed to predict clinical impacts of reporting the likelihood of urinary stone passage and improving inter-observer variation using automatic radiomic analysis software.

Extremely-slow, half-number shockwave lithotripsy for asymptomatic renal stones <20 mm

PURPOSE

To compare the treatment success rate and safety of reduced (30 shocks/min, 1,200 shocks/session) versus standard (60 shocks/min, 2,400 shocks/session) extracorporeal shockwave lithotripsy for the management of renal stones.

MATERIALS AND METHODS

We retrospectively analyzed 404 patients who underwent extracorporeal shockwave lithotripsy for 5-20-mm renal stones between April 2011 and March 2019. Patients selected the reduced or standard protocol (group R and S) after explaining the potential benefits and disadvantages. The primary outcome was treatment success within 12 weeks, which was defined as no residual fragment or fragments <4 mm on ultrasonography and plain radiograph.

RESULTS

In total, 94 and 310 patients underwent shockwave lithotripsy with a reduced and standard protocol, respectively. The background characteristics of the participants did not significantly differ. The treatment success within 12 weeks was achieved in 78 (83.0%) patients in group R and 259 (83.5%) in group S (p=0.88). The median number of the session was 3 (interquartile range, 2-4) in both groups (p=0.53). The total complication rates were 5.4% in group R and 6.1% in group S. Three (1.0%) patients in group S experienced perirenal hematoma, which was conservatively treated. The reduced protocol was not associated with treatment success in the multivariate analysis adjusted for potential confounders (odds ratio, 0.91; 95% confidence interval, 0.46-1.80; p=0.78).

CONCLUSIONS

The new treatment amendment with a slower delivery rate successfully reduced the total number of shocks need to fragment renal stones <20 mm without compromising the stone-free rate.

The gap between ultrasonography and computed tomography in measuring the size of urinary calculi

Objective

Due to a lack of studies regarding the need for computed tomography (CT) in measuring the size of each urinary calculus before surgery, this study was conducted to elucidate the difference between ultrasonography (US) and CT in measuring the size of urinary stones.

Methods

A retrospective review of 100 stones from 83 patients. Each urinary stone was measured using both US and CT; both measurements were then compared.

Results

Of 83 patients, the mean age was 39.29 ± 23.76 years; 47 (56.62%) were male and 36 (43.37%) were female. Most of the urinary stones were <10 mm (50.0%) followed by 11-20 mm (42.0%), (P < 0.001). A cross-tabulation test revealed strong compatibility between US and CT in measuring the size of urinary stones (73.7% in stones <10 mm, 66.7% in stones 11-20 mm and 50% in stones >21 mm), (P < 0.001). Spearman's rho correlation test revealed strong compatibility between stone diameters measured by US and CT (r = 0.755), (P = 0 < 0.001). T-test for equality of means revealed no significant difference in the measured size using US and CT (mean = 11.80 ± 5.83 vs. 11.65 ± 6.59, respectively), mean difference = 0.15, and P = 0.865, 95% confidence interval: -1.584-1.884.

Conclusion

No significant difference in measuring the size of urinary stones using US and CT. However, US may slightly overestimate small stones in some cases.

Kidney Imaging and Biopsy in Pregnancy

Physiologic glomerular, tubular, and structural changes related to pregnancy may complicate the detection of underlying kidney disease in pregnant patients. Imaging studies may provide important clinical information to assist in the diagnosis and treatment of kidney disease during pregnancy. Furthermore, in select patients who develop new or worsening kidney disease in pregnancy, kidney biopsy may be essential to ensure the accuracy of diagnosis and guide treatment choices. This review article will discuss the risks and benefits of various modalities used to image the kidneys and urinary tract during pregnancy to aid in the judicious selection of appropriate imaging studies that are likely to maximize clinical benefit while minimizing fetal risk. It will also highlight the potential benefits and harms associated with antepartum kidney biopsy and will offer strategies for identifying patients who are most likely to benefit from kidney biopsy during pregnancy.

Semi-closed-circuit vacuum-assisted mini percutaneous nephrolithotomy in the pediatric population: the initial experience of two tertiary referral centers

BACKGROUND

Percutaneous nephrolithotomy (PCNL) is the gold-standard for complex renal stones treatment in the pediatric population. While the miniaturization of PCNL reduces the risk of bleeding, it can hinder surgical and functional outcomes. The aim of the study was to assess the safety and feasibility of semi-closed-circuit vacuum-assisted Mini-PCNL (vmPCNL) in pediatric patients.

METHODS

From January 2017 to December 2018, we prospectively collected data on consecutive vmPCNLs from two European tertiary referral centers. The procedure was performed with the ClearPetra^® (Well Lead Medical Co., Ltd., Guangzhou, China) access sheath equipped with a lateral arm connected to the aspiration system (pressure setting ~120-150 cmH<inf>2</inf>O) by a 200 Ml plastic stone collector. Pre-, intra- and postoperative data and costs were analyzed. The stone-free rate (SFR) was defined as absence of residual fragments >4 mm with either ultrasound or kidney, ureter, and bladder X-ray.

RESULTS

Eighteen vmPCNLs were performed in 16 renal units of 13 children. The median age was 119 months (IQR: 97-160) and the weight was 29 Kg (IQR: 25-40). The median cumulative stone size was 32 mm (22-46) with 8 (44.4%) cases of staghorn stones. The OT was 128 min (IQR: 99-167). The basketing was unnecessary in 6/18 (33%) cases. Neither intra-operative complications nor blood transfusions occurred. Postoperative fever was observed in 5/18 (27.8%) cases; in one case a double J ureteral stent was placed for concomitant hydronephrosis. The SFR was 81.3% (13/16), rising to 93.8% (15/16) after ancillary procedures. The materials costs of a vmPCNL (734.8 €) were comparable to mini-PCNL using a reusable set (710.7 €).

CONCLUSIONS

The vmPCNL seems to be sustainable, safe and feasible for kidney stones treatment in the pediatric population.

The Prevalence of Incidentally Detected Urolithiasis in Subjects Undergoing Computerized Tomography

Background and objective

Urolithiasis is defined as the presence of calculi in the urinary tract. Multiple studies have shown that urinary tract stones are one of the most common incidental findings in medical imaging. These stones are potentially dangerous and can cause severe impairment to renal function if they remain undiagnosed for a long time. The objective of this study was to determine the prevalence of incidentally detected urolithiasis in patients undergoing abdominopelvic CT scans.

Materials and methods

A retrospective cross-sectional study was conducted, which involved 721 patients selected by consecutive non-randomized sampling. The study population included patients who underwent an abdominopelvic CT scan in the radiology department of a tertiary care hospital in Pakistan. Patients aged below 10 years and those above 90 years were excluded from the study. Patients undergoing kidney, ureter, and bladder (KUB) scan for urolithiasis-associated symptoms and those with already known urolithiasis were also excluded. The data were recorded in a predesigned pro forma and analyzed with SPSS Statistics version 20.00 (IBM, Armonk, NY).

Results

A total of 721 patients underwent an abdominopelvic CT scan during the six months from July to December in the radiology department of the hospital. Out of these, 336 (46.6%) were males, and 385 (53.4%) were females. Incidental stones were found in 20 of these patients. Among these 20 stone formers, 11 were males, and nine were females. Out of them, six had stones in the right kidney, eight in the left kidney, and four patients had bilateral stones. The remaining two patients had stones in their ureters. In most cases, stones were found in lower poles as compared to the mid pole and upper pole of the kidneys.

Conclusion

The prevalence of incidentally detected urolithiasis was found to be 2.8% in this study. Its frequency was much higher in males (3.27%) compared to females (2.33%). Most of the stones were found in the kidneys whereas no stone was detected in the urinary bladder.

Point-of-care ultrasound for the detection of hydronephrosis in emergency department patients with suspected renal colic

Background

Point-of-care ultrasound (PoCUS) by emergency physicians for renal colic has been proposed as an alternative to computed tomography (CT) to avoid ionizing radiation exposure and shorten emergency department length of stay. Previous studies have employed experienced or credentialed ultrasonographers or required advanced ultrasound skills. We sought to measure the diagnostic accuracy of PoCUS by physicians with varied experience using a simplified binary outcome of presence or absence of hydronephrosis. Secondary outcomes include assessment as to whether the presence of hydronephrosis on PoCUS is predictive of complications, and to evaluate possible causes for the reduced diagnostic accuracy such as body mass index (BMI) and time between PoCUS and formal imaging, and scanner experience.

Results

413 patients were enrolled in the study. PoCUS showed a specificity of 71.8% [95% CI 65.0, 77.9] and sensitivity of 77.1% [95% CI 70.9, 82.6]. Hydronephrosis on PoCUS was predictive of complications (relative risk 3.13; [95% CI 1.30, 7.53]). The time interval between PoCUS and formal imaging, BMI, and scanner experience did not influence the accuracy of PoCUS.

Conclusions

PoCUS for hydronephrosis in suspected renal colic has moderate accuracy when performed by providers with varied experience for the binary outcome of presence or absence of hydronephrosis. Hydronephrosis on PoCUS is associated with increased rates of complications. PoCUS for hydronephrosis is limited in its utility as a stand-alone test, however this inexpensive, readily available test may be useful in conjunction with clinical course to determine which patients would benefit from formal imaging or urologic consultation.

ClinicalTrials.gov Identifier NCT01323842

In-Office Ultrasound Facilitates Timely Clinical Care at a Multidisciplinary Kidney Stone Center

Introduction

A considerable publication record exists comparing sensitivity and specificity of radiological ultrasound (including point of care ultrasound) to computerized tomography for stone disease. However, the practical application of in-office ultrasound to support the growing number of kidney stone centers around the world represents a nuanced topic that is ripe for study and discussion.

Methods

We provide a descriptive analysis of how in-office ultrasound is being used as an adjunct to clinical care based on our experience during 50 days in clinic at an institutionally affiliated, multidisciplinary kidney stone center. Clinic subjects gave consent and underwent ultrasound as part of research studies. Ultrasonograms were shared with and verified by the treating physician before the patient was discharged from care. We counted the number of times research imaging altered the care plan.

Results

Of the 60 patients enrolled the clinician used the information obtained from the studies in 20 (33%) to determine the course of clinical care that resulted in a change in treatment or process.

Conclusions

Ultrasound has the potential to be a cost-effective and valuable tool that can provide more efficient workflow within a kidney stone center or urology clinic.

On the Effects of Constitutive Properties and Roughness of a Hard Inclusion in Soft Tissue on B-mode Images

We perform finite element modeling of pulse-echo ultrasound of a hard inclusion in a soft tissue to gain a better understanding of B-mode image brightness characteristics. We simulate a pressure wave emitted by an ultrasound transducer through the inclusion-tissue medium by prescribing suitable boundary conditions, and collect the scattered wave response to simulate the behavior of the transducer array used for pulse-echo ultrasound. We form B-mode images from simulated channel data using standard delay and sum beamforming. We establish the accuracy of the finite element model by comparing the point spread function with that obtained from Field II ultrasound simulation program. We also demonstrate qualitative validation by comparing the brightness characteristics of rough and smooth surfaced circular inclusions with experimental images of a cylindrical metal tool immersed in a water tank. We next conduct simulation studies to evaluate changes in B-mode image brightness intensity and contrast related to different constitutive properties, namely, compressibility of the inclusion, impedance contrast between the host and inclusion, and surface roughness of the inclusion. We find that the intensity observed behind a hard inclusion in the axial direction is strongly affected by the compressibility and roughness of the inclusion. Also, the perceived width of the stone based on the intensity is greater for rougher stones. Our study indicates that imaging of compressible inclusions may benefit from targeted B-mode image forming algorithms. Our modeling framework can potentially be useful in differentiating hard inclusions from surrounding parenchyma, and for classifying kidney stones or gallstones.

Age-related urologic problems in the complex urologic patient

PURPOSE

Improved medical care throughout childhood and adolescence has enabled patients with complex urological abnormalities to live longer into adulthood. These patients are now at risk of developing common, age-related, urological conditions. This review aims to review existing data and make recommendations in areas where expert opinion is currently lacking METHODS: This review represents the joint SIU-ICUD (Société Internationale d'Urologie-International Consultation on Urological Disease) consultation on congenital lifelong urology. The results of this analysis were first presented at a joint consultation of the ICUD and SIU at the 2018 SIU annual conference in Seoul, South Korea.

RESULTS

BPH may present differently in patients with neurogenic bladder. Thorough assessment of neurological status, bladder and sphincter function is required before offering any bladder outlet surgery. Prostate specific antigen screening should be offered to men aged 50-69 with neurogenic bladders if they have good life expectancy. Multi-parametric MRI and transperineal biopsy would be the investigations of choice if feasible. Surgery for localized disease should only be done by surgeons with the relevant expertise. Bladder cancer in this patient group is more likely to present at a later stage and have a worse prognosis. Parenthood is achievable for most, but often requires assistance with conception. Pregnant women who have had previous urogenital reconstructive surgery should be managed in appropriate obstetric units with the involvement of a reconstructive urologist.

CONCLUSIONS

Most evidence regarding complex urogenital abnormalities comes from the pediatric population. Evidence regarding common, age-related urological issues is generally from the 'normal' adult population. As patients with complex congenital urological conditions live longer, more data will become available to assess the long-term benefits of intervention.

Aktualisierung der S2k-Leitlinie zur Diagnostik, Therapie und Metaphylaxe der Urolithiasis (AWMF Registernummer 043-025)

Die Zunahme des medizinischen Wissens, technische Neuerungen gemeinsam mit demographischem Wandel stellen eine Herausforderung an die Neukonzeption von Leitlinien und klinischen Studien dar. Die vorliegende S2k-Leitlinie, die sich ausschließlich mit Nieren- und Harnleitersteinen beschäftigt, soll die Behandlung von Harnsteinpatienten in Klinik und Praxis unterstützen, aber auch Patienteninformationen zur Urolithiasis geben. Die zunehmende interdisziplinäre Zusammenarbeit in der Steintherapie zeigt sich auch an der Anzahl beteiligter Fachgruppen und Arbeitsgemeinschaften in der Erstellung des neuen Leitlinienupdates. Die vorliegende, aus einem interdisziplinären Konsensusprozess hervorgegangene S2k-Leitlinie stellt die aktuellen Empfehlungen praxisnah dar und gibt Entscheidungshilfen für Diagnostik‑, Therapie- und Metaphylaxemaßnahmen auf Basis von Expertenmeinungen und verfügbaren Evidenzgrundlagen aus der Literatur.

Innovations in Ultrasound Technology in the Management of Kidney Stones

This article reviews new advances in ultrasound technology for urinary stone disease. Recent research to facilitate the diagnosis of nephrolithiasis, including use of the twinkling signal and posterior acoustic shadow, have helped to improve the use of ultrasound examination for detecting and sizing renal stones. New therapeutic applications of ultrasound technology for stone disease have emerged, including ultrasonic propulsion to reposition stones and burst wave lithotripsy to fragment stones noninvasively. The safety, efficacy, and evolution of these technologies in phantom, animal, and human studies are reviewed herein. New developments in these rapidly growing areas of ultrasound research are also highlighted.

Understanding, justifying, and optimizing radiation exposure for CT imaging in nephrourology

An estimated 4-5 million CT scans are performed in the USA every year to investigate nephrourological diseases such as urinary stones and renal masses. Despite the clinical benefits of CT imaging, concerns remain regarding the potential risks associated with exposure to ionizing radiation. To assess the potential risk of harmful biological effects from exposure to ionizing radiation, understanding the mechanisms by which radiation damage and repair occur is essential. Although radiation level and cancer risk follow a linear association at high doses, no strong relationship is apparent below 100 mSv, the doses used in diagnostic imaging. Furthermore, the small theoretical increase in risk of cancer incidence must be considered in the context of the clinical benefit derived from a medically indicated CT and the likelihood of cancer occurrence in the general population. Elimination of unnecessary imaging is the most important method to reduce imaging-related radiation; however, technical aspects of medically justified imaging should also be optimized, such that the required diagnostic information is retained while minimizing the dose of radiation. Despite intensive study, evidence to prove an increased cancer risk associated with radiation doses below ~100 mSv is lacking; however, concerns about ionizing radiation in medical imaging remain and can affect patient care. Overall, the principles of justification and optimization must remain the basis of clinical decision-making regarding the use of ionizing radiation in medicine.

Low-dose CT scan in stone detection for stone treatment follow-up: is there a relation between stone composition and radiation delivery? Study on a porcine-kidney model

BACKGROUND

Non-contrast CT scan (NCCT) is becoming the standard imaging modality in urinary stone disease. Radiation dose remains an issue, especially for those patients who may need to undergo several CT scans for this indication during their lifetime. Low-dose and ultra-low-dose protocols exist, but there is limited data on the relationship between the minimum radiation dose capable of detecting stone fragments and stone composition.

METHODS

Seven different kinds of human kidney stone were selected. Fragments of 1, 2, 4 and 7 mm were obtained for each stone. Four fragments of the same material were placed in a porcine kidney. A CT scan was then used to scan the kidney at decreasing dosages of 140, 70, 30, 15 and 7mAs. The scans were repeated for each type of stone. Images were reviewed by two radiologists independently with the intent of identifying the stone composition and providing information on its position, dimensions and Hounsfield units (HU).

RESULTS

All types of stone were visible at all settings. Only the 1-mm uric-acid fragment was not detected by both radiologists at 7 and 15 mAs. Dose Length product (DLP) decreased with the reduction in mAs. In terms of HU a statistically significant difference was observed between calcium-based and non-calcium-based stones. Stone dimensions and HU were not affected by the reductions in mAs.

CONCLUSIONS

Ultra-low-dose CT has a good detection rate for all kinds of stone, even when the fragment size is small. Only small uric acid fragments need higher energy settings in order to be detected. When the stone composition is known after surgery for urolithiasis, the most appropriate CT scan setting could be suggested by the urologist during their follow-up.

Measurement of Posterior Acoustic Stone Shadow on Ultrasound Is a Learnable Skill for Inexperienced Users to Improve Accuracy of Stone Sizing

INTRODUCTION

Studies suggest that the width of the acoustic shadow on ultrasound (US) more accurately reflects true stone size than the stone width in US images. We evaluated the need for training in the adoption of the acoustic shadow sizing technique by clinical providers.

METHODS

Providers without shadow sizing experience were recruited and assigned in a stratified, alternating manner to receive a training tutorial ("trained") or no intervention ("control"). Each conducted a baseline assessment of 24 clinical US images; where present, shadow width was measured using custom calipers. The trained group subsequently completed a standardized training module on shadow sizing. All subjects repeated measurements after ∼1 week. Group demographics were compared using Fisher's exact test. Measurements were compared to clinically reported stone sizes on corresponding CT and US using mixed-effects models. One millimeter concordance between shadow and CT size was compared using a generalized linear mixed-effects model.

RESULTS

Twenty-six subjects were included. There was no significant difference between groups in demographics, clinical role, or US experience. Mean reported CT and US stone sizes were 6.8 ± 4.0 mm and 10.3 ± 4.1 mm, respectively. At baseline, there was no difference in shadow size measurements between groups (p = 0.18), and shadow size was no more accurate than US stone size (p = 0.28 trained; p = 0.81 control), compared to CT. After training, overestimation bias of shadow size in the trained group decreased to 1.6 ± 0.5 mm (p < 0.01), relative to CT. This was not significantly associated with clinical rank, US experience, or stone-measuring experience. One millimeter concordance with CT size significantly increased from 23% to 35% of stones after training (p = 0.01). No significant improvement occurred in the control group.

CONCLUSION

Acoustic shadow sizing was readily adopted by inexperienced providers, but was not more accurate than reported US stone sizes without training. Education on shadow sizing may be warranted before clinical adoption.

Feasibility of non-linear beamforming ultrasound methods to characterize and size kidney stones

Purpose

Ultrasound methods for kidney stone imaging suffer from poor sensitivity and size overestimation. The study objective was to demonstrate feasibility of non-linear ultrasound beamforming methods for stone imaging, including plane wave synthetic focusing (PWSF), short-lag spatial coherence (SLSC) imaging, mid-lag spatial coherence (MLSC) imaging with incoherent compounding, and aperture domain model image reconstruction (ADMIRE).

Materials and methods

The ultrasound techniques were evaluated in an in vitro kidney stone model and in a pilot study of 5 human stone formers (n = 6 stones). Stone contrast, contrast-to-noise ratio (CNR), sizing, posterior shadow contrast, and shadow width sizing were compared among the different techniques and to B-mode. CT imaging within 60 days was considered the gold standard stone size. Paired t-tests using Bonferroni correction were performed to evaluate comparing each technique with B-mode.

Results

Mean CT measured stone size was 6.0mm (range 2.9–12.2mm) with mean skin-to-stone distance 10.2cm (range 5.4–16.3cm). Compared to B-mode, stone contrast was best with ADMIRE (mean +12.2dB), while SLSC and MLSC showed statistically improved CNR. Sizing was best with ADMIRE (mean +1.3mm error), however this was not significantly improved over B-mode (+2.4mm). PWSF performed similarly to B-mode for stone contrast, CNR, SNR, and stone sizing. In the in vitro model, the shadow contrast was highest with ADMIRE (mean 10.5 dB vs 3.1 dB with B-mode). Shadow sizing was best with SLSC (mean error +0.9mm ± 2.9), however the difference compared to B-mode was not significant.

Conclusions

The detection and sizing of stones are feasible with advanced beamforming methods with ultrasound. ADMIRE, SLSC, and MLSC hold promise for improving stone detection, shadow contrast, and sizing.

Limited sensitivity and size over measurements of ultrasound affect medical decisions for ureteral stone compared to non-contrasted computed tomography

PURPOSE

To evaluate the limited sensitivity and size over measurements of ultrasound (US) for ureteral stone, and demonstrate how this influenced medical decisions.

PATIENTS AND METHODS

Retrospectively, we analyzed the data of patients with ureterolithiasis estimated by US and non-contrasted computed tomography (NCCT) within 48 h at our institution from January 1st 2014 to June 1st 2017. Stone size was grouped by the longest axis diameter on NCCT: < 5, 5-10, and > 10 mm. Then, US and NCCT results were compared for the sensitivity and measurements.

RESULTS

A total of 614 cases of ureterolithiasis were visible on NCCT. The sensitivity of US for ureterolithiasis < 5, 5-10, and > 10 mm were 63.49, 79.06, and 84.67%, respectively (P = 0.001). US overestimated the size in 63.49 and 50.54% of patients with ureterolithiasis < 5 and 5-10 mm compared to NCCT, respectively (P < 0.001). Under the assumptions that patients with ureteral stone < 5, 5-10, and > 10 mm would be simply observed, received medical expulsive therapy (MET), and surgical interventions, 20.94 and 15.33% of patients with stone sized 5-10 and > 10 mm might be improperly observed due to negative US reports. Besides, 63.49 and 50.54% of cases with stone < 5 and 5-10 mm might receive more aggressive interventions ascribed to over measurements of US.

CONCLUSIONS

Limited sensitivity and size over measurements of US might significantly influence medical decisions for ureteral stone. Inaccurate evaluation of US should be taken in consideration for appropriate counseling options.

In vitro feasibility of next generation non-linear beamforming ultrasound methods to characterize and size kidney stones

Ultrasound imaging for kidney stones suffers from poorer sensitivity, diminished specificity, and overestimation of stone size compared to computed tomography (CT). The purpose of this study was to demonstrate in vitro feasibility of novel ultrasound imaging methods comparing traditional B-mode to advanced beamforming techniques including plane wave synthetic focusing (PWSF), short-lag spatial coherence (SLSC) imaging, mid-lag spatial coherence (MLSC) imaging with incoherent compounding, and aperture domain model image reconstruction (ADMIRE). The ultrasound techniques were evaluated using a research-based ultrasound system applied to an in vitro kidney stone model at 4 and 8 cm depths. Stone diameter sizing and stone contrast were compared among the different techniques. Analysis of variance was used to analyze the differences among group means, with p < 0.05 considered significant, and a Student's t test was used to compare each method with B-mode, with p < 0.0025 considered significant. All stones were detectable with each method. MLSC performed best with stone sizing and stone contrast compared to B-mode. On average, B-mode sizing error ± SD was > 1 mm (1.2 ± 1.1 mm), while those for PWSF, ADMIRE, and MLSC were < 1 mm (- 0.3 ± 2.9 mm, 0.6 ± 0.8, 0.8 ± 0.8, respectively). Subjectively, MLSC appeared to suppress the entire background thus highlighting only the stone. The ADMIRE and SLSC techniques appeared to highlight the stone shadow relative to the background. The detection and sizing of stones in vitro are feasible with advanced beamforming methods with ultrasound. Future work will include imaging stones at greater depths and evaluating the performance of these methods in human stone formers.

Retrospective comparison of measured stone size and posterior acoustic shadow width in clinical ultrasound images

PURPOSE

Posterior acoustic shadow width has been proposed as a more accurate measure of kidney stone size compared to direct measurement of stone width on ultrasound (US). Published data in humans to date have been based on a research using US system. Herein, we compared these two measurements in clinical US images.

METHODS

Thirty patient image sets where computed tomography (CT) and US images were captured less than 1 day apart were retrospectively reviewed. Five blinded reviewers independently assessed the largest stone in each image set for shadow presence and size. Shadow size was compared to US and CT stone sizes.

RESULTS

Eighty percent of included stones demonstrated an acoustic shadow; 83% of stones without a shadow were ≤ 5 mm on CT. Average stone size was 6.5 ± 4.0 mm on CT, 10.3 ± 4.1 mm on US, and 7.5 ± 4.2 mm by shadow width. On average, US overestimated stone size by 3.8 ± 2.4 mm based on stone width (p < 0.001) and 1.0 ± 1.4 mm based on shadow width (p < 0.0098). Shadow measurements decreased misclassification of stones by 25% among three clinically relevant size categories (≤ 5, 5.1-10, > 10 mm), and by 50% for stones ≤ 5 mm.

CONCLUSIONS

US overestimates stone size compared to CT. Retrospective measurement of the acoustic shadow from the same clinical US images is a more accurate reflection of true stone size than direct stone measurement. Most stones without a posterior shadow are ≤ 5 mm.

Quantification of Renal Stone Contrast with Ultrasound in Human Subjects

PURPOSE

Greater visual contrast between calculi and tissue would improve ultrasound (US) imaging of urolithiasis and potentially expand clinical use. The color Doppler twinkling artifact has been suggested to provide enhanced contrast of stones compared with brightness mode (B-mode) imaging, but results are variable. This work provides the first quantitative measure of stone contrast in humans for B-mode and color Doppler mode, forming the basis to improve US for the detection of stones.

MATERIALS AND METHODS

Using a research ultrasound system, B-mode imaging was tuned for detecting stones by applying a single transmit angle and reduced signal compression. Stone twinkling with color Doppler was tuned by using low-frequency transmit pulses, longer pulse durations, and a high-pulse repetition frequency. Data were captured from 32 subjects, with 297 B-mode and Doppler images analyzed from 21 subjects exhibiting twinkling signals. The signal to clutter ratio (i.e., stone to background tissue) (SCR) was used to compare the contrast of a stone on B-mode with color Doppler, and the contrast between stone twinkling and blood-flow signals within the kidney.

RESULTS

The stone was the brightest object in only 54% of B-mode images and 100% of Doppler images containing stone twinkling. On average, stones were isoechoic with the tissue clutter on B-mode (SCR = 0 dB). Stone twinkling averaged 37 times greater contrast than B-mode (16 dB, p < 0.0001) and 3.5 times greater contrast than blood-flow signals (5.5 dB, p = 0.088).

CONCLUSIONS

This study provides the first quantitative measure of US stone to tissue contrast in humans. Stone twinkling contrast is significantly greater than the contrast of a stone on B-mode. There was also a trend of stone twinkling signals having greater contrast than blood-flow signals in the kidney. Dedicated optimization of B-mode and color Doppler stone imaging could improve US detection of stones.