Clinical Effectiveness of Prospectively Reported Sonographic Twinkling Artifact for the Diagnosis of Renal Calculus in Patients Without Known Urolithiasis

Dynamics of crevice microbubbles that cause the twinkling artifact

The Doppler ultrasound twinkling artifact, a rapid color shift, appears on pathological mineralizations and is theorized to arise from scattering off micron-sized crevice microbubbles. However, the influence of crevice number and size as well as the bubble dynamics on twinkling is not well-understood. Cylinders with diameters of 0.8-1.2 µm and depths of 1 µm were etched into a silicon wafer and crevice bubbles were driven at 0.75, 2.5, and 5.0 MHz while monitoring with high-speed photography. Experimental results were compared to a derived crevice bubble model. On three separate wafers, cylindrical crevices (10 or 100) with diameters of 1, 10, or 100 µm and depths of 10 µm were etched and imaged with a research ultrasound system in Doppler mode at 5, 7.8, and 18.5 MHz. Within the pressure ranges studied here (∼1MPa), no bubble oscillation was observed for the 0.8-1.2 µm crevice bubbles which matched computational results. Crevices with 1 and 10 µm diameters produced more twinkling than 100 µm crevices at 5 and 7.8 MHz. In contrast, 100 µm crevices produced more twinkling than 1 or 10 µm crevices at 18.5 MHz (p < 0.001 in all cases). These results provide better insight into how crevice bubbles cause twinkling on pathological mineralizations.

Radiation exposure associated with computed tomography for pediatric urolithiasis evaluation: A scoping review of the literature

INTRODUCTION

Computed tomography (CT) imaging is used for assessment of pediatric urolithiasis in cases where ultrasound is inconclusive. The utility of CT imaging must be considered alongside the potential risks of radiation exposure in this patient population due to the increased risk of cancer development. The purpose of this review is to investigate the radiation exposure associated with standard-dose and low-dose computed tomography (CT) imaging for the assessment of pediatric urolithiasis.

METHODS

A scoping literature review over a 23 year period between 2000 and 2023 was conducted of all English-language studies reporting on the use of non-contrast CT imaging for assessment of pediatric urolithiasis. Patients that were specified as pediatric with age ≤20 years at time of intervention and undergoing standard-dose or low/ultra-low-dose CT were included. Low-dose and ultra-low-dose CT were defined as a radiation dose ≤3.0 mSv and ≤1.9 mSv, respectively.

RESULTS

A total of 8121 articles were identified and after screening, 6 articles representing 309 patients were included in this scoping review. Of the articles reviewed, standard non-contrast CT radiation doses for pediatric urolithiasis evaluation ranged from 2.9 to 5.5 mSv and low-dose CT radiation dose was reported to be 1.0-2.72 mSv. Only 2 studies directly evaluated low-dose CT imaging compared to standard-dose CT imaging for pediatric urolithiasis assessment. Radiation reduction approaches did not negatively impact urolithiasis detection or characterization in 2 studies reviewed.

CONCLUSIONS

CT radiation doses for suspected or known pediatric urolithiasis are underreported and vary greatly with underutilization of low-dose/ultra-dose protocols for pediatric urolithiasis especially in comparison to the adult population. Results from this scoping review support that low-dose CTprotocols for pediatric stone disease are feasible to reduce radiation exposure.

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.

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.

Diagnostic accuracy of Doppler twinkling artifact for identifying urolithiasis: a systematic review and meta-analysis

OBJECTIVE

The goal of this study was to perform a comprehensive meta-analysis to assess the overall diagnostic value of Doppler twinkling for the diagnosis of urolithiasis.

METHODS

We systematically searched the PubMed, EMBASE, and Cochrane Library databases from inception through May 31, 2021. Studies including patients with urolithiasis who underwent color flow Doppler sampling to highlight the twinkling artifact and computed tomography were included. Diagnostic test meta-analysis was performed with a bivariate model. We used summary receiver operating characteristic curves to summarize the overall diagnostic performance. The weighted sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio were calculated.

RESULTS

Sixteen studies involving 4572 patients were included in the systematic review and meta-analysis. The weighted sensitivity was 0.86 (95% confidence interval [CI] 0.72-0.94), specificity 0.92 (95% CI 0.75-0.98), positive likelihood ratio 11.3, negative likelihood ratio 0.2, and diagnostic odds ratio 75.5.

CONCLUSION

The Doppler twinkling artifact has good diagnostic value for the diagnosis of urolithiasis and should be used as a complementary tool in the diagnosis of urolithiasis.

Identification of Clinically Insignificant Renal Calculi on Sonography

OBJECTIVE

To determine factors predicting if a radiologists... report of a .. stone... on ultrasound (US) was not actually a clinically significant stone, based on subsequent computed tomogram (CT). US often overestimates stone size and various pathologic entities are also hyperechoic;.ßthus, a subsequent CT without a clinically significant stone may represent unnecessary radiation exposure. A decision-tree and nomogram were developed to predict when stones are unlikely on subsequent CT.

METHODS

Retrospective analysis of patients, of any age, receiving CT within 24.ßhours of a sonographic report documenting a single renal stone, during 2019...2020, in any phase of care, at one institution. Novel stone-likelihood-systems for US and CT (US-SLS, CT-SLS) were devised and validated to classify stones as clinically significant or insignificant, with CT as the gold standard. Binomial logistic regression predicting clinically significant stones was performed with sonographic and patient characteristics.

RESULTS

Eight hundred twenty patients had US followed by CT, 228 (27.8%) reported documented stones, 140 (17.1%) reported a single stone. Clinically significant stones were associated with larger stone size (P: .002), location (P: .002), hydronephrosis (P: .04), shadowing-artifact (P: .02) depth.ßto.ßstone (P: .008), and Body mass Index (BMI) (P: .01). US-SLS had higher sensitivity (95.4%) and negative-predictive-value (81.8%) compared to a multivariate model of significant variables.

CONCLUSION

US-SLS appears to exclude clinically irrelevant .. stones... better than established criteria including twinkle or shadow in this retrospective analysis. A diagnostic algorithm and nomogram are presented. US-SLS and the associated decision tree can assist providers in avoiding unnecessary radiation when clinically significant stones are unlikely.

Imaging urolithiasis: complications and interventions in children

Urolithiasis affects people in all age groups, but over the last decades there has been an increasing incidence in children. Typical symptoms include abdominal or flank pain with haematuria; in acute cases dysuria, fever or vomiting also occur. Ultrasound is considered the modality of choice in paediatric urolithiasis because it can be used to identify most clinically relevant stones. Complementary imaging modalities such as conventional radiographs or non-contrast computed tomography should be limited to specific clinical situations. Management of kidney stones includes dietary, pharmacological and urological interventions, depending on stone size, location or type, and the child's condition. With a very high incidence of underlying metabolic abnormalities and significant recurrence rates in paediatric urolithiasis, thorough metabolic evaluation and follow-up examination studies are of utmost importance.

Pediatric Nephrolithiasis

The prevalence of pediatric nephrolithiasis has increased dramatically in the past two decades for reasons that have yet to be fully elucidated. Workup of pediatric kidney stones should include metabolic assessment to identify and address any risk factors predisposing patients to recurrent stone formation, and treatment should aim to facilitate stone clearance while minimizing complications, radiation and anesthetic exposure, and other risks. Treatment methods include observation and supportive therapy, medical expulsive therapy, and surgical intervention, with choice of treatment method determined by clinicians' assessments of stone size, location, anatomic factors, comorbidities, other risk factors, and preferences and goals of patients and their families. Much of the current research into nephrolithiasis is restricted to adult populations, and more data are needed to better understand many aspects of the epidemiology and treatment of pediatric kidney stones.

The effect of crystal composition and environment on the color Doppler ultrasound twinkling artifact

Objective.Pathological mineralizations form throughout the body and can be difficult to detect using conventional imaging methods. Color Doppler ultrasound twinkling highlights ∼60% of kidney stones with a rapid color shift and is theorized to arise from crevice microbubbles as twinkling disappears on kidney stones at elevated pressures and scratched acrylic balls in ethanol. Twinkling also sometimes appears on other pathological mineralizations; however, it is unclear whether the etiology of twinkling is the same as for kidney stones.Approach.In this study, five cholesterol, calcium phosphate, and uric acid crystals were grownin vitroand imaged in Doppler mode with a research ultrasound system and L7-4 transducer in water. To evaluate the influence of pressure on twinkling, the same crystals were imaged in a high-pressure chamber. Then, the effect of surface tension on twinkling was evaluated by imaging crystals in different concentrations of surfactant (1%, 2%, 3%, 4%) and ethanol (10%, 30%, 50%, 70%), artificial urine, bovine blood, and a tissue-mimicking phantom.Main results. Results showed that all crystals twinkled in water, with cholesterol twinkling significantly more than calcium phosphate and uric acid. When the ambient pressure was increased, twinkling disappeared for all tested crystals when pressures reached 7 MPa (absolute) and reappeared when returned to ambient pressure (0.1 MPa). Similarly, twinkling across all crystals decreased with surface tension when imaged in the surfactant and ethanol (statistically significant when surface tension <22 mN m^-1) and decreased in blood (surface tension = 52.7 mN m^-1) but was unaffected by artificial urine (similar surface tension to water). In the tissue-mimicking phantom, twinkling increased for cholesterol and calcium phosphate crystals with no change observed in uric acid crystals.Significance.Overall, these results support the theory that bubbles are present on crystals and cause twinkling, which could be leveraged to improve twinkling for the detection of other pathological mineralizations.

Diagnostic value ultrasound signs of stones less than or equal to 10 mm and clinico-radiological variants of ureteric colic

Objective

To determine the diagnostic value of ultrasound signs of urinary stones less than or equal to 10 mm and to determine clinico-radiological variants of ureteric colic.

Methods

A total of 455 ultrasound investigations were performed in patients referring to emergency department with urolithiasis and symptoms suspected of ureteric colic between January 2021 and May 2021. In addition to microscopic evaluation of urine sediment to detect different crystals and non-contrast spiral computed tomography to detect stones, B-mode and color Doppler sonography was performed to assess the presence of acoustic shadow (AS) and twinkle artifacts (TA) as possible signs of stone(s) in ureter.

Results

While the sensitivity and specificity of AS and TA were higher than 90% in patients with stones greater than 5 mm; positive prognostic values of these parameters were found to be extremely low for stones with sizes of 1-3 mm with specificity and sensitivity values not exceeding 53%. The sensitivity and specificity of AS and TA in the upper and lower ureters were higher for stones greater than or equal to 5 than for compared to those less than 5 mm. At the same time, the diagnostic values of TA and AS for middle ureter stones were very limited. The most prevalent clinico-radiological variants of ureteric colic were types I, III, and V being observed in 39%, 28% and 21% cases, respectively.

Conclusion

Our results demonstrate that TA and AS parameters seem to have a very low sensitivity and specificity in the diagnosis of urinary stones less than 5 mm. The diagnostic value of TA and AS increase significantly in stones greater than or equal to 5 mm. Therefore, clinicians need to be very careful for overestimating the diagnostic values of TA and AS for stones less than 5 mm and non-contrast spiral computed tomography must be the method of choice for patients presenting to emergency department with ureteric colic.

Real-Time Ultrasound Detection of Breast Microcalcifications Using Multifocus Twinkling Artifact Imaging

Detecting microcalcifications (MCs) in real time is important in the guidance of many breast biopsies. Due to its capability in visualizing biopsy needles without radiation hazards, ultrasound imaging is preferred over X-ray mammography, but it suffers from low sensitivity in detecting MCs. Here, we present a new nonionizing method based on real-time multifocus twinkling artifact (MF-TA) imaging for reliably detecting MCs. Our approach exploits time-varying TAs arising from acoustic random scattering on MCs with rough or irregular surfaces. To obtain the increased intensity of the TAs from MCs, in MF-TA, acoustic transmit parameters, such as the transmit frequency, the number of focuses and f-number, were optimized by investigating acoustical characteristics of MCs. A real-time MF-TA imaging sequence was developed and implemented on a programmable ultrasound research system, and it was controlled with a graphical user interface during real-time scanning. From an in-house 3D phantom and ex vivo breast specimen studies, the MF-TA method showed outstanding visibility and high-sensitivity detection for MCs regardless of their distribution or the background tissue. These results demonstrated that this nonionizing, noninvasive imaging technique has the potential to be one of effective image-guidance methods for breast biopsy procedures.

Twinkle artifact in renal ultrasound, is it a solid point for the diagnosis of renal stone in children?

Background: Twinkle artifact, also known as color Doppler comet-tail artifact, occurs behind very strong, granular, and irregular reflecting interfaces such as crystals, stones, or calcification. This is visualized as a random mixture of red and blue pixels in the high-frequency shift spectrum located deep to the interface. Study results have suggested that the sonographic twinkling artifact may aid in the detection of renal stones with a variety of reference standard imaging modalities, including abdominal radiography, excretory urography, gray-scale sonography, and CT. Material and methods: Our retrospective observational study included children who had undergone abdomen/renal ultrasound for kidneys stones in our radiology department between 2013 and 2019. Presence of the twinkle artifact, and stone numbers and sizes were documented. CT examinations done <3 months prior to or after US were retrospectively assessed to confirm the presence of kidney stones as a reference standard. Results: Thirty-three abdominal renal US scans of 33 patients (21 males, 12 females) fulfilled the entry criteria. The interval between the US and CT was <3 months for all patients. The median overall age of the patients was 4 years (IQR: 3.125, range: 1- 165 months), The median number of days between the US and CT was 13 (IQR: 26, range: 0-81 days). US detected 33 hyperechoic foci suspected to be stones; 26 were confirmed as true positive (i.e. showed the twinkle artifact and were seen in CT), 4 were false positive (showed the twinkle artifact but were not seen in CT), and 3 were false negative (did not show the twinkle artifact but were seen in CT). The overall median stone size was 2 mm in the right kidney, and 5 mm in the left kidney (IQR: 6,11 mm), respectively. Twinkle artifact sensitivity was found to be 89.7% (95% CI 39.574%-90%). The twinkle artifact was assessed in all true-positive stones, determining a relatively high PPV of 26/29 (86.7%) for the twinkle artifact. The twinkle artifact was not dependent on stone size. Specificity for the twinkle artifact could not be calculated due to a lack of true negatives. Conclusion: The twinkle artifact is a sensitive US tool for detecting pediatric kidney and ureter stones, but with a small risk of false positive findings.

Does twinkle artifact truly represent a kidney stone on renal ultrasound?

INTRODUCTION

Nephrolithiasis is detected on ultrasound by the presence of an echogenic focus, posterior acoustic shadowing and/or twinkle artifact (TA). TA has been shown to be highly predictive of nephrolithiasis in adults with renal colic and ureteral stones. We sought to evaluate if TA is reliable for diagnosing nephrolithiasis in the pediatric population.

METHODS

We reviewed renal ultrasound reports indicating presence or absence of TA associated with a single echogenic focus in the kidney or ureter. Exclusion criteria were age >18, multiple echogenic foci or medullary calcinosis, no follow-up, or TA located outside the kidney or ureter. Stone was confirmed either by CT within 3 months of color Doppler ultrasound, visualization on ureteroscopy, or patient report of passing the stone.

RESULTS

Five hundred and ninety-nine ultrasound reports were reviewed and 293 met inclusion criteria. Sixty-nine had diffuse twinkle without echogenic focus and 224 showed TA with single echogenic focus. 135 patients had confirmatory information available (Summary Table). Nephrolithiasis was diagnosed using TA and confirmed on confirmatory studies for 49 ultrasounds. The majority of confirmed stones were in the kidney (n = 40; 82%) and mean size of confirmed stones on ultrasound was 5 mm (range 1.5-10). Sensitivity, specificity, positive predictive value and negative predictive value of TA for detecting nephrolithiasis were 83%, 78%, 74% and 86% respectively.

CONCLUSIONS

Compared to the adult literature, TA in children has lower sensitivity, specificity and positive predictive value, but similar negative predictive value for diagnosing nephrolithiasis. This may be related to renal location and smaller stone size. The presence of TA should be weighed in the setting of other clinical and radiographic evidence of nephrolithiasis.

Evaluation of Stone Features That Cause the Color Doppler Ultrasound Twinkling Artifact

The color Doppler ultrasound twinkling artifact is a rapid color shift that appears on 43%-96% of kidney stones. Surface microbubbles on kidney stones are theorized to cause twinkling as exposure to elevated static pressures of 0.41-1.13 MPa (approximately 0.5-1 times diagnostic ultrasound pressure and 5-10 times ambient pressure) reduced twinkling. However, it is unclear what external and internal stone features support bubbles. Thirteen ex vivo kidney stones were scanned with color Doppler ultrasound at 2.5, 5 and 18.5 MHz. Select stones were imaged with environmental scanning electron microscopy or underwater micro-computed tomography to evaluate features that may cause twinkling. Results revealed that the lower frequencies produced larger volumes of twinkling. Condensation first occurred in the smallest (∼1 µm diameter) surface pores and may be indicative of where bubbles form. Gas pockets were seen inside two of three tested stones that may contribute to twinkling. Overall, these results provide evidence of cavity structures both externally and internally and their correlation to the twinkling artifact. This indicates that microbubbles may be present on and within kidney stones and may contribute to the twinkling artifact.

Value of the color Doppler imaging mode in improving physicians' diagnostic performance in patients with mid-ureteric stones larger than 5 mm: a retrospective study

The aim of this study was to retrospectively evaluate the value of the color Doppler flow imaging mode compared to the gray-scale mode for diagnosing mid-ureteric stones larger than 5 mm. We consecutively collected images from 79 patients possibly suffering from mid-ureteric stones under gray-scale and color Doppler flow imaging modes. Using computed tomography as the gold standard, all the included images were reviewed in a blinded manner for the confirmation of ureteral stones by 15 physicians divided into three groups according to their clinical experience level (resident, attending, and senior). During the evaluation process, the evaluation consistency was calculated and compared using Kendall's coefficient of concordance (Kendall's W). Moreover, diagnostic performance considering gray-scale and color imaging modes was compared. Especially for the diagnosis of mid-ureteric stones larger than 5 mm, the Kendall's W for the combined gray-scale and color Doppler flow imaging ultrasound scanning modes was greater than that for the gray-scale mode (P < 0.05). Additionally, significant improvements in the diagnostic sensitivity, negative predictive value, and accuracy were noted with color Doppler imaging (P < 0.05). Under isolated gray-scale mode, the resident group had reduced diagnostic sensitivity and negative predictive value and poorer accuracy compared with the attending and senior groups (P < 0.05). In contrast, no significant differences in the combined gray-scale and color Doppler flow imaging modes were noted among all groups (P > 0.05). In summary, the color Doppler flow imaging mode is useful for the diagnosis of mid-ureteric stones larger than 5 mm, especially in the resident group.

Pitfalls in Renal Ultrasound

Ultrasound (US) is replete with pitfalls in technique and interpretation, and renal imaging is no exception. Because US of the kidneys is a very common initial and follow-up imaging examination, it is important to be aware of both common and unusual sources of potential error. This essay will review optimal technique and discuss common overcalls, under calls, and misinterpretations with respect to renal size, hydronephrosis, calculi, cysts, masses, and collections.

Evidence of Microbubbles on Kidney Stones in Humans

The color Doppler ultrasound twinkling artifact has been found to improve detection of kidney stones with ultrasound; however, it appears on only ∼60% of stones. Evidence from ex vivo kidney stones suggests twinkling arises from microbubbles stabilized in crevices on the stone surface. Yet it is unknown whether these bubbles are present on stones in humans. Here, we used a research ultrasound system to quantify twinkling in humans with kidney stones in a hyperbaric chamber. Eight human patients with non-obstructive kidney stones previously observed to twinkle were exposed to a maximum pressure of 4 atmospheres absolute (ATA) while breathing air, except during the 10-min pause at 1.6 ATA and while the pressure decreased to 1 ATA, during which patients breathed oxygen to minimize the risk of decompression sickness. A paired one-way t-test was used to compare the mean twinkle power at each pressure pause with baseline twinkling, with p < 0.05 considered to indicate significance. Results revealed that exposure to 3 and 4 ATA of pressure significantly reduced twinkle power by averages of 35% and 39%, respectively, in 7 patients (p = 0.04); data from the eighth patient were excluded because of corruption. This study supports the theory that microbubbles are present on kidney stones in humans.

Detecting Kidney Stones Using Twinkling Artifacts: Survey of Kidney Stones with Varying Composition and Size

In recent years, work has been done to understand the mechanisms of Doppler ultrasound twinkling artifacts (TAs) and why they appear over kidney stones. In the work described here, twinkling artifacts were evaluated as a possible method of locating and characterizing kidney stones. Doppler ultrasound scanning was used to evaluate 47 stones of different types and sizes in the range 1.31-55.76 mm² in cross-sectional area (average = 9.65 mm²). An isolated stone study was used to understand the behavior of the TAs. An ex vivo kidney study was conducted to determine if the renal tissue impeded localization of the TAs to the stones. An ex vivo study of randomly placed stones was used to evaluate the robustness of the method for detecting stones that were placed by an independent party. The TAs were found to be qualitatively consistent in appearance across stone types, sizes and scanning parameters in the isolated stone study. Quantitative assessment of TA amplitude for isolated stones was also found to be consistent for each class of stones across multiple days. The TAs were also found to be isolated to the stone when placed in an ex vivo kidney. The study of randomly placed stones revealed that this method could find all 47 stones used in a clinical situation with only two false positives. A few limitations to this method were noted involving accurate sizing of stones and the specificity of characterizing the stones. Further work will be done to overcome limitations by improving the Doppler acquisition and processing code, as well as by evaluating the use of TAs in human studies.

Systematic radiologic detection of kidney stones in Canadian children: a new era of asymptomatic stones?

INTRODUCTION

Asymptomatic, or incidental, pediatric kidney stones detected on abdominal imaging pose a clinical challenge as their significance and expected outcome are not well described.

OBJECTIVE

Our primary objective was to estimate the incidence of nephrolithiasis in pediatric patients undergoing abdominal ultrasound (US) or computerized tomography (CT), for all indications, in a pediatric tertiary care hospital. Our secondary objective was to determine the clinical outcome of these radiographically detected stones.

METHODS

All abdominal US or CT radiology reports for patients younger than 18 years between January 1, 2011, and December 31, 2016, were retrieved. Reports were automatically flagged using textual analysis if they contained one of the 32 keywords potentially indicating nephrolithiasis. Flagged reports, as well as 10% of unflagged reports, were reviewed to confirm the radiologist impression of presence or absence of stones. Patient and stone-related clinical data were extracted.

RESULTS

Two thousand four hundred forty-nine (5%) of 53 235 imaging reports cited at least one of the keywords. Manual review of flagged reports identified 498 studies having a radiologist impression of stones (244 unique patients). Stone incidence in children undergoing abdominal imaging more than doubled between 2011 and 2016. Medical record review found that 140 patients (57%) were symptomatic, while the other 104 patients (43%) were asymptomatic. Spontaneous resolution was greater (57% vs 34%) in asymptomatic patients compared to symptomatic patients. Asymptomatic patients were younger with a median age of 0.6 compared to 12.3 years. Asymptomatic and symptomatic stones were followed up for similar lengths of time (2.3 vs 2.0 years, p > 0.05) and had a similar number of follow-up USs (3.9 vs 4.6 studies, p > 0.05).

CONCLUSIONS

The incidence of radiologically identified stones in children undergoing abdominal imaging at our center increased over time. Asymptomatic stones follow a benign course with minimal need for intervention; however, they were detected almost as frequently as symptomatic stones. Asymptomatic stones may represent increased healthcare resource utilization due to similar follow-up compared to symptomatic stones. Further research regarding the optimal imaging intervals and long-term follow-up for asymptomatic stones is warranted.

Diagnostic Accuracy of Doppler Twinkling Artifact for Identifying Urinary Tract Calculi

Introduction

Flank pain is a frequent cause of emergency department visits and is often due to renal or ureteric colic. Ultrasound is often the initial imaging study used for the detection of urinary tract calculi. Twinkling artifact is a Doppler artifact usually seen on echogenic rough surfaces such as calculi. Its presence can improve the sensitivity and specificity of ultrasound in stone detection. The objective of the current study was to determine the diagnostic accuracy of the Doppler twinkling artifact for detecting urinary calculi using non-contrast computed tomography as the gold standard.

Materials and methods

In this cross-sectional study, both male and female patients of any age having flank pain, burning micturition with or without hematuria were included. Ultrasound was performed and the presence or absence of Doppler twinkling artifact on calculus was noted. Following ultrasound, patients underwent plain CT scan and findings of stones were documented. Sensitivity, specificity, positive and negative predictive values, and diagnostic accuracy of Doppler twinkling artifact was calculated considering CT findings as the gold standard.

Results

Out of the total 221 patients, 146 (66.1%) were males and 75 (33.9%) were females. The mean age of the patients was 45.98 ± 16.30 years. Urinary tract calculi on ultrasound were observed in 74 (33.50%) patients, while on CT urinary tract calculi were observed in 127 (57.50%) patients. Diagnostic accuracy of Doppler twinkling artifact was found to be 71.49% with sensitivity, specificity, positive predictive value, and negative predictive value of 54.33%, 94.68%, 93.24%, and 60.54%, respectively.

Conclusion

Doppler twinkling artifact has low sensitivity, high specificity, and suboptimal diagnostic accuracy for the diagnosis of urinary tract calculi. Integration of this artifact has a lower sensitivity as compared to non-contrast CT scan. Multicentric studies with larger sample size and focusing on interobserver and intraobserver variability are recommended to have a consensus regarding Doppler twinkling artifact in the evaluation of renal and ureteric calculi.

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.

Acoustic shadowing in pediatric kidney stone ultrasound: a retrospective study with non-enhanced computed tomography as reference standard

BACKGROUND

The usefulness of acoustic shadowing as a feature of pediatric kidney stone ultrasound (US) may be underestimated.

OBJECTIVE

The hypothesis was that the majority of stones in children have acoustic shadowing and that its specificity is high (>90%) in pediatric kidney stones.

MATERIALS AND METHODS

Our retrospective observational study included children who had undergone abdominal non-enhanced computed tomography (CT) for kidney stones in a pediatric renal stone referral centre between 2015 and 2016. US examinations prior to CT were retrospectively assessed for US features such as acoustic shadowing, twinkle artifact and stone size. These features were compared to CT as reference standard.

RESULTS

Thirty-one patients (median age: 13 years, range: 1-17 years) with 77 suspected kidney stones were included. The median stone size was 5 mm (interquartile range [IQR]: 5 mm). For acoustic shadowing, sensitivity was 70% (95% confidence interval [CI] 56-80%) and specificity was 100% (95% CI 56-100%). All kidney stones with a diameter ≥9 mm demonstrated shadowing. Sensitivity for twinkle artifact was 88% (95% CI 72-96%), but specificity for twinkle artifact could not be calculated due to the lack of true negatives. All false-positive stones on US demonstrated twinkle artifact, but none showed shadowing.

CONCLUSION

Acoustic shadowing was demonstrated in the majority of pediatric kidney stones. Specificity was high, but this was not significant. Twinkle artifact is a sensitive US tool for detecting (pediatric) kidney calculi, but with a risk of false-positive findings.

ACR Appropriateness Criteria® Hematuria-Child

Hematuria is the presence of red blood cells in the urine, either visible to the eye (macroscopic hematuria) or as viewed under the microscope (microscopic hematuria). The clinical evaluation of children and adolescents with any form of hematuria begins with a meticulous history and thorough evaluation of the urine. The need for imaging evaluation depends on the clinical scenario in which hematuria presents, including the suspected etiology. Ultrasound and CT are the most common imaging methods used to assess hematuria in children, although other imaging modalities may be appropriate in certain instances. This review focuses on the following clinical variations of childhood hematuria: isolated hematuria (nonpainful, nontraumatic, and microscopic versus macroscopic), painful hematuria (ie, suspected nephrolithiasis or urolithiasis), and renal trauma with hematuria (microscopic versus macroscopic). 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 include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Relation of Color Doppler Twinkling Artifact and Scale or Pulse Repetition Frequency

OBJECTIVE

The aim of this study is to determine the effect of scale/pulse repetition frequency (PRF) on the appearance of color Doppler twinkling artifact.

MATERIALS AND METHODS

We commenced this cross-sectional study for 20 months from November 2014 to July 2016. During routine ultrasound examination, we observed multiple case of twinkling artifact produced by renal stones, calcifications in the thyroid nodules, bony fragments and intestinal gases, etc., We observed twinkling artifact with low- and high-PRF settings in 500 different structures. A total of 500 other structures were included wherein there was no Doppler twinkling artifact produced by them, with usual optimum PRF settings. These structures were also evaluated with low- and high-PRF to determine the effect of PRF on twinkling artifact effectively. All the patients were examined according to the AIUM guideline for appropriate examination protocol. Data were collected from the observation of twinkling artifact with low- and high-PRF/scale and evaluated with the help of IBM SPSS 24 package, the results were summarized as follow.

RESULTS

Change in scale/PRF could not affect the twinkling artifact. The twinkling artifact observed with low-PRF was the same as seen with high-PRF. There was a significant agreement between low- and high-PRF in the production of color twinkling artifact. The kappa value of agreement was estimated as 0.96, whereas the Pearson's correlation was significant with the value of 0.001. Same twinkling artifact was created with low- and high-PRF, with no significant variation.

CONCLUSION

Twinkling artifact is independent of PRF/Scale.

An investigation into the clinical accuracy of twinkling artifacts in patients with urolithiasis smaller than 5 mm in comparison with computed tomography scanning

Background

Ultrasound (US) is a non-invasive method used for the diagnosis of urolithiasis. If the size of the stone is <5 mm, it may be difficult to diagnose. This study aimed to compare the accuracy of twinkling artifact (TA) of color Doppler US imaging with unenhanced computed tomography (CT) for detecting urolithiasis <5 mm.

Materials and Methods

This prospective study was conducted on 100 patients with suspected renal calculus presented to the emergency room at the Imam Khomeini Hospital of Ahwaz in 2018. The US findings such as posterior acoustic shadowing and TA were examined for their ability to detect urinary stones (greatest diameter ≤5 mm) using CT findings as the gold standard.

Results

The mean size of renal stone was 3.43 ± 0.80 mm in CT and 3.49 ± 0.82 mm in color Doppler US. There was no significant difference between CT and color Doppler US report in quantification of urolithiasis sizes (P = 0.603). TA on color Doppler US was detected in 94 (94%) patients while posterior acoustic shadow was detected in 83 (83%) patients (P = 0.004). A significant difference was found between the TA and size of stones (P = 0.036). The sensitivity, accuracy, and positive predictive values of TA for the detection of calculus were 94%, 94%, and 100%, respectively.

Conclusion

The results demonstrated that TA on color Doppler US could be a good and safe alternative imaging modality with comparable results with non-contrast-enhanced computed tomography for the sensitive detection of urolithiasis <5 mm.

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.

Comparison of ultrasound versus computed tomography for the detection of kidney stones in the pediatric population: a clinical effectiveness study

BACKGROUND

The incidence of pediatric nephrolithiasis in the United States is increasing. There is a paucity of literature comparing the diagnostic performance of computed ultrasound (US) to tomography (CT) in the pediatric population.

OBJECTIVE

To determine the diagnostic performance of renal US for nephrolithiasis in children using a clinical effectiveness approach.

MATERIALS AND METHODS

Institutional review board approval with a waiver of informed consent was obtained for this retrospective, HIPAA-complaint investigation. Billing records and imaging reports were used to identify children (≤18 years old) evaluated for nephrolithiasis by both US and unenhanced CT within 24 h between March 2012 and March 2017. Imaging reports were reviewed for presence, number, size and location of kidney stones. Diagnostic performance of US (reference standard=CT) was calculated per renal unit (left/right kidney) and per renal sector (four sectors per kidney). For sector analysis, US was considered truly positive if a stone was identified at CT in the same or an adjacent sector.

RESULTS

There were 68 renal stones identified by CT in 30/69 patients (43%). Mean patient age was 14.7±3.6 years, and 35 were boys. For detecting nephrolithiasis in any kidney, US was 66.7% (48.8-80.8%) sensitive and 97.4% (86.8-99.9%) specific (positive predictive value=95.2% [77.3-99.8%], negative predictive value=79.2% [65.7-88.3%], positive likelihood ratio=26.0). Per renal sector, US was 59.7% (46.7-71.4%) sensitive and 97.4% (95.5-98.5%) specific (positive predictive value=72.3% [58.2-83.1%], negative predictive value=95.4% [93.2-96.9%], positive likelihood ratio=22.5). Of the 30 stones not detected by US, only 3 were >3 mm at CT.

CONCLUSION

In clinical practice, US has high specificity for detecting nephrolithiasis in children but only moderate sensitivity and false negatives are common.

The usefulness of agent emission imaging - high mechanical index ultrasound mode in the diagnosis of urolithiasis: a prospective preliminary study

PURPOSE

We aimed to determine the feasibility and effectiveness of agent emission imaging - high mechanical index (AEI-High MI) mode ultrasonography (US) compared with gray-scale and color Doppler US, alone or in combination, for the diagnosis of urolithiasis with reference to unenhanced computed tomography (CT).

METHODS

This prospective study included 72 consecutive patients (40 males, 32 females; mean age, 45.9±14.7 years) referred by the department of urology for acute or elective symptoms of urolithiasis and confirmed to have urinary calculi on unenhanced abdominal CT, between January 2015 and June 2015. Gray-scale, color Doppler, and AEI-High MI US were performed by two radiologists to determine the effectiveness of these methods in the diagnosis of urinary stones and to compare them with the reference modality.

RESULTS

A total of 189 calculi were detected on CT examination. Gray-scale US had a sensitivity of 66.1% and positive predictive value (PPV) of 88.7% for detecting calculi, while twinkling artifact of color Doppler had a sensitivity of 70.4% and PPV of 94.3%. The scintillation artifact of AEI-High MI mode had a sensitivity of 75.1% and PPV of 95.9%. When all ultrasound-based modalities were combined, the sensitivity and PPV rose to 83.1% and 88.2%, respectively. When calculi were grouped according to their size ( < 5 mm, 5-10 mm, > 10 mm), AEI-High MI mode had a higher sensitivity (60%) compared with gray-scale (32.5%) and color Doppler (41.3%) for calculi < 5 mm.

CONCLUSION

AEI-High MI mode had a higher sensitivity compared with gray-scale and color Doppler for the detection of calculi smaller than 5 mm, but it did not make a significant contribution to detection of larger calculi. The combined use of gray-scale US with AEI-High MI mode could increase the detection rate of calculi smaller than 5 mm and provide a method for verification of suspected calculi on gray-scale US.

The role of trapped bubbles in kidney stone detection with the color Doppler ultrasound twinkling artifact

The color Doppler ultrasound twinkling artifact, which highlights kidney stones with rapidly changing color, has the potential to improve stone detection; however, its inconsistent appearance has limited its clinical utility. Recently, it was proposed stable crevice bubbles on the kidney stone surface cause twinkling; however, the hypothesis is not fully accepted because the bubbles have not been directly observed. In this paper, the micron or submicron-sized bubbles predicted by the crevice bubble hypothesis are enlarged in kidney stones of five primary compositions by exposure to acoustic rarefaction pulses or hypobaric static pressures in order to simultaneously capture their appearance by high-speed photography and ultrasound imaging. On filming stones that twinkle, consecutive rarefaction pulses from a lithotripter caused some bubbles to reproducibly grow from specific locations on the stone surface, suggesting the presence of pre-existing crevice bubbles. Hyperbaric and hypobaric static pressures were found to modify the twinkling artifact; however, the simple expectation that hyperbaric exposures reduce and hypobaric pressures increase twinkling by shrinking and enlarging bubbles, respectively, largely held for rough-surfaced stones but was inadequate for smoother stones. Twinkling was found to increase or decrease in response to elevated static pressure on smooth stones, perhaps because of the compression of internal voids. These results support the crevice bubble hypothesis of twinkling and suggest the kidney stone crevices that give rise to the twinkling phenomenon may be internal as well as external.

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.

Sonographic twinkle artefact in renal calculus detection: Impact of scanning factors in a phantom model

Introduction

A common clinical use of the twinkle artefact is to detect and confirm renal calcification on ultrasound. There is however variable demonstration of this artefact using newer generation ultrasound machines. The purpose of this study was to assess the impact of altering multiple scanning factors on ultrasound machines from four major manufacturers on the demonstration of the twinkle artefact. Two custom-made phantoms and five-point Likert-like Scale were utilised.

Methods

These phantoms contained a range of urinary calculi varying in size, composition, surface contour and depth. The calculi were serially imaged with each ultrasound machine, using manufacturers presets and varying just one imaging factor or parameter at a time. The documented twinkle artefact in the images were subsequently analysed, together with the imaging preset and factor changes that had been made.

Results

Those factors that had the greatest effect in order of impact were colour write priority, colour gain, transducer type, depth of calculus, acoustic power and size of calculus. Variability was also demonstrated between manufacturers.

Conclusion

By isolating the effect of scanning factor changes, their importance and contribution to appearances in the ultrasound image can be assessed. Image interpretation in the clinical setting requires an understanding of the underlying physics, particularly in the evaluation of artefacts associated with renal calculi.

Imaging in the diagnosis of pediatric urolithiasis

Pediatric urolithiasis is an important and increasingly prevalent cause of pediatric morbidity and hospital admission. Ultrasound (US) is the recommended primary imaging modality for suspected urolithiasis in children. There is, however, widespread use of CT as a first-line study for abdominal pain in many institutions involved in pediatric care. The objective of this review is to outline state-of-the-art imaging modalities and methods for diagnosing urolithiasis in children. The pediatric radiologist plays a key role in ensuring that the appropriate imaging modality is performed in the setting of suspected pediatric urolithiasis. Our proposed imaging algorithm starts with US, and describes the optimal technique and indications for the use of CT. We emphasize the importance of improved communication with a greater collaborative approach between pediatric and general radiology departments so children undergo the appropriate imaging evaluation.

Some Work on the Diagnosis and Management of Kidney Stones with Ultrasound

Ultrasound is currently the only noninvasive technology able to completely diagnose and manage kidney stones.