Application value of biplane ultrasound combined with multimodal ultrasound elastography and ultra-micro angiography in stress urinary incontinence: a prospective clinical study

Introduction

Female urinary incontinence constitutes a common urological disorder in women and is conventionally subdivided into the stress urinary incontinence (SUI), urge urinary incontinence, and mixed urinary incontinence subtypes, among which SUI accounts for the largest proportion (1,2). SUI is defined as the involuntary leakage of urine during increases in abdominal pressure, such as during coughing or laughing, and common symptoms include urinary frequency, leakage, and dysuria (3-5). The urethra, serving as the conduit between the bladder and the external environment, plays a pivotal role in preventing urinary incontinence and pelvic organ prolapse through its mucosal closure function, which is supported by anatomical structures such as the bladder neck, urethral sphincter, and pelvic floor support system (6,7). Various diagnostic methods for SUI, including the finger pressure test, urodynamics, cystourethrography, and pelvic-floor ultrasound, each offer distinct advantages and collectively form a comprehensive diagnostic framework for SUI. However, traditional diagnostic methods exhibit limitations in the early diagnosis of SUI and in the assessment of subtle pathological changes.

In recent years, ultrasound elastography has garnered greater prominence in clinical applications by virtue of its noninvasiveness, convenience, repeatability, and safety. This technology, which comprises strain elastography, shear wave elastography (SWE), and viscoelastic elastography (VE), has been extensively applied in the examination of organs such as the breast and liver (8,9). However, its application in SUI remains in the exploratory stage. Among these modalities, SWE quantitatively assesses the biomechanical properties of tissues through the measurement of changes in tissue stiffness, providing insights critical to the early diagnosis of urinary incontinence. VE effectively evaluates tissue viscosity; however, there are no reports on its application for SUI. Additionally, ultra-micro angiography (UMA), which quantitatively analyzes blood flow parameters to detect subtle changes in tissue perfusion (10,11), has demonstrated preliminary success in studies of hypertensive disorders of pregnancy. However, its application in SUI remains to be fully investigated (12,13). Conventional transvaginal ultrasonography (TVUS) and transperineal ultrasonography (TPUS) remain the most widely validated tools for evaluating the urethral sphincter complex. Their real-time capability, broad availability, and well-established normative databases continue to underpin current diagnostic algorithms for female urinary incontinence. These techniques, however, rely on a standardized Valsalva maneuver to elicit anatomical changes such as bladder-neck retroversion and urethral rotation; when pain, cognitive impairment, or poor coordination prevent an effective strain, the resulting insufficient rise in intra-abdominal pressure can mask underlying pathology and generate false-negative results. Moreover, for a subset of patients with “occult SUI”, TVUS/TPUS parameters under resting or routine stress conditions remain within normal limits, whereas urodynamic studies indicate reduced urethral closure pressure, placing these patients at high risk of being overlooked. Equally important, in the earliest stages of the disease, submicroscopic and biomechanical alterations (e.g., diminished rhabdomyocyte density and reduced elastic modulus) precede any macroscopic displacement, rendering these changes invisible to conventional imaging. Transvaginal biplane ultrasound (TV-BPUS) overcomes these limitations through a technical leap that involves the acquisition of high-resolution sagittal and transverse volumes from a single transducer position, eliminating the repositioning artifacts and registration errors inherent to sequential scanning. When augmented by multimodal elastography and UMA, TV-BPUS does not require the Valsalva maneuver to quantify sphincter thickness, elastic stiffness, or microvascular perfusion and can thus effectively capture subclinical alterations. This capability facilitates the prediction of incipient SUI and provides objective imaging evidence for occult cases (14). Although large-scale prospective trials are still required to establish the long-term outcome benefits, this modality already functions as a rigorous adjunct to traditional pelvic-floor imaging whenever fine anatomical detail is required to guide clinical decision-making.

This study aimed to investigate the application of TV-BPUS combined with multimodal ultrasound elastography and UMA techniques in assessing the female urethra. Moreover, we evaluated the role of multiparametric elastography indices and UMA in examining female SUI in order to generate novel imaging evidence for the early diagnosis, treatment, and prognostic assessment of SUI. We present this article in accordance with the STARD reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1147/rc).

Methods

Data source

This prospective study included 52 controls and 50 patients diagnosed with SUI by gynecological pelvic-floor physicians and confirmed by pelvic-floor ultrasound. This study was conducted at The First Affiliated Hospital of Guangzhou Medical University from August 1, 2024, to December 31, 2024. The inclusion criteria for the control group were as follows: (I) good health and no significant abnormalities detected upon examination; (II) normal mental and cognitive function; and (III) written informed consent from the participants and their families, with approval of the hospital’s ethics committee. The inclusion criteria for the SUI group were as follows: (I) meeting the diagnostic criteria for SUI outlined by the 2017 guidelines for the diagnosis and treatment of female SUI (15); (II) confirmed diagnosis of urinary incontinence via clinical assessment and pelvic-floor ultrasound; (III) normal mental and cognitive function; and (IV) written informed consent from the patients and their families, with approval from the hospital’s ethics committee.

This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, the revised edition of the Good Clinical Practice Guidelines of the National Medical Products Administration NMPA (order No. 57-2020), and the Good Clinical Practice guideline of the International Council for Harmonisation (ICH-GCP E6[R2]). This study was reviewed and approved by the Ethics Committee of The First Affiliated Hospital of Guangzhou Medical University (ethics reference No. ES-2025-K020-01). All participants received detailed written and oral information about the study aims, procedures, potential risks and benefits before enrollment. Written informed consent was obtained from each participant prior to any study-related examination.

Pelvic-floor ultrasonography

A physician with ≥5 years of experience in pelvic-floor ultrasound performed all scans using a conventional endovaginal probe (2–10 MHz). After bladder emptying and the provision of written informed consent, the participant was placed in the lithotomy position; the probe was gently applied to the perineum (translabial approach) to visualize the symphysis pubis, bladder neck, and urethra simultaneously. Midsagittal images were acquired at rest and during maximum Valsalva (sustained ≥6 s) and frozen immediately after image stabilization. Off-line measurements included the following: (I) bladder-neck descent (BND), defined as the vertical distance from the inferior border of the symphysis to the bladder neck between rest and Valsalva; (II) the urethral rotation angle (URA), defined as the change in urethral axis from rest to Valsalva; (III) the posterior urethro-vesical angle (PUA); and (IV) the proximal urethral funneling (internal diameter ≥2 mm). Each parameter was measured three times and averaged to reduce random error and ensure accuracy. The diagnostic cutoffs were BND ≥25 mm, URA ≥45°, and PUA ≥140° or the presence of proximal urethral funneling.

Ultrasound elastography examination

Examinations were performed by a physician with over 5 years of experience in pelvic-floor ultrasound using the Nuewa A20 color Doppler ultrasound diagnostic instrument equipped with a 4- to 13-MHz biplane ultrasound transducer (model ELC13-4U, Mindray, Shenzhen, China). Patients were instructed to empty their bladders before the examination. Written informed consent was obtained after thorough communication with the participants. Patients were positioned in the lithotomy position. The examiner used the biplane transducer to measure the internal urethral orifice and mid-urethra during rest. The transducer was held steady for 3–5 seconds at critical positions to stabilize the image. The Q-BOX (sampling frame) was set to 1 cm in diameter to cover parts of the internal urethral orifice and mid-urethra. Elasticity imaging was activated once image stability was confirmed. The system automatically calculated the parameters, including the Young modulus maximum E value (Emax) and mean E value (Emean) and viscosity coefficients, consisting of maximum viscosity (Vimax) and mean viscosity (Vimean). Each parameter was measured independently three times, and the arithmetic mean was calculated and recorded; multiple measurements were used to counter random error and improve data reliability and precision. Biplane ultrasound images collected from patients with urinary incontinence and healthy female controls are shown in Figures 1,2.

Figure 1 SWE and viscoelastography of patients with SUI. (A) Two-dimensional ultrasound comparison obtained with a biplane probe in patients with SUI. (B) SWE obtained with a biplane probe in patients with SUI. The red color indicates stiff tissue, and the blue color indicates soft tissue; the green, yellow, and orange colors indicate intermediate stiffness and possible benign changes. (C) Viscoelastic elastogram. (D) Strain elastogram. BL, bladder; SUI, stress urinary incontinence; SWE, shear wave elastography; U, urethra.

Figure 2 SWE and viscoelastography of the control group. (A) Two-dimensional ultrasound reference scan acquired with a biplane probe in asymptomatic women. (B) Urethral SWE obtained with a biplane probe in healthy women; the proportion of red-coded (stiff) pixels in the mid-urethra is significantly greater than that observed in patients with SUI. (C) Viscoelastic elastogram. (D) Strain elastogram. BL, bladder; SUI, stress urinary incontinence; SWE, shear wave elastography; U, urethra.

UMA examination

UMA was performed on the internal urethral orifice and mid-urethra of the enrolled patients with the same equipment as that used for ultrasound elastography. Patients were instructed to maintain steady breathing and adjust to a suitable position to ensure the accuracy and stability of the ultrasound examination. Once the urethral anatomical structure was clearly visualized, the system was switched to UMA mode, and imaging parameters were optimized. Measurements were taken of the internal urethral orifice and mid-urethra during rest, with the probe held steady for 3–5 seconds at critical positions to stabilize the image. If the blood flow signal was poor or artifacts or color distortion appeared within the region of interest (ROI), the probe position, imaging parameters, or examination conditions were promptly adjusted. Whenever the blood-flow signal within the ROI was weak, artifact-laden, or color-distorted, the probe position, imaging presets, or examination conditions were immediately adjusted to optimize visualization. Off-line quantitative microvascular analysis was then performed according to the following standardized parameters. The parameters are grouped into two broad categories (with distinct subindices embedded within each category): perfusion metrics that reflect microvascular abundance and intensity and morphological metrics that characterize the distribution, course, and complexity of the microvasculature. The system was then switched to HoloUMA mode to determine hemodynamic parameters, including peak systolic velocity (PSV), resistance index (RI), and systolic-to-diastolic ratio (S/D). The specific parameters are detailed in Table 1. Each parameter was measured independently three times, and the arithmetic mean was calculated and recorded; multiple measurements were used to counter random error and improve data reliability and precision (Figure 3).

Figure 3 Figure 3 UMA images of patients with SUI and healthy women. UMA from (A) a healthy woman and (C) a patient with SUI (the perfusion is appreciably richer in the patient with SUI). HoloUMA from (B) a healthy woman and (D) a patient with SUI (the perfusion is appreciably richer in the patient with SUI). ED, End-Diastolic Velocity; PS, peak systolic velocity; RI, resistance index; S/D, systolic-to-diastolic ratio; SUI, stress urinary incontinence; UMA, ultra-micro angiography.

Outcome measures

The efficacy of ultrasound elastography combined with UMA for diagnosing urinary incontinence was evaluated according to sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV), with the gold standard being the combined diagnosis of urogynecologists and pelvic floor ultrasound findings. The formulae for these metrics were as follows: sensitivity = (number of true positives)/(number of true positives + number of false negatives) × 100%; specificity = (number of true negatives)/(number of false positives + number of true negatives) × 100%; accuracy = (number of true positives + number of true negatives)/(total patients) × 100%; PPV = (number of true positives)/(number of true positives + number of false positives) × 100%; NPV = (number of true negatives)/(number of true negatives + number of false negatives) × 100%.

Statistical analysis

In this study, continuous variables with a normal distribution are expressed as the mean ± standard deviation. Group comparisons were conducted with the independent-samples t-test, and associations were evaluated via Pearson correlation. Continuous variables deviating from normality are reported as the median and interquartile range (IQR); inter-group differences were assessed via the Mann-Whitney U test, and correlations were determined via Spearman’s rank correlation. Categorical variables are summarized as frequencies and percentages, and comparisons were performed with the chi-squared test. All analyses were executed in R software version 4.3.3 (IBM Corp., Armonk, NY, USA). Two-sided P values <0.05 were considered statistically significant.

Results

Participant inclusion

Initially, 121 individuals were screened against the predefined inclusion criteria, and 19 were subsequently excluded for the following reasons: (I) declined participation (n=8); (II) age <18 years (n=1); (III) pregnancy (n=5); and (IV) concurrent use of an intrauterine device (n=5). Consequently, 102 participants who fulfilled all the requirements were enrolled. In this prospective, single-center study, all participants provided written informed consent to undergo ultrasound elastography and ultra-micro flow imaging. Based on clinical diagnosis and pelvic-floor ultrasound findings, participants were assigned to the SUI group (n=50) or the normal control group (n=52); all completed the imaging protocol and were included in the final analysis (Figure 4).

Figure 4 Flowchart of participant inclusion. IUD, intrauterine device; SUI, stress urinary incontinence.

General data

Statistical analysis of the aforementioned baseline characteristics revealed statistically significant intergroup differences in age and body mass index (BMI) between controls and patients with SUI (P<0.05). The SUI cohort comprised 50 patients whose median age was 35.50 years (IQR, 30.25–44.00 years) and whose median BMI was 22.80 kg/m² (IQR, 22.03–24.11 kg/m²), whereas the control cohort included 52 participants with a median age of 31.00 years (IQR, 27.00–36.00 years) and a median BMI of 21.51 kg/m² (IQR, 19.93–23.73 kg/m²).

Comparison of ultrasound elastography data

The SUI group and the control group differed significantly in terms of the Emax, Emean, Vimax, and Vimean of the urethral internal orifice (P<0.05, Table 2), as well as the Emax and Emean of the mid-urethra (P<0.05, Table 2).

Comparison of UMA data

The SUI group and the control group differed significantly in terms of vascular density (VD), full wall vessel density (FWVD), flow-perfusion index (FPI), number of branch points per unit area (NBPPA), number of branches per area (NBPA), PSV, RI, and S/D of the urethral internal orifice, as well as the RI and S/D of the mid-urethra (all P values <0.05, Table 3).

Diagnostic value of parameters and correlation analysis of diagnostic indicators

To identify imaging variables with the highest discriminative value, we subjected age, BMI, and 30 ultrasonographic parameters to least absolute shrinkage and selection operator (LASSO) regression. By progressively increasing the penalty weight λ, coefficients of minimally informative variables were driven to zero, yielding a parsimonious set of predictors linked to urinary incontinence. The optimal λ was selected through 10-fold cross-validation under the one-standard-error rule. Consequently, nine candidate diagnostic indices were retained: age; BMI; the VD, FPI, NBPPA, and RI of the urethral orifice; the S/D of the mid-urethra; and the Emean of both the internal and mid-urethra (Figure 5).

Figure 5 LASSO regression analysis for identifying diagnostic indicators of stress urinary incontinence. (A) Trajectories of coefficients for elastography and microvascular indicators. (B) Ten-fold cross-validation mean-squared error with optimal lambda selection. LASSO, least absolute shrinkage and selection operator.

We first incorporated all nine indicators into a multivariable logistic regression model to examine their overall association with SUI. To isolate the genuine effect of urethral elastography from the known confounding influence of age and BMI, we subsequently fitted a covariate-adjusted model that retained the seven optimal elastographic features together with age and BMI. After adjustment, three elastographic indices—RI of the internal urethral orifice, Emax of the internal urethral orifice; and Emax of the mid-urethra—remained independently associated with SUI, confirming their validity as stand-alone imaging biomarkers (Table 4).

The final combined diagnostic model for this study was established (Table 5). For each of the nine selected variables, box-and-whisker plots were generated. Apart from age and BMI, the parameters displayed markedly lower medians and narrower IQRs in patients with SUI than in controls, whose distributions were displaced upward, with several indicators attaining values of 10. These consistent disparities indicate that the variables possess potential as imaging or physiological biomarkers for discriminating SUI, thereby providing an empirical basis for constructing a diagnostic model (Figures 6-8). The results of the receiver operating characteristic curve analysis for the logistic regression model are depicted in Figure 9.

Figure 6 Boxplot of age, BMI, and VD at the urethral internal orifice. BMI, body mass index; SUI, stress urinary incontinence; VD, vascular density.

Figure 7 Boxplot of FPI, NBPPA, and RI at the mid-urethra. FPI, flow-perfusion index; NBPA, number of branches per area; RI, resistance index; SUI, stress urinary incontinence.

Figure 8 Boxplot of the S/D at the mid-urethra and the Emax at the urethral internal orifice and mid-urethra. Emax, maximum E value; S/D, systolic-to-diastolic ratio; SUI, stress urinary incontinence.

Figure 9 ROC curves. AUC, area under the curve; Emax, maximum E value; FPI, flow-perfusion index; NBPA, number of branches per area; RI, resistance index; ROC, receiver operating characteristic; S/D, systolic-to-diastolic ratio; VD, vascular density.

A nomogram integrating the nine selected indicators was developed to estimate the individual probability of SUI in women (Figure 10). In this nomogram, each predictor is assigned a point value proportional to its weighted contribution; these points are summed on the “Total Points” scale, and a vertical line dropped from this sum to the probability axis yields the predicted risk. The calibration curve (Figure 11) demonstrated close agreement between predicted and observed probabilities, indicating satisfactory calibration and predictive accuracy of the model.

Figure 10 Nomogram of the diagnostic model. BMI, body mass index; Emax, maximum E value; FPI, flow-perfusion index; NBPA, number of branch points per unit area; RI, resistance index; S/D, systolic-to-diastolic ratio; VD, vascular density.

Figure 11 Calibration curve of the diagnostic model. SUI, stress urinary incontinence.

Further validation via decision curve analysis (DCA) revealed that the combined diagnostic model developed in this study can provide greater overall net benefit in diagnosing SUI than can single ultrasound parameters. This suggests that multiparameter collaborative assessment can significantly enhance clinical diagnosis (Figure 12).

Figure 12 DCA plot. DCA, decision curve analysis; Emax, maximum E value; FPI, flow-perfusion index; NBPA, number of branch points per unit area; RI, resistance index; S/D, systolic-to-diastolic ratio; VD, vascular density.

Discussion

A meta-analysis of cross-sectional surveys encompassing over 250,000 women worldwide demonstrated a pooled prevalence of SUI of 12.5% (95% CI: 11.8–13.2%). Age-stratified analysis revealed that the prevalence nearly doubled among women aged 60 years and above, reaching 26.7% (IQR: 24.9–28.5%). In mainland China, population-based studies reported a crude SUI prevalence of 18.9%, with the highest prevalence observed in perimenopausal women aged 50–59 years, indicating that this age group represents a critical window for disease risk (14). The annual incidence of SUI exhibits a sustained upward trajectory, underpinned by progressive population aging, greater adiposity at the population level, and the successive expansion of two- and three-child parity policies. Notwithstanding the measurable increase in public awareness attributable to the dissemination of digital health information and sustained socioeconomic development, appreciable improvements in SUI management continue to be limited. Cross-sectional data indicate that one in three symptomatic women perceives the condition as warranting formal clinical assessment. Mild manifestations of SUI are frequently interpreted as an expected physiologic variant, leading to deferred presentation and loss of the early therapeutic window. Consequently, systematic programs that secure prompts objective diagnosis and evidence-based intervention have become a recognized public-health priority (16-18).

Ultrasound elastography and UMA represent evolving sonographic modalities with expanding utility in diagnostic characterization. SWE, in particular, provides a quantitative read-out of tissue stiffness through the tracking of the propagation velocity of induced transverse waves, thereby offering an objective metric that is independent of operator compression. The reconstructed elastic modulus exhibits a direct, linear relationship with tissue stiffness: higher modulus values correspond to increased rigidity and are encoded in warm tones (orange-red), whereas lower values indicative of softer parenchyma are displayed in cool tones (blue) (19-21). Viscoelastic ultrasound imaging simultaneously extracts the storage and loss moduli, yielding separate metrics of elasticity and viscosity that augment the mechanical characterization of biological tissues. UMA, an emerging high-frame rate Doppler modality, resolves low-velocity flow within microvessels that is below the detection threshold of conventional color Doppler flow imaging, thereby extending the sonographic appraisal of tissue perfusion (22). By integrating ultrafast plane-wave acquisitions with spatiotemporal clutter filtering, the technique records low-velocity microvascular flow at the submillimeter resolution while suppressing motion and respiratory artifacts. The resultant images are characterized by elevated frame rates, improved spatial definition, and lower artefactual burden, conferring a diagnostic advantage over conventional color Doppler flow imaging. Quantitative analysis of micro-VD, branching complexity, and flow velocity has generated incremental diagnostic value across multiple organ systems. It provides superior lesion characterization in breast imaging, refines the assessment of intratumoral vascularity in renal masses, and increases the sensitivity in the detection of hepatic artery stenosis after liver transplantation (23). However, these applications remain exploratory in the context of SUI, and prospective studies are required to establish their clinical validity.

TV-BPUS coupled with elastography and UMA has not been extensively deployed in SUI research. In our study, both the Young moduli and viscous-loss moduli at the mid-urethra were significantly lower in women with SUI than in continent controls (P<0.05), indicating a reduction in urethral stiffness and elastic recoil. This mechanical deficit aligns with published evidence that the sphincter complex is thinner and shorter in patients with SUI, a phenotype consistent with pelvic-floor myofiber rupture, denervation atrophy, or age-related degeneration that diminishes contractile reserve. Concomitant connective-tissue laxity—evidenced by fragmented elastic fibers and altered collagen cross-linking—further depresses the elastic modulus, thereby compromising the pressure-buffering capacity of the urethral wall. In our study, the UMA-related results contradicted this understanding: VD and FWVD were consistently lower in the SUI group (P<0.05). The perfusion deficit is best explained by microstructural aberrations in the rarefied capillary networks, intimal thickening, and perivascular fibrosis that increase vascular resistance and limit nutritive flow (24). Inadequate oxygen and substrate delivery may accelerate myocyte metabolic dysfunction, reinforcing the mechanical insufficiency described above and perpetuating a cycle of impaired urethral closure.

A growing body of evidence indicates that continence depends on the integrated function of the entire urethral length (25-27). Because the mid-urethra occupies a key position within the suburethral hammock, it has traditionally been regarded as the critical segment, and mid-urethral sling placement has become the standard surgical intervention for SUI. Emerging data, however, suggest that the internal urethral orifice may play a proportionally greater pathophysiologic role than previously appreciated. In our study cohort, both elastographic stiffness and UMA perfusion deviated more markedly at the internal urethral orifice than at any other urethral level, which could differentiate those with SUI from controls with the highest effect size. This observation suggests that internal urethral orifice compliance and its microvascular supply are primary determinants of closure efficiency, presumably because the internal urethral orifice must synchronize with the bladder neck to form a high-pressure seal. Under physiological conditions, the bladder neck relaxes first at the onset of voiding, which is followed immediately by dilatation of the internal urethral orifice. Conversely, continence is maintained by synchronous closure of both structures. Loss of this spatiotemporal coordination and excessive funneling of the bladder neck or incomplete apposition of the IUO has been shown to precipitate stress leakage (28-30). Our data indicate that such impairment in coordination is primarily associated with internal urethral orifice dysfunction rather than with alterations in the mid-urethral segment. Biomechanically, the internal urethral orifice constitutes a transitional cuff of smooth muscle and collagen-rich connective tissue that must withstand rapid fluctuations in intravesical pressure while remaining anchored by the periurethral musculofascial plate. Impaired microvascular perfusion within this segment, as documented here, is postulated to compromise local nutrient delivery, diminish viscoelastic compliance, and thereby amplify the susceptibility to stress incontinence (31,32).

Incorporating microangiographic metrics with demographic covariates of age and BMI substantially improved the discriminative capacity of the predictive models for SUI. SWE quantifies the mechanical properties of urethral tissue, yet it is inherently insensitive to hemodynamic alterations that are integral to the pathogenesis of the condition. Microangiography complements elastography by supplying a functional vascular layer of perfusion density and microvascular architectural integrity, both of which are frequently impaired in SUI as a consequence of ischemic or degenerative changes. This can be rendered directly visible and e expressed as continuous variables for multivariate modeling. Age and BMI are validated, independent predictors of SUI. Advancing age entails progressive hormonal decline and parenchymal senescence, whereas elevated BMI contributes to chronically raised intra-abdominal pressure, and each pathway amplifies urethral compensatory load and accelerates mechanical failure. The encoding of these nonmorphological yet biologically plausible determinants extends the external validity of the model and strengthens its clinical translatability without additional imaging overhead. A restricted model limited to SWE variables (Emax, Emean, Vimax, and Vimean) would likely yield inferior discrimination, as the individual elastographic indices in our study generated areas under the curve (AUCs) between 0.7175 and 0.7746, and their multivariate combination—despite capturing incremental variance—remained insensitive to both microvascular compromise and demographic burden. Consequently, an SWE-only composite would be expected to remain below 0.90, underscoring the necessity of integrating hemodynamic and systemic covariates to achieve clinically acceptable precision. Omission of age and BMI from the fully specified model attenuates predictive performance, as both covariates exert independent, additive effects on SUI probability. Ultrasound-derived indices of elastographic or microangiographic provide local biomechanical and vascular evidence; in contrast, chronological age and adiposity are proxies for systemic hormonal decline and chronic pressure overload, respectively. Omission of these nonimaging factors typically lowers the AUC from the observed 0.9327 to the 0.85–0.88 interval, a decrement consistent with variable-importance estimates reported in comparable diagnostic algorithms.

Following univariate analysis, the final multivariate logistic regression model incorporated age, BMI, VD at the internal urethral orifice, FPI, NBPPA, RI, and S/D of the mid-urethra, and Emax of both the internal orifice and mid-urethra. Each solitary parameter yielded modest discrimination (AUC ≤0.78), whereas their combination achieved an AUC of 0.9327 (95% CI: 0.907–0.958), equating to high diagnostic accuracy. DCA confirmed a uniformly higher net clinical benefit for the combined model across all reasonable threshold probabilities, underscoring the incremental value of concomitantly quantifying tissue elasticity and microvascular hemodynamics in the ultrasound-based characterization of SUI.

Our study focus was confined to the diagnostic dimension of SUI, and the utility of the models for urgency-predominant or mixed subtypes remains to be validated. Prospective evaluation of the full spectrum of incontinence is required to develop a universally applicable algorithm. Moreover, the capacity of elastography and UMA to serially monitor treatment response or to predict recurrence remains theoretical, and longitudinal cohort studies are needed to determine their prognostic value. Finally, although the multiparametric model exhibited high discrimination, a formal health economic evaluation is needed to establish cost-effectiveness and to inform scalable implementation within routine clinical pathways.

Overall, TV-BPUS augmented by concurrent elastographic and UMA assessment can provide a reproducible, high-resolution framework for the early detection of SUI and constitutes a readily integrable platform for therapeutic monitoring and prognostic stratification.

Conclusions

TV-BPUS integrated with elastography and UMA demonstrated outstanding performance in diagnosing female SUI. The composite model composed of multiparametric indices achieved an AUC of 0.933. This technique can diagnose—with high sensitivity—the occult SUI that conventional imaging frequently misses, enable early diagnosis and risk stratification by quantifying urethral elasticity and microvascular alterations, and serve as a reproducible, scalable tool for longitudinal treatment monitoring, with excellent clinical translational potential.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STARD reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1147/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1147/dss

Funding: This study was supported by the Guangdong Provincial Key Laboratory of Basic and Applied Basic Research Fund for Enterprise Collaboration (No. 2420210404000003), the Guangzhou Science and Technology Bureau’s 2023 Basic Research Plan for City-University (Hospital) Joint Funding “Dengfeng Hospital” Project (No. 2023A03J0360), and the Major Clinical Research Project of the Guangzhou Medical University Research Enhancement Program (No. GMUCR2025-02019).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2025-1147/coif). The authors report that this study was supported by the Guangdong Provincial Key Laboratory of Basic and Applied Basic Research Fund for Enterprise Collaboration (No. 2420210404000003), the Guangzhou Science and Technology Bureau’s 2023 Basic Research Plan for City-University (Hospital) Joint Funding “Dengfeng Hospital” Project (No. 2023A03J0360), and the Major Clinical Research Project of the Guangzhou Medical University Research Enhancement Program (No. GMUCR2025-02019). The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. This study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments, the revised edition of the Good Clinical Practice Guidelines of the National Medical Products Administration NMPA (order No. 57-2020), and the Good Clinical Practice guideline of the International Council for Harmonisation (ICH-GCP E6[R2]). This study was reviewed and approved by the Ethics Committee of The First Affiliated Hospital of Guangzhou Medical University (ethics reference No. ES-2025-K020-01). Written informed consent was obtained from each participant prior to any study-related examination.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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