Use of a three-dimensional ultrasound device for noninvasive urine bladder volume measurement in dogs and cats

Authors: Hugo Kaufmann, Diane Pichard, Aude-Morgane Canonne, Loïc Desquilbet, Christelle Maurey

Abstract

Background

Evaluation of urinary bladder volume (UBV) in companion animals is largely underused although it could be of clinical importance for diagnosis of micturition disorders. Advances in medical technology have led to the development of 3-dimensional (3D) ultrasound bladder scanners.

Hypothesis/Objectives

Assess the agreement between UBVs measured using a new noninvasive 3D ultrasound bladder scanner (Portascan 3D, ref MD-6000) and the actual UBV in dogs and cats.

Animals

Between December 2021 and June 2023, dogs and cats undergoing urinary catheterization for diagnostic or therapeutic reasons were prospectively enrolled.

Methods

For each animal, signalment, urinalysis, and bladder content abnormalities identified on conventional 2-dimensional ultrasound examination were recorded. Agreement between UBV measurements obtained using the 3D ultrasound device and those obtained by catheterization (reference standard) was quantified using Bland–Altman analysis.

Results

Nineteen dogs and 15 cats were enrolled. Bland–Altman analysis determined that the 3D ultrasound bladder scanner underestimated UBV by −6.1% (95% CI, −14.9% to +2.8%) in dogs and overestimated UBV by +13.6% (95% CI, +3.9% to +23.2%) in cats. The analysis also found excellent concordance and reproducibility between the 2 methods, with Lin’s concordance correlation coefficient of 0.99 (95% CI, 0.96-1.00) in dogs and 0.89 (95% CI, 0.66-0.97) in cats.

Conclusions and clinical importance

The 3D ultrasound scanner represents a noninvasive, rapid, and easy-to-use method that provides accurate measurements of UBV in dogs and cats.

Introduction

Assessment of urinary bladder volume (UBV) is of clinical importance in dogs and cats for understanding voiding and the assessment of post-void residual volume (PVRV). Neurologic diseases, obstructive conditions, urinary tract infections, and iatrogenic causes have been shown to increase PVRV in humans and are thought to have similar effects in dogs and cats.^1^ The consequences of chronic increased PVRV in companion animals are largely unknown, but it could lead to conditions such as urinary tract infection, vesicoureteral reflux, pyelonephritis, or detrusor atony.^2^ To date, urethral catheterization remains the reference method for UBV measurement but carries a risk of catheter-associated urinary tract infections (CAUTIs).^3^^,^^4^ Conventional noninvasive 2-dimensional (2D) ultrasonography allows for reliable, but laborious, calculation of UBV in dogs and cats.^2^^,^^5–10^ Advances in medical technology have led to development of 3-dimensional (3D) ultrasound bladder scanners, enabling noninvasive, rapid, and accurate UBV measurement in humans.^11^ They are primarily used as diagnostic tools to identify incomplete bladder emptying (as part of continence assessment), detect urinary retention, and estimate bladder volume, thereby assisting in the decision of whether an indwelling catheter is required in both adults and children with urinary disorders.^12^ Ultrasound bladder scanners are underused in veterinary practice because of a lack of device validation. Recent studies have focused on the 3D BladderScan Prime Plus (Verathon, USA), which is reported to be accurate in dogs weighing > 5.5 kg, but the device tends to underestimate actual UBV.^8^^,^^13^

The Portascan 3D Bladder Scanner MD-6000, another intuitive bladder scanner available in Europe, provides calculated UBVs based on 3D bladder wall detection.^14^ The device consists of a 120° sector scanning ultrasound probe with a motorized mechanism allowing 180° axial rotation. An automatic 15° probe rotation then is initiated for the next cross-sectional scan, resulting in a total of 12 cross-sections. The device calculates UBVs using an integral calculation method implemented in the algorithm, and the result is displayed on a liquid crystal display color touchscreen. The manufacturer claims that the Portascan 3D Bladder Scanner is easy to use and facilitates rapid UBV examinations, acquiring over 3000 lines within 3-5 s without user interference for accurate scans in humans.^14^ Unlike other bladder scanners, calibration is not required, decreasing both time and cost associated with annual maintenance. The device has a measuring range of 20-999 mL, with an accuracy of ±15% in humans, and is considered safe and reliable according to the manufacturer.^14^

To date, the Portascan 3D Bladder Scanner MD-6000 (Meda Co., distributed by Laborie Medical Technologies, Canada) has not been investigated for veterinary use, and no bladder scanner device has been evaluated in cats. Our aim was to evaluate the reliability of the Portascan 3D Bladder Scanner MD-6000 as a noninvasive method for measuring UBV in client-owned dogs and cats. The secondary objective was to assess whether bladder size or patient sex influences the accuracy of 3D ultrasound measurements.

Material and methods

Data collection

Our prospective study was conducted between 2021 and 2023 at the Alfort Veterinary University Hospital (CHUVA), France. All dogs and cats that fulfilled the inclusion criteria were enrolled. The study protocol was reviewed and approved by the Clinical Research Ethics Committee of Alfort (ComERC 2022-02-32). Informed consent forms and information letters were provided and signed by the owners before enrollment. The clinical investigations were performed by 2 clinicians (H.K. and D.P.), both trained in ultrasonography and the use of a 3D ultrasound device during the month preceding the study.

Dogs and cats, regardless of sex, age, or breed, were eligible for inclusion if they had undergone urethral catheterization for diagnostic or therapeutic purposes (eg, urethral obstruction, bladder endoscopy, bladder retention, urodynamic evaluation). Animals were excluded if the bladder exhibited major wall alterations, abdominal effusion was present, clinically relevant intraluminal abnormalities were present (eg, uroliths, masses), or if abnormal external urogenital anatomy or pigmenturia was identified, because these could interfere with accurate 3D bladder reconstruction. Blood analysis or urine culture were not required for study inclusion.

The following data were recorded for each age, sex, breed, body weight, reason for catheterization, underlying disease, ongoing treatments, routine urinalysis results, clinical examination findings, bladder abnormalities reported on conventional 2D ultrasound examination, UBV measured using the 3D ultrasound device, and UBV determined after catheterization and emptying of the bladder.

Procedure

Bladder distension initially was assessed by abdominal palpation. Animals were anesthetized depending on their sex (females underwent general anesthesia) or the procedure performed (eg, anesthesia for endoscopy), and then positioned in dorsal recumbency. Male dogs did not undergo general anesthesia, depending on their level of cooperation. Anesthesia was induced and maintained using injectable agents only. Animals were premedicated with methadone (Methadone Hydrochloride, Dechra Veterinary Products, Northwich, UK) at 0.2 mg/kg IV and midazolam (Midazolam, B. Braun Medical Inc., Bethlehem, Pennsylvania) at 0.2 mg/kg IV. Anesthesia then was induced with propofol (Propofol, Abbott Laboratories Inc, Animal Health Division, North Chicago, Illinois) at 3-8 mg/kg IV to effect. In animals in which a potential cardiac risk was suspected, alfaxalone (Alfaxan, Jurox Pty Ltd, Rutherford, Australia) was used instead at 1-4 mg/kg IV to effect. Throughout anesthesia, physiological variables including ECG, oxygen saturation (SpO₂), heart rate, and respiratory rate were continuously monitored. A 5 × 5 cm area over the ventrocaudal abdomen was shaved and coated with acoustic gel. The bladder was first examined using a 2D ultrasound device to evaluate bladder size, wall integrity, absence of abdominal effusion, and the presence of any intraluminal abnormalities that could result in study exclusion.

Subsequently, a 3D ultrasound device (Portascan 3D, ref MD-6000, Meda Co., distributed by Laborie Medical Technologies, Canada) was used to measure UBV according to the manufacturer’s instructions. The device’s gain was set at 30 dB (“child” setting), as recommended by the manufacturer. Bladder location was identified using the sagittal view in the pre-scan function, and the operator adjusted the probe position to ensure the entire bladder was contained within the sector scanning area, indicated in green on the liquid crystal display interface (Figure 1a and b). If measurements are performed on awake animals, the device can produce erroneous readings if the animal moves during scanning, potentially leading to an underestimation of actual bladder volume. To ensure consistency and reproducibility across animals (whether awake or anesthetized), 5 consecutive UBV measurements were obtained, and the measurement with the graphical representation that most closely matched ideal bladder shape was selected (ie, the green line best traced the subjective margin of the bladder evaluated by B-mode ultrasonography). This methodological choice was established a priori by the investigators who designed the protocol, with the objective of minimizing bias linked to inaccurate segmentation (which can occur more frequently in awake animals). Our objective was to capture the complete image of the bladder at the moment when its ovoid shape was accurately identified by the device, ensuring correct delineation of the bladder wall.

Immediately after ultrasound assessment, a second blinded investigator performed urinary catheterization to directly measure UBV. Urinary catheterization was performed using sterile 3.5-8.0 Fr catheters connected to a 3-way stopcock. Aseptic technique, including cleansing of the genital area with chlorhexidine, was used throughout catheterization. Bladder emptying was performed using 20-mL syringes, and the total collected UBV was recorded. Complete bladder voiding was confirmed by 2D ultrasonography, defined as the absence of residual urine on aspiration associated with sonographic evidence of an empty bladder. Measurement of UBV using the 3D ultrasound device, followed by urinary catheterization, was performed by 2 different researchers (H.K. and D.P.), each responsible for one procedure, with the order determined by clinician availability at the time of the procedure.

Statistical analysis

All statistical analyses were conducted using Microsoft Office Suite Excel 2020 (Microsoft, Redmond, Washington) and R Statistical Software (v4.1.3; R Core Team 2022). Data were expressed as mean ± SD for normally distributed data. Normality was assessed by visual inspection of quantile-quantile plots. Agreement between 3D ultrasound UBV and actual UBV after catheterization was evaluated using a Bland–Altman plot. Bias and 95% limits of agreement were investigated using Bland–Altman analysis.^15^^,^^16^ Lin’s concordance correlation was used to compare the 2 methods.^17^^,^^18^ Medians of differences between 3D ultrasound UBV and actual UBV after catheterization were calculated for both males and females and were tested using a Mann–Whitney U test. Associations between body weight or UBV and device accuracy were assessed using Spearman’s rank correlation test. Statistical significance was set at P ≤ .05.

Results

Inclusion and signalment

Between December 2021 and July 2023, 20 dogs and 16 cats met the inclusion criteria. A single male dog and a single female cat were excluded because of severe bladder abnormalities (after cystotomy and encrusted cystitis, respectively). Ultimately, 19 dogs and 15 cats were enrolled (Table S1). The enrolled dogs included 10 males (4 neutered) and 9 females (5 spayed); the enrolled cats included 14 males (11 neutered) and 1 spayed female.

Most of the animals were included because urethral catheterization had to be performed to empty the bladder. Seven dogs were included because of intervertebral disk extrusion causing neurologic impairment of bladder function, graded as 4 or 5 out of 5 on the modified Frankel score and 12 cats were included because of an obstructive lower urinary tract disease.^19^ The other animals were included either because they required urethral catheterization for disease management (eg, acute kidney injury, urethral neoplasia), or because they were undergoing endoscopic examination of the urinary tract (Table S1). Among the enrolled dogs, 2 had ultrasonographic evidence of cystitis, characterized by increased bladder wall thickness. Among the enrolled cats, 5 had ultrasonographic evidence of mild urinary sediment, and 1 had a small bladder clot, deemed sufficiently limited in size so as not to impact bladder volume. No complications associated with either catheterization or ultrasonography were observed.

The study included the following dog French bulldog (n = 5), Australian shepherd (n = 3), Jack Russell terrier (n = 2), and one each of Cavalier King Charles spaniel, boxer, sheepdog, beauceron, collie, pug, Staffordshire bull terrier, dachshund, and American Staffordshire terrier. Among cats, the breeds included European shorthair (n = 12), Siamese (n = 1), minuet (n = 1), and Norwegian forest cat (n = 1). In dogs, mean ± SD body weight was 17.7 ± 9.9 kg (range, 5.1-44.2 kg) and mean ± SD age was 5.6 ± 2.9 years (range, 1-10 years). In cats, mean ± SD body weight was 5.2 ± 1.3 kg (range, 3.3-7.0 kg) and mean ± SD age was 6.4 ± 3.3 years (range, 2.0-13.0 years).

Bland–Altman analysis

Urine bladder volumes recorded by the 3D ultrasound machine were compared to UBV obtained by catheterization (Table S1). Weight was significantly associated in univariable analyses with UBV obtained by catheterization in both dogs (rs = 0.69; P = .001) and cats (rs = −0.55; P = .03; Figure 2), even if time from last micturition and UBV assessment were not standardized.

In dogs, the differences in UBV between 3D ultrasound and catheterized UBV were normally distributed, with a mean difference of −9.4 mL (SD, 24.1 mL), and maximal positive and negative disagreement of +45 and − 55 mL, respectively. The percent disagreement between mean 3D ultrasound UBV and catheterized UBV had a mean of −6.1% (95% CI, −14.9% to +2.8%), SD of 18.3%, and maximal positive and negative disagreements of +30.0% and − 44.6%, respectively (Figure 3). In cats, the differences in UBV between 3D ultrasound and catheterized measurements also were normally distributed, with a mean difference of 7.1 mL (SD, 11.0 mL), and maximal positive and negative disagreements of +26 mL and − 21 mL, respectively. The percent disagreement between the mean 3D ultrasound UBV and catheterized UBV had a mean of 13.6% (95% CI, +3.9% to +23.2%), SD of 17.5%, and maximal positive and negative disagreements of +42.6% and − 22.4%, respectively (Figure 4). The 95% limits of agreement for the device were − 42.1% to +30.0% in dogs and − 20.8% to +47.9% in cats. These results indicate that, in 95% of cases, the error of the 3D ultrasound scanner relative to the actual UBV fell between −42.1% and + 30.0% in dogs and between −20.8% and + 47.9% in cats.

Fourteen of 19 included dogs (74%) had measurements within the tolerances claimed by the manufacturer for humans (±15% accuracy). All 5 dogs with discrepancies exceeding ±15% (ranging from ±15% to ±45%) had smaller bladder volumes (≤165 mL). In cats, 7 of 15 (47%) had bladder volume errors within the manufacturer’s claimed tolerance (±15%), whereas the remaining 8 cats, with errors ranging from ±15% to ±43%, had either small or large bladder volumes (Figure 4).

Agreement between methods was excellent, with a Lin’s concordance correlation coefficient of 0.99 (95% CI, 0.96-1.00) for dogs (Figure 5) and 0.89 (95% CI, 0.66-0.97) for cats (Figure 6). Concordance was considered almost perfect in dogs and fairly good in cats.

In both study samples, no significant correlation was found between weight and the absolute accuracy of the device (rs = −0.08 and P = .74 in dogs; rs = 0.40 and P = .14 in cats) or between current UBV and the absolute accuracy of the device (rs = −0.22 and P = .36 in dogs; rs = −0.45 and P = .09 in cats). In dogs, no significant difference was found in percent disagreement between the mean 3D ultrasound UBV and the catheterized UBV for males (median, −6.2%) and females (median, −2.5%; P = .54). Because the feline population included only one female, no comparison by sex was possible.

Discussion

Our results provide evidence that the 3D ultrasound bladder scanner (Portascan 3D, ref MD-6000) yields reasonably accurate estimations of UBV in both dogs and cats, with stronger agreement observed in dogs than in cats. Although several studies have assessed the accuracy of 3D ultrasound bladder scanners in dogs, none have evaluated their performance in cats.^8^^,^^13^ The UBVs were compared with actual UBVs obtained by catheterization, which is considered the gold standard for measuring UBVs. The accuracy thresholds defined by the device’s manufacturer for use in humans (±15%) were met in 74% of dogs and 47% of cats. In dogs, the discordance percentages exceeding this threshold were mostly observed at small UBVs (≤165 mL), consistent with previous reports, suggesting that lower UBVs may limit the precision of 3D ultrasound bladder scanners.^8^^,^^13^ The underestimation of UBV by the scan may be partly explained by difficulty in accurately delineating the bladder, particularly the bladder neck, which could result in lower UBV measurements in dogs. Similar observations have been reported in children, where device accuracy is volume-dependent, particularly at volumes < 60 mL.^20^^,^^21^ This explanation is less applicable in cats, where the 3D ultrasound examination tended to overestimate UBV, even at small volumes. Other uncontrolled factors may contribute to interspecies differences in device accuracy, such as a potential influence of peritoneal echogenicity on the 3D bladder reconstruction. The device algorithm also is based on human models, and its preset calculations may not be accurate across species because of differences in bladder shape. Developing adapted algorithms with species-specific correction factors (particularly for cats) could further enhance the accuracy of the device. Quantitative comparisons of UBVs are of limited clinical relevance because of the considerable variation in bladder size among animals, ranging in our study from 17 to 600 mL in dogs and 20 to 105 mL in cats. Given that the relationship between body weight and UBV is not well established in veterinary medicine, evaluating relative differences may offer more clinical utility than normalizing UBV to body weight. In this context, a threshold of ±15% could represent a clinically meaningful difference.

The accuracy of the bladder scanner was evaluated using Bland–Altman analysis, which indicated a slight systematic underestimation of UBV in dogs (bias, −6.1%; 95% CI, −14.9% to +2.8%) and an overestimation in cats (bias, +13.6%; 95% CI, +3.9% to +23.2%), although the bias in dogs was not significantly different from 0. The relatively wide limits of agreement (−42.1% to +30.0% in dogs; −20.8% to +47.9% in cats) suggest that, although the device performs well on average, individual discrepancies may occur, likely influenced by outliers. The precision of the device also can be appreciated by examining the SD, which was similar in dogs (18.3%) and cats (17.5%), indicating that approximately 68% of measurements are expected to fall within ±18% of true bladder volume in both species (relative differences normally distributed). Although the clinical relevance of this level of variability remains to be fully determined, it appears to be acceptable for clinical use. Nevertheless, the performance of the bladder scanner should be validated in a larger clinical field study, particularly with a larger number of female cats, to enhance the generalizability of the results. Lin’s concordance correlation coefficient, which assesses both precision and accuracy to evaluate agreement between the 2 methods of urine measurement, indicated excellent agreement in dogs (ρc = 0.99) and fairly good agreement in cats (ρc = 0.89), supporting the clinical utility of the device. Comparison of this specific bladder scanner with other devices remains challenging, because Bland–Altman analyses have not been consistently performed across studies. However, the Portascan 3D (Ref MD-6000) appears to have lower variability, with a SD of ±18% in both dogs and cats, compared with the BladderScan Prime Plus (Verathon), which has a reported SD of ± 34.9%.^13^

To date, several studies have investigated PVRV in healthy dogs using either ultrasound estimation or catheterization, reporting a wide range of values. Some studies described normal PVRV values in the general canine population ranging from 0.1 to 3.4 mL/kg, whereas other studies have found a mean normal PVRV of 0.21 mL/kg, with a range of 0-0.47 mL/kg, based on direct measurement via catheterization.^2^^,^^5^ Some studies have suggested that age influences PVRV, with older dogs exhibiting higher PVRV compared with younger dogs.^22^ The impact of body weight on PVRV remains unclear, with conflicting findings. Some reports indicate a decrease in PVRV with increasing body weight, whereas others suggest that dogs weighing < 10 kg may have higher PVRV compared with those > 10 kg.^22^^,^^23^ Micturition behavior, particularly in intact male dogs with high prevalence of marking, is also suspected to influence PVRV assessment. The measurement of PVRV is clinically important, as highlighted in the recent American College of Veterinary Internal Medicine (ACVIM) consensus statement, which reported that increased PVRV may indicate a voiding disorder, whereas normal PVRV in the presence of urinary incontinence suggests a storage disorder.^7^ According to current guidelines, a PVRV between 0.2 and 1.0 mL/kg is considered normal in dogs, values > 3.0 mL/kg are indicative of urine retention, and values between 1.0 and 3.0 mL/kg should be interpreted in the context of the signalment and other clinical signs.^7^ The use of 3D ultrasound bladder scanners represents an important paradigm shift in the measurement of PVRV in both dogs and cats, offering a noninvasive alternative to urinary catheterization and thereby decreasing the risk of CAUTIs.^24^ This risk has been estimated to range from 8% to 32% in dogs undergoing catheterization.^4^^,^^25^^,^^26^ Although the 3D ultrasound bladder scanner evaluated in our study did not show perfect agreement—with some outliers observed when dealing with small volumes—it appeared to approach a ± 15% accuracy threshold in dogs and may represent a reliable method for estimating PVRV in dogs. Additional studies are warranted in cats, both to establish reference values for PVRV and to assess the agreement and clinical utility of 3D ultrasound bladder scanners for evaluating PVRV in this species.

Several studies have investigated the use of 2D ultrasonography to estimate UBV using various calculation formulas in dogs.^2^^,^^5–10^ Recently, 2 studies specifically validated a 2D ultrasonographic linear bladder dimension formula in cats.^9^^,^^27^ Despite the increasing availability of point-of-care ultrasonography, urine volume estimation has not been widely adopted in clinical practice, likely because of several limiting factors (eg, the technique can be challenging for inexperienced operators and may increase the duration of the examination). In contrast, 3D bladder scanners offer the advantage of providing a rapid UBV estimation—typically within seconds—and are theoretically operator-independent. A previous study specifically reported that the 3D ultrasound method required significantly less time to measure UBV compared with 2D ultrasound.^8^ However, this expectation must be weighed against previous findings indicating that experienced operators obtained significantly higher volume measurements than novices in dogs.^13^ This aspect was not assessed in our study. Future investigations using a different study design and a larger cohort of both experienced and inexperienced users are warranted to evaluate the influence of operator experience on measurement accuracy. Another important consideration is the use of the “child” setting. According to the manufacturer, this setting (30 dB) was developed based on the assumption that a child’s bladder is located more superficially than that of an adult, because of a thinner abdominal wall.^28^ Consequently, this setting might be more appropriate for use in animals. However, other studies using the BladderScan Prime Plus (Verathon) have reported slightly better performance with the “man” setting.^13^ The impact of these settings should be evaluated prospectively with the current bladder scanner. In addition, adapting the device’s algorithm to specific veterinary species could further improve accuracy. Based on our experience, a major limitation of using a device designed for human patients is the fixed ultrasound depth, which cannot be adjusted and may hinder accurate bladder visualization in small animals. This limitation necessitated performing 5 consecutive UBV measurements to ensure selection of the graphical representation that most closely matched the ideal bladder shape.

Our study sample consisted of a broad range of breeds, body weights, and clinical indications for urethral catheterization. Most animals were enrolled because of neurogenic bladder dysfunction secondary to intervertebral disk extrusion in dogs or because of urethral obstruction in cats. These 2 situations are common clinical scenarios where noninvasive UBV monitoring is particularly valuable to assess the clinical necessity of bladder emptying. The inclusion of cases with various other urologic and systemic diseases increases the external validity of these results. Interestingly, no significant influence of body weight, sex, or actual UBV on the absolute accuracy of the bladder scanner was found in either species. This observation suggests that, within the tested range of body sizes and volumes, the device’s performance is relatively robust. The UBV determination was standardized throughout the all dogs and cats were placed in dorsal recumbency, and nearly all were sedated for catheterization and UBV assessment. Previous studies have compared dorsal and lateral recumbency for bladder volume estimation and found that dorsal positioning yields a more accurate measurement.^29^ Therefore, dorsal recumbency should be the standard positioning for UBV assessment with bladder scanners. To our knowledge, the impact of sedation on bladder morphology and UBV measurement using bladder scanners has not been investigated and warrants further study.

Our study had some limitations. First, although catheterization is a standard reference for UBV assessment, incomplete bladder emptying during catheterization could have introduced minor measurement errors. In addition, the timing between micturition and UBV measurement was not standardized, which could have contributed to variability. Interobserver variability also was not assessed. Although the study sample included clinically relevant cases, further research is warranted to evaluate the device’s performance across a broader spectrum of clinical conditions, particularly in patients with severe urinary tract pathology that may affect bladder imaging and reconstruction. Another limitation is the relatively small sample size, especially in cats, with an underrepresentation of female cats, thereby limiting the generalizability of the findings to the wider feline population. Moreover, almost all measurements were performed in sedated animals positioned in dorsal recumbency. The morphology of the urinary bladder may change based on gravitational effects when animals are awake and in a standing position, potentially leading to discrepancies in UBV measurements. Rather than using an average volume, only the best of the 5 measurements was selected (the one that showed the largest, most centrally positioned bladder and the highest scanned volume). Even if this methodological choice might have introduced selection bias, this approach was chosen to minimize underestimation of bladder volume in awake animals, because movement during scanning can lead to inaccurate delineation of the bladder wall. Future studies should investigate the influence of patient positioning and sedation on measurement accuracy in both species.

In conclusion, the evaluated 3D ultrasound bladder scanner is a noninvasive, fast, and easy-to-use device, which seems to provide accurate UBV estimates in dogs and, to a lesser extent, in cats. While it cannot fully replace catheterization in cases where precise UBV measurement is critical, it appears to be a valuable noninvasive alternative for daily monitoring of bladder volume. Although the accuracy in cats was somewhat lower, the device still provides clinically useful information for monitoring trends in bladder filling and emptying. Given the risks associated with repeated catheterization, including urinary tract infections and urethral trauma, noninvasive UBV assessment may offer substantial advantages in hospitalized animals requiring ongoing urinary monitoring or for initial evaluation of PVRV.

Supplementary Material