INTRODUCTION
Lower urinary tract dysfunction (LUTD) comprises various bladder storage and voiding abnormalities, including overactive bladder (OAB), neurogenic bladder (NB), bladder pain syndrome/interstitial cystitis, underactive bladder (UAB), and bladder cancer [1-3]. These conditions affect millions globally and significantly impair quality of life, manifesting symptoms such as urgency, frequency, incontinence, pelvic pain, and urinary retention [4, 5]. Particularly concerning is the progressive and irreversible nature of neurogenic and fibrotic bladder remodeling, complicating treatment when diagnosis is delayed [6-8].
Conventional diagnostic tools—such as cystoscopy, urodynamic studies (UDS), and postvoid residual measurements via ultrasound—are standard in clinical urology but have significant limitations. UDS often fails to represent physiological bladder behavior accurately, as it is performed under artificial filling conditions; additionally, patients frequently experience considerable discomfort, discouraging subsequent assessments [9]. Cystoscopy, while invaluable for detecting intravesical lesions, involves invasive instrumentation, associated patient discomfort, risk of infection, and substantial procedural costs [10]. Although ultrasound is noninvasive, it is highly operator-dependent and generally limited to static snapshots rather than dynamic functional assessment [11]. These limitations underscore the critical need for advanced diagnostic modalities that are minimally invasive, cost-effective, and suitable for continuous real-world monitoring—criteria that align closely with emerging optical techniques.
Optical imaging and sensing technologies—including near-infrared spectroscopy (NIRS), optical coherence tomography (OCT), and photoacoustic imaging (PAI)—enable noninvasive assessment of tissue oxygenation, vascular perfusion, and microstructural properties [12-22]. These approaches offer several advantages, including portability, lack of ionizing radiation, and high temporal resolution. Importantly, their noninvasive nature allows for repeated application without inducing patient discomfort, making them especially suitable for long-term monitoring of chronic urological conditions and suggesting their potential for use in home-based healthcare settings.
For instance, Molavi et al. [14] demonstrated in a pilot study that a wireless NIRS device could non-invasively measure bladder filling, correlating strongly (r=0.88) with actual bladder volumes, indicating the feasibility of continuous volumetric monitoring. Similarly, Chung et al. [15] observed that NIRS signals correlated significantly with traditional pressure-flow study parameters (r=0.81) in men presenting with lower urinary tract symptoms (LUTS), supporting the potential of NIRS as a noninvasive alternative for detecting detrusor overactivity.
The recent technological integration of optical modalities with wearable sensors, fiber-optic platforms, and artificial intelligence (AI)-driven analytics has markedly enhanced their clinical relevance and versatility. Machine learning algorithms now enable real-time interpretation of optical data streams, facilitating estimation of bladder volume, detection of detrusor contractions, and continuous tracking of oxygenation dynamics [23-26]. For instance, Lee et al. [27] reported that an in-home, wearable monitoring system for nocturnal enuresis achieved a detection accuracy of 89%, highlighting the reliability of ambulatory AI-enhanced devices in tracking bladder-related events outside traditional clinical environments. Wearable NIRS systems, in particular, have demonstrated efficacy for noninvasive, real-world bladder activity monitoring, paving the way for continuous ambulatory care [27-29]. In parallel, OCT-integrated cystoscopes now provide micron-scale resolution for early bladder cancer detection, with one study revealing that OCT improved sensitivity for carcinoma in situ (CIS) detection by 22% over standard white-light cystoscopy [20].
These advances have the potential to transform bladder health diagnostics by shifting the clinical paradigm from episodic, invasive assessments to continuous, noninvasive functional surveillance. As LUTD increasingly intersects with chronic disease management, the ability to monitor bladder physiology longitudinally, without sacrificing patient comfort or mobility, may substantially increase diagnostic precision and facilitate more personalized treatment strategies. This review provides a comprehensive synthesis of these advanced optical technologies, outlining their operating mechanisms, clinical applications, and a proposed integrated clinical pathway for LUTD management.
METHODS
Literature Search and Selection Criteria
We searched PubMed and Embase (January 2000–March 2025) using the following keywords: (“optical imaging” OR “NIRS” OR “near-infrared spectroscopy” OR “OCT” OR “optical coherence tomography” OR “PAI” OR “photoacoustic imaging” OR “fiber-optic sensor”) AND (“bladder” OR “lower urinary tract” OR “LUTD”). Results were restricted to English-language human studies.
The inclusion criteria were as follows:
• Use of NIRS, OCT, PAI, or fiber-optic sensors (FOSs) to assess bladder function or pathology
• Reported clinical outcomes: diagnostic accuracy (e.g., sensitivity, specificity), feasibility, or patient-centered outcomes (comfort, adherence)
• At least 10 human subjects, or a peer-reviewed narrative/systematic review relevant to LUTD
The exclusion criteria included:
• Conference abstracts without full texts
• Animal-only studies
• Studies on pelvic organs other than the bladder (e.g., the prostate or uterus)
• Insufficient methodological details or outcomes
Data Extraction and Quality Assessment
From each included study, we extracted data on study design (randomized vs. observational), sample size, patient population, optical parameters (e.g., resolution, depth), diagnostic performance metrics (e.g., area under the curve, sensitivity, specificity), and main conclusions. Risk of bias was assessed qualitatively based on study characteristics such as sample size, single-center versus multicenter design, prospective versus retrospective methods, and clarity of outcome reporting. We particularly noted potential bias in studies lacking control groups or using unblinded assessments.
Study quality was evaluated narratively, considered adequacy of sample size, thoroughness of diagnostic and methodological reporting, clarity in data presentation, and whether conclusions were fully supported by the data. Due to heterogeneity in study designs and objectives, a formal quantitative quality scoring or meta-analysis was not performed. Instead, we conducted a thematic synthesis, highlighting representative and well-conducted studies for each modality and drawing out common trends and unique insights from the literature.
RESULTS
The Promise of Optical Techniques in Bladder Diagnostics
As limitations of conventional bladder diagnostics become increasingly evident, optical techniques have emerged as promising technologies offering noninvasive, real-time insights into bladder function and pathology. Fig. 1 illustrates how modalities such as NIRS, OCT, PAI, and FOSs harness interactions between light and tissue, highlighting their detection mechanisms, typical depth ranges, and capabilities to assess perfusion, oxygenation, microstructure, and pressure dynamics. Below, we describe each key optical method for bladder assessment.
Near-infrared spectroscopy
NIRS is a noninvasive optical method that measures the differential absorption of near-infrared light by oxygenated and deoxygenated hemoglobin in the 650–1,000 nm range, enabling real-time monitoring of bladder tissue perfusion and oxygenation [12-15, 23, 24]. Clinically, NIRS is able to detect dynamic hemodynamic changes in patients with OAB without requiring invasive catheterization [14, 29-31], and it demonstrates significant correlations with pressure-flow studies in men with LUTS [15]. The advent of wearable NIRS devices has enabled continuous monitoring during routine daily activities [27, 28], and integration with machine learning algorithms has resulted in detection rates of up to 85% for abnormal detrusor overactivity through estimation of bladder fullness and identification of voiding patterns [24, 25]. NIRS enables noninvasive, real-time measurements of bladder function, and its wearable design supports prolonged data collection beyond clinical settings [12, 14, 29]. Its reliance on advanced signal processing and machine learning further improves diagnostic accuracy [12, 14, 29, 31].
One limitation of NIRS is that motion artifacts, skin pigmentation, and subcutaneous fat thickness may introduce measurement variability [12, 31]. Additionally, NIRS lacks the anatomical detail necessary for precise lesion localization, offering less direct structural information than OCT or PAI [16, 23]. Multiple studies report sensitivities of 70%–85% and specificities between 60% and 85% for diagnosing detrusor overactivity using NIRS [24, 25, 31]. Because it is entirely noninvasive and easy to administer, NIRS is well-tolerated by patients and relatively cost-effective compared to other advanced imaging modalities [12, 23]. Research and clinical feasibility trials continue to establish NIRS as one of the leading tools for functional bladder assessment.
Optical coherence tomography
OCT utilizes low-coherence interferometry to generate high-resolution (1–15 μm) cross-sectional images of tissue microstructure, with a typical penetration depth of 1–2 mm, which is ideal for visualizing superficial bladder layers and detecting early pathological changes [17-19, 32]. Clinically, OCT can identify flat lesions and early-stage pathology, such as CIS, which may be missed by white-light cystoscopy [17-20]. By distinguishing the urothelium, lamina propria, and muscularis propria, OCT aids both staging and targeted biopsy site selection [17-19]. Integrated into cystoscopes, OCT provides real-time imaging that supports procedures like transurethral resection of bladder tumors, and reduces inter-observer variability when combined with AI-driven image analysis [32, 33]. OCT’s near-histological resolution enables detection of subtle or flat lesions that conventional cystoscopy might overlook [17-19]. Its ability to provide immediate feedback during surgical procedures is invaluable for improving intraoperative decision-making [19, 20, 32].
Despite these strengths, OCT’s penetration is limited to approximately 2 mm, restricting visualization of deeper tissue and vascular networks [16, 23]. Additionally, the requirement for specialized endoscopic equipment limits its applicability for wearable or home-based monitoring, and OCT is primarily focused on structural rather than functional data [16].
Clinical studies have reported sensitivities of 80%–96% and specificities of 75%–90% for detecting non–muscle-invasive bladder cancer with OCT [17-20]. Although OCT necessitates specialized personnel and equipment, it has been widely adopted in leading centers for bladder cancer detection and surveillance [16, 23].
Photoacoustic imaging
PAI uses pulsed laser light absorbed by chromophores such as hemoglobin to generate thermoelastic expansion, producing ultrasound signals that map vascular architecture and local oxygen saturation. PAI offers penetration depths of several centimeters—significantly greater than that of OCT—allowing visualization of deeper regions of the bladder wall [21, 22, 33].
In clinical applications, PAI identifies hypoxic and angiogenic regions in bladder tumors, aiding early detection and providing valuable information for noninvasive staging [21, 22]. By mapping vascular remodeling and oxygenation gradients within tumors, PAI supports more informed therapeutic planning [33]. Unlike OCT, PAI supplies both structural and functional information, including oxygen saturation, making it particularly advantageous for visualizing tumor-related neovascularization [16, 21, 33]. However, because PAI relies on laser illumination, strict safety protocols and acoustic coupling are necessary, leading to a more complex procedural setup. High costs and the need for specialized operator training further limit routine clinical use [16, 21, 23, 33].
Early research has demonstrated sensitivities of 80%–90% and specificities of 70%–90% for detecting vascular abnormalities in bladder tumors [21, 22, 33]. Although it is noninvasive, the hardware costs and laser safety requirements of PAI remain significant barriers to broad clinical implementation [16, 23].
Fiber-optic sensors
FOSs detect changes in bladder pressure, temperature, or strain in real time using mechanisms such as fiber Bragg gratings or Fabry–Pérot interferometry. Their miniaturized, flexible design makes them suitable for insertion via thin catheters [34-36].
The flexibility and biocompatibility of these probes make them ideal for pediatric and geriatric patients who may not tolerate standard catheters for prolonged periods. FOSs enable continuous pressure monitoring, offering real-time evaluation of detrusor function as an alternative to conventional urodynamic catheters [35, 36]. Current research focuses on integrating these sensors into “smart catheters” for extended, long-term monitoring [34-36]. FOSs rapidly capture changes in intravesical pressure with high temporal resolution, improving patient comfort compared to rigid catheters. They also offer potential integration into wearable monitoring systems [34-36]. However, FOSs must be positioned inside or near the bladder, rendering this modality semi-invasive and necessitating insertion and removal procedures [34, 36]. Manufacturing costs and technical complexity further challenge large-scale deployment. Additionally, the lack of imaging capabilities restricts FOSs to functional measurements (e.g., pressure) only [16, 23].
Pilot studies have reported error margins within ±5% compared to conventional urodynamic catheters [34, 35]. However, requirements for specialized personnel and higher costs continue to restrict widespread adoption in outpatient or home care settings. Nevertheless, FOSs hold considerable promise for integration into next-generation urological monitoring systems [23, 34].
A comparative overview of diagnostic accuracy, invasiveness, usability, and scalability for each modality is provided in Table 1. NIRS is associated with high patient comfort, whereas OCT offers superior spatial resolution. PAI delivers greater tissue penetration than OCT but requires more complex instrumentation, and FOSs enable precise pressure monitoring through a semi-invasive approach. Ultimately, the optimal modality depends on the specific clinical scenario and individual patient requirements.
Case Studies and Clinical Research Examples
Numerous preclinical and clinical studies have established the feasibility, safety, and diagnostic utility of optical techniques for evaluating bladder physiology and pathology. Many investigations underscore the translational promise of these modalities in both diagnostic and longitudinal monitoring contexts. However, it is important to note that much of the current evidence—especially for wearable NIRS and PAI applications—comes from small, single-center pilot studies, limiting generalizability and broader applicability. Fig. 2 offers a visual summary of the operational principles and clinical applications of core optical technologies, including wearable NIRS, OCT, PAI, and FOS.
Wearable NIRS in OAB
Macnab et al. [30] applied a wearable NIRS system to monitor bladder wall oxygenation during urodynamic testing in patients with OAB. Events of detrusor overactivity were reliably associated with drops in oxygenated hemoglobin, supporting the use of NIRS as a real-time surrogate marker for abnormal detrusor contractions. While the wearable design improved patient comfort and supports broader use outside the clinic, the study’s limited participant number and single-center setting highlight the need for larger, multicenter trials to validate this method.
OCT for CIS detection
Goh et al. [20] employed OCT during bladder tumor evaluation, demonstrating that OCT clearly differentiated normal urothelium, dysplastic changes, and invasive lesions. The modality’s high-resolution, real-time imaging significantly increased the diagnostic yield of conventional cystoscopy, particularly for detecting CIS that might otherwise be missed.
PAI for tumor vascular mapping
Alchera et al. [21] showed that photoacoustic imaging with tumor-targeted gold nanorods enabled high-resolution mapping of bladder tumor vasculature and hypoxic regions. This noninvasive method could facilitate early diagnosis and grading of bladder cancers by visualizing angiogenic hotspots not detected by standard cystoscopy. Again, the pilot nature and small sample size stress the importance of expanding research to confirm PAI’s utility.
Fiber-optic pressure monitoring
Hafid et al. [23] and Friedemann et al. [34] highlighted the role of fiber-optic pressure sensors for long-term intravesical monitoring. These sensors, which are designed for integration into soft, wearable or catheter-based systems, deliver high temporal resolution and reduce patient discomfort compared to traditional catheters, making them especially useful for older patients or pediatric populations requiring extended monitoring.
Collectively, these studies showcase the clinical versatility of optical techniques, which may serve as adjuncts or alternatives to standard diagnostics—particularly where conventional methods are impractical or poorly tolerated. The expanding spectrum of clinical applications—from wearable functional monitoring (NIRS) to near-histological imaging (OCT), deeper vascular visualization (PAI), and precision pressure sensing (FOS)—positions optical modalities at the forefront of innovative bladder diagnostics. Nonetheless, continued technological innovation, cost reduction, and especially large, multicenter validation studies are needed to verify preliminary findings and facilitate widespread clinical adoption. Such efforts would accelerate the broader adoption and integration of these emerging modalities into standard clinical workflows.
Table 2 summarizes the principal findings, clinical implications, and limitations of key optical techniques, including wearable NIRS, OCT, PAI, and fiber-optic pressure sensors. The table outlines the study design, sample size, diagnostic performance (e.g., sensitivity and specificity), as well as the main advantages and limitations of each method. This comparison clarifies the potential role of each modality as either a complement or an alternative to existing clinical approaches.
DISCUSSION
This review underscores the promise of optical diagnostics for lower urinary tract disorders, providing real-time physiological data without the invasiveness of conventional cystoscopy or UDS. Notably, wearable NIRS and FOS technologies align well with global trends toward remote patient monitoring, while OCT and PAI show clear potential for improving lesion detection accuracy. However, several important challenges remain to be addressed:
Technological Refinement
Motion artifacts
Optical signal quality is highly susceptible to patient movement, which can introduce noise and degrade measurement accuracy—particularly in ambulatory or pediatric settings. Ongoing development of advanced motion-compensation algorithms, real-time filtering techniques, and robust signal stabilization is a critical area of research.
Limited depth penetration
Although OCT and PAI deliver high spatial resolution, their ability to penetrate beyond superficial bladder layers is restricted. While NIRS and PAI can image somewhat deeper regions, achieving both substantial depth and optimal resolution remains a technical trade-off that continues to drive innovation.
Clinical Validation and Regulatory Approval
Developmental stages of optical modalities
These technologies range from early proof-of-concept and preclinical work to pilot trials and, in some cases, validated clinical applications. Many cited studies—such as those involving early FOS prototypes or certain PAI systems—remain at the preclinical stage, often limited to small-scale animal or ex vivo research. Pilot human studies, including those for wearable NIRS and single-center OCT, have shown early promise but require validation in larger, more diverse cohorts.
Early-stage trials frequently encounter challenges with patient recruitment and may suffer from selection bias due to limited, single-center enrollment. These issues highlight the necessity for broader, multicenter collaborations to ensure robust, generalizable data.
Large-scale studies
A major barrier to clinical translation is the lack of standardized protocols and multicenter clinical trials that rigorously demonstrate safety, accuracy, and cost-effectiveness relative to gold-standard diagnostics. To date, most published studies are small, proof-of-concept efforts lacking population-level validation. Therefore, large, multicenter trials are vital to reducing bias and confirming pilot findings. Standardized methodologies established through such studies will strengthen the evidence base for both regulatory approval and clinical adoption.
Regulatory hurdles
The regulatory environment for medical devices—especially those employing novel modalities or AI interpretation—is complex and varies internationally. Without clearly defined pathways for U.S. Food and Drug Administration or Conformité Européenne Mark approval, many promising prototypes remain restricted to research contexts. Collaborative efforts among clinicians, engineers, regulatory bodies, and industry partners are essential for overcoming these barriers and establishing unified standards for optical diagnostics in urology.
In addition to regulatory challenges, adoption of these modalities—especially in low-resource settings—is constrained by economic and infrastructural barriers. Advanced imaging systems like OCT and PAI require costly equipment, reliable power, and trained personnel, which are resources often lacking in such environments. Further obstacles include the absence of standardized device interfaces, inconsistent manufacturing, and the lack of universal reimbursement codes. To enable equitable, scalable implementation, cost-effectiveness analyses and strategies for broad device distribution must be prioritized.
Real-world use and reimbursement potential
Even after technical and regulatory barriers are overcome, reimbursement remains uncertain. Demonstrating clinical utility and cost-effectiveness through health economic studies will be essential for obtaining insurance coverage and driving widespread clinical adoption.
Wearable and Home-Based Integration
The principal advantage of optical technologies is their compatibility with wearable, wireless, and remote monitoring systems. Wearable NIRS and FOS devices have already proven feasible for home-based bladder monitoring, enabling longitudinal assessment outside traditional clinic visits. Coupling these devices with AI-driven analytics can provide personalized feedback, alert patients and clinicians to early dysfunction, and optimize disease management strategies.
Moreover, as telemedicine and decentralized care models become more prevalent, integrating optical diagnostics with smartphone-connected, cloud-based platforms could enable remote consultations and ongoing data sharing. The resulting closed-loop feedback—incorporating patient-reported outcomes, real-time bladder metrics, and automated analytics—has the potential to greatly enhance patient engagement and clinical decision-making.
Despite challenges, optical modalities are well-positioned to reshape bladder diagnostics and care. When integrated with telemedicine, wearable sensors could support semicontinuous or on-demand assessments across diverse patient populations, including those with neurogenic or UAB who require ongoing surveillance. Additionally, distinguishing idiopathic OAB from other symptomatically similar disorders such as painful bladder syndrome/interstitial cystitis may benefit from adjunctive diagnostic insights, as these conditions demonstrate distinct urodynamic profiles despite overlapping symptoms [37].
Comparative Performance and Modality-Specific Trade-offs
While each optical modality offers distinct clinical advantages, their respective strengths and limitations must be considered. NIRS is notable for its portability and seamless integration into wearable devices, enabling functional hemodynamic monitoring during daily activities. However, it lacks detailed anatomical resolution and is susceptible to motion artifacts and tissue variability. OCT delivers excellent spatial resolution and microstructural imaging but is limited by shallow penetration (<2 mm) and its primary suitability for procedural, not wearable, applications.
PAI offers a compromise between penetration depth and resolution, visualizing vascular and hypoxic features several centimeters deep, which is useful in tumor assessment, but requires pulsed lasers, acoustic coupling, and complex calibration, increasing operational costs and complexity. FOSs excel at high-frequency pressure monitoring with minimal discomfort, though they remain semi-invasive and provide only functional—not anatomical or metabolic—data, making them more suitable as complementary rather than stand-alone solutions.
Accordingly, clinical implementation should be tailored to the diagnostic objective: NIRS for ambulatory monitoring, OCT for high-resolution surface lesion assessment, PAI for deeper vascular pathology, and FOSs for detailed pressure tracking. No single modality is universally optimal, and future hybrid systems may combine multiple techniques to mitigate individual limitations.
Proposed Clinical Pathway for LUTD Management
We propose a simplified clinical decision tree (Fig. 3) outlining how clinicians might incorporate NIRS, OCT, PAI, and FOSs into the routine management of LUTD. This framework addresses common scenarios, from initial screening to anatomical evaluation:
Initial functional screening
Patients presenting with typical LUTD symptoms (e.g., urgency, frequency, incontinence) may undergo initial noninvasive monitoring with NIRS, especially when OAB is suspected, potentially reducing the need for immediate invasive diagnostics.
Structural and functional assessment
For patients with hematuria or suspected bladder lesions, OCT or PAI can be used to visualize both superficial and deeper tissue layers. OCT is especially effective for detecting subtle lesions like CIS, while PAI offers both structural and functional evaluation of deeper bladder wall abnormalities.
CONCLUSIONS AND FUTURE PERSPECTIVES
The emergence of optical technologies for diagnosing lower urinary tract disorders represents a significant advance in urological practice, providing a patient-centered alternative to conventional modalities such as cystoscopy, UDS, and ultrasound. While traditional approaches retain clinical value, their invasiveness, episodic nature, and limited real-world applicability hinder frequent monitoring—especially in patients with chronic or neurologically complex voiding dysfunctions [9, 10, 38, 39].
Optical techniques, particularly NIRS, OCT, PAI, and FOS, address many of these gaps. These modalities offer noninvasive, dynamic assessment of bladder function, tissue oxygenation, and vascular changes, resulting in improved patient comfort and enabling more frequent diagnostic evaluation [12-22].
Wearable NIRS systems have demonstrated feasibility in real-world settings, allowing continuous monitoring of detrusor muscle activity and bladder filling cycles in patients with OAB [23-26]. OCT, integrated into cystoscopy platforms, improves visualization of urothelial architecture and enhances detection of CIS, surpassing traditional white-light endoscopy in certain contexts [17-20]. Additionally, these techniques provide insights into the progression of NB and UAB [6-8, 40]. Photoacoustic imaging enables deeper visualization of angiogenic activity and hypoxia in bladder tumors [21, 33, 34], while FOSs provide high-resolution pressure monitoring with reduced discomfort compared to conventional catheters [3, 20, 23].
Despite these advances, readiness for broad clinical adoption varies by modality. Some systems remain at the prototype or preclinical stage, while others (such as select OCT platforms) are approaching validated clinical use. Regulatory frameworks, standards, and reimbursement pathways continue to evolve and sometimes lack clarity, slowing broader implementation. Large, multicenter trials comparing these technologies to established gold standards are urgently needed to confirm safety, accuracy, and cost-effectiveness, and to accelerate routine adoption.
From a healthcare delivery perspective, optical systems have the potential to reduce procedural risks, enable continuous monitoring, and integrate seamlessly with telemedicine—trends that support the shift toward preventive, patient-centered, and decentralized care [24-27]. Addressing persistent technical challenges, including motion artifacts, limited penetration depth, and interuser variability, is vital for achieving standardized, reliable performance [12, 14, 23]. In parallel, rigorous cost-effectiveness analyses are needed to support insurance coverage and government funding, further facilitating real-world implementation.
In conclusion, optical diagnostics have the potential to transform bladder assessment by combining functional and structural insights with flexible, patient-centric designs. The proposed clinical pathway offers a structured approach for incorporating these advanced optical techniques into LUTD management, enabling more precise, patient-friendly, and continuous bladder health monitoring. As interdisciplinary collaboration and systematic validation increase, these technologies may redefine precision medicine in urology, ultimately improving patient outcomes and quality of life through the establishment of a continuous, home-based model of bladder care.
PDF Links
PubReader
ePub Link
XML Download
Full text via DOI
Download Citation
Print
