Radio-frequency (RF) Bladder Monitor

Spinal cord injury (SCI) presents significant long-term challenges for affected individuals, among which bladder dysfunction is a leading concern. Neurogenic lower urinary tract dysfunction (NLUTD), commonly referred to as neurogenic bladder dysfunction, may result in urinary retention, incomplete bladder emptying, urinary incontinence, urinary tract infections (UTIs), bladder distension, urinary reflux, renal complications, and reduced quality of life. Current bladder management approaches, including clean intermittent catheterization (CIC), indwelling catheterization, and external collection methods, may be associated with substantial time burden, complications, excessive bladder filling or incomplete emptying, and poor adherence. Studies have also shown that improving bladder function remains one of the highest rehabilitation priorities among individuals with SCI.

This study investigates the feasibility of a wearable radio-frequency (RF)-based bladder monitor operating in the microwave (MW) frequency range for non-invasive bladder monitoring and bladder volume estimation. The proposed system is intended to measure and track bladder volume and may ultimately support future development of discreet alerts indicating when the bladder is appropriately full and it is time to void. RF/MW sensing approaches provide several potential advantages for bladder monitoring applications because they are non-invasive, low-cost, safe for repeated use within established exposure limits, and compatible with wearable device designs.

Previous computational and experimental studies investigating RF/MW approaches for bladder-state detection have demonstrated proof-of-concept feasibility; however, many earlier studies relied on simplified anatomical models and limited experimental conditions. More recent work by the investigators demonstrated bladder-state discrimination using realistic anatomical pelvic models and preliminary measurements in healthy volunteers. This study includes measurements in both healthy volunteers and individuals with SCI who self-catheterize.

The objectives of the study are:

i) to provide a clinical proof-of-concept demonstration of MW bladder monitoring and bladder volume quantification; and ii) to provide data regarding the short-term functionality, utility, and comfort of the wearable MW bladder monitoring prototype.

The study will enroll adult healthy volunteers and adult participants with SCI who use self-catheterization for bladder management. Following informed consent, participants with SCI may complete questionnaires related to bladder dysfunction and bladder-related quality of life, including the Neurogenic Bladder Symptom Score Short Form (NBSS-SF).

Participants will undergo bladder filling and voiding cycles during the study visit. At the beginning of the session, participants will be asked to void their bladder using their usual voiding or catheterization method. For participants in whom pregnancy is possible, urine pregnancy testing may be performed prior to RF measurements. Ultrasound bladder scans will be performed at empty and full bladder states and will serve as reference measurements for bladder volume estimation. Voided urine volumes will also be collected during voiding phases.

The MW bladder monitoring prototype will be placed externally on the lower pelvic region by study personnel. Up to six sensors may be used. Sensors will be secured using adhesive bandages or wrap-style fixation methods. No skin preparation, gels, or invasive procedures are required. MW measurements will be collected automatically approximately every five minutes while the bladder fills naturally. Participants may rest or perform sedentary activities during the measurement period. Measurements will continue until bladder fullness is reached or the participant requests to void. The bladder filling and emptying process may then be repeated for a second cycle during the same study visit.

Collected MW measurement data will be analyzed to investigate signal trends and the feasibility of the technology. Planned analyses include:

• Bladder fullness classification through comparison of MW signal trends between non-full and full bladder states;
• Bladder volume quantification using raw measurement data and reconstructed radar image data;
• Comparison of MW-based bladder volume estimates with ultrasound-estimated bladder volumes and voided urine volumes.

Exploratory analyses will evaluate signal trends across the measured frequency range to select optimal frequency points, measurement variability, and sex-based differences in MW measurements. Participant and clinician feedback surveys will additionally be used to assess device comfort, usability, and utility for bladder monitoring applications.

As a final remark, this pilot feasibility study is intended to generate preliminary clinical data supporting further development and optimization of wearable MW bladder monitoring technology and may support future larger clinical investigations aimed at improving bladder management for individuals living with bladder dysfunction, including neurogenic bladder associated with SCI. The investigational device is considered low risk. The device is non-invasive and uses low-power RF/MW signals for sensing and monitoring purposes only.