Background
SUI is the most common type of urinary incontinence symptomatic in 15 million adult women in the U.S. Current treatment strategies either have limitations, are ineffective, or lack applicability to a wide range of patients. Transurethral ultrasound thermal therapy is proposed to induce collagen regeneration to tighten surrounding supportive tissue structures near the urethra for treatment of SUI. Objective of this study is to develop the transurethral ultrasound applicator and evaluate in the GU tract of a large animal model.
Methods
Transurethral ultrasound applicators with bilaterally sectored 3.5mm OD x 10-15 mm long tubular transducers, operating at 6.5 MHz and within an expandable 7 mm urethral cooling balloon, were designed for urethral insertion and placement to precisely deliver thermal energy to discrete regions of endopelvic fascia, pubourethral ligaments, and supportive structures lateral to the urethra. A series of acute (n=4) and survival at 3-4 days (n=6) and 30 days (n=2) experiments were performed in ewes to assess the thermal dosimetry, localization of thermal energy and assess thermal damage and tissue effect. Ultrasound imaging was used to verify catheter placement at both 2 cm and 5 cm from the bladder neck in order for two trials to be performed per animal. Various applied power levels and duration of therapy delivery were evaluated. Post procedure, either acute or after survival, the urethra and surrounding tissues were harvested, gross observations of thermal damage performed, TTC staining, and fixed for histological evaluation with H&E staining.
Results
Both acute and survival in vivo experiments demonstrated that for a duration of 2 minutes at 3-4 Watts acoustic energy delivered at two longitudinal positions, laterally bi-directional in the tissues surrounding the urethra, can penetrate up to 10-15 mm. The histopathology analysis demonstrated thermally treated regions in the connective tissues beyond the urethra, with limited to no thermal damage to the urethral mucosa or the vaginal wall. Analysis of the tissue sections and histology of the survival animals indicates tissue healing, neocollagenisis, and regeneration in the treated region.
Conclusion
These preliminary results suggest catheter-based therapeutic ultrasound may be delivered transurethrally, and used for collagen regeneration and tissue tightening in the female endopelvic fascia, while preserving the urethral mucosa. These dual-sectored transurethral applicators may provide a novel and fast minimally-invasive treatment alternative to the traditional surgical treatment for stress urinary incontinence.