Preclinical feasibility of continuous bladder volume monitoring using wearable near-infrared spectroscopy versus ultrasound in Yucatan minipigs

Patients with neurogenic bladder lack reliable tools for continuous bladder-volume monitoring. We evaluated bladder-volume estimates from a wearable near-infrared spectroscopy (NIRS) patch against a clinical ultrasound residual-urine scanner in a Yucatan minipig feasibility model. Secondary assessments included reproducibility across attachment conditions and short-term tissue safety. Two female minipigs underwent repeated controlled bladder filling under general anesthesia. A single-use suprapubic NIRS patch and ultrasound scanner were tested at matched time points. Primary endpoints were Pearson correlation with infused volume and mean absolute error (MAE), with uncertainty estimated by cluster bootstrap. Across eight infusion cycles in the smaller animal and fifteen in the larger animal, NIRS tracked bladder filling closely ( r = 0.97–0.99), with MAE within the range observed for ultrasound. In head-to-head testing, NIRS versus ultrasound showed MAE 23.1 ± 4.7 versus 32.5 ± 12.2 mL in the smaller animal and 31.1 ± 9.7 versus 30.4 ± 14.5 mL in the larger animal. Accuracy improved with firmer fixation and degraded with inferior displacement. Short-term histopathology showed no device-related injury. This small, anesthetized, saline-infusion study provides feasibility-stage evidence that wearable NIRS can estimate bladder volume under standardized conditions. Further validation in larger, awake, and pathological cohorts is required.