Technological advances in near infrared spectroscopy devices and parameters measured: examples from clinical studies of the urologic system

Background: Since the original application of NIRS to study the bladder, a series of advances have enabled the urologic system to be more comprehensively studied, and range of devices now provide previously unavailable physiologic measurements. As in other fields, this evolution follows progressive improvements in the technology, the availability of new components and materials, and construct of novel software and algorithms. Methods: Review of the literature describing NIRS monitoring of the urologic system (bladder, pelvic floor, urinary sphincter, brain). Results: The advent of lasers and development of fiberoptics established NIRS as a viable entity, and allowed transcutaneous monitoring of physiologic changes in the bladder detrusor muscle during spontaneous voiding. Small light emitting diodes which traded depth of penetration for portability led to wearable devices when combined with wireless capability; emitter and photodiode refinement, spatially resolved geometry, and software and algorithm development spawned the current generation of compact, robust multipotential devices, including a transvaginal interface able to quantify reoxygenation recovery in pelvic floor muscles, and interrogate the urinary sphincter. Functional NIRS allows brain mediated neural activity linked to bladder sensation and control of voiding to be mapped in real time during evaluation of voiding dysfunction; simultaneous fNIRS during fMRI is also feasible. Wearable devices linked to wireless peripherals enable serial monitoring at home of voiding parameters once only available in the hospital setting; exploration of artificial intelligence will further expand the urologic relevance of NIRS. Conclusions: The technological advances evident in urologic applications of NIRS mirror those occurring in other fields.