Ultrasound urodynamic studies (US-UDS): noninvasive estimation of detrusor pressure through ultrasound

Objective: Urodynamic studies (UDS) are vital for evaluating bladder function but require invasive catheterization to measure detrusor pressure (Pdet). Our purpose is to report on technical developments toward a noninvasive and accurate estimation of Pdet through ultrasound, a technique we refer to as Ultrasound Urodynamic Study (US-UDS). Approach: The proposed US-UDS technique produces an estimate of Pdet by using ultrasound to induce and track elastic waves that propagate within and around the bladder wall. Key components of the US-UDS processing include: an ultrasound sequence with dense time sampling; an empirical correction accounting for deviation from a Lamb wave dispersion model; and constrained optimization for Pdet estimation. US-UDS analysis for estimation of Pdet was applied to 533 distinct data points collected from 3 human subjects undergoing concurrent urodynamics study (UDS). Concordance analysis was used to evaluate agreement between US-UDS and UDS measures of Pdet while response operator characteristic analysis was used to evaluate US-UDS for detection of detrusor activity (parameterized as UDS Pdet >15 cmH2O). Main Results: US-UDS was able estimate Pdet within 10 cmH2O and 5 cmH2O of UDS measurements with coverage probabilities of 95.7% and 68.8% respectively. Furthermore, US-UDS was able to detect UDS Pdet measurements greater than 15 cmH2O with a sensitivities and specificities of 0.99 and 0.83 using a fixed threshold (>15 cmH2O for US-UDS) and 1.0 and 0.93 for an optimized threshold (> 11.08 cmH2O for US-UDS). Significance: Our results show that the technical developments of US-UDS put forth in this work are able produce accurate and useful estimates of Pdet as compared to traditional UDS. Although additional research with a large number of subjects is needed to fully characterize the clinical utility of US-UDS, the developments and results from this work demonstrate that clinically useful non-invasive measurements of Pdet are feasible from ultrasound measurements.