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Noninvasive Evaluation of Bladder Wall Mechanical Properties as a Function of Filling Volume: Potential Application in Bladder Compliance Assessment.

Nenadic I, Mynderse L, Husmann D, Mehrmohammadi M, Bayat M, Singh A, Denis M, Urban M, Alizad A, Fatemi M - PLoS ONE (2016)

Bottom Line: Of particular interest is the shear modulus of bladder wall at different volumes, which we hypothesize, is similar to measuring the compliance characteristics of the bladder.The ex vivo studies showed a high correlation between the UBV parameters and direct pressure measurement (R2 = 0.84-0.99).The results of UBV on healthy volunteers, performed without catheterization, were comparable to a compliant bladder patient.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, United States of America.

ABSTRACT

Purpose: We propose a novel method to monitor bladder wall mechanical properties as a function of filling volume, with the potential application to bladder compliance assessment. The proposed ultrasound bladder vibrometry (UBV) method uses ultrasound to excite and track Lamb waves on the bladder wall from which its mechanical properties are derived by fitting measurements to an analytical model. Of particular interest is the shear modulus of bladder wall at different volumes, which we hypothesize, is similar to measuring the compliance characteristics of the bladder.

Materials and methods: Three experimental models were used: 1) an ex vivo porcine model where normal and aberrant (stiffened by formalin) bladders underwent evaluation by UBV; 2) an in vivo study to evaluate the performance of UBV on patients with clinically documented compliant and noncompliant bladders undergoing UDS; and 3) a noninvasive UBV protocol to assess bladder compliance using oral hydration and fractionated voiding on three healthy volunteers.

Results: The ex vivo studies showed a high correlation between the UBV parameters and direct pressure measurement (R2 = 0.84-0.99). A similar correlation was observed for 2 patients with compliant and noncompliant bladders (R2 = 0.89-0.99) undergoing UDS detrusor pressure-volume measurements. The results of UBV on healthy volunteers, performed without catheterization, were comparable to a compliant bladder patient.

Conclusion: The utility of UBV as a method to monitor changes in bladder wall mechanical properties is validated by the high correlation with pressure measurements in ex vivo and in vivo patient studies. High correlation UBV and UDS in vivo studies demonstrated the potential of UBV as a bladder compliance assessment tool. Results of studies on healthy volunteers with normal bladders demonstrated that UBV could be performed noninvasively. Further studies on a larger cohort are needed to fully validate the use of UBV as a clinical tool for bladder compliance assessment.

No MeSH data available.


Related in: MedlinePlus

(a) The bladder wall displacement as a function of time and distance. Group velocity is calculated from the slope of the dashed line. (b) A 2D FFT of the bladder wall displacement results in the k-space representation of the measured UBV data. (c) Lamb wave dispersion curve of the measured data and the analytical fit.
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pone.0157818.g002: (a) The bladder wall displacement as a function of time and distance. Group velocity is calculated from the slope of the dashed line. (b) A 2D FFT of the bladder wall displacement results in the k-space representation of the measured UBV data. (c) Lamb wave dispersion curve of the measured data and the analytical fit.

Mentions: The procedures for estimating bladder wall UBV parameters of group velocity and shear modulus are outlined in Fig 2. In order to analyze motion along the bladder wall, a line is drawn along the bladder wall from the B-mode image. Fig 2A shows the bladder displacement as a function of time (t) and distance (x) calculated using a cross-spectral analysis [17]. The group velocity (cg) is obtained by tracking the displacement peaks and calculating the slope (cg= dx/dt) of the line. A two-dimensional Fast Fourier Transform (FFT) of the displacement data yields the k-space map shown in Fig 2B, whose coordinates are frequency (f) and wave number (k). In Fig 2C, a peak-searching approach is employed to obtain the experimental Lamb wave phase velocity (c = k/f) at each frequency, i.e. the Lamb wave dispersion curve. The Lamb wave dispersion equation was fit to the dispersion data to estimate the shear modulus of elasticity (μ). The thickness of the bladder wall was estimated from the B-mode ultrasound image.


Noninvasive Evaluation of Bladder Wall Mechanical Properties as a Function of Filling Volume: Potential Application in Bladder Compliance Assessment.

Nenadic I, Mynderse L, Husmann D, Mehrmohammadi M, Bayat M, Singh A, Denis M, Urban M, Alizad A, Fatemi M - PLoS ONE (2016)

(a) The bladder wall displacement as a function of time and distance. Group velocity is calculated from the slope of the dashed line. (b) A 2D FFT of the bladder wall displacement results in the k-space representation of the measured UBV data. (c) Lamb wave dispersion curve of the measured data and the analytical fit.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920425&req=5

pone.0157818.g002: (a) The bladder wall displacement as a function of time and distance. Group velocity is calculated from the slope of the dashed line. (b) A 2D FFT of the bladder wall displacement results in the k-space representation of the measured UBV data. (c) Lamb wave dispersion curve of the measured data and the analytical fit.
Mentions: The procedures for estimating bladder wall UBV parameters of group velocity and shear modulus are outlined in Fig 2. In order to analyze motion along the bladder wall, a line is drawn along the bladder wall from the B-mode image. Fig 2A shows the bladder displacement as a function of time (t) and distance (x) calculated using a cross-spectral analysis [17]. The group velocity (cg) is obtained by tracking the displacement peaks and calculating the slope (cg= dx/dt) of the line. A two-dimensional Fast Fourier Transform (FFT) of the displacement data yields the k-space map shown in Fig 2B, whose coordinates are frequency (f) and wave number (k). In Fig 2C, a peak-searching approach is employed to obtain the experimental Lamb wave phase velocity (c = k/f) at each frequency, i.e. the Lamb wave dispersion curve. The Lamb wave dispersion equation was fit to the dispersion data to estimate the shear modulus of elasticity (μ). The thickness of the bladder wall was estimated from the B-mode ultrasound image.

Bottom Line: Of particular interest is the shear modulus of bladder wall at different volumes, which we hypothesize, is similar to measuring the compliance characteristics of the bladder.The ex vivo studies showed a high correlation between the UBV parameters and direct pressure measurement (R2 = 0.84-0.99).The results of UBV on healthy volunteers, performed without catheterization, were comparable to a compliant bladder patient.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota, United States of America.

ABSTRACT

Purpose: We propose a novel method to monitor bladder wall mechanical properties as a function of filling volume, with the potential application to bladder compliance assessment. The proposed ultrasound bladder vibrometry (UBV) method uses ultrasound to excite and track Lamb waves on the bladder wall from which its mechanical properties are derived by fitting measurements to an analytical model. Of particular interest is the shear modulus of bladder wall at different volumes, which we hypothesize, is similar to measuring the compliance characteristics of the bladder.

Materials and methods: Three experimental models were used: 1) an ex vivo porcine model where normal and aberrant (stiffened by formalin) bladders underwent evaluation by UBV; 2) an in vivo study to evaluate the performance of UBV on patients with clinically documented compliant and noncompliant bladders undergoing UDS; and 3) a noninvasive UBV protocol to assess bladder compliance using oral hydration and fractionated voiding on three healthy volunteers.

Results: The ex vivo studies showed a high correlation between the UBV parameters and direct pressure measurement (R2 = 0.84-0.99). A similar correlation was observed for 2 patients with compliant and noncompliant bladders (R2 = 0.89-0.99) undergoing UDS detrusor pressure-volume measurements. The results of UBV on healthy volunteers, performed without catheterization, were comparable to a compliant bladder patient.

Conclusion: The utility of UBV as a method to monitor changes in bladder wall mechanical properties is validated by the high correlation with pressure measurements in ex vivo and in vivo patient studies. High correlation UBV and UDS in vivo studies demonstrated the potential of UBV as a bladder compliance assessment tool. Results of studies on healthy volunteers with normal bladders demonstrated that UBV could be performed noninvasively. Further studies on a larger cohort are needed to fully validate the use of UBV as a clinical tool for bladder compliance assessment.

No MeSH data available.


Related in: MedlinePlus