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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

An ultrasound array transducer is utilized to generate an ARF beam (push beam) on the bladder wall, generating an anti-symmetric Lamb wave displacement field.The displacement field is tracked by a pulse-echo detection beam (detect beam). In order to identify the bladder wall, a line is drawn along the bladder wall on the B-mode image. The displacement field is measured along this line. To obtain appropriate coupling between the transducer and skin surface above the bladder, standard ultrasound coupling gel (US gel) is utilized.
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pone.0157818.g001: An ultrasound array transducer is utilized to generate an ARF beam (push beam) on the bladder wall, generating an anti-symmetric Lamb wave displacement field.The displacement field is tracked by a pulse-echo detection beam (detect beam). In order to identify the bladder wall, a line is drawn along the bladder wall on the B-mode image. The displacement field is measured along this line. To obtain appropriate coupling between the transducer and skin surface above the bladder, standard ultrasound coupling gel (US gel) is utilized.

Mentions: The concept of UBV is to utilize an ultrasound array transducer to generate an ARF beam on the bladder wall (push beam) that excites anti-symmetric Lamb waves in Fig 1. Pulse-echo ultrasound (detect beam) is then used to track the motion of the Lamb wave in the bladder wall. We modeled the bladder wall as an incompressible, homogenous, isotropic solid plate submerged in an incompressible nonviscous fluid [16]. For an in vivo application, the urine below the bladder wall would satisfy the incompressible nonviscous fluid assumption. Meanwhile, the fascial-defined space above the bladder (mainly composing of mostly fluid and fat), has demonstrated minimal effects on the appropriateness of the Lamb wave model [15]. The anti-symmetric Lamb wave dispersion equation for such a geometry is [15,16]:4kL3βtanh(βh)=ks4+(ks2−kL2)tanh(kLh)(1)where , kL= ω/c is the Lamb wave number, ω is the angular frequency, c is the frequency dependent Lamb wave phase velocity, is the shear wave number, ρ is the tissue density, μ = c2/ ρ is the bladder wall shear modulus, and h is the half-thickness of the wall. While the surface of the bladder is curved, the pulse-echo technique (detect beam) measures the axial motion of the propagating shear wave, i.e., the component of tissue motion parallel to the excitation. To correct for the curvature of the bladder wall, the displacement vector x was constructed by recognizing the arc length x = rθ, where r is the radius of curvature and θ is the angle.


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)

An ultrasound array transducer is utilized to generate an ARF beam (push beam) on the bladder wall, generating an anti-symmetric Lamb wave displacement field.The displacement field is tracked by a pulse-echo detection beam (detect beam). In order to identify the bladder wall, a line is drawn along the bladder wall on the B-mode image. The displacement field is measured along this line. To obtain appropriate coupling between the transducer and skin surface above the bladder, standard ultrasound coupling gel (US gel) is utilized.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0157818.g001: An ultrasound array transducer is utilized to generate an ARF beam (push beam) on the bladder wall, generating an anti-symmetric Lamb wave displacement field.The displacement field is tracked by a pulse-echo detection beam (detect beam). In order to identify the bladder wall, a line is drawn along the bladder wall on the B-mode image. The displacement field is measured along this line. To obtain appropriate coupling between the transducer and skin surface above the bladder, standard ultrasound coupling gel (US gel) is utilized.
Mentions: The concept of UBV is to utilize an ultrasound array transducer to generate an ARF beam on the bladder wall (push beam) that excites anti-symmetric Lamb waves in Fig 1. Pulse-echo ultrasound (detect beam) is then used to track the motion of the Lamb wave in the bladder wall. We modeled the bladder wall as an incompressible, homogenous, isotropic solid plate submerged in an incompressible nonviscous fluid [16]. For an in vivo application, the urine below the bladder wall would satisfy the incompressible nonviscous fluid assumption. Meanwhile, the fascial-defined space above the bladder (mainly composing of mostly fluid and fat), has demonstrated minimal effects on the appropriateness of the Lamb wave model [15]. The anti-symmetric Lamb wave dispersion equation for such a geometry is [15,16]:4kL3βtanh(βh)=ks4+(ks2−kL2)tanh(kLh)(1)where , kL= ω/c is the Lamb wave number, ω is the angular frequency, c is the frequency dependent Lamb wave phase velocity, is the shear wave number, ρ is the tissue density, μ = c2/ ρ is the bladder wall shear modulus, and h is the half-thickness of the wall. While the surface of the bladder is curved, the pulse-echo technique (detect beam) measures the axial motion of the propagating shear wave, i.e., the component of tissue motion parallel to the excitation. To correct for the curvature of the bladder wall, the displacement vector x was constructed by recognizing the arc length x = rθ, where r is the radius of curvature and θ is the angle.

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