Design and Testing of a Single-Element Ultrasound Viscoelastography System for Point-of-Care Edema Quantification

Abstract

Management of fluid overload in patients with end stage renal disease represents a unique challenge where clinical practice still lacks accurate and objective measurement methods. Currently, peripheral edema is subjectively assessed by palpation of the patient's extremities, ostensibly a qualitative indication of tissue viscoelastic properties. New robust quantitative estimates of tissue fluid content would allow clinicians to better guide treatment, minimizing reactive treatment decision making. Ultrasound viscoelastography (UVE) can be used to estimate strain in viscoelastic tissue, deriving material properties that can help guide treatment. We are developing and testing a simple, low-cost UVE system using a single-element imaging transducer that is simpler and less computationally demanding than array-based systems. This benchtop validation study tested the UVE system feasibility by measuring the mechanical properties of a tissue-mimicking material under large strains. We generated depth-dependent creep curves and viscoelastic parameter maps of time constants and elastic moduli for the Kelvin model of viscoelasticity. During testing, the UVE system performed well with mean UVE-measured strain matching standard mechanical testing with maximum absolute errors less than or equal to 4%. Motion tracking showed high correlation and signal-to-noise ratios, indicating that the system is reliable.

Methods of ex vivo analysis of tissue status in vascularized composite allografts

“…A limited number of novel developments strive to leverage ultrasound to quantify observations of edema and to measure the depth of pitting edema [ 173 – 175 ]. In a clinical study, the relationship between surface imprint depth, circumferential measurement, and tissue thickness revealed that depth of surface imprints correlate with subcutaneous tissue thickness by a coefficient of 0.736 [ 174 ].…”

“…In a clinical study, the relationship between surface imprint depth, circumferential measurement, and tissue thickness revealed that depth of surface imprints correlate with subcutaneous tissue thickness by a coefficient of 0.736 [ 174 ]. In a similar manner, Pitre and colleagues considered the viscoelasticity of tissue as a measure of edema status and simplified hardware by designing a single-element ultrasound transducer [ 175 ]. Graphing tissue viscoelasticity across simulated edema conditions indicated depth dependency, therefore providing enhanced quantification of superficial edema.…”

Bedside Evaluation of Edema: A simple technique for quantitative evaluation of an important clinical sign

“…(14) Water immersion volumetry has been considered the criterion standard, but even this has been called into question by techniques such as optoelectronic volumetry. (15) Bioimpedance spectroscopy(16) (BIS) or ultrasound viscoelastography (17) offer novel techniques, but require sophisticated technology and presumably high cost. There is one important proviso regarding these techniques: none except for direct edema testers is able to determine whether a patient actually has edema: "volumetry does not quantify edema but rather the short-term variations that re ect changes in edema".…”

Existing and Potential Applications of Elastography for Measuring the Viscoelasticity of Biological Tissues In Vivo

“…However, as the properties of biological tissue were progressively understood, a variety of theoretical frameworks were developed and integrated with earlier elastography techniques. In recent years, although the name of elastography remains largely unchanged (some studies have adopted the term "viscoelastography" [11,12]), it has become more common that quantitative values of various moduli, as we will discuss in detail in later sections, include information of material viscoelasticity.…”