Automated Compression Device for Viscoelasticity Imaging

Abstract

Non-invasive measurement of tissue viscoelastic properties is gaining more attention for screening and diagnostic purposes. Recently, measuring dynamic response of tissue under a constant force has been studied for estimation of tissue viscoelastic properties in terms of retardation times. The essential part of such a test is an instrument that is capable of creating a controlled axial force and is suitable for clinical applications. Such a device should be lightweight, portable and easy to use for patient studies to capture tissue dynamics under external stress. In this paper we present the design of an automated compression device for studying the creep response of materials with tissue-like behaviors. The device can be used to apply a ramp-and-hold force excitation for a predetermined duration of time and it houses an ultrasound probe for monitoring the creep response of the underlying tissue. To validate the performance of the device, several creep tests were performed on tissue-mimicking phantoms and the results were compared against those from a commercial mechanical testing instrument. Using a second order Kelvin-Voigt model and surface measurement of the forces and displacements, retardation times T1 and T2 were estimated from each test. These tests showed strong agreement between our automated compression device and the commercial mechanical testing system, with an average relative error of 2.9% and 12.4 %, for T1 and T2 respectively. Also, we present the application of compression device to measure local retardation times for four different phantoms with different size and stiffness.

Automated In Vivo Sub-Hertz Analysis of Viscoelasticity (SAVE) for Evaluation of Breast Lesions

“…The compression force measurement and imaging setup explained in [16] was used to create axial force as well as acquiring ultrasonic radiofrequency data for in vivo studies. A schematic of the setup is shown in Fig.…”

“…The edges around the two plates were open to allow free motion of the ultrasound gel during compression. Four load cells were mounted at each corner of the extension plate (between the two plates) for simultaneous measurement and control of the desired force profile as explained in [16]. …”

“…Stress-relaxation and creep-compliance tests are two standard mechanical testing methods suitable for this range of frequency. While stress-relaxation is not feasible for in vivo scenarios (due to lack of an accurate estimate of the stress distribution), creep-like tests can be performed with the aim of a force control mechanism that mimics a ramp-and-hold stress excitation while monitoring internal strain field via ultrasonic speckle tracking algorithms [9], [16]. The preliminary study in a group of patients with non-palpable lesions has shown that malignant and benign masses present different viscoelastic features [17] when employing a creep-like test with limited force feedback information [18].…”

Viscoelastic biomarker for differentiation of benign and malignant breast lesion in ultra- low frequency range

“…The inclusion part of the phantom was made with 25.14 grams of gelatin (Sigma-Aldrich, St. Louis, MO), 60 ml propylene glycol (Sigma-Aldrich, St. Louis, MO), and 4 grams cellulose (ultrasound scattering; Sigma-Aldrich) in distilled water for a total volume of 300 ml. The background part of the phantom was made with 32.3 grams gelatin, 30 ml Vanicream Lite (Pharmaceutical Specialties, Inc., Rochester, MN), 6 grams cellulose (ultrasound scatterer; Sigma-Aldrich) and potassium sorbate (preservative; Sigma-Aldrich) in distilled water with a total volume of 600 ml 30 . The inclusion phantom dimensions were 7.5 cm × 5.5 cm × 5.5 cm (L × W × H), with the cylindrical inclusion having a diameter of 1.5 cm.…”

“…In this paper, we introduce the noninvasive, Loss Angle Mapping (LAM) method, which is based on measuring the local displacement and strain behaviors under constant stress as a function of frequency. Technical details were explained in our previous work 30 . The LAM method can monitor the viscoelastic properties of the tissue with high resolution due to its high accuracy in displacement measurement at the micrometer level.…”