Viscoelastic Characterization of Soft Tissue-Mimicking Gelatin Phantoms using Indentation and Magnetic Resonance Elastography

Summary

This article presents a demonstration and summary of protocols of making gelatin phantoms that mimic soft tissues, and the corresponding viscoelastic characterization using indentation and magnetic resonance elastography.

Abstract

Characterization of biomechanical properties of soft biological tissues is important to understand the tissue mechanics and explore the biomechanics-related mechanisms of disease, injury, and development. The mechanical testing method is the most straightforward way for tissue characterization and is considered as verification for in vivo measurement. Among the many ex vivo mechanical testing techniques, the indentation test provides a reliable way, especially for samples that are small, hard to fix, and viscoelastic such as brain tissue. Magnetic resonance elastography (MRE) is a clinically used method to measure the biomechanical properties of soft tissues. Based on shear wave propagation in soft tissues recorded using MRE, viscoelastic properties of soft tissues can be estimated in vivo based on wave equation. Here, the viscoelastic properties of gelatin phantoms with two different concentrations were measured by MRE and indentation. The protocols of phantom fabrication, testing, and modulus estimation have been presented.

Introduction

Most of the soft biological tissues appear to have viscoelastic properties that are important to understand their injury and development^1,2. In addition, viscoelastic properties are important biomarkers in the diagnosis of a variety of diseases such as fibrosis and cancer^3,4,5,6. Therefore, the characterization of viscoelastic properties of soft tissues is crucial. Among the many characterization techniques used, ex vivo mechanical testing of tissue samples and in vivo

Protocol

1. Gelatin phantom preparation

1. Weigh gelatin, glycerol, and water according to Table 1. Mix the gelatin powder with water to obtain the gelatin solution.
   NOTE: The concentrations of the individual components for preparing the two phantoms are shown in Table 1. The higher the concentration of gelatin, the stiffer the phantom.
2. Heat the gelatin solution to 60 °C in a water bath. Add glycerol to the gelatin solution while maintaining the temperature.
   NOTE: Glycerol stabilizes gelatin mixtures by increasing their melting temperature and shear modulus¹⁷.
3. Stir....

Results

Following the MRE protocol, a clear shear wave propagation in the gelatin phantoms at 40 and 50 Hz were observed (Figure 3). The viscoelastic properties measured from MRE, and indentation tests are shown in Figure 4. The estimated G' and G" values at each testing for each phantom are summarized in Table 2. Following the indentation protocol, the viscoelastic properties of each phantom at each test point are summarized in Table 3.......

Discussion

Gelatin phantoms are commonly used as tissue-mimicking materials for testing and validation of algorithms and devices^{17,19,22,23,24,25,26,27}. One of the pioneering studies using the gelatin phantom to compare MRE and dynamic shear testing was presented by O.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
24-channel head & Neck coil	United Imaging Healthcare	100120	Equipment
3T MR Scanner	United Imaging Healthcare	uMR 790	Equipment
Acquisition board	Advantech Co	PCI-1706U	Equipment
Computer-Windows	HP	790-07	Equipment
Electromagnetic actuator	Shanghai Jiao Tong University		Equipment
Function generator	RIGOL	DG1022Z	Equipment
Gelatin	CARTE D’OR		Reagent
Glycerol	Vance Bioenergy Sdn.Bhd		Reagent
Indenter control program	custom-designed		Software; accessed via: https://github.com/aaronfeng369/FengLab_indentation_code.
Laser sensor	Panasonic	HG-C1050	Equipment
Load cell	Transducer Technique	GSO-10	Equipment
MATLAB	Mathworks		Software
Power amplifier	Yamaha	A-S201	Equipment
Voice coil electric motor	SMAC Corporation	DB2583	Equipment