The methodology of this research can be divided into two parts.
Fig.3 summarises the flow of the methodology of this study.
1.
Phantom construction
1.1 Phantoms for calibration of elasticity
The phantoms were constructed to give guidelines as to how much gelatine needs to be added to produce phantoms within required range of elasticity.
Each phantom was constructed without any internal inclusions in them.
Different amount of gelatines (8 to 24 g with 4 g increasing step) were dissolved in 150 ml of water and mixed together with 0.5 g of calcium carbonate (CaCO3) which acts as scatterers in a beaker.
The solution was heated on a hot plate and stirred continuously until everything dissolved into molten gelatine as shown in Fig.4.
The molten gelatine was then poured into containers and left to set as shown in Fig.5.
1.2 Phantom for comparison between SWE and gold standard
Five spherical inclusions with different elasticity were constructed using different amount of gelatine (8 to 24 g with 4 g increasing step) mixed with 0.5 g of CaCO3 and 150 ml of water.
2 hemispherical moulds were submerged into the red molten gelatine and clamped together to form the spherical inclusions as shown in Fig.6.
The inclusions were then incorporated into the phantom to represent different elasticity of lesions.
The final product of the phantom was shown in Fig.7.
1.3 Phantoms for investigations of factors affecting SWE
A phantom consisting of inclusions of varying sizes,
elasticity and depth was constructed to explore the factors affecting elasticity measurement.
The calibration phantom was constructed according to the schematic diagram shown in Fig.8 and the specifications were listed in Table 1. In addition,
another phantom was made to compare the elasticity of spherical and cylindrical inclusions.
Five cylindrical and spherical inclusions of different elasticity were embedded in a homogenous background as shown in Fig.9
2.
Elasticity measurements
2.1 With SWE
The elasticity of the phantoms was first measured using SWE.
All the phantoms were scanned with the SWE probe and the SWE colour map was displayed in real time.
The ROI was placed on the inclusions and the value of its elasticity was displayed as shown in Fig.10.
2.2 With the gold standard
The gold standard to verify the SWE measurement was a calibrated material microtester system (model 5848,
Instron Co,
USA).
After the measurements with SWE,
the inclusions were extracted from the phantom and cut into cylindrical shapes (the Instron can only test cylindrical samples) to be tested on the Instron.
A graph of stress vs.
strain was displayed in real time where the initial slope gives the Young’s modulus of the tested samples as shown in Fig.11.
3.
Comparison of SWE with the Gold Standard
The elasticity of each phantom measured by the SWE and the Instron were presented in graphical forms and their relationships were studied and observed by means of statistical analysis.