2012 Proceedings - International Tissue Elasticity Conference

009 IN VITRO COMPARISON OF ULTRASOUND BASED ELASTOGRAPHY TECHNIQUES
Stéphanie Franchi–Abella 1 , Caroline Ellie 2 , Jean–Michel Correas 2 .
1 Radiopediatrie, Kremlin–Bicêtre Hospital, 78, rue du Général Leclerc 94270 Le Kremlin–Bicêtre,
FRANCE; 2 Radiologie Adulte, Necker Hospital, 149 rue de Sèvres, Paris, FRANCE.
Background: Imaging viscoelastic properties of tissues in vivo has been an important challenge and
research field for the last few decades. Today elastography imaging is available with various techniques
from several ultrasound diagnostic imaging manufacturers. These elastography techniques are based on
two different physical principles: strain and Shear Wave Velocity (SWV).
Aims: The purpose of this study was to assess the performance of these two techniques in vitro on a
calibrated elasticity phantom.
Methods: A skilled ultrasound operator performed all acquisitions on a tissue–mimicking phantom
developed for elastography calibration. This phantom contains spherical inclusions of known elasticity
embedded in a homogeneous background material (BG) (CIRS 049A Elasticity Phantom Elastography
Phantom, USA). With strain elastography, alternative compression and decompression cycles were
applied with adequate pressure (using quality index when available). With SWV, no pressure was applied
by the transducer on the phantom. Two inclusions had a lower elasticity than the BG: Inclusion
1=12±3kPa, Inclusion 2=18±4kPa. Two inclusions had a higher elasticity than the BG; Inclusion
3=44±6kPa, Inclusion 4=74±10kPa. The BG’s elasticity was 30±5kPa. The imaging protocol was
performed using high frequency linear transducers on four different inclusions. Quantitative and
semi–quantitative measurements were acquired using the ratio between the BG and each inclusion.
Based on the elasticity of each inclusion and BG provided by the phantom manufacturer, the theoretical
ratios were calculated. These theoretical ratios were compared to the ratios obtained with measurements
obtained using the different elastography techniques. For the SWV technique, the absolute values of
inclusions and BG were also compared with the phantom values. Five manufacturers were enrolled in
this study (named A, B, C, D and E). A, B and C used the strain principle to estimate tissue elasticity
while D used both principles and E only SWV.
Results: Table 1 provides the relative difference (in percent) between measured elasticity ratios for all
manufacturers/probes and the theoretical ratio for the different inclusions for both strain and SWV.
Table 2 provides the relative difference (in percent) between measured elasticity values for manufacturers
D and E and the theoretical elasticity values for the different inclusions and BG.
Manufacturer–Probe–Technique Inclusion 1 (%) Inclusion 2 (%) Inclusion 3 (%) Inclusion 4 (%)
A–Probe1–Strain 22.50 4.10 –19.00 –17.0
B–Probe1–Strain 60.00 21.00 –12.70 –7.7
B–Probe2–Strain 26.25 14.17 –12.40 –13.7
B–Probe3–Strain 17.50 8.33 –16.50 –23.0
C–Probe1–Strain 25.00 11.70 –18.50 –19.8
D–Probe1–Strain 1779.00 493.00 –47.00 –82.0
D–Probe1–SWV 53.00 31.00 –20.00 –13.0
E–Probe1–SWV –37.00 –8.30 8.2. 1.2
Table 1: Relative difference (in percent) between measured elasticity ratios for all manufacturers/probes and the
theoretical ratio for the different inclusions for both strain and SWV.
Manufacturer–Probe–Technique Inclusion 1 (%) Inclusion 2 (%) Inclusion 3 (%) Inclusion 4 (%) BG (%)
D–Probe1–SWV –35.2 –30.3 –39.0 10.0 –33
E–Probe1–SWV –31.7 –23.3 –1.4 1.3 –8
Table 2: Relative difference (in percent) between measured elasticity values for manufacturers D and E and the
theoretical elasticity values for the different inclusions and BG.
Conclusions: Our study shows both techniques are adequate when assessing whether or not an
inclusion is harder/softer than its surrounding tissue. However, strain stiffness estimation presents high
variability depending on the probe/system, while SWV based elastography is more accurate to assess
both absolute and contrast stiffness especially for system E.
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