A. E. Kerdok, S. M. Cotin, M. P. Ottensmeyer, A. M. Galea, R. D. Howe, and S. L. Dawson, "Truth Cube: Establishing Physical Standards for Real Time Soft Tissue Simulation," Medical Image Analysis, vol. 7, pp. 283-291, 2003. (.pdf)

Paper submitted to Caesar's International Workshop on Deformable Modeling and Soft Tissue Simulation (October 2001)

• Geometry: 8cm x 8cm x 8cm cube with a 7x7 array of 1.58 mm diameter balls spaced 1 cm apart on a rigid 10 cm x 10 cm x 2.75 mm Acrylic base  

From left to right: Schematic of Cube, Mold and Resulting Cube, and the end "product": Truth Cube
 
 
• Materials: RTV6166 2 part Silicone Rubber mixed in 30:70 proportion and 1.58 mm diameter Teflon balls
• Stiffness of unbeaded rubber = 798 N/m (indentation testing)
• Stiffness of beaded rubber = 780 N/m  (2% difference which is less than the standard deviation of the unbeaded stiffness (4.4%))
• Poisson's Ratio assumed to be 0.5
• Young's modulus = 14.9 kPa (small strain (<8 %) uniaxial compression testing)
• Testing:
• Tests were perfromed under nearly frictionless conditions (oil was used to coat the surface of the rubber)
• All tests were performed at Massachusetts General Hospital in a General Electric LightSpeed CT scanner

Uniaxial Compression (strains less than 19%)

Spherical Indentation (nominal strains up to 30%)

 
• Uniaxial Compression Test:
• Set-up:

       From left to right: Test Set-up at rest, Test set-up loaded, Back view of loaded test setup, Investigator fun :)
 
 
• Raw CT Scans: uncompressed , 5% strain (4 mm compression), 12.5 % strain (10 mm compression),

18.25% strain (14.6 mm compression) 
• Our Segmented pictures: All beads tracked over 4 strains, Vector field of first and last bead locations, Center slice displacement vector field
• Table of internal bead displacement: Center Slice (including FEM comparison), All bead positions
• Photos of the top of the cube under the three strains: 5%, 12.5%, 18.25%

 

 
 
 
 
 
 
 
 
 
 
 
 
 

• Spherical IndentationTest:
• Set-up:
•    Same as above, but used 2.54 cm diameter Delrin sphere mounted on a 4.5 cm long 1.9 cm diameter Delrin cylinder. Also added 4 extra registration spheres at corners.

Test set-up with wieght of plate loading the sphere (22% nominal strain)


Test set-up for 36% nominal strain and Result before scan :(





• Raw CT Scans: unloaded ,
                             22 % nominal strain (1.8 cm indentation) ,
                               and 30% nominal strain (2.9 cm indentation).
• Segmented pictures:
            Surface rendering: 
 
Allthe beads tracked over the 3 scans, displacmenet vectors for center slice with CT superimposed, and displacment vectors of both center slices.
• Table of internal bead displacement for all 3 indentations: Table

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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