Strain imaging of corneal tissue with an ultrasound elasticity microscope.
OBJECTIVE
We hypothesize that high-resolution elasticity measurements can guide corrective refractive surgery of the cornea. Elasticity measurements would improve surgical outcomes by adding biomechanical information not used in existing clinical nomograms. As an initial investigation, we determined the usefulness and evaluated the ability of our ultrasound elasticity microscope by measuring strain ex vivo in an intact porcine eye globe.


METHODS
Strain was predicted with a finite element model guided by direct mechanical measurements of corneal elasticity. Next, a porcine cornea was deformed with a slitted plate while being imaged with ultrasound. For high spatial resolution, the ultrasound elasticity microscope uses a 50 MHz transducer with a 1.4 f/number. It produces high-quality conventional ultrasonic B-scans over large thicknesses by confocal processing. Strain was calculated from tracking speckle in these images after deformation. This technique is compatible with in vivo measurements.


RESULTS
Compressional and expansional deformations were the same order of magnitude from -3.5% to as great as +3.5%. Strain imaging indicated the stroma expanded into the slit of the deformation plate while Bowman's layer compressed. This bipolar variation within a specimen is unusual. Within the stroma, a variation of strain with depth was measured suggesting a distribution of elasticity. Results compared favorably with the finite element model.


CONCLUSIONS
An ultrasound elasticity microscope can produce high-resolution strain images throughout the corneal depth. Various layers with different elastic properties appeared as different strains in the images.
Hollman
Kyle W
KW
Department of Biomedical Engineering University of Michigan, Ann Arbor 48109-2125, USA.
Emelianov
Stanislav Y
SY
Neiss
Jason H
JH
Jotyan
Gagik
G
Spooner
Gregory J R
GJ
Juhasz
Tibor
T
Kurtz
Ron M
RM
O'Donnell
Matthew
M
D000818:Animals; D003315:Cornea / Q000000981:diagnostic imaging* / Q000502:physiology*; D004548:Elasticity; D008853:Microscopy / Q000295:instrumentation*; D013314:Stress, Mechanical; D013552:Swine; D014463:Ultrasonography / Q000295:instrumentation*