Reconstructive ultrasound elasticity imaging for renal transplant diagnosis: kidney ex vivo results.

It may be possible to diagnose and monitor scarring, inflammation and edema in transplant kidney using reconstructive ultrasound elasticity imaging. Kidney elasticity is expected to change dramatically with scar, and to a lesser degree, with acute inflammation and edema. The hypothesis that changes in kidney elasticity can be imaged using a clinical ultrasound scanner was experimentally tested with an ex vivo canine kidney model, and results on a single pair of kidneys are reported in this paper. A cross-linking agent affected kidney elasticity both globally and locally. Elasticity changes were monitored with accurate estimates of internal displacement and strain followed by Young's modulus reconstruction. The results of this study strongly suggest that ultrasound elasticity imaging can detect elasticity changes in complex structures such as the kidney. Moreover, it has the potential to become an important clinical tool for renal transplant diagnosis.

High-resolution elasticity imaging for tissue engineering.

An elasticity microscope provides high resolution images of tissue elasticity. With this instrument, it may be possible to monitor cell growth and tissue development in tissue engineering. To test this hypothesis, elasticity micrographs were obtained in two model systems commonly used for tissue engineering. In the first, strain images of a tissue-engineered smooth muscle sample clearly identified a several hundred micron thick cell layer from its supporting matrix. Because a one-dimensional mechanical model was appropriate for this system, strain images alone were sufficient to image the elastic properties. In contrast, a second system was investigated in which a simple one-dimensional mechanical model was inadequate. Uncultured collagen microspheres embedded in an otherwise homogeneous gel were imaged with the elasticity microscope. Strain images alone did not clearly depict the elastic properties of the hard spherical cell carriers. However, reconstructed elasticity images could differentiate the hard inclusion from the background gel. These results strongly suggest that the elasticity microscope may be a valuable tool for tissue engineering and other applications requiring the elastic properties of soft tissue at high spatial resolution (75 microm or less).

Measuring the elastic modulus of small tissue samples.

Independent measurements of the elastic modulus (Young's modulus) of tissue are necessary step in turning elasticity imaging into a clinical tool. A system capable of measuring the elastic modulus of small tissue samples was developed. The system tolerates the constraints of biological tissue, such as limited sample size (< or = 1.5 cm3) and imperfections in sample geometry. A known deformation is applied to the tissue sample while simultaneously measuring the resulting force. These measurements are then converted to an elastic modulus, where the conversion uses prior calibration of the system with plastisol samples of known Young's modulus. Accurate measurements have been obtained from 10 to 80 kPa, covering a wide range of tissue modulus values. In addition, the performance of the system was further investigated using finite element analysis. Finally, preliminary elasticity measurements on canine kidney samples are presented and discussed.