Imaging the stiffness of the vitreous body with acoustic radiation force

Tissue elasticity estimation is a major topic of ultrasound research. While most research focuses on cancer detection, the authors have concentrated on the detection of mechanical changes in the vitreous body of the eye. These changes are believed to contribute to retinal detachment. Thus, an accurate method of imaging vitreous mechanical properties might enable identification of patients at high risk before the presentation of symptoms. The authors are developing a new method of vitreous imaging which attempts to image tissue stiffness by applying acoustic radiation force. Force is applied at either a single location or along a line, with resultant target displacements estimated from returned echoes. This approach yields the dynamic response of targets to the applied forces. Images can be formed of the maximum induced displacement, or the relative elasticity and relative viscosity found by fitting experimental data to the Voigt model. The authors present B-Mode, maximum displacement, relative elasticity, and relative viscosity images of tissue mimicking phantoms and an enzymatically modified porcine eye. Images show the expected correlation between material stiffness and measured displacement. The potential of radiation force imaging was further explored by using a clinical ultrasound system to interrogate a phantom. At 84 mW/cm/sup 2/ small displacements were visible in the B-Mode image, suggesting that measurable displacements may be generated at 50 mW/cm/sup 2/, the historical FDA ophthalmic power limit.