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Ultrasound imaging has been used for decades for medical and industrial imaging. Ultrasound in the range of 1-10 MHz has also been used for evaluating tissue properties characterization for many years. Recently, use of low frequency (audio range) vibration for medical diagnosis and evaluation of tissue properties has attracted increased attention. It has been shown that such vibration can reveal important information about tissue mechanical properties that are related to tissue pathology. We use the radiation force of ultrasound to vibrate tissue at low (kHz) frequency range, and record the resulting acoustic response to produce images that are related to the stiffness of the tissue. This method is tested on human breast, liver, heart valve, and arteries. Results show that small microcalcifications can be detected in human breast, calcium buildups can be seen in arteries, and mass lesions can be detected in liver tissues. In these tests, the vibration frequency ranged from 5 to 50 kHz. Another application of the radiation force method is studying solid structures through modal analysis. [ABSTRACT FROM AUTHOR]

A model for vibration of large bones, such as a femur, is presented. Using this model, the resonance frequencies of an intact, partially fractured, and bonded (healed) bone are determined. To measure bone resonance frequencies experimentally, a non-contact method for bone excitation and motion detection is developed. This method uses the radiation force of focused amplitude-modulated ultrasound to exert a vibrating force directly, and remotely, on excised bone. The vibration frequency is varied in the range of interest to induce resonances in the bone. The resulting bone motion is detected by a laser vibrometer and the resonance frequencies are determined. Experiments are conducted on excised rat femurs and resonance frequencies of intact, fractured, and bonded (simulating healed) bones are measured. The experiments demonstrate that the fractured bone exhibits a lower resonance frequency than the intact bone, and the resonance frequency of the bonded bone approaches that of the intact bone. These results are in agreement with the predictions of the model. It is concluded that the resonance frequencies of bone can be used as markers of its integrity, and the radiation force method may be used as a remote and noninvasive tool for studying one fracture. [ABSTRACT FROM AUTHOR]