Doppler ultrasound detection of tissue motion and flow generated by external energy

Doppler ultrasound is a standard tool for measuring and imaging tissue motion, especially blood flow. Tissue motion and flow can also be induced and controlled with the application of external energy sources. The resulting motion in the soft tissue can be used to study tissue elasticity, where abnormal values in regions may indicate a tumorous or other types of diseased tissue. Ultrasound energy can also cause acoustic streaming in liquid. If streaming is generated and detected in blood, it may help distinguish unclotted from clotted blood or stagnant blood from solid tissue, when conventional B-mode imaging can not make the distinction.; The method of dynamic elastometry was developed to study the detection of High-Intensity Focused Ultrasound (HIFU) lesions in liver. This technique involves applying a low-frequency vibration (≤5 Hz) to the liver sample and measuring the resulting velocity pattern using a spectral Doppler technique. The stiffened lesions were detected by the change of velocity gradient in tissue. The measurements of lesion position and length in twenty liver samples agreed well with the independent geometric measurements. The relative stiffness between the lesions and normal liver tissue was estimated by the velocity gradient ratio. The results correlated strongly with the Young's modulus measurements.; The technique of ultrasound rheology was developed to improve the diagnosis of hematomas. This method uses color Doppler detection of HIFU generated acoustic streaming for distinguishing between stirred blood, stagnant but unclotted blood, and clotted blood. An in vitro study was conducted in tubular models to investigate the effect of geometric setup, blood coagulation and applied intensity on streaming detection. A balloon hematoma model was next developed and tested in an in vivo environment to simulate abdominal hematomas. It was found that a derated spatial peak temporal average intensity (I_SPTA.d) of 30 W/cm2 was needed to generate color Doppler detectable streaming in stirred blood. Streaming was also detected in stagnant blood but at higher intensities (I_SPTA.d > 78 W/cm2). In clots, streaming was not detected even at I_SPTA.d of 300 W/cm2. Both dynamic elastometry and ultrasound rheology techniques may provide new tools for diagnostic ultrasound.