Volume 14, Issue 1, December 2013
Index of content:
- Biomedical Ultrasound/Bioresponse to Vibration
14(2013); http://dx.doi.org/10.1121/1.3681323View Description Hide Description
Current SR estimation methods that use speckle tracking technique are based on conventional delay-and-sum (D&S) imaging method with multiple transmissions, which causes skewed image of moving object resulting in inaccurate SR. To overcome the problem, a method to combine high frame rate imaging method (HFR) with speckle tracking technique was proposed. Using only one or a few transmissions for each image; the new method can obtain a snapshot of moving targets, avoiding the skewing problem in D&S method that uses 91 transmissions. Studies, with simulated and experimental echo data respectively, were performed to verify the method. The new method is compared with D&S imaging method also using one transmission so that the skewing problem existing for D&S with multiple transmissions can be avoided. Both plane wave (PW) and limited diffraction beam (LDB) were studied for the HFR imaging method. Results show that the new method has comparable velocity errors and SR accuracy with the D&S method when using one transmission. Moreover, the new method can measure high velocity in application such as blood flow measurement. Using a full view of the heart image, SR can be localized and then estimated.
14(2013); http://dx.doi.org/10.1121/1.3700239View Description Hide Description
As known, ultrasonic standing waves can be used to concentrate particles and biological cells into separated bands. Acoustic separation in plane standing waves is limited to particles of few microns and larger. This presentation concerns using acoustic radiation force (RF) produced by cylindrical standing waves, for detection of high-density standing waves in pressure nodes and low-density particles (fat globules) in antinodes. Theoretical calculations show that in a cylindrical ultrasonic resonator RF near the central node can exceed the force at the periphery by about 20 times. In a cylindrical standing wave, RF can induce movement of bacteria with a speed of a few mm/s at frequency of 2 MHz and pressure amplitude of 100 kPa, whereas the speed of bacteria in a plane standing wave does not exceed 0.2 mm/s under the same conditions. The cylindrical standing wave system performance was tested for the E. coli bacteria in water and for a multi-component system containing fat globules and somatic cells in milk. Dilute suspensions of bacteria or fat globules were concentrated by at least two orders of magnitude.