A method for real-time three-dimensional (3-D) ultrasound imaging using a mechanically scanned linear phased array is proposed. The high frame rate necessary for real-time volumetric imaging is achieved using a sparse synthetic aperture beamforming technique utilizing only a few transmit pulses for each image. Grating lobes in the two-way radiation pattern are avoided by adjusting the transmit element spacing and the receive aperture functions to account for the missing transmit elements. The signal loss associated with fewer transmit pulses is minimized by increasing the power delivered to each transmit element and by using multiple transmit elements for each transmit pulse. By mechanically rocking the array, in a way similar to what is done with an annular array, a 3-D set of images can be collected in the time normally required for a single image.
To evaluate the association between mammographic density and breast cancer risk, a simple, observer-assisted technique called interactive thresholding was developed that allows reliable quantitative assessment of mammographic density with use of a computer workstation. Use of this technique helps confirm that mammographic density is one of the strongest risk factors for breast cancer and is present in a large proportion of breast cancer cases. The strong 'From Imaging Research.
The development of ultrasound backscatter microscopy (UBM) is described together with initial clinical and biological applications. UBM is essentially an extension of the powerful B-mode backscatter methods developed for clinical imaging in the 3-10-MHz frequency range. The development of new high sensitivity transducers in the 40-100-MHz range now permits visualization of tissue structures with resolution approaching 20 mum and a maximum penetration of approximately 4 mm. The performance characteristics and trade-offs of these new polymer and ceramic devices are reviewed, and the implementation of high-frequency imaging systems is described. Initial clinical applications of UBM include ophthalmic, skin, and intravascular imaging. Examples of images and progress in these areas are presented. The biological application of UBM is illustrated by studies of drug uptake in living tumor spheroids. Significant increases in backscatter levels resulting from drugs targeting oxic and hypoxic cell populations are demonstrated.
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