The objective of this project is to form high-resolution speckle-free quantitative ultrasound images throughout the volume of the breast in vivo by using a hemispheric transducer array for measurements and inverse scattering for image reconstruction. Achievement of this objective will show the clinical feasibility of using non-- ionizing ultrasound imaging to screen for breast cancer without the use of ionizing x-rays and will provide a foundation for risk-free examination of the breast for cancer detection. The proposed methods will overcome x- ray mammography limitations such as low resolution of contrast in dense breasts, compression-induced deformation of anatomy and discomfort in patients, and poor imaging of breasts with implants. Success would ultimately change the way screening for breast cancer is performed and significantly improve detection, diagnosis, and monitoring for recurrence or response to treatment of breast cancer. In the proposed system, ultrasound waves are transmitted into the breast, waves scattered by the breast are received, and the measurements of the scattered waves are stored for subsequent off-line reconstruction of images. The envisioned parallel architecture of the transmit and receive channels associated with each transducer element permits the collection of scattering from the in vivo breast during a short time, e.g., about two seconds, to avoid image-degrading motion artifacts. The planned use of off-line processing by available computing resources for image reconstruction circumvents the need to acquire and configure computer facilities. The hemispheric array is comprised of multiple planar facets so that conventional flat-wafer fabrication technology can be used to implement the array. The system has transmit electronics, receive electronics, and a transmit-receive switch associated with each element. A control unit communicates with the electronics. Image reconstruction begins by using measured pulse waveforms to estimate the gross properties (i.e., contour, average speed of sound, and average slope of attenuation) of the breast. From these properties, background scattering is determined and subtracted from the measured scattering to obtain residual scattering linearly related to tissue variations. The scattering measurements are in the near field but the coefficients of the temporal Fourier transform of the scattered signals emulate far field measurements in local regions that fill a hemisphere of Fourier spatial-- frequency space with components of the spatial Fourier transform of the local tissue variations. These measurements are extrapolated to obtain values of the Fourier spatial-frequency components in the opposite hemisphere. The entire sphere of spatial-frequency components is used to form weighted products of fields that are based on the initial estimate of breast characteristics and are then iteratively refined. The resulting images show sound speed and attenuation slope throughout the breast volume.
The objective of this project is to form significantly improved ultrasonic images throughout the volume of the breast in vivo by using a novel imaging system. Achievement of this objective will show the clinical feasibility of using non-ionizing ultrasound imaging to screen for breast cancer without the use of ionizing x-rays, provide a foundation for risk-free examination of the breast for cancer detection, and overcome x-ray mammography limitations such as low resolution of contrast in dense breast, compression induced deformation of anatomy and discomfort in patients, and poor imaging of breasts with implants. Success would ultimately change the way screening for breast cancer is performed and significantly improve detection, diagnosis, and monitoring for recurrence or response to treatment of breast cancer.
