Development of laser optoacoustic and ultrasonic imaging system for breast cancer utilizing handheld array probes

We describe two laser optoacoustic imaging systems for breast cancer detection based on arrays of acoustic detectors operated manually in a way similar to standard ultrasonic breast imaging. The systems have the advantages of standard light illumination (regardless of the interrogated part of the breast), the ability to visualize any part of the breast, and convenience in operation. The first system could work in both ultrasonic and optoacoustic mode, and was developed based on a linear ultrasonic breast imaging probe with two parallel rectangular optical bundles. We used it in a pilot clinical study to provide for the first time demonstration that the boundaries of the tumors visualized on the optoacoustic and ultrasonic images matched. Such correlation of coregistered images proves that the objects on both images represented indeed the same tumor. In the optoacoustic mode we were also able to visualize blood vessels located in the neighborhood of the tumor. The second system was proposed as a circular array of acoustic transducers with an axisymmetric laser beam in the center. It was capable of 3D optoacoustic imaging with minimized optoacoustic artifacts caused by the distribution of the absorbed optical energy within the breast tissue. The distribution of optical energy absorbed in the bulk tissue of the breast was removed from the image by implementing the principal component analysis on the measured signals. The computer models for optoacoustic imaging using these two handheld probes were developed. The models included three steps: (1) Monte Carlo simulations of the light distribution within the breast tissue, (2) generation of optoacoustic signals by convolving N-shaped pressure signals from spherical voxels with the shape of individual transducers, and (3) back-projecting processed optoacoustic signals onto spherical surfaces for image reconstruction. Using the developed models we demonstrated the importance of the included spatial impulse response of the optoacoustic imaging system.