Efficient three-dimensional cylindrical-geometry ultrasound imaging

A number of new imaging modalities collect data from cylindrical platforms. In vivo imaging needles and intravascular ultrasound imaging catheters are examples of this geometry, where imager rotation and translation parallel to the cylinder axis are the only allowed motions. Efficient three-dimensional ultrasound image formation in these cases can be challenging when the aperture is small and/or highly curved. A frequency-domain imaging algorithm is obtained by approximating the free-space point spread function in cylindrical coordinates and obtaining its Fourier transform by analogy with the equivalent problem in Cartesian coordinates. We further propose an effective use of limited aperture by placing a focused transducer across the aperture, thereby creating a virtual source at the focus which is treated as a real, unfocused source by the imaging algorithm. This approach retains the simplicity and potential angular resolution of a small single element, yet permits full use of the available probe aperture and a higher energy output. Computer simulations and experimental ultrasonic results with wire targets show that this imaging technique attains the theoretical resolution dictated by the operating wavelength and transducer characteristics. [Work supported by NIH CA 079179.]