Fast orthogonal row-column electronic scanning experiments and comparisons

Three-dimensional ultrasound imaging presents the technical challenges of addressing large numbers of elements in 2-D array transducers. Top-orthogonal-to-bottom electrode (TOBE) 2-D transducer arrays can simplify addressing but typical imaging methods with such arrays enable only one-way focusing in azimuth and elevation. Here, experimental results are reported for the fast orthogonal row-column electronic scanning (FORCES) imaging scheme implemented on a 64 × 64 element bias-sensitive electrostrictive relaxor TOBE array. The FORCES imaging scheme involves transmitting along rows to form an elevational transmit focus, while biasing columns with bias patterns selected from a Hadamard matrix. Channel data from columns is received and decoded for synthetic-aperture beamforming in azimuth. This scheme offers two-way azimuthal focusing. The volumetric imaging experiments were conducted using wire phantoms as well as on rat hearts using two different TOBE imaging schemes: Scheme 1 (transmit focusing in elevation and receive focusing in azimuth) and FORCES. Wire phantom experiments at a depth of 2 cm showed an azimuthal resolution of 0.42 and 0.31 mm with Scheme 1 and FORCES, respectively. We also compared the elevational imaging performance of these imaging schemes with a mechanically scanned linear array. The FORCES imaging displayed an elevational resolution of 0.46 mm at a depth of 2 cm, and the linear array displayed an elevational resolution of 0.72 cm. The novel TOBE array architecture and FORCES imaging scheme thus enable high-quality 3-D ultrasound imaging using only row-column addressing and bias control and may prove an enabling technology for many future 3-D imaging platforms.