A multiple frequency array for improved diagnostic imaging

Cost and complexity of phased array diagnostic ultrasound imaging systems is related to the number of parallel channels during both transmit and receive. If the total numberofa ctive elements within a given aperture is reduced so that fewer parallel channels are required, grating lobes may result if the spacing of elements within the array is greater than one-half wavelength. These grating lobes may produce image ambiguities in the form of multiple images and reduced dynamic range. These grating lobes can, however, be reduced if transducers of large bandwidth are utilized. A novel broadband array is described which consists of two transducer arrays of different frequencies (one at 1.5 MHz, the other at 2.5 MHz) mounted one above the other. This method of construction avoids the usual compromise between sensitivity and bandwidth. Experiments indicate a reduction of 5 dB in the off-axis response in the transmit operation when compared to a single frequency array (2.5 MHz) with similar dimensions (16 elements within a 19.7-mm aperture). The routine diagnostic utilization of this array resulted in improved image quality in terms of reduced image artifacts and improved contrast as well as better target acquisition.