20 MHz ultrasound array for medical imaging from design to image evaluation

Over the last decade, ultrasound imaging has been successfully demonstrated at 20 MHz and above using single elements transducer. High frequency arrays are only commercially available below 20 MHz and arrays with higher frequencies are still at the research stage. However, a 20 MHz center frequency exhibits a very interesting trade-off between sensitivity or penetration and expected image resolution. This paper presents the acoustical design, fabrication and evaluation of a 128 elements ultrasound array based on piezo-composite technology, with a 210 μm pitch and a 3 mm elevation aperture. Electro-acoustic characterization is performed on the full array and an average center frequency of 20 MHz is achieved as well as state of the art homogeneity characteristics. Bandwidth, insertion loss results, directivity measurement and cross coupling performance are disclosed. The transducer array is subsequently integrated in a probe housing, interconnected and interfaced to an ultrasound system. Finally, images covering various applications are presented and discussed from a clinical perspective