Key Performance Parameters of a Contemporary Diagnostic Ultrasound Transducer

Abstract

A recently published paper in the European Journal of Echocardiography entitled “High Incidence of Defective Ultrasound Transducers in Use in Routine Clinical Practice” by Mattias Martensson, et al, focused on the testing of 676 transducers located at 32 hospitals that were currently being used to obtain diagnostic information.1 Probes were tested using a commercially available device that examines various performance parameters of each crystal that make up the array (also referred to as an acoustic stack).2 A graphic of the test display is shown in Figure 1. The results of their testing of the 676 probes showed that almost 40% of the probes had some form of performance inhibiting problem ranging from dead or weak elements, breaks in the cable wires, to delaminating lenses. The paper also contained a clinical case study where a suspected patent ductus arteriosus (PDA) was missed because of a then unknown defect in the transducer (the patient was re-scanned at a later time with a known good probe and the PDA was easily visualized). Diagnostic ultrasound is generally considered a “safe” imaging modality because of its non-ionizing radiation conductance. However, if the transducer (also known as a probe or scanhead) being used is not performing optimally due to some unrecognized problem, and subsequently leads to missing pathology or understating the degree of pathology, then it is in fact not as safe an imaging modality as we might have previously thought. Given the mounting evidence seen in the literature that it is clinically unwise to use transducers without first knowing their operational condition, what are the key performance parameters associated with contemporary multi-element composite transducers and how can they be tested by clinical engineers to ensure the transducer is operating both safely and effectively? Before addressing that question we should take a step back and look at the basic construction of an array and how the array is actually excited by the ultrasound system for use in the two basic modes of ultrasound: B-mode imaging and Doppler (Doppler includes all derivative modes such as color flow, pulsed wave, and continuous wave). Contemporary composite arrays are composed of: 1) a piezoelectric (PZ) material that provides the necessary transduction of mechanical to electrical energy and vice versa, and 2) a supporting polymer that isolates the element while shaping the mechanical and electrical properties of the PZ elements. Typical general imaging linear and curved linear arrays have between 128 and 192 elements. It is the physical distribution of Key Performance Parameters of a Contemporary Diagnostic Ultrasound Transducer