A thin, high penetration depth phased array transducer with a metamaterial acoustic backing for cardiac imaging with X-ray computed tomography compatibility

Coronary artery disease (CAD) is one of the leading causes of death globally. Computed tomography coronary angiography (CTCA) is a non-invasive procedure for the diagnosis of CAD. However, CTCA is negatively affected by cardiac motion and thus requires the use of ECG data to ensure the CT system only acquires data during periods of cardiac quiescence. Ultrasound-based cardiac gating can improve the reliability of CTCA by providing more accurate cardiac quiescence detection. To identify cardiac quiescence and thus the time periods for CT acquisition, a 92-element phased array ultrasound transducer was designed for CT compatibility. This array incorporates an acoustic metamaterial within its backing, enabling a thinner transducer with improved CT compatibility. The fabricated array has a bandwidth of 58% and SNR of 17.7 dB. Radiographic properties of the array were characterized using a clinical CT system, and ultrasound imaging performance was evaluated by acoustic characterization, phantom imaging, and in vivo imaging in one human volunteer. The developed array transducer could be useful for providing cardiac gating during CTCA imaging.