High frame rate tri-plane echocardiography with spiral arrays: from simulation to real-time implementation

Major cardiovascular diseases are associated with (regional) dysfunction of the left ventricle. Despite the 3D nature of the heart and its dynamics, the assessment of myocardial function is still largely based on 2D ultrasound imaging thereby making diagnosis heavily susceptible to the operator's expertise. Unfortunately, to date, 3D echocardiography cannot provide an adequate spatio-temporal resolution in real-time. Hence, triplane imaging has been introduced as a compromise between 2D and true volumetric ultrasound imaging. However, tri-plane imaging typically requires high-end ultrasound systems equipped with fully populated matrix array probes embedded with expensive and little flexible electronics for two-stage beamforming. This paper presents an advanced ultrasound system for real-time, high frame rate, tri-plane echocardiography based on low element count sparse arrays, i.e. the so-called spiral arrays. The system was simulated, experimentally validated, and implemented for real-time operation on the ULA-OP 256 system. Five different array configurations were tested together with four different scan sequences, including multi-line and planar diverging wave transmission. In particular, the former can be exploited to achieve, in tri-plane imaging, the same temporal resolution currently used in clinical 2D echocardiography, at the expenses of contrast (-3.5dB) and signal-to-noise ratio (-8.7dB). On the other hand, the transmission of planar diverging waves boosts the frame rate up to 250 Hz, but further compromises contrast (-10.5dB), signal-to-noise ratio (-9.7dB), and lateral resolution (=46%). In conclusion, despite an unavoidable loss in image quality and sensitivity due to the limited number of elements, high frame rate tri-plane imaging with spiral arrays is shown to be feasible in real-time and may enable real-time functional analysis of all left ventricular segments of the heart.