Harmonic Generation in Tissue with Matrix Arrays for 4D Cardiac THI

Combining 4D echocardiography and tissue harmonic imaging (THI) may improve image quality and consequently diagnosis of heart disease. Beamforming considerations such as methodology for sampling the volume with ultrasound beams, beam shape, and the magnitude of the 2
^nd
harmonic component generated in tissue are important for 4D cardiac THI. No studies have yet investigated harmonic generation produced by diagnostic matrix arrays for 4D cardiac THI. The objective of the present work is to evaluate harmonic generation in tissue by matrix arrays by considering different 4D beamforming approaches with a numerical model based on the KZK equation. We evaluated the spatial extent, level of the produced 2
^nd
harmonic component in tissue, and the volume rate of 4D cardiac THI performed by different beamforming approaches. We used different source pressures (applied voltage to the elements) that resulted in peak MI=1.9 in tissue. Beamforming approaches with shallow foci produced the highest peak 2
^nd
harmonic in tissue (1.2 MPa) yet lowest volume rate (1.7 Hz). Beamforming approaches with deep foci produced the highest 2
^nd
harmonic at imaging depth of 150 mm (0.3 MPa). The volume rate of 4D cardiac THI performed with focused ultrasound, PWI, and DWI is 1.7-20, 81, and over 1275 Hz, respectively.