TABLE II.

Theoretical Comparison of Imaging Methods.

	Flash	CPA	SPA	SPA with Hadamard coding
Number of firings per frame	1	16 471a	64	64
Maximum achievable frame rateb	29 615 fps	1.80 fps	463 fps	463 fps
Transmit/Receive focusing	Unfocused/Dynamic	Fixed/Dynamic	Dynamic/Dynamic	Dynamic/Dynamic
SNR gain from beamformingc	$N_{\text{TX}}·\sqrt{N_{\text{RX}}}$ (54 dB)d	$N_{\text{TX}}·\sqrt{N_{\text{RX}}}$ (54 dB)	$\sqrt{N_{\text{TX}}}·\sqrt{N_{\text{RX}}}$ (36 dB)	$N_{\text{TX}}·\sqrt{N_{\text{RX}}}$ (54 dB)

CPA = classic phased array; SPA = synthetic phased array; SNR = signal-to-noise ratio; N_TX = number of transmit elements (64); N_RX = Number of receive elements (64).

^aBeam sampling interval of 1° was assumed in both θ- and ϕ-directions, with viewing angle of 90° in θ and 180° in ϕ.

^bMaximum achievable frame rate was calculated based only on the ultrasound time of flight, assuming a 2.6-cm imaging depth.

^cSNR gain of the reconstructed image, over the SNR of a single-element pulse-echo A-scan.

^dValid only in on-axis region.