Analysis of the Time and Phase Delay Resolutions in Ultrasound Baseband I/Q Beamformers

The ultrasound baseband in-phase/quadrature beamformer (IQBF) has been widely employed in medical ultrasound imaging to reduce the amount of channel data or to decrease the data rate of the beamforming process. The aim of this study is to assess the effect of the time and phase delay compensation accuracies on the IQBF and thereby to suggest the criteria for selecting the delay resolutions of the IQBF.

Mathematical models of the gain loss (GL) and sidelobe level (SL) in closed form are suggested, and the relationships between the parameters (time and phase delay resolutions of the IQBF and the signal bandwidth) and the errors (GL and SL) are investigated. The performance of the IQBF is compared with that of the traditional radio-frequency beamformer (RFBF). Simulation and phantom and in vivo experimental results are shown to corroborate the theoretical analysis.

Theoretical analysis and simulation and experimental results show that a phase delay resolution with a quantization step of 2π/64 is sufficient for phase compensation and that a time delay resolution with a sampling rate of 4f₀ and 2f₀ in the IQBF is sufficient for data with a -6 dB bandwidth of 50% and 25%, respectively, for similar performance as the RFBF with a sampling rate of 16f₀, where f₀ is the center frequency of the ultrasound signal.

The suggested criteria have the potential to be used for designing an efficient IQBF satisfying the desired specifications and beamforming accuracy.