Hadamard encoded multi-pulses for contrast enhanced ultrasound imaging
Contrast enhanced ultrasound (CEUS) imaging is widely used in clinic to enhance blood flow signal using microbubbles (MBs). In conventional CEUS methods such as pulse inversion (PI), amplitude modulation (AM), and pulse inversion amplitude modulation (PIAM) (Fig. 1), two pulses are excited individually in each transmission event (i.e. TX #1 and #2). Pulses in TX #2 are modified based on pulses in TX #1 by changing pulse polarity (i.e. PI), amplitude (i.e. AM), or both (i.e. PIAM). Then the echo signals from both transmission events follow the designed recombination to selectively cancel the linear responses from tissue and amplify the nonlinear responses from the MBs. In this paper, we propose a new CEUS pulse sequence using Hadamard-encoded multi-pulses (HEM) with a fundamental bandpass filter (i.e., filter centered on transmit frequency). HEM emits two Hadamard coded pulses consecutively in each of the two CEUS transmission events, as opposed to conventional CEUS methods which emit individual pulses in two separate transmission events. HEM improves the MB responses by: 1) exciting the MBs with a longer transmit pulse; and 2) using the fast polarity change between the HEM coded pulses to excite strong nonlinear MB responses, further enhancing the contrast-to-tissue ratio (CTR) for HEM-CEUS imaging.
