Phase aberration correction for ultrasound imaging guided extracorporeal shock wave therapy (ESWT): Feasibility study

Image guidance of extracorporeal shock wave therapy (ESWT) is important to enhance its efficacy while lowering pain in patients. Real-time ultrasound imaging is an appropriate modality for image guidance, but its image quality substantially reduces due to severe phase aberration from the different speed of sound between soft tissues and a gel pad, which is utilized to control a therapeutic focal point in ESWT. This paper presents a phase aberration correction method for improving image quality in the ultrasound imaging guided ESWT. To correct an error from phase aberration, a time delay based on a two-layer model with different speeds of sound is calculated for dynamic receive beamforming. For the phantom and in vivo studies, a rubber type gel pad (i.e., 1400 m/s) with a specific thickness (3 or 5-cm) was placed on the top of soft tissue and full scanline RF data were acquired. In the phantom study, with phase aberration correction, image quality was highly increased compared to image reconstructions with a fixed speed of sound (i.e., 1540 or 1400 m/s), i.e., 1.1 vs. 2.2 and 1.3 mm in -6dB lateral resolution and 0.64 vs. 0.61 and 0.56 in contrast-to-noise ratio (CNR), respectively. From an in vivo musculoskeletal (MSK) imaging, the phase aberration correction method provided a clearly improved depiction of muscle fibers in a rectus femoris region. These results indicate that the proposed method enables effective imaging guidance of ESWT by improving image quality of ultrasound imaging in real-time.