Improvement of spatial resolution of medical ultrasound images by constrained least-square method

Spatial resolution of medical ultrasound images is important for accurate observation of fine structures of living organs. Beamforming is a mandatory process for generation of ultrasonic images, and various adaptive methods have been developed for improvement of the performance of the ultrasonic beamformers. However, beamforming methods require access to ultrasonic echo signals received by individual transducer elements in an ultrasonic probe. In the present study, a method based on the constrained least-square method, which can be applicable to beamformed ultrasonic signals, was developed and evaluated by the phantom experiment. The axial and lateral resolutions evaluated as the widths at half maxima of an echo from a string target were improved from 0.24 mm and 0.59 mm to 0.11 mm and 0.34 mm, respectively, by the proposed method.