Completely computer-focused ultrasound imaging. First clinical imaging results.
Completely computer-focused ultrasound imaging has been achieved using the UHB (ultrasound holographic B) method. This is a synthetic aperture method that combines ultrasonic holography and the conventional B-scan method. A wide-angle ultrasound burst (4 MHz) is transmitted into the object and the reflected echoes are measured as a function of the propagation time, but both the amplitude and phase angle are recorded, giving multiple one-dimensional holograms in a cross-sectional plane. This UHB data is rearranged to obtain one-dimensional wave fields, which represent the wave fronts reflected from each depth. The image is then reconstructed by propagating these wave fields backward to their original positions on the image using Fourier transform, a spectrum shift theorem, and inverse Fourier transform. The whole UHB image is obtained by calculating the intensity lines from these wave fields and by scanning these lines one by on the cathode ray tube (CRT) monitor. Following extensive laboratory testing with single and multielement transducers, special 32- and 64-element linear array transducers were fabricated, as was computer software capable of producing a UHB image in 40 seconds. Tissue imaging tests followed by clinical imaging of 30 patients showed that images obtained with this prototype compared favorably with those obtained by state-of-the-art conventional ultrasound scanners. The potential advantages of the new method are enhanced lateral resolution and the incorporation of phase information in tissue characterization. This would be important in diagnostic and intraoperative, especially neurosurgical, imaging.