Speckle Noise Reduction by Superposing Many Higher Harmonic Images

A novel ultrasonic imaging method offering high resolution and high-quality images for clinical diagnosis has been developed. This method produces an image using many higher harmonic components contained in the echoes from the inside of a human body, generated due to ultrasonic nonlinear propagation through biological tissues. A new ultrasonic probe has been designed to detect higher harmonic components efficiently over a broad band produced by nonlinear propagation through biological tissues. This probe has a bilayer structure consisting of a lead zirconate titanate (PZT) transmitter and a polyvinylidene fluoride (PVDF) receiver. Experiments employing the new probe show that the receiving transducer easily detects higher harmonics from the fundamental through the tenth in the spectrum of reflected sound from an agar-gel phantom submerged in water. By scanning the probe, the harmonic images of the fundamental through the ninth harmonic component are successfully obtained. In addition, it is demonstrated that speckle noise can be reduced by averaging many harmonic images.