High frame rate ultrasonic imaging through Fourier transform using an arbitrary known transmission field

Based on the study of limited array diffraction beams, a High Frame Rate (HFR) imaging method which uses a broadband pulsed plane wave, or array beams transmission field from a linear transducer array to illuminate the area to be imaged has been developed by Jian-yu LU. Echoes from the objects are received with the same transducer as is used in transmission. For each array beam parameter in a certain range, the received signals are weighted with that array beam and are summed up. The summations are Fourier transformed from time domain to frequency domain, and then processed further with the so called ‘‘parameter match’’ to produce the spectrum of the imaging. 2D and 3D images are constructed with inverse Fourier transformer respectively. In this way, the frame per transmission imaging rate is achieved. Despite its advantages of high frame rate and high signal to noise ratio, the original HFR method has several drawbacks. It can only use the plane wave or the array beam transmission field, and is difficult to be ported for a non-array beam field, such as a cylindrical or spherical wave. Moreover, since the plane wave transmission field illuminates only a narrow area of its own width, the imaged area is quite small, and the only way to widen it up is to steer the transmission beams several times from different angles, which lowers the frame rate. Besides, the array beam field demands a linear transducer and a very complex weighting process. Therefore, the HFR method needs to allow diffraction wave transmission fields in order to be practically useful. For example, it may use a cylindrical or spherical field and output sector format images like the conventional sector B mode ones, which have contributed a lot in diagnosing myocardial diseases. In this chapter, an extended HFR method for 2D imaging is proposed. It allows all kinds of transmission field, including the cylindrical one and the spherical one, as well as the plane wave one. It is more general than the original HFR method. The extended HFR method works mostly like the original one, except that 1, it implements the weight-and-sum process through the Fourier transform; and 2, it iterates for each frequency in a certain range to obtain firstly a coarse image component at that frequency and then the refined one with the information of the transmission field removed. After the iteration the image components are summed up and that is the final image.