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Synthetic aperture (SA) imaging techniques can enhance spatial resolution in medical ultrasound imaging. However, it suffers from the degradation of image quality close to a virtual source (e.g., transmit focal point) since there is no enough transmit acoustic field energy. In this paper, a new SA imaging technique (i.e., dynamic synthetic aperture, DSA) where the number of synthetic scanlines for acoustic field superposition is dynamically adjusted based on the transmit acoustic field analysis. For the DSA technique, the dynamic apodization window function was generated from the Field II simulation and applied in the phantom and in vivo experiments. The raw radio-frequency (RF) data for phantom and in vivo experiments were captured by an Ultrasonix's SonixTouch research platform connected with a SonixDAQ parallel acquisition system. From the phantom experiment, the proposed DSA method shows the enhanced spatial resolution over the depth compared to the conventional receive dynamic focusing (CRDF). In addition, it doesn't yield any artifacts associated with the lack of enough transmit acoustic energy shown in the conventional SA imaging technique. The consistent results were obtained with the in vivo breast data. This result indicates that the proposed DSA method could be used for enhancing image quality of medical ultrasound imaging.

In photoacoustic imaging, an adaptive beamforming method with coherence factor (ABF-CF) was previously introduced for improving spatial resolution and signal-to-noise ratio (SNR) over a conventional delay-and-sum beamforming method (DAS). However, the ABF-CF method is not suitable for being used in practical diagnosis since it is overly-sensitive for off-axis interferences and noises. In this paper, a new adaptive beamforming method with spatially-smoothed coherence factor (ABF-SSCF) is presented for ultrasound and photoacoustic combined imaging to enhance the contrast and spatial resolution while preserving the target information by applying a spatial-smoothing technique into CF coefficients from multiple sub-arrays within an array probe. To evaluate the ABF-SSCF method, computer simulation and ex vivo experiments were conducted. For the computer simulation, 64-channel radio-frequency (RF) data with one channel amplitude-varying off-axis interference was generated. Also, The ex vivo experiments were conducted where 128-channel pre-beamformed RF data were captured from a microcalcification-contained breast core specimen with a commercial ultrasound system equipped with a research package by using a 7-MHz linear array probe (SonixTouch, Ultrasonix Corp., BC, Canada) and an Nd:Yag laser excitation system (Surelite III-10 and Surelite OPO Plus, Continuum Inc., Santa Clara, CA, USA). From the simulation and ex vivo experiments, the proposed ABF-SSCF method provides better contrast and spatial resolutions comparable than the DAS method. Also, compared to the ABFCF method, image information is clearly presented without being degraded by off-axis interferences. These results indicate that the proposed ABF-SSCF method can simultaneously enhance the image quality and efficacy of the ABF method for ultrasound and photoacoustic combined imaging.

An ultrasound vector Doppler imaging is useful for detecting flow components normal to the ultrasound beam direction. However, the conventional vector Doppler imaging method suffers from the bias of the time interval between samples caused by the mismatch between transmit and receive directions during demodulation. In this paper, a new directional demodulation method, in which demodulation is performed with a modified sample interval depending on the receive beam steered angle to reduce the bias occurred in a conventional ultrasound vector Doppler imaging is presented. To evaluate the performance of the proposed directional demodulation method, the pre-beamformed radio-frequency (RF) data from in-vitro experiments were obtained using a commercial ultrasound system and a Doppler string phantom. The true flow velocity of the phantom was 0.3 m/s. The center frequency of 5 MHz and the pulse repetition frequency of 4 kHz were used for the experiments. Also, a 32-element sub-aperture on a 128-element 7.2-MHz linear array probe were used for emission and reception while changing the flow direction from -45 degrees to 0 degree by a step of 5 degrees. The proposed directional demodulation method successfully visualizes all flow directions. In addition, it lowers a bias on flow estimation compared to the conventional method (i.e., 0.0255±0.0516 m/s vs. 0.0248±0.0469 m/s of error of velocity, 2.4862±3.8911 degrees vs. 2.4857±3.5115 degrees of error of direction, respectively). These results indicate that the proposed directional demodulation method can enhances the accuracy in flow estimation for vector Doppler imaging.

In medical ultrasound imaging, scan conversion is used to geometrically transform polar coordinate ultrasound data into Cartesian raster data for display. In scan conversion, Moiré undersampling artifacts can be avoided by using various interpolation techniques such as nearest neighbor and bilinear. However, this interpolation-based scan conversion introduces blurring of fine details in ultrasound images. In this paper, a new beamforming technique, named compounded direct pixel beamforming (CDPB), is proposed to remove blurring artifacts from scan conversion. In CDPB, receive focusing is performed directly on each display pixel in Cartesian coordinates with raw radio-frequency (RF) data from two adjacent transmit firings so that artifacts from scan conversion can be substantially removed. To evaluate the proposed CDPB method, 64-channel pre-beamformed RF data were captured by a commercial ultrasound machine (SA-9900, Medison Corp., Seoul, Korea) from a tissue mimicking phantom (ATS Laboratories, Bridgeport, CT, USA). To quantify the performance of the proposed method, the information entropy contrast (IEC) value was measured. From the experiments, the proposed method provided IEC improvement by 2.8 over the conventional scan conversion method. These results indicate that the proposed new beamforming method could be used for enhancing the image quality in medical ultrasound imaging.

In medical ultrasound imaging, a multi-beamforming (MBF) method is used for supporting high frame rate imaging or functional imaging where multiple scanlines are reconstructed from a single excitation event. For efficient MBF, a time-sharing technique (i.e., MBF-TS) can be applied. However, the MBF-TS could degrade image quality due to the decreased beamforming frequency. In this paper, the multi-access register-based MBF (MBF-MAR) method running on the post-fractional filtering (PFF) architecture is presented. In PFF-MBF-MAR, instead of lowering beamforming frequency, a multi-access register at each channel is utilized for generating multiple scanlines simultaneously. To evaluate the performance of the proposed PFF-MBF-MAR method, the phantom experiment was conducted where 64- channel pre-beamformed radio-frequency (RF) data were captured from a tissue mimicking phantom by using a modified commercial ultrasound system (SONOLINE G40, Siemens Inc., USA) using a 3-MHz phased array probe. From the phantom experiment, the PFF-MBF-MAR method showed 4.7 dB and 0.6 improvements in the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR), respectively, compared to the PFF-MBF-TS method, while slightly increasing the hardware complexity (<5.2%). The similar results were achieved with the in vivo thyroid data. These results indicate that the proposed PFF-MBF-MAR method can be used for high frame rate imaging or functional imaging without sacrificing image quality while slightly increasing the hardware complexity.