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Objective: To evaluate the feasibility of clinical application for genetic based dosing algorithm in the predication of warfarin maintenance dose in Chinese population., Methods: The clinical data were collected and blood samples harvested from a total of 126 patients undergoing heart valve replacement. The genotypes of VKORC1 and CYP2C9 were determined by melting curve analysis after PCR. They were divided randomly into the study and control groups. In the study group, the first three doses of warfarin were prescribed according to the predicted warfarin maintenance dose while warfarin was initiated at 2.5 mg/d in the control group. The warfarin doses were adjusted according to the measured international normalized ratio (INR) values. And all subjects were followed for 50 days after an initiation of warfarin therapy., Results: At the end of a 50-day follow-up period, the proportions of the patients on a stable dose were 82.4% (42/51) and 62.5% (30/48) for the study and control groups respectively. The mean durations of reaching a stable dose of warfarin were (27.5 ± 1.8) and (34.7 ± 1.8) days and the median durations were (24.0 ± 1.7) and (33.0 ± 4.5) days in the study and control groups respectively. Significant differences existed in the durations of reaching a stable dose between the two groups (P = 0.012). Compared with the control group, the hazard ratio (HR) for the duration of reaching a stable dose was 1.786 in the study group (95%CI 1.088 - 2.875, P = 0.026)., Conclusion: The predicted dosing algorithm incorporating genetic and non-genetic factors may shorten the duration of achieving efficiently a stable dose of warfarin. And the present study validates the feasibility of its clinical application.

Correlation-based speckle tracking methods are commonly used in elasticity imaging to estimate displacements. In the presence of local strain, a larger window size results in larger displacement error. To reduce tracking error, we proposed a short correlation window followed by a correlation coefficient filter. Although simulation and experimental results demonstrated the efficacy of the method, it was not clear why correlation coefficient filtering reduces tracking error since tracking error increases if normalization before filtering is not applied. In this paper, we analyzed tracking errors by estimating phase variances of the cross-correlation function and the correlation coefficient at the true time lag based on statistical properties of these functions' real and imaginary parts. The role of normalization is clarified by identifying the effect of the cross-correlation function's amplitude fluctuation on the function's imaginary part. Furthermore, we present analytic forms for predicting axial displacement error as a function of strain, system parameters (signal-to-noise ratio, center frequency, and signal and noise bandwidths), and tracking parameters (window and filter sizes) for cases with and without normalization before filtering. Simulation results correspond to theory well for both noise-free cases and general cases with an empirical correction term included for strains up to 4%.

Surgery to correct severe heart arrhythmias usually requires detailed maps of the cardiac activation wave prior to ablation. The pinpoint electrical mapping procedure is laborious and limited by its spatial resolution (5-10 mm). We propose ultrasound current source density imaging (UCSDI), a direct 3-D imaging technique that potentially facilitates existing mapping procedures with superior spatial resolution. The technique is based on a pressure-induced change in resistivity known as the acoustoelectric (AE) effect, which is spatially confined to the ultrasound focus. AE-modulated voltage recordings are used to map and reconstruct current densities. In this preliminary study, we tested UCSDI under controlled conditions and compared it with conventional electrical mapping techniques. A 2-D dipole field was produced by a pair of electrodes in a bath of 0.9% NaCl solution. Boundary electrodes detected the AE signal while a 7.5-MHz focused ultrasound transducer was scanned across the bath. UCSDI located the current source and sink to within 1 mm of their actual positions. A future UCSDI system potentially provides real-time 3-D images of the cardiac activation wave coregistered with anatomical ultrasound and would greatly facilitate corrective procedures for heart abnormalities.

In this study, photoacoustic flow measurement methods based on wash-in analysis are presented. These methods use the rod-to-sphere shape transformations of gold nanorods induced by pulsed-laser irradiation. Due to the shape dependence of the optical absorption of the gold nanorods, these shape transitions are associated with a change in the peak optical absorption wavelength. Pulsed-laser irradiation at the wavelength corresponding to the peak optical absorption of the original gold nanorods allows the particles that undergo shape changes to be viewed as "being destructed" by the laser irradiation at that wavelength, hence, flow information can be derived from the change in ultrasound intensity that is directly related to the wash-in rate of the gold nanorods and the laser intensity. Two flow estimation methods based on the wash-in analysis are described. The first method first applies high-energy laser pulses that induce shape changes in all the nanorods. A series of low-energy pulses then are applied to monitor the acoustic signal change as new nanorods flow into the region of interest. The second method uses single-energy laser pulses such that the "destruction" and "detection" are performed simultaneously. The simulation results show that it is valid to fit the time-intensity curves by exponential models. To demonstrate the validity of the proposed methods, an Nd:YAG pulsed laser operating at 1064 nm was used for optical irradiation, and a 1-MHz ultrasonic transducer was used for acoustic detection. Gold nanorods with a peak optical absorption at 1018 nm and a concentration of 0.26 nM were used to estimate flow velocities ranging from 0.35 to 2.83 mm/s. The linear regression results show that the correlation coefficients between the measured velocities and the true values are close to unity (> or = 0.94), thus demonstrating the feasibility of the proposed photoacoustic techniques for relative flow estimation.

Polymer microring resonators are demonstrated as high-frequency, ultrasound detectors. An optical microring resonator consists of a ring waveguide closely coupled to a straight bus waveguide, serving as light input and output. Acoustic waves irradiating the ring induce strain, deforming the waveguide dimensions and changing the refractive index of the waveguide via the elasto-optic effect. These effects modify the effective refractive index of the guided mode inside the waveguide. The sharp wavelength dependence of the microring resonance can enhance the optical response to acoustic strain. Such polymer microring resonators are experimentally demonstrated in detecting broadband ultrasound pulses from a 50 MHz transducer. Measured frequency response shows that these devices have potential in high-frequency, ultrasound detection. Design guidelines for polymer microring resonators forming an ultrasound detector array are discussed.

This paper proposes an approach to designing binary codes suitable for high-frequency applications of coded excitation in medical ultrasound. For a high-frequency ultrasound system, transmitting well-designed binary codes with a low sampling ratio (i.e., the bit rate divided by the transducer center frequency) is a practical way to improve the signal-to-noise ratio (SNR) because the challenge of implementing arbitrary-waveform generators for transmitting nonbinary codes increases with the frequency and the switching speed of square-wave pulsers are limited. One conventional approach designs codes using a base sequence that modulates wideband sequences up to the transducer passband. Because a major portion of codes is excluded as a candidate, codes designed using this approach typically need long compression filters for restoring the axial resolution, and they do not improve the SNR efficiently. In contrast, the approach proposed here searches all the codes that match the transducer passband; hence, the resultant codes exhibit better performance. The technique was tested using a bit rate of 50 MHz and a sampling ratio of 2. For a transducer with an ideal Gaussian frequency response with a center frequency of 25 MHz and a -6 dB bandwidth of 15 MHz, the SNR for the same side-lobe extent was 1 to 6 dB higher for the codes designed using the proposed approach compared with those designed using the conventional approach. When a real transducer response with a center frequency of 26.4 MHz and a one-way -6 dB bandwidth of 20.7 MHz was considered, the codes designed using the proposed approach were superior by 0.5 to 5 dB. Therefore, our approach is better than the conventional approach for designing binary codes for high-frequency ultrasound, with the results indicating that the moderate bit rate of 50 MHz will suffice when the ultrasonic center frequency is 25 MHz.

This paper presents a new coded excitation scheme that efficiently synthesizes codes for arbitrary waveforms using a bipolar square wave pulser. In a coded excitation system, pulse compression is performed to restore the axial resolution. In order to maintain low range sidelobes, the system needs to transmit signals that have smooth spectra. However, such a transmitter requires the generation of arbitrary waveforms and, therefore, is more expensive. In other words, a trade-off is necessary between the compression performance and the transmitter cost. Here we propose a method that preserves the low-cost advantage of a bipolar pulser while achieving approximately the same compression performance as an arbitrary waveform generator. The key idea of the proposed method is the conversion of a nonbinary code (i.e., requiring an arbitrary waveform generator) with good compression performance into a binary code (i.e., requiring only a bipolar pulser) by code translation and code tuning. The code translation is implemented by sending the nonbinary code into a virtual one-bit, sigma-delta modulator, and the code tuning involves minimizing the root-mean-square error between the resultant binary code and the original nonbinary code by sequential and iterative tuning while taking the transducer response into account. Tukey-windowed chirps are known to have good compression performance. Such chirps of different durations (16, 20, and 24 micros), all with a taper ratio of 0.15, a center frequency of 2.5 MHz, and an equivalent bandwidth of 1.5 MHz, were converted into binary Tukey-windowed chirps that were compared with pseudochirps (i.e., direct binary approximations of the original chirp) over the same spectral band. The bit rate was 40 MHz. Simulation results show that the use of binary Tukey-windowed chirps can reduce the code duration by 20.6% or the peak sidelobe level by 6 dB compared to the commonly used pseudochirps. Experimental results obtained under the same settings were in agreement with the simulations. Our results demonstrate that arbitrary waveform coded excitation can be realized using bipolar square wave pulsers for applications in medical ultrasound.

Sidelobe contribution from off-axis targets degrades image quality in a coherent array imaging system. In ultrasound imaging, focusing errors resulting from sound-velocity inhomogeneities in human tissue--also known as phase aberrations reduce the coherence of the received signals and elevate the sidelobe level. This paper proposes an adaptive receive-aperture technique based on thresholding of the coherence factor (CF). The CF describes the coherence of the received array signals and can be used as an index of focusing quality. This paper demonstrates that thresholding of the CF allows the mainlobe-dominated signals to be distinguished from the sidelobe-dominated signals, after which the receive-aperture size at each imaging position can be optimally determined so as to enhance the mainlobe-dominated signals and suppress the sidelobe-dominated signals. Thus, image quality degradation resulting from sound-velocity inhomogeneities can be reduced. Simulations and measured ultrasound data are used to evaluate the efficacy of the proposed technique. The characteristics of the proposed technique including the effects of the signal-to-noise ratio (SNR) and the transmit focal depth, and speckle reduction are discussed. The proposed technique is also compared with the parallel adaptive receive compensation algorithm and shown to produce a better improvement in image quality.

An approach based on limited-angle transmission tomography for reconstruction of the sound velocity distribution in the breast is proposed. The imaging setup is similar to that of x-ray mammography. With this setup, the time-of-flight data are acquired by a linear array positioned at the top of the compressed breast that both transmits and receives, and a metal plate is placed at the bottom as a reflector. The setup allows acoustic data acquisition for simultaneous B-mode image formation and the tomographic sound velocity reconstruction. In order to improve the sound velocity estimation accuracy, a new reconstruction algorithm based on a convex programming formulation has been developed. Extensive simulations for both imaging and time-of-flight data based on a 5-MHz linear array were performed on tissues with different geometries and acoustic parameters. Results show that the sound velocity error was generally 1-3 m/s, with a maximum of 5.8 m/s. The radii of the objects under investigation varied from 2 to 6 mm, and all of them were detected successfully. Thus, the proposed approach has been shown to be both feasible and accurate. The approach can be used to complement conventional B-mode imaging to further enhance the detection of breast cancer.