Split-based elevational localization of photoacoustic guidewire tip by 1D array probe using spatial impulse response.

Objective. Photoacoustic emitters on the tip of a therapeutic device have been intensively studied for echo-guided intervention purposes. In this study, a novel method for localizing the guidewire tip emitter in the elevation direction using a 1D array probe is proposed to resolve the issue of the tip potentially deviating from the ultrasound-imaged plane.Approach. Our method uses the 'interference split' that appears when the emitter is off-plane. Here, a point source from the emitter splits into two points in images. Based on the split, 'split-based elevation localization (SEL)' is introduced to estimate the absolute elevation position of the emitter. Additionally, 'Signed SEL' incorporates an asymmetric feature into the 1D probe to obtain the sign of the elevation localization. An attenuative coupler is attached to the half side of the probe to control the interference split. In SEL and Signed SEL, we propose a modeled split matching (MSM) algorithm to localize the tip position. MSM performs pattern matching of a measured split waveform with modeled split waveforms corresponding to all emitter positions in a region of interest. The modeled waveforms are precalculated using the spatial impulse response. The proposed method is numerically and experimentally validated.Main results. Numerical simulations for time-domain wave propagation clearly demonstrated the interference split phenomena. In the experimental validation with a vessel-mimicking phantom, the proposed methods successfully estimated the elevation positions,yb.SEL exhibited a root-mean-squared error (RMSE) of 2.0 mm for the range of 0 mm ≤yb≤ 30 mm, while Signed SEL estimated the absolute position with an RMSE of 2.4 mm and the sign with an accuracy of 80.8% for the range of -30 mm ≤yb≤ 30 mm.Significance.These results suggest that the proposed method could provide approximate tip positions and help sonographers track it by fanning the probe.

The Evaluation of Fetal Cardiac Remote Screening in the Second Trimester of Pregnancy Using the Spatio-Temporal Image Correlation Method.

We prospectively performed remote fetal cardiac screening using the spatio-temporal image correlation (STIC), and examined the usefulness and problems of remote screening. We performed heart screening for all pregnant women at four obstetrics clinics over the three years from 2009 to 2014. The STIC data from 15,404 examinations in normal pregnancies (16-27 weeks, median 25 weeks) were analyzed. Obstetricians and sonographer collected STIC data from four-chamber view images. Eight pediatric cardiologists analyzed the images offline. A normal heart was diagnosed in 14,002 cases (90.9%), an abnormal heart was diagnosed in 457 cases (3.0%), and poor images were obtained in 945 cases (6.1%). 138 cases had congenital heart disease (CHD) after birth, and severe CHD necessitating hospitalization occurred in 36 cases. We were not able to detect CHD by screening in 12 cases. The sensitivity and specificity of STIC in CHD screening was 50% and 99.5%, respectively. The sensitivity and specificity of STIC in screening for severe CHD was 82% and 99.9%, respectively. The STIC method was useful in fetal remote screening for CHD. However, the fact that > 10% of images that could not be analyzed by this method was a problem.

Ultrasound Sub-pixel Motion-tracking Method with Out-of-plane Motion Detection for Precise Vascular Imaging.

Ultrasound vascularity imaging provides important information for differential diagnosis of tumors. Peak-hold (PH) is a useful technique for precisely imaging small vessels by selecting a maximum brightness in each pixel through the frames obtained sequentially. To use PH successfully one needs motion compensation to reduce image blur, but out-of-plane motion cannot be avoided. To address this problem, we developed a sub-pixel motion-tracking method with out-of-plane motion detection (OPMD). It is a combination of the sum of the absolute differences (SAD) method and the Kanade-Lucas-Tomasi method and can be accurately applied to various motions. The value from OPMD (γ) is defined as a statistical value obtained from the distribution of residual values in the SAD procedure with the obtained frames. The value is ideally 0, and the frames having large γ are removed from the PH procedure. The accuracy of the proposed tracking method was found by a simulation study to be approximately 20 µm. We also found, through a phantom experiment, that the value of γ sensitively increased enough to detect out-of-plane motion. Most important, γ begins to increase before tracking errors occur. This suggests that OPMD can be used to predict tracking errors and effectively remove frames from the PH procedure. An in vivo experiment with a rabbit showed that the PH image obtained with motion tracking clearly revealed peripheral vessels that were blurred in the PH image obtained without motion tracking. We also found that the image quality becomes better when OPMD was used to remove frames including out-of-plane motion.

Ultrasonic Vascular Vector Flow Mapping for 2-D Flow Estimation.

A vascular vector flow mapping (VFM) method visualizes 2-D cardiac flow dynamics by estimating the radial component of flow from the Doppler velocities and wall motion velocities using the mass conservation equation. Although VFM provides 2-D flow, the algorithm is applicable only to bounded regions. Here, a modified VFM algorithm, vascular VFM, is proposed so that the velocities are estimated regardless of the flow geometry. To validate the algorithm, a phantom mimicking a carotid artery was fabricated and VFM velocities were compared with optical particle image velocimetry (PIV) data acquired in the same imaged plane. The validation results indicate that given optimal beam angle condition, VFM velocitiy is fairly accurate, where the correlation coefficient R between VFM and PIV velocities is 0.95. The standard deviation of the total VFM error, normalized by the maximum velocity, ranged from 8.1% to 16.3%, whereas the standard deviation of the measured input errors ranged from 8.9% to 12.7% for color flow mapping and from 4.5% to 5.9% for subbeam calculation. These results indicate that vascular VFM is reliable as its accuracy is comparable to that of conventional Doppler-flow images.

Correction to: Accuracy and limitations of vector flow mapping: left ventricular phantom validation using stereo particle image velocimetory.

The original version of this article unfortunately contained a mistake. The conflict of interest statement was missing in the article. The CoI statement is given below.

A posteriori accuracy estimation of ultrasonic vector-flow mapping (VFM).

ABSTRACT: A novel method, called a posteriori "VFM accuracy estimation" (VAE), for resolving an intrinsic VFM problem is proposed. The problem is that VFM uncertainty can easily vary according to blood flows through an echocardiographic imaged plane (i.e., "through-plane" flows), and it is unknown. Knowing the VFM uncertainty for each patient will make it possible to refine the quality of VFM-based diagnosis. In the present study, VAE was derived on the basis of an error-propagation analysis and a statistical analysis. The accuracy of VAE with a pulsatile left-ventricle phantom was experimentally investigated for realistic cases with through-plane flows. VAE was validated by comparing VFM uncertainty (S.D.) estimated by VAE with VFM uncertainty measured by particle-image velocimetry (PIV) for different imaged planes. VAE accurately estimated the S.D. of VFM uncertainty measured by PIV for all cases with different image planes (R > 0.6 and p < 0.001). These findings on VFM accuracy will provide the basis for widespread clinical application of VFM-based diagnosis.

Accuracy and limitations of vector flow mapping: left ventricular phantom validation using stereo particle image velocimetory.

BACKGROUND: The accuracy of vector flow mapping (VFM) was investigated in comparison to stereo particle image velocimetry (stereo-PIV) measurements using a left ventricular phantom. VFM is an echocardiographic approach to visualizing two-dimensional flow dynamics by estimating the azimuthal component of flow from the mass-conservation equation. VFM provides means of visualizing cardiac flow, but there has not been a study that compared the flow estimated by VFM to the flow data acquired by other methods. METHODS: A reproducible three-dimensional cardiac blood flow was created in an optically and acoustically transparent left-ventricle phantom, that allowed color-flow mapping (CFM) data and stereo-PIV to be simultaneously acquired on the same plane. A VFM algorithm was applied to the CFM data, and the resulting VFM estimation and stereo-PIV data were compared to evaluate the accuracy of VFM. RESULTS: The velocity fields acquired by VFM and stereo-PIV were in excellent agreement in terms of the principle flow features and time-course transitions of the main vortex characteristics, i.e., the overall correlation of VFM and PIV vectors was R = 0.87 (p < 0.0001). The accuracy of VFM was suggested to be influenced by both CFM signal resolution and the three-dimensional flow, which violated the algorithm's assumption of planar flow. Statistical analysis of the vectors revealed a standard deviation of discrepancy averaging at 4.5% over the CFM velocity range for one cardiac cycle, and that value fluctuated up to 10% depending on the phase of the cardiac cycle. CONCLUSIONS: VFM provided fairly accurate two-dimensional-flow information on cardio-hemodynamics. These findings on VFM accuracy provide the basis for VFM-based diagnosis.

The evaluation of diastolic function using the diastolic wall strain (DWS) before and after radical surgery for congenital diaphragmatic hernia.

OBJECTIVE: The measurement of diastolic wall strain (DWS), a new method of evaluating cardiac diastolic function, was employed to evaluate ventricular diastolic function in patients with congenital diaphragmatic hernia (CDH). MATERIALS AND METHODS: Eighteen neonates with a CDH who were born and treated in our hospital between September 2009 and January 2013 were studied. The left ventricular posterior wall thickness during the systolic phase (PWs) and diastolic (PWd) phase was measured using M-mode imaging, and the DWS was calculated as (PWs-PWd)/PWs. The Tei index, the isovolumic relaxation time (IRT), and the fraction shortening (FS) were measured as indices of cardiac function in 14, 15, and 18 cases, respectively. Cardiac function was measured before and after surgery. Statistical analyses were performed using the paired t test. RESULTS: The pre- and postoperative DWS, Tei index, IRT and FS values were 0.19 ± 0.06 and 0.26 ± 0.11 (P < 0.01), 0.40 ± 0.12 and 0.31 ± 0.11 (P < 0.05), 48 ± 14 and 39 ± 5.0 ms (P < 0.05), 30 ± 7.7 and 34 ± 7.4 % (P < 0.05), respectively. CONCLUSION: The diastolic and systolic functions were not only measured by the Tei index, IRT and FS values, but also by the DWS value, which improved after surgery. The measurement of DWS is an easy and useful method for evaluating the diastolic function of CDH patients.

Classification of turbulence modification by dispersed spheres using a novel dimensionless number.

A novel dimensionless parameter, the particle moment number Pa, was derived using dimensional analysis of the particle-laden Navier-Stokes equations, in order to understand the underlying physics of turbulence modification by particles. A set of 80 previous experimental measurements where the turbulent kinetic energy was modified by particles was examined, and all results could clearly be divided into three groups in Re-Pa mappings. The turbulence attenuation region was observed between the augmentation regions with two critical particle momentum numbers.