A Joint Delay-and-Sum and Fourier Beamforming Method for High Frame Rate Ultrasound Imaging

Frame rate is an important metric for ultrasound imaging systems,and high frame rates(HFR)benefit moving-target imaging.One common way to obtain HFR imaging is to transmit a plane wave.Delay-and-sum(DAS)beamformer is a conventional beamforming algorithm,which is simple and has been widely implemented in clinical application.Fourier beamforming is an alternative method for HFR imaging and has high levels of imaging efficiency,imaging speed,and good temporal dynamic characteristics.Nevertheless,the resolution and contrast performance of HFR imaging based on DAS or Fourier beamforming are insufficient due to the single plane wave transmission.To address this problem,a joint DAS and Fourier beamforming method is introduced in this study.The proposed method considers the different distributions of sidelobes in DAS imaging and Fourier imaging and combines the angular spectrum and DAS to reconstruct ultrasound images.The proposed method is evaluated on simulation and experimental phantom datasets to compare its performance with DAS and Fourier beamforming methods.Results demonstrate that the proposed method improves image effective dynamic range and resolution while also retaining a high frame rate of the ultrasound imaging systems.The proposed method improves the effective dynamic range along axial and lateral directions by 10 dB,compared to standard DAS and Fourier beamforming.

An Efficient Algorithm Based on Spectrum Migration for High Frame Rate Ultrasound Imaging

The high frame rate(HFR)imaging technique requires only one emission event for imaging.Therefore,it can achieve ultrafast imaging with frame rates up to the kHz regime,which satisfies the frame rate requirements for imaging moving tissues in scientific research and clinics.Lu’s Fourier migration method is based on a non-diffraction beam to obtain HFR images and can improve computational speed and efficiency.However,in order to obtain high-quality images,Fourier migration needs to make full use of the spectrum of echo signals for imaging,which requires a large number of Fast Fourier Transform(FFT)points and increases the complexity of the hardware when the echo frequency is high.Here,an efficient algorithm using the spectrum migration technique based on the spectrum’s distribution characteristics is proposed to improve the imaging efficiency in HFR imaging.Since the actual echo signal spectrum is of limited bandwidth,low-frequency and high-frequency parts with low-energy have little contribution to the imaging spectrum.We transform the effective part that provides the main energy in the signal spectrum to the imaging spectrum while the ineffective spectrum components are not utilized for imaging.This can significantly reduce the number of Fourier transform points,improve Fourier imaging efficiency,and ensure the imaging quality.The proposed method is evaluated on simulated and experimental datasets.Results demonstrated that the proposed method could achieve equivalent image quality with a reduced point number for FFT compared to the complete spectrum migration.In this paper,it only requires a quarter of the FFT points used in the complete spectrum migration,which can improve the computational efficiency;thus,it is more suitable for real-time data processing.The proposed spectrum migration method has a specific significance for the study and clinical application of HFR imaging.

Quantification of Regional Left Ventricular Systolic Dysfunction in Patients With Coronary Artery Disease by Strain Rate Imaging

Objectives To detect and compare the systolic strain rate (SR) and strain in the infarct and ischemic myocardium by strain rate imaging (SRI), in order to explore the clinical value of SRI in evaluating regional left ventricular systolic dysfunction. Methods Patients with coronary artery disease were divided into angina pectoris (11 cases) and myocardial infarction (21 cases) groups. Twenty age-matched normal subjects served as the control group. Septal, lateral, anterior, inferior, anteroseptal and posterior walls of the left ventricle were respectively scanned using color tissue Doppler imaging (TDI). Then SR and strain curves were derived from TDI for basal, middle and apical segments of each wall. SRI parameters were: Systolic SR (SRsys), systolic strain (εsys) and maximum strain (εmax). Results Compared with normal segments, SRsys, εsys and εmax decreased significantly in the infarct and ischemic segments (P<0.01). Compared with ischemic segments, SRsys, εsys and εmax decreased significantly in the infarct segments (P<0.05). Conclusions SRsys, εsys and εmax measured by SRI can be used to quantitatively analyze regional left ventricular systolic dysfunction in patients with coronary artery disease, and aid in differentiating infarct from ischemic myocardium.

QUANTIFICATION OF RIGHT VENTRICULAR FUNCTION IN ATRIAL SEPTAL DEFECT USING ULTRASOUND- BASED STRAIN RATE IMAGING

Objective To study the validation of ultrasound-based strain rate imaging in the quantitative assessment of right ventricular （RV） function in atrial septal defect （ASD）. Methods Tissue Doppler images （TDI） of RV longitudinal and short axes were recorded from the apical 4-chamber view and the subcostal short-axis view in 18 normal controls, 28 children with ASD and 14 children after Amplazter closure of ASD respectively. Peak systolic velocities （ V）, peak systolic strain rates （SR）, peak systolic strains （S） at the basal segment, middle segment of RV lateral wall and the basal septum from the longitudinal axis, the middle segment of RV free waU from the short axis were quantitatively measured using QLAB^TM tissue velocity quantification software system respectively. Peak dp/ dt from the RV isovolumic contraction determined during the right cardiac catheterization in 28 ASD patients was used as the gold standard of RV contractility. Peak systolic indices were compared against max dp/dt by linear correlation, Results Peak systolic indices at the basal and middle segments of RV lateral wall from the longitudiual axis increased significantly in 28 ASD patients. Peak systolic indices at the basal septum also increased in patient group, but not significantly. Significant decreases in peak systolic indices at the basal and middle segments of RV lateral wall were observed after the Amplatzer closure in 14 ASD patients. There was no significant difference at the middle segment of RV free wall from the short axis between patient group and normal control. A strong correlation was found between max dp/dt and peak systolic indices at the basal and middle segments of RV lateral wal l （ P 〈 0. 05 ）. Conclusion Ultrasound-based strain rate imaging can assess quantitatively RVfunction in CHD. Peak systolic strains determined at the basal and middle segments of RV lateral wall are strong noninvasive indices of RV contractility.

Characteristics of myocardial postsystolic shortening in patients with coronary artery disease assessed by strain rate imaging

Background Postsystolic shortening （PSS） has been proposed as a marker of myocardial dysfunction. Strain rate imaging （SRI） is a novel ultrasonic technique, allowing reliable and noninvasive measurement of myocardial deformation. The purpose of this study was to investigate the characteristics of myocardial longitudinal PSS by SRI in ischemic and infarct myocardium in patients with coronary artery disease, and to explore its clinical applicability. Methods Eleven patients with angina pectoris, 21 patients with myocardial infarction and 20 healthy subjects were included in the study. Apical four-, three- and two-chamber views were displayed; and septal, lateral, anteroseptal, posterior, anterior and inferior walls of the left ventricle were scanned, respectively. PSS strain （εpss）, the ratio of εpss and systolic strain （εpss/εsys）, the ratio of εpss and maximum strain （εpss/εmax） and the duration of PSS （Tpss） in ischemic, infarct and normal myocardium were analyzed. Results PSS was found more frequent in the ischemic and infarct segments compared with the normal segments （39% vs 22% and 56% vs 22%, respectively; both P〈0.01）. It was even more frequent in the infarct segments than in the ischemic segments （56% vs 39%, P〈0.01 ）. The absolute magnitude of εpss, εpss/εsys, εpss/εmax were significantly larger and mpss significantly longer in the ischemic and infarct segments compared with that in the normal myocardium （P〈0.01）. εpss/εsys, εpss/εmax were even larger and Tpss even longer in the infarct than in the ischemic segments （P〈0.01）. Conclusions PSS is a common and important feature of the ischemic and infarct myocardium. εpss, εpss/εsys, εpss/εmax and mpss as measured by SRI may be promising markers for the quantitative assessment of regional myocardial dysfunction in patients with coronary artery disease. εpss/εsys, εpss/εmax and mpss may be helpful in differentiating infarct from ischemic myocardium.

Strain rate imaging in assessing the size of acute ischemic myocardium in dogs

Background Since the size of ischemic myocardium is closely related with both global and regional function of the myocardium, it is of great significance to measure the size of ischemic myocardium with non-invasive methods. Methods Eleven mongrel dogs were subjected to occlusion of the left anterior descending coronary artery for acute ischemia. Strain rate imaging had M-mode of strain-rate （CAMM） curve pointed from the basal segment of the anterior wall to the basal segment of the inferior wall to detect the border of ischemia size. The strain rate （SR） defined the cut-off value of ischemic myocardium in a two-chamber apical view, and marked by the anterior and inferior wall on two-dimensional images respectively. Along the endocardium and epicardium, the ischemic size was curved on two-dimensional images by the trackball method and then compared with the pathologically ischemic size. And then longitudinal strain rates were compared in the cut-off value, adjacent non-ischemic and ischemic segments at which the cut-off point was defined by changing the curve M-mode of strain rate after ischemia. Results Linear correlation existed between pathology and strain rate ischemic size （r=0.884, P 〈0.001）. The SR parameters were lower in ischemia and cut-off point than in non-ischemic segments. The peak SRs of systole （SSR）, early diastole （EsR）, late diastole （ASR）, strain during ejection time （εet）, and the maximum length change during the entire heart cycle （Emax） in ischemic segments lowered （P〈0.05）. Time to onset of regional relaxation （TR） was prolonged （P=0.012）. Conclusion SR imaging can accurately assess the size of ischemic myocardium. Chin Med J 2009; 122（2）： 193-198

An investigation on dissolution kinetics of single sodium carbonate particle with image analysis method

Dissolution kinetics of sodium carbonate is investigated with the image analysis method at the approach of single particle.The dissolution experiments are carried out in an aqueous solution under a series of controlled temperature and p H.The selected sodium carbonate particles are all spherical with the same mass and diameter.The dissolution process is quantified with the measurement of particle diameter from dissolution images.The concentration of dissolved sodium carbonate in solvent is calculated with the measured diameter of particle.Both surface reaction model and mass transport model are implemented to determine the dissolution mechanism and quantify the dissolution rate constant at each experimental condition.According to the fitting results with both two models,it is clarified that the dissolution process at the increasing temperature is controlled by the mass transport of dissolved sodium carbonate travelling from particle surface into solvent.The dissolution process at the increasing pH is controlled by the chemical reaction on particle surface.Furthermore,the dissolution rate constant for each single spherical sodium carbonate particle is quantified and the results show that the dissolution rate constant of single spherical sodium carbonate increases significantly with the rising of temperature,but decreases with the increasing of pH conversely.

Reconstruction and transmission of astronomical image based on compressed sensing

In the process of image transmission, the famous JPEG and JPEG-2000 compression methods need more transmission time as it is difficult for them to compress the image with a low compression rate. Recently the compressed sensing（CS） theory was proposed, which has earned great concern as it can compress an image with a low compression rate, meanwhile the original image can be perfectly reconstructed from only a few compressed data. The CS theory is used to transmit the high resolution astronomical image and build the simulation environment where there is communication between the satellite and the Earth. Number experimental results show that the CS theory can effectively reduce the image transmission and reconstruction time. Even with a very low compression rate, it still can recover a higher quality astronomical image than JPEG and JPEG-2000 compression methods.