Ultrafast ultrasound is an emerging modality that offers new perspectives and opportunities in medical imaging. Plane wave imaging (PWI) allows one to attain very high frame rates by transmission of planar ultrasound wavefronts. As a plane wave reaches a given scatterer, the latter becomes a secondary source emitting upward spherical waves and creating a diffraction hyperbola in the received RF (radio-frequency) signals. To produce an image of the scatterers, all the hyperbolas must be migrated back to their apexes. In order to perform beamforming of plane wave echo RFs and return high-quality images at high frame rates, we propose a new migration method carried out in the frequency-wavenumber (f-k) domain.The f-k migration for PWI has been adapted from the Stolt migration for seismic imaging. This migration technique is based on the exploding reflector model (ERM), which consists in assuming that all the scatterers explode in concert and become acoustic sources. The classical ERM model, however, is not appropriate for PWI. We showed that the ERM can be made suitable for PWI by a spatial transformation of the hyperbolic traces present in the RF data. In vitro experiments were performed to sketch the advantages of PWI with Stolt's f-k migration over the conventional delayand-sum (DAS) approach. The Stolt's f-k migration was also compared with the Fourier-based method developed by J-Y Lu.Our findings show that multi-angle compounded f-k migrated images are of quality similar to those obtained with a state-of-the-art dynamic focusing mode. This remained true even with a very small number of steering angles thus ensuring a highly competitive frame rate. In addition, the new FFT-based f-k migration provides comparable or better contrast-to-noise ratio and lateral resolution than the Lu's and DAS migration schemes. Matlab codes of the Stolt's f-k migration for PWI are provided.

OBJECTIVE The purpose of this article is to provide an overview of ultrasound and MR elastography, including a glossary of relevant terminology, a classification of elastography techniques, and a discussion of their respective strengths and limitations. CONCLUSION Elastography is an emerging technique for the noninvasive assessment of mechanical tissue properties. These techniques report metrics related to tissue stiffness, such as shear-wave speed, magnitude of the complex shear modulus, and the Young modulus.

5 J. MAGN. RESON. IMAGING 2017;45:1276-1295.

This paper describes an evaluation framework that allows a standardized and quantitative comparison of IVUS lumen and media segmentation algorithms. This framework has been introduced at the MICCAI 2011 Computing and Visualization for (Intra)Vascular Imaging (CVII) workshop, comparing the results of eight teams that participated. We describe the available data-base comprising of multi-center, multi-vendor and multi-frequency IVUS datasets, their acquisition, the creation of the reference standard and the evaluation measures. The approaches address segmentation of the lumen, the media, or both borders; semi- or fully-automatic operation; and 2-D vs. 3-D methodology. Three performance measures for quantitative analysis have been proposed. The results of the evaluation indicate that segmentation of the vessel lumen and media is possible with an accuracy that is comparable to manual annotation when semi-automatic methods are used, as well as encouraging results can be obtained also in case of fully-automatic segmentation. The analysis performed in this paper also highlights the challenges in IVUS segmentation that remains to be solved.

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OBJECTIVE-The purpose of the article is to review the diagnostic performance of ultrasound and MR elastography techniques for detection and staging of liver fibrosis, the main current clinical applications of elastography in the abdomen.CONCLUSION-Technical and instrument-related factors and biologic and patient-related factors may constitute potential confounders of stiffness measurements for assessment of liver fibrosis. Future developments may expand the scope of elastography for monitoring liver fibrosis and predict complications of chronic liver disease. Keywords elasticity; elastography; liver fibrosis; MR elastography (MRE); MRI; ultrasound; viscosity In abdominal imaging, liver stiffness estimated by elastography techniques may be used as a quantitative imaging biomarker for detection, staging, and monitoring of liver fibrosis [1][2][3]. Liver stiffness is used to evaluate the severity of the underlying chronic liver disease, guide treatment decision, assess disease outcome, and evaluate response to therapy [4].In this second article of a two-part series [5], we will discuss the clinical applications in the liver. We will focus on diagnostic performance of ultrasound elastography and MR Address correspondence to C. B. Sirlin (csirlin@ucsd.edu).. Technologies developed by the team of G. Cloutier were licensed to Rheolution, Inc., and Acist Medical Systems. HHS Public Access Author Manuscript Author ManuscriptAuthor ManuscriptAuthor Manuscript elastography techniques for detection, staging, and monitoring of liver fibrosis, the main current clinical applications of elastography in the abdomen. We will discuss potential confounders of stiffness measurements for assessment of liver fibrosis, which include technical and instrument-related factors (location and depth of measurements, wave frequencies, and device dependencies) and biologic and patient-related factors (concomitant hepatic steatosis, inflammation, cholestasis; breathing; right heart failure and hepatic venous congestion; and fasting vs postprandial state). Finally, we will briefly discuss future directions and technical innovations in this field of research.As will be shown in this article, elastography techniques integrated to clinical ultrasound and MR systems now provide the capability to examine by imaging what once could be examined only by direct palpation, which is likely to open new opportunities to noninvasively diagnose disease, guide management, and improve outcomes. Key Learning PointsFirst, the main current clinical indications for abdominal elastography techniques are detection and staging of liver fibrosis. In general, elastography techniques provide good-toexcellent diagnostic accuracy for the detection of advanced fibrosis but have more modest performance for detection of early or mild fibrosis. Most studies to date have been in adults; performance characteristics in children are less well known. Research is needed to better understand the performance of elastography for monitoring longitudinal changes in fibrosis. Emerg...

While an increasing amount of evidence demonstrates the homeostatic functions of the cardiac oxytocin (OT) system, less is known about the role of this hormone in the injured heart. The current study examined the effect of OT infusion on cell apoptosis, expression of proliferating cell nuclear antigen (PCNA) and inflammation in the acute and subacute phases of myocardial infarction (MI). Prior MI male Sprague-Dawley rats were infused subcutaneously with OT 25 or 125 ng/(kg h) for 3 or 7 days. Saline-treated MI and sham-operated rats served as controls. Echocardiography and analysis of cardiac sections were used to disclose OT actions. Left ventricular fractional shortening, estimated to be 46.0 +/- 1.8% in sham controls, declined to 21.1 +/- 3.3% in vehicle-treated MI rats and was improved to 34.2 +/- 2.1 and to 30.9 +/- 2.5% after treatment with OT 25 and 125 ng/(kg h), respectively. OT infusion resulted in: (1) increase of cells expressing PCNA in the infarct zone, diminished cell apoptosis and fibrotic deposits in the remote myocardium; (2) suppression of inflammation by reduction of neutrophils, macrophages and T lymphocytes; (3) depression of the expression of proinflammatory cytokines tumor necrosis factor-alpha and interleukin-6 with promotion of transforming growth factor-beta. OT treatment reduced expression of atrial and brain natriuretic peptides in the infarcted ventricle, as well as the concentration of both peptides in the circulation. These results indicate that continuous OT delivery reduces inflammation and apoptosis in infarcted and remote myocardium, thus improving function in the injured heart.

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