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A tissue axial stretching model is described, to study the effects of tissue lateral displacement on echo decorrelation, and a concept called correlation signal-to-noise ratio (CSNR) is used to quantify the decorrelation effect. It is shown that CSNR can be used as a quality indicator of elastography, and a 2-D spatial comprehensive cross-correlation technique can reduce decorrelative noise while slightly decreasing the lateral resolution of the strain image.

Abstract Background The retroperitoneal margin is a common site of positive surgical margins in patients with resectable pancreatic cancer. Preoperative margin-intensive therapy (MIT) involves delivery of a single high dose of ablative radiotherapy (30 Gy) focused on this surgically inaccessible margin, utilizing stereotactic techniques in an effort to reduce local failure following surgery. In this study, we investigated the motion of regional organs at risk (OAR) utilizing 4DCT, evaluated the dosimetric effects of abdominal compression (AC) to reduce regional motion, and compared various planning techniques to optimize MIT. Methods 10 patients were evaluated with 4DCT scans. All 10 patients had scans using AC and seven of the 10 patients had scans both with and without AC. The peak respiratory abdominal organ and major vessel centroid excursion was measured. A "sub-GTV" region was defined by a radiation oncologist and surgical oncologist encompassing the retroperitoneal margin typically lateral and posterior to the superior mesenteric artery (SMA), and a 3-5 mm margin was added to constitute the PTV. Identical 3D non-coplanar SABR (3DSABR) plans were designed for the average compression and non-compression scans. Compression scans were planned with 3DSABR, coplanar IMRT (IMRT), and Cyberknife (CK) planning techniques. Dose volume analysis was undertaken for various endpoints, comparing OAR doses with and without AC and for different planning methods. Results The mean PTV size was 20.2 cm3. Regional vessel motion of the SMA, celiac trunk, and renal vessels was small (< 5 mm) and not significantly impacted by AC. Mean pancreatic motion was > 5 mm, so AC has been used in all patients enrolled thus far. AC did not significantly increase OAR dose including the stomach and traverse colon. There were several statistically significant differences in the doses to OARs as a function of the type of planning modality used. Conclusions AC does not significantly reduce the limited motion of structures in close proximity to the MIT target and does not significantly increase the dose to OARs that can be displaced by the compression plate. The treatment planning techniques evaluated in this study have different advantages with no clearly superior method in our analysis. Dose to adjacent vessels may be reduced with 3DSABR or IMRT techniques, while conformality is increased with IMRT or CK.

The performance of axial displacement estimation in ultrasound elastography can be degraded by tissue lateral displacements, mainly because of the move-in and move-out of tissue scatterers. In our previous work, a tissue axial stretching model was pro- posed to separate the decorrelation effect induced by lateral displacements from other decorrelation sources. In this paper, the tssue axial stretching model is analyzed theoretically. The theoretical result in a closed form indicates that the peak value of the cross-correlation function between the pre- and post-compression echoes is determined mainly by the beam width, the beam position and the lateral strain. Computer simulations are carried out to verify the theoretical conclusion. The theoretical analysis and simulation results can help to understand more clearly the decorrelation effect of tissue laterd displacements and the 2-D spatial comprehensive crossed correlation method presented previously to reduce the decorrelation effect. [ABSTRACT FROM AUTHOR]

Introduction: The study tested the feasibility of differentiating radiofrequency ablation lesions from normal myocardium and quantifying their dimensions by myocardial contrast echocardiography (MCE)., Methods and Results: In 11 normal dogs, we created 14 focal and 4 linear lesions at different left ventricular sites.MCE was performed both before and after ablation by using an intracardiac echocardiography catheter (9 MHz)and infusing contrast microbubbles through the left coronary artery. An independent observer examined the lesion pathology. We found that intracardiac echocardiography alone could not delineate lesion dimensions. However, after ablation, MCE localized the lesions as well-defined, low-contrast areas within the normally opacified myocardium. Lesion dimensions byMCE immediately after ablation and 30 minutes later were similar. In 12 focal lesions, the average maximum depth (5.55 +/- 1.38 mm) and average maximum diameter(10.38 +/- 2.09 mm) by MCE were in excellent agreement with the pathologic depth (5.20 +/- 1.45 mm) and diameter(10.61 +/- 1.67 mm). Two focal lesions could not be detected by MCE and later were found to be superficial. Three-dimensional MCE correctly reconstructed the extent and shape of linear lesions compared to pathology (length: 18.7+/- 5.7 vs 18.5 +/- 5.6 mm; maximum longitudinal cross-sectional area: 81.2 +/- 9.6 vs 76.0 +/-10.3 mm(2))., Conclusion: MCE accurately localized and quantified radiofrequency ablation lesions in the normal leftv entricle. This new application of MCE may advance'ablation for managing ventricular arrhythmias that involve intramural or epicardial regions by providing instantaneous anatomic feedback on the effects of ablation during catheterization.