Acoustical structured illumination for super-resolution ultrasound imaging.

Structured illumination microscopy is an optical method to increase the spatial resolution of wide-field fluorescence imaging beyond the diffraction limit by applying a spatially structured illumination light. Here, we extend this concept to facilitate super-resolution ultrasound imaging by manipulating the transmitted sound field to encode the high spatial frequencies into the observed image through aliasing. Post processing is applied to precisely shift the spectral components to their proper positions in k-space and effectively double the spatial resolution of the reconstructed image compared to one-way focusing. The method has broad application, including the detection of small lesions for early cancer diagnosis, improving the detection of the borders of organs and tumors, and enhancing visualization of vascular features. The method can be implemented with conventional ultrasound systems, without the need for additional components. The resulting image enhancement is demonstrated with both test objects and ex vivo rat metacarpals and phalanges

Ultrasound localization microscopy to image and assess microvasculature in a rat kidney.

The recent development of ultrasound localization microscopy, where individual microbubbles (contrast agents) are detected and tracked within the vasculature, provides new opportunities for imaging the vasculature of entire organs with a spatial resolution below the diffraction limit. In stationary tissue, recent studies have demonstrated a theoretical resolution on the order of microns. In this work, single microbubbles were localized in vivo in a rat kidney using a dedicated high frame rate imaging sequence. Organ motion was tracked by assuming rigid motion (translation and rotation) and appropriate correction was applied. In contrast to previous work, coherence-based non-linear phase inversion processing was used to reject tissue echoes while maintaining echoes from very slowly moving microbubbles. Blood velocity in the small vessels was estimated by tracking microbubbles, demonstrating the potential of this technique to improve vascular characterization. Previous optical studies of microbubbles in vessels of approximately 20 microns have shown that expansion is constrained, suggesting that microbubble echoes would be difficult to detect in such regions. We therefore utilized the echoes from individual MBs as microscopic sensors of slow flow associated with such vessels and demonstrate that highly correlated, wideband echoes are detected from individual microbubbles in vessels with flow rates below 2 mm/s

Evaluation ultrasonore des propriétés de l'os cortical par mesure d'ondes guidées en transmission axiale

La méthode de référence actuelle mesurant la qualité osseuse est une mesure par rayons X de la masse osseuse. Elle ne fournit toutefois pas d information directe sur les paramètres géométriques et mécaniques, déterminants de la résistance osseuse. Les méthodes ultrasonores sont elles sensibles à ces deux paramètres de part la nature des ondes élastiques mesurées. Dans ce travail, nous avons adopté une approche multi émetteurs / multi récepteurs en configuration de transmission axiale. Cette méthode a l avantage d'utiliser un réseau linéaire compact dédié aux mesures cliniques. Un traitement du signal basé sur la décomposition en valeurs singulières de la matrice de réponse permet de mesurer dans le plan (fréquence, nombre d onde) les trajectoires des ondes guidées se propageant dans la coque corticale des os longs. En utilisant le système de mesure clinique, une procédure d inversion a été mise en œuvre et validée sur des fantômes de différentes géométries (plaque, tube), de différentes épaisseurs et de différents matériaux (isotrope, anisotrope). La procédure d inversion permet de déterminer de manière combinée l épaisseur et les propriétés élastiques par comparaison avec un modèle de plaque libre. Les outils développés pour les fantômes ont ensuite été utilisés pour la caractérisation de radius humains ex vivo. Les épaisseurs estimées sur les échantillons humains sont en accord avec des mesures de référence par tomographie rayons X. Pour la caractérisation osseuse, ce travail met en évidence les possibilités offertes par une approche multiparamétrique basée sur l analyse des ondes guidéesPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Correlation magnitude between frames acquired during the thermometry sequence and the matching reference frames for 3-D motion measurements as calculated over the entire ROI.

<p>(A) With a single reference frame and (B) with the proposed multi-reference frame method. With a single reference frame, only a fraction of the sequence shows high correlation and can be processed for temperature estimation. With the proposed method, correlation is maintained during the whole sequence.</p

Comparison of estimated temperature elevation with and without 3-D artificial physiological motion.

<p>Temperature elevation measured for the 3-D diagonal motion with a total displacement of (A) 5.2 mm, (B) 6.9 mm, and (C) 8.7 mm. For all three measurements, HIFU was applied between <i>t</i> = 10 s and <i>t</i> = 40 s. (D) Lower temperature values are associated with out-of-plane periodicity as the probe moves away from the focal spot. A movie of the strain-based temperature map superimposed on the B-mode image in the presence of 3-D diagonal motion is provided in the supplementary materials (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134938#pone.0134938.s005" target="_blank">S3 Movie</a>).</p

PID control of temperature elevation using strain-based temperature measurement.

<p>Comparison between requested temperature and strain-based temperature during PID control of hyperthermia (A) without motion and (B) in the presence of 2-D periodic motion with different displacements.</p

Comparison of estimated temperature elevation with and without artificial 1-D and 2-D physiological motion.

<p>(A) Axial compression in 1-D (ax. comp.), (B) in-plane diagonal motion (2-D) in the presence of a 4°C increase, and (C) in-plane diagonal motion (2-D) in presence of a 7°C increase. (D) Comparison of temperature estimation in presence of periodic 2-D motion (2-s period) and aperiodic motion. For the aperiodic motion, the displacement was diagonal and bounded to a maximum displacement of 7.1 mm but the speed and position was varied randomly during the motion. For all of the measurements, HIFU was applied between <i>t</i> = 10 s and <i>t</i> = 40 s. Movies of the strain-based temperature map superimposed on the B-mode image in the presence of axial compression and 2-D diagonal motion are provided in the supplementary materials <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134938#pone.0134938.s003" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0134938#pone.0134938.s004" target="_blank">S2</a> Movies, respectively.</p

Spatial and Temporal Control of Hyperthermia Using Real Time Ultrasonic Thermal Strain Imaging with Motion Compensation, Phantom Study

<div><p>Mild hyperthermia has been successfully employed to induce reversible physiological changes that can directly treat cancer and enhance local drug delivery. In this approach, temperature monitoring is essential to avoid undesirable biological effects that result from thermal damage. For thermal therapies, Magnetic Resonance Imaging (MRI) has been employed to control real-time Focused Ultrasound (FUS) therapies. However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied. To facilitate such technology, ultrasound thermometry has potential to reliably monitor temperature. Control of mild hyperthermia was previously achieved using a proportional-integral-derivative (PID) controller based on thermocouple measurements. Despite accurate temporal control of heating, this method is limited by the single position at which the temperature is measured. Ultrasound thermometry techniques based on exploiting the thermal dependence of acoustic parameters (such as longitudinal velocity) can be extended to create thermal maps and allow an accurate monitoring of temperature with good spatial resolution. However, <i>in vivo</i> applications of this technique have not been fully developed due to the high sensitivity to tissue motion. Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment. The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring. PID control of mild hyperthermia in presence of motion was then tested with ultrasound thermometry as feedback and temperature was maintained within 0.3°C of the requested value.</p></div