440 research outputs found
3D Quasi-Static Ultrasound Elastography With Plane Wave In Vivo
In biological tissue, an increase in elasticity is often a marker of
abnormalities. Techniques such as quasi-static ultrasound elastography have
been developed to assess the strain distribution in soft tissues in two
dimensions using a quasi-static compression. However, as abnormalities can
exhibit very heterogeneous shapes, a three dimensional approach would be
necessary to accurately measure their volume and remove operator dependency.
Acquisition of volumes at high rates is also critical to performing real-time
imaging with a simple freehand compression. In this study, we developed for the
first time a 3D quasi-static ultrasound elastography method with plane waves
that estimates axial strain distribution in vivo in entire volumes at high
volume rate. Acquisitions were performed with a 2D matrix array probe of 2.5MHz
frequency and 256 elements. Plane waves were emitted at a volume rate of 100
volumes/s during a continuous motorized and freehand compression. 3D B-mode
volumes and 3D cumulative axial strain volumes were successfully estimated in
inclusion phantoms and in ex vivo canine liver before and after a high
intensity focused ultrasound ablation. We also demonstrated the in vivo
feasibility of the method using freehand compression on the calf muscle of a
human volunteer and were able to retrieve 3D axial strain volume at a high
volume rate depicting the differences in stiffness of the two muscles which
compose the calf muscle. 3D ultrasound quasi-static elastography with plane
waves could become an important technique for the imaging of the elasticity in
human bodies in three dimensions using simple freehand scanning
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An Alternative Approach to Spectrum-Based Atherosclerotic Plaque Characterization Techniques Using Intravascular Ultrasound (IVUS) Backscattered Signals
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Texture-Driven Coronary Artery Plaque Characterization Using Wavelet Packet Signatures
High-frequency ultrasound transducers are being widely used to generate high resolution, real time, cross-sectional images of the coronary arteries. In this paper, we present a robust unsupervised texture-derived technique based on multi-channel wavelet frames to delineate atherosclerotic plaque compositions. The intravascular ultrasound (IVUS) signals were acquired from coronary arteries dissected from 32 diseased cadaver hearts employing 40 MHz mechanically rotating, single-element transducers. The wavelet packet representations were classified using a K- means clustering algorithm to generate IVUS-histology color maps (IV-HCMs) and categorize tissues in lipidic, fibrotic and calcified. Finally, two independent observers evaluated the results contrasting the histology images corresponding to the IV-HCMs. Our results show that the proposed algorithm may have great potential as an alternative to existing spectrum-based classification techniques
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Automatic detection of blood versus non-blood regions on intravascular ultrasound (IVUS) images using wavelet packet signatures
Intravascular ultrasound (IVUS) has been proven a reliable imaging modality that is widely employed in cardiac interventional procedures. It can provide morphologic as well as pathologic information on the occluded plaques in the coronary arteries. In this paper, we present a new technique using wavelet packet analysis that differentiates between blood and non-blood regions on the IVUS images. We utilized the multi-channel texture segmentation algorithm based on the discrete wavelet packet frames (DWPF). A k-mean clustering algorithm was deployed to partition the extracted textural features into blood and non-blood in an unsupervised fashion. Finally, the geometric and statistical information of the segmented regions was used to estimate the closest set of pixels to the lumen border and a spline curve was fitted to the set. The presented algorithm may be helpful in delineating the lumen border automatically and more reliably prior to the process of plaque characterization, especially with 40 MHz transducers, where appearance of the red blood cells renders the border detection more challenging, even manually. Experimental results are shown and they are quantitatively compared with manually traced borders by an expert. It is concluded that our two dimensional (2-D) algorithm, which is independent of the cardiac and catheter motions performs well in both in-vivo and in-vitro cases
Getting ahead of Alzheimer’s disease: early intervention with focused ultrasound
The amyloid-β (Aβ) hypothesis implicates Aβ protein accumulation in Alzheimer’s disease (AD) onset and progression. However, therapies targeting Aβ have proven insufficient in achieving disease reversal, prompting a shift to focus on early intervention and alternative therapeutic targets. Focused ultrasound (FUS) paired with systemically-introduced microbubbles (μB) is a non-invasive technique for targeted and transient blood–brain barrier opening (BBBO), which has demonstrated Aβ and tau reduction, as well as memory improvement in models of late-stage AD. However, similar to drug treatments for AD, this approach is not sufficient for complete reversal of advanced, symptomatic AD. Here we aim to determine whether early intervention with FUS-BBBO in asymptomatic AD could delay disease onset. Thus, the objective of this study is to measure the protective effects of FUS-BBBO on anxiety, memory and AD-associated protein levels in female and male triple transgenic (3xTg) AD mice treated at an early age and disease state. Here we show that early, repeated intervention with FUS-BBBO decreased anxiety-associated behaviors in the open field test by 463.02 and 37.42% in male and female cohorts, respectively. FUS-BBBO preserved female aptitude for learning in the active place avoidance paradigm, reducing the shock quadrant time by 30.03 and 31.01% in the final long-term and reversal learning trials, respectively. Finally, FUS-BBBO reduced hippocampal accumulation of Aβ40, Aβ42, and total tau in females by 12.54, 13.05, and 3.57%, respectively, and reduced total tau in males by 18.98%. This demonstration of both cognitive and pathological protection could offer a solution for carriers of AD-associated mutations as a safe, non-invasive technique to delay the onset of the cognitive and pathological effects of AD
Precision estimation and imaging of normal and shear components of the 3D strain tensor in elastography
Abstract. In elastography we have previously developed a tracking and correction method that estimates the axial and lateral strain components along and perpendicular to the compressor/scanning axis following an externally applied compression. However, the resulting motion is a three-dimensional problem. Therefore, in order to fully describe this motion we need to consider a 3D model and estimate all three principal strain components, i.e. axial, lateral and elevational (out-of-plane), for a full 3D tensor description. Since motion is coupled in all three dimensions, the three motion components have to be decoupled prior to their estimation. In this paper, we describe a method that estimates and corrects motion in three dimensions, which is an extension of the 2D motion tracking and correction method discussed before. In a similar way as in the 2D motion estimation, and by assuming that ultrasonic frames are available in more than one parallel elevational plane, we used methods of interpolation and cross-correlation between elevationally displaced RF echo segments to estimate the elevational displacement and strain. In addition, the axial, lateral and elevational displacements were used to estimate all three shear strain components that, together with the normal strain estimates, fully describe the full 3D normal strain tensor resulting from the uniform compression. Results of this method from three-dimensional finite-element simulations are shown
A New Brain Drug Delivery Strategy: Focused Ultrasound-Enhanced Intranasal Drug Delivery
Central nervous system (CNS) diseases are difficult to treat because of the blood-brain barrier (BBB), which prevents most drugs from entering into the brain. Intranasal (IN) administration is a promising approach for drug delivery to the brain, bypassing the BBB; however, its application has been restricted to particularly potent substances and it does not offer localized delivery to specific brain sites. Focused ultrasound (FUS) in combination with microbubbles can deliver drugs to the brain at targeted locations. The present study proposed to combine these two different platform techniques (FUS+IN) for enhancing the delivery efficiency of intranasally administered drugs at a targeted location. After IN administration of 40 kDa fluorescently-labeled dextran as the model drug, FUS targeted at one region within the caudate putamen of mouse brains was applied in the presence of systemically administered microbubbles. To compare with the conventional FUS technique, in which intravenous (IV) drug injection is employed, FUS was also applied after IV injection of the same amount of dextran in another group of mice. Dextran delivery outcomes were evaluated using fluorescence imaging of brain slices. The results showed that FUS+IN enhanced drug delivery within the targeted region compared with that achieved by IN only. Despite the fact that the IN route has limited drug absorption across the nasal mucosa, the delivery efficiency of FUS+IN was not significantly different from that of FUS+IV. As a new drug delivery platform, the FUS+IN technique is potentially useful for treating CNS diseases
In Vivo Feasibility of Real-Time Monitoring of Focused Ultrasound Surgery (FUS) Using Harmonic Motion Imaging (HMI)
Abstract-In this study, the Harmonic Motion Imaging for Focused Ultrasound (HMIFU) technique is applied to monitor changes in mechanical properties of tissues during thermal therapy in a transgenic breast cancer mouse model in vivo. An HMIFU system, composed of a 4.5-MHz focused ultrasound (FUS) and a 3.3-MHz phased-array imaging transducer, was mechanically moved to image and ablate the entire tumor. The FUS transducer was driven by an amplitude-modulated (AM) signal at 15 Hz. The acoustic intensity (I sp ta ) was equal to 1050 W/cm 2 at the focus. A digital low-pass filter was used to filter out the spectrum of the FUS beam and its harmonics prior to displacement estimation. The resulting axial displacement was estimated using 1-D crosscorrelation on the acquired RF signals. Results from two mice with eight lesions formed in each mouse (16 lesions total) showed that the average peak-to-peak displacement amplitude before and after lesion formation was respectively equal to 17.34 ± 1.34 µm and 10.98 ± 1.82 µm (p < 0.001). Cell death was also confirmed by hematoxylin and eosin histology. HMI displacement can be used to monitor the relative tissue stiffness changes in real time during heating so that the treatment procedure can be performed in a timeefficient manner. The HMIFU system may, therefore, constitute a cost-efficient and reliable alternative for real-time monitoring of thermal ablation. Index Terms-Acoustic radiation force, breast cancer, focused ultrasound surgery (FUS), harmonic motion imaging, highintensity focused ultrasound (HIFU), in vivo, monitoring, noninvasive estimation, tissue ablation, ultrasound
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