Quantitative Microvessel Analysis with 3D Super-Resolution Ultrasound and Velocity Mapping

Medical image analysis is becoming increasingly accessible in the clinic. Computed tomography (CT) or magnetic resonance imaging (MRI) scans are usually post-processed to generate a 3-D visualization of the human body for surgical assistance or extract quantitative data to provide additional diagnostic information. Three dimensional super-resolution ultrasound (SR US) imaging can provide similar information at a micro-level without the high cost or ionising radiation. In this study, we implemented a high volumetric-rate 3-D SR US imaging with a 2-D spiral-shaped array and imaged an in vitro microvascular structure. From the 3-D SR US images clinically relevant parameters, such as microvascular flow rate, microvessel density and tortuosity, were extracted and compared with the ground truth

Localization of a Scatterer in 3D with a Single Measurement and Single Element Transducer

Conventionally an A-mode scan, a single measurement with a single element transducer, is only used to detect the depth of a reflector or scatterer. In this case, a single measurement reveals only one-dimensional information; the axial distance. However, if the number of scatterers in the ultrasonic field is sparse, it is possible to detect the location of the scatter in multiple spatial dimensions. In this study, we developed a method to find the location of a scatterer in 3-D with a single-element transducer and single measurement. The feasibility of the proposed method was verified in 2-D with experimental measurements

Effect of Mechanical Index on Repeated Sparse Activation of Nanodroplets in Vivo

Current localization-based super-resolution ultrasound imaging requires a low concentration of flowing microbubbles to visualize microvasculature beyond the diffraction limit and acquisition is slow. Previous studies have shown that sparse activation of nanodroplets can be used for generating fast or even real-time super-resolution imaging. However, the optimal experimental conditions to activate the droplets for generating the super-resolution images are still unknown, especially the activation ultrasound amplitude or mechanical index (MI). An in vivo super-resolution image of a rabbit kidney is obtained in 1.1 seconds using AWSALM pulse sequence. The aim of this study is to investigate the effect of the activation MI on the repeated activation of nanodroplets in the rabbit kidney. It was found that the droplet activation was not observed in the rabbit kidney at a MI of 1.1. The activation of droplet started at an activation MI of 1.3. The contrast of activated droplet signals is maximized at an MI of 1.5 and decreased when the activation MI was increased above 1.5. The possible explanation might be that, at high MIs, the activated droplets were destroyed. Such understanding of the effects of activation MI could help improve droplet-base fast super-resolution imaging

Plane wave imaging challenge

The plane wave imaging challenge (PICMUS) has been introduced for the first time to IUS in order to encourage participants to compete and share their knowledge in medical ultrasound plane wave imaging. To participate in this challenge, we have chosen the contrast enhanced delay and sum (CEDAS) post signal processing method. This technique have been used to improve B-mode image contrast to noise ratio (CNR) without effecting the image spatial resolution. With CEDAS the energy of every envelope signal is calculated, mapped, and clustered in order to identify the cyst and clutter location. CEDAS significantly reduces the clutter inside the cyst by attenuating it from envelope signals before the new B-Mode image is formed. This paper describes in more details the techniques and parameters we have been using for the challenge. Results obtained for CEDAS shows that it outperforms conventional DAS by 18.33% in experiment and 79.24% in simulation for CNR

Determining the grain geometry from ultrasonic measurements of large-grained temperate ice cores

Ice shelf collapse significantly contributes to the global rise of sea levels. This intricate process of fracturing, though not yet fully understood, is intertwined with the mechanical attributes of ice. Among the critical physical attributes related to its mechanical characteristics is the crystal orientation fabric (COF), which encapsulates the dimensions, orientations, and inclinations of the constituent crystal grains within the ice structure. The acquisition of such granular information necessitates the extraction of ice cores from the ice sheets or shelves, followed by their transportation to a controlled laboratory environment. After this, these cores are sectioned into submillimetre slices and examined using polarised light microscopy (PLM). However, this procedure destroys the ice core specimens and only permits the acquisition of two-dimensional images, imparting only a partial depiction of the three-dimensional COF.The principal objective of this work is to explore the possibility of involving ultrasound technology to discern the crystal grains' COF and their geometries. This novel approach does not harm the sample material during the examination

Detecting and Characterizing the Fabella with High Frame-Rate Ultrasound Imaging

The fabella is a sesamoid bone usually located in the tendon of the lateral head of the gastrocnemius muscle, behind the knee joint. Prevalence rates in human populations vary widely with an average of 42.5% people having a fabella. Clinically, it is associated with a number of knee ailments, most notably the osteoarthritis of the knee and generalized knee pain (i.e., fabella syndrome). As the function of the fabella remains unknown, the biomechanical consequences of fabella presence/absence can only be speculated. Successfully detecting the fabella, measuring its size and determining its shape, are off importance for clinical and evolutionary researchers. In this work, we compare plane wave imaging with conventional focused imaging and evaluate their performance for detecting and characterizing the fabella

Velocity estimation error reduction in stenosis areas using a correlation correction method

The advent of ultrafast ultrasound imaging proved beneficial for capturing transient flow patterns which was never readily achievable before. Velocity estimation methods based on 2D block-matching outperform Doppler based methods by offering higher frame rate with the cost of increased uncertainty in presence of out-of-plane motion as a result of turbulent flow. Local median filtering can partially address the estimation error reduction in stenosis areas at the risk of higher inaccuracy, since neighboring values may be also outliers. In this study, a correlation correction method is proposed, where the out-of-plane motion is eliminated by means of multiplying correlation maps from a same area but in two adjacent pairs of RF images. Experimental investigations were performed on a wall-less flow phantom, and proposed method achieved an error reduction of 66% in turbulent flow regions

A phase velocity filter for the measurement of lamb wave dispersion

The complex, multi-modal and dispersive nature of guided waves makes them extremely effective in the non destructive evaluation of plate-like structures. Knowledge of the dispersion relation of a material is a prerequisite to many guided wave experiments. A frequency-phase velocity map is by far the most useful representation of dispersion. These phase velocity curves can be obtained numerically by solving the Lamb equations, however instabilities and unfamiliarity with the specimen's parameters makes experimentally obtained dispersion relation desirable. Transformations can be applied to an experimentally obtained frequency-wave number map but it requires prohibitively high number of sampling points in space to resolve modes across the full bandwidth of the transducer. The phase velocity filter described here is able to extract wavelets of a particular phase velocity irrespective of frequency. When applied to the acquisition of dispersion relation, the technique exhibits reduced artefacts and is able to extract modes across the full bandwidth of the excitation. Results show a bandwidth increase of approximately 58%

Clutter noise reduction in B-Mode image through mapping and clustering signal energy for better cyst classification

Improving the ultrasound image contrast ratio (CR) and contrast to noise ratio (CNR) has many clinical advantages. Breast cancer detection is one example. Anechoic cysts which fill with clutter noise can be easily misinterpreted and classified as malignant lesions instead of benign. Beamforming techniques contribute to off-axis side lobes and clutter. These two side effects inherent in beamforming are undesirable since they will degrade the image quality by lowering the image CR and CNR. To overcome this issue a new post-processing technique known as contrast enhanced delay and sum (CEDAS) is proposed. Here the energy of every envelope signals are calculated, mapped, and clustered in order to identify the cyst and clutter location. CEDAS reduce clutter inside the cyst by attenuating it from envelope signals before the new B-Mode image is formed. With CEDAS, the image CR and CNR improved by average 12 dB and 1.1 dB respectively for cysts size 2 mm to 6 mm and imaging depth from 40 mm to 80 mm

Contrast-Enhanced Ultrasound Imaging with Chirps: Signal Processing and Pulse Compression

Contrast-enhanced ultrasound imaging creates one of the worst case scenarios for pulse compression due to depth and frequency dependent attenuation, high level of harmonic generation, phase variations due to resonance behavior of microbubbles, and increased broadband noise by microbubble destruction. This study investigates the feasibility of pulse compression with a matched filter in the existence of microbubbles with resonant behavior. Simulations and experimental measurements showed that the scattered pressure from a microbubble population excited by a chirp waveform preserves its chirp rate even for harmonic frequencies. Although, pulse compression by a matched filter was possible due to the conservation of the chirp rate, an increase on sidelobe levels were observed at fundamental and second harmonic frequencies. Therefore, using chirp excitation and a matched filter pair will increase the contrast-to-tissue ratio with a trade-off of decreased image quality