Forward model for quantitative pulse-echo speed-of-sound imaging

Computed ultrasound tomography in echo mode (CUTE) allows determining the spatial distribution of speed-of-sound (SoS) inside tissue using handheld pulse-echo ultrasound (US). This technique is based on measuring the changing phase of beamformed echoes obtained under varying transmit (Tx) and/or receive (Rx) steering angles. The SoS is reconstructed by inverting a forward model describing how the spatial distribution of SoS is related to the spatial distribution of the echo phase shift. CUTE holds promise as a novel diagnostic modality that complements conventional US in a single, real-time handheld system. Here we demonstrate that, in order to obtain robust quantitative results, the forward model must contain two features that were not taken into account so far: a) the phase shift must be detected between pairs of Tx and Rx angles that are centred around a set of common mid-angles, and b) it must account for an additional phase shift induced by the error of the reconstructed position of echoes. In a phantom study mimicking liver imaging, this new model leads to a substantially improved quantitative SoS reconstruction compared to the model that has been used so far. The importance of the new model as a prerequisite for an accurate diagnosis is corroborated in preliminary volunteer results

Speckle noise reduction in medical ultrasound RF raw images

Ultrasonography is the commonly used imaging modality for the examination of several pathologies due to its non-invasiveness, affordability and easiness of use. However, ultrasound images are degraded by an intrinsic artifact called 'speckle', which is the result of the constructive and destructive coherent summation of ultrasound echoes. This paper aims to generate B-mode images out of radiofrequency (RF) data following standard procedures, a series of steps such as envelope detection, log-compression and scan conversion. The best set of parameters of this pipeline will be selected in order to achieve B-mode images with high quality.info:eu-repo/semantics/publishedVersio

Increasing the Efficiency of Doppler Processing and Backend Processing in Medical Ultrasound Systems

abstract: Ultrasound imaging is one of the major medical imaging modalities. It is cheap, non-invasive and has low power consumption. Doppler processing is an important part of many ultrasound imaging systems. It is used to provide blood velocity information and is built on top of B-mode systems. We investigate the performance of two velocity estimation schemes used in Doppler processing systems, namely, directional velocity estimation (DVE) and conventional velocity estimation (CVE). We find that DVE provides better estimation performance and is the only functioning method when the beam to flow angle is large. Unfortunately, DVE is computationally expensive and also requires divisions and square root operations that are hard to implement. We propose two approximation techniques to replace these computations. The simulation results on cyst images show that the proposed approximations do not affect the estimation performance. We also study backend processing which includes envelope detection, log compression and scan conversion. Three different envelope detection methods are compared. Among them, FIR based Hilbert Transform is considered the best choice when phase information is not needed, while quadrature demodulation is a better choice if phase information is necessary. Bilinear and Gaussian interpolation are considered for scan conversion. Through simulations of a cyst image, we show that bilinear interpolation provides comparable contrast-to-noise ratio (CNR) performance with Gaussian interpolation and has lower computational complexity. Thus, bilinear interpolation is chosen for our system.Dissertation/ThesisM.S. Electrical Engineering 201

High-Frequency Ultrasound M-Mode Imaging for Identifying Lesion and Bubble Activity During High-Intensity Focused Ultrasound Ablation

Effective real-time monitoring of high-intensity focused ultrasound (HIFU) ablation is important for application of HIFU technology in interventional electrophysiology. This study investigated rapid, high-frequency M-mode ultrasound imaging for monitoring spatiotemporal changes during HIFU application. HIFU (4.33 MHz, 1 kHz PRF, 50% duty cycle, 1 s, 2600 – 6100 W/cm2 ) was applied to ex-vivo porcine cardiac tissue specimens with a confocally and perpendicularly aligned high-frequency imaging system (Visualsonics Vevo 770, 55 MHz center frequency). Radiofrequency (RF) data from M-mode imaging (1 kHz PRF, 2 s × 7 mm) was acquired before, during, and after HIFU treatment (n = 12). Among several strategies, the temporal maximum integrated backscatter with a threshold of +12 dB change showed the best results for identifying final lesion width (receiver-operating characteristic curve area 0.91 ± 0.04, accuracy 85 ± 8%, as compared to macroscopic images of lesions). A criterion based on a line-to-line decorrelation coefficient is proposed for identification of transient gas bodies

Investigation of pulse compression technique and time-frequency analysis in medical ultrasound imaging

Linear frequency modulation (LFM) followed by pulse Compression processing has bee

Semi-blind ultrasound image deconvolution from compressed measurements

The recently proposed framework of ultrasound compressive deconvolution offers the possibility of decreasing the acquired data while improving the image spatial resolution. By combining compressive sampling and image deconvolution, the direct model of compressive deconvolution combines random projections and 2D convolution with a spatially invariant point spread function. Considering the point spread function known, existing algorithms have shown the ability of this framework to reconstruct enhanced ultrasound images from compressed measurements by inverting the forward linear model. In this paper, we propose an extension of the previous approach for compressive blind deconvolution, whose aim is to jointly estimate the ultrasound image and the system point spread function. The performance of the method is evaluated on both simulated and in vivo ultrasound data

Noninvasive Two-Dimensional Strain Imaging of Atherosclerosis: A Preliminary Study in Carotid Arteries In Vivo

AbstractAtherosclerosis remains a major cause of mortality all over the world and the sudden rupture of atherosclerotic plaque is the most important assassin. Vascular ultrasound elastography has shown promise in estimating the elastic properties to evaluate the plaque vulnerability. Contrary to intravascular elastography, noninvasive applications use a transcutaneous ultrasound transducer that is inexpensive, re-useable and convenient. To estimate the strain map, we employ a cross-correlation method in complex field to extract both the magnitude and phase messages of the ultrasound RF-echo signal. Two-dimension noninvasive carotid elastography was studied in atherosclerotic rats and New Zealand Rabbits and also in healthy volunteer, and the results indicate huge potential for diagnosis of the vulnerability of atheromatous plaques