Sensitivity Enhancement Using Chirp Transmission for an Ultrasound Arthroscopic Probe

Meniscal tear in the knee joint is a highly common injury that can require an ablation. However, the success rate of meniscectomy is highly impacted by difficulties in estimating the thin vascularization of the meniscus, which determines the healing capacities of the patient. Indeed, vascularization is estimated using arthroscopic cameras that lack of high sensitivity to blood flow. Here, we propose an ultrasound method for estimating the density of vascularization in the meniscus during surgery. This approach uses an arthroscopic probe driven by ultrafast sequences. To enhance the sensitivity of the method, we propose to use a chirp-coded excitation combined with a mismatched compression filter robust to the attenuation. This chirp approach was compared to a standard ultrafast emission and a Hadamard-coded emission using a flow phantom. The mismatched filter was also compared to a matched filter. Results show that, for a velocity of a few millimeters per second, the mismatched filter gives a 4.4-10.4-dB increase of the signal-to-noise ratio (SNR) compared to the Hadamard emission and a 3.1-6.6-dB increase compared to the matched filter. Such increases are obtained for a loss of axial resolution of 13% when comparing the point spread functions (PSFs) of the mismatched and matched filters. Hence, the mismatched filter allows increasing significantly the probe capacity to detect slow flows at the cost of a small loss in axial resolution. This preliminary study is the first step toward an ultrasensitive ultrasound arthroscopic probe able to assist the surgeon during meniscectomy.

P907Respective pronostic value of the valvular aortic calcifications and the thoracic aorta calcifications in patients with and without low gradient aortic stenosis after TAVI

Background

Both the valvular aortic calcifications (VAC) and the thoracic aorta calcifications (TAC) have a prognostic impact in patients with aortic stenosis. Their respective prognostic values in patients with and without low gradient aortic stenosis (LGAS) remain unknown after TAVI.

Objectives

To assess the prognostic significance of VAC and TAC in patients with and without LGAS regarding cardiovascular mortality after 3 years follow-up.

Methods

The CAPRI-LGAS is an ancillary study of the C4CAPRI trial (NCT02935491) including 1282 consecutive TAVI patients. Calcifications were measured on pre-TAVI CT. The primary outcome was defined as cardiovascular mortality 3 years after TAVI.

Results

Among the 1282 patients, 397 (31%) had a LGAS. Compared to the other patients, LGAS patients were more prone to be men, younger, with atrial fibrillation, and lower left ventricular ejection fraction (LVEF), p<0.05 for all. No statistically significant difference was noticed for pulmonary systolic pressures, history of diabetes, chronic respiratory disease, renal insufficiency or peripheral vascular disease. VAC was lower in LGAS compared to non-LGAS patients (1.05 cm3±0.7 vs 0.75 cm3±0.5), p<0.001, the contrary was noticed for TAC, (3.1 cm3±3 vs 3.7 cm3±3.7), p=0.011. After 3 years follow-up, 227 (17.7%) patients died from cardiovascular causes; respectively 85 (21.4%) and 142 (16.1%) patients with and without LGAS, p=0.02. In univariate analysis, in LGAS patients each increase of 1cm3 TAC was associated with cardiovascular mortality while VAC was not, respectively Hazard Ratio (HR) 1.07 and confidence interval (CI) (1.023–1.119) p=0.003, and HR 0.822 CI (0.523–1.292), p=0.39. In patients without LGAS both TAC and VAC were associated with mortality, respectively HR 1.054 CI (1.006–1.104), p=0.028 and HR 1.363 CI (1.092–1.701), p=0.006. Multivariate analysis was adjusted for TAC, VAC, age, gender, atrial fibrillation, and LVEF. In LGAS patients TAC but not VAC was still a predictor of cardiovascular mortality, respectively HR 1.092 CI (1.031–1.158), p=0.003, and HR 0.743 CI (0.464–1.191), p=0.21. In patients without LGAS TAC was no more associated with cardiovascular mortality while VAC was, respectively HR 1.306 CI (1.024–1.666), p=0.031, and HR 1.038 CI (0.985–1.094), p=0.161. When further adjusting on pulmonary systolic pressures, history of diabetes, chronic respiratory disease, renal insufficiency and peripheral vascular disease, the results remained similar ie in LGAS patients, TAC HR 1.090 CI (1.022–1.162), p=0.009 while in patients without LGAS VAC HR 1.377 CI (1.049–1.809), p=0.021.

Conclusions

The present study shows that VAC and TAC involve different prognostic information in patients with and without LGAS after TAVI. While VAC may be a marker of early and periprocedural mortality and aortic regurgitation in non-LGAS patients, TAC may continue to be harmful and increase afterload in patients with LGAS whom LVEF is often impaired.

3D strain assessment in ultrasound (Straus): a synthetic comparison of five tracking methodologies

This paper evaluates five 3D ultrasound tracking algorithms regarding their ability to quantify abnormal deformation in timing or amplitude. A synthetic database of B-mode image sequences modeling healthy, ischemic and dyssynchrony cases was generated for that purpose. This database is made publicly available to the community. It combines recent advances in electromechanical and ultrasound modeling. For modeling heart mechanics, the Bestel-Clement-Sorine electromechanical model was applied to a realistic geometry. For ultrasound modeling, we applied a fast simulation technique to produce realistic images on a set of scatterers moving according to the electromechanical simulation result. Tracking and strain accuracies were computed and compared for all evaluated algorithms. For tracking, all methods were estimating myocardial displacements with an error below 1 mm on the ischemic sequences. The introduction of a dilated geometry was found to have a significant impact on accuracy. Regarding strain, all methods were able to recover timing differences between segments, as well as low strain values. On all cases, radial strain was found to have a low accuracy in comparison to longitudinal and circumferential components.

Transverse oscillations for tissue motion estimation

This paper gives an overview of the methods developed for tissue motion estimation using transverse oscillation images (TO). TO images are specific radiofrequency ultrasound images featuring oscillations in both spatial directions. The initial studies on TO were published in the late 1990s. This paper reviews the main ideas and applications behind this motion estimation approach. First the origin and motivation of TO is briefly reviewed. Then the beamforming methods that lead to TO images are given, detailing the receive-only approach and the transmit-and-receive approach using synthetic aperture data. The different medical applications where TO has been used are discussed (blood flow, elastography and echocardiography), showing how it can improve motion estimation. Finally, the future perspectives of TO are outlined.

Parallel integral projection transform for straight electrode localization in 3-D ultrasound images

In surgical practice, small metallic instruments are frequently used to perform various tasks inside the human body. We address the problem of their accurate localization in the tissue. Recent experiments using medical ultrasound have shown that this modality is suitable for real-time visualization of anatomical structures as well as the position of surgical instruments. We propose an image-processing algorithm that permits automatic estimation of the position of a line-segment-shaped object. This method was applied to the localization of a thin metallic electrode in biological tissue. We show that the electrode axis can be found through maximizing the parallel integral projection transform that is a form of the Radon transform. To accelerate this step, hierarchical mesh-grid algorithm is implemented. Once the axis position is known, localization of the electrode tip is performed. The method was tested on simulated images, on ultrasound images of a tissue mimicking phantom containing a metallic electrode, and on real ultrasound images from breast biopsy. The results indicate that the algorithm is robust with respect to variations in electrode position and speckle noise. Localization accuracy is of the order of hundreds of micrometers and is comparable to the ultrasound system axial resolution.

Estimation methods for flow imaging with high frequency ultrasound

This article proposes to estimate slow blood flow with high frequency ultrasound imaging. The proposed technique combines 2 methods. First, a statistical method, called Speckle Flow Imaging (SFI) based on the analysis of changes in the speckle pattern along time, gives an index directly related to the total velocity vector. Secondly, a block matching approach estimates the in-plane velocity components. Results on calibrated flow sequences of blood mimicking fluid have shown good agreement with the statistical model. The quantification of flow is achieved with pulsed flow and is also angle independent when the flow is perpendicular to the ultrasound beam. Speckle Tracking has been evaluated on the same data and has shown good estimation of the in-plane velocity vector when the component of velocity perpendicular to the imaging plane is inferior to 1mm/s. The results of these two methods permit the evaluation of the total 3D velocity field and the orthogonal velocity component relative to the imaging plane. This allows the quantification of blood flow (volumetric per time unit across the sequence).