Left Ventricular Border Tracking Using Cardiac Motion Models and Optical Flow

The use of automated methods is becoming increasingly important for assessing cardiac function quantitatively and objectively. In this study, we propose a method for tracking three-dimensional (3-D) left ventricular contours. The method consists of a local optical flow tracker and a global tracker, which uses a statistical model of cardiac motion in an optical-flow formulation. We propose a combination of local and global trackers using gradient-based weights. The algorithm was tested on 35 echocardiographic sequences, with good results (surface error: 1.35 ± 0.46 mm, absolute volume error: 5.4 ± 4.8 mL). This demonstrates the method’s potential in automated tracking in clinical quality echocardiograms, facilitating the quantitative and objective assessment of cardiac functio

Tracking the Endocardial Border in Artifact-Prone 3D Images

Echocardiography is a commonly-used, safe, and noninvasive method for assessing cardiac dysfunction and related coronary artery disease. The analysis of echocardiograms, whether visual or automated, has traditionally been hampered by the presence of ultrasound artifacts, which obscure the moving myocardial wall. In this study, a novel method is proposed for tracking the endocardial surface in 3D ultrasound images. Artifacts which obscure the myocardium are detected in order to improve the quality of cardiac boundary segmentation. The expectation-maximization algorithm is applied in a stationary and dynamic, cardiac-motion frame-of-reference, and weights are derived accordingly. The weights are integrated with an optical-flow based contour tracking method, which incorporates prior knowledge via a statistical model of cardiac motion. Evaluation on 35 three-dimensional echocardiographic sequences shows that this weighed tracking method significantly improves the tracking results. In conclusion, the proposed weights are able to reduce the influence of artifacts, resulting in a more accurate quantitative analysis

Clinical value of two compounding techniques for IVUS palpography

This study aims at the in-vivo assessment of two compounding techniques for IVUS Palpography. To increase the elastographic contrast-to-noise ratio, Doyley et. al. proposed a compounding scheme for IVUS Palpography [1]. The neighboring IVUS frames acquired at diastole are paired to compute the luminal strain profiles or partial palpograms. Subsequently, the obtained strain maps are averaged to form a final compounded strain profile for a given cross-section of a coronary artery. This first scheme is further referred to as the classical compounding. The second scheme explicitly takes into account that the measured strains are only partially available. It attempts at reconstructing the missing elasticity values by using the available strain information in its direct vicinity using the Normalized Convolution method. The improved partial strain profiles are subsequently averaged in the same manner as in classical compounding. This scheme was coined as reconstructive compounding. Eight in-vivo IVUS pullbacks were used for the comparative analysis. The percentage of valid strains was 28:6±13:7% for the scheme without compounding, 94:3±4:4% and 99:7 ± 0:2% for the classical and reconstructive methods, respectively. Implementation of the compounding schemes significantly boosts the diagnostic information coming out of IVUS Palpography with the reconstructive scheme being the best

SPASM: A 3D-ASM for segmentation of sparse and arbitrarily oriented cardiac

MRI dat

Super-harmonic imaging: development of an interleaved phased-array transducer

For several years, the standard in ultrasound imaging has been second-harmonic imaging. A new imaging technique dubbed "super-harmonic imaging" (SHI) was recently proposed. It takes advantage of the higher-third to fifth-harmonics arising from nonlinear propagation or ultrasound-contrast-agent (UCA) response. Next to its better suppression of near-field artifacts, tissue SHI is expected to improve axial and lateral resolutions resulting in clearer images than second-harmonic imaging. When SHI is used in combination with UCAs, a better contrast-to-tissue ratio can be obtained. The use of SHI implies a large dynamic range and requires a sufficiently sensitive array over a frequency range from the transmission frequency up to its fifth harmonic (bandwidth > 130%). In this paper, we present the characteristics and performance of a new interleaved dual frequency array built chiefly for SHI. We report the rationale behind the design choice, frequencies, aperture, and piezomaterials used. The array is efficient both in transmission and reception with well-behaved transfer functions and a combined -6-dB bandwidth of 144%. In addition, there is virtually no contamination of the harmonic components by spurious transducer transmission, due to low element-to-element crosstalk (< 30 dB) and a low transmission efficiency of the odd harmonics (< 46 dB). The interleaved array presented in this article possesses ideal characteristics for SHI and is suitable for other methods like second-harmonic, subharmonic, and second-order ultrasound field (SURF) imagin

Single Pulse Frequency Compounding Protocol for Superharmonic Imaging

ABSTRACT Second harmonic imaging is currently adopted as standard in commercial echographic systems. A new imaging technique, coined as superharmonic imaging (SHI), combines the 3rd till the 5th harmonics, arising during nonlinear sound propagation. It could further enhance resolution and quality of echographic images. To meet the bandwidth requirement for SHI a dedicated phased array has been developed: a low frequency subarray, intended for transmission, interleaved with a high frequency subarray, used in reception. As the bandwidth of the elements is limited, the spectral gaps in between the harmonics cause multiple reflection artifacts. Recently, we introduce a dual-pulse frequency compounding (DPFC) method to suppress those artifacts at price of a reduced frame rate. In this study we investigate the feasibility of performing the frequency compounding protocol within a single transmission. The traditional DPFC method constructs each trace in a post-processing stage by summing echoes from two emitted pulses, the second slightly frequency-shifted compared to the first. In the newly proposed method, the transmit aperture is divided into two parts: the first half is used to send a pulse at the lower center frequency, while the other half simultaneously transmits at the higher center frequency. The suitability of the protocol for medical imaging applications in terms of the steering capabilities was performed in a simulation study using the FIELD II toolkit. Moreover, an experimental study was performed to deduce the optimal parametric set for implementation of the clinical imaging protocol. The latter was subsequently used to obtain the images of a tissue mimicking phantom containing strongly reflecting wires. For in-vitro acquisitions the SHI probe with interleaved phased array (44 odd elements at 1MHz and 44 even elements at 3.7MHz elements, optimized for echocardiography) was connected to a fully programmable ultrasound system. The results of the Field II simulations demonstrated that the angle between the main and grating lobe amounted to 90 • . The difference in the fundamental pressure level between those lobes was equal to −26.8 dB. Those results suggest that the superharmonic content in the grating lobe was acceptably low. A considerable improvement in the axial resolution of the SHI component (0.73 mm) at −6 dB in comparison with the 3rd harmonic (2.23 mm) was observed. A similar comparison in terms of the lateral resolution slightly favored the superharmonic component by 0.2 mm. Additionally, the images of the tissue mimicking phantom exhibited an absence of the multiple reflection artifacts in the focal and post-focal regions. The new method is equally effective in eliminating the ripple artifacts associated with SHI as the dual pulse technique, while the full frame rate is maintained. This work was funded by the Dutch foundation for technical sciences (STW) and OlDelft. (Delft, the Netherlands)