John Albinsson

Improved Tracking Performance of Lagrangian Block-Matching Methodologies Using Block Expansion in the Time Domain: In Silico, Phantom and in Vivo Evaluations

The aim of this study was to evaluate tracking performance when an extra reference block is added to a basic block-matching method, where the two reference blocks originate from two consecutive ultrasound frames. The use of an extra reference block was evaluated for two putative benefits: (i) an increase in tracking performance while maintaining the size of the reference blocks, evaluated using in silico and phantom cine loops; (ii) a reduction in the size of the reference blocks while maintaining the tracking performance, evaluated using in vivo cine loops of the common carotid artery where the longitudinal movement of the wall was estimated. The results indicated that tracking accuracy improved (mean = 48%, p < 0.005 [in silico]; mean = 43%, p < 0.01 [phantom]), and there was a reduction in size of the reference blocks while maintaining tracking performance (mean = 19%, p < 0.01 [in vivo]). This novel method will facilitate further exploration of the longitudinal movement of the arterial wall.

A fast 2D tissue motion estimator based on the phase of the intensity enables visualization of the propagation of the longitudinal movement in the carotid artery wall

A fast 2D motion estimator has been developed and evaluated. The method does not utilize block-matching or iterative solutions and is thus more computationally efficient and suitable for real-time motion estimation over the entire image. The method has been evaluated on 1) phantom measurements and 2) in vivo on the carotid artery wall of 17 subjects, where measurements of the longitudinal displacement of the intima-media complex were compared to our previously validated method. The mean error of the phantom measurements was 2.0±3.3% (velocities between 2-15 mm/s; approx. 60 million estimations). In the in vivo measurements the mean difference (validated-proposed) was 18±44μm. Further the method has enabled visualization of the propagation of the longitudinal movement in the carotid artery wall. Several different phases of the longitudinal propagation, which seem to be connected to the multi-phasic pattern of the longitudinal movement, can be seen. All phases of the longitudinal propagation seem to originate from the direction of the heart.

Combined use of iteration, quadratic interpolation and an extra kernel for high-resolution 2D particle tracking: A first evaluation

A novel 2D particle tracking method, that uses 1) iteration, 2) fast quadratic sub-pixel estimation (with only 28 multiplications per movement), and 3) a previous kernel, has been evaluated and compared with a full-search block-matching method. The comparison with high-frequency ultrasound data (40 MHz) was conducted in silico and on phantoms, which comprised lateral, diagonal, and ellipsoidal movement patterns with speeds of 0–15 mm/s. The mean tracking error was reduced by 68% in silico and 71% for the phantom measurements. When only sub-pixel estimation was used, the decrease in the tracking error was 61% in silico and 57% for the phantom measurements. As well as decreasing the tracking error, the new method only used 70% of the computational time needed by the full-search block-matching method. With a fast method having good tracking ability for high-frequency ultrasound data, we now have a tool to better investigate tissue movements and its dynamic functionality.

Longitudinal Movement of the Common Carotid Artery Wall: New Information on Cardiovascular Aging

Putative changes in the multiphasic pattern of longitudinal movement of the common carotid artery wall in the normal aging process are unknown. The aim of this study was to explore the phases, and resulting patterns, of the longitudinal movement of the intima-media complex of the human common carotid artery with respect to age and gender. One hundred thirty-five healthy non-smoking patients of different ages were investigated using in-house-developed ultrasound methods. The patterns of longitudinal movement seen in middle-aged and older patients were markedly different from those commonly seen in young patients, including the appearance of two additional phases of motion and, thus, new complex patterns. The displacement and maximum velocity of one of the phases, occurring at the time of aortic valve closure, increased quadratically with age in both men and women.

Tracking Performance of Several Combinations of Common Evaluation Metrics and Sub-pixel Methods

Motion estimation in a series of consecutive images is used in a variety of areas, e.g. video compression and investigation of tissue characteristics and organ function in medical images. Several methods exist both for estimating motions on a pixel level, e.g. block-matching in which two blocks in consecutive images are compared by an evaluation metric, and on a sub-pixel level. In this paper, we have evaluated the tracking performance of all combinations between three evaluation metrics and eight sub-pixel estimation methods. The tracking performance of a sub-pixel method varies depending on the evaluation metric used. This indicates that a reported tracking performance for a sub-pixel estimation method can be significantly different when combined with another evaluation metric. Also there is a large variation in the time needed for the motion estimations depending primarily on the sub-pixel method used but also on the evaluation metric.

Volume flow assessment through simultaneous B-mode and Multigate Doppler

The typical approach for volumetric blood flow assessment consists of a velocity measurement performed in a single sample volume placed in the vessel centre, combined to an estimate of the average diameter. This simple approach produces large inaccuracies since it does not account for the complex flow configurations produced by complicated artery geometries and/or pulsatile conditions. Moreover, diameter changes, which in important regions like the common carotid artery can be larger than 10%, are totally neglected. In this work we propose an alternative volume flow method which overcomes some of the aforementioned limitations through the simultaneous measurement of the wall positions and of the velocity distribution in the artery. The wall positions are tracked by a detector based on the First Order Absolute Moment working on B-mode data, while the velocity profile is obtained by a Multigate Spectral Doppler analysis applied to PW-mode data. The method was implemented on the ULA-OP research system and validated on a flow phantom with more than 1700 experiments performed in rigid and flexible pipes. We found a systematic underestimation of 3.7% with 5.0% standard deviation. The mean coefficient of variation (CV) was 1.7%.