Johan G. Bosch

Development and validation of ultrasound speckle tracking to quantify tendon displacement

Ultrasound can be used to study tendon movement. However, measurement of tendon movement is mostly based on manual tracking of anatomical landmarks such as the musculo-tendinous junction, limiting the applicability to a small number of muscle-tendon units. The aim of this study was to quantify tendon displacement without anatomical landmarks using a speckle tracking algorithm optimized for tendons in long B-mode image sequences. A dedicated two-dimensional multi-kernel block-matching scheme with subpixel motion estimation was devised to handle large displacements over long sequences. The accuracy of the tracking on porcine tendons was evaluated during different displacements and velocities. Subsequently, the accuracy of tracking the flexor digitorum superficialis (FDS) of a human cadaver hand was evaluated. Finally, the in-vivo accuracy of the tendon tracking was determined by measuring the movement of the FDS at the wrist level. For the porcine experiment and the human cadaver arm experiment tracking errors were, on average, 0.08 and 0.05mm, respectively (1.3% and 1.0%). For the in-vivo experiment the tracking error was, on average, 0.3mm (1.6%). This study demonstrated that our dedicated speckle tracking can quantify tendon displacement at different physiological velocities without anatomical landmarks with high accuracy. The technique allows tracking over large displacements and in a wider range of tendons than by using anatomical landmarks.

Automated border detection in three-dimensional echocardiography: Principles and promises

Several automated border detection approaches for three-dimensional echocardiography have been developed in recent years, allowing quantification of a range of clinically important parameters. In this review, the background and principles of these approaches and the different classes of methods are described from a practical perspective, as well as the research trends to achieve a robust method.

Current status and future developments of contrast-enhanced ultrasound of carotid atherosclerosis.

B-mode and Doppler ultrasound are commonly used for the evaluation of atherosclerosis in the carotid arteries. Recently, contrast-enhanced ultrasound (CEUS) has been introduced as a technique to improve the detection of carotid atherosclerosis and evaluate the presence of intraplaque neovascularization, which is considered a marker of plaque vulnerability. The present review focuses on the role of CEUS for the assessment of atherosclerosis and plaque instability. Currently available literature and future developments with CEUS are discussed.

Assessment of mitral annular velocities by speckle tracking echocardiography versus tissue Doppler imaging: validation, feasibility, and reproducibility.

BACKGROUND Mitral annular velocity may be measured angle independently by speckle tracking echocardiography (STE), in contrast with tissue Doppler imaging (TDI). The purpose of the current study was to compare STE and TDI, with respect to 1) the accuracy of velocity measurements in a moving phantom, 2) the feasibility and reproducibility of measurement of mitral annular velocities in a clinical setting, and 3) the estimation of left ventricular filling pressures using mitral annular velocities. METHODS The velocity of a moving phantom, using different angles of insonation, and mitral annular velocities of 80 nonselected patients and 50 healthy volunteers were determined using TDI and STE. A subgroup of 20 patients was studied during right-sided heart catheterization. RESULTS When the motion direction of the phantom was parallel to the ultrasound beam, both TDI and STE determined velocities accurately. With increasing angle of insonation, TDI-derived velocity decreased, whereas STE-derived velocity remained unchanged. The feasibility of mitral annular velocities measured by TDI and STE was comparable (98% vs 95%, P = not significant). Although for both techniques correlations between measured mitral annular velocities at repeated examinations were good, the test-retest variability of mitral annular velocities by TDI was higher. E/Em ratio by STE correlated better to pulmonary capillary wedge pressure (R(2) = 0.51, P < .001) compared with E/Em ratio derived from TDI (R(2) = 0.35, P < .01), although the difference in correlation was not statistically significant because of the limited sample size. CONCLUSION Tissue velocities can be accurately determined by STE in a moving phantom and are angle independent, in contrast with TDI measurements. Furthermore, STE is a feasible and better reproducible method for the assessment of mitral annular velocities in a clinical setting.

New Quantification Methods for Carotid Intra-plaque Neovascularization Using Contrast-Enhanced Ultrasound

Carotid intraplaque neovascularization (IPN) has been associated with progressive atherosclerotic disease and plaque vulnerability. Therefore, its accurate quantification might allow early detection of plaque vulnerability. Contrast enhanced ultrasound (CEUS) can detect these small microvessels. To quantify IPN, we developed quantitative methods based on time intensity curve (TIC) and maximum intensity projection (MIP), micro-vascular structure analysis (VSA), and statistical segmentation (SS). Plaque region of interest (ROI) is manually drawn and motion compensation is applied before each analysis. In TIC and MIP, we examine perfusion dynamics and regions within plaques. In VSA, we detect and track contrast spots to examine the microvessel network. In SS, we classify plaque intensities into different components for quantification of IPN. Through an iterative expectation-maximization algorithm, plaque pixels are initially labeled into artifacts, contrast, intermediate, and background class. Next, spatiotemporal and neighborhood information is used to relabel intermediate class pixels, remove artifacts and correct false-contrast. From the applied analyses, we derived several parameters - e.g. MIP based IPN surface area (MIPNSA), MIP based surface ratio (MIPNSR), SS based IPN surface area (SSIPNSA), plaque mean intensity, mean plaque contrast percentage, and number of microvessels (MVN) - and compared them to consensus of visual grading of IPN by two independent physicians. We analyzed 45 carotid arteries with stenosis. To verify if SSIPNSA improves the suppression of artifacts, we analyzed 8 plaques twice, with saturation artifacts included and excluded from the ROI. Five parameters were found to be significantly correlated to visual scoring and may thus have the potential to replace qualitative visual scoring and to measure the degree of carotid IPN. The MIPNSA & SSIPNSA parameters gave the best distinction between visual scores. SSIPNSA proved less sensitive for artifacts than MIPNSA.

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 methods potential in automated tracking in clinical quality echocardiograms, facilitating the quantitative and objective assessment of cardiac function.

Front-end receiver electronics for a matrix transducer for 3-D transesophageal echocardiography

There is a clear clinical need for creating 3-D images of the heart. One promising technique is the use of transesophageal echocardiography (TEE). To enable 3-D TEE, we are developing a miniature ultrasound probe containing a matrix piezoelectric transducer with more than 2000 elements. Because a gastroscopic tube cannot accommodate the cables needed to connect all transducer elements directly to an imaging system, a major challenge is to locally reduce the number of channels, while maintaining a sufficient signal-to-noise ratio. This can be achieved by using front-end receiver electronics bonded to the transducers to provide appropriate signal conditioning in the tip of the probe. This paper presents the design of such electronics, realizing time-gain compensation (TGC) and micro-beamforming using simple, low-power circuits. Prototypes of TGC amplifiers and micro-beamforming cells have been fabricated in 0.35-μm CMOS technology. These prototype chips have been combined on a printed circuit board (PCB) to form an ultrasound-receiver system capable of reading and combining the signals of three transducer elements. Experimental results show that this design is a suitable candidate for 3-D TEE.

Assessment of subclinical atherosclerosis and intraplaque neovascularization using quantitative contrast-enhanced ultrasound in patients with familial hypercholesterolemia.

OBJECTIVE Patients with heterozygous familial hypercholesterolemia (FH) are at severely increased risk of developing atherosclerosis at relatively young age. The aim of this study was to assess the prevalence of subclinical atherosclerosis and intraplaque neovascularization (IPN) in patients with FH, using contrast-enhanced ultrasound (CEUS) of the carotid arteries. METHODS The study population consisted of 69 consecutive asymptomatic patients with FH (48% women, mean age 55 ± 8 years). All patients underwent carotid ultrasound to evaluate the presence and severity of carotid atherosclerosis, and CEUS to assess IPN. IPN was assessed in near wall plaques using a semi-quantitative grading scale and semi-automated quantification software. RESULTS Carotid plaque was present in 62 patients (90%). A total of 49 patients had plaques that were eligible for the assessment of IPN: 7 patients (14%) had no IPN, 39 (80%) had mild to moderate IPN and 3 (6%) had severe IPN. Semi-automated quantification software showed no statistical significant difference in the amount of IPN between patients > 50 years and patients ≤ 50 years and between patients with a defective low-density lipoprotein receptor (LDLR) mutation and patients with a negative LDLR mutation. Plaques with irregular or ulcerated surface had significantly more IPN than plaques with a smooth surface (p < 0.05). CONCLUSION Carotid ultrasound demonstrated atherosclerotic plaque in 90% of asymptomatic patients with FH without known atherosclerosis. IPN assessed with CEUS, was present in 86% of these patients. Irregular and ulcerated plaques exhibited significantly more IPN than plaques with a smooth surface.

Ultrasonographic Assessment of Long Finger Tendon Excursion in Zone V During Passive and Active Tendon Gliding Exercises

PURPOSE Cadaver and in vivo studies report variable results for tendon excursion during active and passive hand movements. The purpose of this study was to measure long finger flexor digitorum profundus (FDP) tendon excursion during active and passive movement using high-resolution ultrasound images. METHODS The FDP tendon excursion was measured at the wrist level in 10 healthy subjects during full tip-to-palm active and passive flexion of the fingers. Passive movement was performed 2 ways: (1) straight to full fist: passive flexion starting at the metacarpophalangeal joint, followed by proximal interphalangeal and distal interphalangeal joint flexion; and (2) hook to full fist: passive flexion starting at the distal interphalangeal joint, followed by proximal interphalangeal and metacarpophalangeal joint flexion. Tendon excursion was measured using an in-house-developed, frame-to-frame analysis of high-resolution ultrasound images. RESULTS Median FDP excursion was 24.3 mm, 14.0 mm, and 13.6 mm for active fist, straight to full fist, and hook to full fist movements, respectively. Tendon excursions during active movements was significantly larger than excursions during passive movements (p = .005). The adjusted median tendon excursion was 12.7 mm/100 degrees , 7.5 mm/100 degrees , and 7.4 mm/100 degrees for active fist, straight to full fist, and hook to full fist movements, respectively. Adjusted tendon excursions during active movement were significantly larger than those achieved during passive straight to full fist movement). Adjusted tendon excursions during straight to full fist movements were significantly larger than those achieved during passive hook to full fist movement. CONCLUSIONS Active motion produced 74% and 79% increases in excursions compared to both passive motions in healthy controls. The study results can serve as a reference for evaluating excursions in patients with tendon pathology, including those who have had tendon repair and reconstruction.

Localized shape variations for classifying wall motion in echocardiograms

To quantitatively predict coronary artery diseases, automated analysis may be preferred to current visual assessment of left ventricular (LV) wall motion. In this paper, a novel automated classification method is presented which uses shape models with localized variations. These sparse shape models were built from four-chamber and two-chamber echocardiographic sequences using principal component analysis and orthomax rotations. The resulting shape parameters were then used to classify local wall-motion abnormalities of LV segments. Various orthomax criteria were investigated. In all cases, higher classification correctness was achieved using significantly less shape parameters than before rotation. Since pathologies are typically spatially localized, many medical applications involving local classification should benefit from orthomax parameterizations.