Measurement of in vitro cardiac deformation by means of 3D digital image correlation and ultrasound 2D speckle-tracking echocardiography

Myocardial strain imaging in Duchenne muscular dystrophy

Cardiomyopathy (CM) is the leading cause of death for individuals with Duchenne muscular dystrophy (DMD). While DMD CM progresses rapidly and fatally for some in teenage years, others can live relatively symptom-free into their thirties or forties. Because CM progression is variable, there is a critical need for biomarkers to detect early onset and rapid progression. Despite recent advances in imaging and analysis, there are still no reliable methods to detect the onset or progression rate of DMD CM. Cardiac strain imaging is a promising technique that has proven valuable in DMD CM assessment, though much more work has been done in adult CM patients. In this review, we address the role of strain imaging in DMD, the mechanical and functional parameters used for clinical assessment, and discuss the gaps where emerging imaging techniques could help better characterize CM progression in DMD. Prominent among these emerging techniques are strain assessment from 3D imaging and development of deep learning algorithms for automated strain assessment. Improved techniques in tracking the progression of CM may help to bridge a crucial gap in optimizing clinical treatment for this devastating disease and pave the way for future research and innovation through the definition of robust imaging biomarkers and clinical trial endpoints.

Ultrasound-Based Estimation of Fibre-Directional Strain: A Simulation Study

Left ventricular (LV) strains are typically represented with respect to the imaging axes. Contraction within the myocardium occurs along myofibres, which vary in orientation. Therefore, a mismatch exists between the direction in which strain is calculated and that in which contraction occurs. In this study, ultrasound-based fibre orientation and 3-D strain estimation were combined to calculate the fibre-directional strain. Three-dimensional ultrasound volumes were created by simulating simple geometrical phantoms and a phantom based on a finite-element (FE) model of LV mechanics. Fibre-like structures were embedded within tissue-mimicking scatterers. Strains were applied to the numerical phantom, whereas the FE phantom was deformed based on the LV model. Fibre orientation was accurately estimated for both phantoms. There was poor agreement in axial and elevational strains (root mean square error = 29.9% and 12.3%), but good agreement in lateral and fibre-directional strains (root mean square error = 6.4% and 5.9% respectively), which aligned in the midwall. Simplifications to reduce computational complexity caused poor axial and elevational strain estimation. However, calculation of fibre-directional strain from single-modality ultrasound volumes was successful. Further studies, in ex vivo setups because of the fundamental limitations of currently available transducers, are needed to verify real-world performance of the method.

Semantic speckle: an auto-located speckle pattern for DIC measurement

Digital image correlation (DIC) has been widely used in both experimental mechanics and engineering fields. The matching algorithm of the DIC method usually requires surfaces containing a random speckle pattern as a deformation information carrier. The speckle pattern plays an irreplaceable role in DIC, which has led to extensive research on it. However, most previous research had always focused on the fabrication and computational performance of the speckle, ignoring the value of intentionally defining the meaning of speckle in design. In this study, we describe a novel, to the best of our knowledge, speckle pattern named semantic speckle. It is a digital speckle composed of several different speckle patterns with similar characteristics. Based on the deep-learning method and matching algorithm, the central location of the semantic part in the overall speckle image can be obtained automatically. Through the intentional definition of the semantic part, it can be possible to calibrate the camera parameters and correct the external parameters of the DIC systems.

Multiscale Anisotropic Tissue Biofabrication via Bulk Acoustic Patterning of Cells and Functional Additives in Hybrid Bioinks

Recapitulation of the microstructural organization of cellular and extracellular components found in natural tissues is an important but challenging feat for tissue engineering, which demands innovation across both process and material fronts. In this work, a highly versatile ultrasound-assisted biofabrication (UAB) approach is demonstrated that utilizes radiation forces generated by superimposing ultrasonic bulk acoustic waves to rapidly organize arrays of cells and other biomaterial additives within single and multilayered hydrogel constructs. UAB is used in conjunction with a novel hybrid bioink system, comprising of cartilage-forming cells (human adipose-derived stem cells or chondrocytes) and additives to promote cell adhesion (collagen microaggregates or polycaprolactone microfibers) encapsulated within gelatin methacryloyl (GelMA) hydrogels, to fabricate cartilaginous tissue constructs featuring bulk anisotropy. The hybrid matrices fabricated under the appropriate synergistic thermo-reversible and photocrosslinking conditions demonstrate enhanced mechanical stiffness, stretchability, strength, construct shape fidelity and aligned encapsulated cell morphology and collagen II secretion in long-term culture. Hybridization of UAB is also shown with extrusion and stereolithography printing to fabricate constructs featuring 3D perfusable channels for vasculature combined with a crisscross or circumferential organization of cells and adhesive bioadditives, which is relevant for further translation of UAB toward complex physiological-scale biomimetic tissue fabrication.

Regenerating dynamic organs using biomimetic patches

The regeneration of dynamic organs remains challenging because they are intrinsically anisotropic and undergo large volumetric deformation during normal or pathological function. This hampers the durability and applicability of regenerative medicine approaches. To address the challenges of organ dynamics, a new class of patches have emerged with anisotropic and auxetic properties that mimic native tissue biomechanics and accommodate volumetric deformation. Here, we outline the critical design, materials, and processing considerations for achieving optimal patch biomechanics according to target pathology and summarize recent advances in biomimetic patches for dynamic organ regeneration. Furthermore, we discuss the challenges and opportunities which, if overcome, would open up new applications in organ regeneration and expedite the clinical translation of patch-based therapeutics.

Joint Generalized Coherence Factor and Minimum Variance Beamformer for Synthetic Aperture Ultrasound Imaging

The delay-and-sum (DAS) beamformer is the most commonly used method in medical ultrasound imaging. Compared with the DAS beamformer, the minimum variance (MV) beamformer has an excellent ability to improve lateral resolution by minimizing the output of interference and noise power. However, it is hard to overcome the tradeoff between satisfactory lateral resolution and speckle preservation performance due to the fixed subarray length of covariance matrix estimation. In this study, a new approach for MV beamforming with adaptive spatial smoothing is developed to address this problem. In the new approach, the generalized coherence factor (GCF) is used as a local coherence detection tool to adaptively determine the subarray length for spatial smoothing, which is called adaptive spatial-smoothed MV (AMV). Furthermore, another adaptive regional weighting strategy based on the local signal-to-noise ratio (SNR) and GCF is devised for AMV to enhance the image contrast, which is called GCF regional weighted AMV (GAMV). To evaluate the performance of the proposed methods, we compare them with the standard MV by conducting the simulation, in vitro experiment, and the in vivo rat mammary tumor study. The results show that the proposed methods outperform MV in speckle preservation without an appreciable loss in lateral resolution. Moreover, GAMV offers excellent performance in image contrast. In particular, AMV can achieve maximal improvements of speckle signal-to-noise ratio (SNR) by 96.19% (simulation) and 62.82% (in vitro) compared with MV. GAMV achieves improvements of contrast-to-noise ratio by 27.16% (simulation) and 47.47% (in vitro) compared with GCF. Meanwhile, the losses in lateral resolution of AMV are 0.01 mm (simulation) and 0.17 mm (in vitro) compared with MV. Overall, this indicates that the proposed methods can effectively address the inherent limitation of the standard MV in order to improve the image quality.

A systematic evaluation on reporting quality of modern studies on pulmonary heart valve implantation in large animals

OBJECTIVES

Before new heart valves can be implanted safely in humans, animal experiments have to be performed. These animal experiments have to be clearly designed, analysed and reported to assess the accuracy and importance of the findings. We aimed to provide an overview of the reporting and methodological quality of preclinical heart valve research.

METHODS

We conducted a systematic literature search on biological and mechanical pulmonary valve implantations in large animals. We used the Animals in Research: Reporting In Vivo Experiments (ARRIVE) guidelines to score the quality of reporting in each article. We compared the scores before and after the introduction of the ARRIVE guidelines (2010).

RESULTS

We screened 348 articles, of which 31 articles were included. The included articles reported a mean of 54.7% adequately scored ARRIVE items (95% confidence interval 52.2-57.3%). We did not identify a difference in reporting quality (54.7% vs 54.8%) between articles published before and after 2010. We found an unclear (lack of description) risk of selection bias, performance bias and detection bias.

CONCLUSIONS

The reporting quality of studies that implanted bioprosthetic or mechanical valves in the pulmonary position in the large animal model is not on the desired level. The introduction of the ARRIVE guidelines in 2010 did not improve the reporting quality in this field of research. Hereby, we want to emphasize the importance of clearly describing the methods and transparently reporting the results in animal experiments. This is of great importance for the safe translation of new heart valves to the clinic.

CLINICAL TRIAL REGISTRATION NUMBER

PROSPERO (CRD42019147895).

An optimisation-based iterative approach for speckle tracking echocardiography

Speckle tracking is the most prominent technique used to estimate the regional movement of the heart based on echocardiograms. In this study, we propose an optimised-based block matching algorithm to perform speckle tracking iteratively. The proposed technique was evaluated using a publicly available synthetic echocardiographic dataset with known ground-truth from several major vendors and for healthy/ischaemic cases. The results were compared with the results from the classic (standard) two-dimensional block matching. The proposed method presented an average displacement error of 0.57 pixels, while classic block matching provided an average error of 1.15 pixels. When estimating the segmental/regional longitudinal strain in healthy cases, the proposed method, with an average of 0.32 ± 0.53, outperformed the classic counterpart, with an average of 3.43 ± 2.84. A similar superior performance was observed in ischaemic cases. This method does not require any additional ad hoc filtering process. Therefore, it can potentially help to reduce the variability in the strain measurements caused by various post-processing techniques applied by different implementations of the speckle tracking. Graphical Abstract Standard block matching versus proposed iterative block matching approach.