The cardiac elastography aims at identification of non-transmural infarctions. Two displacement estimation methods in
such an application using synthetic ultrasonic data are studied. Reference was obtained from Finite Element Modelling.
Models had the form of half of an ellipsoid with 15 mm wall thickness. The homogenous model, models with transmural
and nontransmural inclusion were designed. Deformation of the models was simulated using Abaqus. Ultrasonic data of
LAX and SAX views were generated using Field II. Radial (dR) and lateral (dL) displacements were estimated using a
2D correlation search with 2D stretching (2DCS) and B-spline (BS) method. Strains were estimated using least squares
estimator. Mean Absolute Error (MAE) of the dR in the LAX view was approx. 6[μm] for 2DCS and 8[μm] for BS, that
of the dL 30 and 24[μm] respectively. MAE of the second component of the principal strain (epsilon)<sub>2</sub> was 0.10 and 0.14[%],
respectively. Corresponding values for SAX view were 7, 10, 42, 52[μm] and 0.47 and 1.08[%]. In the LAX view both
estimation methods result in the (epsilon)<sub>2</sub> behavior coherent with the presence of the inclusion, with the 2DCS results closer to
the reference. In the SAX view the BS approach results in high errors of the estimate. The (epsilon)<sub>2</sub> profiles, LAX view, show
minor discrepancies with respect to the reference and show the effect of the inclusion. The (epsilon)<sub>2</sub> profiles, SAX view,
obtained from displacements estimated using the BS method strongly deviate from the reference. Block matching
performs better in application to the local strain estimation.
Cardiac strain quantification using ultrasound is an active area of research. Physical left ventricle (LV) model play a
significant role in the evaluation and development of myocardium strain imaging techniques. Several LV models have
been reported. In spite of increasing interest in LV twist, only one of them implements torsional deformation, but it does
not allow long axis views. This work presents a novel prototype of physical LV model and dedicated measurement setup
which do not have this limitation.
The model was made of Poly(vinyl alcohol) cryogel (PVA-c). The solution for the chamber part was doped with
scattering particles to imitate the echogenicity of myocardium and to facilitate automatic segmentation of the chamber
wall. The model was mounted in a measurement setup allowing computer controlled linear motion of the basis, rotation
of the apex and inflation of the ventricle and the use both ultrasound imaging planes: short (SAX) and long axis (LAX).
During preliminary tests RF signals as well as B-mode and M-mode images were acquired.
Experiment results confirmed the possibility of forcing controlled deformation of the presented LV model wall,
including elongation/shortening in the long axis direction and twist around this axis. In consequence, the model can
mimic deformations of the LV wall to a large extent. The chamber wall can be segmented in B-mode images in both
projections. The model with the measurement setup may be used in development and validation of a wide range of
echocardiographic diagnostic procedures including segmentation, strain estimation and 3D data processing.
The cardiac elastography evolves to enable local strain estimation and identification of non-transmural infarctions. Below we compare the strain values obtained using EchoPAC in physical left ventricular phantoms made of PVA with results of the Finite Element Modelling (FEM) studies on their counterparts. Models had the form of half of an ellipsoid with 15 mm wall thickness. The homogenous model, transmural inclusion model and nontransmural inclusion (5mm thickness) model were designed. The inclusions were located in the mid segment. The material of the ventricle in the FEM studies was modeled as a hyperelastic, isotropic one. The material parameters came from measurements of the PVA samples for the homogenous case and were extrapolated to obtain stiffer inclusions. The model was deformed by applying 36 kPa pressure load to its inner surface. Peak systolic strain values were close to those observed in healthy subjects. A dedicated setup, the Vivid 6 scanner, probe M4S-RS and EchoPAC BT13 software were used in experiments. The values of strains from FEM models were averaged over nodes corresponding to the layers used in the EchoPAC software. The circumferential strain (CS) values from the FEM simulation and the physical experiment are qualitatively very close and correlate well with the clinical data. The experimental CS results also agree with expectations in terms of slope across the wall and effect of the inclusion. Segmental radial strains obtained from EchoPAC and FEM are close. The proposed approach (phantoms, setup) may be used for development of methods for identification of nontransmural infarctions.
Sports cycling is becoming increasingly popular over last years. Obtaining and maintaining a proper position on the bike has been shown to be crucial for performance, comfort and injury avoidance. Various techniques of bike fitting are available - from rough settings based on body dimensions to professional services making use of sophisticated equipment and expert knowledge. Modern fitting techniques use mainly joint angles as a criterion of proper position. In this work we examine performance of two proposed methods for dynamic cyclist position assessment based on video data recorded during stationary cycling. Proposed methods are intended for home use, to help amateur cyclist improve their position on the bike, and therefore no professional equipment is used. As a result of data processing, ranges of angles in selected joints are provided. Finally strengths and weaknesses of both proposed methods are discussed.