Determination of displacement, stress- and strain-distribution in the human heart: a FE-model on the basis of MR imaging.

The determination of characteristic cardiac parameters, such as displacement, stress and strain distribution are essential for an understanding of the mechanics of the heart. The calculation of these parameters has been limited until recently by the use of idealised mathematical representations of biventricular geometries and by applying simple material laws. On the basis of 20 short axis heart slices and in consideration of linear and nonlinear material behaviour we have developed a FE model with about 100,000 degrees of freedom. Marching Cubes and Phong's incremental shading technique were used to visualise the three dimensional geometry. In a quasistatic FE analysis continuous distribution of regional stress and strain corresponding to the endsystolic state were calculated. Substantial regional variation of the Von Mises stress and the total strain energy were observed at all levels of the heart model. The results of both the linear elastic model and the model with a nonlinear material description (Mooney-Rivlin) were compared. While the stress distribution and peak stress values were found to be comparable, the displacement vectors obtained with the nonlinear model were generally higher in comparison with the linear elastic case indicating the need to include nonlinear effects.

Options chirurgicates pour l'insuffisance cardiaque terminale [Surgical options for terminal heart failure]

Terminal heart failure can be the cause or the result of major dysfunctions of the organisms. Although, the outcome of the natural history is the same in both situations, it is of prime importance to differentiate the two, as only heart failure as the primary cause allows for successful mechanical circulatory support as bridge to transplantation or towards recovery. Various objective parameters allow for the establishment of the diagnosis of terminal heart failure despite optimal medical treatment. A cardiac index <2.0 l/min, and a mixed venous oxygen saturation <60%, in combination with progressive renal failure, should trigger a diagnostic work-up in order to identify cardiac defects that can be corrected or to list the patient for transplantation with/without mechanical circulatory support.

Free-breathing inner-volume black-blood imaging of the human heart using two-dimensionally selective local excitation at 3 T.

Black-blood fast spin-echo imaging is a powerful technique for the evaluation of cardiac anatomy. To avoid fold-over artifacts, using a sufficiently large field of view in phase-encoding direction is mandatory. The related oversampling affects scanning time and respiratory chest motion artifacts are commonly observed. The excitation of a volume that exclusively includes the heart without its surrounding structures may help to improve scan efficiency and minimize motion artifacts. Therefore, and by building on previously reported inner-volume approach, the combination of a black-blood fast spin-echo sequence with a two-dimensionally selective radiofrequency pulse is proposed for selective "local excitation" small field of view imaging of the heart. This local excitation technique has been developed, implemented, and tested in phantoms and in vivo. With this method, small field of view imaging of a user-specified region in the human thorax is feasible, scanning becomes more time efficient, motion artifacts can be minimized, and additional flexibility in the choice of imaging parameters can be exploited.