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Angle dependency in the ultrasound modality displacement evaluated in a dynamic test phantom: 117

Pedersen, T. F.; Jensen, B.; Norrild, K.; Sloth, E.

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European Journal of Anaesthesiology: June 2004 - Volume 21 - Issue - p 12-13

Introduction: Tissue velocity imaging (TVI) and derived parameters (tissue deformation, deformation rate and tissue displacement) have recently been introduced in clinical practice to provide quantitative assessment of myocardial deformation and thereby contractility [1]. Transoesophageal echocardiography (TOE) with TVI is a promising future tool for perioperative monitoring of myocardial performance. TVI data is based on the Doppler equation and therefore angle dependent. This may cause an error, which must be evaluated before implementation of TVI in experimental and clinical practice. Thus it is important to evaluate the accuracy of TVI in an experimental in vitro model. The aim of the present study was to investigate angle dependency in a TVI phantom using a TOE and a transthoracic probe.

Method: Our dynamic test phantom consisted of a cylinder shaped “tissuelike” mimicking core of a polyurethane alloy. This core was compressed by a shaker in a controlled setting. The compression reduced the height and increased the radius. This results in radial deformation (equal for all radial directions) perpendicular to cylinder height. The measured displacement should be equal for all segments of the phantom, in the same distance from phantom centre. All measurements were done using Vivid-7 echocardiographic equipment and dedicated software (GE-Ultrasound, Horten, Norway). The transthoracic transducer (M3S) and the transoesophageal transducer (6T) was tested and compared for angle dependency.

Results: The figure displays the results from the TOE and the transthoracic probe. Displacement was measured at 0, 45 and 90 degrees from transducer view. Only 90 degrees showed significant TVI (displacement) measurement error.

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Discussion: The results show that the displacement measured with the M3S or the 6T does not differ. Both transducers show some angle dependency. The use of TVI has to be further investigated before used in clinical practice, but the error seems to be minor at measurement angles below 45 degrees from transducer view.

Reference:

1 D'Hooge J, Heimdal A, Jamal F, et al. Regional strain and strain rate measurements by cardiac ultrasound: principles, implementation and limitations. Eur J Echocardiogr 2000; 1(3): 154-170.
© 2004 European Society of Anaesthesiology