Background: Intravascular ultrasound (IVUS) is frequently used as an adjunct to coronary angiography to guide revascularization procedures and, more recently, to estimate atherosclerotic plaque volumes. Although accuracy of IVUS imaging and analysis is crucial for these measurements, available data are scarce. The purpose of this in vitro study is to determine the extent to which transducer position and equipment-related factors influence measurement accuracy.
Methods: Cross-sectional views of tubular vessel phantoms (diameter 2-14 mm) were acquired using 3.2 French catheters in coaxially centered, eccentric and oblique positions. Catheters were sequentially connected to two different ultrasound systems (A and B) to estimate equipment-related variability. In system B, two software versions were used to analyze ultrasound images. Longitudinal views of phantom segments were reconstructed to document transducer misplacement.
Results: Oblique transducer positioning resulted in a non-linear overestimation of phantom areas that was independent of lumen size and also resulted in dramatic distortions of three-dimensionally reconstructed phantom geometry. Eccentric positioning did not significantly influence measurement accuracy. In coaxial positioning, differences between measured and true areas increased non-linearly from 0.36 to 4.5 mm2 in system B and in a linear fashion from -0.01 to 2.68 mm2 in system A with increasing phantom diameters. Relative differences decreased from 11.4% to 2.9% with increasing reference areas in system B (positive off-set error). When using updated software in system B, the off-set error was negative and relative error diminished from -1.34% to 0.44% with increasing phantom size.
Conclusion: Transducer position and equipment-related factors influence the accuracy of intravascular ultrasound, which may lead to misinterpretation of vessel size and geometry even in straight vessel segments. Transducer position may be controlled by the reconstruction of longitudinal images. Ultrasound equipment should be calibrated before using it for quantitative measurements.