Tissue harmonic imaging in comparison with conventional sonography: effect on image quality and observer variability in the measurement of the intima-media thickness in the common carotid artery

Abstract

The purpose of this study was to determine if tissue harmonic imaging (THI) produced a higher image quality than conventional sonography and if THI reduced the observer availability in the intima media thickness (IMT) measurements of the common carotid artery (ACC). A prospective study was performed on 26 healthy volunteers and IMT was assessed by three experienced sonographers in 52 carotid arteries. A 7.5 MHz transducer was used to measure carotid IMT in both harmonic and fundamental modes. Three measurements of IMT were carried out on the far wall of the ACC along a 1 cm-long section proximal to the bifurcation. Image quality was graded from 1-3 (1 = excellent, 2 = good, 3 = poor). IMT measurements using harmonic and fundamental modes were compared and intra- and inter-observer variability were calculated. Statistical analyses were performed using a kappa analysis, ANOVA and the McNemar/Wilcoxon Test. In the 52 cases image quality was excellent in 51% using THI in comparison to 32% using conventional sonography. Image quality was graded significantly more frequent as excellent using harmonic sonography as compared to conventional sonography (p = 0.001). A significant difference in IMT was found between the measurements obtained by harmonic imaging in comparison to those obtained by conventional imaging (p < 0.0001). Using the harmonic mode inter-observer variability of the IMT measurements was significantly reduced from 8.1% to 5.2% (p < 0.001). THI produced a higher image quality with a better visualisation of carotid IMT and reduced significantly the intra- and inter-observer variability in the IMT measurements.