Performance of ICE and IVUS
In our study, ICE performed better than IVUS with regards to quality of imaging provided and to inter-observer reproducibility of measurements obtained. These findings are likely due to the lower ultrasound frequency used by ICE, which was advantageous in terms of acoustic penetration without a significant loss in spatial resolution. When using ICE, the outer vessel circumference was well-defined in most or all image quadrants, as well as inner structures such as lumen circumference and wall.
We observed no significant differences between the two technologies in terms of trackability: similar additional procedural times were needed for ICE and for IVUS imaging and no procedural complications occurred as result of imaging.
Both lumen and vessel diameters and areas were consistently larger in the ICE-imaged PVs compared to the IVUS-imaged PVs. Moreover, although both imaging techniques showed an elliptical shape of the PV cross-sections, in keeping with previous CT and MRI studies17,18, lumen and vessel sphericity indexes were lower in the ICE-imaged PVs, which is indicative of a more elliptical shape of the PV cross-sections. Our PV measurements determined by IVUS are in line with previously reported PV measurements, obtained from both IVUS images and histological sections15. Taken together, these data might suggest that ICE overestimated the PVs sizes due to non-coaxial cross-sectioning, as indicated by the lower sphericity index when compared to the IVUS images. ICE catheters are not advanced or pulled back over a wire and this different design might have reduced the chance of a coaxial position of the probe within the PV lumen. Despite different lumen and vessel diameters and absolute areas, pre- and post-ablation WTI% were comparable between PV cross-sections imaged either ICE or IVUS, thus suggesting that both imaging modalities can provide similar accuracy in depicting acute changes in tissue thickness after ablation.