Spatial orientation of cross-sectional images of coronary arteries: point of view in intracoronary imaging

We made an asymmetric phantom and investigated it with two different intravascular ultrasound (IVUS) systems and one optical coherence tomography (OCT) system. The asymmetry of the phantom allowed determination of the spatial orientation of the cross-sectional images. On all tested systems, an observer should imagine herself/himself standing proximal to the cross-section when looking at the intravascular images.The tested intracoronary imaging modalities displayed cross-sectional images with a spatial orientation corresponding to a proximal point of view. Knowledge of the spatial orientation is mandatory when comparing and validating different imaging modalities aimed at plaque characterization.Many intravascular ultrasound (IVUS) and optical coherence tomography (OCT) cross-sectional images of coronary arteries are published in biomedical journals. Sometimes these images are presented together with images from microscopic examination of the same arterial positions illustrating how the imaging modality correctly displays tissue characteristics [1,2].When comparing cross-sectional images obtained with different techniques, such as intravascular imaging and microscopy, efforts must be made to assure that the images are from exactly the same arterial position along the longitudinal axis of the coronary artery, and this is often devoted a lot of attention.Also, when comparing cross-sectional images, rotational adjustment is usually required to obtain correct co-localization of identifiable landmark structures such as sidebranches. Rotation of a cross-sectional image does not change area measurements or intraplaque location of a certain component of interest. Therefore rotation does not affect interpretation.However, in addition to longitudinal position and rotation, cross-sectional images also possess a spatial orientation of the cross-sectional plane. This is only rarely commented on but cannot be taken as lightly as rotation [3,4]. Changing spatial orientation, and th