Mieke Bus

98 Chapter 6 Fusion of OCT and ELUS To obtain reliable co-registration of OCT and ELUS, both diagnostic tools should have the same voxel size. Having the same voxel size will result in accurate fusion of image features and measurement of layer thickness. However, optimal merging of OCT with ELUS needs parallel imaging instead of serial imaging. Several research groups have worked on integra- tion of both imaging modalities resulting in a single hybrid catheter. Using this hybrid cath- eter, one-to-one acquisition of integrated OCT and ELUS images was obtained of coronary vessels. (21-23) But standard OCT and ELUS acquisition does not take into account the curvature of the catheter in relation to the imaged lumen. A normal 3D OCT or ELUS dataset is there- fore usually depicted as a rigid tube. Several research groups have shown the possibility to fuse 3D ELUS with CT. Center-line registration of the lumen found in CT data was employed to deform the rigid ELUS data in three dimensions, resulting in a more anatomically correct representation. (22, 24, 25) Sharp curvatures however, resulted in imperfect 2D image spacing within a 3D volume and should be taken into consideration during deformed 3D recon- struction and co-registration. This limitation is especially important when this technology will be applied in-vivo. For example, to examine the lower pole calyces during a URS, the ureterorenoscope has to make a curve of almost 180 degrees. Therefore, OCT and ELUS data acquisition should take this into account to provide the urologist with a reliable and realistic 3D representation of the ureter, pyelum and calyces. Conclusion In this pilot study, it appears that co-registration with CT enables exact spatial OCT and ELUS data matching in this ex-vivo setting. OCT permits high-resolution imaging whereas ELUS provides more depth information of the upper urinary tract. These results warrant hardware integration of both technologies in order to combine larger depth sensitivity with superficial high-resolution images . However, differentiation between non-invasive and invasive tumors is not possible using the 45 MHz ELUS system employed in this study due to low-resolu- tion images.