Mieke Bus

62 Chapter 4 located at the pyelum and UPJ. Cross-sectional images corresponded with pathology (Figure 6). In 3D OCT reconstruction areas with visible protrusions were seen (Figure 6C). Discussion and Conclusion We showed the first intraluminal OCT identification of the anatomical layers of healthy human ureter in vivo. Moreover, UUT-OCT 1) visually distinguished healthy tissue from tumor tissue, 2) visually differentiated between invasive and non-invasive tumors, 3) differentiates between grade 2 and 3 lesions by quantifying µ oct and 4) thus showed potential to provide intra-operative real-time histological information on stage and grade during minimal inva- sive procedures. This study does not provide information on sensitivity and specificity of OCT in the UUT. Additionally, since we included patients consecutively, our study population is limited in pathology. We have not included patients with G1 tumors and patients with T2 tumors. However, our study warrants the importance of future research to determine the accuracy of OCT in grading and staging of UTUC in a larger sample size. The combination of OCT and endo-urological approaches promises to improve diagnosis and therapy of UUT tumors. Several features of OCT make it well suited for intraluminal diagnostics. State-of-the-art flexible OCT probes are compatible with conventional endo- scopes and easy to apply in the ureter, pyelum and calyces, enabling OCT imaging at all sites within the urinary tract that can be reached with an ureterorenoscope and do not interfere with rinsing during URS. OCT measurement duration per patient adds only maximal five minutes during URS, as the probe is easy to use and a single measurement takes 5.2 sec- onds. OCT images appear direct after measurement and can be analyzed intra-operatively. OCT does not require a conducting medium or direct contact, which makes it easily appli- cable in the ureter. Finally, the OCT system is compact and portable, which results in an easy to use system in the operation theatre. The OCT system used in this study is limited to imaging lumen with a maximal diameter of 10 mm, compromising visualization of the pyelum as a whole. Moreover, if tumor thickness transcends scattering-limited imaging depth (~2mm) invasiveness cannot be assessed (case 10, table 2) as a result of this limited imaging depth. This is an important limitation of the technique, since tumors in the pyelum present often as large papillary exophytic masses . Secondly, although normal appearing urothelium and CIS can be visualized on OCT images, the current OCT analyses cannot obtain a reliable µ oct from normal appearing urothelium or CIS due to the limited thickness of these layers. Improvement by increasing resolution of OCT could solve this limitation. Several clinical applications are conceivable for ureteroscopic OCT, e.g. improving the qual- ity of endoscopic treatment of UUT tumors. OCT-assessment of tumor margins may verify complete vaporization at the time of the operation. In low-grade recurrence in patients with