Eur Radiol (2006) 16: 2259–2264 DOI 10.1007/s00330-006-0191-8 EXPERIMENTAL Ulrike L. Mueller-Lisse Oliver A. Meissner Gregor Babaryka Margit Bauer Roger Eibel Christian G. Stief Maximilian F. Reiser Ullrich G. Mueller-Lisse Received: 6 July 2005 Revised: 28 December 2005 Accepted: 31 January 2006 Published online: 28 March 2006 # Springer-Verlag 2006 Catheter-based intraluminal optical coherence tomography (OCT) of the ureter: ex-vivo correlation with histology in porcine specimens Abstract Intraluminal optical coher- ence tomography (OCT) applies co- herent light to provide cross-sectional images with a spatial resolution of 10– 25 μm. We compared OCT and matching whole-mount histology mi- croscopy sections of porcine upper ureters ex vivo for visualization and delineation of different tissue layers of the ureteral wall. Porcine ureters (six specimens, 24 quadrants) were flushed with normal saline solution prior to insertion of the OCT catheter (diameter, 0.014 inch, OCT wave- length, 1,300±20 nm). Cross-sectional OCT images were obtained in marked locations before specimens were fixed in 4% formalin, cut at marked loca- tions, whole-mounted, and stained with hematoxilin and eosin. Visual- ization and delineation of different tissue layers of the ureteral wall by OCT was compared with matching histology by two independent observ- ers (O1,O2). OCT distinguished tissue layers of the ureteral wall in all quadrants. In OCT images, O1/O2 delineated urothelium and lamina propria in 23/24 quadrants, lamina propria and muscle layer in 19/16 quadrants, inner and outer muscle layer in 13/0 quadrants, and urothelial cell layers in 13/2 quadrants, respec- tively. Intraluminal OCT provides histology-like images of the ureter in porcine specimens ex vivo and reli- ably distinguishes between urothelium and deeper tissue layers of the ureteral wall. Keywords Optical coherence tomography . Intraluminal . Upper urinary tract . Ureter . Porcine . Histology Introduction Optical coherence tomography (OCT) applies coherent light to provide cross-sectional images with a spatial resolution of 4–20 μm that resemble low-power micros- copy images in histology. OCT images can be obtained and displayed in real time, such that the method has similarities with ultrasound imaging. However, two- and three-dimensional sets of OCT image data are gathered by means of coherent, near infra-red light (NIR, wavelength range, 800–1,400 nm), whose reflection from biological tissue is evaluated for signal intensity and time from emission to signal return. Distinction between NIR light reflected from biological tissue and stray light is necessary to obtain imaging information from sub-surface tissue layers. In OCT, interference of coherent light is used to recognize and evaluate reflected NIR light. In short, coherent NIR light beams emitted by the OCT scanner are split, such that one part of the beam goes into the measurement arm to be reflected by the biological tissue under investigation, while the other part of the beam enters the reference arm to be reflected by a mirror. Based on the principle of a Michelson inferometer, reflected NIR light from both arms is superimposed by means of a rotating mirror. Interference between NIR light from both arms occurs only when the respective distances the NIR light travels are the same in both the measurement arm and the reference arm. To match the distance within the measurement arm, the position of the reflective mirror in the reference arm is varied. This allows determining the U. L. Mueller-Lisse (*) . C. G. Stief Department of Urology, University of Munich, Nussbaumstrasse 20, 80336 Munich, Germany e-mail: ulrike.mueller-lisse@med. uni-muenchen.de O. A. Meissner . M. Bauer . R. Eibel . M. F. Reiser . U. G. Mueller-Lisse Department of Radiology, University of Munich, Munich, Germany G. Babaryka Department Pathology, University of Munich, Munich, Germany