This study aims to evaluate whether optical coherence tomography (OCT) using both the surface and the endoluminal technique is feasible to investigate the locations and degree of encrustation process in clinically used ureteral stents. After removal from patients, 14 polyurethane JJ stents were investigated. A fresh JJ served as a control. The external surfaces were examined using an endoscopic surface OCT whereas the intraluminal surfaces were investigated by an endoluminal radial OCT device. The focus was on detection of encrustation or crystalline sedimentation. In 12 female and two male patients, the median indwelling time of the ureteral catheter was 100 days (range, 19-217). Using the endoluminal OCT, the size and grade of intraluminal encrustation could be expressed as a percentage relating to the open lumen of the reference stent. The maximum encrustation observed resulted in a remaining unrestricted lumen of 15-35 % compared to the reference. The luminal reduction caused by encrustation was significantly higher at the proximal end of the ureteral stent as compared to its distal part. The extraluminal OCT investigations facilitated the characterization of extraluminal encrustation. OCT techniques were feasible and facilitated the detection of encrustation of double pigtail catheters on both the extra and intra luminal surface. Quantitative expression of the degree of intraluminal encrustation could be achieved, with the most dense and thickened occurrence of intraluminal incrustation in the upper curl of the JJ stent.

Diagnostic imaging of the upper urinary tract is a cumbersome process that involves a multitude of different imaging modalities, including ultrasonography, conventional radiography, X-ray fluoroscopy (retrograde and antegrade ureteropyelography), endoscopy (cystoscopy and ureterorenoscopy) without or with biopsy, multi-detector-row computed tomography (MDCT), and magnetic resonance imaging (MRI). However, these modalities leave a diagnostic gap because they cannot demonstrate different layers of the wall of the upper urinary tract. Recent research shows that catheter-based, intraluminal probes for optical coherence tomography (OCT) with near-infrared light provide cross-sectional images from within the lumen of the upper urinary tract that distinguish between the urothelium, lamina propria, and muscle layer at spatial resolutions of about 10–15μm in axial and about 20–25μm in lateral directions respectively. The feasibility of in vivo imaging and the superiority of OCT to endoluminal ultrasonography (ELUS) have been demonstrated. However, OCT has yet to show that it is capable of characterizing pathologic lesions, e.g., urothelial cancer. The present paper summarizes the basic principles and initial results of catheter-based, time-domain intraluminal OCT in the upper urinary tract.

A fundamental precondition of local radiotherapy by means of 32P-loaded urethral catheters is a precise position with respect to the target tissue. This feasibility study investigates optical coherence tomography (OCT)-assisted examination of the catheter position and its adherence to the tissue surface. OCT investigations were performed using an animal model (rabbit urethra, n=4). A radial scanning OCT probe located in the lumen of the catheter provided OCT images of the catheter structure as well as of the surrounding tissue. Descriptive evaluation of the OCT images gives information about the fitting, the structure of the catheter, as well as of the surrounding urethral tissue. The dimensions of catheter–tissue separation were determined. Radial OCT images provided clear cross-sections of the catheter. The layered structure of the surrounding urethral tissue could be identified and correlated to the histology. Distances between the catheter surface and the tissue could be evaluated indicating gaps of up to 0.4 mm and sector widths of up to 90°. Dosimetric calculations have shown that such changes may reduce the intended β-irradiation dose by 30% in the target tissue depth. Morphological changes (e.g. scar formation), related to wound healing processes after surgical incision, could be observed as well. OCT-mediated tissue differentiation through OCT-wavelength transparent catheters shows the potential for identifying morphological changes. The fitting of the catheter to the urethral wall could be verified. Therefore, OCT techniques may improve the control of the radioactive catheter position resulting in an upgrade of dosimetric calculation for local 32P-β-radiation low-dose brachytherapy. Voraussetzung für die lokale Behandlung der Harnröhre (Urethra) mit radioaktiv dotierten Kathetersegmenten ist deren exakte Positionierung im Bereich des Zielgewebes. Ziel dieser Machbarkeitstudie ist die OCT-gestützte Prüfung der Katheterposition und des Anschmiegeverhaltens urologischer Katheter an das umgebende Urethragewebe. Die Versuche erfolgten im Tiermodell (Kaninchen, n=4). Zur Untersuchung der Katheterposition wurde eine radial-scannende OCT-Sonde in das Lumen der Katheter eingeführt und OCT-Bildsequenzen vom Katheter und dem umliegenden Gewebe erstellt. Die Auswertung umfasste die Beschreibung des Anschmiegeverhaltens der Katheter an das Gewebe, die Identifizierung von Gewebestrukturen sowie die geometrische Bestimmung der Abstände zwischen Katheterwand und Harnröhre. Mittels radialer OCT-Technik war die Querschnittsstruktur der Katheter klar zuzuordnen. Die geschichtete Struktur und der Strukturwechsel im anliegenden Urethragewebe konnte identifiziert und zugeordnet werden. Die Abstände zwischen Katheterwand und Gewebe betrugen in radialer Richtung bis zu 0,4 mm in sektoriellen Bereichen von bis zu 90°. Diese Abstandsvariationen müssen bei der β-Bestrahlungsdosimetrie berücksichtigt werden, da sie eine Reduktion der effektiven β-Bestrahlungsdosis im Zielbereich um ein Drittel bewirken können. Auch morphologische Gewebeveränderungen (Narbenbildung), die auf dem Wundheilungsprozess basieren, konnten mittels radialer OCT durch die Katheterwand hindurch nachgewiesen werden. Mittels OCT ist eine Differenzierung zwischen morphologisch veränderten Gewebebereichen prinzipiell auch durch den urologischen Katheter hindurch gegeben. Der Kontaktbereich zwischen Katheter und Gewebe kann mit Hilfe der OCT verifiziert werden, was die Grundlage für eine solide Dosimetrie bei der lokalen Anwendung der 32P-β-Bestrahlung bildet.

Objective Catheter-based intraluminal optical coherence tomography (OCT) with near-infrared light provides cross-sectional images of hollow organs and vessels, with a lateral resolution of 10–20 μm. We evaluated the technical success rate and demonstration of different wall layers of the human upper urinary tract (UUT) in OCT images obtained in vivo. Materials and methods The study protocol was approved by the local hospital ethics committee. The OCT probe (diameter: 0.014 in) was introduced into the UUT of 14 patients either through a cystoscope and urinary catheter, or through an uretero-renoscope to obtain single-slice cross-sectional images. OCT images were evaluated for delineation of ureteral wall layers by means of OCT software (M2, LightLab, Inc., Westford, MA). Results Catheter-based OCT of the UUT in vivo was technically successful in 14 out of 14 patients (100%). A total of 190 cross-sectional OCT images (760 quadrants) were obtained. Image quality allowed for tissue differentiation in 656/760 quadrants (86.3%). OCT distinguished urothelium and lamina propria in 552/656 quadrants (84.1%), lamina propria and muscle layer in 643/656 quadrants (98.0%), inner and outer muscle layer in 288/656 quadrants (43.9%), and different cell layers within the urothelium in 33/656 quadrants (5.0%) of cross-sectional images in healthy sections of the UUT. Urothelial cancer was presented as a thickening of the urothelium with distortion of the lamina propria. The histological sections confirmed the OCT findings. Conclusion Using OCT it appears to be possible to distinguish between different wall layers of the human upper urinary tract in vivo. Urothelial cancer involves a tumorous thickening of the urothelial layer and distortion of deeper tissue layers.

Encrustation of pigtail catheters with crystalline deposit of urine components is a well-known problem and in addition to lower urinary tract infection, the most common complication of any material placed in the urinary tract. There is neither any data about the beginning of encrustation in literature, nor about location or progression. The aim of this study is to make an analysis of the level of encrustation and to document the longitudinal progression with OCT. Fourteen double-J (DJ) catheters (Neomedical Ch 7/28 cm) with different indwelling times were compared with a new DJ catheter as a reference, after removal. The external surfaces of the catheters were examined using endoscopic surface OCT (Imalux) and the intraluminal surfaces with endoluminal-radial OCT (LightLab Imaging) with regard to possible encrustation or crystalline sedimentation. The resolution of OCT was 20 μm. The pullback mode of the endoluminal radial OCT allowed the documentation in 6 μm sequences. The median indwelling time was 100 days (19–27 days; n=12 female and n=2 male patients). Firstly, the external encrustation was macroscopically rated in “low”, “medium” and “high”. The macroscopic and the extraluminal OCT results were correlated. With the help of endoluminal OCT, the dimension of intraluminal encrustation could be expressed as a percentage relating to the reference catheter. The luminal reduction caused by encrustation is significant higher at the proximal end of the pigtail. An encrustation at the distal end of the pigtail was only present when there was also an encrustation at the proximal end. Only 2 stents showed an encrustation in the middle part. OCT made it possible to detect the encrustation of DJ catheters and express the degree of encrustation quantitatively. The encrustation started at the proximal side and seemed to expand antegrade. Further studies have to be carried out in order to answer the question if an encrustation expands from intra- to extraluminal or vice versa. With the help of OCT, the effect of surface modification of the implanted material could be examined in order to reduce encrustation.