Calculi (stones) in the urinary tract are common in the US population; they occur in nearly one million patients every year. The technique used to treat stones depends on the size and location. Ureteroscopy is often used in the treatment of stones by first passing a cystoscope through the urethra into the bladder. The ureter and collecting system are then cannulated using wires under fluoroscopic guidance. The ureteroscope is then advanced over the wire to the upper collecting system. Once the urologist locates the stone, either in the ureter or kidney, it can be fragmented using a holmium:YAG laser, which acts through an optic fiber introduced through the ureteroscope.

Alternatively, a percutaneous approach may be adopted for large renal stones or in patients with anatomic aberrancies to provide direct access to the stones. In this case, the collecting system is accessed through a percutaneous puncture. A guide wire is inserted through the percutaneous puncture location into the calices. The tract is dilated and either a rigid or flexible (cystoscope and ureteroscope) nephroscope is inserted into the collecting system. Once the stone is located, either a pneumatic ultrasound lithotripter or the holmium:YAG laser is passed through the lumen of the scope to fragment the stones. This method requires puncturing of the kidney using a needle percutaneously, which could in turn result in puncturing neighboring vascular structures or inadvertent entering of the system in a position that can result in damage to the kidney.

For patients with a solitary kidney or a transplant kidney, the challenges amplify due to the requirement of preserving kidney function. The challenges of navigating equipment into a displaced ureteral orifice or throughout a renal pelvis to access the stones have motivated the development of an Image Registration (or “GPS”) navigation system to visualize the cystoscope within the bladder and guide it to the displaced ureteral orifices and also to guide a ureteroscope either antegrade or retrograde throughout the calices of the kidney (see Fig. 29.4) to treat multiple stones or stones in multiple calyces. The navigation system also enables visualization and pre-procedure planning to assess the difficulty of gaining access through the transurethral approach or accessing the stone percutaneously (Fig. 29.5).

In creating viable NOTES procedures, the navigation of instruments safely and effectively in the body was appreciated and recognized as a key requirement [33]. The technique of real-time Image Registration may help address this need. Here are examples of recent animal and cadaver model studies:

Fernandez-Esparrach et al. compared two sites for transgastric access and one for transcolonic access to the peritoneum using a porcine model and CT-based image-registered navigation system to identify preselected targets [34]. The operator display for Image-Registered NOTES (IR-NOTES) included a 3D model and a simulated (virtual) endoscopic view as shown in Fig. 29.6. The results were consistent (but not with statistical significance) with the hypothesis that IR-NOTES procedures had fewer complications but did demonstrate that the operator moved the instruments more smoothly when IR-NOTES guidance was provided.

Azagury et al. endoscopically targeted 15 intra-abdominal organs with and without IR-NOTES via both transgastric and transcolonic routes, by three endoscopists with different levels of expertise, in three human cadavers [35]. Without IR-NOTES, 11.7 % of the targets were not reached, compared to 1 % in the IR-NOTES evaluation (P = 0.002). The IR-NOTES system enhanced both navigation efficacy and ease of intra-abdominal NOTES exploration for operators of all levels.