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PurposeElectromagnetic tracking systems (EMTSs) have been proposed to assist the percutaneous renal access (PRA) during minimally invasive interventions to the renal system. However, the influence of other surgical instruments widely used during PRA (like ureteroscopy and ultrasound equipment) in the EMTS performance is not completely known. This work performs this assessment for two EMTSs [Aurora® Planar Field Generator (PFG); Aurora® Tabletop Field Generator (TTFG)].MethodsAn assessment platform, composed by a scaffold with specific supports to attach the surgical instruments and a plate phantom with multiple levels to precisely translate or rotate the surgical instruments, was developed. The median accuracy and precision in terms of position and orientation were estimated for the PFG and TTFG in a surgical environment using this platform. Then, the influence of different surgical instruments (alone or together), namely analogic flexible ureterorenoscope (AUR), digital flexible ureterorenoscope (DUR), two‐dimensional (2D) ultrasound (US) probe, and four‐dimensional (4D) mechanical US probe, was assessed for both EMTSs by coupling the instruments to 5‐DOF and 6‐DOF sensors.ResultsOverall, the median positional and orientation accuracies in the surgical environment were 0.85 mm and 0.42° for PFG, and 0.72 mm and 0.39° for TTFG, while precisions were 0.10 mm and 0.03° for PFG, and 0.20 mm and 0.12° for TTFG, respectively. No significant differences were found for accuracy between EMTSs. However, PFG showed a tendency for higher precision than TTFG. AUR, DUR, and 2D US probe did not influence the accuracy and precision of both EMTSs. In opposition, the 4D probe distorted the signal near the attached sensor, making readings unreliable.ConclusionsUreteroscopy‐ and ultrasonography‐assisted PRA based on EMTS guidance are feasible with the tested AUR or DUR together with the 2D probe. More studies must be performed to evaluate the probes and ureterorenoscopes’ influence before their use in PRA based on EMTS guidance.

Objective A small common bile duct (CBD) diameter has been associated with complications and with a difficult biliary cannulation. Previous studies suggested that this diameter can be predicted during the endoscopic retrograde cholangiopancreatography (ERCP) simply by observing the papillary morphology. Despite this published suggestion there is no study addressing this topic. This study evaluated a possible association between the morphology of the major papilla and the diameter of the terminal CBD (t-CBD). Methods Observational cross-sectional study including consecutive patients with naïve papillae was referred for ERCP in two affiliated university hospitals. The transverse (p-transv) and longitudinal measures (p-long) of the papilla were obtained using a visual method. Papillae were classified into nonprominent, prominent, bulging or other. The t-CBD was measured 1 cm from the papilla using fluoroscopic images in prone/supine. Measurements were performed by two senior endoscopists and outcomes were evaluated using correlation and linear regression model. Results We included 245 patients with a median age of 76 years. The median p-transv for each type of papillae was as follows: nonprominent = 6 mm, prominent = 9 mm, bulging = 15 mm and other = 6 mm; P < 0.001. The median t-CBD for nonprominent = 7.62 mm, prominent = 8.34 mm, bulging = 8.60 mm and other = 8.52 mm; P = 0.40. The correlation between the transverse and longitudinal measures of papilla and the t-CBD were 0.0092 and 0.0614, respectively. In the regression model, the t-CBD diameter was not explained by papilla’s size or morphology (R 2 = 1.70%; P = 0.80). Conclusion The morphology of the papilla must not be used as a predictor of the diameter of the CBD as there is no correlation between these two items.

Renal ultrasound imaging is the primary imaging modality for the assessment of the kidney's condition and is essential for diagnosis, treatment and surgical intervention planning, and follow-up. In this regard, kidney delineation in three-dimensional ultrasound images represents a relevant and challenging task in clinical practice. In this paper, a novel framework is proposed to accurately segment the kidney in 3D ultrasound images. The proposed framework can be divided into two stages: 1) initialization of the segmentation method; and 2) kidney segmentation. Within the initialization stage, a phase-based feature detection method is used to detect edge points at kidney boundaries, from which the segmentation is automatically initialized. In the segmentation stage, the B-Spline Explicit Active Surface framework is adapted to obtain the final contour of the kidney. Here, a novel hybrid energy functional that combines localized region-based and edge-based terms is used during segmentation. For the edge term, a fast-modified phase-based detection approach is applied. The proposed framework was tested in 15 3D ultrasound images. The method showed to be accurate and feasible in very challenging poor-quality ultrasound images, achieving a Dice overlap of approximately 81% and an average point-to-surface error of 2.4 mm. Moreover, a validation set composed of 24 additional images of healthy kidneys and 8 additional images of pathologic ones was evaluated to corroborate the accuracy of the method. The obtained results demonstrated the potential of the proposed method to be used in clinical practice.

Percutaneous renal access (PRA) is a crucial step in some minimally invasive kidney interventions. During this step, the surgeon inserts a needle through the skin until the kidney target site using fluoroscopy and ultrasound imaging. Recently, new concepts of enhanced image-guided interventions have been introduced in these interventions. However, their validation remains a challenging task. Phantom models have been presented to solve such challenge, using realistic anatomies in a controlled environment. In this work, we evaluate the accuracy of a porcine kidney phantom for validation of novel dual-modal computed tomography (CT)/ultrasound (US) image-guided strategies for PRA. A porcine kidney was combined with a tissue mimicking material (TMM) and implanted fiducial markers (FM). While the TMM mimics the surrounding tissues, the FM are used to accurately assess the registration errors between the US and CT images, providing a valid ground-truth. US and CT image acquisitions of the phantom model were performed and the FM were manually selected on both images. A rigid alignment was performed between the selected FM, presenting a root-mean-square error of 1.1 mm. Moreover, the kidney was manually segmented, presenting volumes of 203 ml and 238 ml for CT and US, respectively. The initial results are promising on achieving a realistic kidney phantom model to develop new strategies for PRA, but further work to improve the manufacturing process and to introduce motion and anatomical artifacts in the phantom is still required.

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Purpose As a crucial step in accessing the kidney in several minimally invasive interventions, percutaneous renal access (PRA) practicality and safety may be improved through the fusion of computed tomography (CT) and ultrasound (US) data. This work aims to assess the potential of a surface‐based registration technique and establish an optimal US acquisition protocol to fuse two‐dimensional (2D) US and CT data for image‐guided PRA. Methods Ten porcine kidney phantoms with fiducial markers were imaged using CT and three‐dimensional (3D) US. Both images were manually segmented and aligned. In a virtual environment, 2D contours were extracted by slicing the 3D US kidney surfaces and using usual PRA US‐guided views, while the 3D CT kidney surfaces were transformed to simulate positional variability. Surface‐based registration was performed using two methods of the iterative closest point algorithm (point‐to‐point, ICP1; and point‐to‐plane, ICP2), while four acquisition variants were studied: (a) use of single‐plane (transverse, SPT; or longitudinal, SPL) vs bi‐plane views (BP); (b) use of different kidney's coverage ranges acquired by a probe's sweep; (c) influence of sweep movements; and (d) influence of the spacing between consecutive slices acquired for a specific coverage range. Results BP view showed the best performance (TRE = 2.26 mm) when ICP2 method, a wide kidney coverage range (20°, with slices spaced by 5°), and a large sweep along the central longitudinal view were used, showing a statistically similar performance (P = 0.097) to a full 3D US surface registration (TRE = 2.28 mm). Conclusions An optimal 2D US acquisition protocol was evaluated. Surface‐based registration, using multiple slices and specific sweep movements and views, is here suggested as a valid strategy for intraoperative image fusion using CT and US data, having the potential to be applied to other image modalities and/or interventions.