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Purpose: Surgical navigation techniques can guide surgeons in localizing pelvic–abdominal malignancies. For abdominal navigation, accurate patient registration is crucial and is generally performed using an intra-operative cone-beam CT (CBCT). However, this method causes 15-min surgical preparation workflow interruption and radiation exposure, and more importantly, it cannot be repeated during surgery to compensate for large patient movement. As an alternative, the accuracy and feasibility of tracked ultrasound (US) registration are assessed in this patient study. Methods: Patients scheduled for surgical navigation during laparotomy of pelvic–abdominal malignancies were prospectively included. In the operating room, two percutaneous tracked US scans of the pelvic bone were acquired: one in supine and one in Trendelenburg patient position. Postoperatively, the bone surface was semiautomatically segmented from US images and registered to the bone surface on the preoperative CT scan. The US registration accuracy was computed using the CBCT registration as a reference and acquisition times were compared. Additionally, both US measurements were compared to quantify the registration error caused by patient movement into Trendelenburg. Results: In total, 18 patients were included and analyzed. US registration resulted in a mean surface registration error of 1.2 ± 0.2 mm and a mean target registration error of 3.3 ± 1.4 mm. US acquisitions were 4 × faster than the CBCT scans (two-sample t-test P < 0.05) and could even be performed during standard patient preparation before skin incision. Patient repositioning in Trendelenburg caused a mean target registration error of 7.7 ± 3.3 mm, mainly in cranial direction. Conclusion: US registration based on the pelvic bone is accurate, fast and feasible for surgical navigation. Further optimization of the bone segmentation algorithm will allow for real-time registration in the clinical workflow. In the end, this would allow intra-operative US registration to correct for large patient movement. Trial registration: This study is registered in ClinicalTrials.gov (NCT05637359).

Shear stress of the blood at the vessel wall plays an important role in many processes in the cardiovascular system primarily focused on the regulation of vessel lumen and wall dimensions. There is ample evidence that atherosclerotic plaques are generated at low shear stress regions in the cardiovascular system, while high shear stress regions are protected. In the course of plaque progression, advanced plaques start to encroach into the lumen, and thereby start to experience high shear stress at the endothelium. Until now the consequences of high shear stress working at the endothelium of an advanced plaque are unknown. As high shear stress influences tissue regression, we hypothesised that high shear stress can destabilise the plaque by cap weakening leading to ulceration. We investigated this hypothesis in a magnetic resonance imaging (MRI) dataset of a 67-year-old woman with a plaque in the carotid artery at baseline and an ulcer at ten-month follow-up. The lumen, plaque components (lipid/necrotic core, intraplaque haemorrhage) and ulcer were reconstructed three dimensionally and the geometry at baseline was used for shear stress calculation using computational fluid dynamics. Correlation of the change in plaque composition with the shear stress at baseline showed that the ulcer was generated exclusively at the high shear stress location. In this serial MRI study we found plaque ulceration at the high shear stress location of a protruding plaque in the carotid artery. Our data suggest that high shear stress influences plaque vulnerability and therefore may become a potential parameter for predicting future events. (Neth Heart J 2008;16:280-3.).