Path Following of a Rolling Disk Using Throttle Only

In this paper we address the problem of controlling a disk, rolling on a horizontal plane, using only throttle as control input The disk is supposed to follow an assigned path in the plane. The problem is difficult because of the high order of underactuation and of the instability of the system. The controller is based upon an internal manifold and a receding horizon technique. By using a backstepping control technique the controller tracks a lean angle trajectory. The lean angle reference trajectory is generated at each instant through a receding horizon algorithm and it is such that, if followed, the system tracks the assigned path with a bounded error

Imaging of pancreatic metastases from renal cell carcinoma

Background: To describe the main imaging characteristics of pancreatic metastases from renal cell carcinoma (RCC) with particular attention to CT features, underlining possible criteria for a differential diagnosis. Methods: 15 patients have been included in this study. 14 patients underwent multislice CT with triphasic acquisition (unenhanced, pancreatic parenchymal and portal venous phases). In 9 cases a delayed phase (120 sec) was also acquired. 5 patients underwent MRI, before and after administration of gadolinium. Results: The mean time interval between nephrectomy and recurrence was 7.5 years (range 1-17 years). On CT metastases avidly enhanced in the parenchymal phase and then demonstrated a significant wash-out, approaching isodensity to the normal pancreatic parenchyma in the portal phase. In the portal phase 20 of the 25 lesions found in the arterial phase were recognizable. On non-enhanced scans, only 13 of the 25 lesions were detected. On MRI, with the limitations due to the paucity of cases, the metastatic foci appeared hypointense to normal pancreatic tissue on T1-weighted images, and hyperintense on T2- and diffusion-weighted images. After gadolinium, the behaviour was similar to that reported for CT, except for one patient in whom two metastatic foci presented a signal intensity almost isointense to the surrounding parenchyma, accompanied also by an unusual lowering of the signal on DWI (diffusion-weighted imaging) with high b-values. Compared to CT, with MRI the lesions appeared all detectable even on non-enhanced acquisitions. Conclusion: Renal Cell Carcinomas require a prolonged CT or MRI follow-up. In patients with RCC history, an early arterial or a pancreatic parenchymal phase is always mandatory, as pancreatic metastases typically present themselves as hypervascular lesions. This behavior is similar to that of neuroendocrine tumors, while the other primary pancreatic tumors tend to be hypovascular

Synovial sarcoma: CT imaging of a rare primary malignant tumour of the thorax.

PURPOSE: This paper presents computed tomography (CT) features of three patients with primary synovial sarcoma of the lung (PSSL) who came to our attention and underwent surgery; reviews of the literature on this rare thoracic tumour are also presented. MATERIALS AND METHODS: The patients, all men, with a mean age of 58 years, underwent clinical and radiological re-evaluation after receiving a histological diagnosis. None of the patients had multifocal disease or other concomitant neoplasms. All patients had undergone both chest X-rays and computed tomography, and two had also been studied with positron emission tomography (PET)-CT. Two patients underwent surgical removal of the tumour, whereas the third initially underwent surgery (following an incorrect diagnosis) and then thoracoscopic biopsy of the pleural lesions that subsequently arose. RESULTS: In each case, chest X-rays showed changes, with the presence of pulmonary masses noted in all patients. In one patient, pleural effusion was also visible. CT scans showed parenchymal masses that were largely of a colliquative nature (in two out of three patients). Ipsilateral pleural effusion was present in two patients, associated in one with solid nodules within the pleura. Mediastinal lymphadenopathy, which was not radiologically significant, was present in only one patient. The two patients who also underwent PET-CT examination showed pathological tracer uptake confined to the lesion site without other thoracoabdominal or musculoskeletal localisations. CT-guided biopsy, performed in one patient only, was positive for mesenchymal tumour. In the two patients who underwent surgery, a definitive diagnosis of monophasic synovial sarcoma of the lung was made. The diagnosis of monophasic synovial sarcoma in the third patient was confirmed using thoracoscopic biopsy DISCUSSION: Both in the cases described and in those identified in the literature review, standard chest X-rays mainly showed a parenchymal mass of pleural origin with either irregular or well-defined margins. CT characteristics are more definite, with evidence of a mass with regular and sharply defined margins, occasionally polycyclic, with inhomogeneous density due to the presence of colliquative areas within the tumour. CONCLUSIONS: Although PSSL is a rare tumour, a pulmonary mass of inhomogeneous density, associated with pleural effusion but without lymphadenopathy, detected in an asymptomatic or poorly symptomatic patient, should lead to PSSL being considered in the differential diagnosis, provided that metastases from the more common synovial sarcomas of the musculoskeletal system have been excluded

Percutaneous and open iliac screw safety and accuracy using a tactile technique with adjunctive anteroposterior fluoroscopy

All currently described percutaneous iliac screw placement methods are entirely dependent on fluoroscopy. The purpose of this study was to determine the safety and the accuracy of percutaneous and open iliac screw placement using a primarily tactile technique with adjunctive anteroposterior (AP) fluoroscopy. All patients who underwent open and percutaneous iliac screw placement over a 5-year period were identified. Charts were reviewed to assess for any instances of neurologic or vascular injury associated with iliac screw placement. Screw accuracy was judged with postoperative computed tomography (CT) scans. A total of 133 patients were identified who underwent open or percutaneous iliac screw placement. Computed tomography scans were available for 57 patients, and all of these patients were included in the study, with a total of 115 iliac screws. Radiographic measurements were performed, consisting of the distance of the iliac screw to the sciatic notch on postoperative radiographs and CT scans. Computed tomography scans were used to determine iliac screw accuracy. Charts were reviewed to assess for any neurologic or vascular injuries related to screw placement. The distance of the iliac screw to the sciatic notch was measured and compared on AP radiography and CT scans. Computed tomography scans were assessed for any screw violation of the iliac cortex or the sciatic notch. The accuracy of open iliac screw placement was compared with minimally invasive percutaneous placement. There were no neurologic or vascular injuries related to screw placement in the 133 patients. Computed tomography scans were available for 115 iliac screws, with 3 cortical breaches, all by less than 2 mm. All 112 other screws were accurately intraosseous. There was a strong correlation between the iliac screw to the sciatic notch distance when measured by CT scan compared with AP radiography (r=0.9), thus validating the accuracy of AP fluoroscopy in guiding iliac screw placement with respect to the sciatic notch. Iliac screw accuracy was equal with the open and percutaneous insertion techniques. The described surgical technique represents a safe and reliable surgical option for iliac screw placement. Intraoperative AP fluoroscopy accurately reflects the distance of the iliac screw to the sciatic notch. Percutaneous iliac screws placed with this technique are as accurate as open iliac screws