Study DesignA retrospective study.PurposeTo evaluate the prevalence and risk factors of asymptomatic cervical or thoracic lesions in elderly patients who have undergone surgery for lumbar spinal stenosis.Overview of LiteratureConcurrent multiple spinal lesions have been reported in many studies with a varied prevalence, and described the characteristics of the disease and its treatment options. However, the cervical or thoracic lesions without apparent symptoms in patients with symptomatic lumbar stenosis had not been evaluated.MethodsA total of 101 elderly patients (aged 65 or more), who had undergone surgery for lumbar spinal stenosis from January 2005 to December 2005, were enrolled in this study. All patients underwent lumbar magnetic resonance imaging (MRI) along with T2-weighted cervical and thoracic sagittal MRI prior to surgery. The concurrent cervical or thoracic lesions were classified according to the disease entity, and the severity of the lesions was graded from grade 0 (no lesion) to grade 4 (any lesion compressing the cord with a signal change). The prevalence of concurrent cervical and thoracic lesions was then analyzed. In addition, the risk factors for the development of concurrent lesions were evaluated, and the risk factors affecting the severity of the concurrent lesion were analyzed individually.ResultsSeventy-seven (76.2%) and 30 (29.7%) patients had a concurrent cervical and thoracic lesion, respectively. Twenty-six patients (25.7%) had both a cervical and thoracic lesion. There was a positive correlation between the symptom duration of lumbar stenosis and the prevalence of both cervical (p = 0.044) and thoracic (p = 0.022) lesions.ConclusionsThe incidence of asymptomatic cervical or thoracic lesions is apparently high in elderly patients who have undergone surgery for lumbar spinal stenosis, particularly in those with longer symptom duration. This highlights the need for a preoperative evaluation of the cervical and thoracic spine in these patients.

No abstract

Micro-Doppler signatures from the rotating propellers of a drone can be utilized to distinguish the drone from clutter or airborne organisms with similar radar cross section (RCS) levels, such as birds and bats. To obtain the micro-Doppler signatures of a drone, calculation or measurement of the electric field scattered from the rotating propellers is essential. In this paper, using the relative angle concept and far-field approximation, we propose a way to rapidly estimate the dynamic RCS of a drone with several propellers according to its movement. In addition, based on the fact that the shape of the propeller does not change even if it rotates, we construct an impedance matrix only once and apply the matrix to the method of moments instead of the iterative process of calculating the impedance matrix and inverse matrix for each rotation angle of the propeller. Finally, by using the Fourier transform of the results from the proposed method, the rotation frequencies of the propellers according to the movement of the drone can be obtained.

No abstract

No abstract