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This paper presents a fast three-dimensional (3D) electromagnetic nonlinear inversion method in a multilayered medium via a novel scattering approximation. Using the superposition principle, we introduce a new source-dependent but diagonal scattering tensor. The approximate analytical expressions for the three scattering diagonal components are derived. Numerical tests show that the new approximation has better accuracy and wider range of applicability than the existing approximations such as the extended Born approximation and the quasi-analytical approximation. The computational speed of the new scattering approximation is essentially the same as the Born approximation.With such a new approximation, we further develop an efficient linearized 3D electromagnetic inversion method in a layered medium. In this method, the inverse problem is cast into a weighted least-squares problem solved via a conjugate gradient scheme. In terms of eigenvalue analysis, we propose a choice of the data and model weighting matrices that can be constructed for a general, complex Fréchet sensitivity matrix. The suggested weights help the selection of the regularization factor within the specified range of [0, 1] for the inverse problem, and improves the condition of the original imaging system. Synthetic tomography experiments demonstrate the efficiency of the new scattering approximation and the fast 3D EM imaging technique.

The aim of this study was to observe and analyze the causes of misplacement of peripherally inserted central catheters (PICCs) in patients with cancer. A total of 3,012 patients who underwent insertion of a PICC were reviewed from August 2000 to March 2012. The locations of the tube tips were recorded by chest X-ray examination. Malposition of the PICC was observed in 237 cases (7.87%), with the most frequently occurring site of misplacement being the jugular vein, followed by the axillary vein. By taking different remedies, all the malpositioned PICCs were relocated back to the superior vena cava or subclavian vein. In order to ensure the safe usage of PICCs, strict placement guidelines, skilled and experienced healthcare professionals and the cooperation of the patient is necessary.

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