Magnetic susceptibility of materials that are used for body implants causes much distortion in MR images. This paper deals with mapping the magnetic field induction in the vicinity of these materials. A modified spin-echo method is used, in which via inserting a time interval of a defined length the range of phase modulation is reduced below the value 2π. Even with a large B0 inhomogeneity it is not necessary to unwrap the phase jumps. The method is suitable for studying the effects of body-implant materials on MR images and for measuring their magnetic susceptibility.
This paper describes a method for measuring of the gradient magnetic field in Nuclear Magnetic Resonance (NMR) tomography, which is one of the modern medical diagnostic methods. A very important prerequisite for high quality imaging is a gradient magnetic field in the instrument with exactly defined properties. Nuclear magnetic resonance enables us to measure the pulse gradient magnetic field characteristics with high accuracy. These interesting precise methods were designed, realised, and tested at the Institute of Scientific Instruments (ISI) of the Academy of Sciences of the Czech Republic. The first of them was the Instantaneous Frequency (IF) method, which was developed into the Instantaneous Frequency of Spin Echo (IFSE) and the Instantaneous Frequency of Spin Echo Series (IFSES) methods. The above named methods are described in this paper and their a comparison is also presented.
The paper deals with measuring magnetic induction by imaging techniques based on magnetic resonance (MR). It describes experimental results of mapping the magnetic induction of helical and toroidal coils performed by modified MR imaging techniques. The results are compared with the theoretical calculation and with the measurement carried out using an ordinary magnetometer. The conclusions derived from the measurement will be used in the design of a new type of coil with complex electronic control of the magnetic field.
The paper deals with modern methods of image processing, especially image segmentation, classification and evaluation of parameters. It focuses primarily on processing medical images of soft tissues obtained by magnetic resonance tomography (MR). It is easy to describe edges of the sought objects using segmented images. The edges found can be useful for further processing of monitored object such as calculating the perimeter, surface and volume evaluation or even three-dimensional shape reconstruction. The proposed solutions can be used for the classification of healthy/unhealthy tissues in MR or other imaging. Application examples of the proposed segmentation methods are shown. Research in the area of image segmentation focuses on methods based on solving partial differential equations. This is a modern method for image processing, often called the active contour method. It is of great advantage in the segmentation of real images degraded by noise with fuzzy edges and transitions between objects. In the paper, results of the segmentation of medical images by the active contour method are compared with results of the segmentation by other existing methods. Experimental applications which demonstrate the very good properties of the active contour method are given.
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