Peter Andris

Measurement and imaging of planar electromagnetic phantoms based on NMR imaging methods

Measurement and Imaging of Planar Electromagnetic Phantoms Based on NMR Imaging Methods Planar electromagnetic phantom design for measurement and imaging using NMR has been performed. Electromagnetic phantom computation and testing on a NMR 0.178 Tesla Esaote Opera imager were accomplished. The classical geometrical and chemical phantoms are generally used for testing of NMR imaging systems. They are simple cylindrical or rectangular objects with different dimensions and shapes with holes filled with specially prepared water solutions. In our experiments a homogeneous phantom (reference medium) - a container filled with water - was used. The resultant image represents the magnetic field distribution in the homogeneous phantom. An image acquired by this method is actually a projection of the sample properties onto the homogeneous phantom. The goal of the paper is to map and image the magnetic field deformation using NMR imaging methods. We are using a double slender rectangular vessel with constant thickness filled with specially prepared water solution in our experiments. For detection a carefully tailored gradient-echo imaging method, susceptible to magnetic field homogeneity, was used.

Indirect Susceptibility Mapping of Thin-Layer Samples Using Nuclear Magnetic Resonance Imaging

We measured and imaged magnetic field distributions of thin layers (2-D objects with negligible thickness) of biological and physical samples, by using nuclear magnetic resonance (NMR). The image represents the magnetic susceptibility distribution in the sample. We used a standard gradient echo imaging method, susceptible to magnetic field homogeneity, for detection. Since the physical and biological samples we investigated do not generate any NMR signal, we used a homogeneous phantom reference - a container filled with water - as a medium. The image acquired by this method is actually a projection of the sample properties onto the homogeneous phantom. The method can be applied in nanotechnology, microelectronics, and especially in the biological and medical sciences.

Magnetic Field Variations Near Weak Magnetic Materials Studied by Magnetic Resonance Imaging Techniques

Imaging based on magnetic resonance (MRI) for mapping and imaging of the weak magnetic materials placed into the homogenous magnetic field of an imager is proposed. Samples made of weak magnetic material were theoretically computed, constructed, and tested on an MRI 0.178 T permanent magnet imager. In laboratory experiments, a homogeneous phantom (reference medium)-a container filled with doped water-was used. The resultant image represents the magnetic field variations (MFV) in the homogeneous phantom. For detection, a carefully tailored gradient-echo (GRE) imaging method, susceptible to magnetic field homogeneities, was used. The first results showed the feasibility of the method and some of the possibilities offered in this field for material research.

Soft Magnetic Material Testing Using Magnetic Resonance Imaging

Soft magnetic field samples were placed into the homogenous magnetic field of an imager based on nuclear magnetic resonance. Several samples made of a soft magnetic material (cut from a data disc) were tested. Theoretical computations on a magnetic double layer were performed. For experimental verification an MRI 0.178 Testa ESAOTE Opera imager was used. For our experiments a homogeneous circular holder (reference medium) - a container filled with doped water - was designed. The resultant image corresponds to the magnetic field variations in the vicinity of the samples. For data detection classical gradient-echo and spin-echo imaging methods, susceptible to magnetic field inhomogeneities, were used. Experiments proved that the proposed method is perspective for soft magnetic material testing using magnetic resonance imaging methods (MRI).

Comparative magnetic field measurements for homogeneity adjustment of magnetic resonance imaging equipments

The goal of this paper is to demonstrate three methods for static magnetic field measurement on a whole body magnetic resonance imager. The measured data are serving for computation of feeding currents of correcting coils for the static magnetic field used in NMR imaging. The methods suggest to measure the magnetic field in selected points twice: 1. correcting coils are switched off and 2. measurement of magnetic field changes caused by switching on the feeding current of particular correcting coil in each of selected measuring points. Measurements are realized using: magnetometer based on Hall effect, NMR point magnetometer and gradient echo imaging method applied to circular test tubes. All three measurements measure magnetic field on a circle (12 measuring points) and one point in the center. A set of linear equations, determination of a target function and optimization computations are procedures that provide optimal values of currents for correcting coils. Results of all three methods are compared and discussed. The proposed method is suitable for periodic testing and magnet in homogeneities correction for MRI magnets.