D. Gogola

Magnetic Resonance Imaging of Surgical Implants Made from Weak Magnetic Materials

Materials with high magnetic susceptibility cause local inhomogeneities in the main field of the magnetic resonance (MR) tomograph. These inhomogeneities lead to loss of phase coherence, and thus to a rapid loss of signal in the image. In our research we investigated inhomogeneous field of magnetic implants such as magnetic fibers, designed for inner suture during surgery. The magnetic field inhomogeneities were studied at low magnetic planar phantom, which was made from four thin strips of magnetic tape, arranged grid-wise. We optimized the properties of imaging sequences with the aim to find the best setup for magnetic fiber visualization. These fibers can be potentially exploited in surgery for internal stitches. Stitches can be visualized by the magnetic resonance imaging (MRI) method after surgery. This study shows that the imaging of magnetic implants is possible by using the low field MRI systems, without the use of complicated post processing techniques (e.g., IDEAL).

Design, Realization and Experiments with a new RF Head Probe Coil for Human Vocal Tract Imaging in an NMR device

Design, Realization and Experiments with a new RF Head Probe Coil for Human Vocal Tract Imaging in an NMR device Magnetic resonance imaging (MRI) is nowadays widely used in medicine for diagnostic imaging and in research studies. The modeling of the human vocal tract acoustics has recently attracted considerable interest. This paper describes the design, realization and first MR scan experiments with a new head probe coil for vocal tract imaging in the open-air MRI equipment working in a weak magnetic field up to 0.2 T. The paper also describes an experimental setting for sound recording during the MR imaging.

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.

Phased Array Receiving Coils for Low Field Lungs MRI: Design and Optimization

Phased Array Receiving Coils for Low Field Lungs MRI: Design and Optimization Recent techniques of radiofrequency (RF) probes and preamplifiers in Magnetic Resonance Imaging (MRI) developments almost reached the physical limits of signal to noise ratio (SNR). More improvements in speed accelerations of data acquisition are very difficult to achieve. One exception, called RF phased array coils, is recently being developed very progressively. The approach is conceptually similar to phased array used in radar techniques; hence it is usually called MRI phased array coils. It is necessary to ensure independence of the individual coil channels in the array by the coil and preamp decoupling and the coil geometry optimization to get maximum benefits from this technique. Thus, the qualitative design and method for optimization of geometric properties of the coil elements in phased arrays, with aim to increase SNR, minimize the G-factor and to limit noise correlation, are proposed in this paper. By the finite element method (FEM) simulations, we obtained the sensitivity maps and inductances of the coils. The introduced program primarily calculates the Sensitivity Encoding (SENSE) G-factor along with other parameters that can be derived from sensitivity maps. By the proposed optimization algorithm, the program is capable to calculate the optimal values of the geometric coil parameters in a relatively small number of iterations.

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).

Design and Construction of Novel Instrumentation for Low-Field MR Tomography

Abstract Magnetic resonance imaging (MRI) is a very popular tool for diagnostic applications and research studies. Low-field MR scanners, usually with an open design, are suitable for claustrophobic and obese patients, as well as for children, who may be fearful in closed MR scanners. However, these types of scanners provide lower spatial resolution and a lower signal-to-noise ratio (SNR) if compared with the same examination performed at the same time at high field scanners. It is dominantly caused by the low field strength and other factors, such as radiofrequency noise. Therefore, a long measurement time is usually necessary. This research paper is focused on the development of novel probes and preamplifiers for low-field MR scanners to improve SNR, and thus, shorten the measurement time. In this study, we describe the design of a high impedance preamplifier and a high temperature superconductor (HTS) coil. This novel instrumentation was compared with uncooled and cooled copper coils. Improvement in SNR in the case of an HTS coil is reported.

Automatic evaluation of noise suppression in speech signal recorded during phonation in the open-air MRI

The paper is focused on the evaluation of successfulness of noise reduction of the speech signal recorded in an open-air magnetic resonance imager during a phonation for the 3D human vocal tract modeling. In more detail is there described the automatic evaluation method based on Gaussian mixture models (GMM) classification. Performed first-step experiments have successfully confirmed that the proposed GMM classifier of the speech quality is functional and fully comparable with the standard evaluation based on the listening test.

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.