Significant Artifact Reduction at 1.5T and 3T MRI by the Use of a Cochlear Implant with Removable Magnet: An Experimental Human Cadaver Study

OBJECTIVE Cochlear implants (CIs) are standard treatment for postlingually deafened individuals and prelingually deafened children. This human cadaver study evaluated diagnostic usefulness, image quality and artifacts in 1.5T and 3T magnetic resonance (MR) brain scans after CI with a removable magnet. METHODS Three criteria (diagnostic usefulness, image quality, artifacts) were assessed at 1.5T and 3T in five cadaver heads with CI. The brain magnetic resonance scans were performed with and without the magnet in situ. The criteria were analyzed by two blinded neuroradiologists, with focus on image distortion and limitation of the diagnostic value of the acquired MR images. RESULTS MR images with the magnet in situ were all compromised by artifacts caused by the CI. After removal of the magnet, MR scans showed an unequivocal artifact reduction with significant improvement of the image quality and diagnostic usefulness, both at 1.5T and 3T. Visibility of the brain stem, cerebellopontine angle, and parieto-occipital lobe ipsilateral to the CI increased significantly after magnet removal. CONCLUSIONS The results indicate the possible advantages for 1.5T and 3T MR scanning of the brain in CI carriers with removable magnets. Our findings support use of CIs with removable magnets, especially in patients with chronic intracranial pathologies.

Zu S. 456-463 [Nachricht] : (Magnet in der jüdischen Literatur) ; zugleich zur Ergänzung meiner Ausführungen über den schwebenden Sarg (MGWJ 1925, 50-52 ; 1926, 271-276)

Bernhard Heller

Comparativa de diferentes tipos de efemérides GNSS en cálculo de grandes líneas base con Magnet Office.

El objetivo de este Trabajo de Fin de Grado es hallar la influencia de cada tipo de efeméride en la precisión a posteriori de las coordenadas de un punto de la línea base. Para ello, se plantea una comparativa entre líneas base en función de la longitud, la duración de la sesión, la constelación y el tipo de efemérides. Todo ello, eligiendo puntos de control en la Península Ibérica y contrastando las soluciones sobre el marco de referencia ETRS89. No se pretende buscar la máxima precisión en cada línea base, sino tratar de emular las características de un uso común del GNSS en topografía y geodesia. En la comparativa se plantean situaciones al límite con sesiones de observación de poca duración y con distancias muy largas. Los tiempos de observación son inferiores a los recomendados en libros y manuales, para así evitar que la redundancia enmascare la verdadera precisión de las efemérides y llevar al límite de lo posible este test.

The golden magnet : a tale of the land of the Incas /

Mode of access: Internet.

Theory and methods of magnet systems design : a senior thesis /

"AEC Contract AT930-1)-2137."

Dynamic field measurements with an EMR magnetometer in the pulsed beam switching magnet /

"AEC Contract AT(04-3)-400."

A pulsed bending magnet for the beam switchyard area of the Stanford two-mile linear electron accelerator /

"AEC Contract AT(04-3)-400."

Magnet report /

Work performed by the Carnegie Institute of Technology, Pittsburgh, Pennsylvania.

A bending magnet with nonsaturating shimming /

"AEC Contract AT(04-3)-400."

HIgh repetition rate pulser for beam switching magnet /

"AEC Contract AT(04-3)-400."

Effect of nuclear radiation on organic materials, specifically magnet insulations in high-energy accelerators /

"March 1965."

Proceedings of the International Symposium on Magnet Technology, Stanford Linear Accelerator Center, Stanford University, Stanford California, September 8-10, 1965.

Mode of access: Internet.

L'hypnotisme et les et́ats analogues au point de vue med́ico-leǵal, les et́ats hypnotiques et les et́ats analogues les suggestions criminelles cabinets de somnambules et societ́eś de magnet́isme et de spiritisme l'hypnotisme devant la loi /

Mode of access: Internet.

Tailoring magnetic field gradient design to magnet cryostat geometry

Eddy currents induced within a magnetic resonance imaging (MRI) cryostat bore during pulsing of gradient coils can be applied constructively together with the gradient currents that generate them, to obtain good quality gradient uniformities within a specified imaging volume over time. This can be achieved by simultaneously optimizing the spatial distribution and temporal pre-emphasis of the gradient coil current, to account for the spatial and temporal variation of the secondary magnetic fields due to the induced eddy currents. This method allows the tailored design of gradient coil/magnet configurations and consequent engineering trade-offs. To compute the transient eddy currents within a realistic cryostat vessel, a low-frequency finite-difference time-domain (FDTD) method using total-field scattered-field (TFSF) scheme has been performed and validated