PURPOSE In this study, we analyzed dielectric shimming by formulating it as an electromagnetic scattering problem using integral equations. METHODS Three-dimensional simulations of the radiofrequency field in two configurations using different materials were analyzed in terms of induced currents and secondary fields. A two-dimensional integral equation method with different backgrounds was us...

The Visual to Infrared SASE Amplifier (VISA) [1] FEL is designed to achieve saturation at radiation wavelengths between 800 and 600 nm with a 4-m pure permanent magnet undulator. The undulator comprises four 99-cm segments each of which has four FODO focusing cells superposed on the beam by means of permanent magnets in the gap alongside the beam. Each segment will also have two beam position m...

PURPOSE We compare the performance of eight parallel transmit (pTx) body arrays with up to 32 channels and a standard birdcage design. Excitation uniformity, local specific absorption rate (SAR), global SAR, and power metrics are analyzed in the torso at 3 T for radiofrequency (RF)-shimming and 2-spoke excitations. METHODS We used a fast cosimulation strategy for field calculation in the pres...

The primary visual cortex (V1) is one of the elementary targets, when visual function and cortical reorganization are investigated. Neurotransmitters like glutamate (Glu), glutamine (Gln), and γ-aminobutyric acid (GABA) or substances of the brain’s energy metabolism like creatine (Cr) and phosphocreatine (PCr) are thought to be key compounds for a deeper understanding of the underlying processe...

The measurement of cerebral metabolites using highly homologous localization techniques and similar shimming methods was performed in the human brain at 1.5 and 4 T as well as in the dog and rat brain at 9.4 T. In rat brain, improved resolution was achieved by shimming all first- and second-order shim coils using a fully adiabatic FASTMAP sequence. The spectra showed a clear improvement in spec...

PURPOSE To determine whether administration of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) and whether placement of the outer volume saturation bands significantly affect shimming and water suppression on hepatic MR spectroscopic prescanning. METHOD Region of interest (ROI) of 2 cm × 2 cm × 2 cm was carefully positioned in the region of the middle portion of the right hepatic lob...

Cardiac magnetic resonance imaging (MRI) at high field presents challenges because of the high specific absorption rate and significant transmit field (B1+ ) inhomogeneities. Parallel transmission MRI offers the ability to correct for both issues at the level of individual radiofrequency (RF) pulses, but must operate within strict hardware and safety constraints. The constraints are themselves ...

Low-field (B 0 < 0.2 T) magnetic resonance imaging (MRI) is emerging as a low cost, point-of-care alternative to provide access diagnostic technology even in resource scarce environments. MRI magnets can be constructed based on permanent neodymium-iron-boron (NdFeB) discretized arrangements, leading substantially lower mass and costs. A challenge with these designs is, however, good B fi...

Most recently, quiescent-interval single-shot (QISS) peripheral MRA [1] has been introduced as a fast and robust alternative to unenhanced MRA methods such as two-dimensional time of flight [2] and fresh blood imaging [3]. Being a single-shot technique, QISS is relatively robust in the presence of respiratory and bowel motion. The method, furthermore, is widely independent of the arterial peak ...