Introduction Dynamic Shimming is a technique for obtaining optimal Bo field homogeneity over a volume by updating the shim coil and gradient currents for every slice in a multislice acquisition in real time [1, 2]. Dynamic shimming can produce better field homogeneity within each slice than global volume shimming methods. It can therefore reduce signal losses and geometric distortions and can b...

Shimming is an essential process for most NMR experiments, and time saving in this process is desired. Here we propose a fast 3D gradient shimming with a low resolution of only 2×2 pixels in the XY plane, and the number of pixels in the Z direction remains unchanged. The proposed pulse sequences employ the selective excitation and the convection compensation. Consequently, the fast 3D gradient ...

Dielectric resonance effects and radio-frequency (RF) power deposition have become challenging issues for magnetic resonance imaging at ultrahigh-field (UHF) strengths. The use of transmit (Tx) coil arrays with independently-driven RF sources using a parallel transmission system is a promising method for alleviating the resulting RF inhomogeneities. In this study, the effect on homogeneity and ...

This paper presents a warm bore ferromagnetic shimming design for a high resolution NMR magnet based on spherical harmonic coefficient reduction techniques. The passive ferromagnetic shimming along with the active shimming is a critically important step to improve magnetic field homogeneity for an NMR Magnet. Here, the technique is applied to an NMR magnet already designed and built at the MIT'...

In functional MRI, magnetic field inhomogeneities due to air-tissue susceptibility differences may lead to severe signal dropouts and geometric distortions in echo-planar images. Therefore, the inhomogeneities in the field are routinely minimized by shimming prior to imaging. However in fMRI, the Blood Oxygen Level Dependent (BOLD) effect is the measure of interest, so the BOLD sensitivity (BS)...

MR imaging and spectroscopy allow the noninvasive measurement of brain function and physiology, but excellent magnetic field homogeneity is required for meaningful results. The homogenization of the magnetic field distribution in the mouse brain (i.e., shimming) is a difficult task due to complex susceptibility-induced field distortions combined with the small size of the object. To date, the a...

shimming. Right: 10gm average RF absorption or SAR for H(1)-(4) for the same B1+ shimming, and mean B1+ of 2.5uT in the brain. Table 1 shows the stats on B1+ and sample SAR variation across subjects for the same B1+ shimming amplitudes and phases. The homogeneity, SAR ave and peak changes were <10 % across the 4 head models H(1)-(4). Figure 1 The Tx array tuning (Smith Chart) on 3 volunteers (d...

We adopted a combination of pieces of permanent magnets and a single-channel (SC) shim coil to shim the magnetic field in a magnetic resonance imaging system dedicated for skeletal age assessment of children. The target magnet was a 0.3-T open and compact permanent magnet tailored to the hand imaging of young children. The homogeneity of the magnetic field was first improved by shimming using p...

The self-extraction cyclotron is a 14 MeV H+ machine from which the beam extracts without a deflector. This is achieved with a special shaping of the magnetic field. Detailed 3D magnetostatic models have been constructed of this cyclotron, in order to accurately calculate the extraction process. Shimming of removable pole tips has been used to isochronize the machine and to remove harmonic erro...