Features of this new technology include variable field operation, higher intrinsic magnetic field homogeneity
, larger fields of view (FOV) elliptical in shape to better fit the subject and automatic field ramping.
One of the most important factors in the magnetic field experiments is magnetic field homogeneity
in the effective volume where the cells are stored.
In this regard, the integral method has at its foundation the numerical minimization of an objective function determined by the design goals, such as the mean-square deviation of the axial components of the magnetic field within the working volume, proposed by , or the magnetic field homogeneity, as has been used in [1,12].
Hence, that definition for the magnetic field homogeneity considers that it is a point-dependent index, not providing global information about the homogeneity within the volume of interest, and consequently the aforementioned definition is not useful to describe the whole volume of interest.
The algorithm converged to a solution satisfying the requirements of magnetic field homogeneity and magnetic flux density inside of the volume of interest, reaching H = 98.7%, [bar.B] = 10.00 mT, [B.sub.max] = 10.05 mT and [B.sub.min] = 9.92 mT for a six-coils (connected in series) system with the constructive parameters and characteristics shown in Table 1.
As was previously discussed, significantly increased sensitivity to T2 * effects can lead to substantial susceptibility artifacts and wider variations in magnetic field homogeneity
Besides the essential goal of maximizing the [.sup.3]He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments.
Additional practical issues for spin filters include decreased constraints on cell lifetimes and magnetic field homogeneity.
MRI requires excellent magnetic field homogeneity
, often better than 10 parts per million over the region of interest.
Within the limitation imposed by the mechanical strength, desired peak field, pulse duration, magnetic field homogeneity
should be evaluated too.
Magnetic field homogeneity
of the system of two separate coils depends on the distance between coils and their own geometry.