Abstract
Several types of volume RF coils such as Helmholtz pair have been used for Magnetic Resonance Imaging. However, the field uniformity of a coil has always been suffering from a critical issue in imaging accuracy. The presented work is a study and design of spherical and improved radiofrequency Helmholtz coil which produces a high B1 magnetic field homogeneity. This coil is composed of four coaxial rings of wire, which are symmetrically located on a spherical surface. Each two rings on the same side have the same tuning capacitor. In contrast with the standard Helmholtz pair, which is of 2nd-order magnetic field homogeneity, the proposed coil provides fourth-order magnetic field homogeneity. The developed spherical structure is tested experimentally in free space and compared with results obtained with equivalent standard Helmholtz coil. The results lead to conclude that the proposed structure provides better B1 Homogeneity than the Standard Helmholtz type coil. Thus, the relative width at 1% of the profile is 1.37 times greater for the spherical Helmholtz coil. Similarly, the spherical Helmholtz coil has shown to have an increased efficiency and quality factor is of great interest.
Highlights
Volume RF coils (Hayes et al, 1985; Syms et al, 2005) are designed to produce a homogeneous RF excitation across a massive volume
Most clinical MRI scanners embed an inbuilt volume coil to perform fullbody imaging and smaller volume coils have been constructed for the head and other extremities
Helmholtz coils or Helmholtz pair coils (Villa et al, 1999), which produces a 2nd order B1 field homogeneity, is a volume coil and constitutes of two circular rings parallel to each other and kept apart by a distance equal to the radius of rings. They are utilized as the z gradient coils in MRI scanners facilitating localization in the z direction
Summary
Volume RF coils (Hayes et al, 1985; Syms et al, 2005) are designed to produce a homogeneous RF excitation across a massive volume. Helmholtz coils or Helmholtz pair coils (Villa et al, 1999), which produces a 2nd order B1 field homogeneity, is a volume coil and constitutes of two circular rings parallel to each other and kept apart by a distance equal to the radius of rings. They are utilized as the z gradient coils in MRI scanners facilitating localization in the z direction (head to foot in a horizontal magnet). Quantification of B1 field in free space permits to compare the probe performances with that of the obtained by standard Helmholtz pair
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