The major advantages of this magnet are its simplity and the relatively remote homogenenous spot. The static magnetic field B0 is parallel to its surface (along z axis in Figure 1) which allows employment of a very simple surface coil with good sensitivity. The size of the measurement spot results from the combination of B0 distribution, bandwidth of the excitation RF pulses, bandwidth of the receiver and parameters of the surface coil like size, shape and quality factor (Q).Figure 1.Schematic (a) and photo (b) of the three-magnet array. The centre of the upper surface of the magnet array corresponds to the position (0,0,0) in the coordinate system.In order to adjust and characterize the magnet, magnetic field measurements were undertaken employing a three axis Hall effect magnetic field probe (Lake-Shore Cryotronics Inc.

, OH, USA) and a computer controlled three axis plotter (Velmex Inc., MI, USA). Figure 2a plots the magnetic field magnitude as a function of distance from the centre of the magnet. The sensitive spot of the magnet array is 8 mm to 17 mm from the magnet surface. The proton resonance frequency at this position is 4.485 MHz. Figure 2b shows a contour plot of the magnetic field along the yz plane over the magnet (x = 0).Figure 2.(a) Plot of magnetic field magnitude B0 as a function of the distance from the centre of the magnet surface. The circled area indicates the sensitive spot position; (b) Contour plot of the magnetic field magnitude B0 in the yz plane. The field is reasonably …2.2. RF CoilA square spiral RF coil, 45 mm in length with 7 turns, fabricated on a 1.

2 mm thick printed circuit board (Figure 3a) was employed for the measurements since the RF field B1 is required GSK-3 to be perpendicular to the static magnetic field B0.The lead width was 1.5 mm and the spacing 1.27 mm. The resistance and inductance of the coil were 0.41 �� and 1.439 ��H, respectively. The loaded quality factor (QL), measured with the coil placed on the magnet was 30. The RF coil was tuned 4.485 MHz, which is the proton resonance frequency at the centre of the spot. The dead time of the coil is 35 us. The RF field above the coil, simulated employing the simulation software Maxwell 3D (Ansoft, Pittsburgh, PA, USA), is shown in Figure 3b. A 4.766 mm (3/16��) fiberglass spacer was placed between the coil and the magnet to assure a better use of the homogeneous spot of the magnet and the B1 of the coil. The distance from the RF coil upper surface to the sensitive spot is 2 mm to 11 mm.Figure 3.(a) Photo of the RF coil; (b) The simulated result of the normalized RF field distribution in the central perpendicular plane. The B1 field is perpendicular to the coil. y = 6 mm is the upper surface of the RF coil.2.3.