Components of magnetic dipolar field in a cylindrical coordinate system. The third component B φ (perpendicular to the plane) is zero.
Magnetometer setup place at the roof of the existing cyclotron building, showing four magnetometers mounted on a wooden cross, each 0.5 m from the center (Ref. 10 ).
Measurement locations (X) for the B field relative to the isocenter of the 18 MeV cyclotron (Cyclone 18, IBA Group), together with the calculated isolines for G net = 0.04 μT/m, Br = 0.4 μT and Bnet = 0.4 μT. The source point (○), also a measurement point, is the input point for the dipole model.
(a) Three components of the magnetic field, Br, Bz and B φ of the 18 MeV cyclotron as a function of distance (l). (b) Two horizontal inplane magnetic field gradients G r and G z. Both the measured and estimated values are plotted. The noise level of the measurement was in the order of 0.01 μT and 0.014 μT/m. As three measurement locations were at the same level as the cyclotron (z = 0), estimated values of G r were 0, as well as the estimated B φ values. Because of the log scale in this figure these B φ and G r values were plotted at noise level. Data can also be found in Table II .
Estimation of maximum allowable magnetic field gradient perturbation for a superconducting whole body MR system depending on the MRI application; for further explanation see text.
Measured and estimated magnetic field components and its spatial gradient at the different locations.
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