Читать книгу Essentials of MRI Safety - Donald W. McRobbie - Страница 67

A nickel coin (length = 1 mm, diameter = 1 cm) is inadvertently brought into the MRI examination room. If the external field is 100 mT what is the field within the coin if it is: (a) lying face on to the magnet; (b) edge on to the magnet? Will the coin’s metal saturate?

1 (a) The ratio l/d = 0.1, so from Figure 2.14 or Equation A1.31 and 2.9a

B_sat for nickel is 0.62 T (Table 2.2) so, in this orientation it will be unsaturated.

1 (b) For the end‐on orientation use d2 and Equation 2.9b

This exceeds B_sat so the internal field will saturate at 0.62 T.