Torque Force: Translational Attraction And Torque Forces

1.1.1.1 Ferromagnetic attraction

The attractions of non-compatible objects to the main magnet are known as translational attraction and torque forces. These attractions happen due to the presence of static magnetic field (Bo).

1.1.1.1.1 Translational attraction

Projectile or missile effects will be resulted from translational attraction. Translational attraction happens when one point of the ferromagnetic object is attracted to greater level than the object’s furthest point from attracting source (Figure 2-6). The difference in the spatial gradient attraction causes a more forceful attraction, which unintentionally increases the speed of object moving towards the magnet bore (Capizzani, 2009) and it will cause tearing of tissue if the implant is a fresh (Chung, 2002). The heavier the

A gurney was pulled into the MRI bore (left) and a metal wheelchair stuck into the magnet (right) (Capizzani, 2009; M. A. Tobias Gilk, 2006).

1.1.1.1.2 Torque force

Torque force a bit different from translation attraction, torque forces aligns the magnetized objects to the static magnetic force of the main magnet (Chung, 2002). Torque force is at the peak in the centre of MRI magnet bore and creating a hazards environment for non-compatible objects (Capizzani, 2009; Ng et al., 2003). Permanent damage may occur to sensitive devices such as pacemaker. Torque effect is strong enough to cause implant displacement and have the potential of life threating condition for patients (Ng et al., 2003).

1.1.1.2 Biological effects

The most controversial topics in MRI safety is biological effects. Some reported literature shows that several structures within our body such as some cell in paranasal sinuses retina, and pineal gland is affected by static magnetic field (Ng et al., 2003). On the other hand, some literature reported vice versa (Martin C.J, 2002; UPMCMRS, 2003).

1.1.2 Gradient Magnetic Field