**3.11. Safety policies and guidelines of MRI**

The most common source of thermal exposure tends to be looped or un-looped medical equipment leads, MRI accessories and sensors. The most serious exposure is located in the bore of the MRI machine and in the axis points, as they possess the highest potential torque forces. Extremity coils could increase the risk but this can be avoided by the use of MRI safe polymeric foam padding (Gilk, 2006). MRI machines are cooled by a super cooling fluid (liquid helium). The release of the super cooling fluid into the atmosphere is called quenching. Most clinical machines have about 700 to 1000 litre volume of this cryogenic. In the event that there is venting, it may cause the oxygen in the MRI room to condense around the vent pipe and accumulate in the MRI machine causing a red fire hazard. Another risk is a quench vent pipe breech which could flood the room with cryogenic fluids creating an asphyxiation hazard for the patient and the staff (Clark,

62 Imaging and Radioanalytical Techniques in Interdisciplinary Research - Fundamentals and Cutting Edge Applications

The MRI system has electromagnetic coils in a transmitter within it that delivers the radio‐ frequency (RF) pulses during imaging. When tissues absorb the RF energy, tissue heating can occur, mostly in patients with poor thermoregulatory control (Dempsey *et al.,* 2002). The rate at which RF energy is deposited in tissue is known as the specific absorption rate (SAR), measured in units of watts per kilogram (w/kg) (Centre for Devices and Radiological Health, 1997). The maximum allowed SAR is 3W/kg which is averaged over ten minutes for head imaging and 4W/kg for whole body imaging, averaged over fifteen minutes (Centre

Radiofrequency fields can cause skin burns if monitor cables or wires are permitted to form conductive loops with themselves or with other body parts (Kanal *et al.,* 2002). Temporary metallic intra cardiac pacing wires will behave like antennae and conduct electromagnetic waves, also resulting in thermal tissue injury (Dempsey *et al.,* 2002). Ra‐ diofrequency signals emitted during the MR examination can affect non- MR-compatible programmed infusion pumps, resulting in erratic performance. Affected pumps could de‐ liver higher or lower than desired volumes of pressor agent, analgesics, sedative or dex‐ trose and electrolytic solutions, all of which cause serious physiological consequences

When an infant is subjected to sudden, rapidly changing gradient magnetic fields during imaging, the magnetic field can induce circulating currents in conductive tissues of the body (Schaefer *et al.,* 2000). These currents have been found to be large enough to produce changes in nerves and muscles function theoretically.Where safety standard limits are prac‐ ticed, it limits the maximum rate of change of magnetic field strength that can be used thus reducing the likelihood of its observation during a clinical MRI (Center for Devices and Ra‐

2007).

**3.9. Radiofrequency electromagnetic fields effects**

for Devices and Radiological Health, 2003).

particularly, infants (Cornette*et al.,* 2002).

**3.10. Gradient magnetic field effects**

diological Health, 2003).

The American College of Radiology (ACR) Guidance Document for Safe MRI Practices-2007 recommends that all MRI sites should maintain MR safety policies (Kanal *et al.,* 2007). These policies, it claims should be reviewed concurrently with the introduction of any significant changes in the safety parameters of the MR environment and updated as needed. It also stat‐ ed that Site Administration is responsible to ensure that the policies and procedures are im‐ plemented and adhered to by all site personnel. Any adverse events, MR safety incidents or near incidents are to be reported and used in continuous quality improvement efforts. To augment the recommendations made by the ACR, the 2008 Joint Commission Sentinel Alert issued by the Medical College of Wisconsin's (2009) accreditation organisation suggested that actions consistent with the ACR recommendations should be used to prevent accidents and injuries in the MRI suite. In other works, the Device Bulletin (2007) produced a docu‐ ment to serve as guidelines covering important aspects of MRI equipment in clinical use with specific reference to safety. They were intended to bring to the attention of those in‐ volved with the clinical use of such equipment, important matters requiring careful consid‐ eration before purchase and after installation of the equipment. It was also to be used as an orientation for those who are not familiar with the type of equipment and act as a reminder for those who are familiar with the equipment (Buxton and Lui, 2007). It was further intend‐ ed to act as a reminder of the legislation and published guidance relating to MRI, draw the attention of the users to the guidance published by the National Radiological Protection Board (NRPB), its successor the Health Protection Agency (HPA), the International Electro‐ chemical Commission (IEC) and the International Commission on Non –Ionizing Radiation Protection (ICNIRP)
