**3.8. Hazards in the MRI suite**

**3.5. Operational principles of MRI**

**3.6. Magnetic fields and the missile effect**

tracting source (Gould, 2008).

**3.7. Magnetic field interactions**

As opposed to conventional x-rays and computed tomography (CT) scans, there is no ioniz‐ ing radiation used in MRI. However, MRI uses an extremely powerful static magnetic field, rapidly changing gradient magnetic fields and radiofrequency electromagnetic impulses to obtain detailed anatomic or functional images of any part of the body (Faulker, 2002; Berger, 2002). Currently, there is no evidence of a short or long term adverse effect due to exposure

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

Despite the relative safety of MRI, there are potential hazards associated with its operations. Some of these are related to the physical properties of the MRI equipment and also to the challenges of maintaining physiologic stability of the individual undergoing the examina‐ tion. In a reported incident in 2001,a small boy undergoing an MRI following surgery to re‐ move a benign tumour was struck and killed by an oxygen tank inadvertently taken into the MRI suite (Emergency Care Research Institute, 2001). In most situations the MR systems

The static magnetic field generated by a powerful magnet is tens of thousands times stronger than the earth's magnetic field which can attract objects containing ferrous mate‐ rials, transforming them into dangerous airborne projectiles (Dempsey *et al.,* 2002). There are two features of the magnetic field that are the source of most MRI incidents; the pro‐ jectile or missile effect which is the ability of the magnet to attract ferromagnetic objects and draw them rapidly into the bore with considerable force (Centre for Devices and Ra‐ diological Health, 1997). Ferromagnetic objects include metallic objects containing iron such as scissors, laryngoscopes, nail clippers, pocket knives and steel buckets. Larger items like wheelchairs, gurneys, intravenous poles have also become MR-system- induced missiles (Centre for Devices and Radiological Health, 1997). The other source of most MRI incidents is the translational attraction which occurs when one point of an object in a magnetic field is attracted to a great extent than the object's furthest point from the at‐

The static magnetic field of an MR system is always on. No sound, sight, smells alerts per‐ sonnel to the presence or the extent of the invisible field surrounding the magnet in all direc‐ tions. The magnetic pull is strongest at the centre of the MR system and weakens with increased distance from the magnet, creating a spatial magnetic field gradient (Price, 1999). The distribution of the magnetic field outside the main magnet called fringe field is impossi‐ ble to see, but it is critical to safety in the MR environment because it can determine whether a ferromagnetic object could become a projectile. MR systems with large fringe field general‐ ly create the greatest hazards (Price, 1999). If the fringe strength decreases more gradually with distance from the magnet, the object's attraction to the magnet progressively strength‐ ens as it becomes closer to the magnet. Personnel within the MR room may notice an in‐

to field strengths of MRI and durations that is clinically used (Schenck, 2000).

cause the disaster due to it interactions with other properties around it.

Various forms of hazards occur in the MRI suite which can be categorized into translational force- missile effect, torque forces, induced magnetic fields, thermal heating and quenching (Colletti, 2004). In the translational force, the effect is manifested on the ferromagnetic mate‐ rials and the static field generated by the MR system usually in the form of the missile effect involving non-compatible objects and miscellaneous patient and visitor objects.A hair or pa‐ per clip within the 5-10 gauss line range could reach a velocity of 40 mph (about 70 kph) and will be attracted to the centre of the lines of force of equal (Lahr and Rowan, 2004).

Just like the translational forces, the torque force is also associated with ferromagnetic mate‐ rials and the static field generated by the MR machine. Ferromagnetic objects that are at‐ tracted by the magnetic field react by aligning parallel to the magnetic lines of the force being created by the MRI machine. The centre of the MRI- generated fields has the highest torque force, creating a serious exposure for all contraindicated items and MRI- conditional items in the MRI suite, depending on the tesla rating of the MRI (Gould, 2008). When any metallic object is introduced into a high flux field, current will be induced if that object is perpendicular and moving to the lines of the force. The new current will create a secondary magnet field that will oppose the original field. This can cause patient discomfort and anxi‐ ety due to the reactive forces on the MRI safe medical implants and a life threatening condi‐ tion may be created under the five- gauss line (Kangarlau and Robitaille, 2000).


Adapted with permission from Centre for Device and Radiological Health of USA

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, 2007).

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

Protection (ICNIRP)

**4. Materials and method**

department (www.korlebuhospital.org).

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

Assessment of Safety Standards of Magnetic Resonance Imaging at the Korle Bu Teaching Hospital…

http://dx.doi.org/10.5772/52699

63

The study employed both qualitative and quantitative design using a structured interview and descriptive survey. A structured interview involves guiding the interview in a particu‐ lar pattern such that the information received falls in line with the objective of the study without it being altered by the interviewer (Brink and Wood, 1994; Pontin, 2000). A descrip‐ tive survey provides a better means of investigating and assessing the attitude and practices

The study was carried out MRI Suite of the Radiology Department of the Korle Bu Teaching Hospital. (KBTH), Accra. Ghana. KBTH is the leading referral hospital in Ghana, with the radiology department being one of the busiest departments in the hospital. Currently, the hospital has a bed capacity of about 2000, with an average 1,500 outpatient attendances dai‐ ly, an admission rate of 250 per day and 65% of the daily attendance visiting the radiology

The Radiology Department of the hospital has a staff population of forty-six. These include thirty-one radiographers, nine radiology residents and six consultant radiologists. Of the

of people when they are involved in a particular situation (Carter, 2000; Gray, 2004).
