Clinical Magnetic Resonance Imaging (MRI) is a specialized diagnostic imaging tool capable of anatomic imaging, tissue chemical analysis as well as functional imaging of certain metabolic processes through using strong magnetic fields in order to induce and detect resonance at the nuclear (atomic) level. As the orientation of the magnetic field is manipulated and atomic nuclei (in particular the hydrogen atomic nuclei) are knocked off-axis, they emit faint radio frequency energy as they return to their polar orientation. These emissions are measured and allow a computer image to be created by the analysis of the frequencies emitted by resonating atoms comprising cell structures. The image is electronically enhanced, recorded on video, stored on tape or optical disk and reproduced as a laser image. The human body contains enormous numbers of hydrogen atoms — especially in water (H₂O) and lipid molecules, therefore MR reflects tissue density and body chemistry and is particularly useful in providing images of soft tissues, [Bronzeno,2006].

The patient to be imaged must be placed in an environment in which several different magnetic fields can be simultaneously or sequentially applied to elicit the desired MR signal. Every MRI scanner utilizes a strong static field magnet in conjunction with a sophisticated set of gradient coils and radiofrequency coils. The gradients and the radiofrequency components are switched on and off in a precisely timed pattern, or pulse sequence. MR images are characterized by excellent contrast between the various forms of soft tissues within the body. For patients who have no ferromagnetic foreign bodies within them, MRI scanning appears to be perfectly safe and can be repeated as often as necessary without danger. This provides one of the major advantages of MRI over conventional X-ray and computed tomographic (CT) scanners. The MR signal is not blocked at all by regions of air or bone within the body, which provides a significant advantage over ultrasound imaging. Also, unlike the case of nuclear medicine scanning, it is not necessary to add radioactive tracer materials to the patient, [Woodward, 2001].

To generate such powerful magnetic fields of tens of thousands of times greater than the Earth's own magnetic field, MRI scanners use high-strength permanent magnets in which the magnetic field cannot be dissipated. More commonly used for clinical imaging, however, are electromagnets which generate the magnetic field from electricity passing through magnetic coils which are bathed in cryogenic liquid (typically liquid helium) to make them superconducting, [Moore and Zouridakis, 2004].

Three types of magnetic fields—main fields or static fields, gradient fields, a radiofrequency (RF) fields —are required in MRI scanners. In practice, it is also usually necessary to use coils or magnets that produce shimming fields to enhance the spatial uniformity of the static field. Most MRI hardware engineering is concerned with producing and controlling these various forms of magnetic fields. The successful implementation of MRI requires a two-way flow of coils, and the gradient and RF power supplies operate in the analog domain. The digital domain is centered and amplitude to the gradient and RF amplifiers, to process time-domain MRI signal data returning from the receiver, and to drive image display and storage systems. The computer also provides miscellaneous control functions, such as permitting the operator to control the position of the patient table. See the Figure 1.

Figure 1. Basic Compartments of the Magnetic Resonance Imaging MRI System, [Moore and Zouridakis,2004]

Basically, an MRI system comprised of three principal components; the gantry, the operating console and the computer. The gantry contains the main magnet, the patient table and several other electromagnetic coils with the cryogenic cooling system. Unlike the CT, there are no moving parts in the MRI gantry. The MRI operating console resembles a CT console, and although many of the control designations are similar, they also serve different functions. Generally, two sets of controls are involved in the operating console of MRI system. One set is for image acquisition and the other set is for image processing. The MRI computer must have high capacity to store data for manipulation due to the nature of the MR signal and the number of signals required for an image. It also must be fast enough to handle the high rate of data acquisition and to accommodate the enormous number of calculations required to produce the MR image. See Figures (2,3 and 4).

Figure 2. MRI RF Room in Al-Yarmouk Teaching Hospital

Figure 3. MRI Control Room in Al-Kadhemiya Teaching Hospital

Figure 4. The MRI Equipment Room in Special Surgeries Hospital of Baghdad's Medical City

The components of the MRI system are distributed over three inter-related and well shielded areas; the control area, the radio frequency RF area and the equipment area. The control area (room) under direct observation should be located at the entrance to the facility, adjacent to the waiting room. The area should include a desk, pneumatic tube, computer and storage cabinets. A wheelchair and stretcher storage area should be located within the control area. A toilets, lockers, and dressing area should be located between the control area and the waiting room. The radiofrequency (RF) area is important that should be designed to include the gantry of the MRI system. Both of RF and control areas should be configured to provide the technologist, when seated at the operating console, a view through the RF shielded window to the patient inside the MRI scanner. The Equipment area should be adjacent to the radiofrequency (RF) and control areas that is includes the electronic and computer components of the MRI system like power supply, amplifiers, and analog to digital converters. See the Figure 5, [Bushong,2003].

Figure 5. Schematic diagram of the principal components of the MRI facility, [Bushong, 2003]

Reception area should be strategically located to control access to the patient areas and to secure the MRI facility from unauthorized access. Most MRI facilities may not represent an integral part of an existing radiology department, therefore a common reception and waiting area may not be available. In such situation, a separate reception area must be provided. Many MRI examinations are conducted on outpatient biases, so the patient is examined in street clothes, eliminating the need for change rooms. However, some sort of security area is required so that the patient can remove metal objects and valuables before the examination. Often patients are asked to wear scrubs so the technologist can be confident that their clothes are not conductive or magnetic, [Bushong,2003].

MRI facilities may be provided as part of the medical imaging or as a free standing unit. It should be located with ready access to the parking, emergency unit, operating unit and critical care area. The location with other diagnostic facilities assists in way finding and coordination of patient services. It should be adjacent to emergency, convenient to surgery and accessible to inpatient travel from the bed units. A mix of inpatient and outpatient services, this facility is preferred to be located on the ground level of the hospital due to its heavy equipment and design requirements, [Gupta, Kant, Chandrashekar and Satpathy, 2007].

Once the MRI system is selected and arrangements have been made for its acceptance testing, its location can be determined according to the following four possible options;

(1) If the MRI system is located in a new building such as an imaging center, the sitting requirement may not be so rigorous. Most new construction will be designed so that only considerations of adjacent imaging apparatus may be necessary. New construction can generally be designed so that shielding of the fringe magnetic field is unnecessary. Exclusion areas may be easy to identify and control, [American Association of Physicists in Medicine, 1986].

(2) The decision to locate an MRI system in an existing hospital building places considerable demands on the precise site location and its preparation. This may preclude the purchase of a superconductive magnet system of high field strength. On the other hand, except for possible weight constraints, permanent magnet systems may be sited nearly anywhere in existing buildings. There are essentially no fringe fields with a permanent magnet, [American Association of Physicists in Medicine, 1986].

(3) Placing the MRI system in a temporary, but fixed location adjacent to the hospital has many attractions. Site preparation costs are low the time required to prepare the site is short, allowing for placing a system into operation quickly. Patient and visitor access can be closely controlled. This approach is appealing because minimum time and expense are involved, and considerable experience can be used to advantage if it is subsequently decided to place an MRI system in a permanent location, [American Association of Physicists in Medicine, 1986].

(4) Mobile MRI is most attractive to facilities that cannot justly full-time operation because of low patient load. Mobile operation suffers from the time required to shim the magnet and tune the electronics after each move. This is especially true with superconducting MRI system. A particular advantage to a mobile system is the lack of long- term commitment on the part of the imaging facility. The experience gained with a mobile system educates all involved (administrator, radiologist, and imaging technologist) for subsequent selection of a stationary facility, [American Association of Physicists in Medicine, 1986].

Always there are two principle concerns regarding site selection for the magnet. First, what will be its effect on equipment and operations in adjacent areas? Second, what characteristics of these adjacent areas could adversely affect the operation of the MRI system?

The unique properties of Magnetic Resonance Imaging result in a number of distinct designing, planning, sitting and operational challenges. Once an MRI system has been selected and the site identified, the facility can be designed. Many design features are independent of the type of MRI system selected. Others must take into account certain characteristics of the type of MRI system. It is important to note that the magnetic field for all MRI scanners, irrespective of strength or format, is a three dimensional volume and requires appropriate site design criteria, [American Institute of Architects,1996].

Because the presence of external ferromagnetic material can degrade the homogeneity of the magnetic field, construction materials must be selected carefully. Large existing metal objects such as cast-iron waste water lines and electrical machinery may have to be moved. In general, the site should be metal free and vibration stable. This requires special material and construction techniques.

It is particularly important that the RF shielding of the MRI facility must remain at least (90 dB) attenuation. This presents special problem for all penetrations through the RF shield. All wires and cables for power or data must be fitted with appropriate RF filters. Heating, ventilation and air-conditioning (HVAC) ducts must be of nonconducting material, such as polyvinyl chloride (PVC) and maintain length to diameter ratio in all sections to provide an RF waveguide of infinite impedance, [American Institute of Architects,1996].

The weight of most MRI systems requires a substantial concrete and with reinforcing rods and corrugated iron sheets. Some of the available fiberglass-impregnated reinforcing rods and epoxy concrete should be used. A sufficient structural foundation is required not only in the radio frequency area but also along the route far installation. Post tension techniques may be necessary to ensure that the foundation is vibration free. Even subtle vibration can encourage cryogen to boil off and degrade image quality.

The areas (rooms) of MRI facility, including the doors and windows, should be completely shielded by a continuous sheeting or wire mesh of copper or aluminum in order to improve the MR signal detection by reduction of the environmental RF. Such a design feature is called a Faraday Cage. The shielding must be continuous and include both of the ceiling and the floor. Secure continuous electrical contact must also be provided. The RF enclosure is often a room built within a room. All wiring and cables that enter the MR scan room must be properly filtered to exclude the environmental RF effect. View windows should be fabricated with sufficiently large mesh so that vision is not compromised and at the same time a continuous RF shielding is provided. See the Figure (6), [American Institute of Architects,1996].

Figure 6. Faraday cage shows the MRI facility shielded by a continuous enclosure of sheet or wire mesh of copper or aluminum, [American Institute of Architects,1996]

All current clinical MRI systems require Radio Frequency (RF) shielding. This shielding prevents incidental RF energies from entering the scan room and disrupting the MR acquisition process. RF shields may be constructed of thin sheets of copper foil, galvanized steel or aluminum. RF shield assemblies must be contiguous on all sides, floor and ceiling. All provided doors and windows in the MRI scanning room must be RF shielded. Similarly, all penetrations into the RF shielded enclosure (including power, HVAC, exhaust, piping, and plumbing) must pass through special RF filters or wave guides. RF shielding typically provides no attenuation of the magnetic fields which will penetrate standard forms of construction. In this regard, RF shielding provided for MR equipment functions opposite of shielding provided for X-ray equipment. Whereas shielding provided for X-ray equipment is installed to contain the potential hazard, RF shielding for MR equipment is intended to keep disruptive signals out of the MRI scanning room and does nothing to contain the magnetic field of the MRI. Passive magnetic shielding, typically provided in the form of sheets of solid or laminated steel alloy plates, can be provided in addition to RF shielding for the purposes of attenuating the reach of the magnetic field beyond the MRI scanning room. Effective siting which provides appropriate separation between the MRI and magnetically sensitive equipment or accessible hazard areas should mitigate the need for passive magnetic shielding, [Bushong,2003].

As MRI measures radiofrequency responses at the atomic level, vibration can be profoundly disruptive to MR processes. Disruptive vibration can be telegraphed through a building's structure from either external (vehicle traffic, construction or trains, for example) or internal sources (pumps, motors or fans, for example) to the MRI equipment. When possible, it may be advisable to structurally isolate the MRI scanner room from the rest of the building. In elevated floors, however, this may not be possible. Structural systems should be designed with the expressed intention of minimizing vibration in the frequency and amplitude ranges defined by the MRI vendor that are known to be disruptive. For retrofits of MRI equipment in existing structures, it is advisable to obtain site vibration testing early in the preliminary design phase. Many MRI vendors offer vibration mitigating solutions, but these often have significant design implications, [Evans,2004].

Many contemporary MRI scanners are capable of producing sound pressure levels well in excess of (110 dB), the human pain threshold, during certain scan procedures and there are many reports of hearing damage. Without proper design considerations, sound from MRI system can be extremely disruptive to other occupants in the building. Just as vibration can travel through a building's structure to an MRI, so, too, can acoustic frequency vibration be telegraphed through building components to surrounding spaces. Construction details and material selections should be carefully considered to maximize absorption and dissipation of acoustic noise from the MRI system, [Evans,2004].

Electrical conduits in the MRI room should be made of either PVC or aluminum. Electrical receptacles and fixtures should be aluminum or ceramic. Electrical distribution transformers should not be located within the 1-mT fringe magnetic field. Lighting in the imaging room must be incandescent; no fluorescent lamps are allowed. The supply should be controls should be direct current or properly filtered. Dimmer controls should not be mounted within the room. Fixtures should be brass or ceramic, [American Institute of Architects,1996].

Supply lines, floor drains, and soil pipes should be nonferrous. Copper or PVC is acceptable. If building codes require a sprinkler system, only brass or copper component should be used. All sprinkler heads that penetrate the RF shielding must be completely electrically grounded, See the Figure (7), [American Institute of Architects,2003].

Figure 7. Very poor piping in the MRI facility design

The ability to view the patient during the MRI examination is mandatory. Although closed-circuit television capable of operating in the magnetic field of the room has been developed, it is expensive and not totally satisfactory. Most facilities find that a direct view window incorporating a wire mesh as an RF shield is better, [American Institute of Architects,2003].

Heating, ventilation, and air conditioning are important engineering considerations for an MRI facility. The HVAC design must deal with not only the normal space occupying activities of a conventional office or laboratory but also requirements of the MRI system. Constant temperature is essential for stability of the magnet and associated electronic components. The main magnetic field strength of a permanent magnet increases approximately 0.1% per degree. Also any computer that accompanies MRI system must be in a cool and dry environment. Temperature must be maintained between (18-20 °C) at a relative humidity of not more than 40%, [American Institute of Architects,2003].

At the threshold of the examination area, space must be reserved for metal detection. Most facilities choose to simply instruct the patient to remove all metal. However, a threshold- type metal surveillance device similar to those used for airport security or a wand type metal detector may be used. Metal detection is important for not only the patient before imaging but also others who may enter the facility. Physicians, attendants, and potential hazards from metal projectiles. Magnets and people can be damaged by projectiles from individuals who may not otherwise be adequately advised, [American Institute of Architects,2003].

Permanent magnet imaging systems have no special cooling requirements beyond those normally needed for electronic and computer components. This feature contributes to the relatively low capital cost and site preparation requirements. A superconducting magnet requires cryogens (liquid helium and sometimes liquid nitrogen). Up to (0.5 L/hr) of helium and (2 L/hr) of liquid nitrogen may be required to maintain the low temperature to support superconductivity. Superconducting magnets require aluminum venting, usually through the ceiling, for cryogen exhaust. It is desirable to have the liquid nitrogen piped in from a storage tank. Loading, handling and storage space for cryogens must also be provided, [American Institute of Architects,2003].

Regardless of the type of MRI system selected, approximately (10 kW) of power is required for computers, operating consoles and other electronic devices. An additional (10-20 kW) is required to power the electromagnetic coils and RF network. Beyond that, a superconducting MRI system requires an additional (20- 30 kW) but only while the imaging system is being brought up to the main magnetic field strength. During operation, no power is required for the primary magnetic coils, [American Institute of Architects,2003].

MRI facilities hold unique dangers for patients and staff. Today's high-strength clinical MRI scanners are up to 60,000 times the strength of the Earth's own ambient magnetic field. While exposure to magnetic energies has shown no harmful biological effects — unlike other medical imaging modalities that rely on ionizing radiation — there are still many accidents and incidents that jeopardize the safety of patients and staff in the MRI facility. Site access restriction considered as an important component of MRI safety,[10]. Therefore, it is recommended to identify the conceptual layout of the MRI facility into the following four zones:

Zone I: This includes all areas that are freely accessible to the general public. This area is typically outside of the MR environment itself, and is the area through which patients, health care personnel, and other employees of the MR site access the MR environment.

Zone II: This area is the interface between the publicly accessible uncontrolled Zone I and the strictly controlled Zones III and IV. Typically the patients are greeted in Zone II and are not free to move throughout Zone II at will, but are rather under the supervision of MR Personnel. It is in Zone II that the answers to MR screening questions, patient histories, physical screening / gowning, medical insurance questions, etc. are typically obtained. Once successfully screened, patients should be moved directly to Zone III.

Zone III: This zone is defined as areas which present physical hazards as a result of the MRI's magnetic field or areas that offer direct access to the MRI scanner room. This area is the zone in which free access by unscreened non-MR personnel and / or ferromagnetic objects and equipment are not permitted as they can result in serious injury or death as a result of interactions between the individuals / equipment and the MR scanner's particular environment. These interactions include but are not limited to those with the MR scanner's static and time varying magnetic fields. All access to at least Zone III is to be strictly restricted with access to regions within it, including Zone IV, controlled by and entirely under the supervision of MR personnel.

Zone IV: This area is synonymous with the MR scanner magnet room itself. Zone IV by definition, will always be located within Zone III as it is the MR magnet and its associated magnetic field which generates the existence of Zone III itself.

It is recommended that MRI facilities install ferromagnetic detection systems for use in screening persons and equipment entering Zones III and IV to interdict potential threat object. While it is possible to install ferromagnetic detection systems at the RF door into the MRI scanner room, the preferred location is at the secured access point between Zones II and III. See the Figure (8), [Glik, Arcb and Kanal,2006].

Figure 8. Plan view shows 4-functional zones of the MRI facility, [Glik, Arcb and Kanal,2006].

Major specialized equipment (like MRI equipment) require special structural designs, electromechanical requirements, or other considerations, close coordination between owner, building designer, installer, construction contractors, and other is required. Such equipment has significant impact on electrical (requires high voltages or currents), mechanical (plumbing, gases, vacuum) and structural requirements.

Throughout field study of the planning, location, design and components organization of the MRI facilities in three major hospitals in Baghdad, which are; Al-Kadhimiya Teaching Hospital, Al-Yarmouk Teaching Hospital, and Special Surgeries Hospital of Baghdad's Medical City, the following features have been found and that need to be taken in consideration;

(1) The MRI systems installed in the three hospitals are nearly of the same type, superconducting magnets of (1.5 T, 400 A), and located in the ground level within the hospital's radiology department.

(2) In general, the RF shielding is insufficient that provides a paramount important effect on the performance of the MRI systems used in these three hospitals. Patient viewing windows of the MRI operating console are inappropriately shielded, that should be made by spatial layers of glass mixed with sets of copper's powder. Such shielding arrangement is recommended because the RF radiation has rebounded property, and the spread direction of this magnetic field is of curved lines from the outside to the inside of the RF area spreading curved lines. The windows multilayered design will attenuate the reach of the magnetic field beyond the MRI scanning room. Therefore, Copper fabric shielding is often utilized to restrict magnetic field plot and to attenuate stray radio frequencies.

(3) The lighting sources were used in the three MRI facilities (especially in the MRI scanning room) are not useful for working in such procedure environment, because they were supplied of normal (un-polarized or partially polarized) light, ordinary fluorescent lamps, and located closely to the MRI system that is highly affecting the quality of the diagnostic MRI image. Use of total polarized, non ferrous material made and opposite directed light to the MRI system will prevent the interference. See the Figure 9.

Figure 9. Un-polarized light sources (upper red arrows) located inside the MRI scanning room

(4) The cooling system used in the three MRI facilities have impeded the operation of the MRI systems for long periods of time due to the high drop in the cryogenic levels, that reaches sometimes to less than 30%. This will require continuous monitoring and recharging the system by the liquid helium in order to compensate the proper cooling mechanism. The multiple shortages in cryogenic level have been existed as a result of the insufficient RF electromagnetic shielding in the whole system. Cryogen facilities should be required in areas where service to replenish supplies is not readily available. Where such facilities are provided, cryogen venting will be required, See the Figure (10).

Figure 10. Cryogenic leakage inside the MRI scanning room

(5) The filter box which involves the wiring connections between the RF and the equipment rooms of the MRI facility should be made of non ferromagnetic material because it is located within the RF shielded area that will provide more flexible performance of the whole system.

(6) Because of the MRI system installation of and its down time is much cost, it may be wise to take future expansion of an MRI facility into account when designing an initial installation, in order to allow uninterrupted operation of the existing facility and to minimize the cost of the necessary infrastructure for additional units.

(7) The MRI system should be provided with a magnet emergency unit with one or two remote push buttons for switching off the magnet field. Those buttons must only used in case of emergencies. Using this magnet emergencies rundown unit causes a rapid decrease of the magnetic field at the cost of a substantial boil-off of liquid helium.

(8) The main existed problems which are described by the technicians of the three MRI facilities are the repeated cease of electricity and the unscheduled period of some examinations that made the patients to wait for many weeks to get examined. Power conditioning and voltage regulation equipment as well as direct current (DC) should be required.

(9) Improved safety in the MRI suite is inhibited by a number of obstacles. Many of those suites are sequestered behind locked doors and are rarely visited by patient care managers or risk management professionals, making accurate assessments of risks and liabilities difficult, if not impossible. The main aspect of patient safety in MRI facility is magnetic safety. A Ferromagnetic object as small as appear clip has a terminal velocity of (40 mph) in a (1.5 Tesla) field and may cause injuries to patient or service person that must not be brought into the neighborhood of the magnet and thus be kept outside the examination room. Also, information on magnetic carries such as floppy disk tapes and magnetic stripes or credit cards can be erased due to the existed high magnetic field.

The almost limitless benefits of MRI facilities for most patients far outweigh the few drawbacks. The obtained results show that a lot of works and efforts need to done in order to enhance the performance of the MRI system in Baghdad's hospitals. MRI quality control concepts must be done according to the recommended standards on regular bases in order to achieve an excellent clinical service besides the safety of both staff and patients.