Radiology_Aug04 6 SA JOURNAL OF RADIOLOGY • August 2004 Abstract An increasing number of patients with metal implants are being referred for magnetic resonance imaging (MRI) investigations. Implants and devices may be divided into two groups, namely active and passive. This article will focus on passive devices. A device is MR-safe when it is used in the MR environment, but pre- sents no additional risk to the patient or other individuals, although the quality of diagnostic information may be affected. MR procedures may be contraindicated due to various inter- actions between the MR environment and medical devices, which include torque, translational force, heating, induced electrical currents, magnetic field interactions, artefacts, and mis- representation. Therefore, before deciding whether any object is MR- safe/compatible, the intended use and the possible retaining mechanisms must be considered. Introduction An ever-increasing number of patients are being referred for mag- netic resonance imaging (MRI) inves- tigations, with a subsequent increase in the number of patients presenting with old and new metal implants. The question arises whether it is safe for these patients to enter a magnetic res- onance (MR) environment. After review of the literature we compiled this quick guide to safety and compat- ibility of implants and devices in an MR environment. General consid- erations Implants and devices may be divided into two groups, namely active (especially electronically acti- vated devices, e.g. cochlear implants, implantable cardiac defibrillators, or any other activated device including ventilator and monitoring devices) and passive (clips, sutures, prostheses and any other device that serves its function without power supply). In this article the focus will be on passive devices. When a device is MR-safe it means that when used in the MR environ- ment the device presents no addition- al risk to the patient or other individ- uals, although the quality of diagnos- tic information may be affected. MR- compatible equipment is MR-safe and can be used in the MR environment with no significant effect on its opera- tion or on the quality of diagnostic information. No metal is totally non- magnetic or non-ferromagnetic, as all metals possess some degree of mag- netism. MR procedures may be con- traindicated due to various interac- tions between the MR environment and medical devices, which include torque (product of axial force and the distance of the line of action from the axis) and translational force, both of which could cause possible move- ment or dislodgement of a ferromag- netic biomedical implant, material, device, or object. Other possible haz- ards and problems include heating, induced electrical currents (in materi- als that are conductors), magnetic field interactions (functional disrup- tion of device), artefacts, and misrep- resentation. Translational attraction is assessed by using the deflection angle test, measured at the point of the ‘highest spatial gradient’ for the specific MR system. The deflection angle test cen- tral to MR safety testing for metallic implants and devices is as follows: For deflections less than 45° in the deflection angle test, the magnetically induced deflection force is less than the force of gravity on the implant. It REVIEW ARTICLE A quick guide to safety and compati- bility of passive implants and devices in an MR environment D J Kotzé MB ChB C de Vries MMed Rad (D) Department of Diagnostic Radiology University of the Free State Bloemfontein implies that any risk imposed by the application of the magnetically induced force is no greater than any risk imposed by normal daily activity in the earth’s gravitational field. There are no concerns about movement or dislodgement in people with implants and devices made from non-ferro- magnetic or weakly ferromagnetic materials with a deflection angle between 0° and 44°. A torque value in any implant/ device that is less than that produced by normal daily activities (which include rapidly accelerating vehicles or amusement park rides) is assumed to be safe. Translational attraction/deflection and torque could lead to movement or dislodging of ferromagnetic implants. This may cause discomfort or even serious injury to a patient.1 Translational attraction effects on external and implanted ferromagnetic objects in the immediate area around the MR system are usually responsible for possible dangers. Translational attraction is proportional to the static magnetic field strength, spatial gradi- ent strength, and mass, shape and magnetic susceptibility of the object. Deflection angles and magnetic field interactions of an implant can differ significantly between long- and short-bore MR. They are usually much higher in a short-bore. Higher magnetic field strength MR systems are rapidly increasing worldwide. Previously investigations were per- formed with magnetic fields only up to 1.5T. Weakly ferromagnetic objects in lower field strengths may experi- ence much more interaction in higher field strengths. According to Faraday’s law any change in a magnet field could induce a current in a conductor. This conductor in the MR environment could be cable, jewellery, metal exter- nal fixation devices or even a patient’s arms if he holds his hands together above his head. The current induces heat in the conductor and that could present as burns on the patient. In order to evaluate whether a device is now safe or compatible in the MR environment we need to keep in mind the things that could happen to this device. In summary the relative risk of injury depends on: • Ferromagnetic properties of the foreign body • Geometry and dimensions of the object • Strength of the static magnetic field • Strength of the spatial gradient of the MR system • Amount of force with which the object is fixed within the tissue (i.e. counter-force or retention force) • Whether it is positioned in or adja- cent to a particularly sensitive site (vital neural, vascular, or soft tissue including eyes). Specific passive devices Heart valve prostheses and annuloplasty rings2-4 Most exhibited no magnetic field interactions but at 3.0 Tesla the Carpentier-Edwards Physio Annulo- plasty Ring, Mitral Model 4450, Edwards Lifesciences, Irvine, USA showed relatively minor magnetic field interactions. The actual magnet- ic field interactions exerted on this implant are minor compared with the force exerted by the beating heart (i.e. approximately 7.2 N), therefore MR procedures at 3.0 Tesla are not consid- ered to be hazardous. Penile implants2,3 Weakly ferromagnetic penile implants may cause discomfort. Several different penile implants have been tested for MR safety in associa- tion with 3.0 Tesla MR systems but only Duraphase and Omniphase demonstrated relatively minor or ‘weak’ magnetic field interactions. Most of the other penile implants are considered safe for patients. Sutures2,3 Two types (Flexon suture and Steel suture, United States Surgical, North Haven, CT) showed minor deflection angles and torque at 3.0 Tesla. The use of these materials will, however, pro- vide sufficient counter-force to pre- vent movement or dislodgment. None of the other evaluated sutures (without their needles) displayed magnetic field interactions and appear to be safe at 3.0 Tesla. Aneurysm clips1-3,5-9 Certain types of intracranial aneurysm clips (e.g. those made from martensitic stainless steels such as 17- 7PH or 405 stainless steel) are absolutely contraindicated in MR procedures because magnetically induced forces may be excessive and these clips may displace or dislodge resulting in serious injury or death. Non-ferromagnetic, non-magnetic or weakly ferromagnetic aneurysm clips (e.g. those made from Phynox, Elgiloy, austentitic stainless steels, titanium alloy, or commercially pure titanium) are safe for MR use. Only one known ferromagnetic aneurysm clip-related fatality has been reported in the peer- reviewed literature. Injury due to the presence of an aneurysm clip made from a non-ferromagnetic or weakly REVIEW ARTICLE 7 SA JOURNAL OF RADIOLOGY • August 2004 ferromagnetic material has never been reported. There have been cases where patients with ferromagnetic aneurysm clips (deduced from the extent of the artefact seen during MR imaging) have undergone MR proce- dures without any injuries. The deflection angle test and some form of evaluation of torque are probably the most appropriate means of determin- ing whether a specific aneurysm clip may present a hazard to a patient or individual in the MR environment. Aneurysm clips that are consid- ered safe for patients or individuals exposed up to an 8.0 Tesla MR system, with deflection angles less than 45° (ASTM guideline) and relatively minor qualitative torque values were manufactured from: commercially pure titanium (Spetzler), Elgiloy (Sugita), titanium alloy (Yasargil, Model FE 750T), and MP35N (Sundt). Shellock’s investigations were highly specific to the types of intracra- nial aneurysm clips that underwent testing (model, shape, size, blade length, material, etc.). Studies indicat- ed that in spite of long-term and/or multiple exposures to 1.5 Tesla MR systems there were no clinically signif- icant changes in their magnetic prop- erties. Jewellery3 Mild-to-moderate movement and/or displacement depending on the body piercing site and the ferro- magnetic qualities (e.g. mass, degree of magnetic susceptibility, etc.) of the jewellery may cause uncomfortable sensations. There is also a theoretical possibility of MRI-related heating that could cause burns. Metallic body- piercing jewellery should be removed prior to entering the MR environ- ment. If metallic jewellery or piercing cannot be removed the patient should be informed about the potential risks and preferably cancel the procedure. If it is not possible to cancel, then some means of stabilisation (e.g. application of adhesive tape or bandage) should be used to prevent movement or dis- placement in the MR. To prevent con- tact with the underlying skin and pre- vent excessive heating, wrap gauze or tape to at least 1 cm thick around piercing jewellery made from conduc- tive materials. Breast devices3 Breast tissue expanders construct- ed with magnetic ports allow for a more accurate detection of the injec- tion site. Therefore, these devices are attracted to the static magnetic field of MR systems and may be uncomfort- able or become dislodged, causing injury to a patient undergoing an MR procedure. Cardiovascular guidewire and catheters3 Patients with cardiovascular catheters and accessories with inter- nally or externally positioned conduc- tive metallic components should not undergo MR procedures. Interven- tional MRI devices and catheters without metallic components were deemed safe and were not included in the overall ex vivo tests for MR safety. It should be noted that these catheters and accessories were evaluated for MR safety without being connected to monitoring equipment. There is at least one report of a car- diovascular catheter that melted in a patient undergoing MR imaging. There has never been a report of an incident or injury related to retained cardiac pacing wires in association with an MR procedure. Coils, filters and stents3,10-13 Several of these displayed magnet- ic field interactions during exposure to an MR environment, although most are incorporated securely into the vessel wall due to tissue ingrowth at about 6 - 8 weeks after placement. Similar devices made from non-ferro- magnetic materials, such as the LGM IVC filter (Vena Tech) used for caval interruption or the Wallstent biliary endoprosthesis (Schneider (USA), Inc.) used for treatment of biliary obstruction, are considered safe for patients undergoing MR procedures. However, not all stents are safe: Gianturco stent (Cook), and the mod- ified Gianturco stent (Song), made of stainless steel, displayed magnetic field interactions where the deflection angles were greater than 45° exceeding the ASTM guideline. Retention by tis- sue ingrowth and stents with hooks or barbs (to prevent migration after placement) may prevent them from posing a substantial risk to an individ- ual. Cranial fixation devices3,14 The clamps used for the cranial bone flap fixation system showed no magnetic field interaction and little heating; therefore they seem to pose no risk to the patient in a < 1.5 Tesla MR environment. Cranial and burr hole fixation implants and devices made from titanium have been tested safe at 3.0 Tesla. Dental devices3,15 Many of the dental implants, devices, materials, and objects evalu- ated for ferromagnetic qualities exhib- ited measurable deflection forces, but REVIEW ARTICLE 8 SA JOURNAL OF RADIOLOGY • August 2004 only the ones that have magnetically activated components present a potential problem for patients during MR procedures. The other dental implants, devices and materials are held in place with sufficient counter- forces to prevent them from causing problems by being moved or dis- lodged by exposure to MR systems operating at 1.5 Telsa or less. Contraceptive devices3,16 Various devices are listed: • Diaphragms contain metallic rings, but they are not a con- traindication at 1.5 Tesla. • ESSURE is a novel metallic implant for permanent female contracep- tion (in the USA). This is a dynam- ically expanding micro-coil that is placed in the proximal section of the fallopian tube via a non-inci- sional technique. An intended benign tissue response that is local, fibrotic and occlusive results in tis- sue in-growth into the device. It is thus anchored into the fallopian tube. There are no magnetic field interactions, the highest tempera- ture changes were < +0.6°C, and the induced electrical currents are minimal. • The Lea shield is a silicon rubber intravaginal barrier. • Intrauterine contraceptive devices (IUCDs) are usually made from non-metallic materials (e.g. plastic) or a combination of non-metallic and metallic materials. Copper is the metal most used in an IUCD without side-effect. • The Mirena device is safe at all sta- tic magnetic field strengths. ECG electrodes3 Some patients need monitoring during the MR procedure, especially if there is a deterioration of vital signs during the investigation. As MR-guid- ed surgery and therapy are also grow- ing, there is an increased need to monitor patients. Investigations that use the electrocardiogram (ECG) for the purpose of gating also require the proper acquisition of the appropriate physiological signal for accurate rep- resentation of the MR images. Patient safety and proper recording of the ECG in the MRI environment require specially developed ECG electrodes. Using them during MRI procedures protects the patient from potentially hazardous conditions and produces minimal MRI-related artifacts. Special fibre-optic ECG recording techniques may be used to prevent burns during MR procedures. Foley catheters2,3 There are Foley catheters available with a temperature sensor. These should never be connected to the tem- perature monitor during the MR pro- cedure because the equipment is not MR-compatible or safe. Cervical fixation devices2,3,17,18 MR procedures should only be performed on patients with halo vests or cervical fixation devices made from non-ferromagnetic and non-conduc- tive materials, that have little or no interaction with the electromagnetic fields generated by MR systems. Halo vests or cervical fixation devices may be constructed from either ferromag- netic, non-ferromagnetic, or a combi- nation of metallic components and other materials. Although some com- mercially available halo vests or cervi- cal fixation devices are composed entirely of non-ferromagnetic materi- als, there is always a theoretical hazard of inducing electrical current in the ring portion of any halo device made from conductive materials (Faraday’s law of electromagnetic induction). The patient is also susceptible to pos- sible burn or electrical injuries. Noteworthy vibration of metallic components of devices like the halo ring, vertical supports, vest bolts, etc. were observed during MR imaging. Haemostatic clips2,3 In several studies at 1.5T no static magnetic field attraction to the clips was observed. At 3.0T the Surgiclip spring made from carbon steel (United States Surgical, North Haven, USA) showed a deflection angle of 90˚ and a qualitative torque of +4. This implant is currently categorised as ‘unsafe’ at 3.0T even though the clos- ing force may provide substantial counterforce to prevent it from being moved or dislodged. Most of these implants were manufactured from non-ferromagnetic materials such as tantalum, commercially pure titani- um, and non-ferromagnetic forms of stainless steel. Some ligating, haemo- static, or other types of clips are made from biodegradable materials. Patients who have haemostatic vascu- lar clips, other clips, fasteners, and sta- ples as mentioned in Shellock’s book- let should not be at risk for injury dur- ing MR procedures. There has never been a report of an injury to a patient associated with a haemostatic vascular clip, other type of clip, fastener, or staple in the MR environment. Patients with non-ferromagnetic ver- sions of these implants may undergo MR procedures immediately after they are placed surgically. Patients with metallic carotid artery vascular clamps have been imaged using static magnetic fields ranging up to 1.5T without experiencing any discomfort REVIEW ARTICLE 9 SA JOURNAL OF RADIOLOGY • August 2004 or neurological consequence, with the exception of the Poppen-Blaylock clamp. A metallic marking clip, the Micromark, made from 316L stainless steel by Biopsys Medical (Irvine, CA), has been developed for percutaneous placement after stereotactic breast biopsy. MicroMark II Clip (316LVM stainless steel, Ethicon Endosurgery, Cincinnati, Ohio) has been tested for MR safety in 1.5 Tesla and 3.0 Tesla MR systems. The findings indicated that there were no magnetic field interactions associated with exposure to 1.5 Tesla and 3.0 Tesla MR systems or MRI-related heating. Owing to excessive ferromagnetism and the associated imaging artefacts that may limit or obscure the area of interest, most biopsy needles, markers and devices are not useful for MR-guided biopsy procedures. Otological implants3,19 The ferromagnetic McGee stape- dectomy piston prosthesis is made from platinum and chromium-nickel alloy stainless steel. The manufacturer has recalled this particular otological implant and patients who received these devices should avoid MR proce- dures. Ocular implants3,20 Beware of intra-ocular foreign bodies. A patient with a Fatio eyelid spring or round wire eyelid spring may experience discomfort but would probably not be injured as a result of exposure to the magnetic fields of an MR system. Patients have undergone MR procedures with eyelid wires after having a protective plastic covering placed around the globe along with a firmly applied eye patch. Although no such case has ever been reported, the Troutman magnetic ocular implant and retinal tacks (made from marten- sitic stainless steel) may cause injuries to a patient during an MR procedure. Orthopaedic implants3,21 Most orthopaedic implants, mate- rials, and devices evaluated for ferro- magnetism are made from non-ferro- magnetic materials and therefore should be safe for patients undergoing MR procedures. Only the Perfix inter- ference screw used for reconstruction of the anterior cruciate ligament has been found to be highly ferromagnet- ic. Because this interference screw is firmly imbedded in bone, it is held in place with sufficient force to counter- balance it and to prevent movement or dislodgement and should not be considered a contraindication to MR. However, it is preferable to use inter- ference screws made from non- or weakly ferromagnetic materials. Pellets and bullets3,22 The risk against benefit and the anatomical location must be consid- ered when deciding to perform an MR procedure in a patient with pel- lets, bullets, shrapnel or any other bal- listic object because it may be contam- inated with ferromagnetic materials. Surgical instruments3,23,24 Interventional MRI procedures include a wide spectrum of minimal- ly invasive surgical and therapeutic techniques that include percutaneous biopsy (e.g. breast, bone, brain, abdominal), endoscopic surgery of the abdomen, spine, and sinuses, open-brain surgery, and MR-guided monitoring of thermal therapies (i.e. laser-induced, RF-induced, and cryo- mediated procedures). For interven- tional MRI procedures surgical instruments and devices must be MR- compatible or at least MR-safe. The key problem of the conventional instruments and devices made from metallic materials in association with interventional MRI procedures is pri- marily image related. Other concerns are: unwanted movement due to magnetic field interactions, the missile effect, transla- tional attraction, torque and heating generated by RF power deposition. The lack of commercially avail- able, MR-compatible medical devices and instruments has hampered the widespread implementation of MR- guided procedures, mainly those involving the use of complicated instruments such as the endoscope. Endoscopy in combination with MR guidance may offer several advantages including a dramatic improvement in the visualisation and orientation of the endoscope, an ability to appreciate complex three-dimensional anatomy in immediate and remote anatomical areas, and a reduction in procedure- related morbidity. The use of com- mercially available endoscopes con- structed from ferromagnetic materials is restricted in the MR environment owing to the associated substantial magnetic field attraction and produc- tion of large imaging artefacts. MR systems like conventional, open-architecture, or the double- donut MR systems (specially designed) for MR-guided biopsy, therapeutic, and minimally invasive surgical procedures are important clinical applications. To support these interventions and procedures innova- tive design and construction of instru- ments and devices are needed. Weakly ferromagnetic, non-ferromagnetic or non-metallic materials are used to make special instruments for inter- REVIEW ARTICLE 10 SA JOURNAL OF RADIOLOGY • August 2004 ventional MR procedures. Metallic surgical instruments and other devices potentially pose hazards (e.g. missile effects) or cause other prob- lems such as image distortion, obscur- ing the region of interest, affecting adequate visualisation of the abnor- mality, and preventing execution of the procedure. Ceramic instruments have excep- tionally good qualities for the MR environment because there is no mag- netic field attraction, negligible heat- ing, and no substantial image distor- tion, as determined by the ex vivo test- ing. Tattoos and permanent cosmetics3,25,26 Permanent cosmetics like tattooed eyeliner and decorative tattoos may cause MR imaging artefacts and rela- tively minor, short-term cutaneous reactions. The presence of a perma- nent cosmetic or decorative tattoo should not prevent the MR examina- tion, since diagnostic information of vital significance may affect manage- ment of the patient. Prostate seed implant3 Prostate cancer is sometimes treat- ed by low-level radiation via a titani- um tube implant with graphite, lead and palladium, the Theraseed. Tests demonstrated safety in an MR envi- ronment of 1.5T. Transdermal patches3 Transdermal delivery system with a metallic component must be removed prior to an MR procedure, as the possibility of burn injury exists. Apply a new patch on completion of the examination. Vascular access ports3 Various implantable vascular access ports and catheters evaluated for compatibility with MR procedures showed no measurable attraction to the static magnetic fields of the MR systems used for testing. The forces were considered to be minor relative to the in vivo application of these implants. Accessories, like the infusion set and needles, showed measurable ferromagnetism, with the PORT-A- CATH Needle (Deltec, Inc., St Paul, MN) exceeding the recommended ASTM deflection angle safety guide- line (i.e. greater than 45°). A small strip of adhesive tape is an effective counterbalance to the ferromagnet- ism. Verify that the specific device is in Shellock’s List and is safe to enter an MR environment. Postoperative patients and MR procedures2,3,12,13 A patient with a metallic object ‘passive implant’ (no electronically or magnetically activated component associated with the operation of the device) that is made from non-ferro- magnetic material (e.g. titanium, tita- nium alloy, nitinol, etc.), may undergo an MR procedure immediately after implantation in an MR system oper- ating at 1.5 Tesla or less. A waiting period of 6 - 8 weeks after placement of other implants or devices that exhibit ‘weakly magnetic’ qualities (e.g. certain stents, atrial septal defect occluders, ventricular septal defect occluders, patent ductus arteriosus occluders) is recommended before performing an MR procedure or allowing the individual or patient to enter the MR environment at < 1.5 Tesla.‘Weakly’ ferromagnetic intravas- cular and intracavitary coils, stents, fil- ters, and cardiac occluders become firmly incorporated into tissue 6 - 8 weeks following placement. Retentive or counter-forces provided by tissue ingrowth, scarring, or granulation essentially serve to prevent these objects from presenting risks or haz- ards to patients or individuals in the MR environment. Rigidly fixed implants or devices that may be ‘weakly magnetic’, such as a bone screw, may be studied immediately after implantation. Unconscious and unrespon- sive patients Protect the hearing of all uncon- scious and unresponsive patients prior to being scanned. Halfway through the procedure all monitoring lead locations should be repositioned as patients may be unable to report an increase in tissue warmth or pending thermal injury. Conclusion Before deciding whether any object is MR-safe/compatible careful- ly consider the intended use and the possible retaining mechanisms like sutures, granulation or tissue ingrowth, thus preventing movement and the possible effect of heating of sensitive tissue. This is a quick guide for passive devices. Active devices will be dis- cussed in a later article. All MR rooms should have an up-to-date list of devices and a copy of F G Shellock’s Pocket Guide to MR Procedures and Metallic Objects, which is about as complete as it gets.27 Another useful site is Shellock’s MRI safety.com.28 Acknowledgement F G Shellock’s information has been reproduced with permission. References 1. Shellock FG, Crues JV. Aneurysm clips: assess- ment of magnetic field interaction associated REVIEW ARTICLE 11 SA JOURNAL OF RADIOLOGY • August 2004 REVIEW ARTICLE 12 SA JOURNAL OF RADIOLOGY • August 2004 with a 0.2-T extremity MR system. Radiology 1998; 208: 407-409. 2. Shellock FG, Curtis JS. MR imaging and bio- medical implants, materials, and devices: an updated review. Radiology 1991; 180: 541-550. 3. Shellock FG, Morisoli S, Kanal E. MR proce- dures and biomedical implants, materials, and devices: 1993 update. Radiology 1993; 189: 587- 599. 4. Shellock FG, Slimp G. Halo vest for cervical spine fixation during MR imaging. Am J Roentgenol 1990; 154: 631-632. 5. Becker RL, Norfray JF, Teitelbaum GP, et al. MR imaging in patients with intracranial aneurysm clips. Am J Neuroradiol 1988; 9: 885-889. 6. Shellock FG, Kanal E. Aneurysm clips: evalua- tion of MR imaging artifacts at 1.5 T. Radiology 1998; 209: 563-566. 7. Klucznik RP, Carrier DA, Pyka R, Haid RW. Placement of a ferromagnetic intracerebral aneurysm clip in a magnetic field with a fatal outcome. Radiology 1993; 187: 855-856. 8. Kanal E, Borgstede JP, Barkovich AJ, et al. American College of Radiology White Paper on MR Safety. Am J Roentgenol 2002; 178: 1335- 1347. 9. Shellock FG, Kanal E. Yasargil aneurysm clips: evaluation of interactions with a 1.5-T MR sys- tem. Radiology 1998; 207: 587-591. 10. Hennemeyer CT, Wicklow K, Feinberg DA, Derdeyn CP. In vitro evaluation of platinum Guglielmi detachable coils at 3 T with a porcine model: safety issues and artifacts. Radiology 2001; 219: 732-737. 11. Hug J, Nagel E, Bornstedt A, Schnackenburg B, Oswald H, Fleck E. Coronary arterial stents: safety and artifacts during MR imaging. Radiology 2000; 216: 781-787. 12. Liebman CE, Messersmith RN, Levin DN, Lu CT. MR imaging of inferior vena caval filters: safety and artifacts. Am J Roentgenol 1988; 150: 1174-1176. 13. Manke C, Nitz WR, Djavidani B, et al. MR imaging-guided stent placement in iliac arterial stenoses: a feasibility study. Radiology 2001; 219: 527-534. 14. Shellock FG, Shellock VJ. Cranial bone flap fix- ation clamps: compatibility at MR imaging. Radiology 1998; 207: 822-825. 15. Teitelbaum GP, Bradley WG Jr, Klein BD. MR imaging artifacts, ferromagnetism, and mag- netic torque of intravascular filters, stents, and coils. Radiology 1988; 166: 657-664. 16. Shellock FG, Shellock VJ. MRI Safety of cardio- vascular implants: evaluation of ferromagnet- ism, heating, and artifacts. Radiology 2000; 214: P19H. 17. Duru F, Luechinger R, Candinas R. MR imaging in patients with cardiac pacemakers. Radiology 2001; 219: 856-858. 18. Malko JA, Hoffman JC Jr, Jarrett PJ. Eddy-cur- rent-induced artifacts caused by an ‘MR-com- patible’ halo device. Radiology 1989; 173: 563- 564. 19. Nogueira M, Shellock F. Otologic bioimplants: ex vivo assessment of ferromagnetism and arte- facts at 1.5 T. Am J Roentgenol 1994; 163: 1472- 1473. 20. Albert DW, Olson KR, Parel JM, Hernandez E, Lee W, Quencer R. Magnetic resonance imaging and retinal tacks. Arch Ophthalmol 1990; 108: 320-321. 21. Shellock FG, Crues JV. High-field-strength MR imaging and metallic bioimplants: an in vitro evaluation of deflection forces and temperature changes induced in large prostheses (Abstract). Radiology 1987; 165: 150. 22. Teitelbaum GP. Metallic ballistic fragments: MR imaging safety and artifacts. Radiology 1990; 177: 883. 23. Jolesz FA. 1996 RSNA Eugene P Pendergrass New Horizons Lecture. Image-guided proce- dures and the operating room of the future. Radiology 1997; 204: 601-612. 24. Shellock FG. Compatibility of an endoscope designed for use in interventional MR imaging procedures. Am J Roentgenol 1998; 171: 1297- 1300. 25. Wagle WA, Smith M. Tattoo-induced skin burn during MR imaging. Am J Roentgenol 2000; 174: 1795. 26. Carr JJ. Danger in performing MR imaging on women who have tattooed eyeliner or similar types of permanent cosmetic injections. Am J Roentgenol 1995; 165: 1546-1547. 27. Shellock FG. Pocket Guide to MR Procedures and Metallic Objects. Update 1996. Philadelphia: Lippincott, 2001. 28. Shellock FG. MRI safety.com. 2001 (accessed February – April 2004). Available at: http//www.mrisafety.com/1