- Email: [email protected]
Undisclosed and undetected foreign bodies during MRI screening resulting in a potentially serious outcome
Magnetic Resonance Imaging 31 (2013) 630–633
Contents lists available at SciVerse ScienceDirect
Magnetic Resonance Imaging journal homepage: www.mrijournal.com
Case report
Undisclosed and undetected foreign bodies during MRI screening resulting in a potentially serious outcome☆,☆☆ Cynthia A. James a, Alexandra Karacozoff b, Frank G. Shellock c,⁎ a b c
Louis A. Johnson VA Medical Center, Clarksburg, WV 26301 Loyola Marymount University, Los Angeles, CA 90045 Keck School of medicine, University of Southern California and Institute for Magnetic Resonance Safety, Education, and Research, Los Angeles, CA 90045
a r t i c l e
i n f o
Article history: Received 7 August 2012 Revised 26 September 2012 Accepted 19 November 2012 Keywords: MRI, safety MRI, injury MRI, screening Foreign body Ferromagnetic detection system
a b s t r a c t The risks associated with performing magnetic resonance imaging (MRI) examinations in patients with ferromagnetic foreign bodies are well known. Accordingly, screening procedures are implemented to identify items that may pose hazards to patients and other individuals before allowing them to enter the MRI system room. This report describes a patient who, despite undergoing proper MRI screening procedures, did not disclose the presence of ferromagnetic foreign bodies, which resulted in a potentially serious outcome. © 2013 Elsevier Inc. All rights reserved.
1. Introduction The importance of conducting comprehensive screening procedures before performing magnetic resonance imaging (MRI) examinations in patients is well known [1–3]. Pre-MRI screening is particularly critical for patients presenting with metallic implants or foreign bodies because these items can pose substantial problems or serious injuries if they are ferromagnetic [1–3]. Accordingly, screening procedures are implemented to identify items that may pose hazards to patients and other individuals before allowing them to enter the MRI system room [1–3]. Unexpected complications may arise when a patient does not provide a complete or accurate medical history during the MRI screening procedure [1–4]. Because of misunderstandings, age, or embarrassment, patients may not disclose the presence of implants, devices, or foreign bodies [2,4]. Importantly, patients may be unaware of the inherent dangers associated with the powerful magnetic field of the MRI system or the fact that excessive heat may be generated in certain objects made from conducting materials, which can cause serious injuries during the MRI examination [1,2]. This report describes a patient who did not disclose the presence of ferromagnetic foreign bodies during pre-MRI screening, which ☆ Grant Support: None. ☆☆ Disclosures: None. ⁎ Corresponding author. Tel.: +1 310 670 7095; fax: +1 310 417 8639. E-mail addresses: [email protected] (C.A. James), [email protected] (A. Karacozoff), [email protected], [email protected] (F.G. Shellock). 0730-725X/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.mri.2012.11.013
resulted in the need to perform medical procedures and a potentially serious outcome. 2. Case report A 43-year-old male resident of an inpatient rehabilitation program presented for an MRI examination of his entire spine for back pain. The initial pre-MRI screening, which involved the use of a written screening form, was performed and documented by the ordering provider. Upon entering the MRI facility, the patient was directed to a locker room where he was instructed to remove all metallic items and to place them into a locker with his shoes. This patient was not requested to change into a gown because he was wearing only a t-shirt, gym shorts, and socks. Ferromagnetic detection systems have recently been employed to help identify ferromagnetic objects and are considered to be a valuable tool for MRI screening [5]. Therefore, as part of the MRI screening procedure implemented to detect ferromagnetic objects, the MRI technologist utilized a hand-held ferromagnetic detection device (SafeScan Target Scanner Mednovus, Inc., Leucadia, CA) to completely scan the patient in a methodical manner, with an emphasis on the patient's pockets where ferromagnetic objects may be found. During this process, no alarms were evident from the ferromagnetic detection device (i.e., a negative result for the identification of a ferromagnetic object). The patient next went into a screening room and underwent a verbal interview, which was performed by the MRI technologist,
C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
using an electronic screening checklist. During this time, the patient indicated that he had no metallic implants, devices, or foreign bodies with the exception of routine dental objects (e.g., fillings). He was led into the MRI system room, where he was positioned head-first, supine into a 1.5-Tesla MRI scanner (Siemens Avanto, Siemens Medical Solutions, Inc., Malvern, PA). As the MRI system table advanced to isocenter, the patient became noticeably agitated and started to shake and kick, which appeared to be related to sensations of being extremely uncomfortable. The MRI technologist quickly removed him from the bore of the scanner because it was felt that the patient may have been suffering from anxiety or claustrophobia. The patient indicated that he was not anxious and, in fact, stated that he had experienced an intense painful sensation localized to the area of his genitals in association with being moved into the scanner. Again, he denied the presence of piercings or metallic foreign bodies. The female MRI technologist left the room so that a male MRI technologist could further question and check the patient for a possible injury. The patient refused to submit to an examination, but did state that something was inserted into his penis when he and his girlfriend were “fooling around”, and that “it didn't block anything,” so he wasn't concerned. The patient was sent for x-rays to help determine the source of pain. The radiographs revealed four spherical, metallic-density objects within the patient's bladder and a less dense, irregularly shaped hyper-density item at the base of his penis (Fig. 1). Based on examination of the radiographs along with the details provided by the patient and the MRI technologist, it was suspected that the metallic foreign bodies (which were apparently ferromagnetic) in the patient's penis became “internal projectiles”, and, thus, were attracted by the powerful static magnetic field of the MRI system. This resulted in these objects moving forcefully from the patient's penis into his bladder when he entered the bore of the 1.5-Tesla scanner. The radiologist recommended urgent follow-up by a urologist. The MRI technologist contacted the patient's primary care provider, who sent the patient to the emergency department (ED) for evaluation. In the ED, the patient was more forthcoming with information and stated that the foreign bodies were placed when he was under the influence of drugs and that he didn't know what was inserted. He stated he was embarrassed and didn't want to reveal this information to the MRI technologist.
Fig. 1. One of the four ball bearings retrieved from the patient referred for an MRI examination (diameter, 7 mm).
631
While in the ED, the patient was unable to void due to apparent inflammation in the urethra and, therefore, was sent to surgery for placement of a suprapubic catheter to drain his bladder. A more extensive surgical procedure could not be performed at this time because the patient had not been NPO (nothing by mouth) for a suitable period of time. The patient later passed the four metallic objects while voiding. He retrieved them and they were submitted for examination. Fig. 2 shows an example of one of the objects recovered from the patient, which appears to be a metallic ball bearing. The nonmetallic foreign body, which turned out to be a portion of snail shell, was later retrieved during removal of the suprapubic catheter. Overall, the patient was expeditiously cared for and recovered from his surgery and injury. To further understand the nature of this incident, magnetic field interaction testing was performed on the metallic foreign bodies [6– 8], along with an additional assessment utilizing another type of ferromagnetic detection system [5]. Tests for magnetic field interactions involved evaluations of translational attraction and characterization using a digital force gauge in association with a 1.5Tesla MR system (Magnetom; Siemens Medical Solutions, Malvern,
Fig. 2. (A) Anteroposterior view x-ray of the patient. Note the four ball bearings and the additional foreign body (non-metallic). (B) Lateral view x-ray of the patient. Note the four ball bearings and the additional foreign body (non-metallic).
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C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
PA), as previously described [6–8]. To determine translational attraction, one ball bearing (diameter, 7 mm; weight 5 grams) was attached to a test fixture that consisted of a protractor with 1-degree graduated markings, with the 0-degree mark oriented vertically [6– 8]. The ball bearing was suspended from a 20-cm length of string (weight less than 1%) attached to the 0-degree indicator of the protractor. The protractor device was positioned at the highest “patient accessible” spatial gradient magnetic field for the 1.5-Tesla MR system, which occurs at an off-axis position, 85 cm from isocenter of the scanner [6,9]. The deflection angle was measured three times and a mean value was calculated, which was 90 degrees for the ball bearing (Fig. 3). Because the deflection angle was found to be 90 degrees (Fig. 3), translational attraction was also evaluated using a digital force gauge, as previously described [6]. The ball bearing was attached to a lightweight string with the other end attached to the digital force gauge (Model 475040, Extech Instruments, Waltham, MA). The gauge was positioned more than 10 feet from the MR system to avoid influence from the static magnetic field. The peak translational force recorded for the ball bearing at the point of highest spatial gradient magnetic field was determined to be 302 Newtons (303 grams). This is a high value considering the relatively small size of the ball bearing. We elected to determine if another type of ferromagnetic detection system could potentially identify these ferromagnetic foreign bodies that were “missed” by the hand-held screening device, acknowledging that different systems have varying capabilities [5]. This other ferromagnetic detection system (Ferroguard Screener, Metrasens, www.Metrasens.com) is configured as a post or pillar that may be installed in a variety of possible places in the MRI environment, outside of the MRI system room [5]. Unlike the handheld device, which must be essentially placed over the metallic object in question, this ferromagnetic detection system was selected because its configuration permits it to be used to effectively screen a patient in an overall manner. This particular ferromagnetic detection system uses multiple fluxgate sensors. A fluxgate sensor is the most sensitive type of solid-state magnetometer that is practical for this application and the use of multiple sensors provides head-to-toe coverage of the individual or patient. The sensors are electronically configured to remove large unwanted magnetic signals, such as the Earth's geomagnetic field and power-line fields. Notably, the combination of high sensitivity to ferromagnetic objects and relative
immunity to environmental noise is essential for reliable detection of small ferromagnetic objects [5]. The following test procedures were utilized with the “pillar” ferromagnetic detection system: (1) A horizontal turntable of 30-cm diameter was mounted 86 cm above floor level to approximate the height of the groin area for a 1.83-m (6’) tall male. The outer perimeter of the turntable was positioned to be 10-cm from the front of the ferromagnetic detection pillar. This turntable set up provided systematic rotation deemed useful for systematic measurements. (2) One metallic ball bearing sample was placed on the perimeter of the turntable and the magnetic signals were recorded using an oscilloscope and personal computer while the turntable was slowly rotated. This procedure was repeated for each ball bearing. (3) Each ball bearing was then demagnetized to render it into its least “magnetic state” (note that the ball bearings only become marginally less magnetic when demagnetized). (4) Procedure 2 (above) was repeated with the demagnetized ball bearings. (5) A human subject without implants was confirmed to be free of ferromagnetic objects by standing two inches away from the ferromagnetic detection system and rotating 360 degrees. A negative finding (i.e., no alarm) was verified. The ball bearings were then held against the groin of this human subject, who underwent the recommended screening procedure using the pillar device. That is, the individual approached the front of the ferromagnetic detection system to a distance of 5 cm and then rotated 360 degrees (note that, with the subject rotating 360 degrees, the distance of the ball bearings from the pillar varies). Data was collected by having the test subject rotate four times at a rate of approximately four seconds per rotation. (6) The ferromagnetic detection system was carefully observed to determine if there was a positive (i.e., as indicated by illumination of amber or red-colored lights) or negative finding during each trial. The findings for the various test procedures indicated that the ferromagnetic detection system gave a positive alarm in each case, demonstrating the potential of this pillar device to identify the ferromagnetic ball bearings in a patient during a screening procedure. 3. Discussion
Fig. 3. Deflection angle measurement performed on ball-bearing in association with a 1.5-Tesla MRI system. Note the deflection angle of 90 degrees.
Extreme caution must be exercised during the screening procedure to ensure that the patient fully understands the dangers associated with the MRI the examination, particularly with respect to the presence of a ferromagnetic object and the potential for a serious injury. Even when an MRI facility takes great care to design and implement a comprehensive MRI safety program, including establishing all critically important screening procedures[1–3], there remains a potential, yet uncontrollable component: the patient and how he or she responds to the questions posed during screening. The patient is expected to provide honest, accurate, and complete information during the screening process. However, language or cultural barriers, embarrassment, and other factors may lead to the intentional exclusion of potentially dangerous objects that might be present and, then, undetected despite the use of proper screening procedures[2,4]. Notably, an additional tool was used for screening by the MRI facility – a hand-held ferromagnetic detection system. But this extra precaution failed to identify the metallic foreign bodies in the patient. As seen in this case report, accidents can still occur if
C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
the ferromagnetic threat is undetected because it is outside the detector's limits or if the detector is not used properly. Although ferromagnetic detectors may assist the MRI operator in discovering ferromagnetic threats, they have inherent limitations that must be understood by the user. The ERCI, in a review of the FDA's MAUDE (Manufacturer and User Facility Device Experience) database, found several ferromagnetic-related incidents that may have been prevented if a ferromagnetic detection system had been used [5]. Therefore, the ERCI conducted an investigation involving 10 different ferromagnetic detection systems of three different configurations: portals, pillars, and hand-held. Various system differences were reported including sensitivity, target localization, siting considerations, and ease of use. Each detector evaluated had some sort of limitation, some of which were related to the user's technique and experience with utilizing the device [5]. Importantly, the signal being detected by any ferromagnetic detection system diminishes with the cube of the distance from the object, and this becomes an important consideration in the detection of small targets or those within the subject versus those external to the subject. Because of the “short detection range” that is present when using a hand‐held device, it needs to be swept over the whole area undergoing evaluation at a consistent range or distance and parallel to the surface that is intended to be screened, typically involving a visible target or suspected position for the object. The procedure needs to involve a careful, systematic scan procedure to ensure that the entire area is swept without gaps. Anything less can limit the effectiveness of the hand-held device, resulting poor detection. Hurrying the process will lead to gaps in the scanned area and inconsistent detector stand‐off (range) from the subject, as well as inconsistent parallelism. For short range detectors like hand-held devices, this means that it is possible to scan an area and miss a target within that area if the range is temporally too great or the angle of the detector is incorrect. In contrast, pillar-type screeners scan approximately 50% of the whole surface area at any given time. Rotation by the subject ensures 100% coverage, provided that the subject stays within range of the sensors, which is accomplished by proper supervision. Thus, compared with a hand-held device, a pillar ferromagnetic detection system appears to be a better choice for supplemental screening when used in the MRI environment. Notably, we demonstrated that the ferromagnetic ball bearings could be identified by the pillar system that was used. It should be noted, however, that ferromagnetic detection systems are not specifically intended for use to identify internal objects. Additional research on this application is warranted.
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3.1. Recommendations In the event that a patient enters the MRI environment and is injured by an undisclosed, undetected metallic object, a procedure should be in place to immediately manage and treat the patient. In this case report, the patient was promptly removed from the MRI system and sent for x-rays, to the ED for examination and medical attention, and then to surgery. At this facility, all of the vital care was accessible and readily available, which resulted in the patient being cared for in a timely manner. If the MRI facility does not have this type of access (e.g., an outpatient MRI center), a contingency plan should be in place to deal with such an emergency. Importantly, if a patient describes discomfort related to the MRI scanner or the examination, he or she must be immediately removed from the MRI environment and examined by suitable means to determine the cause of the complaint. Appropriate foreign body localization radiographs should be obtained, as needed, and prompt medical care must be administered [10].
References [1] Shellock FG, Spinazzi A. MRI safety update 2008: part 2, screening patients for MRI. AJR Am J Roentgenol 2008;191:1140-9. [2] Shellock FG. Reference Manual for Magnetic Resonance Safety, Implants, and Devices: 2012 Edition. Los Angeles: Biomedical Research Publishing Group; 2012. [3] Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document for safe MR practices: 2007. AJR Am J Roentgenol 2007;188:1447-74. [4] Elmquist C, Shellock FG, Stoller D. Screening adolescents for metallic foreign bodies before MR procedures. J Magn Reson Imaging 1995;5:784-5. [5] ECRI Institute. Best ferromagnetic detectors: ratings for 7 products from Kopp Development, Mednovus, and Metrasens. Health Devices 2011;40:6–30. [6] Shellock FG, Tkach JA, Ruggieri PM, Masaryk T, Rasmussen P. Aneurysm clips: evaluation of magnetic field interactions using "long-bore" and "short-bore" 3.0Tesla MR systems. AJNR Am J Neuroradiol 2003;24:463-71. [7] Baker KB, Nyenhuis JA, Hrdlicka G, Rezai AR, Tkach JA, Shellock FG. Neurostimulator implants: assessment of magnetic field interactions associated with 1.5-and 3.0-Tesla MR systems. J Magn Reson Imaging 2005;21:72-7. [8] American Society for Testing and Materials (ASTM) Designation: F 2052. Standard test method for measurement of magnetically induced displacement force on passive implants in the magnetic resonance environment. In: Annual Book of ASTM Standards, Section 13, Medical Devices and Services, Volume 13.01 Medical Devices; Emergency Medical Services. West Conshohocken, PA, pp; 1576–1580. [9] Shellock FG, Kanal E, Gilk T. Confusion regarding the value reported for the term “spatial gradient field” and how this information is applied to labeling of medical implants and devices. AJR Am J Roentgenol 2011;196:142-5. [10] Shaheen F, Singh M, Nazir P. MRI-induced migration of a foreign body into the spinal canal: are present guidelines are safe? Am J Roentgenol 2008;191: W72-3.
Contents lists available at SciVerse ScienceDirect
Magnetic Resonance Imaging journal homepage: www.mrijournal.com
Case report
Undisclosed and undetected foreign bodies during MRI screening resulting in a potentially serious outcome☆,☆☆ Cynthia A. James a, Alexandra Karacozoff b, Frank G. Shellock c,⁎ a b c
Louis A. Johnson VA Medical Center, Clarksburg, WV 26301 Loyola Marymount University, Los Angeles, CA 90045 Keck School of medicine, University of Southern California and Institute for Magnetic Resonance Safety, Education, and Research, Los Angeles, CA 90045
a r t i c l e
i n f o
Article history: Received 7 August 2012 Revised 26 September 2012 Accepted 19 November 2012 Keywords: MRI, safety MRI, injury MRI, screening Foreign body Ferromagnetic detection system
a b s t r a c t The risks associated with performing magnetic resonance imaging (MRI) examinations in patients with ferromagnetic foreign bodies are well known. Accordingly, screening procedures are implemented to identify items that may pose hazards to patients and other individuals before allowing them to enter the MRI system room. This report describes a patient who, despite undergoing proper MRI screening procedures, did not disclose the presence of ferromagnetic foreign bodies, which resulted in a potentially serious outcome. © 2013 Elsevier Inc. All rights reserved.
1. Introduction The importance of conducting comprehensive screening procedures before performing magnetic resonance imaging (MRI) examinations in patients is well known [1–3]. Pre-MRI screening is particularly critical for patients presenting with metallic implants or foreign bodies because these items can pose substantial problems or serious injuries if they are ferromagnetic [1–3]. Accordingly, screening procedures are implemented to identify items that may pose hazards to patients and other individuals before allowing them to enter the MRI system room [1–3]. Unexpected complications may arise when a patient does not provide a complete or accurate medical history during the MRI screening procedure [1–4]. Because of misunderstandings, age, or embarrassment, patients may not disclose the presence of implants, devices, or foreign bodies [2,4]. Importantly, patients may be unaware of the inherent dangers associated with the powerful magnetic field of the MRI system or the fact that excessive heat may be generated in certain objects made from conducting materials, which can cause serious injuries during the MRI examination [1,2]. This report describes a patient who did not disclose the presence of ferromagnetic foreign bodies during pre-MRI screening, which ☆ Grant Support: None. ☆☆ Disclosures: None. ⁎ Corresponding author. Tel.: +1 310 670 7095; fax: +1 310 417 8639. E-mail addresses: [email protected] (C.A. James), [email protected] (A. Karacozoff), [email protected], [email protected] (F.G. Shellock). 0730-725X/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.mri.2012.11.013
resulted in the need to perform medical procedures and a potentially serious outcome. 2. Case report A 43-year-old male resident of an inpatient rehabilitation program presented for an MRI examination of his entire spine for back pain. The initial pre-MRI screening, which involved the use of a written screening form, was performed and documented by the ordering provider. Upon entering the MRI facility, the patient was directed to a locker room where he was instructed to remove all metallic items and to place them into a locker with his shoes. This patient was not requested to change into a gown because he was wearing only a t-shirt, gym shorts, and socks. Ferromagnetic detection systems have recently been employed to help identify ferromagnetic objects and are considered to be a valuable tool for MRI screening [5]. Therefore, as part of the MRI screening procedure implemented to detect ferromagnetic objects, the MRI technologist utilized a hand-held ferromagnetic detection device (SafeScan Target Scanner Mednovus, Inc., Leucadia, CA) to completely scan the patient in a methodical manner, with an emphasis on the patient's pockets where ferromagnetic objects may be found. During this process, no alarms were evident from the ferromagnetic detection device (i.e., a negative result for the identification of a ferromagnetic object). The patient next went into a screening room and underwent a verbal interview, which was performed by the MRI technologist,
C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
using an electronic screening checklist. During this time, the patient indicated that he had no metallic implants, devices, or foreign bodies with the exception of routine dental objects (e.g., fillings). He was led into the MRI system room, where he was positioned head-first, supine into a 1.5-Tesla MRI scanner (Siemens Avanto, Siemens Medical Solutions, Inc., Malvern, PA). As the MRI system table advanced to isocenter, the patient became noticeably agitated and started to shake and kick, which appeared to be related to sensations of being extremely uncomfortable. The MRI technologist quickly removed him from the bore of the scanner because it was felt that the patient may have been suffering from anxiety or claustrophobia. The patient indicated that he was not anxious and, in fact, stated that he had experienced an intense painful sensation localized to the area of his genitals in association with being moved into the scanner. Again, he denied the presence of piercings or metallic foreign bodies. The female MRI technologist left the room so that a male MRI technologist could further question and check the patient for a possible injury. The patient refused to submit to an examination, but did state that something was inserted into his penis when he and his girlfriend were “fooling around”, and that “it didn't block anything,” so he wasn't concerned. The patient was sent for x-rays to help determine the source of pain. The radiographs revealed four spherical, metallic-density objects within the patient's bladder and a less dense, irregularly shaped hyper-density item at the base of his penis (Fig. 1). Based on examination of the radiographs along with the details provided by the patient and the MRI technologist, it was suspected that the metallic foreign bodies (which were apparently ferromagnetic) in the patient's penis became “internal projectiles”, and, thus, were attracted by the powerful static magnetic field of the MRI system. This resulted in these objects moving forcefully from the patient's penis into his bladder when he entered the bore of the 1.5-Tesla scanner. The radiologist recommended urgent follow-up by a urologist. The MRI technologist contacted the patient's primary care provider, who sent the patient to the emergency department (ED) for evaluation. In the ED, the patient was more forthcoming with information and stated that the foreign bodies were placed when he was under the influence of drugs and that he didn't know what was inserted. He stated he was embarrassed and didn't want to reveal this information to the MRI technologist.
Fig. 1. One of the four ball bearings retrieved from the patient referred for an MRI examination (diameter, 7 mm).
631
While in the ED, the patient was unable to void due to apparent inflammation in the urethra and, therefore, was sent to surgery for placement of a suprapubic catheter to drain his bladder. A more extensive surgical procedure could not be performed at this time because the patient had not been NPO (nothing by mouth) for a suitable period of time. The patient later passed the four metallic objects while voiding. He retrieved them and they were submitted for examination. Fig. 2 shows an example of one of the objects recovered from the patient, which appears to be a metallic ball bearing. The nonmetallic foreign body, which turned out to be a portion of snail shell, was later retrieved during removal of the suprapubic catheter. Overall, the patient was expeditiously cared for and recovered from his surgery and injury. To further understand the nature of this incident, magnetic field interaction testing was performed on the metallic foreign bodies [6– 8], along with an additional assessment utilizing another type of ferromagnetic detection system [5]. Tests for magnetic field interactions involved evaluations of translational attraction and characterization using a digital force gauge in association with a 1.5Tesla MR system (Magnetom; Siemens Medical Solutions, Malvern,
Fig. 2. (A) Anteroposterior view x-ray of the patient. Note the four ball bearings and the additional foreign body (non-metallic). (B) Lateral view x-ray of the patient. Note the four ball bearings and the additional foreign body (non-metallic).
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C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
PA), as previously described [6–8]. To determine translational attraction, one ball bearing (diameter, 7 mm; weight 5 grams) was attached to a test fixture that consisted of a protractor with 1-degree graduated markings, with the 0-degree mark oriented vertically [6– 8]. The ball bearing was suspended from a 20-cm length of string (weight less than 1%) attached to the 0-degree indicator of the protractor. The protractor device was positioned at the highest “patient accessible” spatial gradient magnetic field for the 1.5-Tesla MR system, which occurs at an off-axis position, 85 cm from isocenter of the scanner [6,9]. The deflection angle was measured three times and a mean value was calculated, which was 90 degrees for the ball bearing (Fig. 3). Because the deflection angle was found to be 90 degrees (Fig. 3), translational attraction was also evaluated using a digital force gauge, as previously described [6]. The ball bearing was attached to a lightweight string with the other end attached to the digital force gauge (Model 475040, Extech Instruments, Waltham, MA). The gauge was positioned more than 10 feet from the MR system to avoid influence from the static magnetic field. The peak translational force recorded for the ball bearing at the point of highest spatial gradient magnetic field was determined to be 302 Newtons (303 grams). This is a high value considering the relatively small size of the ball bearing. We elected to determine if another type of ferromagnetic detection system could potentially identify these ferromagnetic foreign bodies that were “missed” by the hand-held screening device, acknowledging that different systems have varying capabilities [5]. This other ferromagnetic detection system (Ferroguard Screener, Metrasens, www.Metrasens.com) is configured as a post or pillar that may be installed in a variety of possible places in the MRI environment, outside of the MRI system room [5]. Unlike the handheld device, which must be essentially placed over the metallic object in question, this ferromagnetic detection system was selected because its configuration permits it to be used to effectively screen a patient in an overall manner. This particular ferromagnetic detection system uses multiple fluxgate sensors. A fluxgate sensor is the most sensitive type of solid-state magnetometer that is practical for this application and the use of multiple sensors provides head-to-toe coverage of the individual or patient. The sensors are electronically configured to remove large unwanted magnetic signals, such as the Earth's geomagnetic field and power-line fields. Notably, the combination of high sensitivity to ferromagnetic objects and relative
immunity to environmental noise is essential for reliable detection of small ferromagnetic objects [5]. The following test procedures were utilized with the “pillar” ferromagnetic detection system: (1) A horizontal turntable of 30-cm diameter was mounted 86 cm above floor level to approximate the height of the groin area for a 1.83-m (6’) tall male. The outer perimeter of the turntable was positioned to be 10-cm from the front of the ferromagnetic detection pillar. This turntable set up provided systematic rotation deemed useful for systematic measurements. (2) One metallic ball bearing sample was placed on the perimeter of the turntable and the magnetic signals were recorded using an oscilloscope and personal computer while the turntable was slowly rotated. This procedure was repeated for each ball bearing. (3) Each ball bearing was then demagnetized to render it into its least “magnetic state” (note that the ball bearings only become marginally less magnetic when demagnetized). (4) Procedure 2 (above) was repeated with the demagnetized ball bearings. (5) A human subject without implants was confirmed to be free of ferromagnetic objects by standing two inches away from the ferromagnetic detection system and rotating 360 degrees. A negative finding (i.e., no alarm) was verified. The ball bearings were then held against the groin of this human subject, who underwent the recommended screening procedure using the pillar device. That is, the individual approached the front of the ferromagnetic detection system to a distance of 5 cm and then rotated 360 degrees (note that, with the subject rotating 360 degrees, the distance of the ball bearings from the pillar varies). Data was collected by having the test subject rotate four times at a rate of approximately four seconds per rotation. (6) The ferromagnetic detection system was carefully observed to determine if there was a positive (i.e., as indicated by illumination of amber or red-colored lights) or negative finding during each trial. The findings for the various test procedures indicated that the ferromagnetic detection system gave a positive alarm in each case, demonstrating the potential of this pillar device to identify the ferromagnetic ball bearings in a patient during a screening procedure. 3. Discussion
Fig. 3. Deflection angle measurement performed on ball-bearing in association with a 1.5-Tesla MRI system. Note the deflection angle of 90 degrees.
Extreme caution must be exercised during the screening procedure to ensure that the patient fully understands the dangers associated with the MRI the examination, particularly with respect to the presence of a ferromagnetic object and the potential for a serious injury. Even when an MRI facility takes great care to design and implement a comprehensive MRI safety program, including establishing all critically important screening procedures[1–3], there remains a potential, yet uncontrollable component: the patient and how he or she responds to the questions posed during screening. The patient is expected to provide honest, accurate, and complete information during the screening process. However, language or cultural barriers, embarrassment, and other factors may lead to the intentional exclusion of potentially dangerous objects that might be present and, then, undetected despite the use of proper screening procedures[2,4]. Notably, an additional tool was used for screening by the MRI facility – a hand-held ferromagnetic detection system. But this extra precaution failed to identify the metallic foreign bodies in the patient. As seen in this case report, accidents can still occur if
C.A. James et al. / Magnetic Resonance Imaging 31 (2013) 630–633
the ferromagnetic threat is undetected because it is outside the detector's limits or if the detector is not used properly. Although ferromagnetic detectors may assist the MRI operator in discovering ferromagnetic threats, they have inherent limitations that must be understood by the user. The ERCI, in a review of the FDA's MAUDE (Manufacturer and User Facility Device Experience) database, found several ferromagnetic-related incidents that may have been prevented if a ferromagnetic detection system had been used [5]. Therefore, the ERCI conducted an investigation involving 10 different ferromagnetic detection systems of three different configurations: portals, pillars, and hand-held. Various system differences were reported including sensitivity, target localization, siting considerations, and ease of use. Each detector evaluated had some sort of limitation, some of which were related to the user's technique and experience with utilizing the device [5]. Importantly, the signal being detected by any ferromagnetic detection system diminishes with the cube of the distance from the object, and this becomes an important consideration in the detection of small targets or those within the subject versus those external to the subject. Because of the “short detection range” that is present when using a hand‐held device, it needs to be swept over the whole area undergoing evaluation at a consistent range or distance and parallel to the surface that is intended to be screened, typically involving a visible target or suspected position for the object. The procedure needs to involve a careful, systematic scan procedure to ensure that the entire area is swept without gaps. Anything less can limit the effectiveness of the hand-held device, resulting poor detection. Hurrying the process will lead to gaps in the scanned area and inconsistent detector stand‐off (range) from the subject, as well as inconsistent parallelism. For short range detectors like hand-held devices, this means that it is possible to scan an area and miss a target within that area if the range is temporally too great or the angle of the detector is incorrect. In contrast, pillar-type screeners scan approximately 50% of the whole surface area at any given time. Rotation by the subject ensures 100% coverage, provided that the subject stays within range of the sensors, which is accomplished by proper supervision. Thus, compared with a hand-held device, a pillar ferromagnetic detection system appears to be a better choice for supplemental screening when used in the MRI environment. Notably, we demonstrated that the ferromagnetic ball bearings could be identified by the pillar system that was used. It should be noted, however, that ferromagnetic detection systems are not specifically intended for use to identify internal objects. Additional research on this application is warranted.
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3.1. Recommendations In the event that a patient enters the MRI environment and is injured by an undisclosed, undetected metallic object, a procedure should be in place to immediately manage and treat the patient. In this case report, the patient was promptly removed from the MRI system and sent for x-rays, to the ED for examination and medical attention, and then to surgery. At this facility, all of the vital care was accessible and readily available, which resulted in the patient being cared for in a timely manner. If the MRI facility does not have this type of access (e.g., an outpatient MRI center), a contingency plan should be in place to deal with such an emergency. Importantly, if a patient describes discomfort related to the MRI scanner or the examination, he or she must be immediately removed from the MRI environment and examined by suitable means to determine the cause of the complaint. Appropriate foreign body localization radiographs should be obtained, as needed, and prompt medical care must be administered [10].
References [1] Shellock FG, Spinazzi A. MRI safety update 2008: part 2, screening patients for MRI. AJR Am J Roentgenol 2008;191:1140-9. [2] Shellock FG. Reference Manual for Magnetic Resonance Safety, Implants, and Devices: 2012 Edition. Los Angeles: Biomedical Research Publishing Group; 2012. [3] Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document for safe MR practices: 2007. AJR Am J Roentgenol 2007;188:1447-74. [4] Elmquist C, Shellock FG, Stoller D. Screening adolescents for metallic foreign bodies before MR procedures. J Magn Reson Imaging 1995;5:784-5. [5] ECRI Institute. Best ferromagnetic detectors: ratings for 7 products from Kopp Development, Mednovus, and Metrasens. Health Devices 2011;40:6–30. [6] Shellock FG, Tkach JA, Ruggieri PM, Masaryk T, Rasmussen P. Aneurysm clips: evaluation of magnetic field interactions using "long-bore" and "short-bore" 3.0Tesla MR systems. AJNR Am J Neuroradiol 2003;24:463-71. [7] Baker KB, Nyenhuis JA, Hrdlicka G, Rezai AR, Tkach JA, Shellock FG. Neurostimulator implants: assessment of magnetic field interactions associated with 1.5-and 3.0-Tesla MR systems. J Magn Reson Imaging 2005;21:72-7. [8] American Society for Testing and Materials (ASTM) Designation: F 2052. Standard test method for measurement of magnetically induced displacement force on passive implants in the magnetic resonance environment. In: Annual Book of ASTM Standards, Section 13, Medical Devices and Services, Volume 13.01 Medical Devices; Emergency Medical Services. West Conshohocken, PA, pp; 1576–1580. [9] Shellock FG, Kanal E, Gilk T. Confusion regarding the value reported for the term “spatial gradient field” and how this information is applied to labeling of medical implants and devices. AJR Am J Roentgenol 2011;196:142-5. [10] Shaheen F, Singh M, Nazir P. MRI-induced migration of a foreign body into the spinal canal: are present guidelines are safe? Am J Roentgenol 2008;191: W72-3.