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AJR Integrative Imaging LIFELONG LEARNING FOR RADIOLOGY |
1 Both authors: Department of Radiology, University of Washington, Box 354755, 4245 Roosevelt Way NE, Seattle, WA 98105.
Received February 24, 2007; accepted after revision February 26, 2007.
Address correspondence to F. S. Chew
(fchew{at}u.washington.edu).
The educational objectives for this self-assessment module on safe MR practices are for the participant to exercise, self-assess, and improve his or her knowledge of hazards to patients, medical personnel, and others in the MR scanner environment, and to exercise, self-assess, and improve his or her knowledge of safe practices in the operation of MR scanners.
Keywords: MRI • safety
INTRODUCTION
This self-assessment module on safe MR practices has an educational component and a self-assessment component. The educational component consists of one journal article that the participant should read and study. This journal article consists of the American College of Radiology (ACR) guidelines for safe MR practices. The self-assessment component consists of 10 multiple-choice questions with solutions. All of these materials are available on the ARRS Website (www.arrs.org). To claim CME and SAM credit, each participant must register and then enter his or her responses to the questions online.
EDUCATIONAL OBJECTIVES
By completing this educational activity, the participant will:
REQUIRED READING
(available at www.arrs.org)
INSTRUCTIONS
| QUESTION 1 ACR guidelines divide an MR site into four conceptual zones with progressive restriction of access. Which is the highest zone into which ferromagnetic objects and equipment may be safely taken?
QUESTION 2 Which of the following is considered a safe practice for the operation of a free-standing MR center?
QUESTION 3 If MR safety data are not prospectively available for a given metallic device and negligible attractive forces are observed with a handheld magnet (1,000 gauss), which label should be attached to the device?
QUESTION 4 With regard to the Lenz's forces on a metallic nonferrous infusion pump, what is considered best practice?
QUESTION 5 If, through a failure of the cryogen vent or quench pipe, cryogenic liquids are released into the magnet room (Zone IV), which of the following potential safety concerns is LEAST likely to occur?
QUESTION 6 Concerning pregnancy and MR scanning, which statement is TRUE?
QUESTION 7 Concerning the possibility of tissue heating and thermal injury during MR scanning, all of the following statements are true EXCEPT:
QUESTION 8 Patients with poor renal function may develop nephrogenic systemic fibrosis (NSF) after the administration of gadolinium contrast agents. All of the following are thought to possibly reduce the risk of NSF in patients with severely impaired renal function undergoing contrast-enhanced MRI EXCEPT:
QUESTION 9 Concerning MRI of patients with intracranial aneurysm clips, which of the following statements is TRUE?
QUESTION 10 Concerning MRI of cardiac pacemakers and implantable cardioverter defibrillators (ICDs), which of the following statements is TRUE?
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Solution to Question 1
Zone I includes all areas that are freely accessible to the general public and typically includes the outside waiting room and reception. It is typically outside the actual MR environment. Zone II is the interface between the freely accessible Zone I and the strictly controlled Zones III and IV. It is typically the patient interview, dressing, and holding area. Zone III access is strictly controlled because serious injury or death may be caused by interactions with ferromagnetic objects or equipment and the MR environment. Zone IV is the room in which the MR scanner is located. Ferromagnetic objects and equipment may be safely taken into Zone II but not Zone III. Option B is the best response.
Solution to Question 2
ACR guidelines apply to MR scanners of all field strengths. All MR technologists should be registered radiologic technologists (American Registry of Radiologic Technologists). Option A is not the best response. The scanner room (Zone IV) should be clearly marked with a red light and a lighted sign stating, "The Magnet is On." Except for resistive magnets, this light and sign should be continuously illuminated, even in the event of a general power loss to the site. Option B is the best response. Conventional metal detectors do not differentiate between ferromagnetic and nonferromagnetic metallic objects, and are unreliable in detecting small, potentially dangerous ferromagnetic metal fragments or implanted devices in the body. Option C is not the best response. In the event of a cardiac arrest in a superconducting magnet, cardiopulmonary resuscitation should be initiated immediately while the patient is emergently moved to a predetermined magnetically safe location. Quenching the magnet is not routinely advised because of the time delay and the potential hazards [1]. Option D is not the best response.
Solution to Question 3
The green "MR safe" label is used for those items that are wholly nonmetallic, and the label is actually square, not round. Option A is not the best response. The square green FDA/ASTM (American Society for Testing and Materials) label has the lettering "MR safe," not "MR conditional." The square green label is used for those items that are wholly nonmetallic. The "MR conditional" label is triangular and yellow. Option B is not the best response. The red "not MR safe" label is round, not square. This label is used for items clearly ferromagnetic. An item may be metallic, yet not be ferromagnetic. Whether or not the item is ferromagnetic is determined through use of a handheld magnet (1,000 gauss). Option C is not the best response. The triangular yellow "MR conditional" label is used for metallic items for which MR safety data are not prospectively available and negligible attractive forces are observed with a handheld magnet (1,000 gauss) [1]. Option D is the best response.
Solution to Question 4
It is not necessary to cancel a study when a patient presents with a metallic, nonferrous infusion pump [1]. Option A is not the best response. The more rapidly the patient's metallic, nonferrous infusion pump is moved through the magnetic field, the greater the Lenz's force on the infusion pump and thus the greater the discomfort or danger to the patient. There is no need to remove the patient from Zone IV because this infusion pump represents no danger to the patient as long as patient motion through the Zone IV magnetic field is slow. Moreover, removing the patient from Zone IV (after conclusion of the scan) should be done slowly, not as quickly as possible. Option B is not the best response. Although a patient might detect some tugging or pulling on the implant, the slow movement of the patient into and out of the magnet bore is a key factor in reducing Lenz's forces on the infusion pump, and the examination can proceed as scheduled. Option C is the best response. A metallic, nonferrous infusion pump poses no projectile hazard, although the slow movement of the patient into and out of the Zone IV magnet bore is a key factor in reducing Lenz's forces on the infusion pump, lowering patient discomfort or danger. Option D is not the best response.
Solution to Question 5
Asphyxiation is a possibility because cryogenic gases replace oxygenated air. Option A is not the best response. Fire hazards can exist in the event of the quench if cryogenic gases escape into the magnet room/Zone IV. Option B is not the best response. Frostbite may occur at the exceedingly low temperatures of the escaping cryogenic fluids. Option C is not the best response. Although escaping cryogenic liquids released into the magnet room will cause positive pressure in the room, magnet rooms should be provided with an emergency exhaust pathway so that an exhaust fan draws the vaporous cloud of gas away from the door. This should reduce the positive pressure from the leak and allow the magnet room door to open as customary under normal conditions [1]. Option D is the best response.
Solution to Question 6
Pregnant MR technologists are permitted to work in the MR environment through all stages of their pregnancy [1]. Option A is not the best response. Pregnant patients may undergo MR scanning at any stage of their pregnancy, provided that sonography is not an adequate imaging alternative, the information sought may potentially affect the care of the patient or the fetus during the pregnancy, and the referring physician does not believe it is prudent to wait until the patient is no longer pregnant to obtain the study [1]. Option B is not the best response. Pregnant patients should NOT routinely be administered gadolinium-based MR contrast agents. These agents cross the placental barrier and enter the fetal circulation, where they are filtered by the kidneys and excreted into the third space of the amniotic fluid for an indeterminant amount of time before being resorbed by the mother and excreted. The decision to use contrast material in a pregnant patient depends on an individualized risk–benefit analysis. Option C is not the best response. The risk to the fetus posed by gadolinium-based MR contrast agents is unknown [1]. However, out of an abundance of caution, it is generally assumed that there may be harmful effects. Option D is the best response.
Solution to Question 7
The pigments in dark tattoos may heat up during MR scanning; therefore, cold compresses or ice packs should be placed on extensive or dark tattoos during scanning to mitigate this effect. Option A is true and therefore not the best response. Serious injuries have been reported from heating of the tips of implanted neurologic stimulators during MRI. It is possible for a monitoring lead or wire that heats up during scanning at 1.5 T to be entirely safe during scanning at 3.0 T and vice versa [1]. Option C is the exception, and therefore the best response. Depending on the specific magnet design, body tissues may become heated when in direct contact with the inner bore of the MR scanner; therefore, care may be needed to ensure there is no contact. Pads and other insulating devices may be interposed. Option D is true and is therefore not the best option.
Solution to Question 8
Gadodiamide appears to have a causative role in the development of NSF in patients with severe renal disease (who require dialysis or who have a glomerular filtration rate of 15 mL/min or less). There are also reported cases that follow the administration of other gadolinium-based contrast agents. To reduce the risk, authorities recommend administering the lowest dose that would provide the diagnostic benefit being sought or even refraining completely from using a gadolinium-based contrast agent [1]. Options A and D are not the best responses. In patients receiving hemodialysis, elective gadolinium administration should be scheduled to immediately precede hemodialysis; for emergent gadolinium administration, hemodialysis should immediately follow the study. Option C is not the best response. No evidence exists that premedication with corticosteroids and diphenhydramine hydrochloride (Benadryl) reduces the risk of NSF. Option B is the exception, and therefore the best response.
Solution to Question 9
Some aneurysm clips may deflect in the presence of a strong magnetic field; this may result in catastrophic bleeding. This effect is not dependent on which body part is being scanned. Option A is not the best response. Aneurysm clips are metallic and should therefore be detectable on routine skull radiographs, unless there is overlying metal. However, routine radiographs cannot identify which clips are safe or unsafe in the MR scanner. Option B is not the best response. Patients whose aneurysm clips are made of commercially pure titanium or titanium alloy are safe for MRI. Many nontitanium clips manufactured in 1995 or later have been labeled as having MR compatibility and are therefore considered safe. The clip should be specifically identified as such by the surgeon or other physician in the medical record or other available documentation. Option C is the best response. If there are insufficient data regarding the safety of an individual patient's aneurysm clip, a risk–benefit assessment and review should be performed to determine whether the potential benefits of the MRI justify the possible risk [1]. Option D is false and therefore not the best response.
Solution to Question 10
No ICDs or pacemakers have been labeled as safe or even conditionally safe for MRI at any field strength. Option A is not the best response. Multiple deaths have been reported in patients with pacemakers or ICDs who underwent MRI. The exact circumstances of these deaths have been poorly or incompletely characterized. Option B is not the best response. The ACR guidelines recommend that the presence of a pacemaker or ICD be considered a relative rather than an absolute contraindication. The resistance of pacemakers and ICDs to electromagnetic interference such as that encountered in the MRI environment has improved in recent years. Option C is not the best response. MRI may result in unexpected programming changes, inhibition of pacemaker output, failure to pace, transient asynchronous pacing, rapid cardiac pacing, the induction of ventricular fibrillation, heating of the tissue adjacent to the pacing or ICD system, early battery depletion, and outright device failure requiring replacement in patients with pacemakers or ICDs [1]. Option D is the best response.
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