MR Basics: Module 7 Safety Essentials

Transcription

1 Module 7 Transcript For educational and institutional use. This transcript is licensed for noncommercial, educational inhouse or online educational course use only in educational and corporate institutions. Any broadcast, duplication, circulation, public viewing, conference viewing or Internet posting of this product is strictly prohibited. Purchase of the product constitutes an agreement to these terms. In return for the licensed use, the Licensee hereby releases, and waives any and all claims and/or liabilities that may arise against ASRT as a result of the product and its licensing.

2 MR Basics: Module 7 Safety Essentials 1. MR Basics Safety Essentials Welcome to Module 7 of MR Basics Safety Essentials. This module was written by Randy Carr, R.T.(R)(T)(CT)(MR), CRA. 2. License Agreement and Disclaimer 3. Objectives After completing this module, you will be able to: Discuss the elements of safety that help ensure a magnetic resonance (MR) imaging facility operates safely. Demonstrate proper screening and preparation of patients for MR imaging. Explain how to monitor patients during procedures. Describe when and how to quench the magnet and handle other emergencies in the MR environment. 4. Importance of Safety In mid-1977, the first human was scanned using magnetic resonance (MR) imaging. By the early 1980s, MR scanners were being installed across the country. Today, MRI has become a common household term, much like radiography. Although more people are now familiar with MR imaging, they might not be aware of the safety precautions that must be followed when entering an MR facility. For example, people might not know that the superconducting magnets and permanent magnets used in open MR scanners cannot be powered off. Even if the electrical supply to the equipment is shut down, the magnetic field still is in force. 5. MR Safety Incidents Here s some interesting statistics on MR safety incidents. An independent analysis of a U.S. Food and Drug Administration (FDA) database in 2005 reported 389 safety-related events, including nine deaths. Three of the deaths were associated with pacemaker failure and two to insulin pump failure. The remaining four deaths were related to an implant disturbance, a projectile and asphyxiation from a cryogenic mishap during installation of an MR imaging system. More than 70 percent of the 389 events were burns and 10 percent were projectile-related. Between the years of 2004 and 2008, reported MRI accidents increased by 310 percednt. Updated statistics can be researched on the FDA database, MAUDE, which is the Manufacturer and User Facility Device Experience database. Accidents occur because of the powerful magnetic force of the MR equipment, and MR technologists are the gatekeepers who can prevent these accidents. To reduce the risk associated with the magnetic field, technologists must properly screen and prepare any individual who enters the MR facility, along with all equipment or objects that are taken into the MR scanner room. 6. MR Safety Considerations Let s review the main safety considerations of MR imaging. These factors include the force and torque of the magnetic field on ferromagnetic materials, the potential for injury if a metallic 2012 ASRT. All rights reserved. 1 MR Basics: Module 7

3 object is pulled into the magnet and strikes a person, possible biological effects from the magnetic fields and the radiofrequency pulses, and the potential injuries in the event of a superconducting magnet quench. 7. Magnetic Classification of Objects Substances can be classified into four categories relative to their reactions to magnetic fields: diamagnetic, paramagnetic, superparamagnetic and ferromagnetic. 8. Diamagnetic Substances Diamagnetic substances have no net magnetic moment because they have no unpaired orbital electrons. When exposed to a magnetic field, diamagnetic substances actually demonstrate a negative magnetic susceptibility, which means they are repelled by the magnetic field. As a result, the magnetic field is reduced. 9. Diamagnetic Objects Diamagnetic means the substance contains no materials that are attracted to the magnetic field. Sheets, paper, plastic, or any equipment or device specifically manufactured to be used in or around a magnetic field are considered diamagnetic objects. 10. Paramagnetic substances Paramagnetic substances, on the other hand, have unpaired orbital electrons. When exposed to a magnetic field, paramagnetic substances demonstrate a small positive magnetic susceptibility of less than one. When exposed to the magnetic field, paramagnetic substances are slightly attracted, increasing the field slightly. As a result, the magnetic field is greater. 11. Paramagnetic Materials Paramagnetic materials demonstrate slight magnetic attraction. Gadolinium-based contrast agents used in MR scanning and rare earth metals such as lanthanide are considered to be paramagnetic substances. 12. Superparamagnetic Substances Superparamagnetic substances are individual elements that have ferromagnetic properties in bulk. They behave in the same way as paramagnetic substances, except that instead of each individual atom being independently influenced by an external magnetic field, the magnetic moment of the entire substance reacts to it. When exposed to the magnetic field, superparamagnetic substances are attracted to the magnetic field, demonstrating a magnetic susceptibility much stronger than paramagnetic substances. An example of a superparamagnetic substance is an iron-containing contrast agent. 13. Ferromagnetic Substances When exposed to a magnetic field, ferromagnetic substances demonstrate a positive magnetic susceptibility greater than one. Ferromagnetic substances are highly attracted to the magnetic field and become permanently magnetized when exposed to the field. Ferromagnetic substances that have been exposed to a magnetic field retain their magnetism, even after the magnetic field is removed. 14. Ferromagnetic Objects 2012 ASRT. All rights reserved. 2 MR Basics: Module 7

4 Ferromagnetic objects exhibit a strong magnetic attraction. They are the most dangerous objects that can be brought into an MR environment. Oxygen tanks, stretchers, wheel chairs, intravenous (IV) poles, scissors or hemostats, floor buffers, mops and mop buckets are examples of the many items that could be ferromagnetic. Hospitals and imaging centers can purchase special MR-conditional versions of these products, but MR personnel should check all items with a handheld magnet or metal detector to ensure they are MR conditional as labeled. 15. Knowledge Check Answer the following question. 16. Knowledge Check Answer the following question. 17. Knowledge Check Answer the following question. 18. Field Strength Measurement The main magnetic field used to acquire MR images is known as the static magnetic field. Tesla (T) is the preferred international unit of measure for magnetic force and should always be used to describe an MR magnet s field strength. The static field can range in strength from 0.2 to 3.0 T in most MR equipment, although some research facilities have magnets that exceed 3.0 T field strengths. A 1.5-T scanner has a static field approximately 30,000 times stronger than the earth's magnetic field. The magnetic field around MR equipment also may be measured in terms of the conventional unit, gauss. One T is equal to 10,000 gauss. The 5-gauss line is a perimeter around the scanner defining where the static field is higher than 5 gauss, or potentially hazardous. 19. Field Strengths and Safety According to U.S. Food and Drug Administration (FDA) guidelines, adults, children and infants older than one month can be scanned using a static magnetic field strength up to 8.0 T. If the infant is one month or younger, the maximum static field strength is 4.0 T. MR facilities that perform research studies may use higher magnetic field strengths Gauss Warning All MR personnel should be aware of their MR scanner s 5-gauss line and ensure that the area is marked with the appropriate warning signs. People with non-mr compatible implants should not enter the area marked by these signs because the fringe field might potentially damage their implants. The warning sign should be posted on all entrance areas to the MR facility. If the 5-gauss line extends outside the MR facility, the area should be restricted with a barrier to keep the general population from coming into contact with the fringe field. Facilities with a 3.0-T magnet should alert the public with a 3.0-T sign. Safety risks are directly proportional to magnetic field strength: As the magnetic field strength increases, the safety risks also increase ASRT. All rights reserved. 3 MR Basics: Module 7

5 21. Static Magnetic Field The primary safety concern of the static magnetic field is the magnetic attraction or pulling force against ferromagnetic objects. It s important to remember that the magnet is always on, and the static magnetic field is not confined to the MR scanner bore. The magnetic force extends outside the MR scanner into the scanner room. The magnetic force also may reach outside the scanner room if the walls are not adequately shielded. 22. Fringe Field The invisible magnetic force that extends outside the magnet is referred to as the fringe field. It s important for MR technologists to understand the strength of the fringe field and how far it reaches outside the MR equipment or scanner room. The magnetic fringe field is a 360-degree perimeter around the scanner. Floors above and below the MR scanner room must be taken into account when considering safety issues associated with the fringe field. Two factors affect the fringe field: the main magnet s field strength and the amount of shielding inside the MR scanner. 23. Shielding Minimizing how far the magnetic field extends beyond the MR scanner is an important safety goal. Active and passive shielding techniques are used to limit the magnetic field. Active shielding inside the MR scanner consists of tightly wound electromagnetic coils that alternate electrical current to restrict the magnetic field and reduce fringe field exposure. Iron beams used in room construction provide passive shielding. The iron pulls the magnetic fringe field into the scanner room, which helps keep the fringe field from extending outside the room. Decreasing the fringe field reduces the risk to people with pacemakers or other metallic implants or devices who might enter the magnetic field by mistake. The shielding also decreases the risk of ferromagnetic objects being pulled into the magnetic field and makes it safer to operate mechanical equipment outside the MR scanner room. Passive shielding can help minimize magnetic field interference with patient monitoring equipment, IV pumps or office computer equipment on floors above and below MR equipment. 24. Knowledge Check Answer the following question. 25. Knowledge Check Answer the following question. 26. Knowledge Check Answer the following question. 27. Translational Force Translational force is the primary safety concern involving the static magnetic field. Ferromagnetic objects accidentally brought into the MR scanner room can be pulled into the scanner bore. Objects attracted to the magnetic field accelerate to a high speed and become projectiles that potentially can seriously injure people or damage equipment ASRT. All rights reserved. 4 MR Basics: Module 7

6 A well-known incident involving a MR scanner occurred in July 2001 at Westchester Medical Center in Valhalla, N.Y. An oxygen tank flew through the MR scanner room, striking and killing a 6-year-old boy. 28. Translational Force The translational force of a ferromagnetic object depends on the strength of the magnetic field and the object s mass and distance from the magnet. As a ferromagnetic object gets closer to the magnet, the magnetic force pulling the object increases exponentially. The MR personnel who control access to the MR scanner room are responsible for making sure ferromagnetic objects are not brought into the room. MR personnel also are responsible for checking medical equipment such as wheelchairs and IV poles to determine whether they are MR conditional. Technologists also should transfer patients brought to the MR suite by stretcher to an MR-conditional stretcher. 29. Rotational Force In MR imaging, certain implanted medical devices, such as ferromagnetic aneurysm clips or noncompatible cardiac pacemakers, are subject to torque from the magnetic field. The rotational force can lead to serious complications. If MR personnel discover that a patient has an implanted device after the patient is taken into the MR scanner room, the technologist should back the patient out of the room without turning to minimize the risk of torque. If the patient suddenly turns around and walks out of the room, the turning or spinning motion could cause the implanted device to torque. There is no guarantee that walking the patient out of the scanner room in this manner will prevent the device from being subject to rotational torque, but doing so can minimize the magnetic field s ability to twist the device. If a patient with a noncompatible device is accidentally taken into the scanner room, MR personnel should follow the facility s policies and procedures for evaluating the patient and notifying the appropriate health care providers. 30. Screening and Testing Objects The best method of protection is for MR technologists to screen patients and others who enter the MR suite, but technologists also can test equipment and objects taken into the MR scanner room using a ferromagnetic detection system or a handheld magnet with a strength of at least 1,000 gauss. Objects that test positively as ferromagnetic should not be brought into the MR environment. Testing should be used in addition to, not instead of, screening forms and verbal screening. 31. Summary for Static Magnetic Field Let s review the safety information we ve covered so far. MR personnel must be familiar with all safety concerns related to the static magnetic field. MR technologists must thoroughly screen patients, visitors and anyone who enters the MR environment for materials that could be unsafe. All equipment or devices must be checked before being brought into the MR environment to ensure they are safe for use in a magnetic field and do not possess any ferromagnetic components that can be pulled into the MR scanner ASRT. All rights reserved. 5 MR Basics: Module 7

7 MR personnel should lock the MR scanner room door when the area is unattended to prevent untrained personnel from accidentally entering the room. The appropriate MR safety warning signs should be posted at all entrances of the MR facility. 32. Electromagnetic Spectrum The radiofrequency energy used in MR imaging occurs at the lower end of the electromagnetic spectrum. This illustration shows where different rays occur along the electromagnetic spectrum. 33. RF Radiation Exposure Because RF waves are nonionizing radiation, MR imaging is considered safer than radiography and computed tomography (CT), which use radiation at the higher end of the spectrum. Look at this illustration. It will help you visualize the radiation exposure for different radiographic procedures. 34. RF Radiation Exposure Although RF waves fall at the low end of the electromagnetic spectrum, they still deposit energy into the patient, which can increase tissue temperature. The tissue warming effect is a biological safety concern in MR imaging. The amount of RF energy deposited in the patient depends on several factors, such as the patient s body weight, the imaging pulse sequence, the repetition time (TR), the number of slices, the amount of patient tissue scanned and the type of MR imaging coil. The more RF pulses used, the more energy is deposited into the patient, which can cause tissue temperature to rise. The patient might begin to perspire as the body attempts to reduce its temperature. Fans inside the MR scanner help keep the patient cool, and some MR scanners contain an internal temperature gauge that alerts the MR technologist when temperatures inside the bore are too high. If the temperature exceeds the threshold limit determined by the patient s weight and specific absorption rate level, the equipment stops scanning until the bore temperature drops to a safe operating level. 35. Specific Absorption Rate Specific absorption rate (SAR) is a measure of the amount of RF energy absorbed by the body and is measured in units of watts per kilogram (W/kg). It s very important to enter the patient s correct weight into the computer so that the MR system can regulate the RF energy accurately. Global specific absorption rate is the absorption rate averaged over the entire body or over a small sample volume (typically between 1 g and 10 g of tissue). The calculated value becomes the maximum level measured in the body part studied over the stated volume or mass. 36. How a Scanner Estimates SAR To estimate the SAR, the MR scanner determines the energy needed for a pulse. Next, the scanner adds the energy of all RF pulses in a sequence and divides the total by the pulse TR to get power. The scanner then divides the power by patient weight to reach the whole-body SAR ASRT. All rights reserved. 6 MR Basics: Module 7

8 The International Electrotechnical Commission and FDA have set limits for whole-body and localized tissue heating. For example, the normal mode limit, which is suitable for all patients, is 0.5 degrees C or 2 W/kg. The normal mode limit for the head is 38 degrees C or 3.2 W/kg averaged over the head mass. 37. Heating The RF coil produces an oscillating electromagnetic field. RF pulses are transmitted into the patient and excite tissues to produce a signal that can be converted into an image. The RF field can potentially cause tissue heating when metallic implants, devices and other metallic objects inside or outside of the patient s body overheat when exposed to the RF field. 38. Thermal Increases Sudden increases in body temperature can cause serious complications for patients with poor thermoregulation due to certain cardiac conditions, high blood pressure, diabetes or any other condition that affects the ability to perspire. Tissue warming from the RF field can lead to thermal skin burns if the patient s skin comes into contact with a coil, sides of the bore or a cord. Manufacturer-approved MR padding can help prevent the patient s body from touching the inside wall of the MR bore, especially at highcontact points such as the arms and hands. 39. Preventing Thermal Burns MR technologists should remind patients to keep their arms by their sides and not cross their arms or feet. The nerves conduct electrical charges throughout the body, so it s important that a patient doesn t create a closed-loop connection by allowing the arms and legs to cross. When using any type of imaging coil or electrocardiograph (ECG) lead, the wires should not touch the patient s anatomy while scanning because of the potential for thermal burns. In addition, the MR technologist should make sure that none of the wires are looped. Looped wires can create an arc that also could burn the patient. MR-approved ECG leads are made of silver and silver chloride to prevent thermal burns. MR staff should check the expiration date of the leads to ensure they are up-to-date. All approved MR imaging coils used inside the scanner bore must be plugged into the appropriate slot. Technologists never should send an unplugged coil into the bore because it could cause thermal burns. 40. Preventing Thermal Burns In some instances a technologist can use non-conducting pads to help position a patient. This illustration is an example of how these non-conducting pads might be used. 41. Implanted Medical Devices Implanted medical devices can cause permanent injury or serious complications if the patient is exposed to the static, RF or gradient magnetic field. Knowing the device name and model number can help staff determine if the device is safe for the facility s magnet strength. 42. Medical Devices and Overheating 2012 ASRT. All rights reserved. 7 MR Basics: Module 7

9 Certain implanted devices can cause excessive heating during MR scanning. These devices include: Cardiac pacemakers and implantable cardiac defibrillators (ICDs). Neurostimulation systems. Halo vests and cervical fixation devices. Transdermal medication patches. Damaged ECG leads. Pulse oximeters. 43. Jewelry, Body Piercings and Tattoos MR technologists also must screen patients for jewelry, body piercings, tattoos and permanent makeup, and regular eye makeup if imaging the orbital area. Any of these objects or conditions could potentially cause burns. RF waves can heat any metallic object, even nonferrous materials. So it s important to explain to patients with body piercings that all jewelry should be removed. Body piercing jewelry often is made of stainless steel, which is not attracted to the magnetic field, but can potentially heat up. Even 14-karat gold jewelry can overheat and cause burns. Permanent makeup and tattoo ink can contain metallic flakes. During scanning, the metallic slivers heat up, causing a burning sensation and skin irritation. Patients with tattoos or permanent makeup should be warned of potential skin irritation and instructed to alert the technologist immediately if they feel anything unusual in the area of the tattoo. Patients having orbital scans should remove all eye makeup because some cosmetics contain metallic flakes. These flakes can cause a void artifact in the orbital area, leading to a misdiagnosis. Technologists should instruct patients to notify MR personnel right away if they experience warming or burning sensations on their body or the feeling of something pulling in or on their body. 44. Gradient Magnetic Fields Gradients are used to change the static magnetic field of the MR scanner to produce the parameters required for various MR examinations. The MR scanner has three pairs of gradient coils. Each time a pulse sequence is started, the three pairs of gradient coils are activated. The rapidly changing gradient field can produce acoustic noise and peripheral nerve stimulation, which are safety concerns specific to gradients. 45. Nerve Stimulation The gradients produce rapidly changing magnetic fields to encode information from the patient during scan sequences. The gradient field can potentially stimulate peripheral nerves in the patient, and loud noise from the gradients can lead to permanent hearing loss if the patient is not provided adequate hearing protection ASRT. All rights reserved. 8 MR Basics: Module 7

10 46. Acoustic Noise The loud noises and vibrations created when the gradient coils are turned on and off can potentially damage a patient s hearing. The sequence and duration of the sounds depend on the specific pulse sequence. The FDA has established specific guidelines on the acceptable noise levels for MR scanning. MR technologists should provide patients with hearing protection such as earplugs or headphones. All hearing protection devices must provide at least 29 db of attenuation. The loud acoustic noise also can cause a patient to stop an examination before it s complete. For example, acoustic noise can lower a patient s tolerance or frighten an individual, especially children. Some patients might develop headaches because of constant loud knocking noise and vibrations. Patients should be told what to expect during the examination. Earplugs or headphones can lower the noise level; however, the patient still can hear the sound and feel the vibrations. Technologists should encourage patients to use the call device if they experience discomfort. 47. Peripheral Nerve or Muscle Stimulation Peripheral nerve or muscle stimulation can be a safety concern for patients exposed to the rapidly changing gradient magnetic field. The human body is made up of various conductive materials, such as nerve and muscles fibers and blood vessels. It s possible to induce a current in these structures and produce an electrical charge inside the patient s body. These sensations are not necessarily painful. Peripheral nerve stimulation is similar to the sensation of stroking your bare arm with a feather. The feather stimulates the outer skin layer, or peripheral nerves. Inducing a current in a muscle fiber can cause a slight twitch. Patients should be told about these possible effects so they won t be startled. A patient inside the scanner bore who suddenly experiences peripheral nerve stimulation or an involuntary muscle twitch might move or stop the exam prematurely. Peripheral nerve or muscle stimulation should have no lasting effect; the sensations end once the pulse sequence stops. The FDA has set stimulation threshold limits with respect to how quickly gradient amplitudes can change. 48. Magnetohemodynamic Effect The magnetohemodynamic effect occurs when fluid or blood moves across a magnetic field. An additional electrical charge is generated by the ions in blood moving perpendicular to the field. As the magnetic field strength increases, so does the magnetohemodynamic effect. The effect causes blood velocity to decrease, and blood pressure then rises to compensate for the slower flow. The cardiac cycle returns to normal when the patient is removed from the static magnetic field. 49. Knowledge Check Answer the following question. 50. Knowledge Check 2012 ASRT. All rights reserved. 9 MR Basics: Module 7

11 Answer the following question. 51. Safety Zones The American College of Radiology (ACR) has issued important MR safety information, Guidance Document for Safe MR Practices: The guidelines break down the areas of the MR facility into Zones I through IV according to safety relative to the magnetic field. 52. Zone I Zone I is outside the MR scanner environment; it includes all areas patients, health care personnel and other employees use to access the MR department. Technologists do not control access to Zone I. 53. Zone II Zone II is the interface between the publicly accessible Zone I and Zone III, which is strictly controlled. Typically, Zone II is the area in which patients are greeted. Non-MR personnel can only move about in Zone II under the supervision of MR staff. Patients typically answer questions regarding MR screening, medical histories, medical insurance and other issues while in Zone II. 54. Zone III All access to Zone III should be strictly limited and controlled by MR technologists, with constant consideration of the static and gradient magnetic fields. The presence of unscreened individuals and ferromagnetic objects or equipment in Zone III could result in serious injury or death. 55. Zone IV Zone IV encompasses the room in which the MR magnet is located and always is within the perimeter of Zone III. Designated MR personnel should accompany or visually supervise all non- MR personnel who enter Zone III or Zone IV. 56. Knowledge Check Match the following descriptions with the correct safety zone. 57. Knowledge Check 58. Knowledge Check Match the following descriptions with the correct safety zone. 59. Knowledge Check 60. Safety Classifications of Personnel The ACR safety guidelines classify people who enter the MR facility based on the amount of safety training they have received. The ACR defines each classification as the following: Non-MR personnel include patients, visitors or staff who have not been trained. Specifically, people who have not undergone formal training within the previous 12 months. Level 1 MR personnel are facility staff members who have participated in minimal safety educational programs to ensure their own safety as they work in Zone III. Examples include MR department office staff and patient aides ASRT. All rights reserved. 10 MR Basics: Module 7

12 Level 2 MR personnel are staff members who have been more extensively trained in the broader aspects of MR safety issues, including the potential for thermal burns and peripheral nerve stimulation. Examples include MR technologists, radiologists and radiology department nursing staff. 61. Safety Screening Proper screening of patients or anyone who enters the MR scanning environment is mandatory. First, MR technologists must screen people for metallic objects on their bodies, metallic medicinal patches and any metallic or mechanical implants in their bodies. A detailed safety screening sheet must be completed for each person who enters the MR scanning suite. The ACR MR safety guidelines contain examples of a safety screening form, MR hazard checklist and patient instructions. MR imaging providers may customize this document to their individual needs and protocols. They also should continuously review and update their policies and procedures regarding MR safety screening. 62. Patient and Personnel Safety Screening MR personnel have an ethical and legal responsibility to ensure that anyone who enters the MR department undergoes a thorough safety screening. Ideally, the MR patient is screened 3 times before entering the MR scanner. In addition to patient safety considerations, the high cost of MR examinations is yet another reason to identify patient contraindications before scheduling to minimize patient no-shows and unfinished examinations. 63. Patient Screening Referring Physician The referring physician should prescreen the patient before ordering the MR examination. The physician should check for factors that might contraindicate the examination, such as noncompatible cardiac pacemakers, pacemaker wires or ferromagnetic aneurysm clips. Prescreening also should include verifying that the patient s size and weight do not exceed MR table specifications. Referring physicians should ask whether a woman is pregnant when determining if she is a candidate for MR scanning. Pregnant patients who undergo MR examinations might have to sign a special consent form. If a patient is claustrophobic or has excessive pain, the referring physician should prescribe an antianxiety or pain medication to make it easier for the patient to complete the MR examination or remain still during the exam. 64. Pre-examination Screening Certain exam protocols may require the use of an intravenous MR contrast agent. A patient may require laboratory tests to check for blood, urea and nitrogen, along with creatinine and estimated glomerular filtration rate levels before receiving contrast. If so, MR staff should obtain these laboratory results according to departmental policies and procedures before the patient arrives for the MR examination ASRT. All rights reserved. 11 MR Basics: Module 7

13 Patient care and safety should be the top concern of all MR personnel. By contacting patients before their appointments, the MR facility can let patients know what to expect and how to better prepare for the examination. For example, some exams may require the patient to have nothing by mouth (NPO), and MR personnel can remind patients of any necessary preparation to prevent cancellations. In addition, patients with claustrophobia can be instructed to contact their referring physician for the appropriate antianxiety medication. Many MR patients are anxious about their examinations, and long wait times make them more anxious. Minimizing patient wait times and improving safety at the facility includes preparing for potential complications before the patient arrives. 65. Pre-examination Screening The following checklist reviews steps MR personnel can take to reduce safety incidents: Ensure the patient has the correct order from the referring physician. Prescreen patients for contraindications, such as noncompatible pacemakers or ferromagnetic aneurysm clips. Prescreen patients for surgically implanted devices and details such as device name and model number to verify that the apparatus is safe for the facility s magnet field strength. Ensure that prescreening radiographs are completed, reviewed and approved by a radiologist. If contrast is indicated, ensure the appropriate lab work is completed, reviewed and approved. Ask whether a female patient of childbearing age is pregnant or breast-feeding. Verify that the patient s weight does not exceed the MR scanner s table weight limits. Remind patients with claustrophobia to discuss pre-examination medication with their referring physician, and that they might need a ride home. Inquire whether patients who will receive a contrast injection have any known difficulties with venipuncture. If so, instruct the patient to arrive early to allow a qualified health care provider additional time to start an IV. 66. Patient and Examination Identification When the patient arrives for the examination, a staff person should follow the facility s policies and procedures for correctly identifying the patient. Verification usually involves checking two patient identifiers, such as patient name and date of birth. The patient, guardian or caregiver should give the patient s full name and date of birth verbally so the MR staff can match it with the paperwork, electronic record or identification armband. After the patient has been properly identified, the MR staff person should ask the patient to explain what body area is being scanned. This question gives MR personnel an opportunity to cross-check the physician order to ensure that the correct body part is being imaged. For example, the order might request images of the right knee, but the patient says he or she has pain in the left knee. 67. Final Patient Screening MR technologists who are trained in MR safety do the final patient screening. MR personnel review an MR safety questionnaire with the patient or the patient s legal guardian. If the patient is unable to respond because of dementia or other condition, a person who is qualified to 2012 ASRT. All rights reserved. 12 MR Basics: Module 7

14 answer questions about the patient s medical history, such as a physician, family member or legal guardian, should complete the safety interview. If the patient or the patient s representative is hearing or vision impaired, not fluent in English or has problems with literacy, MR personnel should follow their facility s policies and procedures regarding interpreter services. If a patient is unconscious and no family member or representative is available who knows the patient s medical history, physicians must determine if the MR examination is absolutely indicated. The patient must be examined carefully for scars or any signs of previous surgeries or metal on or in the body, and radiography or CT imaging should be performed and approved before continuing with the MR examination. Physicians requesting the examination must sign special informed consent, and all personnel involved should follow the facility s policies and procedures. 68. Safety Questionnaire The main purpose of the safety questionnaire or MR screening sheet is to check for implanted medical devices or other objects that that could be contraindications to the MR examination. However, the MR safety questionnaire also can contain questions specific to the patient s symptoms or prior health issues that may be relevant to the ordered study. Questions can cover areas such as cancer history, prior chemotherapy or radiation therapy, surgeries, pregnancy, breast-feeding, drug allergies, MR examinations or other diagnostic examinations. This information might be necessary for the radiologist. 69. Safety Questionnaire The patient and the MR staff member who conducted the safety interview must sign and date the completed MR safety questionnaire. Some facilities may require a second staff person to review, sign and date the document before the patient enters the MR scanner room. Anyone who will enter the scanner room should complete the safety screening questionnaire regardless of whether they will be placed inside the MR scanner bore. For example, a parent who accompanies a child into the scanner room must go through the entire safety screening process, which includes completing the MR safety questionnaire. 70. Contraindications and Precautions A contraindication means that a patient s condition or implanted device or object prevents the MR examination from taking place. An MR precaution means that the condition, device or object may need special consideration and further review and approval by the radiologist. 71. Intracranial Vascular Clips Intracranial vascular clips or aneurysm clips made of ferromagnetic materials are absolute contraindications for MR scanning. Patients who have ferromagnetic clips should not enter the MR scanner room under any circumstances because the magnetic field could cause the clip to torque, tearing the vessel. Ferromagnetic clips also are subject to thermal heating. Clips made from titanium have proved to be safe for MR scanning. 72. Pacemakers and Other Implanted Devices Pacemakers generally are contraindicated for MR scanning; however, if the patient s physician believes the benefit of the MR examination outweighs the risks, special arrangements can be 2012 ASRT. All rights reserved. 13 MR Basics: Module 7

15 made to accommodate the patient. Under these circumstances, a dedicated team consisting of the radiologist, cardiologist and other personnel should be present to properly monitor the patient during the MR examination and handle possible complications. The patient also may be asked to sign a consent form that describes the specific risks of pacemakers and the MR examination. The FDA recently approved an MR-conditional pacemaker, so it s important to know the manufacturer and model of the pacemaker, along with when it was implanted. Implanted devices that are electrically, magnetically or mechanically activated might be considered contraindicated or precautionary for MR examinations. MR personnel must research these devices to determine whether they can be placed inside the magnetic field. MR technologists should follow their institution s policies and procedure for checking implanted devices. Some patients have wallet cards that list the implanted device s manufacturer, model number, serial number and date that a device was implanted. The card also might indicate that the device is safe for MR scanning after a certain date, such as six weeks after surgical implantation. If the patient does not have an information card, an MR staff member might have to request surgical records to determine MR compatibility. 73. Implanted Devices and Field Strength In clinical settings, the field strengths of MR scanners can range from 0.2 to 3.0 T. MR technologists need to know at which field strength, if any, an implanted device can be safely scanned. Approved research facilities may use higher magnetic field strengths, which can represent a further contraindication for implanted devices. For example, a device may have been tested and cleared for a 1.5-T field strength or lower. If the facility has a 3.0-T magnet, it may not be safe to scan the implanted device at the higher field strength. MR technologists should follow the facility s policies and procedures regarding the proper safety clearance for implanted devices. 74. Intraocular Ferrous Foreign Bodies Ferrous foreign bodies in the patient s eyes can cause permanent blindness if exposed to highfield magnets. For example, people who have worked with sheet metal can have metal fragments or shavings in and around their eyes. If these metallic slivers are exposed to the strong force of the magnetic field, the fragments could heat up and burn the eye, resulting in permanent blindness. During the patient screening process, MR personnel should ask the following questions regarding intraocular ferrous foreign bodies: Have you ever had metal fragments or shavings in your eye? If so, did you have them removed? Have you ever had eye surgery? Have you ever worked with metal? Have you ever been hit in the eye with anything metal? Is there any chance you might have gotten metal in your eyes? If the patient answers yes to any of these questions or MR personnel have any concerns about metal fragments in or around the patient s eyes, then an additional screening exam must be 2012 ASRT. All rights reserved. 14 MR Basics: Module 7

16 completed and approved by a radiologist before continuing with MR imaging. Most health care providers order two-projection radiography. Technologists should be familiar with their facility s policies and procedures for screening and approving MR patients who might have a metallic object in or around the eye. 75. Patient Preparation After being cleared to enter the MR scanner room, the patient must dress according to the facility s policies and procedures. At some facilities, the patient changes into a hospital gown and pants to prevent accidentally introducing metallic objects into the MR scanner room. Street clothing may contain metal pieces, such as zippers, snaps, buttons, and underwire, clips or snaps on brassieres. These objects tend to overheat in the RF field. Metallic objects also degrade image quality by causing artifacts. Patients should remove all metallic objects such as eye glasses, jewelry, body piercings, hairpins, removable dental work and keys. Some objects that might be overlooked include safety pins, money clips, coins, pens and credit or bank cards that contain a magnetic strip. 76. Objects With Metal No mechanical devices, such as watches, hearing aids, insulin pumps, pain pumps, heart monitors, beepers or cell phones, may be taken into the MR scanner room. Medicinal patches and adhesive electrodes that contain metal should be removed to prevent possible burns. For example, some medicinal patches have a foil backing. Surgical staples, sutures, clips and wires should be evaluated, and the MR personnel should follow the facility s policies and procedures regarding postoperative devices. 77. Contrast Media and Pregnancy MR technologists should follow their facility s policies and procedures for performing MR examinations and administering contrast to women who are pregnant or breast-feeding. The ACR also provides guidance on contrast media injection into pregnant patients. The decision should be handled on a case-by-case basis by the attending radiologist, who assesses the riskbenefit ratio for a particular patient. The decision to administer a gadolinium-based MR contrast agent to a pregnant patient must be based on overwhelming potential benefit to the patient or fetus that outweighs potential risks. Studies have shown that gadolinium-based MR contrast agents pass through the placental barrier and enter the fetal circulation. They are filtered in the fetal kidneys and then excreted into the amniotic fluid. MR providers should obtain written informed consent from any pregnant patient undergoing an MR examination, documenting that the patient understands the potential risks and benefits of the MR procedure, is aware of alternative diagnostic options, and that she agrees to proceed. 78. Patient Monitoring MR technologists must monitor a patient at all times while he or she is inside the MR scanner. Monitoring must be visual and verbal. MR personnel must be able to see the patient through the control room window or use closed-circuit TV monitors and cameras to monitor the patient ASRT. All rights reserved. 15 MR Basics: Module 7

17 79. Verbal Monitoring Many facilities also provide a call bell so that the patient can alert MR personnel about any difficulties. The call bell usually is a rubber squeeze ball that the patient holds in his or her hands. When the patient squeezes the ball, it activates an audible buzzer at the scanner console to alert MR personnel. A call bell gives the patient a better sense of control, and patients should be told that they can stop the examination and be removed from the scanner at any time. MR technologists can stop or pause the scanner and speak to the patient over the MR scanner s two-way intercom system or enter the scanner room and speak directly with the patient. The technologist should tell patients about the length of a given scan, remind them to remain still and alert them before each scan begins. 80. Monitoring Unconscious or Sedated Patients Depending on institutional policy, unconscious or sedated patients can be connected to MRconditional monitoring equipment, such as a pulse oximeter or blood pressure cuff, to check vital signs. However, nothing takes the place of medically trained personnel inside the scanner room directly monitoring a sedated or unconscious patient. If the patient aspirates, there could be a delay of several minutes before the monitoring equipment indicates a drop in oxygen level. Medically trained personnel inside the MR scanner room are able to respond more quickly to the patient and begin the necessary emergency treatment. 81. Patient Emergencies MR facilities should have policies and procedures to handle basic emergencies involving patients and should hold emergency drills on a regular basis. MR technologists should follow these basic steps during a patient emergency situation: 1. Remove the patient from the MR scanning room to a safe area as soon as possible before attempting any lifesaving procedures. An MR-conditional stretcher should be used to move the patient. 2. Close and lock the MR scanner room once the patient is moved to prevent any untrained MR personnel from accidentally entering the room. 3. Activate the facility s emergency response team. 82. Patient Emergencies Some emergency response team members who respond to MR emergencies may not be properly MR-safety trained or screened for contraindicated medical implants and devices. In addition, team members may be wearing or carrying various ferromagnetic materials, such as scissors, beepers, keys and stethoscopes that could be pulled into the MR scanner by the static field. A patient or other personnel could be injured by a ferromagnetic projectile pulled into the scanner. 83. Equipment or Environmental Emergencies MR facilities should have policies and procedures to handle basic equipment or environmental emergencies. MR personnel should participate in regular drills to handle emergencies such as smoke, fire, water leaks or unusual odors that might indicate fires or other problems. 84. Equipment or Environmental Emergencies MR technologists should take the following steps during equipment or environmental emergencies: 2012 ASRT. All rights reserved. 16 MR Basics: Module 7

18 1. Move the patient from the MR scanner room to a safe area as soon as possible. 2. After the patient is removed, close and lock the scanner room door to prevent any untrained personnel from accidentally entering the room. 3. Activate the facility s emergency response code. 4. Participate in the decision regarding whether to quench the magnet if fire department personnel need to enter the scanner room with their emergency equipment. 85. Equipment or Environmental Emergencies Emergency response team members may not be properly screened for contraindicated medical implants and devices. In addition, fire department personnel may carry various ferromagnetic objects such as oxygen tanks, axes, beepers and keys that could be pulled into the MR scanner. Ferromagnetic items could potentially become projectiles and injure patients or other personnel. MR personnel must be involved in a rapid decision whether to quench the magnet if fire personnel need to enter the MR scanner room. Afterward, the MR technologist must contact the service engineer to inspect the room and equipment. After the MR service engineer pronounces the system ready, the facility may resume MR scanning. 86. Ancillary Equipment MR facilities have various quality assurance procedures for the MR scanner and coils. MR personnel always should check to ensure that the RF coils, ECG cables, pulse receptors and disposable electrodes are in good condition. Damaged equipment can lead to serious patient burns and poor image quality. Technologists never should use an RF coil or ECG lead with frayed or damaged cables. They should immediately notify the service engineer and remove the coil from service. Any type of medical equipment, medical devices, tools or supplies that are brought into the MR scanner room must be checked for MR compatibility. 87. Cryogen Gas Monitoring MR facilities that have superconducting magnets must monitor the cryogens and report the readings to the service organization responsible for maintaining cryogen gas levels. It s extremely important to check, record and report the helium level. If the helium drops below the recommended level, a magnet quench could occur. MR technologists should be familiar with their facility s policies and procedures for monitoring cryogen gases. 88. Quenching the Magnet Cryogen gases are used to cool superconducting magnet systems, and the release of these gases can represent a safety concern. A quench is a sudden loss of the magnetic field that involves the release of liquid helium at -452 degrees F or liquid nitrogen at -320 degrees F. In a superconducting magnet, a quench can occur in two distinct ways: as a controlled, or planned, procedure or as an uncontrolled, spontaneous occurrence. 89. Controlled Quench In a controlled quench, the MR technologist might have to rapidly reduce the magnetic field in response to an emergency situation. An example is when a metallic object physically pins a person against the magnet or when a large metal object such as an oxygen tank, floor buffer or stretcher is pulled into the magnet and cannot be detached. If the trapped person or object 2012 ASRT. All rights reserved. 17 MR Basics: Module 7

19 cannot be removed, the MR technologist may have to start a quench by pushing the emergency quench button. Larger metal objects have greater magnetic force and may be difficult to remove from the magnetic field. If there is no immediate danger, the MR service engineer can be called to slowly release the cryogen gases and gradually dissipate the magnetic field so the item can be removed. Another example of a controlled quench is when the magnet undergoes maintenance or is decommissioned. A controlled quench by a qualified service engineer is always the preferred method when possible. 90. Uncontrolled Quench An uncontrolled, or spontaneous, quench can occur when system components fail without warning, and the failure causes the temperature of the cryogen gases to rise. A hissing sound caused by the slow release of the cryogen gases may be heard just before a full quench occurs. 91. During a Quench During a quench, the cryogen gases that normally help cool a superconducting magnet are released into the MR scanning room. An exhaust tube should vent the cryogen gases to the outside air. If the vent flap becomes stuck or frozen shut, the cryogen gases can fill the scanning room, injuring anyone exposed to the gases. Doors in the MR suite should be installed to open outward because the room pressure during a quench would prevent a door that swings inward from opening. All facilities with MR equipment should have emergency evacuation plans as part of their policies and procedures. 92. Cryogen Gas Release Cryogen gases are released into the scanning room in both controlled and uncontrolled quenches. Cold cryogen gases can cause frostbite or asphyxiation. Because the gases tend to remain at floor level, MR technologists and patients should not attempt to crawl out of an MR room filled with cryogen gases. Unvented cryogen gas molecules expand, increasing the pressure inside the room. The sudden increase in pressure can rupture a person s tympanic membrane. 93. Quench Response Technologists should remain calm and evacuate all patients and personnel from the MR suite according to their facility s policies and procedures for quench emergencies. Patients and personnel should remain outside the room until the air has returned to normal. Technologists should contact the MR service engineer to inspect the room and equipment. Once the service engineer replaces cryogen gases and considers the system ready, technologists can resume MR scanning. This process may take several days or weeks, depending on the extent of the damage to system components. A properly designed room should have an exhaust grille in the ceiling opposite the room s entrance for venting gases. The room also should have a passive back-up system that can discharge gases in the event the primary exhaust system malfunctions. These systems should be checked annually by the service engineer ASRT. All rights reserved. 18 MR Basics: Module 7