Elevated Body Mass Index (BMI) MRI Safety Policy

Policy:  

MRI procedures performed will be conducted in accordance with established protocols and in reference to the American College of Radiology Guidelines. Appropriate precautions will be followed to ensure safety of all patients, personnel and equipment. 

Purpose: 

This Policy provides safety guidance, education and scanning guidelines to MRI Level II personnel who may, in the course of their job responsibilities, need to evaluate and scan a patient whose body habitus is at the upper limits of the magnet bore dimensions. This policy applies to patients who when positioned within the magnet bore (without padding) have no natural air gap between their skin and the sides of the magnet bore. 

Background: 

The United States obesity prevalence, as of March 2020, was 41.9% per the Centers for Disease Control and Prevention. UCSF has many campuses and satellites that are home to MRI systems of multiple manufacturers and models. The magnet bore diameters range from 60 to 80 cm. MRI procedures of obese patients are challenging because of the physical limitations of bore diameter and the increased risk of thermal burns. Patient burns are the most common MRI-related adverse event.  

Definitions:  

  • Magnetic resonance imaging (MRI): Medical imaging technique that uses a strong magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in the body.
  • MRI Safety Padding: Refer to UCSF padding policy
  • Medical Supervision (according to IEC 60601-2-33): Requires a positive assessment by a qualified medical practitioner of the risk versus benefit for a particular scan, or a decision by a qualified surrogate of the practitioner that the patient satisfies a set of objective criteria, formulated by a qualified medical practitioner, for the parameters of the scan and the condition of the patient. Medical supervision may entail physiological monitoring of the patient by means of devices designed to measure or assess various physiological states (e.g., heart rate, ECG trace, blood pressure, pulse oximetry).
  • Specific Absorption Rate (SAR): Power absorbed by a kilogram of tissue after exposure to transmitted RF fields/energies (measured as W/Kg). Radiofrequency power deposition results in heating of patient tissues.
  • Normal Operating Mode: “Routine” level at which most clinical MRI imaging parameters currently used are performed, being considered safe for all patients, regardless of their condition.
  • First Level Controlled Operating Mode: FDA regulated mode in which ≥1 outputs may cause physiologic stress. Active medical supervision is required to use this mode to ensure that a careful assessment of benefits vs risks have been assessed. The FDA requires equipment operating in this mode to display and record db/dt and SAR levels. The MRI technologist must positively acknowledge this at the console before being allowed to proceed with scan.
  • Second Level Controlled Operating Mode (for research only): Multiple outputs may produce significant risk for patient, approval by Institutional Review Board is required.
  • International Electrotechnical Commission (IEC): International standards organization that prepares and publishes international standards for all electrical, electronic, and related technologies.

Procedure: 

  1. How to measure the patient’s body habitus and make the decision to safely proceed:
    1. Measure the patient with their body in the position that they will be scanned in. Using a measuring tape, measure the widest part of the body that will enter the magnet bore from left to right. Patient may have their arms above their head or have their arms down, close to the sides of their body without air gaps. Most often will be from left elbow to right elbow.
    2. If patient width measures less than the magnet bore diameter, proceed with the MRI procedure, with proper padding in place.
    3. A “trial run” of patient positioning in the scanner with proper padding in place is recommended when the patient’s diameter is virtually the same as the magnet bore diameter.
    4. There are patients who upon being measured, are significantly larger than the MRI bore and a “trial run” would be fruitless. In this scenario, the decision to attempt a “trial run” is left to the discretion of the MRI technologist who performs the patient measurement.
    5. If the patient’s medical team have identified that the patient is medically unstable, do not attempt a “trial run” for patient safety.
  2. We recognize that transferring to another MRI location cannot be done expeditiously, therefore a “trial run” is of particular importance with patients whom their medical team has determined are medically urgent.
  3. Transfer options to a UCSF wide bore (70cm) MRI system are available.
  4. The patient MUST wear a UCSF provided patient gown – no exceptions.
  5. Padding should be placed between the patient’s thighs, calves, legs to prevent thermal burns. UCSF provided pants are not considered adequate padding.
  6. Do NOT permit patients to wear clothing items (e.g., sportswear, underwear, yoga pants, socks) that have metal-based fibers.
  7. All jewelry must be removed. Visually and verbally verify that there are no metallic objects contacting the patient’s skin (e.g., drug delivery patches with metallic components, jewelry, necklaces, bracelets, key chains)
  8. Patient to be screened with the metal detection wand prior to entrance to Zone IV.
  9. Prepare the patient for the MRI procedure by ensuring that MRI Safety Screening Form has been completed.
  10. Ensure proper placement of hearing protection. Use ear plugs and headphones whenever possible; 2 auditory layers of protection is preferred.
  11. Keep coverings/blankets to no more than 1 or none, to help decrease patient heating. Explanation to the patient may be helpful in this scenario.
  12. There should be no direct contact between the patient’s skin and the transmit RF body coil of the MR system. Approved MRI padding (minimum recommended thickness of 1cm) should be placed between the patient’s skin and transmit RF coil that is used for the MRI procedure (alternatively, the transmit RF coil itself should be padded).
  13. A bed sheet/blanket is not considered appropriate padding.
  14. The patient may need to place his/her arms over his/her head. Usage of padding between the patient’s tissue and the transmit RF body coil of the MR system may accomplish this task. This is especially important for MR examinations that use the transmit RF body coil or other large RF coils for transmission of RF energy.
  15. When possible, confirm and maintain communication with the patient.
  16. Before the start of the MRI procedure, and if the patient is capable, they should be instructed to squeeze the emergency ball if they experience any focal heating sensations or health emergency during the MRI procedure.
  17. If patient is sedated or under general anesthesia, continuous monitoring of the patient, with exam pauses to visually check patient and the position of padding is expected.
  18. The ventilation system of the MRI system should be “On” and at the highest fan setting for the entire MRI procedure.
  19. MRI system room should have low humidity and the room temperature no greater than 70℉or 21℃.
  20. “Normal Operating Mode” is to be used for MRI procedures with obese patients due to having reduced thermoregulatory capacity.
  21. Review protocol to be used for the body part ordered, preferably a “Low SAR” protocol.
  22. Avoid unnecessary sequences and repeating of multiple sequences.
  23. When alteration of sequence parameters is necessary, keep in mind these approaches:
    Flip Angle Reduce flip angles (for FSE sequences, use 60 – 130 degrees rather than 180 degrees refocusing pulses) 
    Number of Slices Reduce number of slices, don’t over scan 
    Number of Echoes Reduce number of echoes in a multi-echo sequence 
    Alternate Alternate high and low SAR sequences to allow for patient cooling 
  24. Use only electrically conductive devices, equipment, accessories (e.g., ECG leads, electrodes), and materials that have been thoroughly tested and determined to be safe or otherwise acceptable for MRI procedures.
  25. Carefully follow the MR Safe or MR Conditional criteria and recommendations for implants and devices made from electrically conductive materials (e.g., bone fusion stimulators, neurostimulation systems, cardiac devices, cochlear implants).
  26. Before using electrical equipment, check the integrity of the insulation and/or housing of all components including surface RF coils, monitoring leads, cables, and wires. Preventive maintenance should be practiced routinely for such equipment.
  27. Remove all non-essential electrically conductive materials from the MR system before the MRI procedure (e.g., unused surface RF coils, ECG leads, EEG leads, cables, wires).
  28. Keep electrically conductive materials (that must remain in the MR system) from directly contacting the patient by placing thermal and/or electrical insulation between the conductive material and the patient.
  29. Keep electrically conductive materials (that must remain within the transmit body RF coil or other transmit RF coil) from forming conductive loops. Note: The patient’s tissue is conductive and, therefore, may be involved in the formation of a conductive loop that can be circular, U-shaped, or S-shaped.
  30. Position electrically conductive materials to prevent “cross points”. A cross point is the point where a cable crosses another cable, where a cable loops across itself, or where a cable touches either the patient or sides of the transmit RF coil more than once. Even the close proximity of conductive materials with each other should be avoided because cables and RF coils can capacitively couple (without any contact or crossover) when placed close together.
  31. Position electrically conductive materials (e.g., cables, wires) to exit down the center of the MR system, not along the side of the MR system or close to the transmit RF body coil or other transmit RF coil.
  32. Do not position electrically conductive materials across an external metallic prosthesis (e.g., external fixation device, cervical fixation device) or similar device that is in direct contact with the patient.
  33. Allow only properly trained individuals to operate devices (e.g., monitoring equipment) in the MR environment.
  34. Follow all manufacturer instructions for the proper operation and maintenance of physiologic monitoring or other similar electronic equipment intended for use during MRI procedures.
  35. Electrical devices that do not appear to be operating properly during the MRI procedure should be removed from the patient immediately.
  36. RF surface coil decoupling failures can cause localized RF power deposition levels to reach excessive levels. The MR system operator will recognize such a failure as a set of concentric semicircles in the tissue on the associated MR image or as an unusual amount of image non-uniformity related to the position of the transmit RF coil.
  37. Closely monitor the patient during the MRI procedure. If the patient reports sensations of heating or other unusual sensation, discontinue the MRI procedure immediately and perform a thorough assessment of the situation including documentation of parameters and outreach to a radiologist for evaluation of the patient.

Responsibilities: 

  1. Always follow UCSF MRI Safety Policies and Procedures including training, screening, signage, and use of MRI Safe scanning guidelines.
    1. Know and reference the policy as needed.
  2. Technologist to review MD order and radiologist protocol prior to MRI procedure start.
  3. Gloves and any other necessary personal protective equipment (PPE) shall be worn.
  4. Communicate any compliance challenges to the MRI Supervisor on duty, MRSO Supervisor or MRI Leadership.
  5. When unsure/unaware of what to do or have questions, contact the MRI Supervisor on duty.
  6. Perform hand hygiene before and after patient care, after touching soiled objects before touching clean objects, in between rooms, and whenever appropriate.
 
IN AN EMERGENCY 
IMMEDIATELY contact MRI Supervisor on duty, Security, or dial 9-911 from a hospital phone, (in this order). 
 

Key Points: 

  1. MRI procedures of obese patients are challenging because of the physical limitations of bore diameter and the increased risk of thermal burns (most common adverse MRI event).
  2. The ultimate decision to proceed in the setting of an elevated BMI patient who exceeds bore size rests with the performing MRI technologist, who can escalate to a supervisor or MRI Safety Officer as needed.
  3. Optimal results are achieved when the exam is tailored to the patient-specific needs.
  4. The adoption and regular practice of these guidelines will ensure that patient safety is maintained.
  5. In an emergency, contact MRI Supervisor on duty (415-443-5408), Security, or dial 9-911 from a hospital phone, (in this order).

Elevated BMI Patient Transfer Policy

The purpose of this policy is to ensure the safe transport of elevated MBI patients from Parnassus to Mission Bay for MRI. The Mission Bay campus has MRI systems with slightly larger bore diameters that can potentially accommodate larger patients. In circumstances where an inpatient cannot be scanned on a Parnassus MRI system due to bore restrictions, transport of that patient to Mission Bay for an MRI scan will be arranged provided:

  1. Radiology staff have determined that an MRI on Parnassus scanners is not feasible. 
  2. No alternative imaging modality can address the clinical question. Vetting, scheduling, transporting and performing these patients is time-consuming. All the effort should be reserved only for those patients who have a strong indication for MRI. The patient’s attending will consult with the attending radiologist regarding the necessity for the patient to have an MRI. An attending radiologist must approve all cases to verify medical necessity.

If these conditions are met, then the transport process will proceed as follows:

  1. The Parnassus MRI technologist will complete the MRI Elevated BMI Patient Transport Checklist (Appendix A below). This form is to be completed by MRI staff in collaboration with the patient’s nurse prior to transport. If there are any affirmative answers noted on the checklist, a hard stop is placed on the transport, and the exam is postponed or canceled. If the elevated BMI patient is not ambulatory, the patient is to be transported by gurney, with a Hoover Matt placed under the patient prior to transport. To ensure that the patient is properly screened, the MRI screening form must also be completed and reviewed by the Parnassus MRI technologist in advance of the transfer.
  2. Scheduling and Coordination of MRI scan at Mission Bay. Generate an inpatient order in Radiant for the MRI exam. Contact the radiologist front desk at Parnassus, 415-353-1968, to reassign the inpatient order to Mission Bay. Contact the Mission Bay MRI supervisor at pager 415-443-5415 (MB Radiology front desk 476-5168) to arrange for scheduling of the MRI exam. Allow for a scheduling window of at least 1 to 2 days.
  3. Transport of patient to Mission Bay. Patients will be transported in accordance to the guidelines outlined in the policy, “Transport and Care of Adult Patients for Off Unit Procedures.” The unit nurse will arrange for ambulance transport for arrival at the MRI suite at least 30 minutes prior to scheduled exam time.
  4. The patient will remain under the care of the referring physician during the transport and standard of care will be maintained. If the patient is in a critical care unit, the patient must be accompanied during transport by appropriate medical personnel including physicians and nurses.

MRI Elevated BMI Patient Transport Checklist

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MRI Safety Guidelines