1.4 Infection Control and Aseptic Technique

Infection Control and Aseptic Technique in MRI

Introduction

In the MRI environment, infection control is a critical component of patient safety and occupational health. The unique physical environment of MRI—characterized by a high-strength static magnetic field, radiofrequency (RF) energy, and rapidly switching gradient magnetic fields—imposes special constraints on how infection control is practiced. This section details standard precautions, transmission-based precautions, and the principles of aseptic technique required for the ARRT MRI registry exam.

Medical Asepsis and Standard Precautions

Medical asepsis, often referred to as "clean technique," involves procedures used to reduce the number and transfer of pathogenic microorganisms. Standard precautions are the foundation of medical asepsis and must be applied to the care of all patients, regardless of their infectious status.

Hand Hygiene Protocols

Hand hygiene is the single most effective measure to prevent the spread of infections.

• Alcohol-Based Hand Rubs: The preferred method for routine hand decontamination if hands are not visibly soiled. It should be applied and rubbed over all surfaces of the hands and fingers for a minimum of 15 to 20 seconds until dry.
• Soap and Water Washing: Mandatory when hands are visibly soiled, contaminated with blood or body fluids, or when caring for patients with known or suspected Clostridioides difficile (C. diff) or Norovirus. The bacterial spores of C. diff are physically resistant to alcohol and must be mechanically washed away under running water using friction for at least 20 seconds.

Personal Protective Equipment (PPE) Selection

PPE must be selected based on the anticipated exposure to blood, body fluids, secretions, or excretions:

• Gloves: Must be worn when touching blood, body fluids, mucous membranes, non-intact skin, or contaminated surfaces. Gloves must be changed between patients and immediately after completing a dirty task on the same patient.
• Gowns: Worn to protect skin and prevent dirtying of clothing during procedures likely to generate splashes or sprays of blood or body fluids (e.g., placing IVs or handling active bleeding).
• Masks, Goggles, and Face Shields: Worn during procedures likely to generate splashes, sprays, or aerosols (e.g., clearing obstructed lines or during invasive MR arthrograms).

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Transmission-Based Precautions

When standard precautions are insufficient to prevent transmission of a known pathogen, transmission-based precautions are implemented. These are divided into three categories based on the route of transmission:

1. Contact Precautions

Contact precautions prevent transmission of infectious agents spread by direct or indirect contact with the patient or the patient's environment. Common pathogens include Methicillin-Resistant Staphylococcus aureus (MRSA), Vancomycin-Resistant Enterococci (VRE), and C. diff.

• PPE Requirements: Gown and gloves must be donned prior to entering the MRI scan room (Zone IV) or patient holding area.
• MRI Equipment Considerations: Cover positioning sponges, coils, and patient tables with protective plastic barriers. All patient-contact surfaces, including the inside of the MRI bore, must be cleaned after the scan with EPA-registered hospital disinfectants. For C. diff, a sporicidal agent (typically a 1:10 bleach-based solution) must be used.

2. Droplet Precautions

Droplet precautions prevent transmission of pathogens spread through close respiratory or mucous membrane contact with respiratory secretions. Examples include influenza, pertussis, mumps, and Neisseria meningitidis.

• PPE Requirements: Healthcare workers must wear a standard surgical mask when working within 3 feet of the patient.
• MRI Equipment Considerations: The patient must wear a surgical mask during transport and during the MRI scan. The technologist must verify that the patient's mask does not contain a metallic nose-strip, which can heat up and cause skin burns during RF transmission.

3. Airborne Precautions

Airborne precautions prevent transmission of infectious agents that remain infectious over long distances when suspended in the air. Examples include active pulmonary Tuberculosis (TB), measles (rubeola), and varicella (chickenpox).

• PPE Requirements: Staff must wear a fit-tested N95 respirator or a Powered Air-Purifying Respirator (PAPR) before entering the patient's room or the scan room.
• MRI Equipment Considerations: The patient must wear a surgical mask (non-metallic) during transport and scanning. Standard MRI suites are not equipped with negative-pressure air circulation. Therefore, after scanning an airborne-precaution patient, the room must remain vacant for a specified time (typically 30 to 60 minutes, depending on the HVAC system's air exchange rate) to allow air filtration to clear infectious particles before scanning the next patient.

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Surgical Asepsis and Sterile Fields

Surgical asepsis, or "sterile technique," is the complete removal of all microorganisms, including spores, from an object or area. This is required during invasive procedures performed in the MRI suite, such as MR-guided breast or prostate biopsies, MR arthrography, and intrathecal gadolinium injections.

Principles of Establishing and Maintaining a Sterile Field

A sterile field is a specified area prepared to receive sterile equipment and materials. The technologist must strictly adhere to the following aseptic principles:

1. Sterile to Sterile: Only sterile objects may touch sterile objects. Any contact with a non-sterile object instantly contaminates the field.
2. The 1-Inch Border: The outer 1-inch (2.5 cm) margin of a sterile drape or sterile wrap is considered unsterile. Items must be dropped or placed within the center of the field, away from this border.
3. Below the Waist Level: Any sterile object or portion of the field held below the level of the waist or table top is considered contaminated, as visual monitoring is impaired.
4. Visibility and Supervision: Never turn your back on a sterile field or leave it unattended. If you cannot see the field, it is considered contaminated.
5. Air Flow Control: Avoid talking, coughing, sneezing, or reaching across a sterile field. Keep air turbulence to a minimum.
6. Moisture and Capillary Action: If a sterile drape becomes wet, liquid can seep through from the unsterile table surface beneath. This is called strike-through (or wet contamination) and immediately contaminates the sterile field.

Opening Sterile Packs

To open a sterile pack or tray without contaminating the contents:

1. Place the pack on a clean, dry surface.
2. Open the first flap away from your body, reaching around the package rather than over it.
3. Open the side flaps.
4. Open the final flap toward your body to prevent your unsterile arm from crossing over the exposed sterile items.

MR-Compatible Sterile Supplies

Every item introduced into Zone IV during a sterile procedure must be verified for MR safety.

• Needles and Syringes: Standard biopsy needles or spinal needles are often ferromagnetic. Technologists must verify that sterile trays contain non-ferromagnetic needles (e.g., made of titanium, aluminum, or high-grade non-magnetic stainless steel) to prevent them from becoming projectiles or suffering torque under the static magnetic field ($B_0$).
• Coil Compatibility: RF coils used for biopsies (e.g., breast biopsy coils) must be cleaned using manufacturer-approved agents. Disinfecting agents must not degrade the plastic housing, as cracks can expose patients to internal high-voltage components and lead to RF burns.