What preparation is required before undergoing magnetic resonance imaging (MRI)?

MRI Preparation Requirements

Yes, specific preparation is required before undergoing MRI, primarily focused on safety screening for metallic objects and implants, with additional considerations for contrast agents and patient comfort.

Mandatory Safety Screening

All patients must complete a standardized safety checklist before entering the MRI suite to identify potentially dangerous items and contraindications 1, 2. This screening process is the cornerstone of MRI safety and must be performed without exception.

Items That Must Be Removed

• All metallic objects including jewelry, watches, credit cards, phones, pagers, pens, dental prostheses, and clothing with zippers or buttons 1, 2, 3
• Transdermal medication patches containing metal (arrange alternative medication delivery during the scan) 2
• Clothing with metallic components like underwire bras 2
• Patients should be provided with cotton clothing free of metal components 1, 2

Critical Implant and Device Assessment

The specific type, location, and material of any implant must be documented and verified before scheduling 1. Request the patient's implant pass and verify with the manufacturer using resources like https://mrisafety.com/ 1.

The three safety categories are 1, 2, 3:

• "MRI unsafe" = absolute contraindication (cannot proceed)
• "MRI conditional" = relative contraindication requiring specific conditions (field strength limits, positioning requirements)
• "MRI safe" = no contraindication

Absolute contraindications include most electronic implants, certain older cerebrovascular clips, and ferromagnetic foreign bodies 2. Pacemakers and implantable cardioverter-defibrillators are relative contraindications, though newer models may be MR conditional 2, 4.

Pre-Scan Physical Preparation

Patient Comfort and Positioning

• Empty bladder before scanning for maximum comfort during the study and to reduce absorbed radiation dose (particularly relevant for PET/MRI) 1
• Patient must be able to lie still for at least 5-20 minutes for static acquisitions (30-50 minutes if dynamic imaging is performed) 1

Specific Anatomical Preparations

For rectal/pelvic MRI specifically:

• Rectal cleansing and injection of appropriate amount of ultrasound gel can be performed before examination 1
• Maintain consistent scan parameters and angles when comparing pre- and post-treatment imaging 1

Contrast Agent Considerations

Gadolinium-Based Contrast Agents (GBCAs)

Assess renal function before administering GBCAs 2. Contraindications include:

• Known allergic reactions to contrast agents 1, 2
• Severe renal insufficiency 2
• Acute renal insufficiency due to hepato-renal syndrome 2

For FDG-PET/MRI Combined Studies

• Patient must fast for 6 hours before imaging 1
• Measure blood glucose before scanning; postpone if >160 mg/dL (>8.9 mmol/L) 1, 2
• Acute insulin correction does not improve brain image quality because quantitation requires steady-state conditions 1
• Document body weight for Standard Uptake Value (SUV) measurements 1

Special Population Considerations

Pediatric Patients

Sedated or restrained children require MRI-compatible pulse oximeters and capnographs capable of continuous function during scanning 1, 5. Critical precautions include:

• Avoid coiling monitoring wires 1, 5
• Place oximeter probe as far from magnetic coil as possible to prevent thermal injuries 1, 5
• Use special MRI-compatible ECG pads 1, 5
• Administer sedation as late as possible after radiotracer injection (typically 30 minutes post-injection) but before imaging 1

Patients with Seizure Risk

Continuous visual monitoring is necessary throughout the investigation, particularly important in patients with metastases-associated seizures 1.

Common Pitfalls to Avoid

• Never assume older implants are safe – always verify with manufacturer documentation 1, 2
• Thermal injuries can occur even with proper precautions if wires are coiled or metallic items remain 1, 2, 3
• Do not bring standard (non-MRI-compatible) monitoring equipment into the MRI suite – ferromagnetic components become dangerous projectiles 5
• Screen all accompanying persons (including parents) for ferromagnetic materials before entry 1, 2
• Image artifacts from implants can create signal voids and geometric distortions that compromise diagnostic quality, even when the implant is MRI-safe 1, 3

Emergency Preparedness

All emergency equipment in the MRI room must be MRI-compatible, including laryngoscope blades, oxygen tanks, and resuscitation equipment 2. Documented emergency protocols for cardiac arrest, magnet quench, and fire must be readily available 2.