1.2 Patient Assessment and Monitoring

Patient Assessment and Monitoring

Patient assessment and continuous monitoring are critical components of a safe MRI examination. Because the MRI scanner environment is a closed, high-noise, and highly magnetic space, patients are subject to both physical and psychological stressors. The MRI technologist must possess the clinical skills to assess a patient's baseline physiological state, recognize deviations from normal parameters, safely employ MR-compatible monitoring equipment, and effectively manage patient anxiety and claustrophobia.

Baseline Vital Signs

Before initiating any scan, a baseline assessment of the patient’s vital signs must be conducted, particularly if the patient is scheduled for contrast administration, sedation, or is critically ill.

• Pulse/Heart Rate: Can be assessed palpatorily at the radial, carotid, or femoral arteries. In patients with irregular rhythms, an apical pulse (measured via stethoscope over the heart for one full minute) is recommended.
• Respiration: Must be monitored by observing the rise and fall of the chest. Tachypnea (>20 breaths/min in adults) can indicate anxiety, hypoxia, or pain, whereas bradypnea (<12 breaths/min) may indicate drug-induced respiratory depression.
• Temperature: Elevated temperature (hyperthermia) is a safety concern in MRI. Because radiofrequency (RF) pulses deposit energy into the body (measured as Specific Absorption Rate, or SAR), patients with pre-existing high fevers are at risk of thermal injury, as their thermoregulatory capacity is already compromised.

MR-Compatible Monitoring Equipment and Patient Safety

Standard clinical monitoring equipment contains ferromagnetic materials and wires that can act as antennas, causing RF-induced heating and burns. All monitors used in Zone IV must be designated as MR Safe or MR Conditional.

1. RF Burn Prevention: When using ECG leads or pulse oximeters, the technologist must ensure that lead wires do not touch the patient’s bare skin. Furthermore, cables must be run in straight lines parallel to the main magnetic field (B0) and must never form loops. Wires that cross or loop can undergo electromagnetic induction, creating high-voltage currents that cause severe, third-degree skin burns.
2. The Magnetohydrodynamic (MHD) Effect: When blood (a conductive fluid containing ions) flows through a strong magnetic field (B0), a voltage is induced. On an ECG trace recorded inside the scanner, this MHD effect manifests as an elevated T-wave (often mimicking myocardial infarction). This is a physical artifact, not a physiological pathology. Technologists must recognize this artifact and rely on pulse oximetry or other metrics to verify actual heart rate and rhythm.

Assessment of Special Populations

• Pediatric Patients: Infants and young children have a high surface area-to-mass ratio and immature thermoregulatory centers. They are highly susceptible to hypothermia (especially when sedated) and must be kept warm using non-metallic blankets. Conversely, they can easily overheat during fast spin-echo sequences, requiring continuous temperature monitoring.
• Geriatric Patients: Elderly patients often present with thin, fragile skin, making them prone to skin tears and pressure ulcers on the hard patient table. Abundant padding under the knees, lower back, and elbows is required. Additionally, sensory deficits (hearing loss, cognitive decline) require clear, face-to-face communication.
• Pregnant Patients: While there are no documented harmful effects of MRI on the human fetus, routine scanning is typically avoided in the first trimester unless the clinical benefit outweighs the risk. Gadolinium contrast is contraindicated in pregnancy because it crosses the placenta and enters the amniotic fluid, where it can dechelate into toxic free gadolinium ions.
• Sedated Patients: Because sedated or anesthetized patients cannot verbally communicate pain or overheating, they must be continuously monitored using MR-conditional pulse oximetry, end-tidal CO2 (for respiration), and ECG.

Managing Claustrophobia and Anxiety

Claustrophobia affects approximately 1% to 15% of patients undergoing MRI, leading to aborted scans or severe motion artifacts.

• Physiological Signs: Panic attacks, hyperventilation, tachycardia, cold sweats, and verbal refusal.
• Technologist-Led Interventions:
  • Communication: Giving the patient a realistic sense of control by providing an emergency squeeze bulb and reminding them that the technologist can hear them via the intercom.
  • Physical Adjustments: Positioning the patient feet-first when possible (which keeps the head near or outside the bore entrance), using wider-bore scanners (70 cm vs. 60 cm), providing maximum bore lighting, and turning on the bore ventilation fan to its highest setting.
  • Visual Aids: Utilizing prism glasses or mirrors that allow the patient to look out of the bore toward the room.
  • Pharmacological Management: For severe claustrophobia, anxiolytics (such as alprazolam or diazepam) may be prescribed by the ordering physician. If oral sedatives are taken, the patient must be observed for respiratory depression, and a designated driver must accompany them home.