📋 Case Study

Hospital MRI Suite Grounding Interference with Life Support Equipment

60 Hz and harmonics from MRI gradient coils induced 120 mV noise on patient monitor analog inputs, triggering false arrhythmia alarms

🏗️ Project Overview

New 3T MRI installation adjacent to ICU wing in urban teaching hospital

🎯 Challenge

60 Hz and harmonics from MRI gradient coils induced 120 mV noise on patient monitor analog inputs, triggering false arrhythmia alarms

🔧 Design Approach

Installed isolated single-point reference ground (SPRG) for MRI room; implemented fiber-optic isolation for all ICU monitor data links; added 100 kHz low-pass filtering on analog sensor paths

📐 Design Diagram

_noise = 120 mV SPRG (Single-Point) Earth V = I×R = 98 mV Fiber Optic Isolation ICU Monitor LP Filter f_c = 95 kHz (100 kHz target) Alarm False Arrhythmia MRI-ICU Grounding & Isolation Design SPRG Ground Fiber Isolation LP Filter Interference

AI-generated project design illustration

📐 Key Calculations

Ground Loop Voltage

V = I × R_ground

Result: 98 mV

Matched measured interference—confirmed ground loop as root cause

Filter Cutoff Frequency

f_c = 1/(2πRC)

Result: 95 kHz

Ensured clinical signal bandwidth (DC–10 kHz) preserved while attenuating MRI switching noise

📊 Results

Zero false alarms over 6-month validation period; ECG waveform distortion reduced from 18% to <0.7% RMS error

💡 Lessons Learned

•Medical-grade grounding requires separation of safety ground (PE), reference ground (SRG), and signal ground (SG)—not just low resistance
•MRI-induced interference is often conducted via shared grounding conductors, not radiation

✅ Key Takeaways

1Medical-grade grounding requires separation of safety ground (PE), reference ground (SRG), and signal ground (SG)—not just low resistance
2MRI-induced interference is often conducted via shared grounding conductors, not radiation