Quantitative Assessment of MRI Bore Fan Airflow and Its Association with Patient Warming Events
Abstract
Purpose
Radiofrequency (RF) power deposition during MRI can cause patient warming, leading to discomfort and potential motion artifacts. Convective heat removal within the magnet bore is provided by the built-in ventilation fan; however, fan performance is not quantitatively assessed during scanner acceptance or routine quality assurance (QA). This study aimed to develop a practical method to quantify MRI bore airflow and to evaluate its association with patient warming events.
Methods
Forty clinical MRI scanners were evaluated using a custom-built, non-metallic pinwheel anemometer. Measurement consistency was assessed on 14 scanners using both 30-second and 1-minute intervals. Following validation, standardized 30-second measurements were then performed on all scanners and converted to rotations per minute (RPM) at multiple locations (isocenter, anterior, left, and right) for two patient table configurations corresponding to typical head and body imaging positions. Patient warming events were documented by MRI technologists over a two-week period and included subjective complaints of excessive warmth and observable signs such as sweating.
Results
Airflow measurements were highly reproducible, with no significant difference between 30-second and 1-minute sampling intervals (p=0.64). Across the fleet, bore airflow varied substantially, ranging from 0 to over 200 RPM. Patient warming was reported on 18 scanners; among these, 12 (67%) demonstrated low airflow (0–66 RPM), including four scanners with nearly no detectable airflow. Statistical analysis confirmed a significant association between reduced bore airflow and patient warming events (p = 0.0004). Quantifiable improvements in RPM were observed following corrective interventions such as fan replacement or optimized table pad placement.
Conclusion
This study demonstrates that MRI bore airflow can be reproducibly quantified using a simple, MR-safe approach. The high variability observed across scanners and the strong correlation between low airflow and patient warming underscores the importance for incorporating bore airflow assessment into routine MRI QA to improve patient thermal comfort.