Fluid Assessment in Dialysis Patients by Point-of-Care Magnetic Relaxometry

Magnetic resonance imaging (MRI) is a powerful diagnostic tool, but its use is restricted to the scanner suite. The experiments described here demonstrate that a portable nuclear magnetic resonance (NMR) sensor can assess individual fluid status changes at the bedside in a fraction of the time. Quantitative T2 measurements of the lower leg of end-stage renal disease (ESRD) patients immediately before and after dialysis were compared to those of euvolemic healthy controls using both a 0.28 T bedside single-voxel sensor and a 1.5 T clinical scanner. We find that the first sign of fluid overload is an expanded muscle extracellular fluid (ECF) space, a finding undetectable at this stage on physical exam. A decrease in muscle ECF upon fluid removal was similarly detectable with the bedside sensor. Bioimpedance results generally perform worse than MRI and comparably to the bedside NMR sensor. These findings suggest that bedside NMR measurements may be an important method to identify fluid overload early in ESRD patients and potentially other patient populations as well.