Fluid assessment in dialysis patients by point-of-care magnetic relaxometry

Abstract

Magnetic resonance imaging (MRI) is a powerful diagnostic tool, but its use is restricted to the scanner suite. Here, we demonstrate that a bedside nuclear magnetic resonance (NMR) sensor can assess fluid status changes in individuals at a fraction of the time and cost compared to MRI. Our study recruited patients with end-stage renal disease (ESRD) who were regularly receiving hemodialysis treatments with intradialytic fluid removal as a model of volume overload and healthy controls as a model of euvolemia. Quantitative T2 measurements of the lower leg of patients with ESRD immediately before and after dialysis were compared to those of euvolemic healthy controls using both a 0.28-T bedside single-voxel NMR sensor and a 1.5-T clinical MRI scanner. In the MRI data, we found that the first sign of fluid overload was an expanded muscle extracellular fluid (ECF) space, a finding undetectable at this stage using physical exam. A decrease in muscle ECF upon fluid removal was similarly detectable with both the bedside sensor and MRI. Bioimpedance measurements performed comparably to the bedside NMR sensor but were generally worse than MRI. These findings suggest that bedside NMR may be a useful method to identify fluid overload early in patients with ESRD and potentially other hypervolemic patient populations.

Dehydration assessment via a portable, single sided magnetic resonance sensor

“…Our prior study in hemodialysis patients showed that excess fluid in hypervolemic patients can be observed by T2 relaxometry localized to skeletal muscle 44 . Of interest, changes in weight and blood chemistry indicated that two healthy control subjects experienced dehydration during this study.…”

“…Lower extremity skeletal muscle offers an easily accessible site due to its relatively large size and a thin subcutaneous tissue layer for a portable MR sensor performing a localized measurement. A prior clinical study in hemodialysis patients from our group suggested that MRI localized to the skeletal muscle could identify fluid depletion . Hemodialysis patients are hypervolemic but 2 of the healthy control subjects became dehydrated based on their blood chemistry (serum osmolality and sodium) and weight change.…”

“…A prior clinical study in hemodialysis patients from our group suggested that MRI localized to the skeletal muscle could identify fluid depletion. 44 Hemodialysis patients are hypervolemic but 2 of the healthy control subjects became dehydrated based on their blood chemistry (serum osmolality and sodium) and weight change. MRI measurements localized toward skeletal muscle within the leg showed sensitivity toward dehydration via a decrease in the intramuscular ECF amplitude.…”

Molecular and physical technologies for monitoring fluid and electrolyte imbalance: A focus on cancer population

“…Fluid assessment in patients by point‐of‐care NMR relaxometry (schematic representation from Ref. [26]). Water loss (intracellular dehydration) is assessed using urinary tests 27 .…”

Realtime optimization of multidimensional NMR spectroscopy on embedded sensing devices

“…Only recently, owing to the advancement of permanent-magnet design 2 , integrated electronics 3,4 , and antenna miniaturization 5 , portable NMR systems 6 have emerged as a viable surrogate. Thanks to the reductions in footprint, maintenance needs and price tag, the miniaturized sensor assemblies have extended their uses beyond conventional NMR laboratories to point-of-care medical diagnostics 7,8 , subterranean explorations 9 , flow metering 10 , fluid authentication 11 , and artefact preservation 12 . In those “field” applications, it is highly desirable that the machinery operates autonomously and self-optimizes based on properties of the samples under investigation.…”