¹H nuclear magnetic resonance (NMR) as a tool to measure dehydration in mice

Abstract

Dehydration is a prevalent pathology, where loss of bodily water can result in variable symptoms. Symptoms can range from simple thirst to dire scenarios involving loss of consciousness. Clinical methods exist that assess dehydration from qualitative weight changes to more quantitative osmolality measurements. These methods are imprecise, invasive, and/or easily confounded, despite being practiced clinically. We investigate a non-invasive, non-imaging (1)H NMR method of assessing dehydration that attempts to address issues with existing clinical methods. Dehydration was achieved by exposing mice (n = 16) to a thermally elevated environment (37 °C) for up to 7.5 h (0.11-13% weight loss). Whole body NMR measurements were made using a Bruker LF50 BCA-Analyzer before and after dehydration. Physical lean tissue, adipose, and free water compartment approximations had NMR values extracted from relaxation data through a multi-exponential fitting method. Changes in before/after NMR values were compared with clinically practiced metrics of weight loss (percent dehydration) as well as blood and urine osmolality. A linear correlation between tissue relaxometry and both animal percent dehydration and urine osmolality was observed in lean tissue, but not adipose or free fluids. Calculated R(2) values for percent dehydration were 0.8619 (lean, P < 0.0001), 0.5609 (adipose, P = 0.0008), and 0.0644 (free fluids, P = 0.3445). R(2) values for urine osmolality were 0.7760 (lean, P < 0.0001), 0.5005 (adipose, P = 0.0022), and 0.0568 (free fluids, P = 0.3739). These results suggest that non-imaging (1)H NMR methods are capable of non-invasively assessing dehydration in live animals.

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

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The MR Cap: A single‐sided MRI system designed for potential point‐of‐care limited field‐of‐view brain imaging

“…Some of these devices, such as the NMR‐MOUSE, are commercially available. Some studies have explored the use of such ultraportable “single‐sided” spectrometers and relaxometers for medical applications, such as for skin profiling, mammographic, and hydration monitoring applications. These single‐sided systems are far smaller than traditional MR scanners where the patient is interior to the magnet and thus have the potential to be true “point‐of‐care” devices.…”

Dehydration assessment via a portable, single sided magnetic resonance sensor

“…A T2‐based MR measurement can provide information related to the composition and volume of a fluid compartment. Our group previously demonstrated that multicomponent T2 relaxometry via whole‐body NMR can identify fluid depletion as a decrease in the signal amplitude from the lean tissue component . This led us to explore the localization of a similar measurement toward the skeletal muscle tissue with the ultimate goal of miniaturizing the magnetic resonance (MR) sensor.…”

“…Our group previously demonstrated that multicomponent T2 relaxometry via whole-body NMR can identify fluid depletion as a decrease in the signal amplitude from the lean tissue component. 36 This led us to explore the localization of a similar measurement toward the skeletal muscle tissue with the ultimate goal of miniaturizing the magnetic resonance (MR) sensor. Multicomponent T2 relaxometry via MRI has demonstrated sensitivity toward distinct fluid compartments within skeletal muscle tissue.…”