Frequently Asked Questions about measurement procedure

• How does the EchoMRI™ system work to measure fat, lean, and free water?
• How is an animal scanned?
• What is the lean mass as measured by the EchoMRI™ system?
• What organs are considered to be lean mass?
• What are “free water”, “free body fluids”, and “total body water”?
• Why is canola oil used to conduct a system test? Can other fat be used as a test sample?
• Can the animals move in the holders?
• Why does the total body weight differ from the sum of the weight of its components?
• What is the difference between measuring body composition by EchoMRI™ in a mouse and in a human (or in substantially different sizes of animals)?

Q. How does the EchoMRI™ system work to measure fat, lean, and free water?
A. In general, NMR instruments create contrast between soft tissues by taking advantage of the differences in relaxation times of the hydrogen spins and/or hydrogen density in these tissues. Radio frequency signals are generated by hydrogen nuclei due to precession of the spin axes. The amplitude, duration, and spatial distribution of these radio frequency signals are related to properties of the material investigated by the NMR technique. Tissue contrast is high between fat, body free fluid, and muscle based on NMR signal amplitude and relaxation times, and can be further enhanced by application of certain radio frequency sequences.

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Q. How is an animal scanned?
A. To be measured, an animal is placed in a specially sized, clear plastic holder without sedation or anesthesia. The holder is then inserted into a tubular space in the side of the EchoMRI™ system. The researcher then presses a button on the LCD screen to scan the animal. The fat, lean mass, body fluids, and total body water are measured in grams.

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Q. What is the lean mass as measured by the EchoMRI™ system?
A. Lean is presented as equivalent of muscle mass. However, this mass includes muscle and organs.

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Q. What organs are considered to be lean mass?
A. All organs are eventually presented as lean mass.

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Q. What are “free water”, “free body fluids”, and “total body water”?
A. “Free body fluids” can be found in the stomach and bladder. In experiments, for a limited time, water can be detected after it is injected into abdominal cavity of an animal, until it gets absorbed. Some of our customers have found a way to correlate free fluids in mice with edema. “Total body water” is analyzed as the sum of “free body fluids” and 80% of lean weight. In practice, the amount of water or lean tissue can depend on hydration, and we choose 80% as a representative fraction.

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Q. Why is canola oil used to conduct a system test? Can other fat be used as a test sample?
A. From our experience with testing many animals (including chemical analysis), we found that, on average, the amount of fat in mice and rats can be well represented by the amount of canola oil. EchoMRI measures the relaxation time of hydrogen in molecules of fat within the subject, and on average, canola oil has the same density of hydrogen as animal fat.

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Q. Can the animals move in the holders?
A. Animals are able to move in the holders since they are without anesthesia or sedation. It is best, however, to use the smallest volume holders that can hold the animal to restrict its movement, and so reduce the measurement errors caused by motion.

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Q. Why does the total body weight differ from the sum of the weight of its components?
A. Our systems do not currently measure and quantify things such as bone, solid intestinal content, and hair. Fat, lean, and free water are directly measured and quantified; everything else is not.

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Q. What is the difference between measuring body composition by EchoMRI™ in a mouse and in a human (or in substantially different sizes of animals)?
A. Due to the vast size differential between the two test subjects, the two systems will obviously operate using different hardware parameters for the system. However, the methodology is exactly the same for our systems, regardless of subject size.

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