Lecturer Gersh Zvi Taicher

Contact michal.neeman@weizmann.ac.il

Abstract During the last decade, Nuclear Magnetic Resonance (NMR) Body Composition Analyzers (BCA) became the ?gold standard? for measuring fat and lean masses, free fluids, and total water. More rapid, accurate, and precise than other methods, NMR technology allows for one-minute measurements without anesthesia. EchoMRI? BCA are currently available for testing ?body composition? in objects as small as 2 milligrams to as large as 250 kg. NMR-MRI based EchoMRI? quantitative method for measuring body soft tissue composition of mice was compared to DEXA and chemical methods. Lean and fat mass measurements by both noninvasive technologies were made on live mice, and then by chemical analysis after euthanasia. Measurement by EchoMRI? required just 0.6 minute compared to 15 to 20 minutes for DEXA scanning and 1 - 3 days for chemical analysis. Unlike DEXA, live measures by EchoMRI? did not require anesthesia. Data from EchoMRI? and DEXA were in good agreement. Precision was found to be better for EchoMRI? than for DEXA. The CV for fat in mice was in the range of 0.3% - 0.4%, compared to 2.9% - 13.0% for DEXA. Changes in body composition in response to dietary manipulation were easily demonstrated using EchoMRI?. An increase in fat mass of 0.6 gram after 1 week in a group of 10 mice was demonstrated without change in mean body weight. The EchoMRI? methodology of Whole Body Composition Analysis provided similar data to DEXA but did not require anesthesia, and was much more rapid and precise. The greatest value of this new technology is its ability to make frequent sequential measurements of changes in body composition. Computed Tomography (CT) technology has recently been applied to small animal research. There are several technologically-unique features that make the LaTheta? micro-CT Scanner for live animals a top instrument in its class. A highly sensitive x-ray detector enables a substantial reduction of radiation dose. This makes it possible to perform longitudinal studies on the same animal. Further, low radiation power also helped to enhance the image contrast. The number of slices scanned can be varied, starting from the single slice in just 4.5 seconds, to a whole body scan in about 8 minutes. The scanning procedure is interactive with every new slice appearing in 4.5 seconds. The system allows for rats up to 1.5 kg to be scanned. The instrument is equipped with four casters which allow taking the device into any room, making it compact and portable. LaTheta? does not require any special knowledge about x-ray technology, the software is very easy to operate, the results produced very fast, and its mobility allows sharing the instrument among several research groups. Quantification of the scanned images implemented in the software includes: visceral, subcutaneous and total fat weight, fat content in liver, muscle or other regions, BMD, mechanical strength and morphology with automatic cortical/trabecular bone recognition, etc. Body Composition Analysis for mice, rats, and other small animals by CT was compared to the NMR method. The correlation coefficient for total body fat and lean mass was 0.99 and 0.98 respectively. The correlation for total fat and visceral fat was 0.99. Although the CT technique provides many important details related to spatial distribution of different tissue types, the NMR technique is much faster and doesn?t require anesthesia.