PIXImus Mouse Densitometer

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Frequently Asked Questions

How does the Lunar PIXImus densitometer work?

PIXImus utilizes Dual Energy X-ray Absorptiometry (DEXA) technology. A small x-ray source exposes the entire animal to a cone shaped beam of both high and low energy x-rays. A high-resolution digital picture (0.18x0.18mm) is taken of an image of the x-rays hitting a luminescent panel. The ratio of attenuation of the high and low energies allows the PIXImus to separate bone from tissue and, from within the tissue samples, the lean and fat. Lunar, now GE Lunar, has been manufacturing densitometers for more than 20 years for use on humans (as well as large and small animals) - so they have lots of experience.

A DEXA device sounds complex. Is the PIXImus easy to use?

GE Lunar products are designed to be user-friendly and highly automated. The software is immediately recognizable because GE Lunar utilizes Microsoft's Windows® XP operating system. Simple buttons operate the software while pictures lead you through precise animal positioning. The analysis for Total Body is completely automated. The results are logged to a file for simple access by most any statistical program.

Can the PIXImus REALLY acquire fat, lean, and bone data from the total body composition data in vivo?

Yes. A safe sedation time for a mouse is a maximum of about 7-10 minutes. With an image acquisition time for the total body of less than five minutes, the PIXImus can safely handle mice in vivo. Results directly measured are bone mineral density (BMD) and %Fat (of tissue). From these results the PIXImus can compute bone, fat and lean mass. Results today, without sacrificing the animal!

How large an animal can the PIXImus handle?

As its name implies, the PIXImus is built for automatic acquisition and analysis of bone and tissue of a mouse (10-50g). The PIXImus has software that can analyze mice and other animals outside of this range, like ob\ob and infant mice, with some manual input. The imaging window (80x65mm) is large enough for the body of a mouse or similar sized animals, but will miss a portion of the head on larger mice. The head is largely inactive bone and tissue, so “total” body composition results are more sensitive when results are determined subcranially. Additionally, the spine, femurs, tibia, abdomen, thigh or other bone and tissue regions of larger animals, such as the rat, guinea pig and marmoset monkey, are beautifully imaged and easily studied with a manually created ROI box.

How accurate is the PIXImus?

Accuracy was initially determined using phantoms of known values in the research labs at Lunar and a correlation study between the PIXImus and gravimetric and chemical extraction techniques was performed by one of their test sites. The test site utilized C57BL/J6 mice weighing between 19-29 grams (n=25), a Soxhlet, and petroleum ether. Correlation to lean tissue mass of the total body was excellent (r=0.99) where as the smaller components of fat mass and bone mass was very good (r=0.93 and r=0.99 respectively)¹. Even the bone mass and density of excised bones are accurately determined with PIXImus. The correlation to ash of excised mouse femurs (n=27) is excellent (r²=0.95). (see the abstract section for details of this study).

With all of the different chemical extraction techniques for determining body composition, how will I know if PIXImus results correlate to my technique?

You’re right, there are differences in lipid quantities extracted by different chemical techniques, so we added a calibration feature that allows you to modify the PIXImus to your technique. But the differences are small and as compared to PIXImus, both linear and reproducible. Results are easily adjusted in the post-analysis data spead.

How precise is the PIXImus?

Precision was determined at test sites where they found the PIXImus to be highly precise on both tissue and bone results when live mice (n=25, 19-29g) were imaged three times each. The mean intra-individual coefficient of variation (CV) was: lean tissue mass 0.86%, fat mass 1.60%, BMC 1.60% and BMD 0.84%. Analysis of in vivo mouse femurs (n=27) have excellent precision at 3.31% for BMC and 1.20% for BMD (see the abstract section for details of these and studies).

Note: Superior precision on live mice requires the animal to be motionless. The PIXImus has a unique, disposable, specimen tray that holds the sedated animal during the fast exposure.

With all the possible bone and tissue results, how does the PIXImus store the data?

PIXImus stores all bone, tissue, animal biographical data, ROI locations, ROI dimensions, date\time of acquisition data, plus a whole lot more, in a text file. This text file is easily imported to almost every statistical spreadsheet program available.

What is the difference between the PIXImus and PIXImusII?

The PIXImus has a more sensitive detection system and some revisions to the internal electronics and software that make it more reliable than the original PIXImus. The more costly PIXImus II replaced the initial version a few years ago.