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A double walled copper vessel, 32 cc in volume, was fabricated for micro-CT scanning tissue specimens maintained at cryogenic temperature. The space between the two nested vessels was evacuated and in two opposing sides of the vessel the copper has been replaced by beryllium foil. Nitrogen gas, boiling off liquid nitrogen, is injected continuously into the top of the chamber during the scanning process. Just prior to venting from the vessel the gas is heated and directed through a narrow gap over the outside of the beryllium windows so as to maintain the beryllium windows frost free. A temperature detector within the chamber is used to control the rate of inflow of the nitrogen gas. The frozen specimen is attached to a small horizontal platform on top of a vertical stainless steel pin which exits the base of the vessel through a closely fitting hole and is attached to the computer-controlled rotating stage under the vessel. The vessel and rotation-stage assembly is mounted on a computer-controlled horizontal translation stage which can move the specimen out of the x- ray beam, from time to time, for x-ray beam calibration purposes. The purpose of this arrangement is to permit scanning of specimens that: 1) either cannot be fixed (e.g., with formalin) because of biomolecular analyses which are incompatible with prior fixation, or 2) are snap-frozen during a transient process, such as the accumulation and/or washout of radiopaque indicators distributed in microvascular or extravascular compartments, which lasts only seconds and hence is too fast for normal micro-CT methods to capture.
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