A double-walled copper vessel, 32 cc in volume, was fabricated for scanning tissue specimens while maintained below freezing point. To keep specimen temperature within +/- 1 degrees C, temperature sensors within the chamber control, the rate of inflow of the cold nitrogen gas vented through the chamber. The specimen is attached to a small platform on top of a vertical pin which is attached to the computer-controlled rotating stage under the vessel. The purpose of this arrangement is to permit scanning of specimens up to 2 cm3 that (1) cannot be "fixed" (e.g., with formalin) because of analyses which are incompatible with prior fixation (certain immunohistochemistry and biomolecular methods), or (2) are "snap"-frozen during a transient process, such as the accumulation and/or washout of radiopaque indicators. Examples of "cryoscans" of porcine carotid and coronary artery wall opacification in either untouched or acutely stented arteries, snap-frozen immediately after selective intra-arterial injection of a contrast agent, show accumulation of contrast in the extravascular space indicating increased endothelial permeability or endothelial and medial disruption following stent placement. The detection of contrast in the adventitia suggest that vasa vasorum deliver the contrast agent from the main lumen to the adventitial extravascular space but not to the media.