Summary: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°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 cm 3 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.
Micro-CT angiography of small laboratory mammal organs visualizes vascular branches on a large range of scales, ranging from root-level branches (~ 1 mm) to endarteriolar vessels (10-40 µm). Multiscale vascular tree segmentation is facilitated by the ability to set a single grayscale threshold value for vessels of all generation levels. Due to the non-ideal modulation transfer function (MTF) of the imaging system, object contrast varies significantly with scale, and the definition of a grayscale threshold for vessel segmentation becomes a problem. We found that performing a point spread function (PSF) deconvolution on the micro-CT projection images significantly reduces the thresholding problem in terms of restoring the smallest vessels' grayscale and delineation. The increased noise from performing a PSF deconvolution will not have a significant effect on the overall signal-to-noise ratio of the images. The PSF deconvolution was successful only when it accommodated the spatial variation of the PSF.
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