X-RAY MICROSCOPY 



avoided. Thr injection of contnist nuMliuni Conventionally fixed material, both ani- 

 into small local arteries produces heautifully mal and linnian, can be readily examined by 

 detailed microangiograms, but cannot be re- the projection method, but it- must be re- 

 garded as other than a blood displacement membered that histological fixatives dena- 

 techni(|ue unrelated to the normal circula- ture protein and appreciably alter x-ray 

 tory picture. X-ray microscopy used in con- transmission. Also no firm conclusions should 

 junction with circulating contrast medium be drawn regarding the functional status of 

 provides a new method of observing the ves- the blood vessels pi'ior to death since fixatives 

 sels of the microcirculation. themselves produce vascular changes. The 



The water soluble iodinated organic class use of such microangiograms should therefore 



of radiopaque compounds may be used for be restricted to the study of vascular anat- 



microangiography, but the best results in the omy. 



living animal have been obtained with The best projection micrographs are ob- 

 Thorotrast, which is a colloidal solution of tained from freshly injected but unfixed ma- 

 25 % thorium dioxide. It is nonirritating to terial, it being possible to record large areas 

 vascular tissue and owing to its small par- of moderately thick (1-5 mm) specimens 

 tide size (0.1 micron) readily enters all parts without a blurring of the superimposed vas- 

 of the vascular network. Its high radiopacity, cular images such as limits conventional 

 combined with the fact that it persists in the microradiography. For example, thick sec- 

 blood stream for several hours or more, tions (taken from the kidney, stomach and 

 makes it very suitable for imaging small intestine of the freshly killed albino rat, after 

 blood vessels in the living animal by x-ray retrograde injection of the aorta with Mi- 

 microscopy. The dose should be based on cropaque) showed that the glomerular tufts 

 the estimated plasma volume of the animal and intertubular capillaries of the kidney 

 to reduce circulatory disturbances, and given could be imaged without diflficulty. The 

 intravenously or intra-arterially at some arteriolar, capillary and venular components 

 point distant from the vascular field under of the mural plexuses of the intestine, In- 

 st udy. A dye should be added to the Thoro- eluding the capillary loops within the villi, 

 trast to increase vessel visibility during could also be clearly visualized, 

 operative procedures, since its accidental Projection studies of the rabbit ear in the 

 escape quickly opacifies a tissue area. Speci- freshly killed animal (following bilateral 

 mens injected with Thorotrast are not fixed carotid injection with Micropacjue) reveal 

 by formalin, but can be fixed with alcohol or the extraordinary complexity of the periph- 

 acids (12). eral vascular network. The continuity of its 



Vascular Results. Projection x-ray mi- small arteries and arterioles with the capil- 

 croscopy is highly suited to the study of the lary bed and the draining venules are demon- 

 small vessels which go to make up the micro- strated with almost diagrammatic clarity, 

 circulation. All the blood vessels remain in The central artery of the ear and its sub- 

 focus owing to the great depth of field of the sidiary branches are seen to give rise to 

 x-ray microscope. This permits the visualiza- smaller arteries that intercommunicate by a 

 tion of the volume pattern of the blood ves- series of arterial arcades, so forming a coarse 

 sels and also its rendition stereoscopically by net or macromesh. Within this coarse periph- 

 simply moving the specimen laterally be- eral net lies a more complex and finer net- 

 tween two successive exposures. Such vas- work or micromesh formed by the arterioles, 

 cular patterns are unobtainable by light capillary bed and ultimate venous radicals, 

 microscopy even with the aid of clearing Micrographs of the ear margin show that 

 techniques. the capillary loops and the small venules 



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