MICROANGIOGRAPHY WITH PKOJKCTION MICROSCOPE 



X-ray line deemed most suitable to the study, aperture, is particularly helpful when ex- 



A target of thin copper foil, either 5 or 10 amining large objects such as a gross section 



microns in thickness, used with an accelerat- of brain, tissue flap, or the ear of a living 



ing kilovoltage of 10 to 30 kv provides rea- rabbit. Both types of stage are used with a 



sonably good resolution and adequate pene- simple metal box camera (2.5 cm high) fitted 



tration for most vascular experiments upon with plate guideways which allow the selec- 



animals. Remarkably contrasty and detailed tion of different target to plate distances. The 



projection micrographs can be obtained with open bottom of the camera rests upon the 



such a target using standard lantern slide specimen stage, while a circular aperture at 



plates (e.g. Ilford Contrasty) while working the top accomodates a fluorescent screen for 



under atmospheric conditions. visual checking of the object or vascular 



Histological sections however require field prior to the introduction and exposure 



x-rays of long wavelengths, such as produced of a plate. 



by an aluminum target. Since better resolu- Specimen Preparation. Microangiog- 

 tion is obtained with a thin target its maxi- raphy, or the x-ray study of microscopic 

 mum thickness should be 4 to 5 microns. An blood vessels necessitates the use of a con- 

 operating voltage of the order of (3 or 7 kilo- trast medium of high radiopacity and small 

 volts or less is essential to the production of particle size, that is readily miscible with 

 reasonable contrast in tissue sections, as is blood, and capable of traversing the capil- 

 the use of a vacuum camera. Focusing is both lary bed. 



critical and difl&cult at these lower kilovolt- Excellent microangiograms of fresh surgi- 



ages owing to the low intensity and reduced cal or cadaveric material, both animal and 



image contrast, but it can be facilitated by human, can be obtained with Micropaque. 



reducing the target-screen distance before This is a colloidal suspension of barium with 



viewing the test grid. A new focussing aid a particle size of half a micron and less, which 



has recently been developed which reduces is capable of entering the smallest capillaries, 



the difficulties to a large extent (11). Its white color lends itself to anatomical 



A mechanical stage is placed over the tar- dissection and makes it easy to determine, 



get when viewing small objects under at- prior to x-ray microscopy, whether good fill- 



mosphevic conditions. The central aperture ing of the blood vessel net has been obtained, 



of the stage is large enough to allow a speci- A 10 to 25 % solution of Micropaque warmed 



men cup to be moved mechanically in the to body temperature and injected intra-ar- 



two horizontal axes across the x-ray beam, terially until whitening of the venous return 



and to be approximated to the target in order is detected, usually gives a clear demonstra- 



to obtain higher magnification. The bottom tion of the vascular pattern of the tissue flap 



of the specimen cup is either covered with a or organ under study. Attention should of 



thin supporting film of plastic (6 micron course be paid to injection pressures espe- 



Mylar) or fitted with rings which give sup- cially in the case of delicate foetal vessels, 



port to the specimen. All parts of the speci- This solution may even be injected into the 



men are in focus at once, and owing to the living animal although eventual clotting of 



great depth of field, stereographic views can the blood is to be expected. Specimens in- 



be produced either by tilting the specimen jected with Micropaque can be fixed in 



at low magnification between two exposures formalin. 



or traversing the specimen across the x-ray In the living animal the concentration, 



cone at high magnification. volume and toxicity of the contrast medium 



A simple stage of sheet plastic or metal, are important if vascular irritation and dis- 



fitted with pressure clamps about a central turbance of circulatory dynamics are to be 



629 



