532 ADVENTURES IN RADIOISOTOPE RESEARCH 



In some pathological cases with impaired circulation, mixing of the 

 injected and circulating red corpuscles takes place at a much slower 

 rate than under physiological conditions and accordingly it may be 

 desirable to follow the path of the labelled erythrocytes in the circulation 



for many hours. 



Such observations can not be carried out by making use of ^sp or 

 42K labelled red corpuscles. 



Recently 5iCr was suggested as labelling agent of erythrocytes. Washed 

 red corpuscles, labelled with Na./iCr04 in vitro, were injected intra- 

 venously into clogs and were found to retain their activity without 

 significant loss to the plasma for approximately 24 hours. The previously 

 determined red corpuscle volume could be re-determinated within 5% 

 for approximately 24 hr.^i^ 



Neither ^-particles nor positrons are emitted by ^^Cr but X-rays 

 and y rays of low intensity. These can be measured very conveniently 

 by making use of a crystal counter which, however, requires expert 

 assistance, in contrast to the running of a Geiger counter. Future 

 progress in the measuring technique may eUminate the diffi- 

 culties encountered today by a clinical institution, when trying to apply 

 red corpuscles labelled with ^^Cr in corpuscle volume measurements. 



In this note a labelling method of red corpuscles is described which 

 permits to produce tagged erythrocytes which in the course of many 

 hours lose only minute amounts of their radioactivity. 



The method is based upon the introduction of thorium emanation 

 (thoron) into the blood sample. The emanation, which has a half-time 

 of 55 sec, penetrates speedily into the red corpuscles, decays inside them 

 producing the active deposit of thorium which remains even for many 

 hours to a very large extent fixed in the red corpuscles. 



The sequence of the radioactive disintegration products of thorium 

 emanation (Tn) is the following: 



Tn — ^ThA >ThB >ThC ^ThC 



55 sec 0.16 sec 10.6 hr 60.5 min 



I 

 ThC" 

 3.1 min 



The ThA decays with a half-time 0.16 sec and can thus be disregarded. 

 ThB, however, which has a half-time of 10.6 hr, comes soon in exchange 

 equilibrium with the following disintegration products. Consequently 

 the activity of the erythrocytes decays with the disintegration period 



W S. J. Gray and K. Sterling, 1950 (A. E. C. U. - 1072); K. Sterling and 

 S. J. Gray, 1950 (A. E. C. U. - 1026). 



