A scintillation counter permits the use of very low doses of I
131
-albumin in the recording of radiocardiograms. In the presence of mild heart failure there is a distinct widening of the interval between the humps derived from the right and left heart. Application of the principle of three-compartment serial dilution suggests that this prolongation may be due in large part to reduced cardiac output; however, cardiac dilatation may contribute significantly. Although radiocardiographic tracings represent time concentration curves, wide angle counting over the heart does not permit a reliable direct estimate of cardiac output. The chief source of error lies in the variable contribution of surrounding extracardiac tissue to the total activity which is recorded.
By 1920, many significant advances had been made in radiographic and fluoroscopic equipment and techniques. The advances were dictated by medical needs and by the disturbing realization that these spectacularly promising x rays were also very dangerous when improperly used, as evidenced by the growing list of radiation martyrs. Equipment that was available by 1920 included: (1) "internuptenless" transformers (alternating current transformers) with mechanical rectifiers, developed by Clyde Snook's Victor Electric Co. (1904) (Figure 1); (2) hot cathode x-ray tubes, devised by W. D. Coolidge in 1912 and commencially available in 1917; (3) "shockproof and ray-proof" systems, developed by H. F. Waite, M.D. (1918); (4) Gustav Bucky's antiscatter grids (191 1), made movable by H. E.
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