GAMMA-RAY DENSITOMETRY IN THE 
ANALYSIS OF HEMODYNAMIC FUNCTION 
J. D. Cohn, K. Ito and L. R. M. Del Guercio* 
An instrument has been developed to record contrast 
dilution curves by a noninvasive technique. Transtho- 
racic roentgen density alterations are recorded by use 
of a solid state radiation detector array. A small amount 
of injected non-radioactive, radiopaque contrast mate- 
rial is distributed throughout the central circulation. 
The detector array, positioned over the cardiopulmonary 
silhouette, records changes in density during the passage 
of the contrast material, and typical indicator dilution 
curves are transcribed. An experimental model was con- 
structed to verify the use of the contrast dilution ana- 
lyzer system in the analysis of transit time functions. 
In animal studies, pulmonary circulation time was com- 
puted from contrast dilution curves obtained across the 
central circulation. The pulmonary circulation time in 
normal, anesthetized dogs was found to be 3.13 seconds. 
INTRODUCTION 
Indicator dilution studies are currently em- 
ployed clinically as an adjunct in the analysis 
of hemodynamic function. In practice, indocy- 
anine green dye is injected into the central cir- 
culation and optical density changes are con- 
tinuously recorded from sampled arterial blood. 
The transcribed indicator dilution curves allow 
calculation of total blood flow, transit times and 
vascular volume distribution.^ Quantitation of 
these hemodynamic parameters and the quali- 
tative description of the shape of the indicator 
dilution curve allow assessment of hemodynamic 
function and document the presence of intravas- 
cular shunting phenomena. 
Contrast dilution analysis through use of 
gamma-ray densitometry allows analysis of 
hemodynamic function within the confines of 
the central circulation and without the use of 
invasive catheter techniques. Campeti and Pal- 
ladoro ^ recognized the analogy between density 
changes on cineangiograms and dye dilution 
curves. The cinedensigrams they published were 
* Surgical Research Laboratory, Saint Barnabas Medical Center, 
i<!v!ngston, New Jersey. 
similar in form to indicator dilution curves and 
demonstrated the effects of intrathoracic shunt- 
ing on the recorded roentgen contrast dilution 
curves. Lind, Spencer and Wegelius^ likewise 
noted the relationship between serial angio- 
graphic density changes and congenital cardiac 
defects. Abnormal contrast dilution curves were 
visualized on recordings taken over individual 
cardiac chambers and vascular segments. 
Roentgen contrast recording techniques have 
been eff'ectively developed and are utilized in 
research. Williams and associates* obtained 
indicator dilution curves by roentgen video 
densitometry following intracardiac injection 
of a radiopaque contrast agent. The dilution 
curves are undistorted by catheter sampling 
systems and areas circumscribed by the pulmo- 
nary or cardiac silhouette may be investigated 
with ease. 
In an attempt to further develop a method 
for the assessment of hemodynamic function 
based on analysis of indicator dilution curves, 
Del Guercio and co-workers-'^ and Cohn et al.^ 
utilized a transducer to record roentgen density 
changes during contrast medium transport. This 
device consisted of a photomultiplier tube cov- 
ered by a small fluorescent screen. The colli- 
mated x-ray beam passed through the subject 
causing the screen to fluoresce, thus exciting 
the photomultiplier cell. Absorption of the x-ray 
beam energy by the contrast material is re- 
flected in the photomultiplier tube output volt- 
age and recording of contrast dilution curves 
are readily obtained over areas inaccessible to 
catheterization techniques. By this technique, 
roentgen contrast dilution curves were serially 
recorded over the lung parenchyma during the 
onset of hemorrhagic shock. Alterations in the 
recorded contrast dilution curves reflected 
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