J. D. COHN, K. ITO AND L. R. M. DEL GUERCIO 
1087 
required since qualitative analysis of the re- 
corded curves allows correlation with physio- 
logic events. Following positioning, as above, 
amplifier gain is adjusted and 5 ml meglumine 
j diatrizoate is injected into the central circula- 
tion and the injection time noted. Contrast 
dilution curves are then transcribed on the six- 
channel strip chart recorder. These indicator 
curves, then, reflect the changes in transit times 
■ related to the passage of blood through the pul- 
monary circulation and cardiac chambers. 
EXPERIMENTAL MODEL 
In order to evaluate this system for the ana- 
lysis of transit time measurements, a model flow 
circuit was constructed employing circulation 
through an open loop, constant flow system. A 
flexible plastic tube was fashioned into a loop 
and connected to a water tap. Constant water 
I flow was maintained through the open-ended 
; tube. A single solid state radiation detector was 
positioned under the plastic tube at the point 
where the loop crosses itself. The radiation 
source was then positioned in line with the de- 
j tector and plastic tubes. By this means the 
I mean particle transit time through the loop 
conflguration is given by the equation, 
t = Li/4 7rdVF (1) 
Where t = transit time (sec) 
L = length of tubing loop (cm) 
d = tubing diameter (cm) 
F = fluid flow (cm^/sec) 
Contrast dilution curves were recorded 
through use of this system following the up- 
stream bolus injection of 5 ml meglumine di- 
atrizoate. Indicator dilution curves were tran- 
scribed on each passage of contrast agent 
through the field of the solid state radiation de- 
I tector. As the contrast agent circulates through 
the tubing loop dispersion occurs and is re- 
flected in the curve recording on the second 
i' passage through the field of the radiation de- 
tector. 
From the recorded contrast dilution curves 
and their respective calibrations, transit time 
I functions are computed by numerical analysis.^ 
The algebraic difference between the mean 
transit time related to each passage of contrast 
agent through the field of the radiation detector 
represents the transit time through the loop sys- 
tem and should be identical to the transit time 
derived from equation (1). Figure 2 illustrates 
the results of this experiment. A plot is shown 
relating the calculated mean transit time to the 
mean transit time based upon computations 
derived from analysis of the contrast dilution 
curves. The abscissa represents transit time 
functions obtained through use of equation (1) 
and the ordinate relates the numerical transit 
time based upon the roentgen dilution curves. 
Excellent agreement is noted along the line of 
identity for all points and the correlation co- 
eflftcient for the data is 0.9980. 
LOOP TUBING MODEL 
" 1 1— 1 1 1 [ 
1 2 3 4 5 6 
CALCULATED M.T.T. second 
Figure 2. — Computation of transit time based on a loop 
circulation model is shown in the above illustration. 
Calculated mean transit time (abscissa) is computed 
from fluid flow and tube dimensions according to 
equation (1) and recorded mean transit time (ordi- 
nate) is calculated solely on the basis of the shape 
of the recorded contrast dilution curves. The line of 
identity extending from the origin is illustrated. The 
least-squares fit of the above data is given by the 
equation, y = 0.9567 X -|-0.1156 and the correlation 
coefficient for the paired data is 0.9980. 
I 
