1086 
MONITORING 
changes in blood flow distribution and transit 
times.' 
Further refinement in methodology has led to 
the recent development of a sensitive solid state 
array system for recording simultaneous indica- 
tor dilution curves over the entire cardiopul- 
monary silhouette. The potential for this mode 
of hemodynamic analysis is great. Through the 
injection of a small amount of non-radioactive, 
radiopaque agent, circulatory parameters are 
recorded over multiple areas of the heart and 
lung. By this means, intrathoracic shunts are 
detected, blood flow distribution may be defined 
and ejection fraction evaluated. 
INSTRUMENTATION 
The roentgen densitometer unit* consists of 
an x-ray or gamma-ray source and a detector 
array attached to a mobile support structure 
(Figure 1). The detector array is mounted on 
a movable support unit under the detector 
housing. By this means, detector position in re- 
lation to the experimental subject may be re- 
motely controlled by use of electronic circuitry 
located on the console panel. The sensor device 
consists of solid state radiation detectors with 
the detector area measuring 20 square mm. The 
diameter of the detector housing structure is 
2.5 cm. Hence, multiple detectors may be placed 
within the confines of the cardiopulmonary 
silhouette. Currently a linear array of six iden- 
tical detectors is utilized and six simultaneous 
contrast dilution curves are thus recorded. 
The radiation detector device operates at 
room temperature. Efficiency with x-ray ener- 
gies of 60 kv is approximately 10 percent and 
the eflSciency increases with decreasing x-ray 
energies. Output signals from the solid state 
detector are processed through pre-amplifiers 
and amplifiers and count rates are noted on rate 
meters connected to each output channel. Filter 
modules are incorporated into each channel for 
optimal signal recordings. All curves are re- 
corded simultaneously on a strip chart recorder. 
Calibration is achieved by recording trans- 
thoracic density changes during the passage of 
step-density wedges between the source and 
detector sites. Calibration curves obtained in 
this manner appear nearly linear within the 
ranges of x-ray voltage employed in these stud- 
ies. Simultaneous recording of six contrast di- 
lution curves is performed by positioning the 
detector array over the cardiopulmonary sil- 
houette. Precise anatomic position control is not 
* Contrast Dilution Analyzer, Physiologic Interface Corporation, 
Box 211, King of Prussia, Pa. 19406 
Figure 1. — The Contrast Dilution Analyzer System con- 
sists of an x-ray or gamma-ray source and a detector 
unit. The source head assembly shown above houses 
a 3 curie americium-241 source. Solid state radiation 
detector devices are housed in the base of the unit and 
their position is controlled through the instrument 
console. The subject is placed between the isotope 
source and detector unit and multiple, simultaneous 
contrast dilution curves are obtained. 
