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Measurement of Flow through Branched Systems Using External Radiation Detectors

University of New Mexico School of Medicine, Albuquerque, New Mexico

Correspondence: For reprints contact: Stephen W. Thompson, Dept. of Neurology, Univ. of New Mexico School of Medicine, 930 Stanford N.E., Albuquerque, N.M. 87106.

ABSTRACT

Time-dilution curves made by monitoring an intravenously injected radioisotope through externally placed radiation detectors provide a way of studying circulation. Attempts have been made to study the peripheral circulation using curves resulting from monitoring that portion of an injected indicator which passes through the peripheral region in question. The classical dilution principal, using the area under such a curve from the periphery, however, lets one measure only cardiac output and gives no information about peripheral flow.

This paper describes an analysis of time-dilution curves made with a branched tube through which fluid is flowing. If a radioactive tracer is injected into the main channel and its passage is monitored downstream by two externally placed detectors, one placed over the main channel and the other over one of the branches, the difference in length between the two resulting curves is inversely proportional to the flow rate through the branch. Thus a factor proportional to flow rate through the branch can be derived. The situation is analogous to that resulting when a radioactive indicator is injected intravenously and monitored by detectors placed over the heart and the periphery. A method for measuring cerebral blood flow based on this concept has been proposed previously.

Tests of this hypothesis using time-dilution curves made with a simple flow model are presented.