Is the indicator dilution theory really the adequate base of many blood flow measurement techniques?

Abstract

The indicator dilution theory is the underlying model of many blood flow measurement techniques used daily in hospitals, for instance in cardiac catheterization laboratories. The basic version of this theory applies to a "stationary" flow system with one inlet and one outlet, into which a small amount M of indicator is injected "suddenly" at time t = 0 at the inlet. The quintessence of the theory consists in three equations, which themselves result from some apparently simple assumptions about the considered flow systems. The first equation states that the (constant) flow Q through the system can be calculated by use of the known amount of indicator, M, and of the indicator concentration-time curve c(t) recorded at the outlet. The second one allows the calculation of the "mean transit time" t* of fluid and indicator particles through the system from the curve c(t). The third equation, V = Qt*, yields the system volume V. It is generally believed that these three equations would be absolutely valid if the assumptions of the theory could be perfectly fulfilled. We show, by considering a simple model, that all three equations are actually incorrect for most flow systems when the detector used to record the curve c(t) is of the "trans-illumination" type, as is the case for instance in dye dilution methods and in many angiographic or CT techniques. A further consequence is that t*, which is truly the "center of mass" of the concentration-time curve c(t), does not have the well known property of being the adequate parameter for flow determinations. Many flow measurement techniques thus appear to have no theoretical base.

Complete monotonicity of flow and cross-sectional impulse response functions for rigid right circular tubes

“…Indicator dilution theory determines flow, or transit time, distributions by employing an "appropriate" injection of an indicator (some type of a fluid flow stream marker) at an "appropriate" upstream injection site with subsequent samples of the fluid taken at an "appropriate" downstream sampling site [13]. Although indicator dilution theory is well-accepted for carefully specified definitions of "appropriate" injection site, subsequent measurement sites, and measurement techniques [13], various controversies remain, with serious concerns raised regarding the use of cross-sectional sampling techniques, such as X-ray angiography [6]. Resolution of a controversy typically requires development of additional theory to begin to address the experimentalist's concerns.…”

“…However, an associated indicator dilution theory for curves obtained from angiographic images (cross-sectionally sampled curves) has not yet been thoroughly developed. In particular, the question of how to accurately and reliably determine parameters of physiologic flow (e.g., descriptors of the velocity profile and the distribution of transit times) between an upstream and a downstream sampling site remains unresolved [6]. The current work presents a mathematical characterization of the impulse response function between an upstream and a downstream sampling site and serves as the initial step in creating a sound theoretical basis from which experimentalists may explore various heuristics in order to provide meaningful estimates of parameters of physiological flows using different sampling modalities and experimental protocols [8,15].…”

Towards measurement of coronary blood flow in patients and its alteration by interventions

“…Although Doriot et al have recently written a critique of indicator dilution methods [10] , all indicator dilution methods are based on the principle of conservation of mass, or in the case of thermodilution, on the conservation of energy. The thermodilution method in the coronary sinus was introduced by Ganz et al in 1971 [11] .…”

Flat panel computed tomography for non-invasive flow measurement: initial results in in-vitro studies

“…Flow is calculated from time-attenuation curves applying indicator dilution theory [9]. Some investigators raised concerns about whether this technique is an adequate approach towards the assessment of flow [10]. Therefore, other techniques are sought.…”