Mean transit time for videodensitometric assessment of myocardial perfusion and the concept of maximal flow ratio: A validation study in the intact dog and a pilot study in man

Abstract

Over the last decade it has become more and more obvious that besides anatomical information about the severity of coronary artery stenoses, information about coronary and myocardial blood flow is necessary to understand the functional significance of these obstructions and to evaluate the result of an intervention. Several methods have been proposed for this purpose, each of these having their particular limitations. In this study a new method is shortly described which allows the accurate calculation of relative maximal myocardial perfusion by ECG-triggered digital radiography (videodensitometry), using mean transit time (Tmn) as time parameter; this technique is based on the original physiologic principles of indicator dilution theory. This method was validated in 8 instrumented dogs in which an excellent linear relation was present between 1/Tmn and flow (r = 0.96 +/- 0.03). Although this method does not allow assessment of resting flow and therefore coronary flow reserve (CFR), it provides a means for the reliable comparison of maximal myocardial flow in different situations and it is independent of most factors affecting coronary flow reserve. The ratio between maximal flow after and before an intervention is called maximal flow ratio (MFR) and this concept was applied in a pilot study in man to evaluate PTCA results in 10 patients undergoing elective angioplasty. MFR was compared with the result of exercise testing 24 hours before and 10 days after the angioplasty. MFR greater than or equal to 1.5 was always accompanied by reversal of exercise test result from positive to negative. We conclude that the accurate calculation of relative maximal perfusion of the myocardium is possible by videodensitometry and suggest that comparison of maximal flow after and before an intervention can be valuable in man for functional evaluation of the result of the intervention.

Improving the applicability of myocardial densitometry and parametric imaging by extended automated densogram analysis

“…for the densitometric parameter 'rise time of the quality weighted mean' compared before and after stimulation of coronary flow with papaverin. In [8,10] the alternative way of considering regions of interest only at special locations, together with corresponding windows outside the myocardium for background subtraction, was investigated. The aim was to obtain high quality densograms.…”

“…For instance, the time of maximum may jump for a smooth change of a densograrn with two local maxima. Even the fitting of a template function to a densogram [8,10] can behave in an unstable manner in certain constellations and this extends to the resulting parameters. An additional classification is therefore desirable to detect densograms that differ from SSD's by shape or mode of origin (superposition of different perfusion beds, collateral supply, late superposition by opacification of the venous system, etc.).…”

“…5. Determination of the parameter MTT requires extrapolation of the densogram [8,10]. The parameter MTT is the preferable time parameter according to the basic models theoretically examined in [ 12].…”

“…This yields 6 densograms associated to the considered heart region and measured at 6 different heart phases. As exhaustive tests for stability of the configuration were performed, these densograms are determined without using an extra window outside the myocardium for background subtraction [8].…”

Quantification of coronary microvascular resistance using angiographic images for volumetric blood flow measurement: in vivo validation

“…Several previous studies have evaluated coronary blood flow by using angiographic images. Pijls et al (40,41,42) measured the mean transit time for the assessment of myocardial perfusion by videodensitometry. Molloi et al (35,37) have shown that the FPA analysis technique can be used to measure absolute coronary blood flow by analyzing the propagation of a contrast material signal in the coronary system.…”