X-ray densitometry for the measurement of regional myocardial perfusion

The evaluation of regional myocardial blood flow (RMBF) during cardiac cath eterization is of particular diagnostic interest. The purpose of this inves tigation was to validate x-ray densitometric parameters for the evaluation of RMBF. In five anesthetized dogs, arterial flow in the circumflex coronary artery was measured continuously with an electromagnetic flowmeter, and RMBF was d etermined by colored microspheres. Five different perfusion levels were cre ated by mechanical obstruction of the coronary artery or by intravenous inf usion of adenosine. At each steady-state perfusion level, digital subtracti on coronary angiograms were obtained for densitometric analysis. Results documented a close correlation between the related time parameters 1/Mean Transit Time (1/MTT, r(2) = 0.969), and 1/Rise Time (1/RT, r(2) = 0. 965) and RMBF over a wide range between 0.36 ml/(min . g) and 11.16 ml/(min . g). Maximum myocardial contrast density (Imax) also showed a good, but i nverse correlation (r(2) = 0.889) with RMBF and, therefore, did not reflect vascular volume. Contrast medium Appearance Time (AT) showed no correlatio n to RMBF (r(2) = 0.017). Repeat densitometric measurements for different p erfusion levels revealed a good reproducibility for MTT (accuracy: 0.001 s; precision: 0.447 s or 6.7%) and RT (accuracy: 0.014 s; precision: 0.202 s or 10.4%), while AT (accuracy: 0.072 s; precision: 0.420 s or 68.5%) and Im ax (accuracy: 0.022 GL; precision: 1.197 GL or 44.5%) showed substantial va riation. Myocardial perfusion reserve (MPR) calculated from RT (r(2) = 0.90 ) or MTT (r(2) = 0.94) showed better correlations to RMBF reserve than MPR calculated from AT (r(2) = 0.04). In conclusion, only 1/MTT and 1/RT showed a good reproducibility and a clos e correlation to RMBF Therefore, only these parameters can be recommended f or calculations of RMBF and its reserve under clinical conditions.